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//! Lifetime information for types.
#![allow(dead_code)]
use super::IdentBuf;
use crate::ast;
use core::fmt::Debug;
use core::hash::Hash;
use smallvec::{smallvec, SmallVec};
use std::borrow::{Borrow, Cow};
/// Convenience const representing the number of lifetimes a [`LifetimeEnv`]
/// can hold inline before needing to dynamically allocate.
pub(crate) const INLINE_NUM_LIFETIMES: usize = 4;
/// The lifetimes and bounds found on a method or type definition
#[derive(Debug)]
pub struct LifetimeEnv {
/// List of named lifetimes in scope of the method, and their bounds
nodes: SmallVec<[BoundedLifetime; INLINE_NUM_LIFETIMES]>,
/// Only relevant for method LifetimeEnvs (otherwise this is nodes.len())
///
/// The number of named _and_ anonymous lifetimes in the method.
/// We store the sum since it represents the upper bound on what indices
/// are in range of the graph. If we make a [`Lifetimes`] with
/// `num_lifetimes` entries, then `Lifetime`s that convert into
/// `Lifetime`s will fall into this range, and we'll know that it's
/// a named lifetime if it's < `nodes.len()`, or that it's an anonymous
/// lifetime if it's < `num_lifetimes`. Otherwise, we'd have to make a
/// distinction in `Lifetime` about which context it's in.
num_lifetimes: usize,
}
impl LifetimeEnv {
/// Format a lifetime indexing this env for use in code
pub fn fmt_lifetime(&self, lt: impl Borrow<Lifetime>) -> Cow<str> {
// we use Borrow here so that this can be used in templates where there's autoborrowing
let lt = *lt.borrow();
if let Some(lt) = self.nodes.get(lt.0) {
Cow::from(lt.ident.as_str())
} else if lt.0 < self.num_lifetimes {
format!("anon_{}", lt.0 - self.nodes.len()).into()
} else {
panic!("Found out of range lifetime: Got {lt:?} for env with {} nodes and {} total lifetimes", self.nodes.len(), self.num_lifetimes);
}
}
/// Get an iterator of all lifetimes that this must live as long as (including itself)
/// with the first lifetime always being returned first
pub fn all_shorter_lifetimes(
&self,
lt: impl Borrow<Lifetime>,
) -> impl Iterator<Item = Lifetime> + '_ {
// we use Borrow here so that this can be used in templates where there's autoborrowing
let lt = *lt.borrow();
// longer = true, since we are looking for lifetimes this is longer than
LifetimeTransitivityIterator::new(self, lt.0, false)
}
/// Same as all_shorter_lifetimes but the other way
pub fn all_longer_lifetimes(
&self,
lt: impl Borrow<Lifetime>,
) -> impl Iterator<Item = Lifetime> + '_ {
// we use Borrow here so that this can be used in templates where there's autoborrowing
let lt = *lt.borrow();
LifetimeTransitivityIterator::new(self, lt.0, true)
}
// List all named and unnamed lifetimes
pub fn num_lifetimes(&self) -> usize {
self.num_lifetimes
}
pub fn all_lifetimes(&self) -> impl ExactSizeIterator<Item = Lifetime> {
(0..self.num_lifetimes()).map(Lifetime::new)
}
/// Get the bounds for a named lifetime (none for unnamed lifetimes)
pub(super) fn get_bounds(&self, named_lifetime: Lifetime) -> Option<&BoundedLifetime> {
self.nodes.get(named_lifetime.0)
}
/// Returns a new [`LifetimeEnv`].
pub(super) fn new(
nodes: SmallVec<[BoundedLifetime; INLINE_NUM_LIFETIMES]>,
num_lifetimes: usize,
) -> Self {
Self {
nodes,
num_lifetimes,
}
}
/// Returns a fresh [`Lifetimes`] corresponding to `self`.
pub fn lifetimes(&self) -> Lifetimes {
let indices = (0..self.num_lifetimes)
.map(|index| MaybeStatic::NonStatic(Lifetime::new(index)))
.collect();
Lifetimes { indices }
}
/// Returns a new [`SubtypeLifetimeVisitor`], which can visit all reachable
/// lifetimes
pub fn subtype_lifetimes_visitor<F>(&self, visit_fn: F) -> SubtypeLifetimeVisitor<'_, F>
where
F: FnMut(Lifetime),
{
SubtypeLifetimeVisitor::new(self, visit_fn)
}
}
/// A lifetime in a [`LifetimeEnv`], which keeps track of which lifetimes it's
/// longer and shorter than.
///
/// Invariant: for a BoundedLifetime found inside a LifetimeEnv, all short/long connections
/// should be bidirectional.
#[derive(Debug)]
pub(super) struct BoundedLifetime {
pub(super) ident: IdentBuf,
/// Lifetimes longer than this (not transitive)
///
/// These are the inverse graph edges compared to `shorter`
pub(super) longer: SmallVec<[Lifetime; 2]>,
/// Lifetimes this is shorter than (not transitive)
///
/// These match `'a: 'b + 'c` bounds
pub(super) shorter: SmallVec<[Lifetime; 2]>,
}
impl BoundedLifetime {
/// Returns a new [`BoundedLifetime`].
pub(super) fn new(
ident: IdentBuf,
longer: SmallVec<[Lifetime; 2]>,
shorter: SmallVec<[Lifetime; 2]>,
) -> Self {
Self {
ident,
longer,
shorter,
}
}
}
/// Visit subtype lifetimes recursively, keeping track of which have already
/// been visited.
pub struct SubtypeLifetimeVisitor<'lt, F> {
lifetime_env: &'lt LifetimeEnv,
visited: SmallVec<[bool; INLINE_NUM_LIFETIMES]>,
visit_fn: F,
}
impl<'lt, F> SubtypeLifetimeVisitor<'lt, F>
where
F: FnMut(Lifetime),
{
fn new(lifetime_env: &'lt LifetimeEnv, visit_fn: F) -> Self {
Self {
lifetime_env,
visited: smallvec![false; lifetime_env.nodes.len()],
visit_fn,
}
}
/// Visit more sublifetimes. This method tracks which lifetimes have already
/// been visited, and uses this to not visit the same lifetime twice.
pub fn visit_subtypes(&mut self, method_lifetime: Lifetime) {
if let Some(visited @ false) = self.visited.get_mut(method_lifetime.0) {
*visited = true;
(self.visit_fn)(method_lifetime);
for longer in self.lifetime_env.nodes[method_lifetime.0].longer.iter() {
self.visit_subtypes(*longer)
}
} else {
debug_assert!(
method_lifetime.0 > self.lifetime_env.num_lifetimes,
"method lifetime has an internal index that's not in range of the lifetime env"
);
}
}
}
/// Wrapper type for `Lifetime` and `Lifetime`, indicating that it may
/// be the `'static` lifetime.
#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq, PartialOrd, Ord)]
#[allow(clippy::exhaustive_enums)] // this will only ever have two variants
pub enum MaybeStatic<T> {
Static,
NonStatic(T),
}
impl<T> MaybeStatic<T> {
/// Maps the lifetime, if it's not the `'static` lifetime, to another
/// non-static lifetime.
pub(super) fn map_nonstatic<F, R>(self, f: F) -> MaybeStatic<R>
where
F: FnOnce(T) -> R,
{
match self {
MaybeStatic::Static => MaybeStatic::Static,
MaybeStatic::NonStatic(lifetime) => MaybeStatic::NonStatic(f(lifetime)),
}
}
/// Maps the lifetime, if it's not the `'static` lifetime, to a potentially
/// static lifetime.
pub(super) fn flat_map_nonstatic<R, F>(self, f: F) -> MaybeStatic<R>
where
F: FnOnce(T) -> MaybeStatic<R>,
{
match self {
MaybeStatic::Static => MaybeStatic::Static,
MaybeStatic::NonStatic(lifetime) => f(lifetime),
}
}
}
/// A lifetime that exists as part of a type name, struct signature, or method signature.
///
/// This index only makes sense in the context of a surrounding type or method; since
/// this is essentially an index into that type/method's lifetime list.
#[derive(Copy, Clone, Hash, PartialEq, Eq, PartialOrd, Ord, Debug)]
pub struct Lifetime(usize);
/// A set of lifetimes found on a type name, struct signature, or method signature
#[derive(Clone, Debug)]
pub struct Lifetimes {
indices: SmallVec<[MaybeStatic<Lifetime>; 2]>,
}
impl Lifetime {
pub(super) const fn new(index: usize) -> Self {
Self(index)
}
}
impl Lifetimes {
/// Returns an iterator over the contained [`Lifetime`]s.
pub fn lifetimes(&self) -> impl ExactSizeIterator<Item = MaybeStatic<Lifetime>> + '_ {
self.indices.iter().copied()
}
pub(super) fn as_slice(&self) -> &[MaybeStatic<Lifetime>] {
self.indices.as_slice()
}
}
impl Lifetime {
/// Returns a [`Lifetime`] from its AST counterparts.
pub(super) fn from_ast(named: &ast::NamedLifetime, lifetime_env: &ast::LifetimeEnv) -> Self {
let index = lifetime_env
.id(named)
.unwrap_or_else(|| panic!("lifetime `{named}` not found in lifetime env"));
Self::new(index)
}
/// Returns a new [`MaybeStatic<Lifetime>`] representing `self` in the
/// scope of the method that it appears in.
///
/// For example, if we have some `Foo<'a>` type with a field `&'a Bar`, then
/// we can call this on the `'a` on the field. If `Foo` was `Foo<'static>`
/// in the method, then this will return `MaybeStatic::Static`. But if it
/// was `Foo<'b>`, then this will return `MaybeStatic::NonStatic` containing
/// the `Lifetime` corresponding to `'b`.
pub fn as_method_lifetime(self, method_lifetimes: &Lifetimes) -> MaybeStatic<Lifetime> {
method_lifetimes.indices[self.0]
}
}
impl Lifetimes {
pub(super) fn from_fn<F>(lifetimes: &[ast::Lifetime], lower_fn: F) -> Self
where
F: FnMut(&ast::Lifetime) -> MaybeStatic<Lifetime>,
{
Self {
indices: lifetimes.iter().map(lower_fn).collect(),
}
}
/// Append an additional lifetime. Used to tack on anon lifetimes
pub(super) fn append_lifetime(&mut self, lifetime: MaybeStatic<Lifetime>) {
self.indices.push(lifetime)
}
/// Returns a new [`Lifetimes`] representing the lifetimes in the scope
/// of the method this type appears in.
///
/// # Examples
///
/// ```rust
/// # struct Alice<'a>(&'a ());
/// # struct Bob<'b>(&'b ());
/// struct Foo<'a, 'b> {
/// alice: Alice<'a>,
/// bob: Bob<'b>,
/// }
///
/// fn bar<'x, 'y>(arg: Foo<'x, 'y>) {}
/// ```
/// Here, `Foo` will have a [`Lifetimes`] containing `['a, 'b]`,
/// and `bar` will have a [`Lifetimes`] containing `{'x: 'x, 'y: 'y}`.
/// When we enter the scope of `Foo` as a type, we use this method to combine
/// the two to get a new [`Lifetimes`] representing the mapping from
/// lifetimes in `Foo`'s scope to lifetimes in `bar`s scope: `{'a: 'x, 'b: 'y}`.
///
/// This tells us that `arg.alice` has lifetime `'x` in the method, and
/// that `arg.bob` has lifetime `'y`.
pub fn as_method_lifetimes(&self, method_lifetimes: &Lifetimes) -> Lifetimes {
let indices = self
.indices
.iter()
.map(|maybe_static_lt| {
maybe_static_lt.flat_map_nonstatic(|lt| lt.as_method_lifetime(method_lifetimes))
})
.collect();
Lifetimes { indices }
}
}
struct LifetimeTransitivityIterator<'env> {
env: &'env LifetimeEnv,
visited: Vec<bool>,
queue: Vec<usize>,
longer: bool,
}
impl<'env> LifetimeTransitivityIterator<'env> {
// Longer is whether we are looking for lifetimes longer or shorter than this
fn new(env: &'env LifetimeEnv, starting: usize, longer: bool) -> Self {
Self {
env,
visited: vec![false; env.num_lifetimes()],
queue: vec![starting],
longer,
}
}
}
impl<'env> Iterator for LifetimeTransitivityIterator<'env> {
type Item = Lifetime;
fn next(&mut self) -> Option<Lifetime> {
while let Some(next) = self.queue.pop() {
if self.visited[next] {
continue;
}
self.visited[next] = true;
if let Some(named) = self.env.nodes.get(next) {
let edge_dir = if self.longer {
&named.longer
} else {
&named.shorter
};
self.queue.extend(edge_dir.iter().map(|i| i.0));
}
return Some(Lifetime::new(next));
}
None
}
}
/// Convenience type for linking the lifetimes found at a type *use* site (e.g. `&'c Foo<'a, 'b>`)
/// with the lifetimes found at its *def* site (e.g. `struct Foo<'x, 'y>`).
///
/// Construct this by calling `.linked_lifetimes()` on a StructPath or OpaquePath
pub struct LinkedLifetimes<'def, 'tcx> {
env: &'tcx LifetimeEnv,
self_lt: Option<MaybeStatic<Lifetime>>,
lifetimes: &'def Lifetimes,
}
impl<'def, 'tcx> LinkedLifetimes<'def, 'tcx> {
pub(crate) fn new(
env: &'tcx LifetimeEnv,
self_lt: Option<MaybeStatic<Lifetime>>,
lifetimes: &'def Lifetimes,
) -> Self {
debug_assert_eq!(
lifetimes.lifetimes().len(),
env.all_lifetimes().len(),
"Should only link lifetimes between a type and its def"
);
Self {
env,
self_lt,
lifetimes,
}
}
/// Takes a lifetime at the def site and produces one at the use site
pub fn def_to_use(&self, def_lt: Lifetime) -> MaybeStatic<Lifetime> {
*self
.lifetimes
.as_slice()
.get(def_lt.0)
.expect("All def site lifetimes must be used!")
}
/// The lifetime env at the def site. Def lifetimes should be resolved
/// against this.
pub fn def_env(&self) -> &'tcx LifetimeEnv {
self.env
}
/// Link lifetimes from the use site to lifetimes from the def site, only including
/// lifetimes found at the def site.
///
/// This will *not* include the self-lifetime, i.e. for an opaque use site `&'c Foo<'a, 'b>`
/// this will not include `'c` (but you can obtain it from [`Self::self_lifetime()`]))
///
/// The return iterator returns pairs of (use_lt, def_lt), in order.
///
/// This behaves identically to [`Self::lifetimes_all()`] for `LinkedLifetimes` constructed
/// from anything other than a borrowing opaque.
pub fn lifetimes_def_only(
&self,
) -> impl Iterator<Item = (MaybeStatic<Lifetime>, Lifetime)> + '_ {
self.lifetimes.lifetimes().zip(self.env.all_lifetimes())
}
/// If there is a self-lifetime (e.g. `'c` on `&'c Foo<'a, 'b>`), return it. This lifetime
/// isn't found at the def site.
pub fn self_lifetime(&self) -> Option<MaybeStatic<Lifetime>> {
self.self_lt
}
/// Link lifetimes from the use site to lifetimes from the def site, including self lifetimes.
///
/// This returns Options since self-lifetimes do not map to anything at the def site.
///
/// The return iterator returns pairs of (use_lt, def_lt), in order, with the first entry potentially being
/// the self lifetime (which has a def_lt of None).
///
/// This behaves identically to [`Self::lifetimes_all()`] for `LinkedLifetimes` constructed
/// from anything other than a borrowing opaque.
pub fn lifetimes_all(
&self,
) -> impl Iterator<Item = (MaybeStatic<Lifetime>, Option<Lifetime>)> + '_ {
self.self_lt.iter().map(|i| (*i, None)).chain(
self.lifetimes
.lifetimes()
.zip(self.env.all_lifetimes().map(Some)),
)
}
}