From 8ac0edb280e06cfd1f421ae628b02d527809da18 Mon Sep 17 00:00:00 2001
From: Dana Jansens <danakj@orodu.net>
Date: Wed, 29 Jul 2026 11:18:43 -0400
Subject: [PATCH] Add a failing test where frozen `.Self` is passed in generic
 argument and never thawed (#7582)

---
 .../check/testdata/facet/period_self.carbon   | 22 +++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/toolchain/check/testdata/facet/period_self.carbon b/toolchain/check/testdata/facet/period_self.carbon
index 20604855a5b6..a4a564cb6e75 100644
--- a/toolchain/check/testdata/facet/period_self.carbon
+++ b/toolchain/check/testdata/facet/period_self.carbon
@@ -800,6 +800,28 @@ interface Z(T: type);
 // CHECK:STDERR:
 fn F(generic _: C(Z(.Self))) {}
 
+// --- fail_todo_period_self_in_generic_argument.carbon
+library "[[@TEST_NAME]]";
+
+interface Z {
+  let Z1: type;
+}
+interface Y(T: type) {
+  // The type here is `Z where .Z1 = ()` with a thawed `.Self` in the access of `.Z1`.
+  let Y1: Z where .Z1 = ();
+  // The type here ends up being `Z where .Z1 = ()` with a frozen `.Self` in the
+  // access of `.Z1`. So it can't convert to the type of `Y1`, which is a bug.
+  eval fn YF() -> T;
+}
+
+// TODO: We crash if this impl is not generic, as the call to `.YF()` produces a
+// symbolic-dependent instruction, but there's no generic eval block for it.
+// CHECK:STDERR: fail_todo_period_self_in_generic_argument.carbon:[[@LINE+4]]:60: error: cannot convert type `<cannot stringify inst5D0000AF: {kind: Call, arg0: inst5D0000AD, arg1: inst_block_empty, type: type(inst5D000088)}>` that implements `Z where .(Z.Z1) = ()` into type implementing `Z where .(Z.Z1) = ()` [ConversionFailureFacetToFacet]
+// CHECK:STDERR: impl forall [T: type] T as Y(Z where .Z1 = ()) where .Y1 = .YF() {}
+// CHECK:STDERR:                                                            ^~~~~
+// CHECK:STDERR:
+impl forall [T: type] T as Y(Z where .Z1 = ()) where .Y1 = .YF() {}
+
 // CHECK:STDOUT: --- period_self_param.carbon
 // CHECK:STDOUT:
 // CHECK:STDOUT: constants {