Subject: Re: [PATCH v3 07/10] git-zlib: cast away potential constness of `next_in` pointer

From: Patrick Steinhardt <[email-masked]>
Date: Tue, 28 Jan 2025 09:35:45 +0100

On Sun, Jan 26, 2025 at 06:58:40PM -0600, Justin Tobler wrote:
> On 25/01/16 10:17AM, Patrick Steinhardt wrote:
> > The `struct git_zstream::next_in` variable points to the input data and
> > is used in combination with `struct z_stream::next_in`. While that
> > latter field is not marked as a constant in zlib, it is marked as such
> > in zlib-ng. This causes a couple of compiler errors when we try to
> > assign these fields to one another due to mismatching constness.
> > 
> > Fix the issue by casting away the potential constness of `next_in`.
> > 
> > Signed-off-by: Patrick Steinhardt <[email-masked]>
> > ---
> >  git-zlib.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/git-zlib.c b/git-zlib.c
> > index 2e973320c2..519b3647ac 100644
> > --- a/git-zlib.c
> > +++ b/git-zlib.c
> > @@ -59,7 +59,7 @@ static void zlib_post_call(git_zstream *s)
> >  
> >  	s->total_out = s->z.total_out;
> >  	s->total_in = s->z.total_in;
> > -	s->next_in = s->z.next_in;
> > +	s->next_in = (unsigned char *) s->z.next_in;
> 
> Without the context of the commit, its not obvious to me why this cast
> is happening and looks curious. It might be nice to leave a comment here
> explaining its purpose.

Fair, otherwise someone using zlib might wonder why we have a seemingly
unnecessary cast in the first place.

Thanks for your input!

Patrick