Re: [PATCH] hash: Allow building with the external sha1dc library

[Takashi Iwai <tiwai@suse.de>]

On Tue, 01 Aug 2017 17:56:00 +0200,
Junio C Hamano wrote:
> 
> Takashi Iwai <tiwai@suse.de> writes:
> 
> > On Fri, 28 Jul 2017 17:58:14 +0200,
> > Ævar Arnfjörð Bjarmason wrote:
> >>  ...
> >> * We now have much of the same header code copy/pasted between
> >> sha1dc_git.h and sha1dc_git_ext.h, did you consider just always
> >> including the former but making what it's doing conditional on
> >> DC_SHA1_EXTERNAL? I don't know if it would be worth it from a cursory
> >> glance, but again your commit message doesn't list that among options
> >> considered & discarded.
> >
> > I don't mind either way, there is no perfect solution in this case.
> > As you know, many people think the ifdef ugly no matter how.
> >
> > I leave the decision to maintainer.  Just let me know which option is
> > preferred.
> 
> Yeah, I also found it somewhat confusing to have these two headers
> that look quite similar to each other at the top-level of the tree.
> 
> What's the "conditional" part between the two headers?  Is it just
> whether the header for underlying library is included?  I wonder if
> it's just the matter of adjusting "hash.h" to read like this
> 
>     ...
>     #if defined(DC_SHA1_EXTERNAL)
>    -#include "sha1dc_git_ext.h"
>    +#include <sha1dc/sha1.h>
>    +#include "sha1dc_git.h"
>     #elif  defined(DC_SHA1_SUBMODULE)
>     ...
> 
> or are there heavier tweaks needed that won't be solved by continuing
> along the same line?  As _ext.h variant is included only at this place,
> if we can do with minimum tweaks around here without introducing it,
> it may be ideal, I would think.

Well, a tricky part is that currently sha1dc_git.h is included from
sha1dc/sha1.h implicitly by SHA1DC_CUSTOM_TRAILING_INCLUDE_SHA1_H
definition.  IMO, we should stop this, and use the standard inclusion
instead, i.e. in hash.h,

#if defined(DC_SHA1_EXTERNAL)
#include <sha1dc/sha1.h>
#elif defined(DC_SHA1_SUBMODULE)
#include "sha1collisiondetection/lib/sha1.h"
#else
#include "sha1dc/sha1.h"
#endif
#include "sha1dc_git.h"

In sha1dc_git.h, we'd need another ifdef for DC_SHA1_EXTERNAL to
define the own git_SHA1DCInit(), but it's trivial. 


Takashi