rust/compiler/rustc_expand/src/mbe.rs

//! This module implements declarative macros: old `macro_rules` and the newer
//! `macro`. Declarative macros are also known as "macro by example", and that's
//! why we call this module `mbe`. For external documentation, prefer the
//! official terminology: "declarative macros".

crate mod macro_check;
crate mod macro_parser;
crate mod macro_rules;
crate mod metavar_expr;
crate mod quoted;
crate mod transcribe;

use metavar_expr::MetaVarExpr;
use rustc_ast::token::{self, NonterminalKind, Token, TokenKind};
use rustc_ast::tokenstream::DelimSpan;
use rustc_data_structures::sync::Lrc;
use rustc_span::symbol::Ident;
use rustc_span::Span;

/// Contains the sub-token-trees of a "delimited" token tree such as `(a b c)`. The delimiter itself
/// might be `NoDelim`.
#[derive(Clone, PartialEq, Encodable, Decodable, Debug)]
struct Delimited {
    delim: token::DelimToken,
    /// Note: This contains the opening and closing delimiters tokens (e.g. `(` and `)`). Note that
    /// these could be `NoDelim`. These token kinds must match `delim`, and the methods below
    /// debug_assert this.
    all_tts: Vec<TokenTree>,
}

impl Delimited {
    /// Returns a `self::TokenTree` with a `Span` corresponding to the opening delimiter. Panics if
    /// the delimiter is `NoDelim`.
    fn open_tt(&self) -> &TokenTree {
        let tt = self.all_tts.first().unwrap();
        debug_assert!(matches!(
            tt,
            &TokenTree::Token(token::Token { kind: token::OpenDelim(d), .. }) if d == self.delim
        ));
        tt
    }

    /// Returns a `self::TokenTree` with a `Span` corresponding to the closing delimiter. Panics if
    /// the delimiter is `NoDelim`.
    fn close_tt(&self) -> &TokenTree {
        let tt = self.all_tts.last().unwrap();
        debug_assert!(matches!(
            tt,
            &TokenTree::Token(token::Token { kind: token::CloseDelim(d), .. }) if d == self.delim
        ));
        tt
    }

    /// Returns the tts excluding the outer delimiters.
    ///
    /// FIXME: #67062 has details about why this is sub-optimal.
    fn inner_tts(&self) -> &[TokenTree] {
        // These functions are called for the assertions within them.
        let _open_tt = self.open_tt();
        let _close_tt = self.close_tt();
        &self.all_tts[1..self.all_tts.len() - 1]
    }
}

#[derive(Clone, PartialEq, Encodable, Decodable, Debug)]
struct SequenceRepetition {
    /// The sequence of token trees
    tts: Vec<TokenTree>,
    /// The optional separator
    separator: Option<Token>,
    /// Whether the sequence can be repeated zero (*), or one or more times (+)
    kleene: KleeneToken,
    /// The number of `Match`s that appear in the sequence (and subsequences)
    num_captures: usize,
}

#[derive(Clone, PartialEq, Encodable, Decodable, Debug, Copy)]
struct KleeneToken {
    span: Span,
    op: KleeneOp,
}

impl KleeneToken {
    fn new(op: KleeneOp, span: Span) -> KleeneToken {
        KleeneToken { span, op }
    }
}

/// A Kleene-style [repetition operator](https://en.wikipedia.org/wiki/Kleene_star)
/// for token sequences.
#[derive(Clone, PartialEq, Encodable, Decodable, Debug, Copy)]
enum KleeneOp {
    /// Kleene star (`*`) for zero or more repetitions
    ZeroOrMore,
    /// Kleene plus (`+`) for one or more repetitions
    OneOrMore,
    /// Kleene optional (`?`) for zero or one repetitions
    ZeroOrOne,
}

/// Similar to `tokenstream::TokenTree`, except that `Sequence`, `MetaVar`, `MetaVarDecl`, and
/// `MetaVarExpr` are "first-class" token trees. Useful for parsing macros.
#[derive(Debug, Clone, PartialEq, Encodable, Decodable)]
enum TokenTree {
    Token(Token),
    /// A delimited sequence, e.g. `($e:expr)` (RHS) or `{ $e }` (LHS).
    Delimited(DelimSpan, Lrc<Delimited>),
    /// A kleene-style repetition sequence, e.g. `$($e:expr)*` (RHS) or `$($e),*` (LHS).
    Sequence(DelimSpan, Lrc<SequenceRepetition>),
    /// e.g., `$var`.
    MetaVar(Span, Ident),
    /// e.g., `$var:expr`. Only appears on the LHS.
    MetaVarDecl(Span, Ident /* name to bind */, Option<NonterminalKind>),
    /// A meta-variable expression inside `${...}`.
    MetaVarExpr(DelimSpan, MetaVarExpr),
}

impl TokenTree {
    /// Returns `true` if the given token tree is delimited.
    fn is_delimited(&self) -> bool {
        matches!(*self, TokenTree::Delimited(..))
    }

    /// Returns `true` if the given token tree is a token of the given kind.
    fn is_token(&self, expected_kind: &TokenKind) -> bool {
        match self {
            TokenTree::Token(Token { kind: actual_kind, .. }) => actual_kind == expected_kind,
            _ => false,
        }
    }

    /// Retrieves the `TokenTree`'s span.
    fn span(&self) -> Span {
        match *self {
            TokenTree::Token(Token { span, .. })
            | TokenTree::MetaVar(span, _)
            | TokenTree::MetaVarDecl(span, _, _) => span,
            TokenTree::Delimited(span, _)
            | TokenTree::MetaVarExpr(span, _)
            | TokenTree::Sequence(span, _) => span.entire(),
        }
    }

    fn token(kind: TokenKind, span: Span) -> TokenTree {
        TokenTree::Token(Token::new(kind, span))
    }
}