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From: Phillip Wood <phillip.wood123@gmail.com>
To: Johannes Schindelin <Johannes.Schindelin@gmx.de>,
	phillip.wood@dunelm.org.uk
Cc: Jochen Sprickerhof <jochen@sprickerhof.de>,
	Junio C Hamano <gitster@pobox.com>,
	git@vger.kernel.org
Subject: Re: [PATCH] add -p: coalesce hunks before testing applicability
Date: Sun, 2 Jun 2019 15:17:13 +0100	[thread overview]
Message-ID: <a23789e9-ee99-d23b-ee25-1acef8d8d114@gmail.com> (raw)
In-Reply-To: <nycvar.QRO.7.76.6.1903221453360.41@tvgsbejvaqbjf.bet>

Hi Dscho


Sorry it's taken me so long to get round to replying to this

On 22/03/2019 14:06, Johannes Schindelin wrote:
> Hi,
> 
> On Thu, 13 Sep 2018, Phillip Wood wrote:
> 
>> On 03/09/2018 20:01, Jochen Sprickerhof wrote:
>>
>>> * Phillip Wood <phillip.wood@talktalk.net> [2018-08-30 14:47]:
>>>> When $newhunk is created it is marked as dirty to prevent
>>>> coalesce_overlapping_hunks() from coalescing it. This patch does not
>>>> change that. What is happening is that by calling
>>>> coalesce_overlapping_hunks() the hunks that are not currently selected
>>>> are filtered out and any hunks that can be coalesced are (I think that
>>>> in the test that starts passing with this patch the only change is the
>>>> filtering as there's only a single hunk selected).
>>>
>>> Agreed here. It would be enough to include the first hunk in the test to
>>> make it fail again. Still I would see the patch as going in the right
>>> direction as we need something like coalesce_overlapping_hunks() to make
>>> the hunks applicable after the edit.
>>
>> Yes in the long term we want to be able to coalesce edited hunks, but I
>> think it is confusing to call coalesce_overlapping_hunks() at the moment
>> as it will not coalesce the edited hunks.
> 
> Agreed. I actually have code to coalesce even edited hunks, but it is all
> in C.
> 
>>>> This is a subtle change to the test for the applicability of an
>>>> edited hunk. Previously when all the hunks were used to create the
>>>> test patch we could be certain that if the test patch applied then if
>>>> the user later selected any unselected hunk or deselected any
>>>> selected hunk then that operation would succeed. I'm not sure that is
>>>> true now (but I haven't thought about it for very long).
>>>
>>> I'm not sure here. If we use the same test from t3701, do s(plit),
>>> y(es), e(dit), it would fail later on. Can you come up with an
>>> example?
>>
>> I think that if you split a hunk, edit the first subhunk, transforming a
>> trailing context line to a deletion then try if you try to stage the
>> second subhunk it will fail. With your patch the edit will succeed as
>> the second subhunk is skipped when testing the edited patch. Then when
>> you try to stage the second subhunk it will fail as it's leading context
>> will contradict the trailing lines of the edited subhunk. With the old
>> method the edit failed but didn't store up trouble for the future.
> 
> Indeed, this is a problem I also stumbled over.
> 
>>>> We could restore the old test condition and coalesce the hunks by
>>>> copying all the hunks and setting $hunk->{USE}=1 when creating the
>>>> test patch if that turns out to be useful (it would be interesting to
>>>> see if the test still passes with that change).
>>>
>>> We set USE=1 for $newhunk already, or where would you set it?
>>
>> To match the old test it needs to be set on the hunks we've skipped or
>> haven't got to yet so they're all in the patch that's tested after
>> editing a hunk.
> 
> The way I fixed this in the C code is by teaching the equivalent of the
> `coalesce_overlapping_hunks()` function to simply ignore the equivalent of
> `$hunk->{USE}`: the function signature takes an additional `use_all`
> parameter, which will override the `use` field.

That sounds like a good solution. Thanks for working on the conversion 
to C, I'll try and find time look at the code on github.

Best Wishes

Phillip

> 
> Furthermore, my C code actually does the coalescing as part of the
> `reassemble_patch()` function, feeding the output directly into the
> `stdin` of the `git apply` process (with, or without `--check`).
> 
> And crucially, my C code does not try to assemble a new `hunks` array, but
> simply works in-place, reverting the changes if the hunk edits result in a
> patch that does not apply. The Perl version probably does not need that
> part, as it is pretty careless with memory (as Perl encourages to do).
> 
> See for yourself:
> https://github.com/dscho/git/commit/6f8ac4809280f2cd018683ab5199b004ada2350e#diff-f58d2179be56b196b9f35c6d24799a8eR337
> 
> Ciao,
> Dscho
> 
> P.S.: Yes, this is part of my work to complete Slavica's "`git add -i`
> in C" project. There are quite a few loose ends to tie, but I can already
> use it myself to call `git add -p`, which is what I care most about, as it
> regularly takes more than one second to spin up Perl on Windows, which is
> friggin' annoying, I tell ya.
> 

  reply	other threads:[~2019-06-02 14:17 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-08-28  8:58 [PATCH] add -p: coalesce hunks before testing applicability Jochen Sprickerhof
2018-08-28 18:07 ` Junio C Hamano
2018-08-30 13:47   ` Phillip Wood
2018-08-30 14:51     ` Junio C Hamano
2018-09-03 19:01     ` Jochen Sprickerhof
2018-09-13 10:20       ` Phillip Wood
2018-09-23 17:16         ` Jochen Sprickerhof
2019-03-22 14:06         ` Johannes Schindelin
2019-06-02 14:17           ` Phillip Wood [this message]
2019-06-03 13:40             ` Johannes Schindelin
2019-06-03 14:59               ` Phillip Wood
2019-06-04 13:32                 ` Johannes Schindelin

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