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Jujutsu

Jujutsu (jj) is a version control system that can share a repository with Git: in a colocated repository, .jj/ and .git/ live side by side, and plain Git commands still work. git-splice doesn't work there yet (#41). This page says what it needs.

git-splice in a colocated repository​

jj keeps Git's HEAD detached, at the parent of the working-copy commit (@-). Every git-splice command that syncs with an upstream branch stops there, since it follows the branch named like the current one:

$ git splice status
!!   not on a branch (detached HEAD) -- git splice requires a named branch

Two branches​

git-splice reads two branches from Git, and maps each to a branch of the upstream (design):

In GitUpstream branchAlso used for
The current branch, which HEAD namesThe one with the same name, unless it's the default branch (next row)Which branch status, pull and push sync with
The default branch: origin/HEAD, else init.defaultBranchThe upstream's default-branch if .splice records one, else the same name as the default branch of what it lives inWhether clone and init record default-branch in .splice

jj has neither as Git has them. What could stand for each, and what's open:

  • The current branch. jj has bookmarks, but none is current: @ isn't on one, and a commit doesn't move a bookmark, so the one at @- may be missing or lag behind. Candidates are the bookmark at @-, the nearest bookmark among @'s ancestors, or a branch named explicitly, per command or in .splice (package managers). Each has to refuse when it finds none, or more than one.
  • The default branch. jj's trunk() revset names it: by default, the main, master or trunk bookmark of the remote. The bookmark's name would take the place of origin/HEAD.

What has to be settled (#41):

  • Which upstream branch, from the two branches above.
  • Which commit is HEAD. The working-copy commit @ holds the current changes, which Git sees as uncommitted.
  • Where pull and clone commit. A commit on a detached HEAD is imported by jj's next command, and should then be an ordinary change.