PR c++/79056 - C++17 ICE with invalid template syntax.

	* parser.c (cp_parser_simple_type_specifier): Don't assume that type
	is a TYPE_DECL.
	(cp_parser_check_for_invalid_template_id): Handle TYPE_DECL.
	* pt.c (template_placeholder_p): New.
	* cp-tree.h: Declare it.

From-SVN: r249614

gcc/cp/ChangeLog

+2017-06-23  Jason Merrill  <jason@redhat.com>
+
+	PR c++/79056 - C++17 ICE with invalid template syntax.
+	* parser.c (cp_parser_simple_type_specifier): Don't assume that type
+	is a TYPE_DECL.
+	(cp_parser_check_for_invalid_template_id): Handle TYPE_DECL.
+	* pt.c (template_placeholder_p): New.
+	* cp-tree.h: Declare it.
+
 2017-06-23  Marc Glisse  <marc.glisse@inria.fr>
 
 	* decl.c (duplicate_decls): Use builtin_structptr_types.

gcc/cp/cp-tree.h

@@ -6413,6 +6413,7 @@ extern void check_template_variable		(tree);
 extern tree make_auto				(void);
 extern tree make_decltype_auto			(void);
 extern tree make_template_placeholder		(tree);
+extern bool template_placeholder_p		(tree);
 extern tree do_auto_deduction                   (tree, tree, tree);
 extern tree do_auto_deduction                   (tree, tree, tree,
                                                  tsubst_flags_t,

gcc/cp/parser.c

@@ -2983,7 +2983,9 @@ cp_parser_check_for_invalid_template_id (cp_parser* parser,
 
   if (cp_lexer_next_token_is (parser->lexer, CPP_LESS))
     {
-      if (TYPE_P (type))
+      if (TREE_CODE (type) == TYPE_DECL)
+	type = TREE_TYPE (type);
+      if (TYPE_P (type) && !template_placeholder_p (type))
 	error_at (location, "%qT is not a template", type);
       else if (identifier_p (type))
 	{
@@ -17060,7 +17062,7 @@ cp_parser_simple_type_specifier (cp_parser* parser,
       /* There is no valid C++ program where a non-template type is
 	 followed by a "<".  That usually indicates that the user
 	 thought that the type was a template.  */
-      cp_parser_check_for_invalid_template_id (parser, TREE_TYPE (type),
+      cp_parser_check_for_invalid_template_id (parser, type,
 					       none_type,
 					       token->location);
     }

gcc/cp/pt.c

@@ -24799,6 +24799,14 @@ make_template_placeholder (tree tmpl)
   return t;
 }
 
+/* True iff T is a C++17 class template deduction placeholder.  */
+
+bool
+template_placeholder_p (tree t)
+{
+  return is_auto (t) && CLASS_PLACEHOLDER_TEMPLATE (t);
+}
+
 /* Make a "constrained auto" type-specifier. This is an
    auto type with constraints that must be associated after
    deduction.  The constraint is formed from the given

gcc/testsuite/g++.dg/parse/template28.C

+// PR c++/79056
+
+template<class> struct A {};
+
+template<class T> void foo(A<T>=A<T>()) {} // { dg-error "" }
+
+void bar()
+{
+  foo(A<int>());		// { dg-error "" }
+}