Regression test for issue #60654.

Author: pnkfelix

src/test/ui/rfc1598-generic-associated-types/gat-dont-ice-on-absent-feature.rs

@@ -0,0 +1,14 @@
+// rust-lang/rust#60654: Do not ICE on an attempt to use GATs that is
+// missing the feature gate.
+
+struct Foo;
+
+impl Iterator for Foo {
+    type Item<'b> = &'b Foo; //~ ERROR generic associated types are unstable [E0658]
+
+    fn next(&mut self) -> Option<Self::Item> {
+        None
+    }
+}
+
+fn main() { }

src/test/ui/rfc1598-generic-associated-types/gat-dont-ice-on-absent-feature.stderr

@@ -0,0 +1,12 @@
+error[E0658]: generic associated types are unstable
+  --> $DIR/gat-dont-ice-on-absent-feature.rs:7:5
+   |
+LL |     type Item<'b> = &'b Foo;
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: for more information, see https://github.com/rust-lang/rust/issues/44265
+   = help: add #![feature(generic_associated_types)] to the crate attributes to enable
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0658`.