Subject: Re: [Bug] fetch --deepen truncates history in v2.54.0

From: René Scharfe <[email-masked]>
Date: Sat, 2 May 2026 11:22:49 +0200

On 4/29/26 1:27 PM, Owen Stephens wrote:
>> What did you do before the bug happened? (Steps to reproduce your issue)
> 
> Repeatedy called `git fetch --deepen 2` inside a shallow repo that was a
> file:// clone of another repo. Once all commits had been fetched, a subsequent
> `fetch --deepen` appears to "reset" the repo back to being shallow with a depth
> of 2. A reproduction script is included below. This issue appears to have been
> introduced in v2.54.0.
> 
>> What did you expect to happen? (Expected behavior)
> 
> I expected `git fetch --deepen` in a non-shallow repo with no upstream commits
> to be a no-op.
> 
>> What happened instead? (Actual behavior)
> 
> `git log` history is truncated to two commits, and repo is considered shallow
> by `git rev-parse --is-shallow-repository`.
> 
>> What's different between what you expected and what actually happened?
> 
> The previously-present commits in `git log` are missing, and the repo is again
> considered shallow.
> 
>> Anything else you want to add:
> 
> Commit 3ef68ff seems relevant.

Indeed, bisect identifies 3ef68ff40e (shallow: handling fetch relative-deepen,
2026-02-15) and reverting it fixes the issue.  Copying its author.
> The following script reproduces the issue in 2.54.0, and does not reproduce the
> issue in 2.53.0:
> 
> ```
> mkdir repro.git
> cd repro.git
> 
> git init
> 
> for i in $(seq 1 4); do
>   echo "$i" >> file.txt
>   git add file.txt
>   git commit -m "Change $i"
> done
> 
> cd ..
> 
> git clone --depth 2 "file://$PWD/repro.git" repro_clone.git
> cd repro_clone.git
> 
> echo "Shallow repo? $(git rev-parse --is-shallow-repository)"
> git log --oneline
> 
> for i in $(seq 1 3); do
>   git fetch --deepen 2
>   echo "Shallow repo? $(git rev-parse --is-shallow-repository)"
>   git log --oneline
> done
> ```

Nice!  Here's a test for that:

diff --git a/t/t5537-fetch-shallow.sh b/t/t5537-fetch-shallow.sh
index 6588ce6226..fdb1dd9823 100755
--- a/t/t5537-fetch-shallow.sh
+++ b/t/t5537-fetch-shallow.sh
@@ -251,6 +251,16 @@ test_expect_success '.git/shallow is edited by repack' '
 		origin "+refs/heads/*:refs/remotes/origin/*"
 '
 
+test_expect_success 'fetch --deepen does not truncate' '
+	git clone --no-local .git full-clone &&
+	git rev-parse --is-shallow-repository >expect &&
+	git log --oneline >>expect &&
+	git -C full-clone fetch --deepen=1 &&
+	git -C full-clone rev-parse --is-shallow-repository >actual &&
+	git -C full-clone log --oneline >>actual &&
+	test_cmp expect actual
+'
+
 . "$TEST_DIRECTORY"/lib-httpd.sh
 start_httpd