Re: [PATCH][RFC] -Wno-... option to suppress builtin macro redefined warnings

[Simon Baldwin <simonb@google.com>]

Simon Baldwin wrote:
> Tom Tromey wrote:
>>>>>>> "Simon" == Simon Baldwin <simonb@google.com> writes:
>>>>>>>             
>>
>> ...
>> However, it seems to me that we would want to allow redefinition of
>> some macros (__TIME__ et al) but not others (e.g., __LINE__).
>>
>> So, how about splitting builtin_array into two pieces (and just FYI,
>> there's a comment above referring to "two tables" that should be
>> changed) and then unconditionally setting NODE_WARN for one table but
>> not the other?  Or, just adding a special case in the builtin
>> definition loop for the BT_* constants we care to allow.
>>   
>
> Thank you for the note.
>
> I guess that in general it just seems more, um, seamless to either 
> allow or disallow any builtin macro to be redefined.  It means that 
> there's no "is it redefinable or not?" decision to be made when new 
> builtins are added.  It also neatly sidesteps the issue of then having 
> to document which builtins are redefinable and which aren't (also no 
> update to this doc should new builtins be added), or having to deal 
> with requests to move builtins between redefinable/fixed groups.  In 
> other words, the lowest impact on future code maintainers consistent 
> with low impact on current code.
>
> Granted, somebody could well redefine __LINE__ or similar and make a 
> mess of compilation, but there are of course plenty of other ways to 
> make a mess of compilation with other gcc flags.  
> -Wno-builtin-macro-redefined is aimed at the control-freak automated 
> build system rather than the casual user, so it seemed okay, to me 
> anyway, for it to bear closer resemblance to a chainsaw than to a 
> scalpel.
>
> That said, I'm not wildly opposed to creating two "classes" of 
> builtin.  It just seems like doing so might sow slightly more 
> confusion than it prevents.

Tom, any further thoughts on this?

It's certainly not hard to split built-in macros into two tiers, those 
where redefinition warning can be suppressed by providing 
-Wno-builtin-macro-redefined, and those where it can't.  However, since 
it's all just about suppressing a warning, it may be that one policy to 
cover all of them will suffice, and be simpler to manage and maintain.

Thanks.