From 509fd16da8528444dccc98cef57a18a295c3f1b4 Mon Sep 17 00:00:00 2001
From: Patrick Palka <ppalka@redhat.com>
Date: Thu, 28 Apr 2022 13:10:56 -0400
Subject: [PATCH] c++: partial ordering and dependent operator expr [PR105425]

Here ever since r12-6022-gbb2a7f80a98de3 we stopped deeming the partial
specialization #2 to be more specialized than #1 ultimately because
dependent operator expressions now have a DEPENDENT_OPERATOR_TYPE type
instead of an empty type, and this made unify stop deducing T(2) == 1
for K during partial ordering for #1 and #2.

This minimal patch fixes this by making the relevant logic in unify
treat DEPENDENT_OPERATOR_TYPE like an empty type.

	PR c++/105425

gcc/cp/ChangeLog:

	* pt.cc (unify) <case TEMPLATE_PARM_INDEX>: Treat
	DEPENDENT_OPERATOR_TYPE like an empty type.

gcc/testsuite/ChangeLog:

	* g++.dg/template/partial-specialization13.C: New test.
---
 gcc/cp/pt.cc                                          |  3 ++-
 .../g++.dg/template/partial-specialization13.C        | 11 +++++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/template/partial-specialization13.C

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index e785c5db1420..81f7ef5c42b5 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -24276,7 +24276,8 @@ unify (tree tparms, tree targs, tree parm, tree arg, int strict,
 	    }
 	}
 
-      if (!TREE_TYPE (arg))
+      if (!TREE_TYPE (arg)
+	  || TREE_CODE (TREE_TYPE (arg)) == DEPENDENT_OPERATOR_TYPE)
 	/* Template-parameter dependent expression.  Just accept it for now.
 	   It will later be processed in convert_template_argument.  */
 	;
diff --git a/gcc/testsuite/g++.dg/template/partial-specialization13.C b/gcc/testsuite/g++.dg/template/partial-specialization13.C
new file mode 100644
index 000000000000..b0903f0d60af
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/partial-specialization13.C
@@ -0,0 +1,11 @@
+// PR c++/105425
+// { dg-do compile { target c++11 } }
+
+template<bool> struct when;
+template<class, class> struct A;
+template<class T, bool K> struct A<T, when<K>>;            // #1
+template<class T>         struct A<T, when<T(2) == 1>> {}; // #2
+A<int, when<true>> a1; // { dg-error "incomplete" }
+A<int, when<false>> a2;
+A<bool, when<true>> a3;
+A<bool, when<false>> a4; // { dg-error "incomplete" }
-- 
2.39.2