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

["Samo Pogačnik" <samo_pogacnik@t-2.net>]

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On Sat, 2026-05-02 at 22:26 +0200, René Scharfe wrote:
> On 5/2/26 11:22 AM, René Scharfe wrote:
> > 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.
> 
> Here's a simple fix, but it feels like cheating.  A proper one should
> live in shallow.c, no?
> 
> 
> diff --git a/builtin/fetch.c b/builtin/fetch.c
> index a22c319467..310099b96d 100644
> --- a/builtin/fetch.c
> +++ b/builtin/fetch.c
> @@ -2664,7 +2664,8 @@ int cmd_fetch(int argc,
>  			die(_("negative depth in --deepen is not
> supported"));
>  		if (depth)
>  			die(_("options '%s' and '%s' cannot be used
> together"), "--deepen", "--depth");
> -		depth = xstrfmt("%d", deepen_relative);
> +		if (is_repository_shallow(the_repository))
> +			depth = xstrfmt("%d", deepen_relative);
>  	}
>  	if (unshallow) {
>  		if (depth)
> 

Hi, thanks for pointing out this edge case. Would you care to check the
following change (the provided test is also a bit modified):

diff --git a/shallow.c b/shallow.c
index a156006d88..ec95653132 100644
--- a/shallow.c
+++ b/shallow.c
@@ -245,7 +245,11 @@ struct commit_list *get_shallow_commits(struct object_array
*heads,
                                        int depth, int shallow_flag, int
not_shallow_flag)
 {
        if (shallows && deepen_relative) {
-               depth += get_shallows_depth(heads, shallows);
+               int cur_shallow_depth = get_shallows_depth(heads, shallows);
+               if (cur_shallow_depth)
+                       depth += cur_shallow_depth;
+               else
+                       return NULL;
        }
        return get_shallows_or_depth(heads, NULL, NULL,
                                     depth, shallow_flag, not_shallow_flag);
diff --git a/t/t5537-fetch-shallow.sh b/t/t5537-fetch-shallow.sh
index 6588ce6226..9982dd2aa6 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 -C full-clone rev-parse --is-shallow-repository >expect &&
+       git -C full-clone 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


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