Mark Mitchell wrote:
> I understand what you're after: tolerate uses of the extension where
> it's sufficiently harmless.
>
> I don't think your proposed solution is correct, though, because we want
> to maintain the invariant that all conforming programs compile and
> behave as required by the standard in all compilation modes. In other
> words, supplying -fpermissive and friends can make non-conforming
> programs compile, when they otherwise wouldn't, but conforming programs
> should behave identically in all modes.
I think this is consistent with my proposal -- the first example was
non-conforming, but accepted without -pedantic (as we do with other
zero-sized arrays). The second example was conforming and the only way
to alter its behavior was with the -fpermissive option.
> I would imagine that if we encounter a zero-sized array when the
> "complain" flag is tf_error, then we can just issue a conditional
> pedwarn, with "if (pedantic) pedwarn (...)". But, if tf_error is not
> set, we must reject the instantiation.
>
> I know that sounds backwards. The point is that when tf_error is set,
> we're committed to the instantiation. When tf_error is not set, SFINAE
> applies. And, in a conforming program, we must reject the instantiation
> in that case.
This is interesting - that's exactly the approach I came up (well, the
part about using the complain flag to determine whether to reject the
instantiation), but I was concerned about whether it would be accepted,
since it seemed a bit awkward.
FWIW, attached is my last iteration of the patch -- it does pass all
regression tests on i686-linux and arm-elf. If we can come to an
agreement on the desired behavior and it matches, I'll submit it for
official approval.
Thanks!
- Josh
Index: gcc/cp/pt.c
===================================================================
--- gcc/cp/pt.c (revision 106267)
+++ gcc/cp/pt.c (working copy)
@@ -7065,25 +7065,27 @@ tsubst (tree t, tree args, tsubst_flags_
max = tsubst_template_arg (omax, args, complain, in_decl);
max = fold_decl_constant_value (max);
- if (integer_zerop (omax))
- {
- /* Still allow an explicit array of size zero. */
- if (pedantic)
- pedwarn ("creating array with size zero");
- }
- else if (integer_zerop (max)
- || (TREE_CODE (max) == INTEGER_CST
- && INT_CST_LT (max, integer_zero_node)))
- {
- /* [temp.deduct]
+ /* [temp.deduct]
- Type deduction may fail for any of the following
- reasons:
+ Type deduction may fail for any of the following
+ reasons:
- Attempting to create an array with a size that is
- zero or negative. */
+ Attempting to create an array with a size that is
+ zero or negative. */
+ if (integer_zerop (max) && flag_pedantic_errors
+ && ! (complain & tf_error))
+ {
+ /* We must fail if performing argument deduction (as
+ indicated by the state of complain), so that
+ another substitution can be found (unless -fpermissive
+ was given). */
+ return error_mark_node;
+ }
+ else if (TREE_CODE (max) == INTEGER_CST
+ && INT_CST_LT (max, integer_zero_node))
+ {
if (complain & tf_error)
- error ("creating array with size zero (%qE)", max);
+ error ("creating array with negative size (%qE)", max);
return error_mark_node;
}
