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

[Tilman Vogel <tilman.vogel@web.de>]

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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.

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.

Best regards,

Tilman

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From bc941f9357518a34cfa11788dfb8e7fa7f711705 Mon Sep 17 00:00:00 2001
From: Tilman Vogel <tilman.vogel@web.de>
Date: Mon, 3 Jan 2022 18:31:59 +0100
Subject: [PATCH] t5521: Show inconsistent rebase behavior (--autostash vs.
 rebase.autostash)

When pull --rebase can be done as a fast-forward, the rebase.autostash
config is neglected such that the second test-case added in this commit
will fail to autostash and succeed.
In fact, setting merge.autostash as a workaround would cause autostash to
be done.

The other three test-cases added in this commit document that autostashing
works as expected when either requested explicitly with --autostash or when
pull --rebase cannot be done as a fast-forward.

Signed-off-by: Tilman Vogel <tilman.vogel@web.de>
---
 t/t5521-pull-options.sh | 52 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)

diff --git a/t/t5521-pull-options.sh b/t/t5521-pull-options.sh
index 66cfcb09c5..4046a74cad 100755
--- a/t/t5521-pull-options.sh
+++ b/t/t5521-pull-options.sh
@@ -252,4 +252,56 @@ test_expect_success 'git pull --no-verify --verify passed to merge' '
 	test_must_fail git -C dst pull --no-ff --no-verify --verify
 '
 
+test_expect_success 'git pull --rebase --autostash succeeds on ff' '
+	test_when_finished "rm -fr src dst actual" &&
+	git init src &&
+	test_commit -C src "initial" file "content" &&
+	git clone src dst &&
+	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
+'
+
+test_expect_success 'git pull --rebase with rebase.autostash succeeds on ff' '
+	test_when_finished "rm -fr src dst actual" &&
+	git init src &&
+	test_commit -C src "initial" file "content" &&
+	git clone src dst &&
+	test_commit -C src --printf "more_content" file "more content\ncontent\n" &&
+	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
+'
+
+test_expect_success 'git pull --rebase --autostash succeeds on non-ff' '
+	test_when_finished "rm -fr src dst actual" &&
+	git init src &&
+	test_commit -C src "initial" file "content" &&
+	git clone src dst &&
+	test_commit -C src --printf "src_content" file "src content\ncontent\n" &&
+	test_commit -C dst --append "dst_content" file "dst content" &&
+	echo "dirty" >>dst/file &&
+	git -C dst pull --rebase --autostash >actual 2>&1 &&
+	grep -q "Successfully rebased and updated refs/heads/main." actual &&
+	grep -q "Applied autostash." actual
+'
+
+test_expect_success 'git pull --rebase with rebase.autostash succeeds on non-ff' '
+	test_when_finished "rm -fr src dst actual" &&
+	git init src &&
+	test_commit -C src "initial" file "content" &&
+	git clone src dst &&
+	test_commit -C src --printf "src_content" file "src content\ncontent\n" &&
+	test_commit -C dst --append "dst_content" file "dst content" &&
+	echo "dirty" >>dst/file &&
+	test_config -C dst rebase.autostash true &&
+	git -C dst pull --rebase >actual 2>&1 &&
+	grep -q "Successfully rebased and updated refs/heads/main." actual &&
+	grep -q "Applied autostash." actual
+'
+
 test_done
-- 
2.34.1