Re: Lost file after git merge

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

On Thu, Jul 28 2022, Laďa Tesařík wrote:

> 1. I added a file called 'new_file' to a master branch.
> 2. Then I created branch feature/2 and deleted the file in master
> 3. Then I deleted the file in branch feature/2 as well.
> 4. I created 'new_file' on branch feature/2 again.
> 5. I merged feature/2 into master, merge introduced no changes, file 'new_file' is not present in master.
>
> This could cause problems to our team in the future, fortunately we noticed it this time.
> Please, does anybody have any explanation for this behavior?
>
> Or is anybody aware of any Git or Source option that changes this behaviour?
>
> Thank you very much,
>
> Lada Tesarik
>
> P. S.
> In the picture the steps were done with git revert command, but result is the same if I delete file manually and perform git commit.
> Tested with git versions 2.26 and 2.37

Those who know "merge" better will chime in, but I believe this is known
behavior, and you can see why if your "topic" branch doesn't
(re)introduce the file as it was on master, but adds a small change to
it.

I quickly experimented with this (with the fast-export stream at the
end). If you had a "hello" as the content on "master" and introduced
"hello2" on the topic you'd get:

	$ git merge topic
	CONFLICT (modify/delete): file.txt deleted in HEAD and modified in topic.  Version topic of file.txt left in tree.
	Automatic merge failed; fix conflicts and then commit the result.

So others will know better, but I vaguely recall this having to do with
this being the same in your version (not the below hello2 version, but
if you s/hello2/hello/):

	git rev-parse $(git merge-base topic master):
	git rev-parse topic:

I.e. the topic is the TREESAME as its divergence point with "master",
which IIRC is a shortcut the merge takes when deciding what changes to
keep, and whether they conflict.

--
blob
mark :1
data 6
hello

reset refs/heads/master
commit refs/heads/master
mark :2
author Ævar Arnfjörð Bjarmason <avarab@gmail.com> 1659010359 +0200
committer Ævar Arnfjörð Bjarmason <avarab@gmail.com> 1659010359 +0200
data 9
Add file
M 100644 :1 file.txt

commit refs/heads/master
mark :3
author Ævar Arnfjörð Bjarmason <avarab@gmail.com> 1659010437 +0200
committer Ævar Arnfjörð Bjarmason <avarab@gmail.com> 1659010437 +0200
data 81
Revert "Add file"

This reverts commit 75aa73c55b19219d47dfc7ec3883c88466678718.
from :2
D file.txt

commit refs/heads/topic
mark :4
author Ævar Arnfjörð Bjarmason <avarab@gmail.com> 1659010369 +0200
committer Ævar Arnfjörð Bjarmason <avarab@gmail.com> 1659010369 +0200
data 81
Revert "Add file"

This reverts commit 75aa73c55b19219d47dfc7ec3883c88466678718.
from :2
D file.txt

blob
mark :5
data 7
hello2

commit refs/heads/topic
mark :6
author Ævar Arnfjörð Bjarmason <avarab@gmail.com> 1659010359 +0200
committer Ævar Arnfjörð Bjarmason <avarab@gmail.com> 1659010644 +0200
data 9
Add file
from :4
M 100644 :5 file.txt