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

From: Ævar Arnfjörð Bjarmason <[email-masked]>
Date: Wed, 24 Apr 2019 17:37:10 +0200

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/[email-masked]/
> 2. https://public-inbox.org/git/[email-masked]/

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.

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.

But the "-G<regex> --pickaxe-raw-diff" feature I have as-is is very
useful, 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}
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/[email-masked]/