[PATCH] D3976: -Wcomma, a new warning for questionable uses of the comma operator

[Aaron Ballman via Phabricator via cfe-commits]

aaron.ballman added a comment.

In D3976#3721421 <https://reviews.llvm.org/D3976#3721421>, @gpakosz wrote:

> Hello,
>
> As of today, `-Wcomma` is not really documented: https://clang.llvm.org/docs/DiagnosticsReference.html#wcomma
>
>> The current whitelisted expressions are increments, decrements, assignments, compound assignments, overloaded versions of these operators, **and void returning functions**

FWIW, none of our diagnostics get documentation beyond what you see there (it's auto-generated from the diagnostic definition file).

> About `void` returning functions, the following example <https://godbolt.org/z/Wa8qxKv8j> emits `-Wcomma`:
>
>   void foo()
>   {
>   
>   }
>   
>   int bar(int i)
>   {
>     return i;
>   }
>   
>   int main(int argc, char* argv[])
>   {
>     if (foo(), bar(argc))
>       return 0;
>   
>     return -1;
>   }
>
>
>
>   <source>:13:12: warning: possible misuse of comma operator here [-Wcomma]
>     if (foo(), bar(argc))
>              ^
>   <source>:13:7: note: cast expression to void to silence warning
>     if (foo(), bar(argc))
>         ^~~~~
>         (void)( )
>   1 warning generated.
>
> Should I open a bug?

I think opening a bug is appropriate, good catch!


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