[cfe-dev] Clang Static Analyzer: False Positive Suppression Support

[Craig, Ben via cfe-dev]

On 8/29/2016 11:49 AM, Anna Zaks wrote:
>
>> On Aug 29, 2016, at 7:59 AM, Gábor Horváth <xazax.hun at gmail.com 
>> <mailto:xazax.hun at gmail.com>> wrote:
>> * Using pragmas one can introduce convenience macros, it might also 
>> be better to suppress code regions
>> * It is better to suppress based on bug type or something like that 
>> rather than using the name of the checker (which is not intended to 
>> leak out)
>> * It is good idea to have line offsets to avoid too much noise when 
>> reading code
>> * Anything against pragmas?
>
> Another reason pragmas are better than comments is because this is 
> what the compiler uses for suppressions.

I'm not opposed to pragmas in concept, but I don't like the typical way 
they are used for compiler warning suppression.  In particular, I 
strongly dislike the following pattern as the "default" pattern for 
warning suppression:

#if __clang_analyzer__
#pragma static analyzer push
#pragma static analyzer disable deadcode
#endif
// bad code here
#if __clang_analyzer__
#pragma static analyzer pop
#endif

Things I don't like about that pattern:
* verbose
* requires modifying code before and after the offending line of code
* usually requires compiler specific guards.
* if you forget the trailer, code still works, but you lose diagnostics
* if you don't know the push / pop pattern, you end up losing diagnostics

I'm fine with that pattern existing in addition to a much more terse and 
friendly syntax.  I can see the push / pop pattern being useful for 
blocks of code.  Just don't make that the default.

Here's a pattern that I'd prefer:
// Common header...
#ifdef __clang_analyzer__
#define CLANG_SUPPRESS_WARNING(category, line_offset) _Pragma(category, 
line_offset)
#else
#define CLANG_SUPPRESS_WARNING(category, line_offset)
#endif
// Source file...
CLANG_SUPPRESS_WARNING(deadcode, +1)
// bad code here

-- 
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project

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