[cfe-commits] [PATCH] Remove -Wdisabled-macro-expansion

[Eli Friedman]

On Tue, Oct 30, 2012 at 2:52 PM, Abramo Bagnara
<abramo.bagnara at bugseng.com> wrote:
> Il 30/10/2012 21:58, Eli Friedman ha scritto:
>> On Tue, Oct 30, 2012 at 12:27 AM, Abramo Bagnara
>> <abramo.bagnara at bugseng.com> wrote:
>>> Il 30/10/2012 05:07, Ted Kremenek ha scritto:
>>>> On Oct 29, 2012, at 8:38 PM, Eli Friedman <eli.friedman at gmail.com
>>>> <mailto:eli.friedman at gmail.com>> wrote:
>>>>
>>>>> I think there's a reasonable workflow for small projects which
>>>>> involves using -Weverything and subtracting out the warnings which
>>>>> don't make sense.
>>>>
>>>> Right.  I commented about this in my other email before I saw your response.
>>>>
>>>>>  I agree that there are limits to what we can/should
>>>>> do with -Weverything; I'm not trying to argue for getting rid of
>>>>> warnings because they make -Weverything too noisy.  On the other hand,
>>>>> I think we should have a high standard for the usefulness of
>>>>> off-by-default warnings.  And I think that there's future
>>>>> infrastructure work we can do both to help people write higher quality
>>>>> code.
>>>>
>>>> Agreed.  FWIW, the developers we have spoken to about -Weverything
>>>> really like how it has been very helpful in discovering warning flags
>>>> that are very good for their codebase.
>>>>
>>>>>
>>>>>>> it isn't acceptable for it to trigger warnings for usage
>>>>>>> of headers included with the compiler, and as far as I can tell, there
>>>>>>> isn't any way to fix the header. (See patch for a testcase that
>>>>>>> checks we don't trigger any warnings from stdbool.h.)
>>>>>>>
>>>>>>> I'm planning to commit this unless someone has an alternative
>>>>>>> suggestion.
>>>>>>
>>>>>> Could you suppress the warning if the spelling location for the token
>>>>>> which would have been expanded is in a system header?
>>>>>
>>>>> I think that would end up being more confusing than helpful because it
>>>>> suppresses some, but not all, loops involving system macros.
>>>>>
>>>>> I would put more effort into this if I thought it was generally
>>>>> useful, but the fact that it isn't on by default, and that the headers
>>>>> included with clang manage to trigger it, and there isn't any specific
>>>>> class of users this is useful for, all indicate it isn't worth the
>>>>> effort.
>>>>
>>>> If others agree with this argument, I can see a strong argument here to
>>>> remove the warning entirely.
>>>
>>> This thread clarifies why the warning is very important for a class of
>>> users and why to reach the same aim has no pratical alternatives
>>>
>>> http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20111226/050687.html
>>>
>>> Please do not remove it.
>>
>> Unless I'm missing something, this warning doesn't address any of the
>> pieces of "Specifically, the use of token pasting (cf. MISRA-C:2004
>> Rules 19.12 and 19.13), variable argument lists (ellipses) (cf.
>> MISRA-C:2004 Rule 16.1), and recursive macro calls are excluded by
>> this rule. All macros are required to expand into complete syntactic
>> units (cf. MISRA-C:2004 Rule 19.4)."  Actually, as far as I can tell,
>> "#define true true" doesn't violate any guidelines at all in the
>> document you cite, ignoring the vague restriction that macros should
>> be "simple".
>
> It is a recursive macro, just as

How is it recursive?  The whole point of the C rules here is that it
*does't* recurse.

-Eli