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

From: Junio C Hamano <gitster@pobox.com>
Date: Mar 23, 2020, 20:50 UTC
Message-ID: <xmqq8sjq4wyf.fsf@gitster.c.googlers.com>
In-Reply-To: <20200323150449.GC11801@danh.dev>

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 ;-)

IOW, I think I am fine with assuming "diff -u" is available, like Dscho's patch does.

Thanks.

[Footnote]

*1* It used to be my desire to teach "git apply" and "git diff" to
    also work with copied context format, but procrastination made
    it less and less relevant X-<.