Re: [PATCH] tests: drop dependency on `git diff` in check-chainlint

[Junio C Hamano <gitster@pobox.com>]

Patrick Steinhardt <ps@pks.im> writes:

> This strongly reminds me of the thread at [1], where a similar issue was
> discussed for git-grep(1). Quoting Junio: 
>
>> I actually do not think these "we are allowing Git tools to be used
>> on random garbage" is a good idea to begin with X-<.  If we invented
>> something nice for our variant in "git grep" and wish we can use it
>> outside the repository, contributing the feature to implementations
>> of "grep" would have been the right way to move forward, instead of
>> contaminating the codebase with things that are not related to Git.
>
> So this might not be the best way to go.

That is not a conclusion I want people to draw.

Like it or not, "git diff --no-index" will be with us to stay, and
"--no-index" being "we have abused the rest of Git code to implement
'diff' that works _outside_ a Git repository---now go and do your
thing", we would eventually want to correct it, if it is misbehaving
when a repository it finds is in a shape it does not like, no?

We should have what you quoted in mind as a general principle, and
think twice when we are tempted to hoard useful features for another
tool we initially wrote for Git and allow them to be used with the
"--no-index" option, instead of contributing them to the tool that
does not know or care "git" repositories (like "diff" and "grep").