Suggest adding {} for 'label: non_block_expr

compiler/rustc_parse/src/parser/expr.rs

@@ -13,10 +13,12 @@ use rustc_ast::tokenstream::Spacing;
 use rustc_ast::util::classify;
 use rustc_ast::util::literal::LitError;
 use rustc_ast::util::parser::{prec_let_scrutinee_needs_par, AssocOp, Fixity};
+use rustc_ast::StmtKind;
 use rustc_ast::{self as ast, AttrStyle, AttrVec, CaptureBy, ExprField, Lit, UnOp, DUMMY_NODE_ID};
 use rustc_ast::{AnonConst, BinOp, BinOpKind, FnDecl, FnRetTy, MacCall, Param, Ty, TyKind};
 use rustc_ast::{Arm, Async, BlockCheckMode, Expr, ExprKind, Label, Movability, RangeLimits};
 use rustc_ast_pretty::pprust;
+use rustc_data_structures::thin_vec::ThinVec;
 use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed, PResult};
 use rustc_session::lint::builtin::BREAK_WITH_LABEL_AND_LOOP;
 use rustc_session::lint::BuiltinLintDiagnostics;
@@ -1548,9 +1550,33 @@ impl<'a> Parser<'a> {
             Ok(self.mk_expr_err(lo))
         } else {
             let msg = "expected `while`, `for`, `loop` or `{` after a label";
-            self.struct_span_err(self.token.span, msg).span_label(self.token.span, msg).emit();
+
+            let mut err = self.struct_span_err(self.token.span, msg);
+            err.span_label(self.token.span, msg);
+
             // Continue as an expression in an effort to recover on `'label: non_block_expr`.
-            self.parse_expr()
+            let expr = self.parse_expr().map(|expr| {
+                let span = expr.span;
+                let sugg_msg = "consider enclosing expression in a block";
+                let suggestions = vec![
+                    (span.shrink_to_lo(), "{".to_owned()),
+                    (span.shrink_to_hi(), "}".to_owned()),
+                ];
+
+                err.multipart_suggestion_verbose(
+                    sugg_msg,
+                    suggestions,
+                    Applicability::MachineApplicable,
+                );
+
+                // Replace `'label: non_block_expr` with `'label: {non_block_expr}` in order to supress future errors about `break 'label`.
+                let stmt = self.mk_stmt(span, StmtKind::Expr(expr));
+                let blk = self.mk_block(vec![stmt], BlockCheckMode::Default, span);
+                self.mk_expr(span, ExprKind::Block(blk, label), ThinVec::new())
+            });
+
+            err.emit();
+            expr
         }?;
 
         if !ate_colon && consume_colon {

src/test/ui/parser/labeled-no-colon-expr.stderr

@@ -47,6 +47,11 @@ error: expected `while`, `for`, `loop` or `{` after a label
    |
 LL |     'l4 0;
    |         ^ expected `while`, `for`, `loop` or `{` after a label
+   |
+help: consider enclosing expression in a block
+   |
+LL |     'l4 {0};
+   |         + +
 
 error: labeled expression must be followed by `:`
   --> $DIR/labeled-no-colon-expr.rs:8:9

src/test/ui/parser/recover-labeled-non-block-expr.fixed

@@ -0,0 +1,25 @@
+// run-rustfix
+#![feature(label_break_value)]
+fn main() {
+    #[allow(unused_labels)]
+    'label: {1 + 1}; //~ ERROR expected `while`, `for`, `loop` or `{` after a label
+
+    'label: {match () { () => break 'label, }}; //~ ERROR expected `while`, `for`, `loop` or `{` after a label
+
+    let x = 1;
+    let _i = 'label: {match x { //~ ERROR expected `while`, `for`, `loop` or `{` after a label
+        0 => 42,
+        1 if false => break 'label 17,
+        1 => {
+            if true {
+                break 'label 13
+            } else {
+                break 'label 0;
+            }
+        }
+        _ => 1,
+    }};
+
+    let other = 3;
+    let _val = 'label: {(1, if other == 3 { break 'label (2, 3) } else { other })}; //~ ERROR expected `while`, `for`, `loop` or `{` after a label
+}

src/test/ui/parser/recover-labeled-non-block-expr.rs

@@ -1,5 +1,25 @@
+// run-rustfix
+#![feature(label_break_value)]
 fn main() {
+    #[allow(unused_labels)]
     'label: 1 + 1; //~ ERROR expected `while`, `for`, `loop` or `{` after a label
 
-    let _recovery_witness: () = 0; //~ ERROR mismatched types
+    'label: match () { () => break 'label, }; //~ ERROR expected `while`, `for`, `loop` or `{` after a label
+
+    let x = 1;
+    let _i = 'label: match x { //~ ERROR expected `while`, `for`, `loop` or `{` after a label
+        0 => 42,
+        1 if false => break 'label 17,
+        1 => {
+            if true {
+                break 'label 13
+            } else {
+                break 'label 0;
+            }
+        }
+        _ => 1,
+    };
+
+    let other = 3;
+    let _val = 'label: (1, if other == 3 { break 'label (2, 3) } else { other }); //~ ERROR expected `while`, `for`, `loop` or `{` after a label
 }

src/test/ui/parser/recover-labeled-non-block-expr.stderr

@@ -1,17 +1,51 @@
 error: expected `while`, `for`, `loop` or `{` after a label
-  --> $DIR/recover-labeled-non-block-expr.rs:2:13
+  --> $DIR/recover-labeled-non-block-expr.rs:5:13
    |
 LL |     'label: 1 + 1;
    |             ^ expected `while`, `for`, `loop` or `{` after a label
-
-error[E0308]: mismatched types
-  --> $DIR/recover-labeled-non-block-expr.rs:4:33
    |
-LL |     let _recovery_witness: () = 0;
+help: consider enclosing expression in a block
-   |                            --   ^ expected `()`, found integer
+   |
-   |                            |
+LL |     'label: {1 + 1};
-   |                            expected due to this
+   |             +     +
 
-error: aborting due to 2 previous errors
+error: expected `while`, `for`, `loop` or `{` after a label
+  --> $DIR/recover-labeled-non-block-expr.rs:7:13
+   |
+LL |     'label: match () { () => break 'label, };
+   |             ^^^^^ expected `while`, `for`, `loop` or `{` after a label
+   |
+help: consider enclosing expression in a block
+   |
+LL |     'label: {match () { () => break 'label, }};
+   |             +                                +
+
+error: expected `while`, `for`, `loop` or `{` after a label
+  --> $DIR/recover-labeled-non-block-expr.rs:10:22
+   |
+LL |     let _i = 'label: match x {
+   |                      ^^^^^ expected `while`, `for`, `loop` or `{` after a label
+   |
+help: consider enclosing expression in a block
+   |
+LL ~     let _i = 'label: {match x {
+LL |         0 => 42,
+LL |         1 if false => break 'label 17,
+LL |         1 => {
+LL |             if true {
+LL |                 break 'label 13
+ ...
+
+error: expected `while`, `for`, `loop` or `{` after a label
+  --> $DIR/recover-labeled-non-block-expr.rs:24:24
+   |
+LL |     let _val = 'label: (1, if other == 3 { break 'label (2, 3) } else { other });
+   |                        ^ expected `while`, `for`, `loop` or `{` after a label
+   |
+help: consider enclosing expression in a block
+   |
+LL |     let _val = 'label: {(1, if other == 3 { break 'label (2, 3) } else { other })};
+   |                        +                                                         +
+
+error: aborting due to 4 previous errors
 
-For more information about this error, try `rustc --explain E0308`.