From 9e44a9932c11f028269f3aa7e3031e703d151b0b Mon Sep 17 00:00:00 2001
From: Jason Merrill <jason@redhat.com>
Date: Tue, 14 Mar 2023 16:32:31 -0400
Subject: [PATCH] c++: variable tmpl partial specialization [PR108468]

Generally we expect TPARMS_PRIMARY_TEMPLATE to be set, but sometimes it
isn't for partial instantiations.  This ought to be improved, but it's
trivial to work around it in this case.

	PR c++/108468

gcc/cp/ChangeLog:

	* pt.cc (unify_pack_expansion): Check that TPARMS_PRIMARY_TEMPLATE
	is non-null.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp1y/var-templ78.C: New test.
---
 gcc/cp/pt.cc                             |  2 ++
 gcc/testsuite/g++.dg/cpp1y/var-templ78.C | 12 ++++++++++++
 2 files changed, 14 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/cpp1y/var-templ78.C

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 65341c4..c53d8e2 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -24148,6 +24148,8 @@ unify_pack_expansion (tree tparms, tree targs, tree packed_parms,
 	     arguments if it is not otherwise deduced.  */
 	  if (cxx_dialect >= cxx20
 	      && TREE_VEC_LENGTH (new_args) < TREE_VEC_LENGTH (old_args)
+	      /* FIXME This isn't set properly for partial instantiations.  */
+	      && TPARMS_PRIMARY_TEMPLATE (tparms)
 	      && builtin_guide_p (TPARMS_PRIMARY_TEMPLATE (tparms)))
 	    TREE_VEC_LENGTH (old_args) = TREE_VEC_LENGTH (new_args);
 	  if (!comp_template_args (old_args, new_args,
diff --git a/gcc/testsuite/g++.dg/cpp1y/var-templ78.C b/gcc/testsuite/g++.dg/cpp1y/var-templ78.C
new file mode 100644
index 0000000..48366c9
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/var-templ78.C
@@ -0,0 +1,12 @@
+// PR c++/108468
+// { dg-do compile { target c++14 } }
+
+template<int> struct C {
+  template<class, class>
+  static constexpr int x = 1;
+};
+
+template<int I> template<class... A>
+int C<I>::x<void(A...), void(A...)> = 2;
+
+int y = C<0>::x<void(int), void()>;
-- 
2.7.4