pre-expansion gate label_break_value

src/libsyntax/feature_gate/check.rs

@@ -514,12 +514,6 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
                                        "type ascription is experimental");
                 }
             }
-            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)
@@ -814,6 +808,7 @@ pub fn check_crate(krate: &ast::Crate,
     gate_all!(box_patterns, "box pattern syntax is experimental");
     gate_all!(exclusive_range_pattern, "exclusive range pattern syntax is experimental");
     gate_all!(try_blocks, "`try` blocks are unstable");
+    gate_all!(label_break_value, "labels on blocks are unstable");
 
     visit::walk_crate(&mut visitor, krate);
 }

src/libsyntax/parse/parser/expr.rs

@@ -1260,6 +1260,10 @@ impl<'a> Parser<'a> {
         blk_mode: BlockCheckMode,
         outer_attrs: ThinVec<Attribute>,
     ) -> PResult<'a, P<Expr>> {
+        if let Some(label) = opt_label {
+            self.sess.gated_spans.label_break_value.borrow_mut().push(label.ident.span);
+        }
+
         self.expect(&token::OpenDelim(token::Brace))?;
 
         let mut attrs = outer_attrs;

src/libsyntax/sess.rs

@@ -46,6 +46,8 @@ crate struct GatedSpans {
     pub exclusive_range_pattern: Lock<Vec<Span>>,
     /// Spans collected for gating `try_blocks`, e.g. `try { a? + b? }`.
     pub try_blocks: Lock<Vec<Span>>,
+    /// Spans collected for gating `label_break_value`, e.g. `'label: { ... }`.
+    pub label_break_value: Lock<Vec<Span>>,
 }
 
 /// Info about a parsing session.

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

@@ -1,5 +1,8 @@
-pub fn main() {
+#[cfg(FALSE)]
+pub fn foo() {
     'a: { //~ ERROR labels on blocks are unstable
         break 'a;
     }
 }
+
+fn main() {}

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

@@ -1,5 +1,5 @@
 error[E0658]: labels on blocks are unstable
-  --> $DIR/feature-gate-label_break_value.rs:2:5
+  --> $DIR/feature-gate-label_break_value.rs:3:5
    |
 LL |     'a: {
    |     ^^