Test that label break value only works on actual blocks

src/test/ui/label_break_value_illegal_uses.rs

@@ -0,0 +1,29 @@
+// 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.
+
+// These are forbidden occurences of label-break-value
+
+fn labeled_unsafe() {
+    unsafe 'b: {} //~ ERROR expected one of `extern`, `fn`, or `{`
+}
+
+fn labeled_if() {
+    if true 'b: {} //~ ERROR expected `{`, found `'b`
+}
+
+fn labeled_else() {
+    if true {} else 'b: {} //~ ERROR expected `{`, found `'b`
+}
+
+fn labeled_match() {
+    match false 'b: {} //~ ERROR expected one of `.`, `?`, `{`, or an operator
+}
+
+pub fn main() {}

src/test/ui/label_break_value_illegal_uses.stderr

@@ -0,0 +1,31 @@
+error: expected one of `extern`, `fn`, or `{`, found `'b`
+  --> $DIR/label_break_value_illegal_uses.rs:14:12
+   |
+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
+   |
+LL |     if true 'b: {} //~ ERROR expected `{`, found `'b`
+   |     --      ^^----
+   |     |       |
+   |     |       help: try placing this code inside a block: `{ 'b: { } }`
+   |     this `if` statement has a condition, but no block
+
+error: expected `{`, found `'b`
+  --> $DIR/label_break_value_illegal_uses.rs:22:21
+   |
+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
+   |
+LL |     match false 'b: {} //~ ERROR expected one of `.`, `?`, `{`, or an operator
+   |                 ^^ expected one of `.`, `?`, `{`, or an operator here
+
+error: aborting due to 4 previous errors
+