PR c++/90572 - wrong disambiguation in friend declaration.

	* parser.c (cp_parser_constructor_declarator_p): Don't allow missing
	typename for friend declarations.

	* g++.dg/cpp2a/typename16.C: New test.
	* g++.dg/parse/friend13.C: New test.

From-SVN: r271619

gcc/cp/ChangeLog

+2019-05-25  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/90572 - wrong disambiguation in friend declaration.
+	* parser.c (cp_parser_constructor_declarator_p): Don't allow missing
+	typename for friend declarations.
+
 2019-05-23  Jonathan Wakely  <jwakely@redhat.com>
 
 	* cp-tree.h (CP_AGGREGATE_TYPE_P): Fix whitespace.

gcc/cp/parser.c

@@ -27593,9 +27593,19 @@ cp_parser_constructor_declarator_p (cp_parser *parser, cp_parser_flags flags,
 	  parser->num_template_parameter_lists = 0;
 
 	  /* Look for the type-specifier.  It's not optional, but its typename
-	     might be.  */
+	     might be.  Unless this is a friend declaration; we don't want to
+	     treat
+
+	       friend S (T::fn)(int);
+
+	     as a constructor, but with P0634, we might assume a type when
+	     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.  */
 	  cp_parser_type_specifier (parser,
-				    (flags & ~CP_PARSER_FLAGS_OPTIONAL),
+				    (friend_p ? CP_PARSER_FLAGS_NONE
+				     : (flags & ~CP_PARSER_FLAGS_OPTIONAL)),
 				    /*decl_specs=*/NULL,
 				    /*is_declarator=*/true,
 				    /*declares_class_or_enum=*/NULL,

gcc/testsuite/ChangeLog

+2019-05-25  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/90572 - wrong disambiguation in friend declaration.
+	* g++.dg/cpp2a/typename16.C: New test.
+	* g++.dg/parse/friend13.C: New test.
+
 2019-05-24  Jakub Jelinek  <jakub@redhat.com>
 
 	* c-c++-common/gomp/lastprivate-conditional-2.c (foo): Don't expect

gcc/testsuite/g++.dg/cpp2a/typename16.C

+// PR c++/90572
+// { dg-do compile { target c++2a } }
+
+struct X { X(int); };
+
+template<typename T> struct S {
+  friend X::X(T::t);
+};
+
+struct W { using t = int; };
+S<W> s;

gcc/testsuite/g++.dg/parse/friend13.C

+// PR c++/90572
+
+template <typename T> struct C {
+  friend C(T::fn)();
+  friend C(T::fn)(int);
+  friend C(T::fn)(int, int);
+};
+
+struct X { };
+
+template<typename T>
+struct B {
+  friend X(T::fn)();
+  friend X(T::fn)(int);
+  friend X(T::fn)(int, int);
+};