Here tsubst_pack_expansion assumes that we should have arguments for
all packs if we're not in a template, but we might not if there's an
auto pack.
Tested x86_64-pc-linux-gnu, applying to trunk.
commit 445cd04fd16f17dd499f2f7eb2ac8a723e9071a4
Author: Jason Merrill <ja...@redhat.com>
Date: Wed Apr 4 14:53:08 2018 -0400
PR c++/85006 - -fconcepts ICE with A<auto...> return type
* pt.c (tsubst_pack_expansion): Allow unsubstituted auto pack.
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 80670a4826b..dbbc7666721 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -11860,7 +11860,7 @@ tsubst_pack_expansion (tree t, tree args, tsubst_flags_t complain,
/* We can't substitute for this parameter pack. We use a flag as
well as the missing_level counter because function parameter
packs don't have a level. */
- gcc_assert (processing_template_decl);
+ gcc_assert (processing_template_decl || is_auto (parm_pack));
unsubstituted_packs = true;
}
}
diff --git a/gcc/testsuite/g++.dg/concepts/auto4.C b/gcc/testsuite/g++.dg/concepts/auto4.C
new file mode 100644
index 00000000000..e80341ec038
--- /dev/null
+++ b/gcc/testsuite/g++.dg/concepts/auto4.C
@@ -0,0 +1,11 @@
+// PR c++/85006
+// { dg-additional-options "-std=c++17 -fconcepts" }
+
+template<typename... Ts> struct A {};
+
+template<typename... Us> A<auto...> foo() { return A{}; }
+
+void bar()
+{
+ foo();
+}
