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

> 
> 
> On Tue, Aug 01 2017, Takashi Iwai jotted:
> 
> > 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,
> 
> It's just like this because when I hacked up that facility I was making
> the bare minimum change needed to not make local modifications to the
> upstream code. If there's better ways to do this in the presence of
> DC_SHA1_EXTERNAL & without that would be most welcome. Thanks.

> > #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
>