Re: diff-index --cc no longer permitted, gitk is now broken (slightly)

From: Junio C Hamano <gitster@pobox.com>
Date: Sep 9, 2021, 17:07 UTC
Message-ID: <xmqqilz91xvq.fsf@gitster.g>
In-Reply-To: <cbd0d173-ef17-576b-ab7a-465d42c82265@kdbg.org>

Johannes Sixt <j6t@kdbg.org> writes:

Show 5 quoted lines

> Gitk does not want to look at a commit and then decide which incarnation
> of the command it wants to use (--cc vs. -p) depending on whether it is
> a merge commit or not. This decision is delegated to command that is
> invoked. Therefore, silent fall-back from --cc to -p in case of
> non-merge commits or non-conflicted index is absolutely necessary.

Well explained.

"-p" in general is an instruction to show some form of textual patch, and "--cc" and "-c" are the variants (i.e. compare with each parent and combine the comparison results) of it that naturally degenerates to the normal patch output when there is only one parent.

"--cc" also flips the "m" bit, which controls if there is any tree comparison should be made for merge commits, which matters for "log" family of commands, so in that sense "--cc" was made to imply "-m", but "--cc" inherently means "-p" for non-merge commits without any need to say X implies Y.

Thanks.