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Don't make pattern nonterminals match statement nonterminals
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compiler-errors committed Aug 26, 2024
1 parent 22572d0 commit c61f85b
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Showing 5 changed files with 65 additions and 42 deletions.
57 changes: 36 additions & 21 deletions compiler/rustc_ast/src/token.rs
Original file line number Diff line number Diff line change
Expand Up @@ -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) =>
Expand All @@ -504,34 +507,46 @@ 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,
}
}

/// 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,
}
}
Expand Down
20 changes: 1 addition & 19 deletions compiler/rustc_parse/src/parser/nonterminal.rs
Original file line number Diff line number Diff line change
Expand Up @@ -86,25 +86,7 @@ impl<'a> Parser<'a> {
token::Interpolated(nt) => may_be_ident(nt),
_ => false,
},
NonterminalKind::Pat(pat_kind) => match &token.kind {
// box, ref, mut, and other identifiers (can stricten)
token::Ident(..) | token::NtIdent(..) |
token::OpenDelim(Delimiter::Parenthesis) | // tuple pattern
token::OpenDelim(Delimiter::Bracket) | // slice pattern
token::BinOp(token::And) | // reference
token::BinOp(token::Minus) | // negative literal
token::AndAnd | // double reference
token::Literal(_) | // literal
token::DotDot | // range pattern (future compat)
token::DotDotDot | // range pattern (future compat)
token::PathSep | // path
token::Lt | // path (UFCS constant)
token::BinOp(token::Shl) => true, // path (double UFCS)
// leading vert `|` or-pattern
token::BinOp(token::Or) => matches!(pat_kind, PatWithOr),
token::Interpolated(nt) => may_be_ident(nt),
_ => false,
},
NonterminalKind::Pat(pat_kind) => token.can_begin_pattern(pat_kind),
NonterminalKind::Lifetime => match &token.kind {
token::Lifetime(_) | token::NtLifetime(..) => true,
_ => false,
Expand Down
6 changes: 5 additions & 1 deletion compiler/rustc_parse/src/parser/pat.rs
Original file line number Diff line number Diff line change
Expand Up @@ -444,7 +444,11 @@ impl<'a> Parser<'a> {

let mut lo = self.token.span;

if self.token.is_keyword(kw::Let) && self.look_ahead(1, |tok| tok.can_begin_pattern()) {
if self.token.is_keyword(kw::Let)
&& self.look_ahead(1, |tok| {
tok.can_begin_pattern(token::NtPatKind::PatParam { inferred: false })
})
{
self.bump();
self.dcx().emit_err(RemoveLet { span: lo });
lo = self.token.span;
Expand Down
5 changes: 4 additions & 1 deletion compiler/rustc_parse/src/parser/path.rs
Original file line number Diff line number Diff line change
Expand Up @@ -378,7 +378,10 @@ impl<'a> Parser<'a> {
if self.may_recover()
&& prev_token_before_parsing == token::PathSep
&& (style == PathStyle::Expr && self.token.can_begin_expr()
|| style == PathStyle::Pat && self.token.can_begin_pattern())
|| style == PathStyle::Pat
&& self.token.can_begin_pattern(token::NtPatKind::PatParam {
inferred: false,
}))
{
snapshot = Some(self.create_snapshot_for_diagnostic());
}
Expand Down
19 changes: 19 additions & 0 deletions tests/ui/pattern/patterns-dont-match-nt-statement.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,19 @@
//@ check-pass

// Make sure that a `stmt` nonterminal does not eagerly match against
// a `pat`, since this will always cause a parse error...

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

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

m2! { let x = 1 }

fn main() {}

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