Don't accidentally promote union access in MIR

src/librustc_mir/transform/qualify_consts.rs

@@ -515,7 +515,7 @@ fn visit_place(&mut self,
                             if let Some(def) = base_ty.ty_adt_def() {
                                 if def.is_union() {
                                     match this.mode {
-                                        Mode::Fn => {},
+                                        Mode::Fn => this.not_const(),
                                         Mode::ConstFn => {
                                             if !this.tcx.sess.features_untracked().const_fn_union {
                                                 emit_feature_err(

src/test/ui/const-eval/union_promotion.nll.stderr

@@ -1,11 +0,0 @@
-error: internal compiler error: unexpected region for local data ReStatic
-  --> $DIR/union_promotion.rs:19:29
-   |
-LL |       let x: &'static bool = &unsafe { //~ borrowed value does not live long enough
-   |  _____________________________^
-LL | |         Foo { a: &1 }.b == Foo { a: &2 }.b
-LL | |     };
-   | |_____^
-
-error: aborting due to previous error
-