Emacs

project.el

Emacs modes like eglot, the first-party LSP integration, rely on project.el to discover workspace roots. PR for JJ project root detecting is merged. but not included in released version(Planed to included on v2.9). Install projectile from git or add below codes on your emacs config. project.el's heuristics include checks for .git, which will fail in jj repositories that are not colocated. This can be addressed by adding ".jj" to project-vc-extra-root-markers, e.g.:

(use-package project
  :config
  (add-to-list 'project-vc-extra-root-markers ".jj"))

ediff as a merge tool

.jjconfig.toml

[merge-tools.ediff]
program = 'sh'
merge-args = ['-c',
  'emacsclient -c --eval "(ediff-merge-files-with-ancestor \"$0\" \"$1\" \"$2\" nil \"$3\")"',
  '$left', '$right', '$base', '$output']