Re: [BUG] git pull --rebase ignores rebase.autostash config when fast-forwarding

[Philippe Blain <levraiphilippeblain@gmail.com>]

Hi Tilman,

Le 2022-01-04 à 07:59, Philip Oakley a écrit :
> On 03/01/2022 18:08, Tilman Vogel wrote:
>> Hi git-people,
>>
>> I ran into strange behavior when having rebase.autostash enabled and
>> doing a git pull --rebase:
>>
>>> git config rebase.autostash true
>>> git pull --rebase
>> Updating cd9ff8a..f3c9840
>> error: Your local changes to the following files would be overwritten by
>> merge:
>>          content
>> Please commit your changes or stash them before you merge.
>> Aborting
>>
>> Confusingly, this fixes the issue:
>>
>>> git config merge.autostash true
>>> git pull --rebase
>> Updating cd9ff8a..f3c9840
>> Created autostash: c615fda
>> Fast-forward
>>   content | 1 +
>>   1 file changed, 1 insertion(+)
>> Applied autostash.
>>
>> Leaving me wonder why merge config options fix rebase behavior.
>>
>> So, in order to make it easier to check the problem, I added some
>> test-cases to the git test-suite. Please see the attached patch.

Thanks, this really makes it easier to bisect the issue.

>>
>> Or here:
>> https://github.com/tvogel/git/commit/bc941f9357518a34cfa11788dfb8e7fa7f711705
>>
>> I did not try to find the root-cause as I am not experienced with the
>> code-base but if there are questions, let me know.
> 
> Which version are you running?
> 

That's a good info to include indeed. I'm guessing you are using v2.34.1 as that's the version
indicated at the bottom of your attached patch. I can replicate the behaviour on my side on 2.34.1.
I did not bisect manually but I'm pretty sure it's a regression caused by 340062243a (pull: cleanup autostash
check, 2021-06-17) (author CC'ed). I checked that the parent of that commit passes all 4 of your added tests, provided
this is squashed in:

diff --git a/t/t5521-pull-options.sh b/t/t5521-pull-options.sh
index 4046a74cad..5ad19b1028 100755
--- a/t/t5521-pull-options.sh
+++ b/t/t5521-pull-options.sh
@@ -260,7 +260,6 @@ test_expect_success 'git pull --rebase --autostash succeeds on ff' '
  	test_commit -C src --printf "more_content" file "more content\ncontent\n" &&
  	echo "dirty" >>dst/file &&
  	git -C dst pull --rebase --autostash >actual 2>&1 &&
-	grep -q "Fast-forward" actual &&
  	grep -q "Applied autostash." actual
  '
  
@@ -273,7 +272,6 @@ test_expect_success 'git pull --rebase with rebase.autostash succeeds on ff' '
  	echo "dirty" >>dst/file &&
  	test_config -C dst rebase.autostash true &&
  	git -C dst pull --rebase  >actual 2>&1 &&
-	grep -q "Fast-forward" actual &&
  	grep -q "Applied autostash." actual
  '

After that commit, in case of fast-forward, 'git pull --rebase --autostash' delegates the fast-forward
operation to 'git merge' under the hood, which was not the case before. The '--autostash' flag seems
to be forwarded correctly to that 'git merge' invocation, but the config 'rebase.autostash' seems to not
be passed along.

I did not yet look into why in the code itself. That does explain however why 'merge.autostash' makes it
work - the 'git merge' invocation does check its own config, and if merge.autostash is there the autostash
behaviour is activated.

Philippe.