bjoernager/rust
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Rollup merge of #120221 - compiler-errors:statements-are-not-patterns, r=nnethercote

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Don't make statement nonterminals match pattern nonterminals

Right now, the heuristic we use to check if a token may begin a pattern nonterminal falls back to `may_be_ident`:
ef71f1047e/compiler/rustc_parse/src/parser/nonterminal.rs (L21-L37)

This has the unfortunate side effect that a `stmt` nonterminal eagerly matches against a `pat` nonterminal, leading to a parse error:
```rust
macro_rules! m {
    ($pat:pat) => {};
    ($stmt:stmt) => {};
}

macro_rules! m2 {
    ($stmt:stmt) => {
        m! { $stmt }
    };
}

m2! { let x = 1 }
```

This PR fixes it by more accurately reflecting the set of nonterminals that may begin a pattern nonterminal.

As a side-effect, I modified `Token::can_begin_pattern` to work correctly and used that in `Parser::nonterminal_may_begin_with`.
This commit is contained in:
Matthias Krüger 2024-08-31 10:08:51 +02:00 • committed by GitHub
commit 1fd0c71818
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5 changed files with 65 additions and 42 deletions
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57
compiler/rustc_ast/src/token.rs
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@ -486,6 +486,9 @@ impl Token {
}
/// Returns `true` if the token can appear at the start of an expression.
///
/// **NB**: Take care when modifying this function, since it will change
/// the stable set of tokens that are allowed to match an expr nonterminal.
pub fn can_begin_expr(&self) -> bool {
match self.uninterpolate().kind {
Ident(name, is_raw) =>
@ -504,10 +507,13 @@ impl Token {
PathSep | // global path
Lifetime(..) | // labeled loop
Pound => true, // expression attributes
Interpolated(ref nt) => matches!(&**nt, NtLiteral(..) |
NtExpr(..) |
NtBlock(..) |
NtPath(..)),
Interpolated(ref nt) =>
matches!(&**nt,
NtBlock(..) |
NtExpr(..) |
NtLiteral(..) |
NtPath(..)
),
_ => false,
}
}
@ -515,23 +521,32 @@ impl Token {
/// Returns `true` if the token can appear at the start of a pattern.
///
/// Shamelessly borrowed from `can_begin_expr`, only used for diagnostics right now.
pub fn can_begin_pattern(&self) -> bool {
match self.uninterpolate().kind {
Ident(name, is_raw) =>
ident_can_begin_expr(name, self.span, is_raw), // value name or keyword
| OpenDelim(Delimiter::Bracket | Delimiter::Parenthesis) // tuple or array
| Literal(..) // literal
| BinOp(Minus) // unary minus
| BinOp(And) // reference
| AndAnd // double reference
// DotDotDot is no longer supported
| DotDot | DotDotDot | DotDotEq // ranges
| Lt | BinOp(Shl) // associated path
| PathSep => true, // global path
Interpolated(ref nt) => matches!(&**nt, NtLiteral(..) |
NtPat(..) |
NtBlock(..) |
NtPath(..)),
pub fn can_begin_pattern(&self, pat_kind: NtPatKind) -> bool {
match &self.uninterpolate().kind {
// box, ref, mut, and other identifiers (can stricten)
Ident(..) | NtIdent(..) |
OpenDelim(Delimiter::Parenthesis) | // tuple pattern
OpenDelim(Delimiter::Bracket) | // slice pattern
BinOp(And) | // reference
BinOp(Minus) | // negative literal
AndAnd | // double reference
Literal(_) | // literal
DotDot | // range pattern (future compat)
DotDotDot | // range pattern (future compat)
PathSep | // path
Lt | // path (UFCS constant)
BinOp(Shl) => true, // path (double UFCS)
// leading vert `|` or-pattern
BinOp(Or) => matches!(pat_kind, PatWithOr),
Interpolated(nt) =>
matches!(&**nt,
| NtExpr(..)
| NtLiteral(..)
| NtMeta(..)
| NtPat(..)
| NtPath(..)
| NtTy(..)
),
_ => false,
}
}