Re: [PATCH 0/6] Optionally restrict range-diff output to "left" or "right" range only

Hi Peff,

On Fri, 5 Feb 2021, Jeff King wrote:

On Thu, Feb 04, 2021 at 04:56:16PM -0800, Junio C Hamano wrote:

quoted

quoted

As an aside: I am curious if I'm missing something when you say the
"only way" is to ask for a 'git range-diff ...@{u}'. IIUC what you're
describing, I often resort to using 'git cherry' for that exact thing.
But, I may not be quite understanding your use-case (and why git-cherry
doesn't do what you want already).

My latter question is purely for satisfying my own curiosity; I don't
have any problem with a '--{left,right}-only' option in range-diff. From
my quick read of the patches, it all looks pretty sane to me.

The question is addressed to Dscho, and I am also somewhat curious.
Perhaps the reason would be that the output from cherry is not as
easy to read as range-diff, without any post-processing.

I had the same curiosity; I'd use git-cherry (or rev-list --cherry) for
this.

I suspect the big difference is the quality of the matching. git-cherry
is purely looking at patch-ids.

Indeed. Whenever I had tried `git cherry` in the past (which, admittedly,
has been with geometrically decreasing frequency given the results), it
completely failed to help me. And it's not only its reliance on perfect
matches of the diff _with context lines_, it is also that the commit
messages are completely ignored.

`git cherry`'s track record with me is so perfect that I want to put this
line into all my Bash profiles:

	eval "$(set | sed -n '/^__git_main /,/^}$/{s/--list-cmds=list-mainporcelain[^)]*/& | grep -v ^cherry\$/;p}')"

So it is quite likely to say "this was not applied upstream" when what
got applied differed slightly (e.g., fixups upstream, applied to a
different base, etc). Whereas range-diff has some cost heuristics for
deciding that two patches are basically the same thing.  So it would
find more cases (and as a bonus, give you the diff to see what tweaks
were made upstream).

It does make me wonder if it would be useful for rev-list, etc to have
an option to make "--cherry" use the more clever heuristics instead of
just a patch-id. It would never show the same diff output as range-diff,
but maybe more scripts would find the advanced heuristic useful.

I know it would probably make rebase's "ignore if in upstream" feature
less clunky when I rebase topics. But it would also make it more
dangerous! E.g., right now I see any upstream tweaks as potential
conflicts when I rebase, and I manually review them for sanity.

Yeah, I thought the same when I read the paragraphs before this one. It
might sound convenient, but there _are_ false positives in `git
range-diff`'s output, therefore I would recommend never using
`git range-diff --left-only` or `[...] --right-only` with `-s`. IOW
_always_ inspect the differences.

Ciao,
Dscho