[cfe-dev] Does `#pragma GCC diagnostic warning` intentionally win over -Werror?

[Whisperity via cfe-dev]

How about joining stdout and stderr of the compiler, tee-ing the
output to a file too and then checking if there was any output... or
grepping for "[-W" or something. Then you could kill the build (or
send a mail or just signal or something) if a warning is emitted if
you need that specific behaviour for your build.

PATH is very powerful.

James Y Knight via cfe-dev <cfe-dev at lists.llvm.org> ezt írta (időpont:
2019. jan. 24., Cs, 18:00):
>
> Perhaps a lint rule triggering on "#pragma GCC diagnostic warning", saying "We don't allow warnings, please use `#pragma GCC diagnostic error` (or ignored)" would solve the problem sufficiently.
>
> Separately, I note that "#pragma GCC diagnostic error" allows errors to bypass -Wfatal-errors. That certainly seems to serve no useful purpose and could be removed.
>
> On Thu, Jan 24, 2019 at 11:20 AM Nico Weber <thakis at chromium.org> wrote:
>>
>> On Thu, Jan 24, 2019 at 11:12 AM James Y Knight <jyknight at google.com> wrote:
>>>
>>> I don't think we should have such a flag. The explicit intent of '#pragma gcc diagnostic warning' is to allow downgrading an error to a warning, while still allowing it to be emitted.
>>>
>>> Perhaps a new value for pragma diagnostic which emits an upgradeable warning would be reasonable.
>>
>>
>> The use case here is that we don't allow non-error diagnostics in chrome. Some subproject used `#pragma GCC diagnostic warning` because they wanted to configure warning flags in cc files instead of in build files for some reason. They didn't expect this to trigger a warning instead of an error. A new pragma would meet that use case, but I don't want source code to be able to opt out of -Werror. In my experience, once it's known that such an option exist, someone will use it. So we do need some kind of "_all_ warnings are errors" toggle.
>>
>>>
>>>
>>> On Thu, Jan 24, 2019 at 9:56 AM Nico Weber via cfe-dev <cfe-dev at lists.llvm.org> wrote:
>>>>
>>>> Re "intentional?", it matches gcc which explicitly documents on https://gcc.gnu.org/onlinedocs/gcc/Diagnostic-Pragmas.html that the pragma wins over -Werror.
>>>>
>>>> Does anyone know if there's a flag that says "I want all warnings to be errors, not just most of them"?
>>>>
>>>> If there isn't one yet, what would be a good UI for that?
>>>>
>>>> On Wed, Jan 23, 2019 at 11:11 PM Nico Weber <thakis at chromium.org> wrote:
>>>>>
>>>>> Consider:
>>>>>
>>>>> $ cat test.cc
>>>>> #pragma GCC diagnostic warning "-Wsign-compare"
>>>>>
>>>>> bool f(int a, unsigned b) {
>>>>>   return a != b;
>>>>> }
>>>>> $ out/gn/bin/clang -c test.cc -Werror
>>>>> test.cc:4:12: warning: comparison of integers of different signs: 'int' and 'unsigned int' [-Wsign-compare]
>>>>>   return a != b;
>>>>>          ~ ^  ~
>>>>> 1 warning generated.
>>>>>
>>>>>
>>>>> I found it surprising that this is emitted as a warning, not as an error. If this is intentional, is there some other way to say "I want my compiler warnings to always be errors"?
>>>>>
>>>>> Thanks,
>>>>> Nico
>>>>
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>
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