diff --git a/compiler/rustc_ast/src/token.rs b/compiler/rustc_ast/src/token.rs index 43d87b96ead90..f1dddb3acacaa 100644 --- a/compiler/rustc_ast/src/token.rs +++ b/compiler/rustc_ast/src/token.rs @@ -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, } } diff --git a/compiler/rustc_parse/src/parser/nonterminal.rs b/compiler/rustc_parse/src/parser/nonterminal.rs index 999f6f0eeb0ce..e66d0df012bcb 100644 --- a/compiler/rustc_parse/src/parser/nonterminal.rs +++ b/compiler/rustc_parse/src/parser/nonterminal.rs @@ -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, diff --git a/compiler/rustc_parse/src/parser/pat.rs b/compiler/rustc_parse/src/parser/pat.rs index cc68ae237ba18..8233f9a79435f 100644 --- a/compiler/rustc_parse/src/parser/pat.rs +++ b/compiler/rustc_parse/src/parser/pat.rs @@ -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; diff --git a/compiler/rustc_parse/src/parser/path.rs b/compiler/rustc_parse/src/parser/path.rs index d8bf10e6021cc..8ee40ecd77e3f 100644 --- a/compiler/rustc_parse/src/parser/path.rs +++ b/compiler/rustc_parse/src/parser/path.rs @@ -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()); } diff --git a/tests/ui/pattern/patterns-dont-match-nt-statement.rs b/tests/ui/pattern/patterns-dont-match-nt-statement.rs new file mode 100644 index 0000000000000..c8d41459383ac --- /dev/null +++ b/tests/ui/pattern/patterns-dont-match-nt-statement.rs @@ -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() {}