Re: [PATCH 2/2] diffcore-pickaxe: add --pickaxe-raw-diff for use with -G

[Eugeniu Rosca <erosca@de.adit-jv.com>]

Hi Ævar,

Thanks for the amazingly fast reply and for the useful feature (yay!).

On Wed, Apr 24, 2019 at 05:37:10PM +0200, Ævar Arnfjörð Bjarmason wrote:
> 
> On Wed, Apr 24 2019, Ævar Arnfjörð Bjarmason wrote:
> 
> > Add the ability for the -G<regex> pickaxe to search only through added
> > or removed lines in the diff, or even through an arbitrary amount of
> > context lines when combined with -U<n>.
> >
> > This has been requested[1][2] a few times in the past, and isn't
> > currently possible. Instead users need to do -G<regex> and then write
> > their own post-parsing script to see if the <regex> matched added or
> > removed lines, or both. There was no way to match the adjacent context
> > lines other than running and grepping the equivalent of a "log -p -U<n>".
> >
> > 1. https://public-inbox.org/git/xmqqwoqrr8y2.fsf@gitster-ct.c.googlers.com/
> > 2. https://public-inbox.org/git/20190424102609.GA19697@vmlxhi-102.adit-jv.com/
> 
> I see now once I actually read Eugeniu Rosca's E-Mail upthread instead
> of just knee-jerk sending out patches that this doesn't actually solve
> his particular problem fully.
> 
> I.e. if you want some AND/OR matching support this --pickaxe-raw-diff
> won't give you that, but it *does* make it much easier to script up such
> an option. Run it twice with -G"\+<regex>" and -G"-<regex>", "sort |
> uniq -c" the commit list, and see which things occur once or twice.
> 
> Of course that doesn't give you more complex nested and/or cases, but if
> git-log grew support for that like git-grep has the -G option could use
> that, although at that point we'd probably want to spend effort on
> making the underlying machinery smarter to avoid duplicate work.

Purely from user's standpoint, I feel more comfortable with `git grep`
and `git log --grep` particularly b/c they support '--all-match' [2],
allowing more flexible multi-line searches. Based on your feedback, it
looks to me that `git log -G/-S` did not have a chance to develop their
features to the same level.

> 
> Furthermore, and quoting Eugeniu upthread:
> 
>     In the context of [1], I would like to find all Linux commits which
>     replaced:
>     	'devm_request_threaded_irq(* IRQF_SHARED *)'
>     by:
>     	'devm_request_threaded_irq(* IRQF_ONESHOT *)'
> 
> Such AND/OR machinery would give you what you wanted *most* of the time,
> but it would also find removed/added pairs that were "unrelated" as well
> as "related". Solving *that* problem is more complex, but something the
> diff machinery could in principle expose.

I expect some false positives, since git is agnostic on the language
used to write the versioned files (the latter sounds like a research
topic to me - I hope there is somebody willing to experiment with that
in future).

> 
> But the "-G<regex> --pickaxe-raw-diff" feature I have as-is is very
> useful, 

I agree. I am a bit bothered by the fact that
`git log --oneline -Ux -G<regex> --pickaxe-raw-diff` outputs the
contents/patch of a commit. My expectation is that we have the
`log -p` knob for that?

> I've had at least two people off-list ask me about a problem
> that would be solved by it just in the last 1/2 year (unrelated to them
> having seen the WIP patch I sent last October).
> 
> It's more general than Junio's suggested --pickaxe-ignore-{add,del}

As a user, I would be happier to freely grep in the raw commit contents
rather than learning a dozen of new options which provide small subsets
of the same functionality. So, I personally vote for the approach taken
by --pickaxe-raw-diff. This would also reduce the complexity of my
current git aliases and/or allow dropping some of them altogether.

Quite off topic, but I also needed to come up with a solution to get
the C functions modified/touched by a git commit [3]. It is my
understanding that --pickaxe-raw-diff can't help here and I still have
to rely on parsing the output of `git log -p`?

> options[1], but those could be implemented in terms of this underlying
> code if anyone cared to have those as aliases. You'd just take the
> -G<regex> and prefix the <regex> with "^\+" or "^-" as appropriate and
> turn on the DIFF_PICKAXE_G_RAW_DIFF flag.
> 
> 1. https://public-inbox.org/git/xmqqwoqrr8y2.fsf@gitster-ct.c.googlers.com/

Thanks!

[2] https://gitster.livejournal.com/30195.html
[3] https://stackoverflow.com/questions/50707171/how-to-get-all-c-functions-modified-by-a-git-commit

-- 
Best regards,
Eugeniu.