Re: [PATCH v2] setup: don't die if realpath(3) fails on getcwd(3)

> On Tue, May 24, 2022 at 7:02 AM Kevin Locke <kevin@kevinlocke.name> wrote:
>>
>> On Mon, 2022-05-23 at 14:57 -0400, Derrick Stolee wrote:
>>> On 5/21/22 9:53 AM, Kevin Locke wrote:
>>>> +           free((char*)tmp_original_cwd);
>>>
>>> Hm. I'm never a fan of this casting, but it existed before. It's
>>> because tmp_original_cwd is exposed globally in cache.h, which
>>> is _really widely_. However, there are only two uses: setup.c,
>>> which defines it, and common-main.c, which initializes it during
>>> process startup.

>> not clear to me which is preferable in this case.  How to balance the
>> trade-offs between exposing const interfaces, limiting (internal)
>> interfaces to headers, and avoiding casts might be worth discussing
>> and documenting a matter of project coding style.  `grep -rF 'free(('`
>> lists about 100 casts to free, suggesting the discussion may be
>> worthwhile.  Introducing a free_const() macro could be another option
>> to consider.
> 
> I'd prefer either a free_const() as you suggest (though as a separate
> patch from what you are submitting here), or leaving the code as-is.
> free() could have been written to take a const void* instead of just
> void*, since it's not going to modify what the pointer points at.  The
> reason we call free() is because the variable isn't needed anymore,
> and using a non-const value after freeing is just as wrong as using a
> const one after freeing, so casting away the constness cannot really
> cause any new problems.  So, I think the signature of free() is just
> wrong: it should have taken a const void* all along.  Unfortunately,
> the wrong type signature sadly makes people feel like they have to
> choose between (a) dropping the added safety of const that the
> compiler can enforce for you during the lifetime of the variable, or
> (b) leaking memory you no longer need.  I think it's a bad choice and
> you should just typecast when free'ing, but clearly others just don't
> want to see any typecasts and are willing to dispense with const on
> constant variables.