[cfe-dev] -Wheader-guard emits warning after #undef of guard macro

[Prathamesh Kulkarni]

On Tue, Jan 14, 2014 at 11:28 AM, Prathamesh Kulkarni
<bilbotheelffriend at gmail.com> wrote:
> On Tue, Jan 14, 2014 at 1:57 AM, Richard Trieu <rtrieu at google.com> wrote:
>> Prathamesh,
>>
>> Can you tell me more about your use case?  Is this a common pattern you have
>> encountered?
> Um no, it's a contrived test case.
>
> #ifndef Macro1
> #define Macro2
> Should warning be suppressed, if Macro2 gets undefined later in the
> same header ?
> eg:  (they are literally named Macro1 and Macro2)
> #ifndef Macro1
> #define Macro2
> ...
> #undef Macro2
> #endif
>
> Is it better to suppress the warning because it's equivalent to:
> #ifndef Macro1
> #endif
>
>>
>> The header guard warning triggers on files with the following format:
>>
>> // Start of file
>> #ifndef Macro1
>> #define Macro2
>> ...
>> #endif // matches the #ifndef on the first line.
>> // End of file
>>
>> and warns when Macro1 and Macro2 are close, but not exactly the same.  The
>> warning already ignores cases where Macro1 and Macro2 are very different
>> (edit distance is over half the length).  A similar exemption maybe be
>> warranted in this case too.
>
> Thanks for pointing that out. However that's not the issue.
> Could you please explain in short heuristics used by clang to decide
> when the two macros are
> "sufficiently" different ? Thanks ;)
I meant to ask how is edit_distance computed. Found it here, thanks.
// The algorithm implemented below is the "clasic"
// dynamic-programming algorithm for computing the Levenshtein
// distance, which is described here:
//
//   http://en.wikipedia.org/wiki/Levenshtein_distance

>
>>
>> Richard
>>
>>
>> On Mon, Jan 13, 2014 at 3:06 AM, Prathamesh Kulkarni
>> <bilbotheelffriend at gmail.com> wrote:
>>>
>>> For the following test-case:
>>> #ifndef FOO
>>> #define FOO2
>>>
>>> #undef FOO2
>>> #endif
>>>
>>> -Wheader-guard emits warning:
>>> ./foo.h:4:9: warning: 'FOO' is used as a header guard here, followed
>>> by #define of a different macro [-Wheader-guard]
>>> #ifndef FOO
>>>         ^~~
>>> ./foo.h:5:9: note: 'FOO2' is defined here; did you mean 'FOO'?
>>> #define FOO2
>>>         ^~~~
>>>
>>> Is this appropriate or should it suppress warning in this case
>>> since it's equivalent to the following: ?
>>> #ifndef FOO
>>> #endif
>>>
>>> Thanks and Regards,
>>> Prathamesh
>>> _______________________________________________
>>> cfe-dev mailing list
>>> cfe-dev at cs.uiuc.edu
>>> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev
>>
>>