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

[Abramo Bagnara]

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

#define p q
#define q p

expanding it the `true' token is marked to have disabled expansion.

We already use it in ECLAIR with success in the implementation of a few
coding standard rules that needs that.


-- 
Abramo Bagnara

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mailto:abramo.bagnara at bugseng.com