HEAD@git gets misplaced when the first non-root commit is edited in a colocated repo #1495

ilyagr · 2023-04-07T21:23:17Z

Let's say I do the following in an empty repo:

$ git init
Initialized empty Git repository in /home/ilyagr/dev/temp/a/.git/
$ jj init --git-repo=.
Initialized repo in "."
$ jj describe -m 'commit'
$ jj duplicate

At this point, things are OK. jj log looks like

◉  TQXLZQ ilyagr@ 58 seconds ago e3cfcf
│  (empty) commit
│ @  QSTUSW ilyagr@ 1 minute ago 684d5d
├─╯  (empty) commit
◉  ZZZZZZ @ 53 years ago 000000
   (empty) (no description set)

and git status reports "no commits yet". There isn't yet a HEAD.

If I then do jj co t && jj edit q, I end up in this bad state:

◉  TQXLZQ ilyagr@ 1 minute ago main HEAD@git e3cfcf
│  (empty) commit
│ @  QSTUSW ilyagr@ 1 minute ago 684d5d
├─╯  (empty) commit
◉  ZZZZZZ @ 53 years ago 000000
   (empty) (no description set)

Note how HEAD is in the wrong place.

The text was updated successfully, but these errors were encountered:

martinvonz · 2023-04-07T21:36:09Z

I think this is a limitation in Git. See the comment here:
https://github.com/martinvonz/jj/blob/cfdfc452dc9fecb3fd962dedbf0a183b91d502a8/lib/tests/test_git.rs#L743-L745

martinvonz · 2023-04-07T21:38:41Z

I think an alternative might be to create a placeholder branch when we export to git from this state.

I'll add a workaround for the root parent issue jj-vcs#1495 there. We can pass in the wc parent id instead of the wc_commit object, but we might want to use wc_commit.id() to generate a unique placeholder ref name.

I'll add a workaround for the root parent issue #1495 there. We can pass in the wc parent id instead of the wc_commit object, but we might want to use wc_commit.id() to generate a unique placeholder ref name.

I considered using the working-copy commit id to generate a unique ref, but the placeholder ref can be "born" by committing changes by git, and the ref name can conflict later by editing the original (hidden) commit. So I think it's better to generate a random name instead. Fixes jj-vcs#1495

As we can set HEAD to an arbitrary ref by using .reference_symbolic(), we don't have to manage a ref that can also be valid as a branch name. Fixes jj-vcs#1495

ilyagr added the 🐛bug Something isn't working label Apr 7, 2023

ilyagr added the colocated label Apr 7, 2023

ilyagr changed the title ~~Colocated repos misplace HEAD@git when the first non-root commit is edited~~ HEAD@git gets misplaced when the first non-root commit is edited in a colocated repo Apr 7, 2023

shavitmichael mentioned this issue Aug 8, 2023

BUG: jj checkout and HEAD@git out of sync #2011

Closed

yuja mentioned this issue Oct 4, 2023

git: add hack to unset Git HEAD by using random ref name #2330

Merged

4 tasks

yuja closed this as completed in a302090 Oct 4, 2023

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HEAD@git gets misplaced when the first non-root commit is edited in a colocated repo #1495

HEAD@git gets misplaced when the first non-root commit is edited in a colocated repo #1495

ilyagr commented Apr 7, 2023

martinvonz commented Apr 7, 2023

martinvonz commented Apr 7, 2023

HEAD@git gets misplaced when the first non-root commit is edited in a colocated repo #1495

HEAD@git gets misplaced when the first non-root commit is edited in a colocated repo #1495

Comments

ilyagr commented Apr 7, 2023

martinvonz commented Apr 7, 2023

martinvonz commented Apr 7, 2023