Support using 'auto' in a function parameter list to introduce an implicit template parameter.

	* cp-tree.h (type_uses_auto_or_concept): Declare.
	(is_auto_or_concept): Declare.
	* decl.c (grokdeclarator): Allow 'auto' parameters in lambdas with
	-std=gnu++1y or -std=c++1y or, as a GNU extension, in plain functions.
	* type-utils.h: New header defining ...
	(find_type_usage): ... this new function based on pt.c (type_uses_auto)
	for searching a type tree given a predicate.
	* pt.c (type_uses_auto): Reimplement via type-utils.h (find_type_usage).
	(is_auto_or_concept): New function.
	(type_uses_auto_or_concept): New function.
	* parser.h (struct cp_parser): Add fully_implicit_function_template_p.
	* parser.c (cp_parser_new): Initialize fully_implicit_function_template_p.
	(cp_parser_new): Initialize fully_implicit_function_template_p.
	(cp_parser_lambda_expression): Copy and restore value of
	fully_implicit_function_template_p as per other parser fields.
	(cp_parser_parameter_declaration_list): Count generic
	parameters and call ...
	(add_implicit_template_parms): ... this new function to synthesize them
	with help from type-utils.h (find_type_usage), ...
	(tree_type_is_auto_or_concept): ... this new static function and ...
	(make_generic_type_name): ... this new static function.
	(cp_parser_direct_declarator): Account for implicit template parameters.
	(cp_parser_lambda_declarator_opt): Finish fully implicit template if
	necessary by calling ...
	(finish_fully_implicit_template): ... this new function.
	(cp_parser_member_declaration): Likewise.
	(cp_parser_function_definition_after_declarator): Likewise.
	* Make-lang.in (cp/pt.o): Add dependency on type-utils.h.
	(cp/parser.o): Likewise.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@202540 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 17 insertions, 2 deletions

diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index b4223aa5706..6e026b2e016 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -10320,8 +10320,23 @@ grokdeclarator (const cp_declarator *declarator,
 
       if (type_uses_auto (type))
 	{
-	  error ("parameter declared %<auto%>");
-	  type = error_mark_node;
+	  if (current_class_type && LAMBDA_TYPE_P (current_class_type))
+	    {
+	      if (cxx_dialect < cxx1y)
+		pedwarn (location_of (type), 0,
+			 "use of %<auto%> in lambda parameter declaration "
+			 "only available with "
+			 "-std=c++1y or -std=gnu++1y");
+	    }
+	  else if (cxx_dialect < cxx1y)
+	    pedwarn (location_of (type), 0,
+		     "use of %<auto%> in parameter declaration "
+		     "only available with "
+		     "-std=c++1y or -std=gnu++1y");
+	  else
+	    pedwarn (location_of (type), OPT_Wpedantic,
+		     "ISO C++ forbids use of %<auto%> in parameter "
+		     "declaration");
 	}
 
       /* A parameter declared as an array of T is really a pointer to T.