CheckLoopVisitor: also visit break expressions

Fixes rust-lang#50802

Author: est31

src/librustc_passes/loops.rs

@@ -89,6 +89,8 @@ impl<'a, 'hir> Visitor<'hir> for CheckLoopVisitor<'a, 'hir> {
                 self.with_context(LabeledBlock, |v| v.visit_block(&b));
             }
             hir::ExprBreak(label, ref opt_expr) => {
+                opt_expr.as_ref().map(|e| self.visit_expr(e));
+
                 if self.require_label_in_labeled_block(e.span, &label, "break") {
                     // If we emitted an error about an unlabeled break in a labeled
                     // block, we don't need any further checking for this break any more

src/test/ui/issue-50802.rs

@@ -0,0 +1,18 @@
+// 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.
+
+#[allow(unreachable_code)]
+
+fn main() {
+    loop {
+        break while continue { //~ ERROR E0590
+        }
+    }
+}

src/test/ui/issue-50802.stderr

@@ -0,0 +1,9 @@
+error[E0590]: `break` or `continue` with no label in the condition of a `while` loop
+  --> $DIR/issue-50802.rs:15:21
+   |
+LL |         break while continue { //~ ERROR E0590
+   |                     ^^^^^^^^ unlabeled `continue` in the condition of a `while` loop
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0590`.