diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs index 1e14446efb5..1efde7fc54b 100644 --- a/compiler/rustc_parse/src/parser/expr.rs +++ b/compiler/rustc_parse/src/parser/expr.rs @@ -2329,7 +2329,8 @@ impl<'a> Parser<'a> { let capture_clause = self.parse_capture_clause()?; let (fn_decl, fn_arg_span) = self.parse_fn_block_decl()?; let decl_hi = self.prev_token.span; - let mut body = match fn_decl.output { + let mut body = match &fn_decl.output { + // No return type. FnRetTy::Default(_) => { let restrictions = self.restrictions - Restrictions::STMT_EXPR - Restrictions::ALLOW_LET; @@ -2341,11 +2342,8 @@ impl<'a> Parser<'a> { Err(err) => self.recover_closure_body(err, before, prev, token, lo, decl_hi)?, } } - _ => { - // If an explicit return type is given, require a block to appear (RFC 968). - let body_lo = self.token.span; - self.parse_expr_block(None, body_lo, BlockCheckMode::Default)? - } + // Explicit return type (`->`) needs block `-> T { }`. + FnRetTy::Ty(ty) => self.parse_closure_block_body(ty.span)?, }; match coroutine_kind { @@ -2397,6 +2395,49 @@ impl<'a> Parser<'a> { Ok(closure) } + /// If an explicit return type is given, require a block to appear (RFC 968). + fn parse_closure_block_body(&mut self, ret_span: Span) -> PResult<'a, P> { + if self.may_recover() + && self.token.can_begin_expr() + && !matches!(self.token.kind, TokenKind::OpenDelim(Delimiter::Brace)) + && !self.token.is_whole_block() + { + let snapshot = self.create_snapshot_for_diagnostic(); + let restrictions = + self.restrictions - Restrictions::STMT_EXPR - Restrictions::ALLOW_LET; + let tok = self.token.clone(); + match self.parse_expr_res(restrictions, AttrWrapper::empty()) { + Ok((expr, _)) => { + let descr = super::token_descr(&tok); + let mut diag = self + .dcx() + .struct_span_err(tok.span, format!("expected `{{`, found {descr}")); + diag.span_label( + ret_span, + "explicit return type requires closure body to be enclosed in braces", + ); + diag.multipart_suggestion_verbose( + "wrap the expression in curly braces", + vec![ + (expr.span.shrink_to_lo(), "{ ".to_string()), + (expr.span.shrink_to_hi(), " }".to_string()), + ], + Applicability::MachineApplicable, + ); + diag.emit(); + return Ok(expr); + } + Err(diag) => { + diag.cancel(); + self.restore_snapshot(snapshot); + } + } + } + + let body_lo = self.token.span; + self.parse_expr_block(None, body_lo, BlockCheckMode::Default) + } + /// Parses an optional `move` or `use` prefix to a closure-like construct. fn parse_capture_clause(&mut self) -> PResult<'a, CaptureBy> { if self.eat_keyword(exp!(Move)) { diff --git a/tests/ui/parser/closure-return-syntax.stderr b/tests/ui/parser/closure-return-syntax.stderr index 6f2106b77ad..763f19ccc64 100644 --- a/tests/ui/parser/closure-return-syntax.stderr +++ b/tests/ui/parser/closure-return-syntax.stderr @@ -2,9 +2,11 @@ error: expected `{`, found `22` --> $DIR/closure-return-syntax.rs:5:23 | LL | let x = || -> i32 22; - | ^^ expected `{` + | --- ^^ + | | + | explicit return type requires closure body to be enclosed in braces | -help: you might have meant to write this as part of a block +help: wrap the expression in curly braces | LL | let x = || -> i32 { 22 }; | + + @@ -13,9 +15,11 @@ error: expected `{`, found `(` --> $DIR/closure-return-syntax.rs:12:34 | LL | let x = || -> (i32, i32) (1, 2); - | ^ expected `{` + | ---------- ^ + | | + | explicit return type requires closure body to be enclosed in braces | -help: you might have meant to write this as part of a block +help: wrap the expression in curly braces | LL | let x = || -> (i32, i32) { (1, 2) }; | + + @@ -24,9 +28,11 @@ error: expected `{`, found `[` --> $DIR/closure-return-syntax.rs:17:32 | LL | let c = || -> [i32; 2] [1, 2]; - | ^ expected `{` + | -------- ^ + | | + | explicit return type requires closure body to be enclosed in braces | -help: you might have meant to write this as part of a block +help: wrap the expression in curly braces | LL | let c = || -> [i32; 2] { [1, 2] }; | + +