Don't resolve generic instances if they may be shadowed by dyn

2 files changed, 50 insertions, 0 deletions

diff --git a/tests/ui/const_prop/dont-propagate-generic-instance-2.rs b/tests/ui/const_prop/dont-propagate-generic-instance-2.rs
new file mode 100644
index 00000000000..e5525af23f0
--- /dev/null
+++ b/tests/ui/const_prop/dont-propagate-generic-instance-2.rs
@@ -0,0 +1,26 @@
+// run-pass
+
+#![feature(inline_const)]
+
+// Makes sure we don't propagate generic instances of `Self: ?Sized` blanket impls.
+// This is relevant when we have an overlapping impl and builtin dyn instance.
+// See <https://github.com/rust-lang/rust/pull/114941> for more context.
+
+trait Trait {
+    fn foo(&self) -> &'static str;
+}
+
+impl<T: ?Sized> Trait for T {
+    fn foo(&self) -> &'static str {
+        std::any::type_name::<T>()
+    }
+}
+
+fn bar<T: ?Sized>() -> fn(&T) -> &'static str {
+    const { Trait::foo as fn(&T) -> &'static str }
+    // If const prop were to propagate the instance
+}
+
+fn main() {
+    assert_eq!("i32", bar::<dyn Trait>()(&1i32));
+}
diff --git a/tests/ui/const_prop/dont-propagate-generic-instance.rs b/tests/ui/const_prop/dont-propagate-generic-instance.rs
new file mode 100644
index 00000000000..5994961b887
--- /dev/null
+++ b/tests/ui/const_prop/dont-propagate-generic-instance.rs
@@ -0,0 +1,24 @@
+// run-pass
+
+// Makes sure we don't propagate generic instances of `Self: ?Sized` blanket impls.
+// This is relevant when we have an overlapping impl and builtin dyn instance.
+// See <https://github.com/rust-lang/rust/pull/114941> for more context.
+
+trait Trait {
+    fn foo(&self) -> &'static str;
+}
+
+impl<T: ?Sized> Trait for T {
+    fn foo(&self) -> &'static str {
+        std::any::type_name::<T>()
+    }
+}
+
+const fn bar<T: ?Sized>() -> fn(&T) -> &'static str {
+    Trait::foo
+    // If const prop were to propagate the instance
+}
+
+fn main() {
+    assert_eq!("i32", bar::<dyn Trait>()(&1i32));
+}