Add feature gate label_break_value

src/librustc_passes/diagnostics.rs

@@ -278,6 +278,7 @@ fn foo() {}
 Make sure to always label the `break`:
 
 ```
+# #![feature(label_break_value)]
 'l: loop {
     'a: {
         break 'l;

src/libsyntax/feature_gate.rs

@@ -466,6 +466,9 @@ pub fn walk_feature_fields<F>(&self, mut f: F)
 
     // inconsistent bounds in where clauses
     (active, trivial_bounds, "1.28.0", Some(48214), None),
+
+    // 'a: { break 'a; }
+    (active, label_break_value, "1.28.0", Some(48594), None),
 );
 
 declare_features! (
@@ -1696,6 +1699,12 @@ fn visit_expr(&mut self, e: &'a ast::Expr) {
                                     "multiple patterns in `if let` and `while let` are unstable");
                 }
             }
+            ast::ExprKind::Block(_, opt_label) => {
+                if let Some(label) = opt_label {
+                    gate_feature_post!(&self, label_break_value, label.ident.span,
+                                    "labels on blocks are unstable");
+                }
+            }
             _ => {}
         }
         visit::walk_expr(self, e);

src/test/run-pass/label_break_value.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(label_break_value)]
+
 // Test control flow to follow label_break_value semantics
 fn label_break(a: bool, b: bool) -> u32 {
     let mut v = 0;

src/test/ui/feature-gate-label_break_value.rs

+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+pub fn main() {
+    'a: { //~ ERROR labels on blocks are unstable
+        break 'a;
+    }
+}

src/test/ui/feature-gate-label_break_value.stderr

+error[E0658]: labels on blocks are unstable (see issue #48594)
+  --> $DIR/feature-gate-label_break_value.rs:12:5
+   |
+LL |     'a: { //~ ERROR labels on blocks are unstable
+   |     ^^
+   |
+   = help: add #![feature(label_break_value)] to the crate attributes to enable
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0658`.

src/test/ui/label_break_value_continue.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(label_break_value)]
+
 // Simple continue pointing to an unlabeled break should yield in an error
 fn continue_simple() {
     'b: {

src/test/ui/label_break_value_continue.stderr

 error[E0695]: unlabeled `continue` inside of a labeled block
-  --> $DIR/label_break_value_continue.rs:14:9
+  --> $DIR/label_break_value_continue.rs:16:9
    |
 LL |         continue; //~ ERROR unlabeled `continue` inside of a labeled block
    |         ^^^^^^^^ `continue` statements that would diverge to or through a labeled block need to bear a label
 
 error[E0696]: `continue` pointing to a labeled block
-  --> $DIR/label_break_value_continue.rs:21:9
+  --> $DIR/label_break_value_continue.rs:23:9
    |
 LL |         continue 'b; //~ ERROR `continue` pointing to a labeled block
    |         ^^^^^^^^^^^ labeled blocks cannot be `continue`'d
    |
 note: labeled block the continue points to
-  --> $DIR/label_break_value_continue.rs:20:5
+  --> $DIR/label_break_value_continue.rs:22:5
    |
 LL | /     'b: {
 LL | |         continue 'b; //~ ERROR `continue` pointing to a labeled block
@@ -19,7 +19,7 @@ LL | |     }
    | |_____^
 
 error[E0695]: unlabeled `continue` inside of a labeled block
-  --> $DIR/label_break_value_continue.rs:29:13
+  --> $DIR/label_break_value_continue.rs:31:13
    |
 LL |             continue; //~ ERROR unlabeled `continue` inside of a labeled block
    |             ^^^^^^^^ `continue` statements that would diverge to or through a labeled block need to bear a label

src/test/ui/label_break_value_illegal_uses.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(label_break_value)]
+
 // These are forbidden occurences of label-break-value
 
 fn labeled_unsafe() {

src/test/ui/label_break_value_illegal_uses.stderr

 error: expected one of `extern`, `fn`, or `{`, found `'b`
-  --> $DIR/label_break_value_illegal_uses.rs:14:12
+  --> $DIR/label_break_value_illegal_uses.rs:16:12
    |
 LL |     unsafe 'b: {} //~ ERROR expected one of `extern`, `fn`, or `{`
    |            ^^ expected one of `extern`, `fn`, or `{` here
 
 error: expected `{`, found `'b`
-  --> $DIR/label_break_value_illegal_uses.rs:18:13
+  --> $DIR/label_break_value_illegal_uses.rs:20:13
    |
 LL |     if true 'b: {} //~ ERROR expected `{`, found `'b`
    |     --      ^^----
@@ -14,7 +14,7 @@ LL |     if true 'b: {} //~ ERROR expected `{`, found `'b`
    |     this `if` statement has a condition, but no block
 
 error: expected `{`, found `'b`
-  --> $DIR/label_break_value_illegal_uses.rs:22:21
+  --> $DIR/label_break_value_illegal_uses.rs:24:21
    |
 LL |     if true {} else 'b: {} //~ ERROR expected `{`, found `'b`
    |                     ^^----
@@ -22,7 +22,7 @@ LL |     if true {} else 'b: {} //~ ERROR expected `{`, found `'b`
    |                     help: try placing this code inside a block: `{ 'b: { } }`
 
 error: expected one of `.`, `?`, `{`, or an operator, found `'b`
-  --> $DIR/label_break_value_illegal_uses.rs:26:17
+  --> $DIR/label_break_value_illegal_uses.rs:28:17
    |
 LL |     match false 'b: {} //~ ERROR expected one of `.`, `?`, `{`, or an operator
    |                 ^^ expected one of `.`, `?`, `{`, or an operator here

src/test/ui/label_break_value_unlabeled_break.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(label_break_value)]
+
 // Simple unlabeled break should yield in an error
 fn unlabeled_break_simple() {
     'b: {

src/test/ui/label_break_value_unlabeled_break.stderr

 error[E0695]: unlabeled `break` inside of a labeled block
-  --> $DIR/label_break_value_unlabeled_break.rs:14:9
+  --> $DIR/label_break_value_unlabeled_break.rs:16:9
    |
 LL |         break; //~ ERROR unlabeled `break` inside of a labeled block
    |         ^^^^^ `break` statements that would diverge to or through a labeled block need to bear a label
 
 error[E0695]: unlabeled `break` inside of a labeled block
-  --> $DIR/label_break_value_unlabeled_break.rs:22:13
+  --> $DIR/label_break_value_unlabeled_break.rs:24:13
    |
 LL |             break; //~ ERROR unlabeled `break` inside of a labeled block
    |             ^^^^^ `break` statements that would diverge to or through a labeled block need to bear a label