Re: [PATCH] t3424: new rebase testcase documenting a stat-dirty-like failure

From: Phillip Wood <phillip.wood123@gmail.com>
Date: Feb 19, 2020, 11:01 UTC
Message-ID: <deae766d-f552-2e30-fb49-e7e187ee984b@gmail.com>
In-Reply-To: <CABPp-BHBv+_HkExM1q6WAZZyMhR=UPNQZDhE8jFSQFNoCtgytg@mail.gmail.com>

Hi Elijah

On 18/02/2020 15:59, Elijah Newren wrote:

Show 31 quoted lines

> On Tue, Feb 18, 2020 at 7:05 AM Phillip Wood <phillip.wood123@gmail.com> wrote:
>>
>> Hi Elijah
>>
>> On 17/02/2020 19:12, Elijah Newren wrote:
>>> I forgot to add some cc's in GitGitGadget before submitting; adding now...
>>>
>>> On Mon, Feb 17, 2020 at 9:15 AM Elijah Newren via GitGitGadget
>>> <gitgitgadget@gmail.com> wrote:
>>>>
>>>> From: Elijah Newren <newren@gmail.com>
>>>>
>>>> A user discovered a case where they had a stack of 20 simple commits to
>>>> rebase, and the rebase would succeed in picking the first commit and
>>>> then error out with a pair of "Could not execute the todo command" and
>>>> "Your local changes to the following files would be overwritten by
>>>> merge" messages.
>>>>
>>>> Their steps actually made use of the -i flag, but I switched it over to
>>>> -m to make it simpler to trigger the bug.  With that flag, it bisects
>>>> back to commit 68aa495b590d (rebase: implement --merge via the
>>>> interactive machinery, 2018-12-11), but that's misleading.  If you
>>>> change the -m flag to --keep-empty, then the problem persists and will
>>>> bisect back to 356ee4659bb5 (sequencer: try to commit without forking
>>>> 'git commit', 2017-11-24)
>>>>
>>>> After playing with the testcase for a bit, I discovered that added
>>>> --exec "sleep 1" to the command line makes the rebase succeed, making me
>>>> suspect there is some kind of discard and reloading of caches that lead
>>>> us to believe that something is stat dirty, but I didn't succeed in
>>>> digging any further than that.

I think `--exec true` would be better as it makes it clear that it's not a timing issue. I've changed do_recursive_merge() to print the mtime and mode of "DS" before and after the merge which gives

HEAD is now at abd8fe3 side1
Rebasing (1/2) # picking commit1
DS mtime, mode before merge 1582109854, 120000
DS mtime, mode after merge 0, 120000
Rebasing (2/2) # picking commit2
DS mtime, mode before merge 0, 120000
error: Your local changes to the following files would be overwritten by 
merge:
	DS

So it looks like the problem is that when we pick commit1 we don't update the index entry for DS properly in merge_trees()

Best Wishes

Phillip

Show 16 quoted lines

>> Intriguing - it's strange that it errors out picking commit2, not
>> commit1 I'll try and have a look at it. There seem to be some leftover
>> bits at the start of the test that want removing see below
> 
> I know, right?  It's kinda weird.
> 
>>>> +test_expect_success 'setup' '
>>>> +       rm -rf ../stupid &&
>>>> +       git init ../stupid &&
>>>> +       cd ../stupid &&
>>
>> I think these 3 lines must be left over from you trying this out before
>> making it a test
> 
> Whoops, yes you are exactly right.  I'll remove them.
>