Re: [PATCH] Use ^=1 to toggle between 0 and 1

["René Scharfe" <l.s.r@web.de>]

Am 15.12.23 um 18:09 schrieb Junio C Hamano:
> Phillip Wood <phillip.wood123@gmail.com> writes:
>
>> Even if it unlikely that we would directly compare a boolean variable
>> to "true" or "false" it is certainly conceivable that we'd compare two
>> boolean variables directly. For the integer fallback to be safe we'd
>> need to write
>>
>> 	if (!cond_a == !cond_b)
>>
>> rather than
>>
>> 	if (cond_a == cond_b)
>
> Eek, it defeats the benefit of using true Boolean type if we had to
> train ourselves to write the former, doesn't it?

Indeed.

>> [1] 7bc341e21b (git-compat-util: add a test balloon for C99 support,
>> 2021-12-01)
>
> Nice to be reminded of this one.
>
> The cited commit does not start to use any specific feature from
> C99, other than that we now require that the compiler claims C99
> conformance by __STDC_VERSION__ set appropriately.  The commit log
> message says C99 "provides a variety of useful features, including
> ..., many of which we already use.", which implies that our wish was
> to officially allow any and all features in C99 to be used in our
> codebase after a successful flight of this test balloon.
>
> Now, I think we saw a successful flight of this test balloon by now.
> Is allowing all the C99 the next step we really want to take?
>
> I still personally have an aversion against decl-after-statement and
> //-comments, not due to portability reasons at all, but because I
> find that the code is easier to read without it. But in principle,
> it is powerful to be able to say "OK, as long as the feature is in
> C99 you can use it", instead of having to decide on individual
> features, and I am not fundamentally against going that route if it
> is where people want to go.

C99 added a lot of features, but we already use several of them.
Support for individual features may vary, though -- who knows?

E.g. http://www.compilers.de/vbcc.html claims to support "most of
ISO/IEC 9899:1999 (C99)", yet _Bool is not mentioned in its docs (but
__STDC_VERSION__ 199901L is).  It's not a particularly interesting
compiler for us, but still a real-world example of selective C99
support.

The table at the bottom of https://en.cppreference.com/w/c/99 would be
useful if it was filled out for more compilers.  And it also doesn't
mention _Bool and stdbool.h.

TenDRA and the M/o/Vfuscator are the only compilers without stdbool.h
support on https://godbolt.org/ as far as I can see, but that website
doesn't have a lot of commercial compilers (understandably).

So I guess in practice we still need to check each new feature, even
though in theory we should be fine after the two-year test.

René