Add regression test for issue 120600

Author: WaffleLapkin

tests/ui/never_type/eq-never-types.rs

@@ -0,0 +1,22 @@
+//@ known-bug: #120600
+//
+// Regression test for <https://github.com/rust-lang/rust/issues/120600>.
+
+//@ failure-status: 101
+//@ normalize-stderr-test: "DefId\(.*?\]::" -> "DefId("
+//@ normalize-stderr-test: "(?m)note: we would appreciate a bug report.*\n\n" -> ""
+//@ normalize-stderr-test: "(?m)note: rustc.*running on.*\n\n" -> ""
+//@ normalize-stderr-test: "(?m)note: compiler flags.*\n\n" -> ""
+//@ normalize-stderr-test: "(?m)note: delayed at.*$" -> ""
+//@ normalize-stderr-test: "(?m)^ *\d+: .*\n" -> ""
+//@ normalize-stderr-test: "(?m)^ *at .*\n" -> ""
+
+#![allow(internal_features)]
+#![feature(never_type, rustc_attrs)]
+#![rustc_never_type_options(fallback = "never")]
+
+fn ice(a: !) {
+    a == a;
+}
+
+fn main() {}

tests/ui/never_type/eq-never-types.stderr

@@ -0,0 +1,20 @@
+note: no errors encountered even though delayed bugs were created
+
+note: those delayed bugs will now be shown as internal compiler errors
+
+error: internal compiler error: broken MIR in DefId(ice) (Terminator { source_info: SourceInfo { span: $DIR/eq-never-types.rs:19:5: 19:11 (#0), scope: scope[0] }, kind: _3 = <! as PartialEq>::eq(move _4, move _5) -> [return: bb1, unwind: bb2] }): bad arg #0 (&'?4 ! <- !): NoSolution
+  --> $DIR/eq-never-types.rs:19:10
+   |
+LL |     a == a;
+   |          ^
+   |
+
+  --> $DIR/eq-never-types.rs:19:10
+   |
+LL |     a == a;
+   |          ^
+
+note: using internal features is not supported and expected to cause internal compiler errors when used incorrectly
+
+query stack during panic:
+end of query stack