[PATCH] c++: fix alias CTAD [PR114377]

[centurion]

>From b34312d82b236601c348382d30e625558f37d40c Mon Sep 17 00:00:00 2001
From: centurion <centurion009@proton.me>
Date: Mon, 25 Mar 2024 01:57:21 +0400
Subject: [PATCH] c++: fix alias CTAD [PR114377]

PR c++/114377

gcc/cp/ChangeLog:

	PR c++/114377
	* pt.cc (find_template_parameter_info::found): Use TREE_TYPE for
	TEMPLATE_DECL instead of DECL_INITIAL.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/class-deduction-alias19.C: New test.
---
 gcc/cp/pt.cc                                      |  3 ++-
 .../g++.dg/cpp2a/class-deduction-alias19.C        | 15 +++++++++++++++
 2 files changed, 17 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/class-deduction-alias19.C

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 8cf0d5b7a8d..d8a02f1cd7f 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -11032,7 +11032,8 @@ find_template_parameter_info::found (tree parm)
 {
   if (TREE_CODE (parm) == TREE_LIST)
     parm = TREE_VALUE (parm);
-  if (TREE_CODE (parm) == TYPE_DECL)
+  if (TREE_CODE (parm) == TYPE_DECL
+      || TREE_CODE(parm) == TEMPLATE_DECL)
     parm = TREE_TYPE (parm);
   else
     parm = DECL_INITIAL (parm);
diff --git a/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias19.C b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias19.C
new file mode 100644
index 00000000000..1ea79bd7691
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias19.C
@@ -0,0 +1,15 @@
+// PR c++/114377
+// { dg-do compile { target c++20 } }
+
+template <template <typename> typename Iterator>
+struct K {};
+
+template <typename C, typename IteratorPolicy>
+class Foo {};
+
+template <typename C, template<typename> typename TTP>
+using Bar = Foo<C, K<TTP>>;
+
+void s() {
+    Bar(1); // { dg-error "failed|no match" }
+}
-- 
2.44.0