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From: Pratyush Yadav <me@yadavpratyush.com>
To: Jeff King <peff@peff.net>
Cc: git@vger.kernel.org
Subject: Re: How to reset selected lines?
Date: Wed, 14 Aug 2019 17:18:44 +0530	[thread overview]
Message-ID: <20190814114844.gvb5znje7cpzehkd@localhost.localdomain> (raw)
In-Reply-To: <20190813154239.GA22514@sigill.intra.peff.net>

On 13/08/19 11:42AM, Jeff King wrote:
> On Tue, Aug 13, 2019 at 07:48:16PM +0530, Pratyush Yadav wrote:
> 
> > To put things into context of why I am asking this, git-gui has a 
> > feature where you can select parts of a displayed diff, and can 
> > stage/unstage those parts. That feature is implemented in git-gui by 
> > just generating a diff from the selected lines, and then applying it. 
> > Check git-gui/lib/diff.tcl:643 for the implementation.
> > 
> > Now, I want to add a similar feature, but one that discards/resets the 
> > selected lines. And I'd like to avoid the hack that git-gui's 
> > apply_range_or_line is. So, is there a cleaner way to do this that does 
> > not involve generating a diff and then applying it?
> 
> To answer your second question first:
> 
> Git's index and trees only understand whole files, so at some point you
> must generate the final file content. A diff is an easy way to represent
> the changes, apply them to the existing state, and then get that final
> content. But it doesn't _have_ to be. You could make some modifications
> to what is in the working tree and then say "OK, now stage this.".
> 
> BUT. That is probably not what the user wants, if the content in the
> index actually has some modifications that are not in the working tree
> (i.e., you wouldn't want to overwrite them). Hence we tend to work with
> diffs, saying "make these changes to what is already in the index, and
> if they conflict, then bail".
> 
> So "git add -p", for example, also works by creating diffs, modifying
> them, and feeding the result to "apply". You can see the implementation
> in git-add--interactive.perl, where it literally calls diff and apply
> commands.
> 
> And that leads us to the answer to the first question. That script
> implements "add -p", but also "checkout -p" (which is what you want),
> "reset -p", "stash -p", etc. They differ only in what we diff and how we
> apply the result; the main engine of slicing and dicing the diff through
> user interaction is the same. See the %patch_modes hash for the list.

Ah, so that means I do have to dive into generating diffs. Too bad, I 
was hoping for a cleaner (read: easier) way.

On that note, I don't suppose there is a way to use 
git-add--interactive's diff engine from a script, is there?  That'd 
allow me to not write potentially buggy code and solve problems someone 
already solved.

Thanks for your detailed answer.

-- 
Regards,
Pratyush Yadav

  parent reply	other threads:[~2019-08-14 11:48 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-13 14:18 How to reset selected lines? Pratyush Yadav
2019-08-13 15:42 ` Jeff King
2019-08-13 17:32   ` Junio C Hamano
2019-08-14 11:48   ` Pratyush Yadav [this message]
2019-08-14 14:52     ` Jeff King
2019-08-13 22:07 ` Johannes Sixt
2019-08-14 11:11   ` Pratyush Yadav

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