[vsnakul]

CC: Patrick Steinhardt ps@pks.im, Junio C Hamano gitster@pobox.com
cc: Phillip Wood phillip.wood123@gmail.com

[gitgitgadget]

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[dscho]

/allow

[gitgitgadget]

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[vsnakul]

/preview

[gitgitgadget]

Preview email sent as pull.2273.git.1792576610744.gitgitgadget@gmail.com

[vsnakul]

/preview

[gitgitgadget]

Preview email sent as pull.2273.git.1792577202069.gitgitgadget@gmail.com

[vsnakul]

/submit

[gitgitgadget]

Submitted as pull.2273.git.1792577381142.gitgitgadget@gmail.com

To fetch this version into FETCH_HEAD:

git fetch https://github.com/gitgitgadget/git/ pr-2273/vsnakul/sequencer-shallow-boundary-check-v1

To fetch this version to local tag pr-2273/vsnakul/sequencer-shallow-boundary-check-v1:

git fetch --no-tags https://github.com/gitgitgadget/git/ tag pr-2273/vsnakul/sequencer-shallow-boundary-check-v1

[gitgitgadget]

Phillip Wood wrote on the Git mailing list (how to reply to this email):

Hi Nakul

On 21/10/2026 11:09, Nakul V S via GitGitGadget wrote:
> From: Nakul V S <vsnakul@gmail.com>
> > When a repository is cloned with --depth=1, Git records the boundary
> commit in .git/shallow and rewrites its parent links via the graft
> mechanism, making it appear as a root commit. Reverting such a commit
> will therefore delete all tracked files, which is almost always
> unintended by the user.
> > Add a check in do_pick_commit() that detects when the target commit is
> a shallow boundary (nr_parent < 0 in the commit graft) and refuses the
> operation by default. A new --allow-shallow-boundary flag is provided
> for the rare cases where the user genuinely intends this behavior.

Thanks for working on this, it is a useful and timely improvement as there was some discussion about improving the behavior of git with regard to shallow boundaries at the recent git merge conference. I wonder if it would be better to refuse to cherry-pick and rebase a shallow boundary commit as well. Do you know of a sensible use for reverting a shallow boundary or is the new option added out of caution in case someone wants it?

> diff --git a/builtin/revert.c b/builtin/revert.c
> index 52100a20cb..f27397fdec 100644
> --- a/builtin/revert.c
> +++ b/builtin/revert.c
> @@ -24,7 +24,7 @@
>    */
>   >   static const char * const revert_usage[] = {
> -	N_("git revert [--[no-]edit] [-n] [-m <parent-number>] [-s] [-S[<keyid>]] <commit>..."),
> +	N_("git revert [--[no-]edit] [-n] [-m <parent-number>] [-s] [-S[<keyid>]] [--allow-shallow-boundary] <commit>..."),

For such a rarely used option I don't think we need to add it to the synopsis (we already omit some other options like --rerere-autoupdate)

> diff --git a/sequencer.c b/sequencer.c
> index efbfd1315b..6de59bf6aa 100644
> --- a/sequencer.c
> +++ b/sequencer.c
> @@ -2366,6 +2367,19 @@ static enum pick_result do_pick_commit(struct repository *r,
>   	}
>   	discard_index(r->index);
>   > +	if (is_repository_shallow(r)) {
> +		struct commit_graft *graft = lookup_commit_graft(r, &commit->object.oid);
> +		if (graft && graft->nr_parent < 0 && !opts->allow_shallow_boundary) {

It would be good to extract this into a helper function so that we don't have to copy the code to detect a shallow boundary each time we need to detect one.

Thanks

Phillip

> +			return error(_("%s: commit %s is a shallow boundary commit.\n"
> +				       "Reverting it will remove all tracked files because its\n"
> +				       "true parent history is not present in this clone.\n"
> +				       "Use --allow-shallow-boundary to override, or\n"
> +				       "'git fetch --unshallow' to restore full history first."),
> +				     command_to_string(command),
> +				     oid_to_hex(&commit->object.oid));
> +		}
> +	}
> +
>   	if (!commit->parents)
>   		parent = NULL;
>   	else if (commit->parents->next) {
> diff --git a/sequencer.h b/sequencer.h
> index a5d12a1070..f334bc5357 100644
> --- a/sequencer.h
> +++ b/sequencer.h
> @@ -57,6 +57,7 @@ struct replay_opts {
>   	int committer_date_is_author_date;
>   	int ignore_date;
>   	int commit_use_reference;
> +	int allow_shallow_boundary;
>   >   	struct strvec trailer_args;
>   > diff --git a/t/t3501-revert-cherry-pick.sh b/t/t3501-revert-cherry-pick.sh
> index 939e7a16a6..508464004f 100755
> --- a/t/t3501-revert-cherry-pick.sh
> +++ b/t/t3501-revert-cherry-pick.sh
> @@ -256,4 +256,29 @@ test_expect_success 'cherry-pick is unaware of --reference (for now)' '
>   	test_grep "^usage: git cherry-pick" actual
>   '
>   > +# Tests for shallow boundary safeguard
> +
> +test_expect_success 'setup shallow boundary tests' '
> +	git init src &&
> +	test_commit -C src A &&
> +	test_commit -C src B &&
> +	git clone --no-local --depth=1 src shallow-repo
> +'
> +
> +test_expect_success 'revert of shallow boundary commit is refused by default' '
> +	test_must_fail git -C shallow-repo revert --no-edit HEAD 2>err &&
> +	test_grep "shallow boundary commit" err
> +'
> +
> +test_expect_success 'revert of shallow boundary succeeds with --allow-shallow-boundary' '
> +	git -C shallow-repo revert --no-edit --allow-shallow-boundary HEAD
> +'
> +
> +test_expect_success 'revert in non-shallow repo is unaffected' '
> +	git init non-shallow &&
> +	test_commit -C non-shallow A &&
> +	test_commit -C non-shallow B &&
> +	git -C non-shallow revert --no-edit HEAD
> +'
> +
>   test_done
> > base-commit: 47fdf2208c5b94c8cc01c106b8f7c85efb91c926

[gitgitgadget]

User Phillip Wood <phillip.wood123@gmail.com> has been added to the cc: list.

[gitgitgadget]

Junio C Hamano wrote on the Git mailing list (how to reply to this email):

Phillip Wood <phillip.wood123@gmail.com> writes:

> Hi Nakul
>
> On 21/10/2026 11:09, Nakul V S via GitGitGadget wrote:
>> From: Nakul V S <vsnakul@gmail.com>
>> 
>> When a repository is cloned with --depth=1, Git records the boundary
>> commit in .git/shallow and rewrites its parent links via the graft
>> mechanism, making it appear as a root commit. Reverting such a commit
>> will therefore delete all tracked files, which is almost always
>> unintended by the user.
>> 
>> Add a check in do_pick_commit() that detects when the target commit is
>> a shallow boundary (nr_parent < 0 in the commit graft) and refuses the
>> operation by default. A new --allow-shallow-boundary flag is provided
>> for the rare cases where the user genuinely intends this behavior.
>
> Thanks for working on this, it is a useful and timely improvement as 
> there was some discussion about improving the behavior of git with 
> regard to shallow boundaries at the recent git merge conference. I 
> wonder if it would be better to refuse to cherry-pick and rebase a 
> shallow boundary commit as well. Do you know of a sensible use for 
> reverting a shallow boundary or is the new option added out of caution 
> in case someone wants it?

Very good point.

The next natural question is where the modification should go if we
want to make sure we protect these shallow boundaries not just from
revert but also from "cherry-pick", "rebase", and possibly "commit
--amend".  Is sequencer.c:do_pick_commit() the right place to cover
all of them?  If not, would it make sense to have a helper function
that different code paths to protect shallow boundaries from these
operations can call, and add the first call to that helper funcion
to the location this patch adds new code to?

Thanks.