From b9dc9ef63fc7bf742f97e1b9618d5818f3383c73 Mon Sep 17 00:00:00 2001
From: Jason Merrill <jason@redhat.com>
Date: Thu, 4 Aug 2016 12:06:22 -0400
Subject: [PATCH] PR c++/72415 - member template with fold-expression
 constraint

	* pt.c (tsubst_pack_expansion): Pull a single pack expansion out
	of the TREE_VEC.

From-SVN: r239138
---
 gcc/cp/ChangeLog                        |  4 ++++
 gcc/cp/pt.c                             |  6 ++++++
 gcc/testsuite/g++.dg/concepts/memfun2.C | 21 +++++++++++++++++++++
 3 files changed, 31 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/concepts/memfun2.C

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index e7854f7505e..573ece8bbad 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,5 +1,9 @@
 2016-08-04  Jason Merrill  <jason@redhat.com>
 
+	PR c++/72415
+	* pt.c (tsubst_pack_expansion): Pull a single pack expansion out
+	of the TREE_VEC.
+
 	* cp-tree.h (TYPE_UNNAMED_P): Rename from TYPE_ANONYMOUS_P.
 	(TYPE_WAS_UNNAMED): Rename from TYPE_WAS_ANONYMOUS.
 	* class.c, decl.c, decl2.c, error.c, lambda.c, mangle.c,
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index bf729ea3107..60c87e001c0 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -11160,6 +11160,12 @@ tsubst_pack_expansion (tree t, tree args, tsubst_flags_t complain,
       local_specializations = saved_local_specializations;
     }
   
+  /* If the dependent pack arguments were such that we end up with only a
+     single pack expansion again, there's no need to keep it in a TREE_VEC.  */
+  if (len == 1 && TREE_CODE (result) == TREE_VEC
+      && PACK_EXPANSION_P (TREE_VEC_ELT (result, 0)))
+    return TREE_VEC_ELT (result, 0);
+
   return result;
 }
 
diff --git a/gcc/testsuite/g++.dg/concepts/memfun2.C b/gcc/testsuite/g++.dg/concepts/memfun2.C
new file mode 100644
index 00000000000..c186a183762
--- /dev/null
+++ b/gcc/testsuite/g++.dg/concepts/memfun2.C
@@ -0,0 +1,21 @@
+// PR c++/72415
+// { dg-options "-std=c++1z -fconcepts" }
+
+template<int... Indices>
+struct indices {};
+
+template<typename Dummy>
+struct foo_type {
+    template<int... Indices>
+    static void impl(indices<Indices...>)
+        requires (... && (Indices, true));
+
+    static auto caller()
+    { return impl(indices<0, 1, 2> {}); }
+};
+
+int main()
+{
+    // internal compiler error: in satisfy_predicate_constraint, at cp/constraint.cc:2013
+    foo_type<void>::caller();
+}
-- 
2.30.2