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#[cfg(feature = "parsing")]
use crate::error::Result;
#[cfg(feature = "parsing")]
use crate::parse::{Parse, ParseStream, Parser};
use crate::path::Path;
use crate::token::{Brace, Bracket, Paren};
use proc_macro2::extra::DelimSpan;
#[cfg(feature = "parsing")]
use proc_macro2::Delimiter;
use proc_macro2::TokenStream;
#[cfg(feature = "parsing")]
use proc_macro2::TokenTree;
ast_struct! {
/// A macro invocation: `println!("{}", mac)`.
#[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
pub struct Macro {
pub path: Path,
pub bang_token: Token![!],
pub delimiter: MacroDelimiter,
pub tokens: TokenStream,
}
}
ast_enum! {
/// A grouping token that surrounds a macro body: `m!(...)` or `m!{...}` or `m![...]`.
#[cfg_attr(docsrs, doc(cfg(any(feature = "full", feature = "derive"))))]
pub enum MacroDelimiter {
Paren(Paren),
Brace(Brace),
Bracket(Bracket),
}
}
impl MacroDelimiter {
pub fn span(&self) -> &DelimSpan {
match self {
MacroDelimiter::Paren(token) => &token.span,
MacroDelimiter::Brace(token) => &token.span,
MacroDelimiter::Bracket(token) => &token.span,
}
}
#[cfg(all(feature = "full", any(feature = "parsing", feature = "printing")))]
pub(crate) fn is_brace(&self) -> bool {
match self {
MacroDelimiter::Brace(_) => true,
MacroDelimiter::Paren(_) | MacroDelimiter::Bracket(_) => false,
}
}
}
impl Macro {
/// Parse the tokens within the macro invocation's delimiters into a syntax
/// tree.
///
/// This is equivalent to `syn::parse2::<T>(mac.tokens)` except that it
/// produces a more useful span when `tokens` is empty.
///
/// # Example
///
/// ```
/// use syn::{parse_quote, Expr, ExprLit, Ident, Lit, LitStr, Macro, Token};
/// use syn::ext::IdentExt;
/// use syn::parse::{Error, Parse, ParseStream, Result};
/// use syn::punctuated::Punctuated;
///
/// // The arguments expected by libcore's format_args macro, and as a
/// // result most other formatting and printing macros like println.
/// //
/// // println!("{} is {number:.prec$}", "x", prec=5, number=0.01)
/// struct FormatArgs {
/// format_string: Expr,
/// positional_args: Vec<Expr>,
/// named_args: Vec<(Ident, Expr)>,
/// }
///
/// impl Parse for FormatArgs {
/// fn parse(input: ParseStream) -> Result<Self> {
/// let format_string: Expr;
/// let mut positional_args = Vec::new();
/// let mut named_args = Vec::new();
///
/// format_string = input.parse()?;
/// while !input.is_empty() {
/// input.parse::<Token![,]>()?;
/// if input.is_empty() {
/// break;
/// }
/// if input.peek(Ident::peek_any) && input.peek2(Token![=]) {
/// while !input.is_empty() {
/// let name: Ident = input.call(Ident::parse_any)?;
/// input.parse::<Token![=]>()?;
/// let value: Expr = input.parse()?;
/// named_args.push((name, value));
/// if input.is_empty() {
/// break;
/// }
/// input.parse::<Token![,]>()?;
/// }
/// break;
/// }
/// positional_args.push(input.parse()?);
/// }
///
/// Ok(FormatArgs {
/// format_string,
/// positional_args,
/// named_args,
/// })
/// }
/// }
///
/// // Extract the first argument, the format string literal, from an
/// // invocation of a formatting or printing macro.
/// fn get_format_string(m: &Macro) -> Result<LitStr> {
/// let args: FormatArgs = m.parse_body()?;
/// match args.format_string {
/// Expr::Lit(ExprLit { lit: Lit::Str(lit), .. }) => Ok(lit),
/// other => {
/// // First argument was not a string literal expression.
/// // Maybe something like: println!(concat!(...), ...)
/// Err(Error::new_spanned(other, "format string must be a string literal"))
/// }
/// }
/// }
///
/// fn main() {
/// let invocation = parse_quote! {
/// println!("{:?}", Instant::now())
/// };
/// let lit = get_format_string(&invocation).unwrap();
/// assert_eq!(lit.value(), "{:?}");
/// }
/// ```
#[cfg(feature = "parsing")]
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
pub fn parse_body<T: Parse>(&self) -> Result<T> {
self.parse_body_with(T::parse)
}
/// Parse the tokens within the macro invocation's delimiters using the
/// given parser.
#[cfg(feature = "parsing")]
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
pub fn parse_body_with<F: Parser>(&self, parser: F) -> Result<F::Output> {
let scope = self.delimiter.span().close();
crate::parse::parse_scoped(parser, scope, self.tokens.clone())
}
}
#[cfg(feature = "parsing")]
pub(crate) fn parse_delimiter(input: ParseStream) -> Result<(MacroDelimiter, TokenStream)> {
input.step(|cursor| {
if let Some((TokenTree::Group(g), rest)) = cursor.token_tree() {
let span = g.delim_span();
let delimiter = match g.delimiter() {
Delimiter::Parenthesis => MacroDelimiter::Paren(Paren(span)),
Delimiter::Brace => MacroDelimiter::Brace(Brace(span)),
Delimiter::Bracket => MacroDelimiter::Bracket(Bracket(span)),
Delimiter::None => {
return Err(cursor.error("expected delimiter"));
}
};
Ok(((delimiter, g.stream()), rest))
} else {
Err(cursor.error("expected delimiter"))
}
})
}
#[cfg(feature = "parsing")]
pub(crate) mod parsing {
use crate::error::Result;
use crate::mac::{parse_delimiter, Macro};
use crate::parse::{Parse, ParseStream};
use crate::path::Path;
#[cfg_attr(docsrs, doc(cfg(feature = "parsing")))]
impl Parse for Macro {
fn parse(input: ParseStream) -> Result<Self> {
let tokens;
Ok(Macro {
path: input.call(Path::parse_mod_style)?,
bang_token: input.parse()?,
delimiter: {
let (delimiter, content) = parse_delimiter(input)?;
tokens = content;
delimiter
},
tokens,
})
}
}
}
#[cfg(feature = "printing")]
mod printing {
use crate::mac::{Macro, MacroDelimiter};
use crate::token;
use proc_macro2::{Delimiter, TokenStream};
use quote::ToTokens;
impl MacroDelimiter {
pub(crate) fn surround(&self, tokens: &mut TokenStream, inner: TokenStream) {
let (delim, span) = match self {
MacroDelimiter::Paren(paren) => (Delimiter::Parenthesis, paren.span),
MacroDelimiter::Brace(brace) => (Delimiter::Brace, brace.span),
MacroDelimiter::Bracket(bracket) => (Delimiter::Bracket, bracket.span),
};
token::printing::delim(delim, span.join(), tokens, inner);
}
}
#[cfg_attr(docsrs, doc(cfg(feature = "printing")))]
impl ToTokens for Macro {
fn to_tokens(&self, tokens: &mut TokenStream) {
self.path.to_tokens(tokens);
self.bang_token.to_tokens(tokens);
self.delimiter.surround(tokens, self.tokens.clone());
}
}
}