Re: [PATCH v4 1/1] MacOS: precompose_argv_prefix()

From: Junio C Hamano <gitster@pobox.com>
To: tboegi@web.de
Cc: git@vger.kernel.org, random_n0body@icloud.com,
	levraiphilippeblain@gmail.com
Subject: Re: [PATCH v4 1/1] MacOS: precompose_argv_prefix()
Date: Wed, 03 Feb 2021 14:13:53 -0800	[thread overview]
Message-ID: <xmqqh7msbxzy.fsf@gitster.c.googlers.com> (raw)
In-Reply-To: <xmqq35ydc5g3.fsf@gitster.c.googlers.com> (Junio C. Hamano's message of "Wed, 03 Feb 2021 11:33:00 -0800")

Junio C Hamano <gitster@pobox.com> writes:

> Just as the prefix-less variant was idempotent and that was the
> reason why cmd_diff_files() had its own precompose() even if the
> incoming argv[] is supposed to be already precomposed because it
> was processed in another call to precompose() in run_builtin(),
> this patch keeps these seemingly redundant calls, because it is not
> meant as a clean-up but as a bugfix for the prefix part.
>
> OK. ... Ah, no, the call in run_builtin() is a new thing.  We didn't
> have it, and the redundant call is what this patch introduced, so
> we need to be a bit more careful about the analysis here.  It is one
> thing to say "we leave the existing iffy code and address only a
> single bug" and do so.  It is entirely different to say so and then
> do "we introduce an iffy code and address only a single bug".  We
> need to admit that what we added _is_ iffy but supposed to be safe.
> Just saying "it is supposed to be safe" without saying why it is
> iffy is dishonest and does not help future developers who may want
> to jump in and clean the code.
>
> Perhaps
>
> 	Now add it into git.c::run_builtin() as well.  Existing
> 	precompose calls in diff-files.c and others would become
> 	redundant but because we do not want to make sure that there
> 	is no way for the control to reach them without passing
> 	run_builtin(), we'll keep them in place just in case.  The
> 	calls to precompose() are idempotent so it should not hurt.
>
> or something?

FYI, I've tweaked the proposed log message like the following before
queuing.  I think that would be explicit enough to remind us that we
may be able to improve the situation fairly easily.

Thanks.

1:  071dfe8793 ! 1:  5c327502db MacOS: precompose_argv_prefix()
    @@ Commit message

         The original patch for preocomposed unicode, 76759c7dff53, placed
         precompose_argv() into parse-options.c
    -    Now add it into git.c (as well) for commands that don't use parse-options.
    -    Note that precompose() may be called twice - it is idempotent.
    +
    +    Now add it into git.c::run_builtin() as well.  Existing precompose
    +    calls in diff-files.c and others may become redundant, and if we
    +    audit the callflows that reach these places to make sure that they
    +    can never be reached without going through the new call added to
    +    run_builtin(), we might be able to remove these existing ones.
    +
    +    But in this commit, we do not bother to do so and leave these
    +    precompose callsites as they are.  Because precompose() is
    +    idempotent and can be called on an already precomposed string
    +    safely, this is safer than removing existing calls without fully
    +    vetting the callflows.

         There is certainly room for cleanups - this change intends to be a bug fix.
         Cleanups needs more tests in e.g. t/t3910-mac-os-precompose.sh, and should