Re: [patch] Use __builtin_FILE and __builtin_LINE in assert implementation in C++

[Florian Weimer <fweimer@redhat.com>]

* Jonathan Wakely:

>>>>> I think __builtin_FILE and __builtin_LINE are farily recent GCC/Clang
>
> Added to GCC 4.8.0 in 2012. I don't know about Clang.

Oh, I didn't realize it's been this long.

>> > __FILE__ expansion needs to be delayed, otherwise it refers to assert.h.
>> >
>> > I think the builtins also have the advantage that they avoid ODR
>> > violations because the definition is the same no matter what the file is
>> > called.
>
> It's not that simple though, the definition consists of the same
> sequence of tokens, but can still result in incompatible definitions:
>
> char* f()
> {
>   static char array[__builtin_LINE()];
>   return array;
> }
>
> c.f. https://cplusplus.github.io/CWG/issues/2678.html

Ugh, I was worried about something like that.  And the location
functions need to be constexpr.

There's also the issue that <cassert> is defined in terms of ISO C,
and ISO C specifies that __FILE__ and __LINE__ must be used.  Is that
another defect?  But maybe the difference is not observable because
__FILE__ cannot be redefined?

Thanks,
Florian