Fix bad caching of ~const Drop bounds

src/test/ui/rfc-2632-const-trait-impl/issue-92111.rs

@@ -0,0 +1,29 @@
+// Regression test for #92111.
+//
+// The issue was that we normalize trait bounds before caching
+// results of selection. Checking that `impl NoDrop for S` requires
+// checking `S: !Drop` because it cannot overlap with the blanket
+// impl. Then we save the (unsatisfied) result from checking `S: Drop`.
+// Then the call to `a` checks whether `S: ~const Drop` but we normalize
+// it to `S: Drop` which the cache claims to be unsatisfied.
+//
+// check-pass
+
+#![feature(const_trait_impl)]
+#![feature(const_fn_trait_bound)]
+
+pub trait Tr {}
+
+#[allow(drop_bounds)]
+impl<T: Drop> Tr for T {}
+
+#[derive(Debug)]
+pub struct S(i32);
+
+impl Tr for S {}
+
+const fn a<T: ~const Drop>(t: T) {}
+
+fn main() {
+    a(S(0));
+}