re PR c++/67012 (decltype(auto) with trailing return type)

	PR c++/67012
	PR c++/86942
	* decl.c (grokdeclarator): Disallow functions with trailing return
        type with decltype(auto) as its type.  Also check the function if
        it's inner declarator doesn't exist

	* g++.dg/cpp0x/auto52.C: New test.
	* g++.dg/cpp1y/auto-fn52.C: New test.
	* g++.dg/cpp1y/auto-fn53.C: New test.
	* g++.dg/cpp1y/auto-fn54.C: New test.

From-SVN: r263836

gcc/cp/ChangeLog

+2018-08-24  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/67012
+	PR c++/86942
+	* decl.c (grokdeclarator): Disallow functions with trailing return
+	type with decltype(auto) as its type.  Also check the function if
+	it's inner declarator doesn't exist
+
 2018-08-21  Marek Polacek  <polacek@redhat.com>
 
 	PR c++/86499

gcc/cp/decl.c

@@ -11246,7 +11246,10 @@ grokdeclarator (const cp_declarator *declarator,
 
 	    /* Handle a late-specified return type.  */
 	    tree late_return_type = declarator->u.function.late_return_type;
-	    if (funcdecl_p)
+	    if (funcdecl_p
+		/* This is the case e.g. for
+		   using T = auto () -> int.  */
+		|| inner_declarator == NULL)
 	      {
 		if (tree auto_node = type_uses_auto (type))
 		  {
@@ -11278,6 +11281,16 @@ grokdeclarator (const cp_declarator *declarator,
 			       name, type);
 			return error_mark_node;
 		      }
+		    else if (is_auto (type) && AUTO_IS_DECLTYPE (type))
+		      {
+			if (funcdecl_p)
+			  error ("%qs function with trailing return type has "
+				 "%<decltype(auto)%> as its type rather than "
+				 "plain %<auto%>", name);
+			else
+			  error ("invalid use of %<decltype(auto)%>");
+			return error_mark_node;
+		      }
 		    tree tmpl = CLASS_PLACEHOLDER_TEMPLATE (auto_node);
 		    if (!tmpl)
 		      if (tree late_auto = type_uses_auto (late_return_type))

gcc/testsuite/ChangeLog

+2018-08-24  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/67012
+	PR c++/86942
+	* g++.dg/cpp0x/auto52.C: New test.
+	* g++.dg/cpp1y/auto-fn52.C: New test.
+	* g++.dg/cpp1y/auto-fn53.C: New test.
+	* g++.dg/cpp1y/auto-fn54.C: New test.
+
 2018-08-24  Richard Sandiford  <richard.sandiford@arm.com>
 
 	* lib/target-supports.exp (vect_perm_supported): Only return

gcc/testsuite/g++.dg/cpp0x/auto52.C

+// PR c++/86942
+// { dg-do compile { target c++11 } }
+
+using T = auto() -> int;
+using U = void() -> int; // { dg-error "function with trailing return type not declared with .auto." }
+using W = auto(); // { dg-error "invalid use of .auto." }

gcc/testsuite/g++.dg/cpp1y/auto-fn52.C

+// PR c++/67012
+// { dg-do compile { target c++14 } }
+
+decltype(auto) f() -> int; // { dg-error "function with trailing return type has" }

gcc/testsuite/g++.dg/cpp1y/auto-fn53.C

+// PR c++/86942
+// { dg-do compile { target c++14 } }
+
+using T = decltype(auto) () -> int; // { dg-error "invalid use of" }

gcc/testsuite/g++.dg/cpp1y/auto-fn54.C

+// { dg-do compile { target c++14 } }
+
+using T = int () -> decltype(auto); // { dg-error "function with trailing return type not declared with .auto." }