Rollup merge of #109380 - Randl:patch-1, r=oli-obk

add `known-bug` test for unsoundness issue

Test for #97156

Author: matthiaskrgr

tests/ui/const-generics/generic_const_exprs/typeid-equality-by-subtyping.rs

@@ -0,0 +1,52 @@
+// check-pass
+// known-bug: #97156
+
+#![feature(const_type_id, generic_const_exprs)]
+#![allow(incomplete_features)]
+
+use std::any::TypeId;
+// `One` and `Two` are currently considered equal types, as both
+// `One <: Two` and `One :> Two` holds.
+type One = for<'a> fn(&'a (), &'a ());
+type Two = for<'a, 'b> fn(&'a (), &'b ());
+trait AssocCt {
+    const ASSOC: usize;
+}
+const fn to_usize<T: 'static>() -> usize {
+    const WHAT_A_TYPE: TypeId = TypeId::of::<One>();
+    match TypeId::of::<T>() {
+        WHAT_A_TYPE => 0,
+        _ => 1000,
+    } 
+}
+impl<T: 'static> AssocCt for T {
+    const ASSOC: usize = to_usize::<T>();
+}
+
+trait WithAssoc<U> {
+    type Assoc;
+}
+impl<T: 'static> WithAssoc<()> for T where [(); <T as AssocCt>::ASSOC]: {
+    type Assoc = [u8; <T as AssocCt>::ASSOC];
+}
+
+fn generic<T: 'static, U>(x: <T as WithAssoc<U>>::Assoc) -> <T as WithAssoc<U>>::Assoc
+where
+    [(); <T as AssocCt>::ASSOC]:,
+    T: WithAssoc<U>,
+{
+    x
+}
+
+
+fn unsound<T>(x: <One as WithAssoc<T>>::Assoc) -> <Two as WithAssoc<T>>::Assoc
+where
+    One: WithAssoc<T>,
+{
+    let x: <Two as WithAssoc<T>>::Assoc = generic::<One, T>(x);
+    x
+}
+
+fn main() {
+    println!("{:?}", unsound::<()>([]));
+}