Re: C PATCH to reject va_arg (ap, void) (PR c/65901)

[Marek Polacek <polacek at redhat dot com>]

On Tue, Apr 28, 2015 at 09:07:09PM -0600, Martin Sebor wrote:
> The error message in the test cases below isn't quite right.
> The type of the aggregates isn't undefined, it's incomplete.
> Looking at the function, I wonder if the first argument
> should be EXPR rather than than NULL_TREE? Alternatively,
> experimenting with other cases where GCC diagnoses invalid
> uses of incomplete type, I see that it issues:
> 
>   "invalid application of %qs to incomplete type %qT"
> 
> which might work even better here since we could name the
> expression (va_arg).

Yeah, I haven't concerned myself with the exact wording of the error
message much, and I agree it could be improved.  But passing down the
EXPR would mean that the compiler outputs "'ap' has an incomplete type"
and that looks wrong as well.  I think I'm going to apply the following
tomorrow if I hear no objections (and it passes testing).  Thanks for noticing.

(And I think c_incomplete_type_error deserves some TLC; I'll post a separate
patch.)

2015-04-29  Marek Polacek  <polacek@redhat.com>

	* c-typeck.c (c_build_va_arg): Clarify the error message.

	* gcc.dg/pr65901.c (foo): Adjust dg-error.

diff --git gcc/c/c-typeck.c gcc/c/c-typeck.c
index c58e918..028d2f81 100644
--- gcc/c/c-typeck.c
+++ gcc/c/c-typeck.c
@@ -12645,14 +12645,17 @@ c_build_qualified_type (tree type, int type_quals)
 tree
 c_build_va_arg (location_t loc, tree expr, tree type)
 {
-  if (warn_cxx_compat && TREE_CODE (type) == ENUMERAL_TYPE)
-    warning_at (loc, OPT_Wc___compat,
-		"C++ requires promoted type, not enum type, in %<va_arg%>");
-  if (type == error_mark_node || !COMPLETE_TYPE_P (type))
+  if (error_operand_p (type))
+    return error_mark_node;
+  else if (!COMPLETE_TYPE_P (type))
     {
-      c_incomplete_type_error (NULL_TREE, type);
+      error_at (loc, "second argument to %<va_arg%> is of incomplete "
+		"type %qT", type);
       return error_mark_node;
     }
+  else if (warn_cxx_compat && TREE_CODE (type) == ENUMERAL_TYPE)
+    warning_at (loc, OPT_Wc___compat,
+		"C++ requires promoted type, not enum type, in %<va_arg%>");
   return build_va_arg (loc, expr, type);
 }
 
diff --git gcc/testsuite/gcc.dg/pr65901.c gcc/testsuite/gcc.dg/pr65901.c
index 8708a1e..b40eea3 100644
--- gcc/testsuite/gcc.dg/pr65901.c
+++ gcc/testsuite/gcc.dg/pr65901.c
@@ -9,8 +9,8 @@ union U;
 void
 foo (__builtin_va_list ap)
 {
-  __builtin_va_arg (ap, void);  /* { dg-error "invalid use of void expression" } */
-  __builtin_va_arg (ap, struct S);  /* { dg-error "invalid use of undefined type" } */
-  __builtin_va_arg (ap, enum E);  /* { dg-error "invalid use of undefined type" } */
-  __builtin_va_arg (ap, union U);  /* { dg-error "invalid use of undefined type" } */
+  __builtin_va_arg (ap, void);  /* { dg-error "second argument to .va_arg. is of incomplete type .void." } */
+  __builtin_va_arg (ap, struct S);  /* { dg-error "second argument to .va_arg. is of incomplete type .struct S." } */
+  __builtin_va_arg (ap, enum E);  /* { dg-error "second argument to .va_arg. is of incomplete type .enum E." } */
+  __builtin_va_arg (ap, union U);  /* { dg-error "second argument to .va_arg. is of incomplete type .union U." } */
 }

	Marek