Silence "skipping const checks" if outside a const context

Author: ecstatic-morse

src/librustc_mir/transform/qualify_consts.rs

@@ -678,7 +678,9 @@ struct Checker<'a, 'tcx> {
 macro_rules! unleash_miri {
     ($this:expr) => {{
         if $this.tcx.sess.opts.debugging_opts.unleash_the_miri_inside_of_you {
-            $this.tcx.sess.span_warn($this.span, "skipping const checks");
+            if $this.mode.requires_const_checking() {
+                $this.tcx.sess.span_warn($this.span, "skipping const checks");
+            }
             return;
         }
     }}

src/test/ui/consts/miri_unleashed/mutable_references.rs

@@ -27,9 +27,7 @@ static OH_YES: &mut i32 = &mut 42;
 
 fn main() {
     unsafe {
-        *MEH.x.get() = 99; //~ WARN skipping const checks
-        //~^ WARN skipping const checks
+        *MEH.x.get() = 99;
     }
     *OH_YES = 99; //~ ERROR cannot assign to `*OH_YES`, as `OH_YES` is an immutable static item
-    //~^ WARN skipping const checks
 }

src/test/ui/consts/miri_unleashed/mutable_references.stderr

@@ -1,23 +1,5 @@
-warning: skipping const checks
-  --> $DIR/mutable_references.rs:30:10
-   |
-LL |         *MEH.x.get() = 99;
-   |          ^^^^^
-
-warning: skipping const checks
-  --> $DIR/mutable_references.rs:30:9
-   |
-LL |         *MEH.x.get() = 99;
-   |         ^^^^^^^^^^^^^^^^^
-
-warning: skipping const checks
-  --> $DIR/mutable_references.rs:33:5
-   |
-LL |     *OH_YES = 99;
-   |     ^^^^^^^^^^^^
-
 error[E0594]: cannot assign to `*OH_YES`, as `OH_YES` is an immutable static item
-  --> $DIR/mutable_references.rs:33:5
+  --> $DIR/mutable_references.rs:32:5
    |
 LL |     *OH_YES = 99;
    |     ^^^^^^^^^^^^ cannot assign

src/test/ui/consts/miri_unleashed/mutable_references_ice.rs

@@ -24,6 +24,6 @@ const MUH: Meh = Meh {
 
 fn main() {
     unsafe {
-        *MUH.x.get() = 99; //~ WARN skipping const checks
+        *MUH.x.get() = 99;
     }
 }

src/test/ui/consts/miri_unleashed/mutable_references_ice.stderr

@@ -1,9 +1,3 @@
-warning: skipping const checks
-  --> $DIR/mutable_references_ice.rs:27:9
-   |
-LL |         *MUH.x.get() = 99;
-   |         ^^^^^^^^^^^^^^^^^
-
 thread 'rustc' panicked at 'assertion failed: `(left != right)`
   left: `Const`,
  right: `Const`: UnsafeCells are not allowed behind references in constants. This should have been prevented statically by const qualification. If this were allowed one would be able to change a constant at one use site and other use sites could observe that mutation.', src/librustc_mir/interpret/intern.rs:LL:CC