Respect lint attributes on match arms

src/librustc/lint/mod.rs

@@ -852,6 +852,12 @@ impl<'a, 'tcx> intravisit::Visitor<'tcx> for LintLevelMapBuilder<'a, 'tcx> {
         })
     }
 
+    fn visit_arm(&mut self, a: &'tcx hir::Arm) {
+        self.with_lint_attrs(a.hir_id, &a.attrs, |builder| {
+            intravisit::walk_arm(builder, a);
+        })
+    }
+
     fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem) {
         self.with_lint_attrs(trait_item.hir_id, &trait_item.attrs, |builder| {
             intravisit::walk_trait_item(builder, trait_item);

src/test/ui/lint/lint-match-arms.rs

@@ -0,0 +1,18 @@
+fn deny_on_arm() {
+    match 0 {
+        #[deny(unused_variables)]
+        //~^ NOTE lint level defined here
+        y => (),
+        //~^ ERROR unused variable
+    }
+}
+
+#[deny(unused_variables)]
+fn allow_on_arm() {
+    match 0 {
+        #[allow(unused_variables)]
+        y => (), // OK
+    }
+}
+
+fn main() {}

src/test/ui/lint/lint-match-arms.stderr

@@ -0,0 +1,14 @@
+error: unused variable: `y`
+  --> $DIR/lint-match-arms.rs:5:9
+   |
+LL |         y => (),
+   |         ^ help: consider prefixing with an underscore: `_y`
+   |
+note: lint level defined here
+  --> $DIR/lint-match-arms.rs:3:16
+   |
+LL |         #[deny(unused_variables)]
+   |                ^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+