Re: Why doesn't `git log -m` imply `-p`?

[Alex Henrie <alexhenrie24@gmail.com>]

On Mon, May 10, 2021 at 6:11 AM Sergey Organov <sorganov@gmail.com> wrote:
>
> Alex Henrie <alexhenrie24@gmail.com> writes:
>
> > I read the following in `man git-log` today:
> >
> > --diff-merges=separate, --diff-merges=m, -m
> >     This makes merge commits show the full diff with respect to each of
> >     the parents. Separate log entry and diff is generated for each
> >     parent.  -m doesn't produce any output without -p.
> >
> > --diff-merges=combined, --diff-merges=c, -c
> >     With this option, diff output for a merge commit shows the
> >     differences from each of the parents to the merge result
> >     simultaneously instead of showing pairwise diff between a parent and
> >     the result one at a time. Furthermore, it lists only files which
> >     were modified from all parents.  -c implies -p.
> >
> > --diff-merges=dense-combined, --diff-merges=cc, --cc
> >     With this option the output produced by --diff-merges=combined is
> >     further compressed by omitting uninteresting hunks whose contents
> >     in the parents have only two variants and the merge result picks one
> >     of them without modification.  --cc implies -p.
> >
> > Why do -c and -cc imply -p, but -m does not? I tried to use both `git
> > log -c` and `git log -m` today and was confused when the latter didn't
> > produce any output. Could we change this behavior in a future version
> > of Git?
>
> Patches to fix this are almost ready, but I'd like to make a warning
> that you'd likely be even more confused by the current output of "-m",
> unless you set "log.diffMerges" configuration option to "first-parent".
> These diffs with respect to /second/ parent at the end of the output
> made me really mad once upon a time.

Good observation. I'm not sure what would be the ideal default here,
but certainly having -m turn on /some/ kind of diff is better than
nothing. Thanks!

-Alex