git move not working as expected: deletes branches, doesn't rebase anything

[ryan-williams]

Description of the bug

I learned about git-branchless move from this @arxanas SO answer, but it's not working as expected.

Create empty repo, initialize as in example above

mkdir git-branchless-move-test && cd git-branchless-move-test
git init --initial-branch master
git commit --allow-empty -m A
git commit --allow-empty -m B
git branch feature
git commit --allow-empty -m F
git checkout feature
git commit --allow-empty -m C
git checkout -b feature-a
git commit --allow-empty -m D
git checkout -b feature-b feature
git commit --allow-empty -m E
git checkout feature
git branchless init --main-branch master

Verify repo state:

git log --graph --all --format=%s%d
# * E (feature-b)
# | * D (feature-a)
# |/
# * C (HEAD -> feature)
# | * F (master)
# |/
# * B
# * A

Run suggested git move command:

git move -b feature -d master

Expected behavior

Subtree rooted at "C"/feature (including "D"/feature-a and "E"/feature-b) is rebased onto "F"/master:

git log --graph --all --format=%s%d
# * E' (feature-b)
# | * D' (feature-a)
# |/
# * C' (HEAD -> feature)
# * F (master)
# * B
# * A

Actual behavior

My branches have been deleted (feature, feature-a, feature-b), and nothing has been rebased or moved, from what I can tell:

git log --graph --all --format=%s%d
# * F (HEAD -> master)
# * B
# * A

Version of rustc

No response

Automated bug report

Software version

git-branchless 0.7.0 (6c6faec-modified)

Operating system

macOS 13.1 (Darwin 22.2.0)

Command-line

/Users/ryan/.cargo/bin/git-branchless bug-report 

Environment variables

SHELL=/bin/bash
EDITOR=emacs

Git version

> git version 
git version 2.40.0

Hooks

Show 7 hooks

Hook post-applypatch

#!/bin/sh
## START BRANCHLESS CONFIG

git branchless hook post-applypatch "$@"

## END BRANCHLESS CONFIG

Hook post-checkout

#!/bin/sh
## START BRANCHLESS CONFIG

git branchless hook post-checkout "$@"

## END BRANCHLESS CONFIG

Hook post-commit

#!/bin/sh
## START BRANCHLESS CONFIG

git branchless hook post-commit "$@"

## END BRANCHLESS CONFIG

Hook post-merge

#!/bin/sh
## START BRANCHLESS CONFIG

git branchless hook post-merge "$@"

## END BRANCHLESS CONFIG

Hook post-rewrite

#!/bin/sh
## START BRANCHLESS CONFIG

git branchless hook post-rewrite "$@"

## END BRANCHLESS CONFIG

Hook pre-auto-gc

#!/bin/sh
## START BRANCHLESS CONFIG

git branchless hook pre-auto-gc "$@"

## END BRANCHLESS CONFIG

Hook reference-transaction

#!/bin/sh
## START BRANCHLESS CONFIG

# Avoid canceling the reference transaction in the case that `branchless` fails
# for whatever reason.
git branchless hook reference-transaction "$@" || (
echo 'branchless: Failed to process reference transaction!'
echo 'branchless: Some events (e.g. branch updates) may have been lost.'
echo 'branchless: This is a bug. Please report it.'
)

## END BRANCHLESS CONFIG

Events

Show 5 events

Event ID: 1, transaction ID: 1 (message: move)

1. RefUpdateEvent { timestamp: 1681996830.387656, event_tx_id: EventTransactionId(1), ref_name: ReferenceName("refs/heads/redacted-ref-0"), old_oid: a1dc7976f3acbd8daa03e26216e5c45c265083d0, new_oid: 0000000000000000000000000000000000000000, message: None }
2. RefUpdateEvent { timestamp: 1681996830.387656, event_tx_id: EventTransactionId(1), ref_name: ReferenceName("refs/heads/redacted-ref-1"), old_oid: 8dc5c5ea575ab652149f41f8d6576988bd08bdbb, new_oid: 0000000000000000000000000000000000000000, message: None }
3. RefUpdateEvent { timestamp: 1681996830.387656, event_tx_id: EventTransactionId(1), ref_name: ReferenceName("refs/heads/redacted-ref-2"), old_oid: 4e2f69c85f503655d7df4ecc9cb47f59caa07779, new_oid: 0000000000000000000000000000000000000000, message: None }
4. RewriteEvent { timestamp: 1681996830.57985, event_tx_id: EventTransactionId(1), old_commit_oid: 8dc5c5ea575ab652149f41f8d6576988bd08bdbb, new_commit_oid: 0000000000000000000000000000000000000000 }
5. RewriteEvent { timestamp: 1681996830.57985, event_tx_id: EventTransactionId(1), old_commit_oid: 4e2f69c85f503655d7df4ecc9cb47f59caa07779, new_commit_oid: 0000000000000000000000000000000000000000 }
6. RewriteEvent { timestamp: 1681996830.57985, event_tx_id: EventTransactionId(1), old_commit_oid: a1dc7976f3acbd8daa03e26216e5c45c265083d0, new_commit_oid: 0000000000000000000000000000000000000000 }
7. WorkingCopySnapshot { timestamp: 1681996830.599858, event_tx_id: EventTransactionId(1), head_oid: 8dc5c5ea575ab652149f41f8d6576988bd08bdbb, commit_oid: NonZeroOid(a33f73208bba12d31d48754228f319a376a0a4ec), ref_name: None }
8. RefUpdateEvent { timestamp: 1681996830.746192, event_tx_id: EventTransactionId(1), ref_name: ReferenceName("HEAD"), old_oid: 8dc5c5ea575ab652149f41f8d6576988bd08bdbb, new_oid: 8c224301419717fd8afeb72446fd5f4c1f75742c, message: None }

:
@ 8c22430 8m (> master) x

There are no previous available events.

:
@ 8c22430 8m (> master) x

There are no previous available events.

:
@ 8c22430 8m (> master) x

There are no previous available events.

:
@ 8c22430 8m (> master) x

There are no previous available events.

:
@ 8c22430 8m (> master) x

Version of git-branchless

No response

Version of git

No response

[ryan-williams]

I guess this was an artifact of my test commits being empty; git-branchless basically discards them? I get the expected result when initializing the repo with actual content in the commits:

make_commit() {
    touch "$1" && git add "$1" && git commit -m "$1"
}
git init --initial-branch master
make_commit A
make_commit B
git branch feature
make_commit F
git checkout feature
make_commit C
git checkout -b feature-a
make_commit D
git checkout -b feature-b feature
make_commit E
git checkout feature
git branchless init --main-branch master

In this case, git move -b feature -d master gives me the expected tree:

git log --graph --all --format=%s%d
# * D (feature-a)
# | * E (feature-b)
# |/  
# * C (HEAD -> feature)
# * F (master)
# * B
# * A

So I will close this. I ran into this problem while trying to minimize a different problem with git move (which may have to do with rebasing onto an unrelated history, e.g. across repositories), but I'll try to minimize+file that separately.

[ryan-williams]

FWIW, I tried the original example with git move -b feature -d master --no-deduplicate-commits to try to preserve the empty commits, but it didn't work / I got the same behavior (branches deleted, structure not preserved).

[arxanas]

Under git rebase, there are a few situations in which commits will be dropped:

• The commit is empty before being applied.
  • Git: configured with --keep-empty/--no-keep-empty.
  • git-branchless: not configurable.
• The commit was already applied upstream, as per git cherry.
  • Git: configured with --reapply-cherry-picks/--no-reapply-cherry-picks.
  • git-branchless: configured with the --no-deduplicate-commits flag.
• The patch was applied but the result was empty. This can happen if a set of commits were squashed upstream.
  • Git: configured with --empty={keep,drop,ask}.
  • git-branchless: not configurable.

You saw this behavior because it modeled the first situation, and that's why toggling --no-deduplicate-commits didn't affect the behavior.

[korrat]

I came across this issue after encountering surprising behaviour in git move: When moving a branch with an empty HEAD commit, but other commits, the non-empty commits are moved correctly, but the branch is deleted.

[arxanas]

@korrat that might be addressable in a fix for #1205, if you want to try it.