re PR c/55976 (-Werror=return-type should error on returning a value from a void function)

2018-05-30  David Pagan  <dave.pagan@oracle.com>

	PR c/55976
	* c-decl.c (grokdeclarator): Update check for return type warnings.
	(start_function): Likewise.
	(finish_function): Likewise.
	* c-typeck.c (c_finish_return): Update check for return type warnings.
	Pass OPT_Wreturn_type to pedwarn when appropriate.

	PR c/55976
	* c-opts.c (c_common_post_options): Set default for warn_return_type
	for C++/C++ with ObjC extensions only. For C, makes it possible to
	differentiate between default (no option), -Wreturn-type, and
	-Wno-return-type.

	PR c/55976
	* gcc.dg/noncompile/pr55976-1.c: New test.
	* gcc.dg/noncompile/pr55976-2.c: New test.

From-SVN: r260978

gcc/c-family/ChangeLog

+2018-04-22  David Pagan  <dave.pagan@oracle.com>
+
+	PR c/55976
+	* c-opts.c (c_common_post_options): Set default for warn_return_type
+	for C++/C++ with ObjC extensions only. For C, makes it possible to 
+	differentiate between default (no option), -Wreturn-type, and
+	-Wno-return-type.
+
 2018-05-29  Jason Merrill  <jason@redhat.com>
 
 	* c.opt (Winit-list-lifetime): New flag.

gcc/c-family/c-opts.c

@@ -994,8 +994,9 @@ c_common_post_options (const char **pfilename)
 	flag_extern_tls_init = 1;
     }
 
-  if (warn_return_type == -1)
-    warn_return_type = c_dialect_cxx ();
+  /* Enable by default only for C++ and C++ with ObjC extensions.  */
+  if (warn_return_type == -1 && c_dialect_cxx ())
+    warn_return_type = 1;
 
   if (num_in_fnames > 1)
     error ("too many filenames given.  Type %s --help for usage",

gcc/c/ChangeLog

+2018-05-30  David Pagan  <dave.pagan@oracle.com>
+
+	PR c/55976
+	* c-decl.c (grokdeclarator): Update check for return type warnings.
+	(start_function): Likewise.
+	(finish_function): Likewise.
+	* c-typeck.c (c_finish_return): Update check for return type warnings.
+	Pass OPT_Wreturn_type to pedwarn when appropriate.
+
 2018-05-18  Richard Sandiford  <richard.sandiford@linaro.org>
 
 	* gimple-parser.c (c_parser_gimple_postfix_expression): Remove

gcc/c/c-decl.c

@@ -5758,7 +5758,7 @@ grokdeclarator (const struct c_declarator *declarator,
       /* Issue a warning if this is an ISO C 99 program or if
 	 -Wreturn-type and this is a function, or if -Wimplicit;
 	 prefer the former warning since it is more explicit.  */
-      if ((warn_implicit_int || warn_return_type || flag_isoc99)
+      if ((warn_implicit_int || warn_return_type > 0 || flag_isoc99)
 	  && funcdef_flag)
 	warn_about_return_type = 1;
       else
@@ -8752,7 +8752,7 @@ start_function (struct c_declspecs *declspecs, struct c_declarator *declarator,
 
   if (warn_about_return_type)
     warn_defaults_to (loc, flag_isoc99 ? OPT_Wimplicit_int
-			   : (warn_return_type ? OPT_Wreturn_type
+			   : (warn_return_type > 0 ? OPT_Wreturn_type
 			      : OPT_Wimplicit_int),
 		      "return type defaults to %<int%>");
 
@@ -9463,8 +9463,9 @@ finish_function (void)
 
   finish_fname_decls ();
 
-  /* Complain if there's just no return statement.  */
-  if (warn_return_type
+  /* Complain if there's no return statement only if option specified on
+     command line.  */
+  if (warn_return_type > 0
       && TREE_CODE (TREE_TYPE (TREE_TYPE (fndecl))) != VOID_TYPE
       && !current_function_returns_value && !current_function_returns_null
       /* Don't complain if we are no-return.  */

gcc/c/c-typeck.c

@@ -10133,13 +10133,13 @@ c_finish_return (location_t loc, tree retval, tree origtype)
   if (!retval)
     {
       current_function_returns_null = 1;
-      if ((warn_return_type || flag_isoc99)
+      if ((warn_return_type >= 0 || flag_isoc99)
 	  && valtype != NULL_TREE && TREE_CODE (valtype) != VOID_TYPE)
 	{
 	  bool warned_here;
 	  if (flag_isoc99)
 	    warned_here = pedwarn
-	      (loc, 0,
+	      (loc, warn_return_type >= 0 ? OPT_Wreturn_type : 0,
 	       "%<return%> with no value, in function returning non-void");
 	  else
 	    warned_here = warning_at
@@ -10157,7 +10157,7 @@ c_finish_return (location_t loc, tree retval, tree origtype)
       bool warned_here;
       if (TREE_CODE (TREE_TYPE (retval)) != VOID_TYPE)
 	warned_here = pedwarn
-	  (xloc, 0,
+	  (xloc, warn_return_type >= 0 ? OPT_Wreturn_type : 0,
 	   "%<return%> with a value, in function returning void");
       else
 	warned_here = pedwarn

gcc/testsuite/ChangeLog

+2018-05-30  David Pagan  <dave.pagan@oracle.com>
+
+	PR c/55976
+	* gcc.dg/noncompile/pr55976-1.c: New test.
+	* gcc.dg/noncompile/pr55976-2.c: New test.
+
 2018-05-30  Jan Hubicka  <hubicka@ucw.cz>
 
 	* gcc.dg/lto/20111213-1_0.c: Fix template.

gcc/testsuite/gcc.dg/noncompile/pr55976-1.c

+/* PR c/55976 */
+/* { dg-do compile } */
+/* { dg-options "-Werror=return-type" } */
+
+/* Verify warnings for return type become errors.  */
+
+void t () { return 1; } /* { dg-error "return" "function returning void" } */
+int b () { return; } /* { dg-error "return" "function returning non-void" } */
+
+int main()
+{
+  t(); b();
+  return 0;
+}

gcc/testsuite/gcc.dg/noncompile/pr55976-2.c

+/* PR c/55976 */
+/* { dg-do compile } */
+/* { dg-options "-Wno-return-type" } */
+
+/* Verify that -Wno-return-type turns off warnings about function return
+   type.  */
+
+void t () { return 1; } /* normally generates function returning void */
+int b () { return; } /* normally generates function returning non-void */
+
+int main()
+{
+  t (); b ();
+  return 0;
+}
+