Add regression test for ICE

src/test/ui/issue-55846.rs

@@ -0,0 +1,39 @@
+// run-pass
+
+// Regression test for #55846, which once caused an ICE.
+
+use std::marker::PhantomData;
+
+struct Foo;
+
+struct Bar<A> {
+    a: PhantomData<A>,
+}
+
+impl Fooifier for Foo {
+    type Assoc = Foo;
+}
+
+trait Fooifier {
+    type Assoc;
+}
+
+trait Barifier<H> {
+    fn barify();
+}
+
+impl<H> Barifier<H> for Bar<H> {
+    fn barify() {
+        println!("All correct!");
+    }
+}
+
+impl Bar<<Foo as Fooifier>::Assoc> {
+    fn this_shouldnt_crash() {
+        <Self as Barifier<<Foo as Fooifier>::Assoc>>::barify();
+    }
+}
+
+fn main() {
+    Bar::<Foo>::this_shouldnt_crash();
+}