Fix a bug with type constraints in constructors.

gcc/cp/
	* parser.c (cp_parser_constructor_declarator_p): Pass an empty
	decl-specifier-seq to make sure we parse type constraints as part
	of a type-specifier.

gcc/testsuite/
	* g++.dg/cpp2a/concepts5.C: New test.

From-SVN: r277323

gcc/cp/ChangeLog

@@ -126,6 +126,12 @@
 	* decl.c (cxx_maybe_build_cleanup): When clearing location of cleanup,
 	if cleanup is a nop, clear location of its operand too.
 
+2019-10-15  Andrew Sutton  <asutton@lock3software.com>
+
+	* parser.c (cp_parser_constructor_declarator_p): Pass an empty
+	decl-specifier-seq to make sure we parse type constraints as part
+	of a type-specifier.
+
 2019-10-15  Nathan Sidwell  <nathan@acm.org>
 
 	* class.c (build_clones): Break out of clone_function_decl.  Just

gcc/cp/parser.c

@@ -28336,11 +28336,19 @@ cp_parser_constructor_declarator_p (cp_parser *parser, cp_parser_flags flags,
 	     looking for the type-specifier.  It is actually a function named
 	     `T::fn' that takes one parameter (of type `int') and returns a
 	     value of type `S'.  Constructors can be friends, but they must
-	     use a qualified name.  */
+	     use a qualified name.
+
+	     Parse with an empty set of declaration specifiers since we're
+	     trying to match a decl-specifier-seq of the first parameter.  
+	     This must be non-null so that cp_parser_simple_type_specifier
+	     will recognize a constrained placeholder type such as:
+	     'C<int> auto' where C is a type concept.  */
+	  cp_decl_specifier_seq ctor_specs;
+	  clear_decl_specs (&ctor_specs);
 	  cp_parser_type_specifier (parser,
 				    (friend_p ? CP_PARSER_FLAGS_NONE
 				     : (flags & ~CP_PARSER_FLAGS_OPTIONAL)),
-				    /*decl_specs=*/NULL,
+				    /*decl_specs=*/&ctor_specs,
 				    /*is_declarator=*/true,
 				    /*declares_class_or_enum=*/NULL,
 				    /*is_cv_qualifier=*/NULL);

gcc/testsuite/ChangeLog

@@ -344,6 +344,10 @@
 	* gcc.dg/ipa/pr91089.c: Add sub-test for range analysis.
 	* g++.dg/tree-ssa/ivopts-3.C: Force a function to be noinline.
 
+2019-10-15  Andrew Sutton  <asutton@lock3software.com>
+
+	* g++.dg/cpp2a/concepts5.C: New test.
+
 2019-10-15  Andrew Pinski  <apinski@marvell.com>
 
 	* gcc.c-torture/compile/20191015-1.c: New test.

gcc/testsuite/g++.dg/cpp2a/concepts5.C

+// { dg-do compile { target c++2a } }
+
+
+template <typename T, typename U>
+concept same_as = __is_same_as(T, U);
+
+template<typename T>
+concept character = same_as<T, char>;
+
+struct T
+{
+  constexpr T(same_as<int> auto const x) : val(0) { }
+
+  constexpr T(character auto const x) : val(1) { }
+
+  int val;
+};
+
+void test()
+{
+  static_assert(T(0).val == 0);
+  static_assert(T('a').val == 1);
+}
+