Re: Newbie contribution idea for 'git log --children': input requested

From: Jeff King <peff@peff.net>
Date: Sep 20, 2022, 22:28 UTC
Message-ID: <Yyo+iBNF1bydcQt+@coredump.intra.peff.net>
In-Reply-To: <YyaOJa1FNyWK+M4U.jacob@initialcommit.io>

On Sat, Sep 17, 2022 at 08:19:01PM -0700, Jacob Stopak wrote:

Show 14 quoted lines

> On Thu, Sep 15, 2022 at 12:08:10AM -0500, Jeff King wrote:
> > 
> > I usually solve this by doing a single traversal, and asking the pager
> > to jump straight to the commit of interest, at which point I can scroll
> > up and down to see the context. Like:
> > 
> >   git log --color | less +/$some_old_commit
> > 
> > I'm not 100% sure I understand the original use case. But if I do, and
> > that solves it, I wonder if we could make it more ergonomic somehow.
> 
> Great points thanks for the details. I do think your method addresses the use
> case I was trying to describe, which is being able to quickly see context in
> both directions when you jump to a commit far from any branch/tag.

One thing my suggestion doesn't help with is when $some_old_commit is the current HEAD. Something like:

  git checkout HEAD~50
  git log --magically-start-at=HEAD

wouldn't work, because to get context you need to start traversing from somewhere else. So really you want to start with "--branches --tags", or maybe even "--all" as traversal points, and then show whatever commit (be it HEAD or something else) in context.

Show 13 quoted lines

> But like you implied, it would be nice to be able to do it with a real command
> line option to git log instead of repiping into less, something like:
> 
>     git log --scroll-to=commit_id
> 
> I peeked into builtin/log.c and saw how it calls setup_pager(); at the end of
> cmd_log_init_finish(...). I have a basic understanding now of how the default
> pager and pager environment are roped in.
> 
> One obvious issue is that different pagers might have different ways (or no way
> at all) to auto-scroll to a pattern. But this might be solved by allowing the
> user to add their pager option such as +/ to the pager environment, which would
> only be applied when the user adds the --scroll-to=commit_id option to git log.

Yes, exactly. It's awkward to assume too much about the pager, because it could be literally anything. I think the worst thing we can do is stick extra bits on the command-line like this, because it may actually break other pagers. As you noted, we do have a default LESS variable, which is OK, because at worst it is simply ignored.

I think we _could_ append "+/whatever" into $LESS, and that would work. It feels kind of dirty somehow, though.

> Anyway, then the commit_id would be dynamically added after, probably in a format like
> "commit <commit_id>" so that the same pattern in commit messages doesn't match.

Right, and you can anchor it with "+/^commit ...". But of course that depends on the output format. Something like "--oneline" would have a partial commit. If done inside Git, it would know the format it will use. But if you don't mind being a little sloppy, you can probably write a regex which works well enough.

Taking it all together, a script like this works:

-- >8 -- #!/bin/sh

focus=$1; shift

# use --short rather than --verify so we match --oneline short=$(git rev-parse --short "$focus") || exit 1

# this regex tries to match a variety of formats: # # - anchor to the left to avoid false positives # - make "commit" optional to catch both regular and oneline # - skip --graph markers # - we can ignore colors; less skips ANSI codes when matching regex='^[*|\\ ]*(commit )?'

# yuck, there's no way to ask "which pager would you use for git-log". # Stuffing the value inside $LESS works, but if we override Git's # internal value, then we have to recreate it. LESS="${LESS-FRX} +/$regex$short" export LESS

exec git log --branches --tags "$@" -- >8 --

Saving that as git-focus and setting the execute bit lets you do stuff like:

  git checkout HEAD~50
  git focus HEAD

I think this could be done inside Git, though it would be a little awkward. Maybe it's worth living with that script for a while and seeing if you like it.

-Peff