C++ PATCH for c++/86192, ICE with template argument of anonymous union type

[Jason Merrill]

Someone found a sneaky way to use an anonymous union type as a
template argument.  That seems to me like it ought to be ill-formed,
but this patch is a simple enough way to make this testcase work.

Tested x86_64-pc-linux-gnu, applying to trunk.

commit 4f51a88ed61f69fd483a46b93f0ba9cff352324a
Author: Jason Merrill <ja...@redhat.com>
Date:   Mon Jun 18 21:20:29 2018 -0400

            PR c++/86192 - ICE with anonymous union passed to template.
    
            * pt.c (tsubst_expr) [DECL_EXPR]: Handle an anonymous union type
            used to declare a named variable.

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 1ecc6fb373d..3386385b3f8 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -16678,7 +16678,7 @@ tsubst_expr (tree t, tree args, tsubst_flags_t complain, tree in_decl,
 		   do.  */
 		if (VAR_P (decl))
 		  DECL_TEMPLATE_INSTANTIATED (decl) = 1;
-		if (VAR_P (decl)
+		if (VAR_P (decl) && !DECL_NAME (decl)
 		    && ANON_AGGR_TYPE_P (TREE_TYPE (decl)))
 		  /* Anonymous aggregates are a special case.  */
 		  finish_anon_union (decl);
diff --git a/gcc/testsuite/g++.dg/template/anonunion3.C b/gcc/testsuite/g++.dg/template/anonunion3.C
new file mode 100644
index 00000000000..1ac8165fa78
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/anonunion3.C
@@ -0,0 +1,16 @@
+// PR c++/86192
+// { dg-do compile { target c++11 } }
+
+extern "C" int printf (const char *, ...);
+
+template<typename T> static char const * f(T *t) {
+ T u(*t);
+ u.x = "hello world";
+ printf("%s\n", u.x);
+ return "initialized";
+}
+
+int main() {
+ union { char const *x = f(this); };
+ printf("%s\n", x);
+}