Re: [PATCH v2 7/8] t4124: fix test for non-compliant diff(1)

> On 2020-03-23 13:50:48-0700, Junio C Hamano <gitster@pobox.com> wrote:
> > Danh Doan <congdanhqx@gmail.com> writes:
> >
> > > A comment in test-lib-functions::test_cmp mentions that
> > > there _is_ a diff out there that doesn't understand "-u".
> >
> > That came from 82ebb0b6 (add test_cmp function for test scripts,
> > 2008-03-12).
> >
> > The change history at the end of the page:
> >
> >   https://pubs.opengroup.org/onlinepubs/9699919799/utilities/diff.html
> >
> > suggests that POSIX did not require "diff -u" until Issue 7, so it
> > is not surprising that the lack of "diff -u" to cause test_cmp to
> > fail was of real concern back in March 2008, as the application of
> > the errata have been only an year and half old, according to:
> >
> >   https://www.opengroup.org/austin/docs/austin_325.txt
> >
> > I vaguely recall that some open source projects only took the copied
> > context diffs and not unified ones the last time I checked, but
> > admittedly (1) that "last time" was a long time ago and (2) our
> > popularity and the fact that we do not understand copied context
> > [*1*] may have forced people to move away from "-c" and adopt "-u"
> > at the same time.
> >
> > So it might be OK to write off any system that does not understand
> > "diff -u" as an unusable trash these days ;-)
>
> From the setting in "config.mak.uname", it's likely those systems
> don't understand "diff -u":
>
> - Solaris 5.6, 5.7, 5.8, 5.9: both of them are un-supported version
>   by their vendor
> - AIX, only AIX 5.3 doesn't understand "-u",
>   the end-of-support AIX 6.1's diff(1) understand "-u" (1)
> - HP-UX: From what I can collect, HP-UX still conforms to UNIX-03, and
>   its diff(1) doesn't understand "-u"
>
> Hence, if we're going to drop support for system that doesn't
> understand "diff -u", we're going to:
> - remove support for those variables:
>   + GIT_TEST_CMP_USE_COPIED_CONTEXT
>   + GIT_TEST_CMP
> - drop support for:
>   + Solaris 5.{6,7,8,} and AIX 5.3, which will be fine
>   + HP-UX: which needs to be discussed
>
> [1]: https://public.dhe.ibm.com/systems/power/docs/aix/61/aixcmds2_pdf.pdf page 133(143)