[cfe-commits] [PATCH][driver] Frontend parsing of warnings and compliance with gcc

[Chad Rosier]

If there's no additional feedback, I'll go ahead and commit the patch later this afternoon.

 Chad

On Jan 31, 2012, at 3:39 PM, Jeremy Huddleston <jeremyhu at apple.com> wrote:

> That looks about right to me, and it's doing the right thing for me ...
> 
> Tested-by: Jeremy Huddleston <jeremyhu at apple.com>
> Reviewed-by: Jeremy Huddleston <jeremyhu at apple.com>
> 
> On Jan 31, 2012, at 2:49 PM, Chad Rosier wrote:
> 
>> The clang frontend currently parses warning options in the canonical "last option wins" paradigm.  This leads to what odd behavior IMO and non-compliance to how gcc handles things.
>> 
>> For example,
>> 
>> mcrosier$ cat t.c
>> int main() { return implicit(); }
>> 
>> mcrosier$ clang -Werror=implicit -Wall -c t.c -o /dev/null
>> t.c:1:21: warning: implicit declaration of function 'implicit' is invalid in C99 [-Wimplicit-function-declaration]
>> int main() { return implicit(); }
>>                   ^
>> 1 warning generated.
>> 
>> Reversing the order of the warning options results in an error:
>> mcrosier$ clang -Wall -Werror=implicit -c t.c -o /dev/null
>> t.c:1:21: error: implicit declaration of function 'implicit' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
>> int main() { return implicit(); }
>>                   ^
>> 1 error generated.
>> 
>> AFAIK gcc always emits an error.
>> 
>> If I understand the gcc standard correctly (and admittedly I'm no expert), I believe a -W option should never downgrade something that has already been marked as an error/fatal warning.
>> 
>> The attached patch does precisely this.  The other practical effect is that if you would like to change a warning that is an error by default to just a warning you need to use the -Wno-error=foo option rather then -Wfoo.
>> 
>> Chad
>> 
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>