From: Ben Peart <peartben@gmail.com>
To: Junio C Hamano <gitster@pobox.com>
Cc: git@vger.kernel.org, asottile@umich.edu, benpeart@microsoft.com,
pclouds@gmail.com
Subject: Re: [PATCH v2 0/2] Fix regression in checkout -b
Date: Tue, 22 Jan 2019 14:31:16 -0500 [thread overview]
Message-ID: <2a3ac803-133c-98fb-45e9-43f6e4a018d1@gmail.com> (raw)
In-Reply-To: <xmqq4la0h6am.fsf@gitster-ct.c.googlers.com>
On 1/22/2019 1:54 PM, Junio C Hamano wrote:
> Ben Peart <peartben@gmail.com> writes:
>
>> diff --git a/builtin/checkout.c b/builtin/checkout.c
>> index af6b5c8336..9c6e94319e 100644
>> --- a/builtin/checkout.c
>> +++ b/builtin/checkout.c
>> @@ -517,12 +517,6 @@ static int skip_merge_working_tree(const struct checkout_opts *opts,
>> if (core_apply_sparse_checkout && !checkout_optimize_new_branch)
>> return 0;
>>
>> - /*
>> - * We must do the merge if this is the initial checkout
>> - */
>> - if (is_cache_unborn())
>> - return 0;
>> -
>> /*
>> * We must do the merge if we are actually moving to a new commit.
>> */
>> @@ -598,6 +592,13 @@ static int skip_merge_working_tree(const struct checkout_opts *opts,
>> * Remaining variables are not checkout options but used to track state
>> */
>>
>> + /*
>> + * Do the merge if this is the initial checkout
>> + *
>> + */
>> + if (!file_exists(get_index_file()))
>> + return 0;
>> +
>> return 1;
>> }
>
> This is curious. The location the new special case is added is
> different, and the way the new special case is detected is also
> different, between v1 and v2. Are both of them significant? IOW,
> if we moved the check down but kept using is_cache_unborn(), would
> it break? Or if we did not move the check but switched to check the
> index file on the filesystem instead of calling is_cache_unborn(),
> would it break?
>
I had to change the check to not use is_cache_unborn() because at this
point, the index has not been loaded so cache_nr and timestamp.sec are
always zero (thus defeating the entire optimization). Since part of the
optimization was to avoid loading the index when it isn't necessary, the
only replacement I could think of was to check for the existence of the
index file as if it is missing entirely, it is clearly unborn. This
solved the behavior change for the --no-checkout sequence reported.
The only reason I moved it lower in the function was a micro perf
optimization. Since file_exists() does file I/O, I thought I'd do all
the in memory/flag checks first in case they drop out early and we can
avoid the unnecessary file I/O. As long as it is tested before the
'return 1;' call, it is logically correct.
> There are three existing callers of is_{cache,index}_unborn(), all
> of which want to use it to decide if we are in this funny "unborn"
> state. If this fixes the issue we saw in v1 of these two patches,
> does that mean these three existing callers also are buggy in the
> same way and we are better off rewriting is_index_unborn() to see if
> the index file is on the disk?
>
It is just the fact that I needed to check for an unborn index _before_
it was loaded that makes me unable to use is_{cache,index}_unborn()
here. The other callers should still be fine. I could add a comment in
the code to clarify this if you think it will cause confusion later.
> I am *not* suggesting to make such a drastic change to the existing
> system. I am wondering why they are working fine but only this new
> code has to avoid the existing is_index_unborn() logic and go
> directly to the filesystem. Especially as this new exception added
> to "skip-merge-working-tree" is to allow the special case code in
> merge-working-tree that depends on is_cache_unborn() to trigger.
>
> Thanks for working on this.
>
next prev parent reply other threads:[~2019-01-22 19:31 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-01 23:17 Regression `git checkout $rev -b branch` while in a `--no-checkout` clone does not check out files Anthony Sottile
2019-01-02 11:08 ` Duy Nguyen
2019-01-02 16:18 ` Anthony Sottile
2019-01-03 10:04 ` Duy Nguyen
2019-01-03 20:25 ` Junio C Hamano
2019-01-03 20:35 ` Anthony Sottile
2019-01-03 21:51 ` Junio C Hamano
2019-01-03 22:05 ` Anthony Sottile
2019-01-16 14:39 ` Ben Peart
2019-01-18 18:55 ` [PATCH v1 0/2] Fix regression in checkout -b Ben Peart
2019-01-18 18:55 ` [PATCH v1 1/2] checkout: add test to demonstrate regression with checkout -b on initial commit Ben Peart
2019-01-18 19:23 ` SZEDER Gábor
2019-01-18 18:55 ` [PATCH v1 2/2] checkout: fix regression in checkout -b on intitial checkout Ben Peart
2019-01-18 20:00 ` Junio C Hamano
2019-01-19 0:52 ` SZEDER Gábor
2019-01-19 1:26 ` [PATCH v1 0/2] Fix regression in checkout -b Junio C Hamano
2019-01-21 19:50 ` [PATCH v2 " Ben Peart
2019-01-21 19:50 ` [PATCH v2 1/2] checkout: add test to demonstrate regression with checkout -b on initial commit Ben Peart
2019-01-23 17:57 ` SZEDER Gábor
2019-01-21 19:50 ` [PATCH v2 2/2] checkout: fix regression in checkout -b on intitial checkout Ben Peart
2019-01-22 14:35 ` Johannes Schindelin
2019-01-22 18:42 ` Junio C Hamano
2019-01-22 18:49 ` Jeff King
2019-01-22 18:54 ` [PATCH v2 0/2] Fix regression in checkout -b Junio C Hamano
2019-01-22 19:31 ` Ben Peart [this message]
2019-01-23 19:14 ` Junio C Hamano
2019-01-23 20:01 ` [PATCH v3 " Ben Peart
2019-01-23 20:02 ` [PATCH v3 1/2] checkout: add test demonstrating regression with checkout -b on initial commit Ben Peart
2019-01-23 20:02 ` [PATCH v3 2/2] checkout: fix regression in checkout -b on intitial checkout Ben Peart
2019-01-23 21:23 ` [PATCH v3 0/2] Fix regression in checkout -b Junio C Hamano
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