Native Jujutsu (jj) support

.github/workflows/ci.yml

@@ -36,6 +36,16 @@ jobs:
           sudo apt-get update
           sudo apt-get install -y git lua5.1 tmux
 
+      - name: Install jj
+        env:
+          JJ_VERSION: v0.46.0
+        run: |
+          mkdir -p "$HOME/.local/bin"
+          curl -fsSL "https://github.com/jj-vcs/jj/releases/download/${JJ_VERSION}/jj-${JJ_VERSION}-x86_64-unknown-linux-musl.tar.gz" \
+            | tar -xz -C "$HOME/.local/bin" ./jj
+          echo "$HOME/.local/bin" >> "$GITHUB_PATH"
+          "$HOME/.local/bin/jj" --version
+
       - name: Install Neovim
         uses: rhysd/action-setup-vim@v1
         with:

README.md

@@ -35,6 +35,9 @@ documents without distorting either one.
 - Merge conflict group in the commit panel with a local/result/remote resolver,
   editable result pane with editor integrations, gutter-guided accept actions,
   and resolve-on-write staging.
+- Native [Jujutsu (jj)](https://github.com/jj-vcs/jj) support: the same
+  review, hunk staging (squash workflow into `@-`), commit panel, log, compare,
+  and conflict resolution, plus `bin/diffbandit` as jj's merge and diff editor.
 - Recursive folder comparison with efficient external digest checks and child
   file diffs that return to the folder view.
 - One-column overview gutters that show changed regions proportionally across
@@ -262,6 +265,80 @@ list that command among its load triggers. Set `DIFFBANDIT_NVIM_APPNAME` to use
 a dedicated config (`NVIM_APPNAME`) or `DIFFBANDIT_NVIM` to pick the nvim
 executable.
 
+### External merge and diff tool
+
+The same script can be called with file or folder paths, outside any
+repository. This is how jj and git use it as an external tool:
+
+```sh
+diffbandit merge BASE LEFT RIGHT OUTPUT [--path P]  # 3-way merge; :w resolves
+diffbandit edit LEFT RIGHT     # editable folder/file diff (jj split, squash -i)
+diffbandit diff LEFT RIGHT     # read-only folder/file diff
+```
+
+A branch or path named `merge`, `edit`, or `diff` needs a leading `--`
+(`diffbandit -- diff`). `merge` writes `OUTPUT` when you `:w` the result. Quitting without resolving
+exits non-zero, so the conflict is kept. In `edit`, you edit the right side in
+place, through hunk apply actions or by hand, and `:w` saves each file. `:cq`
+aborts the operation.
+
+Git:
+
+```sh
+git config --global mergetool.diffbandit.cmd 'diffbandit merge "$BASE" "$LOCAL" "$REMOTE" "$MERGED" --path "$MERGED"'
+git config --global mergetool.diffbandit.trustExitCode true
+git config --global difftool.diffbandit.cmd 'diffbandit diff "$LOCAL" "$REMOTE"'
+```
+
+## Jujutsu (jj)
+
+In a jj workspace (colocated or not), every Git command, the launcher, and the
+panel switch to the jj backend automatically. Set `vcs.prefer = "git"` to
+force Git in a colocated repo. Revisions accept any jj revset.
+
+| DiffBandit | jj |
+|---|---|
+| unstaged view (default) | `@-` → `@` (what `jj diff` shows) |
+| staged view (`--cached`) | `@--` → `@-` |
+| all view | `@--` → `@`, with stage indicators |
+| stage hunk / file | move it from `@` into the staging change `@-` (`@`'s content is unchanged) |
+| unstage hunk / file | move it from `@-` back into `@` |
+| discard | restore the file in `@` from `@-` |
+| commit (`:w` in the panel) | describe the staging change and open a fresh one under `@`. With nothing staged, all of `@` is committed. Without a staging change, `jj commit` |
+| amend | stage into and re-describe the commit `@-` |
+| conflicts | `jj resolve --list` entries open in the merge resolver; `:w` writes the working copy |
+| checkout | `jj new <rev>` |
+
+This is the jj "squash workflow". The staging change is an undescribed,
+mutable `@-`, and `@` is your scratch space. If `@-` is a described commit (for
+example right after `jj commit`), your first stage from the unstaged view
+creates an empty staging change under `@` (`jj new --insert-before @`), so an
+existing commit is never changed by accident. To change that commit, turn on
+amend: it abandons an empty staging change left by the last commit, stages
+straight into `@-`, and `:w` rewrites its description. `jj.default_mode = "all"`
+opens the all view instead.
+
+To use diffbandit as jj's merge and diff editor (`jj resolve`, `jj split`,
+`jj squash -i`, `jj commit -i`), add this to `~/.config/jj/config.toml`:
+
+```toml
+[merge-tools.diffbandit]
+program = "diffbandit"   # bin/diffbandit on PATH
+merge-args = ["merge", "$base", "$left", "$right", "$output", "--path", "$path"]
+edit-args = ["edit", "$left", "$right"]
+diff-args = ["diff", "$left", "$right"]
+merge-tool-edits-conflict-markers = false
+
+[ui]
+merge-editor = "diffbandit"
+diff-editor = "diffbandit"
+```
+
+Current limits:
+- Conflicts with more than two sides, or that involve a deletion, are left to
+  `jj resolve`.
+- When `@` is a merge commit, the review lists only its conflicts.
+
 ## Default Keys
 
 Inside a diff view:
@@ -435,6 +512,12 @@ require("diffbandit").setup({
     },
     snap_key = "]s",
   },
+  vcs = {
+    prefer = "auto", -- "auto" (jj in jj workspaces), "git", or "jj"
+  },
+  jj = {
+    default_mode = "unstaged", -- or "all"
+  },
   git = {
     default_mode = "all",
     include_untracked = true,
@@ -649,6 +732,7 @@ diffbandit.git_compare("main", "feature")
 diffbandit.git_compare_branches({})
 diffbandit.git_checkout("feature")
 diffbandit.merge("path/to/conflicted-file")
+diffbandit.merge_files({ base = "B", left = "L", right = "R", output = "O" }) -- external 3-way merge
 diffbandit.commit_panel({})
 diffbandit.git_panel({})             -- working-tree changes, panel open on the first file
 diffbandit.launch({ "main...HEAD" }) -- what bin/diffbandit runs (git diff-style args)

bin/diffbandit

@@ -16,6 +16,14 @@ usage: diffbandit [--cached] [--no-untracked] [<rev> [<rev>] | <a>..<b> | <a>...
   <a>...<b>       read-only review of <b> against its merge base with <a>
   show <rev>      read-only review of a single commit
 
+External tool mode (jj merge-tools, git mergetool/difftool):
+  diffbandit merge <base> <left> <right> <output> [--path P]
+                  three-way merge; exits non-zero unless resolved with :w
+  diffbandit edit <left> <right>
+                  diff editor: edit the right folder/file (jj split, squash -i)
+  diffbandit diff <left> <right>
+                  read-only folder or file diff
+
 Environment:
   DIFFBANDIT_NVIM          nvim executable (default: nvim)
   DIFFBANDIT_NVIM_APPNAME  NVIM_APPNAME for a dedicated nvim config
@@ -38,8 +46,11 @@ if [ $# -gt 0 ]; then
   DIFFBANDIT_ARGV=$(printf '%s\037' "$@")
 fi
 DIFFBANDIT_ERRFILE=$(mktemp "${TMPDIR:-/tmp}/diffbandit.XXXXXX") || exit 1
-export DIFFBANDIT_ARGV DIFFBANDIT_ERRFILE
-trap 'rm -f "$DIFFBANDIT_ERRFILE"' EXIT
+# The merge subcommand records "resolved" here; quitting without resolving
+# must fail so jj/git keep the conflict.
+DIFFBANDIT_STATUSFILE=$(mktemp "${TMPDIR:-/tmp}/diffbandit-status.XXXXXX") || exit 1
+export DIFFBANDIT_ARGV DIFFBANDIT_ERRFILE DIFFBANDIT_STATUSFILE
+trap 'rm -f "$DIFFBANDIT_ERRFILE" "$DIFFBANDIT_STATUSFILE"' EXIT
 
 # Prefer the command: lazy plugin managers load the plugin on its commands,
 # not on require().
@@ -60,4 +71,8 @@ status=$?
 if [ -s "$DIFFBANDIT_ERRFILE" ]; then
   cat "$DIFFBANDIT_ERRFILE" >&2
 fi
+if [ "$1" = merge ] && [ "$status" -eq 0 ] && ! grep -q resolved "$DIFFBANDIT_STATUSFILE"; then
+  echo "diffbandit: merge not resolved (save the result with :w)" >&2
+  status=1
+fi
 exit $status

doc/diffbandit.txt

@@ -16,6 +16,7 @@ CONTENTS                                                     *diffbandit*
  11. Configuration                                 |diffbandit-configuration|
  12. Lua API                                       |diffbandit-lua-api|
  13. Testing                                       |diffbandit-testing|
+ 14. Jujutsu (jj)                                  |diffbandit-jj|
 
 ==============================================================================
 OVERVIEW                                            *diffbandit-overview*
@@ -309,6 +310,16 @@ lazy-loaded plugin should list that command among its load triggers.
 `DIFFBANDIT_NVIM_APPNAME` selects a dedicated config (`NVIM_APPNAME`) and
 `DIFFBANDIT_NVIM` the nvim executable.
 
+External tool mode works outside any repository:
+>sh
+  diffbandit merge BASE LEFT RIGHT OUTPUT [--path P]  # :w resolves
+  diffbandit edit LEFT RIGHT     # edit the right folder/file in place
+  diffbandit diff LEFT RIGHT     # read-only
+<
+`merge` exits non-zero unless the result was saved with `:w`, so jj and
+`git mergetool` (with trustExitCode) keep the conflict. See |diffbandit-jj|
+for the jj configuration.
+
 ==============================================================================
 COMMIT PANEL                                  *diffbandit-commit-panel*
 
@@ -558,6 +569,7 @@ LUA API                                              *diffbandit-lua-api*
   diffbandit.git_compare_branches({})
   diffbandit.git_checkout("feature")
   diffbandit.merge("path/to/conflicted-file")
+  diffbandit.merge_files({ base = "B", left = "L", right = "R", output = "O" })
   diffbandit.commit_panel({})
 
   diffbandit.toggle_stage_hunk()
@@ -587,4 +599,52 @@ they can verify connector geometry, backgrounds, underline spans, Git actions,
 commit panel behavior, binary diffs, and scrolling behavior.
 
 ==============================================================================
+
+==============================================================================
+JUJUTSU (JJ)                                                  *diffbandit-jj*
+
+In a jj workspace (colocated or not), the Git commands, the launcher, and the
+commit panel use the jj backend automatically. `vcs.prefer = "git"` forces Git
+in a colocated repository. Revisions accept jj revsets.
+
+The jj "squash workflow" maps onto staging:
+
+  unstaged view (default)   @-  -> @   (what `jj diff` shows)
+  staged view (--cached)    @-- -> @-
+  all view                  @-- -> @   (with stage indicators)
+  stage hunk/file           moves it from @ into the staging change @-
+                            (@ keeps its content)
+  unstage hunk/file         moves it from @- back into @
+  discard                   restores the file in @ from @-
+  commit (:w)               describes the staging change and opens a fresh
+                            one under @; with nothing staged, all of @ is
+                            committed; without a staging change, `jj commit`
+  amend                     stages into and re-describes the commit @-
+  conflicts                 `jj resolve --list` entries open the merge
+                            resolver; :w writes the working copy
+  checkout                  `jj new <rev>`
+
+The staging change is an undescribed, mutable @-. When @- is a described
+commit, the first stage from the unstaged view creates an empty staging
+change under @ (`jj new --insert-before @`), so an existing commit is never
+changed by accident. Amend changes that commit instead: it abandons an empty
+staging change left by the last commit, stages straight into @-, and :w
+rewrites its description. `jj.default_mode = "all"` opens the all view.
+
+Merge and diff editor for `jj resolve`, `jj split`, `jj squash -i`:
+>toml
+  [merge-tools.diffbandit]
+  program = "diffbandit"
+  merge-args = ["merge", "$base", "$left", "$right", "$output", "--path", "$path"]
+  edit-args = ["edit", "$left", "$right"]
+  diff-args = ["diff", "$left", "$right"]
+  merge-tool-edits-conflict-markers = false
+
+  [ui]
+  merge-editor = "diffbandit"
+  diff-editor = "diffbandit"
+<
+Conflicts with more than two sides, or that involve a deletion, are left to
+`jj resolve`. When @ is a merge commit the review lists only its conflicts.
+
  vim:tw=78:ts=8:ft=help:norl:

doc/tags

@@ -37,6 +37,7 @@ diffbandit-folder-diff	diffbandit.txt	/*diffbandit-folder-diff*
 diffbandit-git	diffbandit.txt	/*diffbandit-git*
 diffbandit-hunk-actions	diffbandit.txt	/*diffbandit-hunk-actions*
 diffbandit-installation	diffbandit.txt	/*diffbandit-installation*
+diffbandit-jj	diffbandit.txt	/*diffbandit-jj*
 diffbandit-launcher	diffbandit.txt	/*diffbandit-launcher*
 diffbandit-lua-api	diffbandit.txt	/*diffbandit-lua-api*
 diffbandit-mappings	diffbandit.txt	/*diffbandit-mappings*

lua/diffbandit/config.lua

@@ -108,6 +108,16 @@ local defaults = {
     prompt_message = "Reached final change in this diff. Open next file with changes?",
     on_request_next_file = nil,
   },
+  vcs = {
+    -- "auto": jj when the repository has a .jj workspace (and jj is
+    -- installed), git otherwise. "git" / "jj" force a backend.
+    prefer = "auto",
+  },
+  jj = {
+    -- Initial review mode in jj repos: "unstaged" (@- -> @, like `jj diff`)
+    -- or "all" (@-- -> @, with stage indicators for hunks already in @-).
+    default_mode = "unstaged",
+  },
   git = {
     default_mode = "all",
     default_scope = "repo",

lua/diffbandit/folder/init.lua

@@ -374,6 +374,9 @@ function Folder.start(left_path, right_path, config, opts)
   self.left_root = left_root
   self.right_root = right_root
   self.open_file_diff = opts.open_file_diff
+  -- Diff-editor mode: the right folder is edited in place (jj split etc.).
+  self.editable_right = opts.editable_right == true
+  self.hide_patterns = opts.hide or {}
   self.disposed = false
   self.expanded = {}
   self.filter = "all"
@@ -463,6 +466,10 @@ function Folder:refresh()
   self.active_jobs = 0
   self.pending_batches = {}
   local filters = folder_config(self).filters or {}
+  if #self.hide_patterns > 0 then
+    local exclude = vim.list_extend(vim.deepcopy(filters.exclude or {}), self.hide_patterns)
+    filters = vim.tbl_extend("force", {}, filters, { exclude = exclude })
+  end
   self.left_entries = folder_model.scan_tree(self.left_root, filters)
   self.right_entries = folder_model.scan_tree(self.right_root, filters)
   self.rows, self.rows_by_rel = folder_model.build_rows(self.left_entries, self.right_entries)
@@ -820,8 +827,14 @@ function Folder:restore_from_child(context)
   if context and context.selected_rel then
     self.selected_rel = context.selected_rel
   end
-  self:build_visible_rows()
-  self:render()
+  if self.editable_right then
+    -- The child diff may have written the right side: rescan so statuses
+    -- (and newly created files) are current.
+    self:refresh()
+  else
+    self:build_visible_rows()
+    self:render()
+  end
   if context and context.topline then
     local win = context.cursor_side == "right" and self.right_win or self.left_win
     if win and vim.api.nvim_win_is_valid(win) then

lua/diffbandit/git/init.lua

@@ -630,10 +630,6 @@ function M.queue(opts, config)
   return queue, nil
 end
 
-function M.current_branch(root)
-  return current_branch_label(root)
-end
-
 function M.root(opts)
   opts = opts or {}
   local uv = vim.uv or vim.loop
@@ -725,11 +721,13 @@ function M.log(root, opts)
 end
 
 function M.commit_metadata(root, rev)
-  local commits, err = M.log(root, { rev = "-1", max_count = 1 })
-  if not commits then
-    return nil, err
-  end
-  if rev and rev ~= "" then
+  local commits, err
+  if not rev or rev == "" then
+    commits, err = M.log(root, { rev = "-1", max_count = 1 })
+    if not commits then
+      return nil, err
+    end
+  else
     local args = { "log" }
     vim.list_extend(args, log_format_args())
     args[#args + 1] = "-1"
@@ -996,6 +994,10 @@ local function current_branch_label(root)
   return short and ("detached " .. short) or "detached HEAD"
 end
 
+function M.current_branch(root)
+  return current_branch_label(root)
+end
+
 local function commit_name(root, rev)
   local name = git_output(root, { "name-rev", "--name-only", "--exclude=tags/*", rev })
   name = name and vim.trim(name) or ""
@@ -1083,10 +1085,6 @@ function M.abs_path(root, path)
   return abs_path(root, path)
 end
 
-function M.relpath(root, path)
-  return relpath(root, path)
-end
-
 function M.git_output(root, args)
   return git_output(root, args)
 end
@@ -1584,4 +1582,18 @@ M._private = {
   split_char = split_char,
 }
 
+-- Worktree/buffer readers the jj backend reuses (the working copy is plain
+-- files in both systems).
+M._shared = {
+  abs_path = abs_path,
+  normalize_path = normalize_path,
+  read_worktree = read_worktree,
+  read_worktree_raw = read_worktree_raw,
+  read_worktree_symlink = read_worktree_symlink,
+  find_loaded_buffer = find_loaded_buffer,
+  has_modified_loaded_buffer = has_modified_loaded_buffer,
+  entry_uses_modified_buffer = entry_uses_modified_buffer,
+  worktree_mode = worktree_mode,
+}
+
 return M