Make C1X anonymous structs/unions follow N1549

Make C1X anonymous structs/unions follow N1549

[Joseph S. Myers]

This week's London WG14 meeting agreed to disallow the use of typedefs
in declaring anonymous structure and union fields, as per N1549.  This
patch implements this, restricting the use of typedefs in this case to
-fms-extensions and -fplan9-extensions as in 4.5 and earlier releases.

Bootstrapped with no regressions on x86_64-unknown-linux-gnu.  Applied
to mainline.  Any comments from other RMs about whether this should go
in 4.6 as well, to avoid 4.6.0 being more lenient in this area than
both 4.5 and 4.7?  (The issue is about what is accepted by default
rather than -std=c1x, since -std=c1x users in 4.6 should know it's
experimental and subject to change.)

2011-03-18  Joseph Myers  <joseph@codesourcery.com>

	* c-decl.c (grokfield): Don't allow typedefs for structures or
	unions with no tag by default.
	* doc/extend.texi (Unnamed Fields): Update.

testsuite:
2011-03-18  Joseph Myers  <joseph@codesourcery.com>

	* gcc.dg/c1x-anon-struct-1.c: Don't test use of typedefs.
	* gcc.dg/c1x-anon-struct-3.c: New test.
	* gcc.dg/anon-struct-11.c: Update.

Index: doc/extend.texi
===================================================================
--- doc/extend.texi	(revision 171110)
+++ doc/extend.texi	(working copy)
@@ -13352,12 +13352,11 @@ The compiler gives errors for such const
 @opindex fms-extensions
 Unless @option{-fms-extensions} is used, the unnamed field must be a
 structure or union definition without a tag (for example, @samp{struct
-@{ int a; @};}), or a @code{typedef} name for such a structure or
-union.  If @option{-fms-extensions} is used, the field may
+@{ int a; @};}).  If @option{-fms-extensions} is used, the field may
 also be a definition with a tag such as @samp{struct foo @{ int a;
 @};}, a reference to a previously defined structure or union such as
 @samp{struct foo;}, or a reference to a @code{typedef} name for a
-previously defined structure or union type with a tag.
+previously defined structure or union type.
 
 @opindex fplan9-extensions
 The option @option{-fplan9-extensions} enables
Index: testsuite/gcc.dg/c1x-anon-struct-3.c
===================================================================
--- testsuite/gcc.dg/c1x-anon-struct-3.c	(revision 0)
+++ testsuite/gcc.dg/c1x-anon-struct-3.c	(revision 0)
@@ -0,0 +1,34 @@
+/* Test for anonymous structures and unions in C1X.  Test for invalid
+   cases: typedefs disallowed by N1549.  */
+/* { dg-do compile } */
+/* { dg-options "-std=c1x -pedantic-errors" } */
+
+typedef struct
+{
+  int i;
+} s0;
+
+typedef union
+{
+  int i;
+} u0;
+
+struct s1
+{
+  int a;
+  u0; /* { dg-error "declaration does not declare anything" } */
+  struct
+  {
+    int b;
+  };
+};
+
+union u1
+{
+  int b;
+  s0; /* { dg-error "declaration does not declare anything" } */
+  union
+  {
+    int c;
+  };
+};
Index: testsuite/gcc.dg/anon-struct-11.c
===================================================================
--- testsuite/gcc.dg/anon-struct-11.c	(revision 171110)
+++ testsuite/gcc.dg/anon-struct-11.c	(working copy)
@@ -50,7 +50,7 @@ struct E {
   struct F { char f; };	/* { dg-warning "does not declare anything" } */
   char c;
   union {
-    D;
+    D;			/* { dg-warning "does not declare anything" } */
   };
   char e;
 };
@@ -85,7 +85,7 @@ test2 (void)
   e.e = 5;
   f2 (&e);		/* { dg-warning "incompatible pointer type" } */
   f3 (&e);		/* { dg-warning "incompatible pointer type" } */
-  if (e.d != 4)
+  if (e.d != 4)		/* { dg-error "no member" } */
     abort ();
   if (e.f != 6)		/* { dg-error "no member" } */
     abort ();
Index: testsuite/gcc.dg/c1x-anon-struct-1.c
===================================================================
--- testsuite/gcc.dg/c1x-anon-struct-1.c	(revision 171110)
+++ testsuite/gcc.dg/c1x-anon-struct-1.c	(working copy)
@@ -4,20 +4,13 @@
 
 #include <stddef.h>
 
-typedef struct
-{
-  int i;
-} s0;
-
-typedef union
-{
-  int i;
-} u0;
-
 struct s1
 {
   int a;
-  u0;
+  union
+  {
+    int i;
+  };
   struct
   {
     int b;
@@ -27,7 +20,10 @@ struct s1
 union u1
 {
   int b;
-  s0;
+  struct
+  {
+    int i;
+  };
   union
   {
     int c;
@@ -44,7 +40,10 @@ struct s2
 
 struct s3
 {
-  u0;
+  union
+  {
+    int i;
+  };
 };
 
 struct s4
Index: c-decl.c
===================================================================
--- c-decl.c	(revision 171110)
+++ c-decl.c	(working copy)
@@ -6674,11 +6674,14 @@ grokfield (location_t loc,
 		      || TREE_CODE (type) == UNION_TYPE);
       bool ok = false;
 
-      if (type_ok)
+      if (type_ok
+	  && (flag_ms_extensions
+	      || flag_plan9_extensions
+	      || !declspecs->typedef_p))
 	{
 	  if (flag_ms_extensions || flag_plan9_extensions)
 	    ok = true;
-	  else if (TYPE_NAME (TYPE_MAIN_VARIANT (type)) == NULL)
+	  else if (TYPE_NAME (type) == NULL)
 	    ok = true;
 	  else
 	    ok = false;

-- 
Joseph S. Myers
joseph@codesourcery.com

Re: Make C1X anonymous structs/unions follow N1549

[Jakub Jelinek]

On Fri, Mar 18, 2011 at 09:16:55PM +0000, Joseph S. Myers wrote:
> This week's London WG14 meeting agreed to disallow the use of typedefs
> in declaring anonymous structure and union fields, as per N1549.  This
> patch implements this, restricting the use of typedefs in this case to
> -fms-extensions and -fplan9-extensions as in 4.5 and earlier releases.

If I understand it right, your patch restores the 4.5 code except for
-fplan9-extensions and with flag_iso not being checked.

I guess it is ok for 4.6.0 too.

	Jakub

Re: Make C1X anonymous structs/unions follow N1549

[Mark Mitchell]

On 3/18/2011 2:52 PM, Jakub Jelinek wrote:

>> This week's London WG14 meeting agreed to disallow the use of typedefs
>> in declaring anonymous structure and union fields, as per N1549.  This
>> patch implements this, restricting the use of typedefs in this case to
>> -fms-extensions and -fplan9-extensions as in 4.5 and earlier releases.

> I guess it is ok for 4.6.0 too.

I think avoiding the ping-pong in behavior between 4.5 and 4.7 is a good
call.  So, I think the patch is OK for 4.6.

Thank you,

-- 
Mark Mitchell
CodeSourcery
mark@codesourcery.com
(650) 331-3385 x713

Re: Make C1X anonymous structs/unions follow N1549

[Joseph S. Myers]

On Fri, 18 Mar 2011, Jakub Jelinek wrote:

> On Fri, Mar 18, 2011 at 09:16:55PM +0000, Joseph S. Myers wrote:
> > This week's London WG14 meeting agreed to disallow the use of typedefs
> > in declaring anonymous structure and union fields, as per N1549.  This
> > patch implements this, restricting the use of typedefs in this case to
> > -fms-extensions and -fplan9-extensions as in 4.5 and earlier releases.
> 
> If I understand it right, your patch restores the 4.5 code except for
> -fplan9-extensions and with flag_iso not being checked.

Yes, that's the intent of the grokfield changes in this patch.  (All the 
other front-end changes in 4.6 relating to anonymous structs and unions 
are unaffected by this typedef change.)

-- 
Joseph S. Myers
joseph@codesourcery.com