Do not suggest adding labeled block if there are no labeled breaks

Author: WaffleLapkin

compiler/rustc_parse/src/parser/expr.rs

@@ -13,6 +13,7 @@ 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::visit::Visitor;
 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};
@@ -1556,6 +1557,28 @@ impl<'a> Parser<'a> {
 
             // Continue as an expression in an effort to recover on `'label: non_block_expr`.
             let expr = self.parse_expr().map(|expr| {
+                let found_labeled_breaks = {
+                    struct FindLabeledBreaksVisitor(bool);
+
+                    impl<'ast> Visitor<'ast> for FindLabeledBreaksVisitor {
+                        fn visit_expr_post(&mut self, ex: &'ast Expr) {
+                            if let ExprKind::Break(Some(_label), _) = ex.kind {
+                                self.0 = true;
+                            }
+                        }
+                    }
+
+                    let mut vis = FindLabeledBreaksVisitor(false);
+                    vis.visit_expr(&expr);
+                    vis.0
+                };
+
+                // Suggestion involves adding a (as of time of writing this, unstable) labeled block
+                // so if the label is not used, just return the unmodified expression
+                if !found_labeled_breaks {
+                    return expr;
+                }
+
                 let span = expr.span;
                 let sugg_msg = "consider enclosing expression in a block";
                 let suggestions = vec![

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

@@ -47,11 +47,6 @@ 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

@@ -1,8 +1,9 @@
 // run-rustfix
 #![feature(label_break_value)]
 fn main() {
-    #[allow(unused_labels)]
-    'label: {1 + 1}; //~ ERROR expected `while`, `for`, `loop` or `{` after a label
+    // FIXME(waffle): add this back
+    // #[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
 

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

@@ -1,8 +1,9 @@
 // run-rustfix
 #![feature(label_break_value)]
 fn main() {
-    #[allow(unused_labels)]
-    'label: 1 + 1; //~ ERROR expected `while`, `for`, `loop` or `{` after a label
+    // FIXME(waffle): add this back
+    // #[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
 

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

@@ -1,16 +1,5 @@
 error: expected `while`, `for`, `loop` or `{` after a label
-  --> $DIR/recover-labeled-non-block-expr.rs:5:13
-   |
-LL |     'label: 1 + 1;
-   |             ^ expected `while`, `for`, `loop` or `{` after a label
-   |
-help: consider enclosing expression in a block
-   |
-LL |     'label: {1 + 1};
-   |             +     +
-
-error: expected `while`, `for`, `loop` or `{` after a label
-  --> $DIR/recover-labeled-non-block-expr.rs:7:13
+  --> $DIR/recover-labeled-non-block-expr.rs:8:13
    |
 LL |     'label: match () { () => break 'label, };
    |             ^^^^^ expected `while`, `for`, `loop` or `{` after a label
@@ -21,7 +10,7 @@ LL |     'label: {match () { () => break 'label, }};
    |             +                                +
 
 error: expected `while`, `for`, `loop` or `{` after a label
-  --> $DIR/recover-labeled-non-block-expr.rs:10:22
+  --> $DIR/recover-labeled-non-block-expr.rs:11:22
    |
 LL |     let _i = 'label: match x {
    |                      ^^^^^ expected `while`, `for`, `loop` or `{` after a label
@@ -37,7 +26,7 @@ LL |                 break 'label 13
  ...
 
 error: expected `while`, `for`, `loop` or `{` after a label
-  --> $DIR/recover-labeled-non-block-expr.rs:24:24
+  --> $DIR/recover-labeled-non-block-expr.rs:25:24
    |
 LL |     let _val = 'label: (1, if other == 3 { break 'label (2, 3) } else { other });
    |                        ^ expected `while`, `for`, `loop` or `{` after a label
@@ -47,5 +36,5 @@ 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
+error: aborting due to 3 previous errors