Fix const qualification when executed after promotion

The const qualification was so far performed before the promotion and
the implementation assumed that it will never encounter a promoted.

With `const_precise_live_drops` feature, checking for live drops is
delayed until after drop elaboration, which in turn runs after
promotion. so the assumption is no longer true. When evaluating
`NeedsNonConstDrop` it is now possible to encounter promoteds.

Use type base qualification for the promoted. It is a sound
approximation in general, and in the specific case of promoteds and
`NeedsNonConstDrop` it is precise.

Author: tmiasko

compiler/rustc_const_eval/src/transform/check_consts/qualifs.rs

@@ -309,8 +309,9 @@ where
 
     // Check the qualifs of the value of `const` items.
     if let Some(ct) = constant.literal.const_for_ty() {
-        if let ty::ConstKind::Unevaluated(ty::Unevaluated { def, substs_: _, promoted }) = ct.val {
-            assert!(promoted.is_none());
+        if let ty::ConstKind::Unevaluated(ty::Unevaluated { def, substs_: _, promoted: None }) =
+            ct.val
+        {
             // Don't peek inside trait associated constants.
             if cx.tcx.trait_of_item(def.did).is_none() {
                 let qualifs = if let Some((did, param_did)) = def.as_const_arg() {

src/test/ui/consts/precise-drop-with-promoted.rs

@@ -0,0 +1,9 @@
+// Regression test for issue #89938.
+// check-pass
+// compile-flags: --crate-type=lib
+#![feature(const_precise_live_drops)]
+
+pub const fn f() {
+    let _: Option<String> = None;
+    let _: &'static Option<String> = &None;
+}