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/*!
Types and routines specific to lazy DFAs.
This module is the home of [`hybrid::dfa::DFA`](DFA).
This module also contains a [`hybrid::dfa::Builder`](Builder) and a
[`hybrid::dfa::Config`](Config) for configuring and building a lazy DFA.
*/
use core::{iter, mem::size_of};
use alloc::vec::Vec;
use crate::{
hybrid::{
error::{BuildError, CacheError},
id::{LazyStateID, LazyStateIDError},
search,
},
nfa::thompson,
util::{
alphabet::{self, ByteClasses, ByteSet},
determinize::{self, State, StateBuilderEmpty, StateBuilderNFA},
empty,
prefilter::Prefilter,
primitives::{PatternID, StateID as NFAStateID},
search::{
Anchored, HalfMatch, Input, MatchError, MatchKind, PatternSet,
},
sparse_set::SparseSets,
start::{Start, StartByteMap},
},
};
/// The minimum number of states that a lazy DFA's cache size must support.
///
/// This is checked at time of construction to ensure that at least some small
/// number of states can fit in the given capacity allotment. If we can't fit
/// at least this number of states, then the thinking is that it's pretty
/// senseless to use the lazy DFA. More to the point, parts of the code do
/// assume that the cache can fit at least some small number of states.
const MIN_STATES: usize = SENTINEL_STATES + 2;
/// The number of "sentinel" states that get added to every lazy DFA.
///
/// These are special states indicating status conditions of a search: unknown,
/// dead and quit. These states in particular also use zero NFA states, so
/// their memory usage is quite small. This is relevant for computing the
/// minimum memory needed for a lazy DFA cache.
const SENTINEL_STATES: usize = 3;
/// A hybrid NFA/DFA (also called a "lazy DFA") for regex searching.
///
/// A lazy DFA is a DFA that builds itself at search time. It otherwise has
/// very similar characteristics as a [`dense::DFA`](crate::dfa::dense::DFA).
/// Indeed, both support precisely the same regex features with precisely the
/// same semantics.
///
/// Where as a `dense::DFA` must be completely built to handle any input before
/// it may be used for search, a lazy DFA starts off effectively empty. During
/// a search, a lazy DFA will build itself depending on whether it has already
/// computed the next transition or not. If it has, then it looks a lot like
/// a `dense::DFA` internally: it does a very fast table based access to find
/// the next transition. Otherwise, if the state hasn't been computed, then it
/// does determinization _for that specific transition_ to compute the next DFA
/// state.
///
/// The main selling point of a lazy DFA is that, in practice, it has
/// the performance profile of a `dense::DFA` without the weakness of it
/// taking worst case exponential time to build. Indeed, for each byte of
/// input, the lazy DFA will construct as most one new DFA state. Thus, a
/// lazy DFA achieves worst case `O(mn)` time for regex search (where `m ~
/// pattern.len()` and `n ~ haystack.len()`).
///
/// The main downsides of a lazy DFA are:
///
/// 1. It requires mutable "cache" space during search. This is where the
/// transition table, among other things, is stored.
/// 2. In pathological cases (e.g., if the cache is too small), it will run
/// out of room and either require a bigger cache capacity or will repeatedly
/// clear the cache and thus repeatedly regenerate DFA states. Overall, this
/// will tend to be slower than a typical NFA simulation.
///
/// # Capabilities
///
/// Like a `dense::DFA`, a single lazy DFA fundamentally supports the following
/// operations:
///
/// 1. Detection of a match.
/// 2. Location of the end of a match.
/// 3. In the case of a lazy DFA with multiple patterns, which pattern matched
/// is reported as well.
///
/// A notable absence from the above list of capabilities is the location of
/// the *start* of a match. In order to provide both the start and end of
/// a match, *two* lazy DFAs are required. This functionality is provided by a
/// [`Regex`](crate::hybrid::regex::Regex).
///
/// # Example
///
/// This shows how to build a lazy DFA with the default configuration and
/// execute a search. Notice how, in contrast to a `dense::DFA`, we must create
/// a cache and pass it to our search routine.
///
/// ```
/// use regex_automata::{hybrid::dfa::DFA, HalfMatch, Input};
///
/// let dfa = DFA::new("foo[0-9]+")?;
/// let mut cache = dfa.create_cache();
///
/// let expected = Some(HalfMatch::must(0, 8));
/// assert_eq!(expected, dfa.try_search_fwd(
/// &mut cache, &Input::new("foo12345"))?,
/// );
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
#[derive(Clone, Debug)]
pub struct DFA {
config: Config,
nfa: thompson::NFA,
stride2: usize,
start_map: StartByteMap,
classes: ByteClasses,
quitset: ByteSet,
cache_capacity: usize,
}
impl DFA {
/// Parse the given regular expression using a default configuration and
/// return the corresponding lazy DFA.
///
/// If you want a non-default configuration, then use the [`Builder`] to
/// set your own configuration.
///
/// # Example
///
/// ```
/// use regex_automata::{hybrid::dfa::DFA, HalfMatch, Input};
///
/// let dfa = DFA::new("foo[0-9]+bar")?;
/// let mut cache = dfa.create_cache();
///
/// let expected = HalfMatch::must(0, 11);
/// assert_eq!(
/// Some(expected),
/// dfa.try_search_fwd(&mut cache, &Input::new("foo12345bar"))?,
/// );
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
#[cfg(feature = "syntax")]
pub fn new(pattern: &str) -> Result<DFA, BuildError> {
DFA::builder().build(pattern)
}
/// Parse the given regular expressions using a default configuration and
/// return the corresponding lazy multi-DFA.
///
/// If you want a non-default configuration, then use the [`Builder`] to
/// set your own configuration.
///
/// # Example
///
/// ```
/// use regex_automata::{hybrid::dfa::DFA, HalfMatch, Input};
///
/// let dfa = DFA::new_many(&["[0-9]+", "[a-z]+"])?;
/// let mut cache = dfa.create_cache();
///
/// let expected = HalfMatch::must(1, 3);
/// assert_eq!(
/// Some(expected),
/// dfa.try_search_fwd(&mut cache, &Input::new("foo12345bar"))?,
/// );
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
#[cfg(feature = "syntax")]
pub fn new_many<P: AsRef<str>>(patterns: &[P]) -> Result<DFA, BuildError> {
DFA::builder().build_many(patterns)
}
/// Create a new lazy DFA that matches every input.
///
/// # Example
///
/// ```
/// use regex_automata::{hybrid::dfa::DFA, HalfMatch, Input};
///
/// let dfa = DFA::always_match()?;
/// let mut cache = dfa.create_cache();
///
/// let expected = HalfMatch::must(0, 0);
/// assert_eq!(Some(expected), dfa.try_search_fwd(
/// &mut cache, &Input::new(""))?,
/// );
/// assert_eq!(Some(expected), dfa.try_search_fwd(
/// &mut cache, &Input::new("foo"))?,
/// );
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
pub fn always_match() -> Result<DFA, BuildError> {
let nfa = thompson::NFA::always_match();
Builder::new().build_from_nfa(nfa)
}
/// Create a new lazy DFA that never matches any input.
///
/// # Example
///
/// ```
/// use regex_automata::{hybrid::dfa::DFA, Input};
///
/// let dfa = DFA::never_match()?;
/// let mut cache = dfa.create_cache();
///
/// assert_eq!(None, dfa.try_search_fwd(&mut cache, &Input::new(""))?);
/// assert_eq!(None, dfa.try_search_fwd(&mut cache, &Input::new("foo"))?);
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
pub fn never_match() -> Result<DFA, BuildError> {
let nfa = thompson::NFA::never_match();
Builder::new().build_from_nfa(nfa)
}
/// Return a default configuration for a `DFA`.
///
/// This is a convenience routine to avoid needing to import the [`Config`]
/// type when customizing the construction of a lazy DFA.
///
/// # Example
///
/// This example shows how to build a lazy DFA that heuristically supports
/// Unicode word boundaries.
///
/// ```
/// # if cfg!(miri) { return Ok(()); } // miri takes too long
/// use regex_automata::{hybrid::dfa::DFA, HalfMatch, MatchError, Input};
///
/// let re = DFA::builder()
/// .configure(DFA::config().unicode_word_boundary(true))
/// .build(r"\b\w+\b")?;
/// let mut cache = re.create_cache();
///
/// // Since our haystack is all ASCII, the DFA search sees then and knows
/// // it is legal to interpret Unicode word boundaries as ASCII word
/// // boundaries.
/// let input = Input::new("!!foo!!");
/// let expected = HalfMatch::must(0, 5);
/// assert_eq!(Some(expected), re.try_search_fwd(&mut cache, &input)?);
///
/// // But if our haystack contains non-ASCII, then the search will fail
/// // with an error.
/// let input = Input::new("!!βββ!!");
/// let expected = MatchError::quit(b'\xCE', 2);
/// assert_eq!(Err(expected), re.try_search_fwd(&mut cache, &input));
///
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
pub fn config() -> Config {
Config::new()
}
/// Return a builder for configuring the construction of a `Regex`.
///
/// This is a convenience routine to avoid needing to import the
/// [`Builder`] type in common cases.
///
/// # Example
///
/// This example shows how to use the builder to disable UTF-8 mode
/// everywhere for lazy DFAs.
///
/// ```
/// # if cfg!(miri) { return Ok(()); } // miri takes too long
/// use regex_automata::{hybrid::dfa::DFA, util::syntax, HalfMatch, Input};
///
/// let re = DFA::builder()
/// .syntax(syntax::Config::new().utf8(false))
/// .build(r"foo(?-u:[^b])ar.*")?;
/// let mut cache = re.create_cache();
///
/// let input = Input::new(b"\xFEfoo\xFFarzz\xE2\x98\xFF\n");
/// let expected = Some(HalfMatch::must(0, 9));
/// let got = re.try_search_fwd(&mut cache, &input)?;
/// assert_eq!(expected, got);
///
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
pub fn builder() -> Builder {
Builder::new()
}
/// Create a new cache for this lazy DFA.
///
/// The cache returned should only be used for searches for this
/// lazy DFA. If you want to reuse the cache for another DFA, then
/// you must call [`Cache::reset`] with that DFA (or, equivalently,
/// [`DFA::reset_cache`]).
pub fn create_cache(&self) -> Cache {
Cache::new(self)
}
/// Reset the given cache such that it can be used for searching with the
/// this lazy DFA (and only this DFA).
///
/// A cache reset permits reusing memory already allocated in this cache
/// with a different lazy DFA.
///
/// Resetting a cache sets its "clear count" to 0. This is relevant if the
/// lazy DFA has been configured to "give up" after it has cleared the
/// cache a certain number of times.
///
/// Any lazy state ID generated by the cache prior to resetting it is
/// invalid after the reset.
///
/// # Example
///
/// This shows how to re-purpose a cache for use with a different DFA.
///
/// ```
/// # if cfg!(miri) { return Ok(()); } // miri takes too long
/// use regex_automata::{hybrid::dfa::DFA, HalfMatch, Input};
///
/// let dfa1 = DFA::new(r"\w")?;
/// let dfa2 = DFA::new(r"\W")?;
///
/// let mut cache = dfa1.create_cache();
/// assert_eq!(
/// Some(HalfMatch::must(0, 2)),
/// dfa1.try_search_fwd(&mut cache, &Input::new("Δ"))?,
/// );
///
/// // Using 'cache' with dfa2 is not allowed. It may result in panics or
/// // incorrect results. In order to re-purpose the cache, we must reset
/// // it with the DFA we'd like to use it with.
/// //
/// // Similarly, after this reset, using the cache with 'dfa1' is also not
/// // allowed.
/// dfa2.reset_cache(&mut cache);
/// assert_eq!(
/// Some(HalfMatch::must(0, 3)),
/// dfa2.try_search_fwd(&mut cache, &Input::new("☃"))?,
/// );
///
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
pub fn reset_cache(&self, cache: &mut Cache) {
Lazy::new(self, cache).reset_cache()
}
/// Returns the total number of patterns compiled into this lazy DFA.
///
/// In the case of a DFA that contains no patterns, this returns `0`.
///
/// # Example
///
/// This example shows the pattern length for a DFA that never matches:
///
/// ```
/// use regex_automata::hybrid::dfa::DFA;
///
/// let dfa = DFA::never_match()?;
/// assert_eq!(dfa.pattern_len(), 0);
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
///
/// And another example for a DFA that matches at every position:
///
/// ```
/// use regex_automata::hybrid::dfa::DFA;
///
/// let dfa = DFA::always_match()?;
/// assert_eq!(dfa.pattern_len(), 1);
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
///
/// And finally, a DFA that was constructed from multiple patterns:
///
/// ```
/// use regex_automata::hybrid::dfa::DFA;
///
/// let dfa = DFA::new_many(&["[0-9]+", "[a-z]+", "[A-Z]+"])?;
/// assert_eq!(dfa.pattern_len(), 3);
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
pub fn pattern_len(&self) -> usize {
self.nfa.pattern_len()
}
/// Returns the equivalence classes that make up the alphabet for this DFA.
///
/// Unless [`Config::byte_classes`] was disabled, it is possible that
/// multiple distinct bytes are grouped into the same equivalence class
/// if it is impossible for them to discriminate between a match and a
/// non-match. This has the effect of reducing the overall alphabet size
/// and in turn potentially substantially reducing the size of the DFA's
/// transition table.
///
/// The downside of using equivalence classes like this is that every state
/// transition will automatically use this map to convert an arbitrary
/// byte to its corresponding equivalence class. In practice this has a
/// negligible impact on performance.
pub fn byte_classes(&self) -> &ByteClasses {
&self.classes
}
/// Returns this lazy DFA's configuration.
pub fn get_config(&self) -> &Config {
&self.config
}
/// Returns a reference to the underlying NFA.
pub fn get_nfa(&self) -> &thompson::NFA {
&self.nfa
}
/// Returns the stride, as a base-2 exponent, required for these
/// equivalence classes.
///
/// The stride is always the smallest power of 2 that is greater than or
/// equal to the alphabet length. This is done so that converting between
/// state IDs and indices can be done with shifts alone, which is much
/// faster than integer division.
fn stride2(&self) -> usize {
self.stride2
}
/// Returns the total stride for every state in this lazy DFA. This
/// corresponds to the total number of transitions used by each state in
/// this DFA's transition table.
fn stride(&self) -> usize {
1 << self.stride2()
}
/// Returns the memory usage, in bytes, of this lazy DFA.
///
/// This does **not** include the stack size used up by this lazy DFA. To
/// compute that, use `std::mem::size_of::<DFA>()`. This also does not
/// include the size of the `Cache` used.
///
/// This also does not include any heap memory used by the NFA inside of
/// this hybrid NFA/DFA. This is because the NFA's ownership is shared, and
/// thus not owned by this hybrid NFA/DFA. More practically, several regex
/// engines in this crate embed an NFA, and reporting the NFA's memory
/// usage in all of them would likely result in reporting higher heap
/// memory than is actually used.
pub fn memory_usage(&self) -> usize {
// The only thing that uses heap memory in a DFA is the NFA. But the
// NFA has shared ownership, so reporting its memory as part of the
// hybrid DFA is likely to lead to double-counting the NFA memory
// somehow. In particular, this DFA does not really own an NFA, so
// including it in the DFA's memory usage doesn't seem semantically
// correct.
0
}
}
impl DFA {
/// Executes a forward search and returns the end position of the leftmost
/// match that is found. If no match exists, then `None` is returned.
///
/// In particular, this method continues searching even after it enters
/// a match state. The search only terminates once it has reached the
/// end of the input or when it has entered a dead or quit state. Upon
/// termination, the position of the last byte seen while still in a match
/// state is returned.
///
/// # Errors
///
/// This routine errors if the search could not complete. This can occur
/// in a number of circumstances:
///
/// * The configuration of the lazy DFA may permit it to "quit" the search.
/// For example, setting quit bytes or enabling heuristic support for
/// Unicode word boundaries. The default configuration does not enable any
/// option that could result in the lazy DFA quitting.
/// * The configuration of the lazy DFA may also permit it to "give up"
/// on a search if it makes ineffective use of its transition table
/// cache. The default configuration does not enable this by default,
/// although it is typically a good idea to.
/// * When the provided `Input` configuration is not supported. For
/// example, by providing an unsupported anchor mode.
///
/// When a search returns an error, callers cannot know whether a match
/// exists or not.
///
/// # Example
///
/// This example shows how to run a basic search.
///
/// ```
/// use regex_automata::{hybrid::dfa::DFA, HalfMatch, Input};
///
/// let dfa = DFA::new("foo[0-9]+")?;
/// let mut cache = dfa.create_cache();
/// let expected = HalfMatch::must(0, 8);
/// assert_eq!(Some(expected), dfa.try_search_fwd(
/// &mut cache, &Input::new("foo12345"))?,
/// );
///
/// // Even though a match is found after reading the first byte (`a`),
/// // the leftmost first match semantics demand that we find the earliest
/// // match that prefers earlier parts of the pattern over later parts.
/// let dfa = DFA::new("abc|a")?;
/// let mut cache = dfa.create_cache();
/// let expected = HalfMatch::must(0, 3);
/// assert_eq!(Some(expected), dfa.try_search_fwd(
/// &mut cache, &Input::new("abc"))?,
/// );
///
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
///
/// # Example: specific pattern search
///
/// This example shows how to build a lazy multi-DFA that permits searching
/// for specific patterns.
///
/// ```
/// use regex_automata::{
/// hybrid::dfa::DFA,
/// Anchored, HalfMatch, PatternID, Input,
/// };
///
/// let dfa = DFA::builder()
/// .configure(DFA::config().starts_for_each_pattern(true))
/// .build_many(&["[a-z0-9]{6}", "[a-z][a-z0-9]{5}"])?;
/// let mut cache = dfa.create_cache();
/// let haystack = "foo123";
///
/// // Since we are using the default leftmost-first match and both
/// // patterns match at the same starting position, only the first pattern
/// // will be returned in this case when doing a search for any of the
/// // patterns.
/// let expected = Some(HalfMatch::must(0, 6));
/// let got = dfa.try_search_fwd(&mut cache, &Input::new(haystack))?;
/// assert_eq!(expected, got);
///
/// // But if we want to check whether some other pattern matches, then we
/// // can provide its pattern ID.
/// let expected = Some(HalfMatch::must(1, 6));
/// let input = Input::new(haystack)
/// .anchored(Anchored::Pattern(PatternID::must(1)));
/// let got = dfa.try_search_fwd(&mut cache, &input)?;
/// assert_eq!(expected, got);
///
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
///
/// # Example: specifying the bounds of a search
///
/// This example shows how providing the bounds of a search can produce
/// different results than simply sub-slicing the haystack.
///
/// ```
/// use regex_automata::{hybrid::dfa::DFA, HalfMatch, Input};
///
/// // N.B. We disable Unicode here so that we use a simple ASCII word
/// // boundary. Alternatively, we could enable heuristic support for
/// // Unicode word boundaries since our haystack is pure ASCII.
/// let dfa = DFA::new(r"(?-u)\b[0-9]{3}\b")?;
/// let mut cache = dfa.create_cache();
/// let haystack = "foo123bar";
///
/// // Since we sub-slice the haystack, the search doesn't know about the
/// // larger context and assumes that `123` is surrounded by word
/// // boundaries. And of course, the match position is reported relative
/// // to the sub-slice as well, which means we get `3` instead of `6`.
/// let expected = Some(HalfMatch::must(0, 3));
/// let got = dfa.try_search_fwd(
/// &mut cache,
/// &Input::new(&haystack[3..6]),
/// )?;
/// assert_eq!(expected, got);
///
/// // But if we provide the bounds of the search within the context of the
/// // entire haystack, then the search can take the surrounding context
/// // into account. (And if we did find a match, it would be reported
/// // as a valid offset into `haystack` instead of its sub-slice.)
/// let expected = None;
/// let got = dfa.try_search_fwd(
/// &mut cache,
/// &Input::new(haystack).range(3..6),
/// )?;
/// assert_eq!(expected, got);
///
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
#[inline]
pub fn try_search_fwd(
&self,
cache: &mut Cache,
input: &Input<'_>,
) -> Result<Option<HalfMatch>, MatchError> {
let utf8empty = self.get_nfa().has_empty() && self.get_nfa().is_utf8();
let hm = match search::find_fwd(self, cache, input)? {
None => return Ok(None),
Some(hm) if !utf8empty => return Ok(Some(hm)),
Some(hm) => hm,
};
// We get to this point when we know our DFA can match the empty string
// AND when UTF-8 mode is enabled. In this case, we skip any matches
// whose offset splits a codepoint. Such a match is necessarily a
// zero-width match, because UTF-8 mode requires the underlying NFA
// to be built such that all non-empty matches span valid UTF-8.
// Therefore, any match that ends in the middle of a codepoint cannot
// be part of a span of valid UTF-8 and thus must be an empty match.
// In such cases, we skip it, so as not to report matches that split a
// codepoint.
//
// Note that this is not a checked assumption. Callers *can* provide an
// NFA with UTF-8 mode enabled but produces non-empty matches that span
// invalid UTF-8. But doing so is documented to result in unspecified
// behavior.
empty::skip_splits_fwd(input, hm, hm.offset(), |input| {
let got = search::find_fwd(self, cache, input)?;
Ok(got.map(|hm| (hm, hm.offset())))
})
}
/// Executes a reverse search and returns the start of the position of the
/// leftmost match that is found. If no match exists, then `None` is
/// returned.
///
/// # Errors
///
/// This routine errors if the search could not complete. This can occur
/// in a number of circumstances:
///
/// * The configuration of the lazy DFA may permit it to "quit" the search.
/// For example, setting quit bytes or enabling heuristic support for
/// Unicode word boundaries. The default configuration does not enable any
/// option that could result in the lazy DFA quitting.
/// * The configuration of the lazy DFA may also permit it to "give up"
/// on a search if it makes ineffective use of its transition table
/// cache. The default configuration does not enable this by default,
/// although it is typically a good idea to.
/// * When the provided `Input` configuration is not supported. For
/// example, by providing an unsupported anchor mode.
///
/// When a search returns an error, callers cannot know whether a match
/// exists or not.
///
/// # Example
///
/// This routine is principally useful when used in
/// conjunction with the
/// [`nfa::thompson::Config::reverse`](crate::nfa::thompson::Config::reverse)
/// configuration. In general, it's unlikely to be correct to use both
/// `try_search_fwd` and `try_search_rev` with the same DFA since any
/// particular DFA will only support searching in one direction with
/// respect to the pattern.
///
/// ```
/// use regex_automata::{
/// nfa::thompson,
/// hybrid::dfa::DFA,
/// HalfMatch, Input,
/// };
///
/// let dfa = DFA::builder()
/// .thompson(thompson::Config::new().reverse(true))
/// .build("foo[0-9]+")?;
/// let mut cache = dfa.create_cache();
/// let expected = HalfMatch::must(0, 0);
/// assert_eq!(
/// Some(expected),
/// dfa.try_search_rev(&mut cache, &Input::new("foo12345"))?,
/// );
///
/// // Even though a match is found after reading the last byte (`c`),
/// // the leftmost first match semantics demand that we find the earliest
/// // match that prefers earlier parts of the pattern over latter parts.
/// let dfa = DFA::builder()
/// .thompson(thompson::Config::new().reverse(true))
/// .build("abc|c")?;
/// let mut cache = dfa.create_cache();
/// let expected = HalfMatch::must(0, 0);
/// assert_eq!(Some(expected), dfa.try_search_rev(
/// &mut cache, &Input::new("abc"))?,
/// );
///
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
///
/// # Example: UTF-8 mode
///
/// This examples demonstrates that UTF-8 mode applies to reverse
/// DFAs. When UTF-8 mode is enabled in the underlying NFA, then all
/// matches reported must correspond to valid UTF-8 spans. This includes
/// prohibiting zero-width matches that split a codepoint.
///
/// UTF-8 mode is enabled by default. Notice below how the only zero-width
/// matches reported are those at UTF-8 boundaries:
///
/// ```
/// use regex_automata::{
/// hybrid::dfa::DFA,
/// nfa::thompson,
/// HalfMatch, Input, MatchKind,
/// };
///
/// let dfa = DFA::builder()
/// .thompson(thompson::Config::new().reverse(true))
/// .build(r"")?;
/// let mut cache = dfa.create_cache();
///
/// // Run the reverse DFA to collect all matches.
/// let mut input = Input::new("☃");
/// let mut matches = vec![];
/// loop {
/// match dfa.try_search_rev(&mut cache, &input)? {
/// None => break,
/// Some(hm) => {
/// matches.push(hm);
/// if hm.offset() == 0 || input.end() == 0 {
/// break;
/// } else if hm.offset() < input.end() {
/// input.set_end(hm.offset());
/// } else {
/// // This is only necessary to handle zero-width
/// // matches, which of course occur in this example.
/// // Without this, the search would never advance
/// // backwards beyond the initial match.
/// input.set_end(input.end() - 1);
/// }
/// }
/// }
/// }
///
/// // No matches split a codepoint.
/// let expected = vec![
/// HalfMatch::must(0, 3),
/// HalfMatch::must(0, 0),
/// ];
/// assert_eq!(expected, matches);
///
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
///
/// Now let's look at the same example, but with UTF-8 mode on the
/// underlying NFA disabled:
///
/// ```
/// use regex_automata::{
/// hybrid::dfa::DFA,
/// nfa::thompson,
/// HalfMatch, Input, MatchKind,
/// };
///
/// let dfa = DFA::builder()
/// .thompson(thompson::Config::new().reverse(true).utf8(false))
/// .build(r"")?;
/// let mut cache = dfa.create_cache();
///
/// // Run the reverse DFA to collect all matches.
/// let mut input = Input::new("☃");
/// let mut matches = vec![];
/// loop {
/// match dfa.try_search_rev(&mut cache, &input)? {
/// None => break,
/// Some(hm) => {
/// matches.push(hm);
/// if hm.offset() == 0 || input.end() == 0 {
/// break;
/// } else if hm.offset() < input.end() {
/// input.set_end(hm.offset());
/// } else {
/// // This is only necessary to handle zero-width
/// // matches, which of course occur in this example.
/// // Without this, the search would never advance
/// // backwards beyond the initial match.
/// input.set_end(input.end() - 1);
/// }
/// }
/// }
/// }
///
/// // No matches split a codepoint.
/// let expected = vec![
/// HalfMatch::must(0, 3),
/// HalfMatch::must(0, 2),
/// HalfMatch::must(0, 1),
/// HalfMatch::must(0, 0),
/// ];
/// assert_eq!(expected, matches);
///
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
#[inline]
pub fn try_search_rev(
&self,
cache: &mut Cache,
input: &Input<'_>,
) -> Result<Option<HalfMatch>, MatchError> {
let utf8empty = self.get_nfa().has_empty() && self.get_nfa().is_utf8();
let hm = match search::find_rev(self, cache, input)? {
None => return Ok(None),
Some(hm) if !utf8empty => return Ok(Some(hm)),
Some(hm) => hm,
};
empty::skip_splits_rev(input, hm, hm.offset(), |input| {
let got = search::find_rev(self, cache, input)?;
Ok(got.map(|hm| (hm, hm.offset())))
})
}
/// Executes an overlapping forward search and returns the end position of
/// matches as they are found. If no match exists, then `None` is returned.
///
/// This routine is principally only useful when searching for multiple
/// patterns on inputs where multiple patterns may match the same regions
/// of text. In particular, callers must preserve the automaton's search
/// state from prior calls so that the implementation knows where the last
/// match occurred.
///
/// When using this routine to implement an iterator of overlapping
/// matches, the `start` of the search should remain invariant throughout
/// iteration. The `OverlappingState` given to the search will keep track
/// of the current position of the search. (This is because multiple
/// matches may be reported at the same position, so only the search
/// implementation itself knows when to advance the position.)
///
/// If for some reason you want the search to forget about its previous
/// state and restart the search at a particular position, then setting the
/// state to [`OverlappingState::start`] will accomplish that.
///
/// # Errors
///
/// This routine errors if the search could not complete. This can occur
/// in a number of circumstances:
///
/// * The configuration of the lazy DFA may permit it to "quit" the search.
/// For example, setting quit bytes or enabling heuristic support for
/// Unicode word boundaries. The default configuration does not enable any
/// option that could result in the lazy DFA quitting.
/// * The configuration of the lazy DFA may also permit it to "give up"
/// on a search if it makes ineffective use of its transition table
/// cache. The default configuration does not enable this by default,
/// although it is typically a good idea to.
/// * When the provided `Input` configuration is not supported. For
/// example, by providing an unsupported anchor mode.
///
/// When a search returns an error, callers cannot know whether a match
/// exists or not.
///
/// # Example
///
/// This example shows how to run a basic overlapping search. Notice
/// that we build the automaton with a `MatchKind::All` configuration.
/// Overlapping searches are unlikely to work as one would expect when
/// using the default `MatchKind::LeftmostFirst` match semantics, since
/// leftmost-first matching is fundamentally incompatible with overlapping
/// searches. Namely, overlapping searches need to report matches as they
/// are seen, where as leftmost-first searches will continue searching even
/// after a match has been observed in order to find the conventional end
/// position of the match. More concretely, leftmost-first searches use
/// dead states to terminate a search after a specific match can no longer
/// be extended. Overlapping searches instead do the opposite by continuing
/// the search to find totally new matches (potentially of other patterns).
///
/// ```
/// # if cfg!(miri) { return Ok(()); } // miri takes too long
/// use regex_automata::{
/// hybrid::dfa::{DFA, OverlappingState},
/// HalfMatch, Input, MatchKind,
/// };
///
/// let dfa = DFA::builder()
/// .configure(DFA::config().match_kind(MatchKind::All))
/// .build_many(&[r"\w+$", r"\S+$"])?;
/// let mut cache = dfa.create_cache();
///
/// let haystack = "@foo";
/// let mut state = OverlappingState::start();
///
/// let expected = Some(HalfMatch::must(1, 4));
/// dfa.try_search_overlapping_fwd(
/// &mut cache, &Input::new(haystack), &mut state,
/// )?;
/// assert_eq!(expected, state.get_match());
///
/// // The first pattern also matches at the same position, so re-running
/// // the search will yield another match. Notice also that the first
/// // pattern is returned after the second. This is because the second
/// // pattern begins its match before the first, is therefore an earlier
/// // match and is thus reported first.
/// let expected = Some(HalfMatch::must(0, 4));
/// dfa.try_search_overlapping_fwd(
/// &mut cache, &Input::new(haystack), &mut state,
/// )?;
/// assert_eq!(expected, state.get_match());
///
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
#[inline]
pub fn try_search_overlapping_fwd(
&self,
cache: &mut Cache,
input: &Input<'_>,
state: &mut OverlappingState,
) -> Result<(), MatchError> {
let utf8empty = self.get_nfa().has_empty() && self.get_nfa().is_utf8();
search::find_overlapping_fwd(self, cache, input, state)?;
match state.get_match() {
None => Ok(()),
Some(_) if !utf8empty => Ok(()),
Some(_) => skip_empty_utf8_splits_overlapping(
input,
state,
|input, state| {
search::find_overlapping_fwd(self, cache, input, state)
},
),
}
}
/// Executes a reverse overlapping search and returns the start of the
/// position of the leftmost match that is found. If no match exists, then
/// `None` is returned.
///
/// When using this routine to implement an iterator of overlapping
/// matches, the `start` of the search should remain invariant throughout
/// iteration. The `OverlappingState` given to the search will keep track
/// of the current position of the search. (This is because multiple
/// matches may be reported at the same position, so only the search
/// implementation itself knows when to advance the position.)
///
/// If for some reason you want the search to forget about its previous
/// state and restart the search at a particular position, then setting the
/// state to [`OverlappingState::start`] will accomplish that.
///
/// # Errors
///
/// This routine errors if the search could not complete. This can occur
/// in a number of circumstances:
///
/// * The configuration of the lazy DFA may permit it to "quit" the search.
/// For example, setting quit bytes or enabling heuristic support for
/// Unicode word boundaries. The default configuration does not enable any
/// option that could result in the lazy DFA quitting.
/// * The configuration of the lazy DFA may also permit it to "give up"
/// on a search if it makes ineffective use of its transition table
/// cache. The default configuration does not enable this by default,
/// although it is typically a good idea to.
/// * When the provided `Input` configuration is not supported. For
/// example, by providing an unsupported anchor mode.
///
/// When a search returns an error, callers cannot know whether a match
/// exists or not.
///
/// # Example: UTF-8 mode
///
/// This examples demonstrates that UTF-8 mode applies to reverse
/// DFAs. When UTF-8 mode is enabled in the underlying NFA, then all
/// matches reported must correspond to valid UTF-8 spans. This includes
/// prohibiting zero-width matches that split a codepoint.
///
/// UTF-8 mode is enabled by default. Notice below how the only zero-width
/// matches reported are those at UTF-8 boundaries:
///
/// ```
/// use regex_automata::{
/// hybrid::dfa::{DFA, OverlappingState},
/// nfa::thompson,
/// HalfMatch, Input, MatchKind,
/// };
///
/// let dfa = DFA::builder()
/// .configure(DFA::config().match_kind(MatchKind::All))
/// .thompson(thompson::Config::new().reverse(true))
/// .build_many(&[r"", r"☃"])?;
/// let mut cache = dfa.create_cache();
///
/// // Run the reverse DFA to collect all matches.
/// let input = Input::new("☃");
/// let mut state = OverlappingState::start();
/// let mut matches = vec![];
/// loop {
/// dfa.try_search_overlapping_rev(&mut cache, &input, &mut state)?;
/// match state.get_match() {
/// None => break,
/// Some(hm) => matches.push(hm),
/// }
/// }
///
/// // No matches split a codepoint.
/// let expected = vec![
/// HalfMatch::must(0, 3),
/// HalfMatch::must(1, 0),
/// HalfMatch::must(0, 0),
/// ];
/// assert_eq!(expected, matches);
///
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
///
/// Now let's look at the same example, but with UTF-8 mode on the
/// underlying NFA disabled:
///
/// ```
/// use regex_automata::{
/// hybrid::dfa::{DFA, OverlappingState},
/// nfa::thompson,
/// HalfMatch, Input, MatchKind,
/// };
///
/// let dfa = DFA::builder()
/// .configure(DFA::config().match_kind(MatchKind::All))
/// .thompson(thompson::Config::new().reverse(true).utf8(false))
/// .build_many(&[r"", r"☃"])?;
/// let mut cache = dfa.create_cache();
///
/// // Run the reverse DFA to collect all matches.
/// let input = Input::new("☃");
/// let mut state = OverlappingState::start();
/// let mut matches = vec![];
/// loop {
/// dfa.try_search_overlapping_rev(&mut cache, &input, &mut state)?;
/// match state.get_match() {
/// None => break,
/// Some(hm) => matches.push(hm),
/// }
/// }
///
/// // Now *all* positions match, even within a codepoint,
/// // because we lifted the requirement that matches
/// // correspond to valid UTF-8 spans.
/// let expected = vec![
/// HalfMatch::must(0, 3),
/// HalfMatch::must(0, 2),
/// HalfMatch::must(0, 1),
/// HalfMatch::must(1, 0),
/// HalfMatch::must(0, 0),
/// ];
/// assert_eq!(expected, matches);
///
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
#[inline]
pub fn try_search_overlapping_rev(
&self,
cache: &mut Cache,
input: &Input<'_>,
state: &mut OverlappingState,
) -> Result<(), MatchError> {
let utf8empty = self.get_nfa().has_empty() && self.get_nfa().is_utf8();
search::find_overlapping_rev(self, cache, input, state)?;
match state.get_match() {
None => Ok(()),
Some(_) if !utf8empty => Ok(()),
Some(_) => skip_empty_utf8_splits_overlapping(
input,
state,
|input, state| {
search::find_overlapping_rev(self, cache, input, state)
},
),
}
}
/// Writes the set of patterns that match anywhere in the given search
/// configuration to `patset`. If multiple patterns match at the same
/// position and the underlying DFA supports overlapping matches, then all
/// matching patterns are written to the given set.
///
/// Unless all of the patterns in this DFA are anchored, then generally
/// speaking, this will visit every byte in the haystack.
///
/// This search routine *does not* clear the pattern set. This gives some
/// flexibility to the caller (e.g., running multiple searches with the
/// same pattern set), but does make the API bug-prone if you're reusing
/// the same pattern set for multiple searches but intended them to be
/// independent.
///
/// If a pattern ID matched but the given `PatternSet` does not have
/// sufficient capacity to store it, then it is not inserted and silently
/// dropped.
///
/// # Errors
///
/// This routine errors if the search could not complete. This can occur
/// in a number of circumstances:
///
/// * The configuration of the lazy DFA may permit it to "quit" the search.
/// For example, setting quit bytes or enabling heuristic support for
/// Unicode word boundaries. The default configuration does not enable any
/// option that could result in the lazy DFA quitting.
/// * The configuration of the lazy DFA may also permit it to "give up"
/// on a search if it makes ineffective use of its transition table
/// cache. The default configuration does not enable this by default,
/// although it is typically a good idea to.
/// * When the provided `Input` configuration is not supported. For
/// example, by providing an unsupported anchor mode.
///
/// When a search returns an error, callers cannot know whether a match
/// exists or not.
///
/// # Example
///
/// This example shows how to find all matching patterns in a haystack,
/// even when some patterns match at the same position as other patterns.
///
/// ```
/// # if cfg!(miri) { return Ok(()); } // miri takes too long
/// use regex_automata::{
/// hybrid::dfa::DFA,
/// Input, MatchKind, PatternSet,
/// };
///
/// let patterns = &[
/// r"\w+", r"\d+", r"\pL+", r"foo", r"bar", r"barfoo", r"foobar",
/// ];
/// let dfa = DFA::builder()
/// .configure(DFA::config().match_kind(MatchKind::All))
/// .build_many(patterns)?;
/// let mut cache = dfa.create_cache();
///
/// let input = Input::new("foobar");
/// let mut patset = PatternSet::new(dfa.pattern_len());
/// dfa.try_which_overlapping_matches(&mut cache, &input, &mut patset)?;
/// let expected = vec![0, 2, 3, 4, 6];
/// let got: Vec<usize> = patset.iter().map(|p| p.as_usize()).collect();
/// assert_eq!(expected, got);
///
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
#[inline]
pub fn try_which_overlapping_matches(
&self,
cache: &mut Cache,
input: &Input<'_>,
patset: &mut PatternSet,
) -> Result<(), MatchError> {
let mut state = OverlappingState::start();
while let Some(m) = {
self.try_search_overlapping_fwd(cache, input, &mut state)?;
state.get_match()
} {
let _ = patset.try_insert(m.pattern());
// There's nothing left to find, so we can stop. Or the caller
// asked us to.
if patset.is_full() || input.get_earliest() {
break;
}
}
Ok(())
}
}
impl DFA {
/// Transitions from the current state to the next state, given the next
/// byte of input.
///
/// The given cache is used to either reuse pre-computed state
/// transitions, or to store this newly computed transition for future
/// reuse. Thus, this routine guarantees that it will never return a state
/// ID that has an "unknown" tag.
///
/// # State identifier validity
///
/// The only valid value for `current` is the lazy state ID returned
/// by the most recent call to `next_state`, `next_state_untagged`,
/// `next_state_untagged_unchecked`, `start_state_forward` or
/// `state_state_reverse` for the given `cache`. Any state ID returned from
/// prior calls to these routines (with the same `cache`) is considered
/// invalid (even if it gives an appearance of working). State IDs returned
/// from _any_ prior call for different `cache` values are also always
/// invalid.
///
/// The returned ID is always a valid ID when `current` refers to a valid
/// ID. Moreover, this routine is defined for all possible values of
/// `input`.
///
/// These validity rules are not checked, even in debug mode. Callers are
/// required to uphold these rules themselves.
///
/// Violating these state ID validity rules will not sacrifice memory
/// safety, but _may_ produce an incorrect result or a panic.
///
/// # Panics
///
/// If the given ID does not refer to a valid state, then this routine
/// may panic but it also may not panic and instead return an invalid or
/// incorrect ID.
///
/// # Example
///
/// This shows a simplistic example for walking a lazy DFA for a given
/// haystack by using the `next_state` method.
///
/// ```
/// use regex_automata::{hybrid::dfa::DFA, Input};
///
/// let dfa = DFA::new(r"[a-z]+r")?;
/// let mut cache = dfa.create_cache();
/// let haystack = "bar".as_bytes();
///
/// // The start state is determined by inspecting the position and the
/// // initial bytes of the haystack.
/// let mut sid = dfa.start_state_forward(
/// &mut cache, &Input::new(haystack),
/// )?;
/// // Walk all the bytes in the haystack.
/// for &b in haystack {
/// sid = dfa.next_state(&mut cache, sid, b)?;
/// }
/// // Matches are always delayed by 1 byte, so we must explicitly walk the
/// // special "EOI" transition at the end of the search.
/// sid = dfa.next_eoi_state(&mut cache, sid)?;
/// assert!(sid.is_match());
///
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
#[inline]
pub fn next_state(
&self,
cache: &mut Cache,
current: LazyStateID,
input: u8,
) -> Result<LazyStateID, CacheError> {
let class = usize::from(self.classes.get(input));
let offset = current.as_usize_untagged() + class;
let sid = cache.trans[offset];
if !sid.is_unknown() {
return Ok(sid);
}
let unit = alphabet::Unit::u8(input);
Lazy::new(self, cache).cache_next_state(current, unit)
}
/// Transitions from the current state to the next state, given the next
/// byte of input and a state ID that is not tagged.
///
/// The only reason to use this routine is performance. In particular, the
/// `next_state` method needs to do some additional checks, among them is
/// to account for identifiers to states that are not yet computed. In
/// such a case, the transition is computed on the fly. However, if it is
/// known that the `current` state ID is untagged, then these checks can be
/// omitted.
///
/// Since this routine does not compute states on the fly, it does not
/// modify the cache and thus cannot return an error. Consequently, `cache`
/// does not need to be mutable and it is possible for this routine to
/// return a state ID corresponding to the special "unknown" state. In
/// this case, it is the caller's responsibility to use the prior state
/// ID and `input` with `next_state` in order to force the computation of
/// the unknown transition. Otherwise, trying to use the "unknown" state
/// ID will just result in transitioning back to itself, and thus never
/// terminating. (This is technically a special exemption to the state ID
/// validity rules, but is permissible since this routine is guarateed to
/// never mutate the given `cache`, and thus the identifier is guaranteed
/// to remain valid.)
///
/// See [`LazyStateID`] for more details on what it means for a state ID
/// to be tagged. Also, see
/// [`next_state_untagged_unchecked`](DFA::next_state_untagged_unchecked)
/// for this same idea, but with bounds checks forcefully elided.
///
/// # State identifier validity
///
/// The only valid value for `current` is an **untagged** lazy
/// state ID returned by the most recent call to `next_state`,
/// `next_state_untagged`, `next_state_untagged_unchecked`,
/// `start_state_forward` or `state_state_reverse` for the given `cache`.
/// Any state ID returned from prior calls to these routines (with the
/// same `cache`) is considered invalid (even if it gives an appearance
/// of working). State IDs returned from _any_ prior call for different
/// `cache` values are also always invalid.
///
/// The returned ID is always a valid ID when `current` refers to a valid
/// ID, although it may be tagged. Moreover, this routine is defined for
/// all possible values of `input`.
///
/// Not all validity rules are checked, even in debug mode. Callers are
/// required to uphold these rules themselves.
///
/// Violating these state ID validity rules will not sacrifice memory
/// safety, but _may_ produce an incorrect result or a panic.
///
/// # Panics
///
/// If the given ID does not refer to a valid state, then this routine
/// may panic but it also may not panic and instead return an invalid or
/// incorrect ID.
///
/// # Example
///
/// This shows a simplistic example for walking a lazy DFA for a given
/// haystack by using the `next_state_untagged` method where possible.
///
/// ```
/// use regex_automata::{hybrid::dfa::DFA, Input};
///
/// let dfa = DFA::new(r"[a-z]+r")?;
/// let mut cache = dfa.create_cache();
/// let haystack = "bar".as_bytes();
///
/// // The start state is determined by inspecting the position and the
/// // initial bytes of the haystack.
/// let mut sid = dfa.start_state_forward(
/// &mut cache, &Input::new(haystack),
/// )?;
/// // Walk all the bytes in the haystack.
/// let mut at = 0;
/// while at < haystack.len() {
/// if sid.is_tagged() {
/// sid = dfa.next_state(&mut cache, sid, haystack[at])?;
/// } else {
/// let mut prev_sid = sid;
/// // We attempt to chew through as much as we can while moving
/// // through untagged state IDs. Thus, the transition function
/// // does less work on average per byte. (Unrolling this loop
/// // may help even more.)
/// while at < haystack.len() {
/// prev_sid = sid;
/// sid = dfa.next_state_untagged(
/// &mut cache, sid, haystack[at],
/// );
/// at += 1;
/// if sid.is_tagged() {
/// break;
/// }
/// }
/// // We must ensure that we never proceed to the next iteration
/// // with an unknown state ID. If we don't account for this
/// // case, then search isn't guaranteed to terminate since all
/// // transitions on unknown states loop back to itself.
/// if sid.is_unknown() {
/// sid = dfa.next_state(
/// &mut cache, prev_sid, haystack[at - 1],
/// )?;
/// }
/// }
/// }
/// // Matches are always delayed by 1 byte, so we must explicitly walk the
/// // special "EOI" transition at the end of the search.
/// sid = dfa.next_eoi_state(&mut cache, sid)?;
/// assert!(sid.is_match());
///
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
#[inline]
pub fn next_state_untagged(
&self,
cache: &Cache,
current: LazyStateID,
input: u8,
) -> LazyStateID {
debug_assert!(!current.is_tagged());
let class = usize::from(self.classes.get(input));
let offset = current.as_usize_unchecked() + class;
cache.trans[offset]
}
/// Transitions from the current state to the next state, eliding bounds
/// checks, given the next byte of input and a state ID that is not tagged.
///
/// The only reason to use this routine is performance. In particular, the
/// `next_state` method needs to do some additional checks, among them is
/// to account for identifiers to states that are not yet computed. In
/// such a case, the transition is computed on the fly. However, if it is
/// known that the `current` state ID is untagged, then these checks can be
/// omitted.
///
/// Since this routine does not compute states on the fly, it does not
/// modify the cache and thus cannot return an error. Consequently, `cache`
/// does not need to be mutable and it is possible for this routine to
/// return a state ID corresponding to the special "unknown" state. In
/// this case, it is the caller's responsibility to use the prior state
/// ID and `input` with `next_state` in order to force the computation of
/// the unknown transition. Otherwise, trying to use the "unknown" state
/// ID will just result in transitioning back to itself, and thus never
/// terminating. (This is technically a special exemption to the state ID
/// validity rules, but is permissible since this routine is guarateed to
/// never mutate the given `cache`, and thus the identifier is guaranteed
/// to remain valid.)
///
/// See [`LazyStateID`] for more details on what it means for a state ID
/// to be tagged. Also, see
/// [`next_state_untagged`](DFA::next_state_untagged)
/// for this same idea, but with memory safety guaranteed by retaining
/// bounds checks.
///
/// # State identifier validity
///
/// The only valid value for `current` is an **untagged** lazy
/// state ID returned by the most recent call to `next_state`,
/// `next_state_untagged`, `next_state_untagged_unchecked`,
/// `start_state_forward` or `state_state_reverse` for the given `cache`.
/// Any state ID returned from prior calls to these routines (with the
/// same `cache`) is considered invalid (even if it gives an appearance
/// of working). State IDs returned from _any_ prior call for different
/// `cache` values are also always invalid.
///
/// The returned ID is always a valid ID when `current` refers to a valid
/// ID, although it may be tagged. Moreover, this routine is defined for
/// all possible values of `input`.
///
/// Not all validity rules are checked, even in debug mode. Callers are
/// required to uphold these rules themselves.
///
/// Violating these state ID validity rules will not sacrifice memory
/// safety, but _may_ produce an incorrect result or a panic.
///
/// # Safety
///
/// Callers of this method must guarantee that `current` refers to a valid
/// state ID according to the rules described above. If `current` is not a
/// valid state ID for this automaton, then calling this routine may result
/// in undefined behavior.
///
/// If `current` is valid, then the ID returned is valid for all possible
/// values of `input`.
#[inline]
pub unsafe fn next_state_untagged_unchecked(
&self,
cache: &Cache,
current: LazyStateID,
input: u8,
) -> LazyStateID {
debug_assert!(!current.is_tagged());
let class = usize::from(self.classes.get(input));
let offset = current.as_usize_unchecked() + class;
*cache.trans.get_unchecked(offset)
}
/// Transitions from the current state to the next state for the special
/// EOI symbol.
///
/// The given cache is used to either reuse pre-computed state
/// transitions, or to store this newly computed transition for future
/// reuse. Thus, this routine guarantees that it will never return a state
/// ID that has an "unknown" tag.
///
/// This routine must be called at the end of every search in a correct
/// implementation of search. Namely, lazy DFAs in this crate delay matches
/// by one byte in order to support look-around operators. Thus, after
/// reaching the end of a haystack, a search implementation must follow one
/// last EOI transition.
///
/// It is best to think of EOI as an additional symbol in the alphabet of a
/// DFA that is distinct from every other symbol. That is, the alphabet of
/// lazy DFAs in this crate has a logical size of 257 instead of 256, where
/// 256 corresponds to every possible inhabitant of `u8`. (In practice, the
/// physical alphabet size may be smaller because of alphabet compression
/// via equivalence classes, but EOI is always represented somehow in the
/// alphabet.)
///
/// # State identifier validity
///
/// The only valid value for `current` is the lazy state ID returned
/// by the most recent call to `next_state`, `next_state_untagged`,
/// `next_state_untagged_unchecked`, `start_state_forward` or
/// `state_state_reverse` for the given `cache`. Any state ID returned from
/// prior calls to these routines (with the same `cache`) is considered
/// invalid (even if it gives an appearance of working). State IDs returned
/// from _any_ prior call for different `cache` values are also always
/// invalid.
///
/// The returned ID is always a valid ID when `current` refers to a valid
/// ID.
///
/// These validity rules are not checked, even in debug mode. Callers are
/// required to uphold these rules themselves.
///
/// Violating these state ID validity rules will not sacrifice memory
/// safety, but _may_ produce an incorrect result or a panic.
///
/// # Panics
///
/// If the given ID does not refer to a valid state, then this routine
/// may panic but it also may not panic and instead return an invalid or
/// incorrect ID.
///
/// # Example
///
/// This shows a simplistic example for walking a DFA for a given haystack,
/// and then finishing the search with the final EOI transition.
///
/// ```
/// use regex_automata::{hybrid::dfa::DFA, Input};
///
/// let dfa = DFA::new(r"[a-z]+r")?;
/// let mut cache = dfa.create_cache();
/// let haystack = "bar".as_bytes();
///
/// // The start state is determined by inspecting the position and the
/// // initial bytes of the haystack.
/// let mut sid = dfa.start_state_forward(
/// &mut cache, &Input::new(haystack),
/// )?;
/// // Walk all the bytes in the haystack.
/// for &b in haystack {
/// sid = dfa.next_state(&mut cache, sid, b)?;
/// }
/// // Matches are always delayed by 1 byte, so we must explicitly walk
/// // the special "EOI" transition at the end of the search. Without this
/// // final transition, the assert below will fail since the DFA will not
/// // have entered a match state yet!
/// sid = dfa.next_eoi_state(&mut cache, sid)?;
/// assert!(sid.is_match());
///
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
#[inline]
pub fn next_eoi_state(
&self,
cache: &mut Cache,
current: LazyStateID,
) -> Result<LazyStateID, CacheError> {
let eoi = self.classes.eoi().as_usize();
let offset = current.as_usize_untagged() + eoi;
let sid = cache.trans[offset];
if !sid.is_unknown() {
return Ok(sid);
}
let unit = self.classes.eoi();
Lazy::new(self, cache).cache_next_state(current, unit)
}
/// Return the ID of the start state for this lazy DFA when executing a
/// forward search.
///
/// Unlike typical DFA implementations, the start state for DFAs in this
/// crate is dependent on a few different factors:
///
/// * The [`Anchored`] mode of the search. Unanchored, anchored and
/// anchored searches for a specific [`PatternID`] all use different start
/// states.
/// * The position at which the search begins, via [`Input::start`]. This
/// and the byte immediately preceding the start of the search (if one
/// exists) influence which look-behind assertions are true at the start
/// of the search. This in turn influences which start state is selected.
/// * Whether the search is a forward or reverse search. This routine can
/// only be used for forward searches.
///
/// # Errors
///
/// This may return a [`MatchError`] (not a [`CacheError`]!) if the search
/// needs to give up when determining the start state (for example, if
/// it sees a "quit" byte or if the cache has been cleared too many
/// times). This can also return an error if the given `Input` contains an
/// unsupported [`Anchored`] configuration.
#[cfg_attr(feature = "perf-inline", inline(always))]
pub fn start_state_forward(
&self,
cache: &mut Cache,
input: &Input<'_>,
) -> Result<LazyStateID, MatchError> {
if !self.quitset.is_empty() && input.start() > 0 {
let offset = input.start() - 1;
let byte = input.haystack()[offset];
if self.quitset.contains(byte) {
return Err(MatchError::quit(byte, offset));
}
}
let start_type = self.start_map.fwd(input);
let start = LazyRef::new(self, cache)
.get_cached_start_id(input, start_type)?;
if !start.is_unknown() {
return Ok(start);
}
Lazy::new(self, cache).cache_start_group(input, start_type)
}
/// Return the ID of the start state for this lazy DFA when executing a
/// reverse search.
///
/// Unlike typical DFA implementations, the start state for DFAs in this
/// crate is dependent on a few different factors:
///
/// * The [`Anchored`] mode of the search. Unanchored, anchored and
/// anchored searches for a specific [`PatternID`] all use different start
/// states.
/// * The position at which the search begins, via [`Input::start`]. This
/// and the byte immediately preceding the start of the search (if one
/// exists) influence which look-behind assertions are true at the start
/// of the search. This in turn influences which start state is selected.
/// * Whether the search is a forward or reverse search. This routine can
/// only be used for reverse searches.
///
/// # Errors
///
/// This may return a [`MatchError`] (not a [`CacheError`]!) if the search
/// needs to give up when determining the start state (for example, if
/// it sees a "quit" byte or if the cache has been cleared too many
/// times). This can also return an error if the given `Input` contains an
/// unsupported [`Anchored`] configuration.
#[cfg_attr(feature = "perf-inline", inline(always))]
pub fn start_state_reverse(
&self,
cache: &mut Cache,
input: &Input<'_>,
) -> Result<LazyStateID, MatchError> {
if !self.quitset.is_empty() && input.end() < input.haystack().len() {
let offset = input.end();
let byte = input.haystack()[offset];
if self.quitset.contains(byte) {
return Err(MatchError::quit(byte, offset));
}
}
let start_type = self.start_map.rev(input);
let start = LazyRef::new(self, cache)
.get_cached_start_id(input, start_type)?;
if !start.is_unknown() {
return Ok(start);
}
Lazy::new(self, cache).cache_start_group(input, start_type)
}
/// Returns the total number of patterns that match in this state.
///
/// If the lazy DFA was compiled with one pattern, then this must
/// necessarily always return `1` for all match states.
///
/// A lazy DFA guarantees that [`DFA::match_pattern`] can be called with
/// indices up to (but not including) the length returned by this routine
/// without panicking.
///
/// # Panics
///
/// If the given state is not a match state, then this may either panic
/// or return an incorrect result.
///
/// # Example
///
/// This example shows a simple instance of implementing overlapping
/// matches. In particular, it shows not only how to determine how many
/// patterns have matched in a particular state, but also how to access
/// which specific patterns have matched.
///
/// Notice that we must use [`MatchKind::All`] when building the DFA. If we
/// used [`MatchKind::LeftmostFirst`] instead, then the DFA would not be
/// constructed in a way that supports overlapping matches. (It would only
/// report a single pattern that matches at any particular point in time.)
///
/// Another thing to take note of is the patterns used and the order in
/// which the pattern IDs are reported. In the example below, pattern `3`
/// is yielded first. Why? Because it corresponds to the match that
/// appears first. Namely, the `@` symbol is part of `\S+` but not part
/// of any of the other patterns. Since the `\S+` pattern has a match that
/// starts to the left of any other pattern, its ID is returned before any
/// other.
///
/// ```
/// # if cfg!(miri) { return Ok(()); } // miri takes too long
/// use regex_automata::{hybrid::dfa::DFA, Input, MatchKind};
///
/// let dfa = DFA::builder()
/// .configure(DFA::config().match_kind(MatchKind::All))
/// .build_many(&[
/// r"\w+", r"[a-z]+", r"[A-Z]+", r"\S+",
/// ])?;
/// let mut cache = dfa.create_cache();
/// let haystack = "@bar".as_bytes();
///
/// // The start state is determined by inspecting the position and the
/// // initial bytes of the haystack.
/// let mut sid = dfa.start_state_forward(
/// &mut cache, &Input::new(haystack),
/// )?;
/// // Walk all the bytes in the haystack.
/// for &b in haystack {
/// sid = dfa.next_state(&mut cache, sid, b)?;
/// }
/// sid = dfa.next_eoi_state(&mut cache, sid)?;
///
/// assert!(sid.is_match());
/// assert_eq!(dfa.match_len(&mut cache, sid), 3);
/// // The following calls are guaranteed to not panic since `match_len`
/// // returned `3` above.
/// assert_eq!(dfa.match_pattern(&mut cache, sid, 0).as_usize(), 3);
/// assert_eq!(dfa.match_pattern(&mut cache, sid, 1).as_usize(), 0);
/// assert_eq!(dfa.match_pattern(&mut cache, sid, 2).as_usize(), 1);
///
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
#[inline]
pub fn match_len(&self, cache: &Cache, id: LazyStateID) -> usize {
assert!(id.is_match());
LazyRef::new(self, cache).get_cached_state(id).match_len()
}
/// Returns the pattern ID corresponding to the given match index in the
/// given state.
///
/// See [`DFA::match_len`] for an example of how to use this method
/// correctly. Note that if you know your lazy DFA is configured with a
/// single pattern, then this routine is never necessary since it will
/// always return a pattern ID of `0` for an index of `0` when `id`
/// corresponds to a match state.
///
/// Typically, this routine is used when implementing an overlapping
/// search, as the example for `DFA::match_len` does.
///
/// # Panics
///
/// If the state ID is not a match state or if the match index is out
/// of bounds for the given state, then this routine may either panic
/// or produce an incorrect result. If the state ID is correct and the
/// match index is correct, then this routine always produces a valid
/// `PatternID`.
#[inline]
pub fn match_pattern(
&self,
cache: &Cache,
id: LazyStateID,
match_index: usize,
) -> PatternID {
// This is an optimization for the very common case of a DFA with a
// single pattern. This conditional avoids a somewhat more costly path
// that finds the pattern ID from the corresponding `State`, which
// requires a bit of slicing/pointer-chasing. This optimization tends
// to only matter when matches are frequent.
if self.pattern_len() == 1 {
return PatternID::ZERO;
}
LazyRef::new(self, cache)
.get_cached_state(id)
.match_pattern(match_index)
}
}
/// A cache represents a partially computed DFA.
///
/// A cache is the key component that differentiates a classical DFA and a
/// hybrid NFA/DFA (also called a "lazy DFA"). Where a classical DFA builds a
/// complete transition table that can handle all possible inputs, a hybrid
/// NFA/DFA starts with an empty transition table and builds only the parts
/// required during search. The parts that are built are stored in a cache. For
/// this reason, a cache is a required parameter for nearly every operation on
/// a [`DFA`].
///
/// Caches can be created from their corresponding DFA via
/// [`DFA::create_cache`]. A cache can only be used with either the DFA that
/// created it, or the DFA that was most recently used to reset it with
/// [`Cache::reset`]. Using a cache with any other DFA may result in panics
/// or incorrect results.
#[derive(Clone, Debug)]
pub struct Cache {
// N.B. If you're looking to understand how determinization works, it
// is probably simpler to first grok src/dfa/determinize.rs, since that
// doesn't have the "laziness" component.
/// The transition table.
///
/// Given a `current` LazyStateID and an `input` byte, the next state can
/// be computed via `trans[untagged(current) + equiv_class(input)]`. Notice
/// that no multiplication is used. That's because state identifiers are
/// "premultiplied."
///
/// Note that the next state may be the "unknown" state. In this case, the
/// next state is not known and determinization for `current` on `input`
/// must be performed.
trans: Vec<LazyStateID>,
/// The starting states for this DFA.
///
/// These are computed lazily. Initially, these are all set to "unknown"
/// lazy state IDs.
///
/// When 'starts_for_each_pattern' is disabled (the default), then the size
/// of this is constrained to the possible starting configurations based
/// on the search parameters. (At time of writing, that's 4.) However,
/// when starting states for each pattern is enabled, then there are N
/// additional groups of starting states, where each group reflects the
/// different possible configurations and N is the number of patterns.
starts: Vec<LazyStateID>,
/// A sequence of NFA/DFA powerset states that have been computed for this
/// lazy DFA. This sequence is indexable by untagged LazyStateIDs. (Every
/// tagged LazyStateID can be used to index this sequence by converting it
/// to its untagged form.)
states: Vec<State>,
/// A map from states to their corresponding IDs. This map may be accessed
/// via the raw byte representation of a state, which means that a `State`
/// does not need to be allocated to determine whether it already exists
/// in this map. Indeed, the existence of such a state is what determines
/// whether we allocate a new `State` or not.
///
/// The higher level idea here is that we do just enough determinization
/// for a state to check whether we've already computed it. If we have,
/// then we can save a little (albeit not much) work. The real savings is
/// in memory usage. If we never checked for trivially duplicate states,
/// then our memory usage would explode to unreasonable levels.
states_to_id: StateMap,
/// Sparse sets used to track which NFA states have been visited during
/// various traversals.
sparses: SparseSets,
/// Scratch space for traversing the NFA graph. (We use space on the heap
/// instead of the call stack.)
stack: Vec<NFAStateID>,
/// Scratch space for building a NFA/DFA powerset state. This is used to
/// help amortize allocation since not every powerset state generated is
/// added to the cache. In particular, if it already exists in the cache,
/// then there is no need to allocate a new `State` for it.
scratch_state_builder: StateBuilderEmpty,
/// A simple abstraction for handling the saving of at most a single state
/// across a cache clearing. This is required for correctness. Namely, if
/// adding a new state after clearing the cache fails, then the caller
/// must retain the ability to continue using the state ID given. The
/// state corresponding to the state ID is what we preserve across cache
/// clearings.
state_saver: StateSaver,
/// The memory usage, in bytes, used by 'states' and 'states_to_id'. We
/// track this as new states are added since states use a variable amount
/// of heap. Tracking this as we add states makes it possible to compute
/// the total amount of memory used by the determinizer in constant time.
memory_usage_state: usize,
/// The number of times the cache has been cleared. When a minimum cache
/// clear count is set, then the cache will return an error instead of
/// clearing the cache if the count has been exceeded.
clear_count: usize,
/// The total number of bytes searched since the last time this cache was
/// cleared, not including the current search.
///
/// This can be added to the length of the current search to get the true
/// total number of bytes searched.
///
/// This is generally only non-zero when the
/// `Cache::search_{start,update,finish}` APIs are used to track search
/// progress.
bytes_searched: usize,
/// The progress of the current search.
///
/// This is only non-`None` when callers utlize the `Cache::search_start`,
/// `Cache::search_update` and `Cache::search_finish` APIs.
///
/// The purpose of recording search progress is to be able to make a
/// determination about the efficiency of the cache. Namely, by keeping
/// track of the
progress: Option<SearchProgress>,
}
impl Cache {
/// Create a new cache for the given lazy DFA.
///
/// The cache returned should only be used for searches for the given DFA.
/// If you want to reuse the cache for another DFA, then you must call
/// [`Cache::reset`] with that DFA.
pub fn new(dfa: &DFA) -> Cache {
let mut cache = Cache {
trans: alloc::vec![],
starts: alloc::vec![],
states: alloc::vec![],
states_to_id: StateMap::new(),
sparses: SparseSets::new(dfa.get_nfa().states().len()),
stack: alloc::vec![],
scratch_state_builder: StateBuilderEmpty::new(),
state_saver: StateSaver::none(),
memory_usage_state: 0,
clear_count: 0,
bytes_searched: 0,
progress: None,
};
debug!("pre-init lazy DFA cache size: {}", cache.memory_usage());
Lazy { dfa, cache: &mut cache }.init_cache();
debug!("post-init lazy DFA cache size: {}", cache.memory_usage());
cache
}
/// Reset this cache such that it can be used for searching with the given
/// lazy DFA (and only that DFA).
///
/// A cache reset permits reusing memory already allocated in this cache
/// with a different lazy DFA.
///
/// Resetting a cache sets its "clear count" to 0. This is relevant if the
/// lazy DFA has been configured to "give up" after it has cleared the
/// cache a certain number of times.
///
/// Any lazy state ID generated by the cache prior to resetting it is
/// invalid after the reset.
///
/// # Example
///
/// This shows how to re-purpose a cache for use with a different DFA.
///
/// ```
/// # if cfg!(miri) { return Ok(()); } // miri takes too long
/// use regex_automata::{hybrid::dfa::DFA, HalfMatch, Input};
///
/// let dfa1 = DFA::new(r"\w")?;
/// let dfa2 = DFA::new(r"\W")?;
///
/// let mut cache = dfa1.create_cache();
/// assert_eq!(
/// Some(HalfMatch::must(0, 2)),
/// dfa1.try_search_fwd(&mut cache, &Input::new("Δ"))?,
/// );
///
/// // Using 'cache' with dfa2 is not allowed. It may result in panics or
/// // incorrect results. In order to re-purpose the cache, we must reset
/// // it with the DFA we'd like to use it with.
/// //
/// // Similarly, after this reset, using the cache with 'dfa1' is also not
/// // allowed.
/// cache.reset(&dfa2);
/// assert_eq!(
/// Some(HalfMatch::must(0, 3)),
/// dfa2.try_search_fwd(&mut cache, &Input::new("☃"))?,
/// );
///
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
pub fn reset(&mut self, dfa: &DFA) {
Lazy::new(dfa, self).reset_cache()
}
/// Initializes a new search starting at the given position.
///
/// If a previous search was unfinished, then it is finished automatically
/// and a new search is begun.
///
/// Note that keeping track of search progress is _not necessary_
/// for correct implementations of search using a lazy DFA. Keeping
/// track of search progress is only necessary if you want the
/// [`Config::minimum_bytes_per_state`] configuration knob to work.
#[inline]
pub fn search_start(&mut self, at: usize) {
// If a previous search wasn't marked as finished, then finish it
// now automatically.
if let Some(p) = self.progress.take() {
self.bytes_searched += p.len();
}
self.progress = Some(SearchProgress { start: at, at });
}
/// Updates the current search to indicate that it has search to the
/// current position.
///
/// No special care needs to be taken for reverse searches. Namely, the
/// position given may be _less than_ the starting position of the search.
///
/// # Panics
///
/// This panics if no search has been started by [`Cache::search_start`].
#[inline]
pub fn search_update(&mut self, at: usize) {
let p =
self.progress.as_mut().expect("no in-progress search to update");
p.at = at;
}
/// Indicates that a search has finished at the given position.
///
/// # Panics
///
/// This panics if no search has been started by [`Cache::search_start`].
#[inline]
pub fn search_finish(&mut self, at: usize) {
let mut p =
self.progress.take().expect("no in-progress search to finish");
p.at = at;
self.bytes_searched += p.len();
}
/// Returns the total number of bytes that have been searched since this
/// cache was last cleared.
///
/// This is useful for determining the efficiency of the cache. For
/// example, the lazy DFA uses this value in conjunction with the
/// [`Config::minimum_bytes_per_state`] knob to help determine whether it
/// should quit searching.
///
/// This always returns `0` if search progress isn't being tracked. Note
/// that the lazy DFA search routines in this crate always track search
/// progress.
pub fn search_total_len(&self) -> usize {
self.bytes_searched + self.progress.as_ref().map_or(0, |p| p.len())
}
/// Returns the total number of times this cache has been cleared since it
/// was either created or last reset.
///
/// This is useful for informational purposes or if you want to change
/// search strategies based on the number of times the cache has been
/// cleared.
pub fn clear_count(&self) -> usize {
self.clear_count
}
/// Returns the heap memory usage, in bytes, of this cache.
///
/// This does **not** include the stack size used up by this cache. To
/// compute that, use `std::mem::size_of::<Cache>()`.
pub fn memory_usage(&self) -> usize {
const ID_SIZE: usize = size_of::<LazyStateID>();
const STATE_SIZE: usize = size_of::<State>();
// NOTE: If you make changes to the below, then
// 'minimum_cache_capacity' should be updated correspondingly.
self.trans.len() * ID_SIZE
+ self.starts.len() * ID_SIZE
+ self.states.len() * STATE_SIZE
// Maps likely use more memory than this, but it's probably close.
+ self.states_to_id.len() * (STATE_SIZE + ID_SIZE)
+ self.sparses.memory_usage()
+ self.stack.capacity() * ID_SIZE
+ self.scratch_state_builder.capacity()
// Heap memory used by 'State' in both 'states' and 'states_to_id'.
+ self.memory_usage_state
}
}
/// Keeps track of the progress of the current search.
///
/// This is updated via the `Cache::search_{start,update,finish}` APIs to
/// record how many bytes have been searched. This permits computing a
/// heuristic that represents the efficiency of a cache, and thus helps inform
/// whether the lazy DFA should give up or not.
#[derive(Clone, Debug)]
struct SearchProgress {
start: usize,
at: usize,
}
impl SearchProgress {
/// Returns the length, in bytes, of this search so far.
///
/// This automatically handles the case of a reverse search, where `at`
/// is likely to be less than `start`.
fn len(&self) -> usize {
if self.start <= self.at {
self.at - self.start
} else {
self.start - self.at
}
}
}
/// A map from states to state identifiers. When using std, we use a standard
/// hashmap, since it's a bit faster for this use case. (Other maps, like
/// one's based on FNV, have not yet been benchmarked.)
///
/// The main purpose of this map is to reuse states where possible. This won't
/// fully minimize the DFA, but it works well in a lot of cases.
#[cfg(feature = "std")]
type StateMap = std::collections::HashMap<State, LazyStateID>;
#[cfg(not(feature = "std"))]
type StateMap = alloc::collections::BTreeMap<State, LazyStateID>;
/// A type that groups methods that require the base NFA/DFA and writable
/// access to the cache.
#[derive(Debug)]
struct Lazy<'i, 'c> {
dfa: &'i DFA,
cache: &'c mut Cache,
}
impl<'i, 'c> Lazy<'i, 'c> {
/// Creates a new 'Lazy' wrapper for a DFA and its corresponding cache.
fn new(dfa: &'i DFA, cache: &'c mut Cache) -> Lazy<'i, 'c> {
Lazy { dfa, cache }
}
/// Return an immutable view by downgrading a writable cache to a read-only
/// cache.
fn as_ref<'a>(&'a self) -> LazyRef<'i, 'a> {
LazyRef::new(self.dfa, self.cache)
}
/// This is marked as 'inline(never)' to avoid bloating methods on 'DFA'
/// like 'next_state' and 'next_eoi_state' that are called in critical
/// areas. The idea is to let the optimizer focus on the other areas of
/// those methods as the hot path.
///
/// Here's an example that justifies 'inline(never)'
///
/// ```ignore
/// regex-cli find hybrid dfa \
/// @all-codepoints-utf8-100x '\pL{100}' --cache-capacity 10000000
/// ```
///
/// Where 'all-codepoints-utf8-100x' is the UTF-8 encoding of every
/// codepoint, in sequence, repeated 100 times.
///
/// With 'inline(never)' hyperfine reports 1.1s per run. With
/// 'inline(always)', hyperfine reports 1.23s. So that's a 10% improvement.
#[cold]
#[inline(never)]
fn cache_next_state(
&mut self,
mut current: LazyStateID,
unit: alphabet::Unit,
) -> Result<LazyStateID, CacheError> {
let stride2 = self.dfa.stride2();
let empty_builder = self.get_state_builder();
let builder = determinize::next(
self.dfa.get_nfa(),
self.dfa.get_config().get_match_kind(),
&mut self.cache.sparses,
&mut self.cache.stack,
&self.cache.states[current.as_usize_untagged() >> stride2],
unit,
empty_builder,
);
let save_state = !self.as_ref().state_builder_fits_in_cache(&builder);
if save_state {
self.save_state(current);
}
let next = self.add_builder_state(builder, |sid| sid)?;
if save_state {
current = self.saved_state_id();
}
// This is the payoff. The next time 'next_state' is called with this
// state and alphabet unit, it will find this transition and avoid
// having to re-determinize this transition.
self.set_transition(current, unit, next);
Ok(next)
}
/// Compute and cache the starting state for the given pattern ID (if
/// present) and the starting configuration.
///
/// This panics if a pattern ID is given and the DFA isn't configured to
/// build anchored start states for each pattern.
///
/// This will never return an unknown lazy state ID.
///
/// If caching this state would otherwise result in a cache that has been
/// cleared too many times, then an error is returned.
#[cold]
#[inline(never)]
fn cache_start_group(
&mut self,
input: &Input<'_>,
start: Start,
) -> Result<LazyStateID, MatchError> {
let mode = input.get_anchored();
let nfa_start_id = match mode {
Anchored::No => self.dfa.get_nfa().start_unanchored(),
Anchored::Yes => self.dfa.get_nfa().start_anchored(),
Anchored::Pattern(pid) => {
if !self.dfa.get_config().get_starts_for_each_pattern() {
return Err(MatchError::unsupported_anchored(mode));
}
match self.dfa.get_nfa().start_pattern(pid) {
None => return Ok(self.as_ref().dead_id()),
Some(sid) => sid,
}
}
};
let id = self
.cache_start_one(nfa_start_id, start)
.map_err(|_| MatchError::gave_up(input.start()))?;
self.set_start_state(input, start, id);
Ok(id)
}
/// Compute and cache the starting state for the given NFA state ID and the
/// starting configuration. The NFA state ID might be one of the following:
///
/// 1) An unanchored start state to match any pattern.
/// 2) An anchored start state to match any pattern.
/// 3) An anchored start state for a particular pattern.
///
/// This will never return an unknown lazy state ID.
///
/// If caching this state would otherwise result in a cache that has been
/// cleared too many times, then an error is returned.
fn cache_start_one(
&mut self,
nfa_start_id: NFAStateID,
start: Start,
) -> Result<LazyStateID, CacheError> {
let mut builder_matches = self.get_state_builder().into_matches();
determinize::set_lookbehind_from_start(
self.dfa.get_nfa(),
&start,
&mut builder_matches,
);
self.cache.sparses.set1.clear();
determinize::epsilon_closure(
self.dfa.get_nfa(),
nfa_start_id,
builder_matches.look_have(),
&mut self.cache.stack,
&mut self.cache.sparses.set1,
);
let mut builder = builder_matches.into_nfa();
determinize::add_nfa_states(
&self.dfa.get_nfa(),
&self.cache.sparses.set1,
&mut builder,
);
let tag_starts = self.dfa.get_config().get_specialize_start_states();
self.add_builder_state(builder, |id| {
if tag_starts {
id.to_start()
} else {
id
}
})
}
/// Either add the given builder state to this cache, or return an ID to an
/// equivalent state already in this cache.
///
/// In the case where no equivalent state exists, the idmap function given
/// may be used to transform the identifier allocated. This is useful if
/// the caller needs to tag the ID with additional information.
///
/// This will never return an unknown lazy state ID.
///
/// If caching this state would otherwise result in a cache that has been
/// cleared too many times, then an error is returned.
fn add_builder_state(
&mut self,
builder: StateBuilderNFA,
idmap: impl Fn(LazyStateID) -> LazyStateID,
) -> Result<LazyStateID, CacheError> {
if let Some(&cached_id) =
self.cache.states_to_id.get(builder.as_bytes())
{
// Since we have a cached state, put the constructed state's
// memory back into our scratch space, so that it can be reused.
self.put_state_builder(builder);
return Ok(cached_id);
}
let result = self.add_state(builder.to_state(), idmap);
self.put_state_builder(builder);
result
}
/// Allocate a new state ID and add the given state to this cache.
///
/// The idmap function given may be used to transform the identifier
/// allocated. This is useful if the caller needs to tag the ID with
/// additional information.
///
/// This will never return an unknown lazy state ID.
///
/// If caching this state would otherwise result in a cache that has been
/// cleared too many times, then an error is returned.
fn add_state(
&mut self,
state: State,
idmap: impl Fn(LazyStateID) -> LazyStateID,
) -> Result<LazyStateID, CacheError> {
if !self.as_ref().state_fits_in_cache(&state) {
self.try_clear_cache()?;
}
// It's important for this to come second, since the above may clear
// the cache. If we clear the cache after ID generation, then the ID
// is likely bunk since it would have been generated based on a larger
// transition table.
let mut id = idmap(self.next_state_id()?);
if state.is_match() {
id = id.to_match();
}
// Add room in the transition table. Since this is a fresh state, all
// of its transitions are unknown.
self.cache.trans.extend(
iter::repeat(self.as_ref().unknown_id()).take(self.dfa.stride()),
);
// When we add a sentinel state, we never want to set any quit
// transitions. Technically, this is harmless, since sentinel states
// have all of their transitions set to loop back to themselves. But
// when creating sentinel states before the quit sentinel state,
// this will try to call 'set_transition' on a state ID that doesn't
// actually exist yet, which isn't allowed. So we just skip doing so
// entirely.
if !self.dfa.quitset.is_empty() && !self.as_ref().is_sentinel(id) {
let quit_id = self.as_ref().quit_id();
for b in self.dfa.quitset.iter() {
self.set_transition(id, alphabet::Unit::u8(b), quit_id);
}
}
self.cache.memory_usage_state += state.memory_usage();
self.cache.states.push(state.clone());
self.cache.states_to_id.insert(state, id);
Ok(id)
}
/// Allocate a new state ID.
///
/// This will never return an unknown lazy state ID.
///
/// If caching this state would otherwise result in a cache that has been
/// cleared too many times, then an error is returned.
fn next_state_id(&mut self) -> Result<LazyStateID, CacheError> {
let sid = match LazyStateID::new(self.cache.trans.len()) {
Ok(sid) => sid,
Err(_) => {
self.try_clear_cache()?;
// This has to pass since we check that ID capacity at
// construction time can fit at least MIN_STATES states.
LazyStateID::new(self.cache.trans.len()).unwrap()
}
};
Ok(sid)
}
/// Attempt to clear the cache used by this lazy DFA.
///
/// If clearing the cache exceeds the minimum number of required cache
/// clearings, then this will return a cache error. In this case,
/// callers should bubble this up as the cache can't be used until it is
/// reset. Implementations of search should convert this error into a
/// [`MatchError::gave_up`].
///
/// If 'self.state_saver' is set to save a state, then this state is
/// persisted through cache clearing. Otherwise, the cache is returned to
/// its state after initialization with two exceptions: its clear count
/// is incremented and some of its memory likely has additional capacity.
/// That is, clearing a cache does _not_ release memory.
///
/// Otherwise, any lazy state ID generated by the cache prior to resetting
/// it is invalid after the reset.
fn try_clear_cache(&mut self) -> Result<(), CacheError> {
let c = self.dfa.get_config();
if let Some(min_count) = c.get_minimum_cache_clear_count() {
if self.cache.clear_count >= min_count {
if let Some(min_bytes_per) = c.get_minimum_bytes_per_state() {
let len = self.cache.search_total_len();
let min_bytes =
min_bytes_per.saturating_mul(self.cache.states.len());
// If we've searched 0 bytes then probably something has
// gone wrong and the lazy DFA search implementation isn't
// correctly updating the search progress state.
if len == 0 {
trace!(
"number of bytes searched is 0, but \
a minimum bytes per state searched ({}) is \
enabled, maybe Cache::search_update \
is not being used?",
min_bytes_per,
);
}
if len < min_bytes {
trace!(
"lazy DFA cache has been cleared {} times, \
which exceeds the limit of {}, \
AND its bytes searched per state is less \
than the configured minimum of {}, \
therefore lazy DFA is giving up \
(bytes searched since cache clear = {}, \
number of states = {})",
self.cache.clear_count,
min_count,
min_bytes_per,
len,
self.cache.states.len(),
);
return Err(CacheError::bad_efficiency());
} else {
trace!(
"lazy DFA cache has been cleared {} times, \
which exceeds the limit of {}, \
AND its bytes searched per state is greater \
than the configured minimum of {}, \
therefore lazy DFA is continuing! \
(bytes searched since cache clear = {}, \
number of states = {})",
self.cache.clear_count,
min_count,
min_bytes_per,
len,
self.cache.states.len(),
);
}
} else {
trace!(
"lazy DFA cache has been cleared {} times, \
which exceeds the limit of {}, \
since there is no configured bytes per state \
minimum, lazy DFA is giving up",
self.cache.clear_count,
min_count,
);
return Err(CacheError::too_many_cache_clears());
}
}
}
self.clear_cache();
Ok(())
}
/// Clears _and_ resets the cache. Resetting the cache means that no
/// states are persisted and the clear count is reset to 0. No heap memory
/// is released.
///
/// Note that the caller may reset a cache with a different DFA than what
/// it was created from. In which case, the cache can now be used with the
/// new DFA (and not the old DFA).
fn reset_cache(&mut self) {
self.cache.state_saver = StateSaver::none();
self.clear_cache();
// If a new DFA is used, it might have a different number of NFA
// states, so we need to make sure our sparse sets have the appropriate
// size.
self.cache.sparses.resize(self.dfa.get_nfa().states().len());
self.cache.clear_count = 0;
self.cache.progress = None;
}
/// Clear the cache used by this lazy DFA.
///
/// If 'self.state_saver' is set to save a state, then this state is
/// persisted through cache clearing. Otherwise, the cache is returned to
/// its state after initialization with two exceptions: its clear count
/// is incremented and some of its memory likely has additional capacity.
/// That is, clearing a cache does _not_ release memory.
///
/// Otherwise, any lazy state ID generated by the cache prior to resetting
/// it is invalid after the reset.
fn clear_cache(&mut self) {
self.cache.trans.clear();
self.cache.starts.clear();
self.cache.states.clear();
self.cache.states_to_id.clear();
self.cache.memory_usage_state = 0;
self.cache.clear_count += 1;
self.cache.bytes_searched = 0;
if let Some(ref mut progress) = self.cache.progress {
progress.start = progress.at;
}
trace!(
"lazy DFA cache has been cleared (count: {})",
self.cache.clear_count
);
self.init_cache();
// If the state we want to save is one of the sentinel
// (unknown/dead/quit) states, then 'init_cache' adds those back, and
// their identifier values remains invariant. So there's no need to add
// it again. (And indeed, doing so would be incorrect!)
if let Some((old_id, state)) = self.cache.state_saver.take_to_save() {
// If the state is one of the special sentinel states, then it is
// automatically added by cache initialization and its ID always
// remains the same. With that said, this should never occur since
// the sentinel states are all loop states back to themselves. So
// we should never be in a position where we're attempting to save
// a sentinel state since we never compute transitions out of a
// sentinel state.
assert!(
!self.as_ref().is_sentinel(old_id),
"cannot save sentinel state"
);
let new_id = self
.add_state(state, |id| {
if old_id.is_start() {
// We don't need to consult the
// 'specialize_start_states' config knob here, because
// if it's disabled, old_id.is_start() will never
// return true.
id.to_start()
} else {
id
}
})
// The unwrap here is OK because lazy DFA creation ensures that
// we have room in the cache to add MIN_STATES states. Since
// 'init_cache' above adds 3, this adds a 4th.
.expect("adding one state after cache clear must work");
self.cache.state_saver = StateSaver::Saved(new_id);
}
}
/// Initialize this cache from emptiness to a place where it can be used
/// for search.
///
/// This is called both at cache creation time and after the cache has been
/// cleared.
///
/// Primarily, this adds the three sentinel states and allocates some
/// initial memory.
fn init_cache(&mut self) {
// Why multiply by 2 here? Because we make room for both the unanchored
// and anchored start states. Unanchored is first and then anchored.
let mut starts_len = Start::len().checked_mul(2).unwrap();
// ... but if we also want start states for every pattern, we make room
// for that too.
if self.dfa.get_config().get_starts_for_each_pattern() {
starts_len += Start::len() * self.dfa.pattern_len();
}
self.cache
.starts
.extend(iter::repeat(self.as_ref().unknown_id()).take(starts_len));
// This is the set of NFA states that corresponds to each of our three
// sentinel states: the empty set.
let dead = State::dead();
// This sets up some states that we use as sentinels that are present
// in every DFA. While it would be technically possible to implement
// this DFA without explicitly putting these states in the transition
// table, this is convenient to do to make `next_state` correct for all
// valid state IDs without needing explicit conditionals to special
// case these sentinel states.
//
// All three of these states are "dead" states. That is, all of
// them transition only to themselves. So once you enter one of
// these states, it's impossible to leave them. Thus, any correct
// search routine must explicitly check for these state types. (Sans
// `unknown`, since that is only used internally to represent missing
// states.)
let unk_id =
self.add_state(dead.clone(), |id| id.to_unknown()).unwrap();
let dead_id = self.add_state(dead.clone(), |id| id.to_dead()).unwrap();
let quit_id = self.add_state(dead.clone(), |id| id.to_quit()).unwrap();
assert_eq!(unk_id, self.as_ref().unknown_id());
assert_eq!(dead_id, self.as_ref().dead_id());
assert_eq!(quit_id, self.as_ref().quit_id());
// The idea here is that if you start in an unknown/dead/quit state and
// try to transition on them, then you should end up where you started.
self.set_all_transitions(unk_id, unk_id);
self.set_all_transitions(dead_id, dead_id);
self.set_all_transitions(quit_id, quit_id);
// All of these states are technically equivalent from the FSM
// perspective, so putting all three of them in the cache isn't
// possible. (They are distinct merely because we use their
// identifiers as sentinels to mean something, as indicated by the
// names.) Moreover, we wouldn't want to do that. Unknown and quit
// states are special in that they are artificial constructions
// this implementation. But dead states are a natural part of
// determinization. When you reach a point in the NFA where you cannot
// go anywhere else, a dead state will naturally arise and we MUST
// reuse the canonical dead state that we've created here. Why? Because
// it is the state ID that tells the search routine whether a state is
// dead or not, and thus, whether to stop the search. Having a bunch of
// distinct dead states would be quite wasteful!
self.cache.states_to_id.insert(dead, dead_id);
}
/// Save the state corresponding to the ID given such that the state
/// persists through a cache clearing.
///
/// While the state may persist, the ID may not. In order to discover the
/// new state ID, one must call 'saved_state_id' after a cache clearing.
fn save_state(&mut self, id: LazyStateID) {
let state = self.as_ref().get_cached_state(id).clone();
self.cache.state_saver = StateSaver::ToSave { id, state };
}
/// Returns the updated lazy state ID for a state that was persisted
/// through a cache clearing.
///
/// It is only correct to call this routine when both a state has been
/// saved and the cache has just been cleared. Otherwise, this panics.
fn saved_state_id(&mut self) -> LazyStateID {
self.cache
.state_saver
.take_saved()
.expect("state saver does not have saved state ID")
}
/// Set all transitions on the state 'from' to 'to'.
fn set_all_transitions(&mut self, from: LazyStateID, to: LazyStateID) {
for unit in self.dfa.classes.representatives(..) {
self.set_transition(from, unit, to);
}
}
/// Set the transition on 'from' for 'unit' to 'to'.
///
/// This panics if either 'from' or 'to' is invalid.
///
/// All unit values are OK.
fn set_transition(
&mut self,
from: LazyStateID,
unit: alphabet::Unit,
to: LazyStateID,
) {
assert!(self.as_ref().is_valid(from), "invalid 'from' id: {:?}", from);
assert!(self.as_ref().is_valid(to), "invalid 'to' id: {:?}", to);
let offset =
from.as_usize_untagged() + self.dfa.classes.get_by_unit(unit);
self.cache.trans[offset] = to;
}
/// Set the start ID for the given pattern ID (if given) and starting
/// configuration to the ID given.
///
/// This panics if 'id' is not valid or if a pattern ID is given and
/// 'starts_for_each_pattern' is not enabled.
fn set_start_state(
&mut self,
input: &Input<'_>,
start: Start,
id: LazyStateID,
) {
assert!(self.as_ref().is_valid(id));
let start_index = start.as_usize();
let index = match input.get_anchored() {
Anchored::No => start_index,
Anchored::Yes => Start::len() + start_index,
Anchored::Pattern(pid) => {
assert!(
self.dfa.get_config().get_starts_for_each_pattern(),
"attempted to search for a specific pattern \
without enabling starts_for_each_pattern",
);
let pid = pid.as_usize();
(2 * Start::len()) + (Start::len() * pid) + start_index
}
};
self.cache.starts[index] = id;
}
/// Returns a state builder from this DFA that might have existing
/// capacity. This helps avoid allocs in cases where a state is built that
/// turns out to already be cached.
///
/// Callers must put the state builder back with 'put_state_builder',
/// otherwise the allocation reuse won't work.
fn get_state_builder(&mut self) -> StateBuilderEmpty {
core::mem::replace(
&mut self.cache.scratch_state_builder,
StateBuilderEmpty::new(),
)
}
/// Puts the given state builder back into this DFA for reuse.
///
/// Note that building a 'State' from a builder always creates a new alloc,
/// so callers should always put the builder back.
fn put_state_builder(&mut self, builder: StateBuilderNFA) {
let _ = core::mem::replace(
&mut self.cache.scratch_state_builder,
builder.clear(),
);
}
}
/// A type that groups methods that require the base NFA/DFA and read-only
/// access to the cache.
#[derive(Debug)]
struct LazyRef<'i, 'c> {
dfa: &'i DFA,
cache: &'c Cache,
}
impl<'i, 'c> LazyRef<'i, 'c> {
/// Creates a new 'Lazy' wrapper for a DFA and its corresponding cache.
fn new(dfa: &'i DFA, cache: &'c Cache) -> LazyRef<'i, 'c> {
LazyRef { dfa, cache }
}
/// Return the ID of the start state for the given configuration.
///
/// If the start state has not yet been computed, then this returns an
/// unknown lazy state ID.
#[cfg_attr(feature = "perf-inline", inline(always))]
fn get_cached_start_id(
&self,
input: &Input<'_>,
start: Start,
) -> Result<LazyStateID, MatchError> {
let start_index = start.as_usize();
let mode = input.get_anchored();
let index = match mode {
Anchored::No => start_index,
Anchored::Yes => Start::len() + start_index,
Anchored::Pattern(pid) => {
if !self.dfa.get_config().get_starts_for_each_pattern() {
return Err(MatchError::unsupported_anchored(mode));
}
if pid.as_usize() >= self.dfa.pattern_len() {
return Ok(self.dead_id());
}
(2 * Start::len())
+ (Start::len() * pid.as_usize())
+ start_index
}
};
Ok(self.cache.starts[index])
}
/// Return the cached NFA/DFA powerset state for the given ID.
///
/// This panics if the given ID does not address a valid state.
fn get_cached_state(&self, sid: LazyStateID) -> &State {
let index = sid.as_usize_untagged() >> self.dfa.stride2();
&self.cache.states[index]
}
/// Returns true if and only if the given ID corresponds to a "sentinel"
/// state.
///
/// A sentinel state is a state that signifies a special condition of
/// search, and where every transition maps back to itself. See LazyStateID
/// for more details. Note that start and match states are _not_ sentinels
/// since they may otherwise be real states with non-trivial transitions.
/// The purposes of sentinel states is purely to indicate something. Their
/// transitions are not meant to be followed.
fn is_sentinel(&self, id: LazyStateID) -> bool {
id == self.unknown_id() || id == self.dead_id() || id == self.quit_id()
}
/// Returns the ID of the unknown state for this lazy DFA.
fn unknown_id(&self) -> LazyStateID {
// This unwrap is OK since 0 is always a valid state ID.
LazyStateID::new(0).unwrap().to_unknown()
}
/// Returns the ID of the dead state for this lazy DFA.
fn dead_id(&self) -> LazyStateID {
// This unwrap is OK since the maximum value here is 1 * 512 = 512,
// which is <= 2047 (the maximum state ID on 16-bit systems). Where
// 512 is the worst case for our equivalence classes (every byte is a
// distinct class).
LazyStateID::new(1 << self.dfa.stride2()).unwrap().to_dead()
}
/// Returns the ID of the quit state for this lazy DFA.
fn quit_id(&self) -> LazyStateID {
// This unwrap is OK since the maximum value here is 2 * 512 = 1024,
// which is <= 2047 (the maximum state ID on 16-bit systems). Where
// 512 is the worst case for our equivalence classes (every byte is a
// distinct class).
LazyStateID::new(2 << self.dfa.stride2()).unwrap().to_quit()
}
/// Returns true if and only if the given ID is valid.
///
/// An ID is valid if it is both a valid index into the transition table
/// and is a multiple of the DFA's stride.
fn is_valid(&self, id: LazyStateID) -> bool {
let id = id.as_usize_untagged();
id < self.cache.trans.len() && id % self.dfa.stride() == 0
}
/// Returns true if adding the state given would fit in this cache.
fn state_fits_in_cache(&self, state: &State) -> bool {
let needed = self.cache.memory_usage()
+ self.memory_usage_for_one_more_state(state.memory_usage());
trace!(
"lazy DFA cache capacity check: {:?} ?<=? {:?}",
needed,
self.dfa.cache_capacity
);
needed <= self.dfa.cache_capacity
}
/// Returns true if adding the state to be built by the given builder would
/// fit in this cache.
fn state_builder_fits_in_cache(&self, state: &StateBuilderNFA) -> bool {
let needed = self.cache.memory_usage()
+ self.memory_usage_for_one_more_state(state.as_bytes().len());
needed <= self.dfa.cache_capacity
}
/// Returns the additional memory usage, in bytes, required to add one more
/// state to this cache. The given size should be the heap size, in bytes,
/// that would be used by the new state being added.
fn memory_usage_for_one_more_state(
&self,
state_heap_size: usize,
) -> usize {
const ID_SIZE: usize = size_of::<LazyStateID>();
const STATE_SIZE: usize = size_of::<State>();
self.dfa.stride() * ID_SIZE // additional space needed in trans table
+ STATE_SIZE // space in cache.states
+ (STATE_SIZE + ID_SIZE) // space in cache.states_to_id
+ state_heap_size // heap memory used by state itself
}
}
/// A simple type that encapsulates the saving of a state ID through a cache
/// clearing.
///
/// A state ID can be marked for saving with ToSave, while a state ID can be
/// saved itself with Saved.
#[derive(Clone, Debug)]
enum StateSaver {
/// An empty state saver. In this case, no states (other than the special
/// sentinel states) are preserved after clearing the cache.
None,
/// An ID of a state (and the state itself) that should be preserved after
/// the lazy DFA's cache has been cleared. After clearing, the updated ID
/// is stored in 'Saved' since it may have changed.
ToSave { id: LazyStateID, state: State },
/// An ID that of a state that has been persisted through a lazy DFA
/// cache clearing. The ID recorded here corresponds to an ID that was
/// once marked as ToSave. The IDs are likely not equivalent even though
/// the states they point to are.
Saved(LazyStateID),
}
impl StateSaver {
/// Create an empty state saver.
fn none() -> StateSaver {
StateSaver::None
}
/// Replace this state saver with an empty saver, and if this saver is a
/// request to save a state, return that request.
fn take_to_save(&mut self) -> Option<(LazyStateID, State)> {
match core::mem::replace(self, StateSaver::None) {
StateSaver::None | StateSaver::Saved(_) => None,
StateSaver::ToSave { id, state } => Some((id, state)),
}
}
/// Replace this state saver with an empty saver, and if this saver is a
/// saved state (or a request to save a state), return that state's ID.
///
/// The idea here is that a request to save a state isn't necessarily
/// honored because it might not be needed. e.g., Some higher level code
/// might request a state to be saved on the off chance that the cache gets
/// cleared when a new state is added at a lower level. But if that new
/// state is never added, then the cache is never cleared and the state and
/// its ID remain unchanged.
fn take_saved(&mut self) -> Option<LazyStateID> {
match core::mem::replace(self, StateSaver::None) {
StateSaver::None => None,
StateSaver::Saved(id) | StateSaver::ToSave { id, .. } => Some(id),
}
}
}
/// The configuration used for building a lazy DFA.
///
/// As a convenience, [`DFA::config`] is an alias for [`Config::new`]. The
/// advantage of the former is that it often lets you avoid importing the
/// `Config` type directly.
///
/// A lazy DFA configuration is a simple data object that is typically used
/// with [`Builder::configure`].
///
/// The default configuration guarantees that a search will never return a
/// "gave up" or "quit" error, although it is possible for a search to fail
/// if [`Config::starts_for_each_pattern`] wasn't enabled (which it is not by
/// default) and an [`Anchored::Pattern`] mode is requested via [`Input`].
#[derive(Clone, Debug, Default)]
pub struct Config {
// As with other configuration types in this crate, we put all our knobs
// in options so that we can distinguish between "default" and "not set."
// This makes it possible to easily combine multiple configurations
// without default values overwriting explicitly specified values. See the
// 'overwrite' method.
//
// For docs on the fields below, see the corresponding method setters.
match_kind: Option<MatchKind>,
pre: Option<Option<Prefilter>>,
starts_for_each_pattern: Option<bool>,
byte_classes: Option<bool>,
unicode_word_boundary: Option<bool>,
quitset: Option<ByteSet>,
specialize_start_states: Option<bool>,
cache_capacity: Option<usize>,
skip_cache_capacity_check: Option<bool>,
minimum_cache_clear_count: Option<Option<usize>>,
minimum_bytes_per_state: Option<Option<usize>>,
}
impl Config {
/// Return a new default lazy DFA builder configuration.
pub fn new() -> Config {
Config::default()
}
/// Set the desired match semantics.
///
/// The default is [`MatchKind::LeftmostFirst`], which corresponds to the
/// match semantics of Perl-like regex engines. That is, when multiple
/// patterns would match at the same leftmost position, the pattern that
/// appears first in the concrete syntax is chosen.
///
/// Currently, the only other kind of match semantics supported is
/// [`MatchKind::All`]. This corresponds to classical DFA construction
/// where all possible matches are added to the lazy DFA.
///
/// Typically, `All` is used when one wants to execute an overlapping
/// search and `LeftmostFirst` otherwise. In particular, it rarely makes
/// sense to use `All` with the various "leftmost" find routines, since the
/// leftmost routines depend on the `LeftmostFirst` automata construction
/// strategy. Specifically, `LeftmostFirst` adds dead states to the
/// lazy DFA as a way to terminate the search and report a match.
/// `LeftmostFirst` also supports non-greedy matches using this strategy
/// where as `All` does not.
///
/// # Example: overlapping search
///
/// This example shows the typical use of `MatchKind::All`, which is to
/// report overlapping matches.
///
/// ```
/// # if cfg!(miri) { return Ok(()); } // miri takes too long
/// use regex_automata::{
/// hybrid::dfa::{DFA, OverlappingState},
/// HalfMatch, Input, MatchKind,
/// };
///
/// let dfa = DFA::builder()
/// .configure(DFA::config().match_kind(MatchKind::All))
/// .build_many(&[r"\w+$", r"\S+$"])?;
/// let mut cache = dfa.create_cache();
/// let haystack = "@foo";
/// let mut state = OverlappingState::start();
///
/// let expected = Some(HalfMatch::must(1, 4));
/// dfa.try_search_overlapping_fwd(
/// &mut cache, &Input::new(haystack), &mut state,
/// )?;
/// assert_eq!(expected, state.get_match());
///
/// // The first pattern also matches at the same position, so re-running
/// // the search will yield another match. Notice also that the first
/// // pattern is returned after the second. This is because the second
/// // pattern begins its match before the first, is therefore an earlier
/// // match and is thus reported first.
/// let expected = Some(HalfMatch::must(0, 4));
/// dfa.try_search_overlapping_fwd(
/// &mut cache, &Input::new(haystack), &mut state,
/// )?;
/// assert_eq!(expected, state.get_match());
///
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
///
/// # Example: reverse automaton to find start of match
///
/// Another example for using `MatchKind::All` is for constructing a
/// reverse automaton to find the start of a match. `All` semantics are
/// used for this in order to find the longest possible match, which
/// corresponds to the leftmost starting position.
///
/// Note that if you need the starting position then
/// [`hybrid::regex::Regex`](crate::hybrid::regex::Regex) will handle this
/// for you, so it's usually not necessary to do this yourself.
///
/// ```
/// use regex_automata::{
/// hybrid::dfa::DFA,
/// nfa::thompson::NFA,
/// Anchored, HalfMatch, Input, MatchKind,
/// };
///
/// let input = Input::new("123foobar456");
/// let pattern = r"[a-z]+r";
///
/// let dfa_fwd = DFA::new(pattern)?;
/// let dfa_rev = DFA::builder()
/// .thompson(NFA::config().reverse(true))
/// .configure(DFA::config().match_kind(MatchKind::All))
/// .build(pattern)?;
/// let mut cache_fwd = dfa_fwd.create_cache();
/// let mut cache_rev = dfa_rev.create_cache();
///
/// let expected_fwd = HalfMatch::must(0, 9);
/// let expected_rev = HalfMatch::must(0, 3);
/// let got_fwd = dfa_fwd.try_search_fwd(&mut cache_fwd, &input)?.unwrap();
/// // Here we don't specify the pattern to search for since there's only
/// // one pattern and we're doing a leftmost search. But if this were an
/// // overlapping search, you'd need to specify the pattern that matched
/// // in the forward direction. (Otherwise, you might wind up finding the
/// // starting position of a match of some other pattern.) That in turn
/// // requires building the reverse automaton with starts_for_each_pattern
/// // enabled.
/// let input = input
/// .clone()
/// .range(..got_fwd.offset())
/// .anchored(Anchored::Yes);
/// let got_rev = dfa_rev.try_search_rev(&mut cache_rev, &input)?.unwrap();
/// assert_eq!(expected_fwd, got_fwd);
/// assert_eq!(expected_rev, got_rev);
///
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
pub fn match_kind(mut self, kind: MatchKind) -> Config {
self.match_kind = Some(kind);
self
}
/// Set a prefilter to be used whenever a start state is entered.
///
/// A [`Prefilter`] in this context is meant to accelerate searches by
/// looking for literal prefixes that every match for the corresponding
/// pattern (or patterns) must start with. Once a prefilter produces a
/// match, the underlying search routine continues on to try and confirm
/// the match.
///
/// Be warned that setting a prefilter does not guarantee that the search
/// will be faster. While it's usually a good bet, if the prefilter
/// produces a lot of false positive candidates (i.e., positions matched
/// by the prefilter but not by the regex), then the overall result can
/// be slower than if you had just executed the regex engine without any
/// prefilters.
///
/// Note that unless [`Config::specialize_start_states`] has been
/// explicitly set, then setting this will also enable (when `pre` is
/// `Some`) or disable (when `pre` is `None`) start state specialization.
/// This occurs because without start state specialization, a prefilter
/// is likely to be less effective. And without a prefilter, start state
/// specialization is usually pointless.
///
/// By default no prefilter is set.
///
/// # Example
///
/// ```
/// use regex_automata::{
/// hybrid::dfa::DFA,
/// util::prefilter::Prefilter,
/// Input, HalfMatch, MatchKind,
/// };
///
/// let pre = Prefilter::new(MatchKind::LeftmostFirst, &["foo", "bar"]);
/// let re = DFA::builder()
/// .configure(DFA::config().prefilter(pre))
/// .build(r"(foo|bar)[a-z]+")?;
/// let mut cache = re.create_cache();
/// let input = Input::new("foo1 barfox bar");
/// assert_eq!(
/// Some(HalfMatch::must(0, 11)),
/// re.try_search_fwd(&mut cache, &input)?,
/// );
///
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
///
/// Be warned though that an incorrect prefilter can lead to incorrect
/// results!
///
/// ```
/// use regex_automata::{
/// hybrid::dfa::DFA,
/// util::prefilter::Prefilter,
/// Input, HalfMatch, MatchKind,
/// };
///
/// let pre = Prefilter::new(MatchKind::LeftmostFirst, &["foo", "car"]);
/// let re = DFA::builder()
/// .configure(DFA::config().prefilter(pre))
/// .build(r"(foo|bar)[a-z]+")?;
/// let mut cache = re.create_cache();
/// let input = Input::new("foo1 barfox bar");
/// assert_eq!(
/// // No match reported even though there clearly is one!
/// None,
/// re.try_search_fwd(&mut cache, &input)?,
/// );
///
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
pub fn prefilter(mut self, pre: Option<Prefilter>) -> Config {
self.pre = Some(pre);
if self.specialize_start_states.is_none() {
self.specialize_start_states =
Some(self.get_prefilter().is_some());
}
self
}
/// Whether to compile a separate start state for each pattern in the
/// lazy DFA.
///
/// When enabled, a separate **anchored** start state is added for each
/// pattern in the lazy DFA. When this start state is used, then the DFA
/// will only search for matches for the pattern specified, even if there
/// are other patterns in the DFA.
///
/// The main downside of this option is that it can potentially increase
/// the size of the DFA and/or increase the time it takes to build the
/// DFA at search time. However, since this is configuration for a lazy
/// DFA, these states aren't actually built unless they're used. Enabling
/// this isn't necessarily free, however, as it may result in higher cache
/// usage.
///
/// There are a few reasons one might want to enable this (it's disabled
/// by default):
///
/// 1. When looking for the start of an overlapping match (using a reverse
/// DFA), doing it correctly requires starting the reverse search using the
/// starting state of the pattern that matched in the forward direction.
/// Indeed, when building a [`Regex`](crate::hybrid::regex::Regex), it
/// will automatically enable this option when building the reverse DFA
/// internally.
/// 2. When you want to use a DFA with multiple patterns to both search
/// for matches of any pattern or to search for anchored matches of one
/// particular pattern while using the same DFA. (Otherwise, you would need
/// to compile a new DFA for each pattern.)
///
/// By default this is disabled.
///
/// # Example
///
/// This example shows how to use this option to permit the same lazy DFA
/// to run both general searches for any pattern and anchored searches for
/// a specific pattern.
///
/// ```
/// use regex_automata::{
/// hybrid::dfa::DFA,
/// Anchored, HalfMatch, Input, PatternID,
/// };
///
/// let dfa = DFA::builder()
/// .configure(DFA::config().starts_for_each_pattern(true))
/// .build_many(&[r"[a-z0-9]{6}", r"[a-z][a-z0-9]{5}"])?;
/// let mut cache = dfa.create_cache();
/// let haystack = "bar foo123";
///
/// // Here's a normal unanchored search that looks for any pattern.
/// let expected = HalfMatch::must(0, 10);
/// let input = Input::new(haystack);
/// assert_eq!(Some(expected), dfa.try_search_fwd(&mut cache, &input)?);
/// // We can also do a normal anchored search for any pattern. Since it's
/// // an anchored search, we position the start of the search where we
/// // know the match will begin.
/// let expected = HalfMatch::must(0, 10);
/// let input = Input::new(haystack).range(4..);
/// assert_eq!(Some(expected), dfa.try_search_fwd(&mut cache, &input)?);
/// // Since we compiled anchored start states for each pattern, we can
/// // also look for matches of other patterns explicitly, even if a
/// // different pattern would have normally matched.
/// let expected = HalfMatch::must(1, 10);
/// let input = Input::new(haystack)
/// .range(4..)
/// .anchored(Anchored::Pattern(PatternID::must(1)));
/// assert_eq!(Some(expected), dfa.try_search_fwd(&mut cache, &input)?);
///
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
pub fn starts_for_each_pattern(mut self, yes: bool) -> Config {
self.starts_for_each_pattern = Some(yes);
self
}
/// Whether to attempt to shrink the size of the lazy DFA's alphabet or
/// not.
///
/// This option is enabled by default and should never be disabled unless
/// one is debugging the lazy DFA.
///
/// When enabled, the lazy DFA will use a map from all possible bytes
/// to their corresponding equivalence class. Each equivalence class
/// represents a set of bytes that does not discriminate between a match
/// and a non-match in the DFA. For example, the pattern `[ab]+` has at
/// least two equivalence classes: a set containing `a` and `b` and a set
/// containing every byte except for `a` and `b`. `a` and `b` are in the
/// same equivalence classes because they never discriminate between a
/// match and a non-match.
///
/// The advantage of this map is that the size of the transition table
/// can be reduced drastically from `#states * 256 * sizeof(LazyStateID)`
/// to `#states * k * sizeof(LazyStateID)` where `k` is the number of
/// equivalence classes (rounded up to the nearest power of 2). As a
/// result, total space usage can decrease substantially. Moreover, since a
/// smaller alphabet is used, DFA compilation during search becomes faster
/// as well since it will potentially be able to reuse a single transition
/// for multiple bytes.
///
/// **WARNING:** This is only useful for debugging lazy DFAs. Disabling
/// this does not yield any speed advantages. Namely, even when this is
/// disabled, a byte class map is still used while searching. The only
/// difference is that every byte will be forced into its own distinct
/// equivalence class. This is useful for debugging the actual generated
/// transitions because it lets one see the transitions defined on actual
/// bytes instead of the equivalence classes.
pub fn byte_classes(mut self, yes: bool) -> Config {
self.byte_classes = Some(yes);
self
}
/// Heuristically enable Unicode word boundaries.
///
/// When set, this will attempt to implement Unicode word boundaries as if
/// they were ASCII word boundaries. This only works when the search input
/// is ASCII only. If a non-ASCII byte is observed while searching, then a
/// [`MatchError::quit`] error is returned.
///
/// A possible alternative to enabling this option is to simply use an
/// ASCII word boundary, e.g., via `(?-u:\b)`. The main reason to use this
/// option is if you absolutely need Unicode support. This option lets one
/// use a fast search implementation (a DFA) for some potentially very
/// common cases, while providing the option to fall back to some other
/// regex engine to handle the general case when an error is returned.
///
/// If the pattern provided has no Unicode word boundary in it, then this
/// option has no effect. (That is, quitting on a non-ASCII byte only
/// occurs when this option is enabled _and_ a Unicode word boundary is
/// present in the pattern.)
///
/// This is almost equivalent to setting all non-ASCII bytes to be quit
/// bytes. The only difference is that this will cause non-ASCII bytes to
/// be quit bytes _only_ when a Unicode word boundary is present in the
/// pattern.
///
/// When enabling this option, callers _must_ be prepared to handle
/// a [`MatchError`](crate::MatchError) error during search.
/// When using a [`Regex`](crate::hybrid::regex::Regex), this
/// corresponds to using the `try_` suite of methods. Alternatively,
/// if callers can guarantee that their input is ASCII only, then a
/// [`MatchError::quit`] error will never be returned while searching.
///
/// This is disabled by default.
///
/// # Example
///
/// This example shows how to heuristically enable Unicode word boundaries
/// in a pattern. It also shows what happens when a search comes across a
/// non-ASCII byte.
///
/// ```
/// use regex_automata::{
/// hybrid::dfa::DFA,
/// HalfMatch, Input, MatchError,
/// };
///
/// let dfa = DFA::builder()
/// .configure(DFA::config().unicode_word_boundary(true))
/// .build(r"\b[0-9]+\b")?;
/// let mut cache = dfa.create_cache();
///
/// // The match occurs before the search ever observes the snowman
/// // character, so no error occurs.
/// let haystack = "foo 123 ☃";
/// let expected = Some(HalfMatch::must(0, 7));
/// let got = dfa.try_search_fwd(&mut cache, &Input::new(haystack))?;
/// assert_eq!(expected, got);
///
/// // Notice that this search fails, even though the snowman character
/// // occurs after the ending match offset. This is because search
/// // routines read one byte past the end of the search to account for
/// // look-around, and indeed, this is required here to determine whether
/// // the trailing \b matches.
/// let haystack = "foo 123 ☃";
/// let expected = MatchError::quit(0xE2, 8);
/// let got = dfa.try_search_fwd(&mut cache, &Input::new(haystack));
/// assert_eq!(Err(expected), got);
///
/// // Another example is executing a search where the span of the haystack
/// // we specify is all ASCII, but there is non-ASCII just before it. This
/// // correctly also reports an error.
/// let input = Input::new("β123").range(2..);
/// let expected = MatchError::quit(0xB2, 1);
/// let got = dfa.try_search_fwd(&mut cache, &input);
/// assert_eq!(Err(expected), got);
///
/// // And similarly for the trailing word boundary.
/// let input = Input::new("123β").range(..3);
/// let expected = MatchError::quit(0xCE, 3);
/// let got = dfa.try_search_fwd(&mut cache, &input);
/// assert_eq!(Err(expected), got);
///
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
pub fn unicode_word_boundary(mut self, yes: bool) -> Config {
// We have a separate option for this instead of just setting the
// appropriate quit bytes here because we don't want to set quit bytes
// for every regex. We only want to set them when the regex contains a
// Unicode word boundary.
self.unicode_word_boundary = Some(yes);
self
}
/// Add a "quit" byte to the lazy DFA.
///
/// When a quit byte is seen during search time, then search will return a
/// [`MatchError::quit`] error indicating the offset at which the search
/// stopped.
///
/// A quit byte will always overrule any other aspects of a regex. For
/// example, if the `x` byte is added as a quit byte and the regex `\w` is
/// used, then observing `x` will cause the search to quit immediately
/// despite the fact that `x` is in the `\w` class.
///
/// This mechanism is primarily useful for heuristically enabling certain
/// features like Unicode word boundaries in a DFA. Namely, if the input
/// to search is ASCII, then a Unicode word boundary can be implemented
/// via an ASCII word boundary with no change in semantics. Thus, a DFA
/// can attempt to match a Unicode word boundary but give up as soon as it
/// observes a non-ASCII byte. Indeed, if callers set all non-ASCII bytes
/// to be quit bytes, then Unicode word boundaries will be permitted when
/// building lazy DFAs. Of course, callers should enable
/// [`Config::unicode_word_boundary`] if they want this behavior instead.
/// (The advantage being that non-ASCII quit bytes will only be added if a
/// Unicode word boundary is in the pattern.)
///
/// When enabling this option, callers _must_ be prepared to handle a
/// [`MatchError`](crate::MatchError) error during search. When using a
/// [`Regex`](crate::hybrid::regex::Regex), this corresponds to using the
/// `try_` suite of methods.
///
/// By default, there are no quit bytes set.
///
/// # Panics
///
/// This panics if heuristic Unicode word boundaries are enabled and any
/// non-ASCII byte is removed from the set of quit bytes. Namely, enabling
/// Unicode word boundaries requires setting every non-ASCII byte to a quit
/// byte. So if the caller attempts to undo any of that, then this will
/// panic.
///
/// # Example
///
/// This example shows how to cause a search to terminate if it sees a
/// `\n` byte. This could be useful if, for example, you wanted to prevent
/// a user supplied pattern from matching across a line boundary.
///
/// ```
/// # if cfg!(miri) { return Ok(()); } // miri takes too long
/// use regex_automata::{hybrid::dfa::DFA, MatchError, Input};
///
/// let dfa = DFA::builder()
/// .configure(DFA::config().quit(b'\n', true))
/// .build(r"foo\p{any}+bar")?;
/// let mut cache = dfa.create_cache();
///
/// let haystack = "foo\nbar";
/// // Normally this would produce a match, since \p{any} contains '\n'.
/// // But since we instructed the automaton to enter a quit state if a
/// // '\n' is observed, this produces a match error instead.
/// let expected = MatchError::quit(b'\n', 3);
/// let got = dfa.try_search_fwd(
/// &mut cache,
/// &Input::new(haystack),
/// ).unwrap_err();
/// assert_eq!(expected, got);
///
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
pub fn quit(mut self, byte: u8, yes: bool) -> Config {
if self.get_unicode_word_boundary() && !byte.is_ascii() && !yes {
panic!(
"cannot set non-ASCII byte to be non-quit when \
Unicode word boundaries are enabled"
);
}
if self.quitset.is_none() {
self.quitset = Some(ByteSet::empty());
}
if yes {
self.quitset.as_mut().unwrap().add(byte);
} else {
self.quitset.as_mut().unwrap().remove(byte);
}
self
}
/// Enable specializing start states in the lazy DFA.
///
/// When start states are specialized, an implementor of a search routine
/// using a lazy DFA can tell when the search has entered a starting state.
/// When start states aren't specialized, then it is impossible to know
/// whether the search has entered a start state.
///
/// Ideally, this option wouldn't need to exist and we could always
/// specialize start states. The problem is that start states can be quite
/// active. This in turn means that an efficient search routine is likely
/// to ping-pong between a heavily optimized hot loop that handles most
/// states and to a less optimized specialized handling of start states.
/// This causes branches to get heavily mispredicted and overall can
/// materially decrease throughput. Therefore, specializing start states
/// should only be enabled when it is needed.
///
/// Knowing whether a search is in a start state is typically useful when a
/// prefilter is active for the search. A prefilter is typically only run
/// when in a start state and a prefilter can greatly accelerate a search.
/// Therefore, the possible cost of specializing start states is worth it
/// in this case. Otherwise, if you have no prefilter, there is likely no
/// reason to specialize start states.
///
/// This is disabled by default, but note that it is automatically
/// enabled (or disabled) if [`Config::prefilter`] is set. Namely, unless
/// `specialize_start_states` has already been set, [`Config::prefilter`]
/// will automatically enable or disable it based on whether a prefilter
/// is present or not, respectively. This is done because a prefilter's
/// effectiveness is rooted in being executed whenever the DFA is in a
/// start state, and that's only possible to do when they are specialized.
///
/// Note that it is plausibly reasonable to _disable_ this option
/// explicitly while _enabling_ a prefilter. In that case, a prefilter
/// will still be run at the beginning of a search, but never again. This
/// in theory could strike a good balance if you're in a situation where a
/// prefilter is likely to produce many false positive candidates.
///
/// # Example
///
/// This example shows how to enable start state specialization and then
/// shows how to check whether a state is a start state or not.
///
/// ```
/// use regex_automata::{hybrid::dfa::DFA, MatchError, Input};
///
/// let dfa = DFA::builder()
/// .configure(DFA::config().specialize_start_states(true))
/// .build(r"[a-z]+")?;
/// let mut cache = dfa.create_cache();
///
/// let haystack = "123 foobar 4567".as_bytes();
/// let sid = dfa.start_state_forward(&mut cache, &Input::new(haystack))?;
/// // The ID returned by 'start_state_forward' will always be tagged as
/// // a start state when start state specialization is enabled.
/// assert!(sid.is_tagged());
/// assert!(sid.is_start());
///
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
///
/// Compare the above with the default lazy DFA configuration where
/// start states are _not_ specialized. In this case, the start state
/// is not tagged and `sid.is_start()` returns false.
///
/// ```
/// use regex_automata::{hybrid::dfa::DFA, MatchError, Input};
///
/// let dfa = DFA::new(r"[a-z]+")?;
/// let mut cache = dfa.create_cache();
///
/// let haystack = "123 foobar 4567".as_bytes();
/// let sid = dfa.start_state_forward(&mut cache, &Input::new(haystack))?;
/// // Start states are not tagged in the default configuration!
/// assert!(!sid.is_tagged());
/// assert!(!sid.is_start());
///
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
pub fn specialize_start_states(mut self, yes: bool) -> Config {
self.specialize_start_states = Some(yes);
self
}
/// Sets the maximum amount of heap memory, in bytes, to allocate to the
/// cache for use during a lazy DFA search. If the lazy DFA would otherwise
/// use more heap memory, then, depending on other configuration knobs,
/// either stop the search and return an error or clear the cache and
/// continue the search.
///
/// The default cache capacity is some "reasonable" number that will
/// accommodate most regular expressions. You may find that if you need
/// to build a large DFA then it may be necessary to increase the cache
/// capacity.
///
/// Note that while building a lazy DFA will do a "minimum" check to ensure
/// the capacity is big enough, this is more or less about correctness.
/// If the cache is bigger than the minimum but still "too small," then the
/// lazy DFA could wind up spending a lot of time clearing the cache and
/// recomputing transitions, thus negating the performance benefits of a
/// lazy DFA. Thus, setting the cache capacity is mostly an experimental
/// endeavor. For most common patterns, however, the default should be
/// sufficient.
///
/// For more details on how the lazy DFA's cache is used, see the
/// documentation for [`Cache`].
///
/// # Example
///
/// This example shows what happens if the configured cache capacity is
/// too small. In such cases, one can override the cache capacity to make
/// it bigger. Alternatively, one might want to use less memory by setting
/// a smaller cache capacity.
///
/// ```
/// # if cfg!(miri) { return Ok(()); } // miri takes too long
/// use regex_automata::{hybrid::dfa::DFA, HalfMatch, Input};
///
/// let pattern = r"\p{L}{1000}";
///
/// // The default cache capacity is likely too small to deal with regexes
/// // that are very large. Large repetitions of large Unicode character
/// // classes are a common way to make very large regexes.
/// let _ = DFA::new(pattern).unwrap_err();
/// // Bump up the capacity to something bigger.
/// let dfa = DFA::builder()
/// .configure(DFA::config().cache_capacity(100 * (1<<20))) // 100 MB
/// .build(pattern)?;
/// let mut cache = dfa.create_cache();
///
/// let haystack = "ͰͲͶͿΆΈΉΊΌΎΏΑΒΓΔΕΖΗΘΙ".repeat(50);
/// let expected = Some(HalfMatch::must(0, 2000));
/// let got = dfa.try_search_fwd(&mut cache, &Input::new(&haystack))?;
/// assert_eq!(expected, got);
///
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
pub fn cache_capacity(mut self, bytes: usize) -> Config {
self.cache_capacity = Some(bytes);
self
}
/// Configures construction of a lazy DFA to use the minimum cache capacity
/// if the configured capacity is otherwise too small for the provided NFA.
///
/// This is useful if you never want lazy DFA construction to fail because
/// of a capacity that is too small.
///
/// In general, this option is typically not a good idea. In particular,
/// while a minimum cache capacity does permit the lazy DFA to function
/// where it otherwise couldn't, it's plausible that it may not function
/// well if it's constantly running out of room. In that case, the speed
/// advantages of the lazy DFA may be negated. On the other hand, the
/// "minimum" cache capacity computed may not be completely accurate and
/// could actually be bigger than what is really necessary. Therefore, it
/// is plausible that using the minimum cache capacity could still result
/// in very good performance.
///
/// This is disabled by default.
///
/// # Example
///
/// This example shows what happens if the configured cache capacity is
/// too small. In such cases, one could override the capacity explicitly.
/// An alternative, demonstrated here, let's us force construction to use
/// the minimum cache capacity if the configured capacity is otherwise
/// too small.
///
/// ```
/// # if cfg!(miri) { return Ok(()); } // miri takes too long
/// use regex_automata::{hybrid::dfa::DFA, HalfMatch, Input};
///
/// let pattern = r"\p{L}{1000}";
///
/// // The default cache capacity is likely too small to deal with regexes
/// // that are very large. Large repetitions of large Unicode character
/// // classes are a common way to make very large regexes.
/// let _ = DFA::new(pattern).unwrap_err();
/// // Configure construction such it automatically selects the minimum
/// // cache capacity if it would otherwise be too small.
/// let dfa = DFA::builder()
/// .configure(DFA::config().skip_cache_capacity_check(true))
/// .build(pattern)?;
/// let mut cache = dfa.create_cache();
///
/// let haystack = "ͰͲͶͿΆΈΉΊΌΎΏΑΒΓΔΕΖΗΘΙ".repeat(50);
/// let expected = Some(HalfMatch::must(0, 2000));
/// let got = dfa.try_search_fwd(&mut cache, &Input::new(&haystack))?;
/// assert_eq!(expected, got);
///
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
pub fn skip_cache_capacity_check(mut self, yes: bool) -> Config {
self.skip_cache_capacity_check = Some(yes);
self
}
/// Configure a lazy DFA search to quit after a certain number of cache
/// clearings.
///
/// When a minimum is set, then a lazy DFA search will *possibly* "give
/// up" after the minimum number of cache clearings has occurred. This is
/// typically useful in scenarios where callers want to detect whether the
/// lazy DFA search is "efficient" or not. If the cache is cleared too many
/// times, this is a good indicator that it is not efficient, and thus, the
/// caller may wish to use some other regex engine.
///
/// Note that the number of times a cache is cleared is a property of
/// the cache itself. Thus, if a cache is used in a subsequent search
/// with a similarly configured lazy DFA, then it could cause the
/// search to "give up" if the cache needed to be cleared, depending
/// on its internal count and configured minimum. The cache clear
/// count can only be reset to `0` via [`DFA::reset_cache`] (or
/// [`Regex::reset_cache`](crate::hybrid::regex::Regex::reset_cache) if
/// you're using the `Regex` API).
///
/// By default, no minimum is configured. Thus, a lazy DFA search will
/// never give up due to cache clearings. If you do set this option, you
/// might consider also setting [`Config::minimum_bytes_per_state`] in
/// order for the lazy DFA to take efficiency into account before giving
/// up.
///
/// # Example
///
/// This example uses a somewhat pathological configuration to demonstrate
/// the _possible_ behavior of cache clearing and how it might result
/// in a search that returns an error.
///
/// It is important to note that the precise mechanics of how and when
/// a cache gets cleared is an implementation detail.
///
/// ```
/// # if cfg!(miri) { return Ok(()); } // miri takes too long
/// use regex_automata::{hybrid::dfa::DFA, Input, MatchError, MatchErrorKind};
///
/// // This is a carefully chosen regex. The idea is to pick one
/// // that requires some decent number of states (hence the bounded
/// // repetition). But we specifically choose to create a class with an
/// // ASCII letter and a non-ASCII letter so that we can check that no new
/// // states are created once the cache is full. Namely, if we fill up the
/// // cache on a haystack of 'a's, then in order to match one 'β', a new
/// // state will need to be created since a 'β' is encoded with multiple
/// // bytes. Since there's no room for this state, the search should quit
/// // at the very first position.
/// let pattern = r"[aβ]{100}";
/// let dfa = DFA::builder()
/// .configure(
/// // Configure it so that we have the minimum cache capacity
/// // possible. And that if any clearings occur, the search quits.
/// DFA::config()
/// .skip_cache_capacity_check(true)
/// .cache_capacity(0)
/// .minimum_cache_clear_count(Some(0)),
/// )
/// .build(pattern)?;
/// let mut cache = dfa.create_cache();
///
/// // Our search will give up before reaching the end!
/// let haystack = "a".repeat(101).into_bytes();
/// let result = dfa.try_search_fwd(&mut cache, &Input::new(&haystack));
/// assert!(matches!(
/// *result.unwrap_err().kind(),
/// MatchErrorKind::GaveUp { .. },
/// ));
///
/// // Now that we know the cache is full, if we search a haystack that we
/// // know will require creating at least one new state, it should not
/// // be able to make much progress.
/// let haystack = "β".repeat(101).into_bytes();
/// let result = dfa.try_search_fwd(&mut cache, &Input::new(&haystack));
/// assert!(matches!(
/// *result.unwrap_err().kind(),
/// MatchErrorKind::GaveUp { .. },
/// ));
///
/// // If we reset the cache, then we should be able to create more states
/// // and make more progress with searching for betas.
/// cache.reset(&dfa);
/// let haystack = "β".repeat(101).into_bytes();
/// let result = dfa.try_search_fwd(&mut cache, &Input::new(&haystack));
/// assert!(matches!(
/// *result.unwrap_err().kind(),
/// MatchErrorKind::GaveUp { .. },
/// ));
///
/// // ... switching back to ASCII still makes progress since it just needs
/// // to set transitions on existing states!
/// let haystack = "a".repeat(101).into_bytes();
/// let result = dfa.try_search_fwd(&mut cache, &Input::new(&haystack));
/// assert!(matches!(
/// *result.unwrap_err().kind(),
/// MatchErrorKind::GaveUp { .. },
/// ));
///
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
pub fn minimum_cache_clear_count(mut self, min: Option<usize>) -> Config {
self.minimum_cache_clear_count = Some(min);
self
}
/// Configure a lazy DFA search to quit only when its efficiency drops
/// below the given minimum.
///
/// The efficiency of the cache is determined by the number of DFA states
/// compiled per byte of haystack searched. For example, if the efficiency
/// is 2, then it means the lazy DFA is creating a new DFA state after
/// searching approximately 2 bytes in a haystack. Generally speaking, 2
/// is quite bad and it's likely that even a slower regex engine like the
/// [`PikeVM`](crate::nfa::thompson::pikevm::PikeVM) would be faster.
///
/// This has no effect if [`Config::minimum_cache_clear_count`] is not set.
/// Namely, this option only kicks in when the cache has been cleared more
/// than the minimum number. If no minimum is set, then the cache is simply
/// cleared whenever it fills up and it is impossible for the lazy DFA to
/// quit due to ineffective use of the cache.
///
/// In general, if one is setting [`Config::minimum_cache_clear_count`],
/// then one should probably also set this knob as well. The reason is
/// that the absolute number of times the cache is cleared is generally
/// not a great predictor of efficiency. For example, if a new DFA state
/// is created for every 1,000 bytes searched, then it wouldn't be hard
/// for the cache to get cleared more than `N` times and then cause the
/// lazy DFA to quit. But a new DFA state every 1,000 bytes is likely quite
/// good from a performance perspective, and it's likely that the lazy
/// DFA should continue searching, even if it requires clearing the cache
/// occasionally.
///
/// Finally, note that if you're implementing your own lazy DFA search
/// routine and also want this efficiency check to work correctly, then
/// you'll need to use the following routines to record search progress:
///
/// * Call [`Cache::search_start`] at the beginning of every search.
/// * Call [`Cache::search_update`] whenever [`DFA::next_state`] is
/// called.
/// * Call [`Cache::search_finish`] before completing a search. (It is
/// not strictly necessary to call this when an error is returned, as
/// `Cache::search_start` will automatically finish the previous search
/// for you. But calling it where possible before returning helps improve
/// the accuracy of how many bytes have actually been searched.)
pub fn minimum_bytes_per_state(mut self, min: Option<usize>) -> Config {
self.minimum_bytes_per_state = Some(min);
self
}
/// Returns the match semantics set in this configuration.
pub fn get_match_kind(&self) -> MatchKind {
self.match_kind.unwrap_or(MatchKind::LeftmostFirst)
}
/// Returns the prefilter set in this configuration, if one at all.
pub fn get_prefilter(&self) -> Option<&Prefilter> {
self.pre.as_ref().unwrap_or(&None).as_ref()
}
/// Returns whether this configuration has enabled anchored starting states
/// for every pattern in the DFA.
pub fn get_starts_for_each_pattern(&self) -> bool {
self.starts_for_each_pattern.unwrap_or(false)
}
/// Returns whether this configuration has enabled byte classes or not.
/// This is typically a debugging oriented option, as disabling it confers
/// no speed benefit.
pub fn get_byte_classes(&self) -> bool {
self.byte_classes.unwrap_or(true)
}
/// Returns whether this configuration has enabled heuristic Unicode word
/// boundary support. When enabled, it is possible for a search to return
/// an error.
pub fn get_unicode_word_boundary(&self) -> bool {
self.unicode_word_boundary.unwrap_or(false)
}
/// Returns whether this configuration will instruct the lazy DFA to enter
/// a quit state whenever the given byte is seen during a search. When at
/// least one byte has this enabled, it is possible for a search to return
/// an error.
pub fn get_quit(&self, byte: u8) -> bool {
self.quitset.map_or(false, |q| q.contains(byte))
}
/// Returns whether this configuration will instruct the lazy DFA to
/// "specialize" start states. When enabled, the lazy DFA will tag start
/// states so that search routines using the lazy DFA can detect when
/// it's in a start state and do some kind of optimization (like run a
/// prefilter).
pub fn get_specialize_start_states(&self) -> bool {
self.specialize_start_states.unwrap_or(false)
}
/// Returns the cache capacity set on this configuration.
pub fn get_cache_capacity(&self) -> usize {
self.cache_capacity.unwrap_or(2 * (1 << 20))
}
/// Returns whether the cache capacity check should be skipped.
pub fn get_skip_cache_capacity_check(&self) -> bool {
self.skip_cache_capacity_check.unwrap_or(false)
}
/// Returns, if set, the minimum number of times the cache must be cleared
/// before a lazy DFA search can give up. When no minimum is set, then a
/// search will never quit and will always clear the cache whenever it
/// fills up.
pub fn get_minimum_cache_clear_count(&self) -> Option<usize> {
self.minimum_cache_clear_count.unwrap_or(None)
}
/// Returns, if set, the minimum number of bytes per state that need to be
/// processed in order for the lazy DFA to keep going. If the minimum falls
/// below this number (and the cache has been cleared a minimum number of
/// times), then the lazy DFA will return a "gave up" error.
pub fn get_minimum_bytes_per_state(&self) -> Option<usize> {
self.minimum_bytes_per_state.unwrap_or(None)
}
/// Returns the minimum lazy DFA cache capacity required for the given NFA.
///
/// The cache capacity required for a particular NFA may change without
/// notice. Callers should not rely on it being stable.
///
/// This is useful for informational purposes, but can also be useful for
/// other reasons. For example, if one wants to check the minimum cache
/// capacity themselves or if one wants to set the capacity based on the
/// minimum.
///
/// This may return an error if this configuration does not support all of
/// the instructions used in the given NFA. For example, if the NFA has a
/// Unicode word boundary but this configuration does not enable heuristic
/// support for Unicode word boundaries.
pub fn get_minimum_cache_capacity(
&self,
nfa: &thompson::NFA,
) -> Result<usize, BuildError> {
let quitset = self.quit_set_from_nfa(nfa)?;
let classes = self.byte_classes_from_nfa(nfa, &quitset);
let starts = self.get_starts_for_each_pattern();
Ok(minimum_cache_capacity(nfa, &classes, starts))
}
/// Returns the byte class map used during search from the given NFA.
///
/// If byte classes are disabled on this configuration, then a map is
/// returned that puts each byte in its own equivalent class.
fn byte_classes_from_nfa(
&self,
nfa: &thompson::NFA,
quit: &ByteSet,
) -> ByteClasses {
if !self.get_byte_classes() {
// The lazy DFA will always use the equivalence class map, but
// enabling this option is useful for debugging. Namely, this will
// cause all transitions to be defined over their actual bytes
// instead of an opaque equivalence class identifier. The former is
// much easier to grok as a human.
ByteClasses::singletons()
} else {
let mut set = nfa.byte_class_set().clone();
// It is important to distinguish any "quit" bytes from all other
// bytes. Otherwise, a non-quit byte may end up in the same class
// as a quit byte, and thus cause the DFA stop when it shouldn't.
//
// Test case:
//
// regex-cli find hybrid regex -w @conn.json.1000x.log \
// '^#' '\b10\.55\.182\.100\b'
if !quit.is_empty() {
set.add_set(&quit);
}
set.byte_classes()
}
}
/// Return the quit set for this configuration and the given NFA.
///
/// This may return an error if the NFA is incompatible with this
/// configuration's quit set. For example, if the NFA has a Unicode word
/// boundary and the quit set doesn't include non-ASCII bytes.
fn quit_set_from_nfa(
&self,
nfa: &thompson::NFA,
) -> Result<ByteSet, BuildError> {
let mut quit = self.quitset.unwrap_or(ByteSet::empty());
if nfa.look_set_any().contains_word_unicode() {
if self.get_unicode_word_boundary() {
for b in 0x80..=0xFF {
quit.add(b);
}
} else {
// If heuristic support for Unicode word boundaries wasn't
// enabled, then we can still check if our quit set is correct.
// If the caller set their quit bytes in a way that causes the
// DFA to quit on at least all non-ASCII bytes, then that's all
// we need for heuristic support to work.
if !quit.contains_range(0x80, 0xFF) {
return Err(
BuildError::unsupported_dfa_word_boundary_unicode(),
);
}
}
}
Ok(quit)
}
/// Overwrite the default configuration such that the options in `o` are
/// always used. If an option in `o` is not set, then the corresponding
/// option in `self` is used. If it's not set in `self` either, then it
/// remains not set.
fn overwrite(&self, o: Config) -> Config {
Config {
match_kind: o.match_kind.or(self.match_kind),
pre: o.pre.or_else(|| self.pre.clone()),
starts_for_each_pattern: o
.starts_for_each_pattern
.or(self.starts_for_each_pattern),
byte_classes: o.byte_classes.or(self.byte_classes),
unicode_word_boundary: o
.unicode_word_boundary
.or(self.unicode_word_boundary),
quitset: o.quitset.or(self.quitset),
specialize_start_states: o
.specialize_start_states
.or(self.specialize_start_states),
cache_capacity: o.cache_capacity.or(self.cache_capacity),
skip_cache_capacity_check: o
.skip_cache_capacity_check
.or(self.skip_cache_capacity_check),
minimum_cache_clear_count: o
.minimum_cache_clear_count
.or(self.minimum_cache_clear_count),
minimum_bytes_per_state: o
.minimum_bytes_per_state
.or(self.minimum_bytes_per_state),
}
}
}
/// A builder for constructing a lazy deterministic finite automaton from
/// regular expressions.
///
/// As a convenience, [`DFA::builder`] is an alias for [`Builder::new`]. The
/// advantage of the former is that it often lets you avoid importing the
/// `Builder` type directly.
///
/// This builder provides two main things:
///
/// 1. It provides a few different `build` routines for actually constructing
/// a DFA from different kinds of inputs. The most convenient is
/// [`Builder::build`], which builds a DFA directly from a pattern string. The
/// most flexible is [`Builder::build_from_nfa`], which builds a DFA straight
/// from an NFA.
/// 2. The builder permits configuring a number of things.
/// [`Builder::configure`] is used with [`Config`] to configure aspects of
/// the DFA and the construction process itself. [`Builder::syntax`] and
/// [`Builder::thompson`] permit configuring the regex parser and Thompson NFA
/// construction, respectively. The syntax and thompson configurations only
/// apply when building from a pattern string.
///
/// This builder always constructs a *single* lazy DFA. As such, this builder
/// can only be used to construct regexes that either detect the presence
/// of a match or find the end location of a match. A single DFA cannot
/// produce both the start and end of a match. For that information, use a
/// [`Regex`](crate::hybrid::regex::Regex), which can be similarly configured
/// using [`regex::Builder`](crate::hybrid::regex::Builder). The main reason
/// to use a DFA directly is if the end location of a match is enough for your
/// use case. Namely, a `Regex` will construct two lazy DFAs instead of one,
/// since a second reverse DFA is needed to find the start of a match.
///
/// # Example
///
/// This example shows how to build a lazy DFA that uses a tiny cache capacity
/// and completely disables Unicode. That is:
///
/// * Things such as `\w`, `.` and `\b` are no longer Unicode-aware. `\w`
/// and `\b` are ASCII-only while `.` matches any byte except for `\n`
/// (instead of any UTF-8 encoding of a Unicode scalar value except for
/// `\n`). Things that are Unicode only, such as `\pL`, are not allowed.
/// * The pattern itself is permitted to match invalid UTF-8. For example,
/// things like `[^a]` that match any byte except for `a` are permitted.
///
/// ```
/// use regex_automata::{
/// hybrid::dfa::DFA,
/// nfa::thompson,
/// util::syntax,
/// HalfMatch, Input,
/// };
///
/// let dfa = DFA::builder()
/// .configure(DFA::config().cache_capacity(5_000))
/// .thompson(thompson::Config::new().utf8(false))
/// .syntax(syntax::Config::new().unicode(false).utf8(false))
/// .build(r"foo[^b]ar.*")?;
/// let mut cache = dfa.create_cache();
///
/// let haystack = b"\xFEfoo\xFFar\xE2\x98\xFF\n";
/// let expected = Some(HalfMatch::must(0, 10));
/// let got = dfa.try_search_fwd(&mut cache, &Input::new(haystack))?;
/// assert_eq!(expected, got);
///
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
#[derive(Clone, Debug)]
pub struct Builder {
config: Config,
#[cfg(feature = "syntax")]
thompson: thompson::Compiler,
}
impl Builder {
/// Create a new lazy DFA builder with the default configuration.
pub fn new() -> Builder {
Builder {
config: Config::default(),
#[cfg(feature = "syntax")]
thompson: thompson::Compiler::new(),
}
}
/// Build a lazy DFA from the given pattern.
///
/// If there was a problem parsing or compiling the pattern, then an error
/// is returned.
#[cfg(feature = "syntax")]
pub fn build(&self, pattern: &str) -> Result<DFA, BuildError> {
self.build_many(&[pattern])
}
/// Build a lazy DFA from the given patterns.
///
/// When matches are returned, the pattern ID corresponds to the index of
/// the pattern in the slice given.
#[cfg(feature = "syntax")]
pub fn build_many<P: AsRef<str>>(
&self,
patterns: &[P],
) -> Result<DFA, BuildError> {
let nfa = self
.thompson
.clone()
// We can always forcefully disable captures because DFAs do not
// support them.
.configure(
thompson::Config::new()
.which_captures(thompson::WhichCaptures::None),
)
.build_many(patterns)
.map_err(BuildError::nfa)?;
self.build_from_nfa(nfa)
}
/// Build a DFA from the given NFA.
///
/// Note that this requires owning a `thompson::NFA`. While this may force
/// you to clone the NFA, such a clone is not a deep clone. Namely, NFAs
/// are defined internally to support shared ownership such that cloning is
/// very cheap.
///
/// # Example
///
/// This example shows how to build a lazy DFA if you already have an NFA
/// in hand.
///
/// ```
/// use regex_automata::{
/// hybrid::dfa::DFA,
/// nfa::thompson,
/// HalfMatch, Input,
/// };
///
/// let haystack = "foo123bar";
///
/// // This shows how to set non-default options for building an NFA.
/// let nfa = thompson::Compiler::new()
/// .configure(thompson::Config::new().shrink(true))
/// .build(r"[0-9]+")?;
/// let dfa = DFA::builder().build_from_nfa(nfa)?;
/// let mut cache = dfa.create_cache();
/// let expected = Some(HalfMatch::must(0, 6));
/// let got = dfa.try_search_fwd(&mut cache, &Input::new(haystack))?;
/// assert_eq!(expected, got);
///
/// # Ok::<(), Box<dyn std::error::Error>>(())
/// ```
pub fn build_from_nfa(
&self,
nfa: thompson::NFA,
) -> Result<DFA, BuildError> {
let quitset = self.config.quit_set_from_nfa(&nfa)?;
let classes = self.config.byte_classes_from_nfa(&nfa, &quitset);
// Check that we can fit at least a few states into our cache,
// otherwise it's pretty senseless to use the lazy DFA. This does have
// a possible failure mode though. This assumes the maximum size of a
// state in powerset space (so, the total number of NFA states), which
// may never actually materialize, and could be quite a bit larger
// than the actual biggest state. If this turns out to be a problem,
// we could expose a knob that disables this check. But if so, we have
// to be careful not to panic in other areas of the code (the cache
// clearing and init code) that tend to assume some minimum useful
// cache capacity.
let min_cache = minimum_cache_capacity(
&nfa,
&classes,
self.config.get_starts_for_each_pattern(),
);
let mut cache_capacity = self.config.get_cache_capacity();
if cache_capacity < min_cache {
// When the caller has asked us to skip the cache capacity check,
// then we simply force the cache capacity to its minimum amount
// and mush on.
if self.config.get_skip_cache_capacity_check() {
debug!(
"given capacity ({}) is too small, \
since skip_cache_capacity_check is enabled, \
setting cache capacity to minimum ({})",
cache_capacity, min_cache,
);
cache_capacity = min_cache;
} else {
return Err(BuildError::insufficient_cache_capacity(
min_cache,
cache_capacity,
));
}
}
// We also need to check that we can fit at least some small number
// of states in our state ID space. This is unlikely to trigger in
// >=32-bit systems, but 16-bit systems have a pretty small state ID
// space since a number of bits are used up as sentinels.
if let Err(err) = minimum_lazy_state_id(&classes) {
return Err(BuildError::insufficient_state_id_capacity(err));
}
let stride2 = classes.stride2();
let start_map = StartByteMap::new(nfa.look_matcher());
Ok(DFA {
config: self.config.clone(),
nfa,
stride2,
start_map,
classes,
quitset,
cache_capacity,
})
}
/// Apply the given lazy DFA configuration options to this builder.
pub fn configure(&mut self, config: Config) -> &mut Builder {
self.config = self.config.overwrite(config);
self
}
/// Set the syntax configuration for this builder using
/// [`syntax::Config`](crate::util::syntax::Config).
///
/// This permits setting things like case insensitivity, Unicode and multi
/// line mode.
///
/// These settings only apply when constructing a lazy DFA directly from a
/// pattern.
#[cfg(feature = "syntax")]
pub fn syntax(
&mut self,
config: crate::util::syntax::Config,
) -> &mut Builder {
self.thompson.syntax(config);
self
}
/// Set the Thompson NFA configuration for this builder using
/// [`nfa::thompson::Config`](crate::nfa::thompson::Config).
///
/// This permits setting things like whether the DFA should match the regex
/// in reverse or if additional time should be spent shrinking the size of
/// the NFA.
///
/// These settings only apply when constructing a DFA directly from a
/// pattern.
#[cfg(feature = "syntax")]
pub fn thompson(&mut self, config: thompson::Config) -> &mut Builder {
self.thompson.configure(config);
self
}
}
/// Represents the current state of an overlapping search.
///
/// This is used for overlapping searches since they need to know something
/// about the previous search. For example, when multiple patterns match at the
/// same position, this state tracks the last reported pattern so that the next
/// search knows whether to report another matching pattern or continue with
/// the search at the next position. Additionally, it also tracks which state
/// the last search call terminated in.
///
/// This type provides little introspection capabilities. The only thing a
/// caller can do is construct it and pass it around to permit search routines
/// to use it to track state, and also ask whether a match has been found.
///
/// Callers should always provide a fresh state constructed via
/// [`OverlappingState::start`] when starting a new search. Reusing state from
/// a previous search may result in incorrect results.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct OverlappingState {
/// The match reported by the most recent overlapping search to use this
/// state.
///
/// If a search does not find any matches, then it is expected to clear
/// this value.
pub(crate) mat: Option<HalfMatch>,
/// The state ID of the state at which the search was in when the call
/// terminated. When this is a match state, `last_match` must be set to a
/// non-None value.
///
/// A `None` value indicates the start state of the corresponding
/// automaton. We cannot use the actual ID, since any one automaton may
/// have many start states, and which one is in use depends on several
/// search-time factors.
pub(crate) id: Option<LazyStateID>,
/// The position of the search.
///
/// When `id` is None (i.e., we are starting a search), this is set to
/// the beginning of the search as given by the caller regardless of its
/// current value. Subsequent calls to an overlapping search pick up at
/// this offset.
pub(crate) at: usize,
/// The index into the matching patterns of the next match to report if the
/// current state is a match state. Note that this may be 1 greater than
/// the total number of matches to report for the current match state. (In
/// which case, no more matches should be reported at the current position
/// and the search should advance to the next position.)
pub(crate) next_match_index: Option<usize>,
/// This is set to true when a reverse overlapping search has entered its
/// EOI transitions.
///
/// This isn't used in a forward search because it knows to stop once the
/// position exceeds the end of the search range. In a reverse search,
/// since we use unsigned offsets, we don't "know" once we've gone past
/// `0`. So the only way to detect it is with this extra flag. The reverse
/// overlapping search knows to terminate specifically after it has
/// reported all matches after following the EOI transition.
pub(crate) rev_eoi: bool,
}
impl OverlappingState {
/// Create a new overlapping state that begins at the start state of any
/// automaton.
pub fn start() -> OverlappingState {
OverlappingState {
mat: None,
id: None,
at: 0,
next_match_index: None,
rev_eoi: false,
}
}
/// Return the match result of the most recent search to execute with this
/// state.
///
/// A searches will clear this result automatically, such that if no
/// match is found, this will correctly report `None`.
pub fn get_match(&self) -> Option<HalfMatch> {
self.mat
}
}
/// Runs the given overlapping `search` function (forwards or backwards) until
/// a match is found whose offset does not split a codepoint.
///
/// This is *not* always correct to call. It should only be called when the
/// underlying NFA has UTF-8 mode enabled *and* it can produce zero-width
/// matches. Calling this when both of those things aren't true might result
/// in legitimate matches getting skipped.
#[cold]
#[inline(never)]
fn skip_empty_utf8_splits_overlapping<F>(
input: &Input<'_>,
state: &mut OverlappingState,
mut search: F,
) -> Result<(), MatchError>
where
F: FnMut(&Input<'_>, &mut OverlappingState) -> Result<(), MatchError>,
{
// Note that this routine works for forwards and reverse searches
// even though there's no code here to handle those cases. That's
// because overlapping searches drive themselves to completion via
// `OverlappingState`. So all we have to do is push it until no matches are
// found.
let mut hm = match state.get_match() {
None => return Ok(()),
Some(hm) => hm,
};
if input.get_anchored().is_anchored() {
if !input.is_char_boundary(hm.offset()) {
state.mat = None;
}
return Ok(());
}
while !input.is_char_boundary(hm.offset()) {
search(input, state)?;
hm = match state.get_match() {
None => return Ok(()),
Some(hm) => hm,
};
}
Ok(())
}
/// Based on the minimum number of states required for a useful lazy DFA cache,
/// this returns the minimum lazy state ID that must be representable.
///
/// It's not likely for this to have any impact 32-bit systems (or higher), but
/// on 16-bit systems, the lazy state ID space is quite constrained and thus
/// may be insufficient if our MIN_STATES value is (for some reason) too high.
fn minimum_lazy_state_id(
classes: &ByteClasses,
) -> Result<LazyStateID, LazyStateIDError> {
let stride = 1 << classes.stride2();
let min_state_index = MIN_STATES.checked_sub(1).unwrap();
LazyStateID::new(min_state_index * stride)
}
/// Based on the minimum number of states required for a useful lazy DFA cache,
/// this returns a heuristic minimum number of bytes of heap space required.
///
/// This is a "heuristic" because the minimum it returns is likely bigger than
/// the true minimum. Namely, it assumes that each powerset NFA/DFA state uses
/// the maximum number of NFA states (all of them). This is likely bigger
/// than what is required in practice. Computing the true minimum effectively
/// requires determinization, which is probably too much work to do for a
/// simple check like this.
///
/// One of the issues with this approach IMO is that it requires that this
/// be in sync with the calculation above for computing how much heap memory
/// the DFA cache uses. If we get it wrong, it's possible for example for the
/// minimum to be smaller than the computed heap memory, and thus, it may be
/// the case that we can't add the required minimum number of states. That in
/// turn will make lazy DFA panic because we assume that we can add at least a
/// minimum number of states.
///
/// Another approach would be to always allow the minimum number of states to
/// be added to the lazy DFA cache, even if it exceeds the configured cache
/// limit. This does mean that the limit isn't really a limit in all cases,
/// which is unfortunate. But it does at least guarantee that the lazy DFA can
/// always make progress, even if it is slow. (This approach is very similar to
/// enabling the 'skip_cache_capacity_check' config knob, except it wouldn't
/// rely on cache size calculation. Instead, it would just always permit a
/// minimum number of states to be added.)
fn minimum_cache_capacity(
nfa: &thompson::NFA,
classes: &ByteClasses,
starts_for_each_pattern: bool,
) -> usize {
const ID_SIZE: usize = size_of::<LazyStateID>();
const STATE_SIZE: usize = size_of::<State>();
let stride = 1 << classes.stride2();
let states_len = nfa.states().len();
let sparses = 2 * states_len * NFAStateID::SIZE;
let trans = MIN_STATES * stride * ID_SIZE;
let mut starts = Start::len() * ID_SIZE;
if starts_for_each_pattern {
starts += (Start::len() * nfa.pattern_len()) * ID_SIZE;
}
// The min number of states HAS to be at least 4: we have 3 sentinel states
// and then we need space for one more when we save a state after clearing
// the cache. We also need space for one more, otherwise we get stuck in a
// loop where we try to add a 5th state, which gets rejected, which clears
// the cache, which adds back a saved state (4th total state) which then
// tries to add the 5th state again.
assert!(MIN_STATES >= 5, "minimum number of states has to be at least 5");
// The minimum number of non-sentinel states. We consider this separately
// because sentinel states are much smaller in that they contain no NFA
// states. Given our aggressive calculation here, it's worth being more
// precise with the number of states we need.
let non_sentinel = MIN_STATES.checked_sub(SENTINEL_STATES).unwrap();
// Every `State` has 5 bytes for flags, 4 bytes (max) for the number of
// patterns, followed by 32-bit encodings of patterns and then delta
// varint encodings of NFA state IDs. We use the worst case (which isn't
// technically possible) of 5 bytes for each NFA state ID.
//
// HOWEVER, three of the states needed by a lazy DFA are just the sentinel
// unknown, dead and quit states. Those states have a known size and it is
// small.
let dead_state_size = State::dead().memory_usage();
let max_state_size = 5 + 4 + (nfa.pattern_len() * 4) + (states_len * 5);
let states = (SENTINEL_STATES * (STATE_SIZE + dead_state_size))
+ (non_sentinel * (STATE_SIZE + max_state_size));
// NOTE: We don't double count heap memory used by State for this map since
// we use reference counting to avoid doubling memory usage. (This tends to
// be where most memory is allocated in the cache.)
let states_to_sid = (MIN_STATES * STATE_SIZE) + (MIN_STATES * ID_SIZE);
let stack = states_len * NFAStateID::SIZE;
let scratch_state_builder = max_state_size;
trans
+ starts
+ states
+ states_to_sid
+ sparses
+ stack
+ scratch_state_builder
}
#[cfg(all(test, feature = "syntax"))]
mod tests {
use super::*;
// Tests that we handle heuristic Unicode word boundary support in reverse
// DFAs in the specific case of contextual searches.
//
// I wrote this test when I discovered a bug in how heuristic word
// boundaries were handled. Namely, that the starting state selection
// didn't consider the DFA's quit byte set when looking at the byte
// immediately before the start of the search (or immediately after the
// end of the search in the case of a reverse search). As a result, it was
// possible for '\bfoo\b' to match 'β123' because the trailing \xB2 byte
// in the 'β' codepoint would be treated as a non-word character. But of
// course, this search should trigger the DFA to quit, since there is a
// non-ASCII byte in consideration.
//
// Thus, I fixed 'start_state_{forward,reverse}' to check the quit byte set
// if it wasn't empty. The forward case is tested in the doc test for the
// Config::unicode_word_boundary API. We test the reverse case here, which
// is sufficiently niche that it doesn't really belong in a doc test.
#[test]
fn heuristic_unicode_reverse() {
let dfa = DFA::builder()
.configure(DFA::config().unicode_word_boundary(true))
.thompson(thompson::Config::new().reverse(true))
.build(r"\b[0-9]+\b")
.unwrap();
let mut cache = dfa.create_cache();
let input = Input::new("β123").range(2..);
let expected = MatchError::quit(0xB2, 1);
let got = dfa.try_search_rev(&mut cache, &input);
assert_eq!(Err(expected), got);
let input = Input::new("123β").range(..3);
let expected = MatchError::quit(0xCE, 3);
let got = dfa.try_search_rev(&mut cache, &input);
assert_eq!(Err(expected), got);
}
}