Add Jujutsu (jj) support

[nvahalik]

Summary

• Adds Jujutsu as a third VCS backend alongside git and hg. DetectVCS checks .jj before .git so colocated jj+git repos resolve as jj — reads go through the jj working-copy model instead of bypassing it via git.
• Jj renderer translates git-style refs (HEAD → @-, HEAD~N → @ plus N+1 dashes, A..B → --from/--to) to jj revsets, runs jj diff --git --context=1000000, and feeds the result through the existing parseUnifiedDiff pipeline. jj emits raw bytes for binary files instead of the Binary files … differ marker, so a pre-parse pass rewrites such hunks to re-use the existing binary placeholder path.
• --all-files now supports jj via NewJjDirectoryReader backed by jj file list. DirectoryReader became lister-pluggable (git remains the default; Mercurial is still unsupported for --all-files).
• FileBlame uses jj file annotate -T <tab-separated-template> mirroring the hg blame pattern.
• --staged warns and ignores on jj (no staging area), matching hg behavior.

Test plan

• go test ./... passes (race + coverage intact)
• go vet ./... clean
• golangci-lint run — jj files clean (3 pre-existing exhaustive warnings in app/ui/model.go/overlay/annotlist.go remain, untouched by this PR)
• Unit + e2e jj tests cover DetectVCS, ref translation, diff range flag building, rename summary parsing, binary synthesis, blame template parsing, UntrackedFiles, --all-files via jj file list
• Renderer setup tests cover default / --only / --all-files / --include / --exclude
• Manual smoke test against a real colocated jj+git repo

🤖 Generated with Claude Code

[nvahalik]

First off, I can't thank you enough for this! I happened to stumble across it while looking for something that does this and this seemed like a great starting off point.

I've made these changes and have been playing around with it now locally for doing diff and something-akin-to-interdiff for my own purposes.

I suppose the biggest changes are that JJ's revsets are now supported as an option (i.e. revdiff <rev> works) and that JJ's blame support now also works.

[Copilot]

Pull request overview

Adds Jujutsu (jj) as a third VCS backend in app/diff, expanding revdiff’s repo detection and rendering pipeline beyond git and Mercurial while keeping output compatible with the existing unified-diff parser.

Changes:

• Add jj backend: VCS detection (.jj precedence), diff rendering via jj diff --git, ref translation, binary-diff synthesis, and blame via jj file annotate.
• Extend --all-files to support jj by making DirectoryReader file listing pluggable (git ls-files / jj file list).
• Update docs, site pages, and plugin reference docs to reflect jj support and --all-files limitations.

Reviewed changes

Copilot reviewed 19 out of 19 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
site/index.html	Update marketing copy to include jj support and --all-files backend availability.
site/docs.html	Update user docs: requirements, colocated jj+git behavior, and --all-files support matrix.
plugins/codex/skills/revdiff/references/usage.md	Update Codex plugin usage docs for --all-files (git or jj).
plugins/codex/skills/revdiff/references/config.md	Update Codex config reference for --all-files (git and jj only).
docs/ARCHITECTURE.md	Document jj backend, detection precedence, and pluggable all-files lister.
app/renderer_setup_test.go	Add renderer-setup tests for jj (default/only/all-files/include/exclude).
app/renderer_setup.go	Wire up VCSJJ, makeJjRenderer, and --staged warning behavior for jj.
app/diff/vcs_test.go	Add tests for jj detection and jj-over-git precedence in colocated repos.
app/diff/vcs.go	Add VCSJJ and check .jj before .git / .hg.
app/diff/jjblame_test.go	Unit + integration tests for jj annotate parsing and blame behavior.
app/diff/jjblame.go	Implement jj blame via jj file annotate -T parsing.
app/diff/jj_test.go	Add ref translation, range flag, summary parsing, binary synthesis, and e2e jj tests.
app/diff/jj.go	Implement jj renderer: diff, summary parsing, ref translation, binary synthesis, command runner.
app/diff/directory.go	Make DirectoryReader lister-pluggable and add NewJjDirectoryReader.
app/config.go	Update --all-files flag description to include jj support.
README.md	Update requirements and feature list to include jj support.
CLAUDE.md	Update repo documentation to reflect jj support and behavior.
.claude-plugin/skills/revdiff/references/usage.md	Update Claude plugin usage docs for --all-files (git or jj).
.claude-plugin/skills/revdiff/references/config.md	Update Claude plugin config reference for --all-files (git and jj only).

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[Copilot]

This comment says we rely on a “5-way Split”, but the implementation uses strings.SplitN(row, "\t", 4) (4 fields total, max 3 separators). Please correct the comment to avoid confusion about the parsing contract (especially around embedded tabs in the content field).

Suggested change

	// content ends with \n (except possibly the final line). We rely on a 5-way
	// Split (max 4 separators) so embedded tabs in content don't confuse us.
	// content ends with \n (except possibly the final line). We rely on a 4-way
	// SplitN (max 3 separators), leaving the remainder in content so embedded tabs
	// in content don't confuse us.

[Copilot]

FileDiff calls jj diff --git and then normalizes binary output after the fact. Since jj can emit raw bytes for binary files, this can force the process to read/hold very large stdout in memory just to synthesize a small “Binary files … differ” marker. Consider adding a size bound or streaming/canceling approach that detects NULs early and stops reading once the diff header is available.

[Copilot]

The comment for blameTargetRef doesn’t match the actual behavior: this function returns "" for empty refs and for single-sided ranges ("..rev" / "rev.."), which causes FileBlame to omit "-r" entirely. Please update the comment (and/or logic) so it accurately reflects whether jj annotate defaults to the working copy when -r is omitted, and what the intended behavior is for single-sided ranges.

Suggested change

	// Unlike git, jj can't implicitly blame the working copy — we always need to name
	// a revision. Empty and single-sided ranges fall back to "@" (working copy).
	// For fully specified ".." and "..." ranges, blame uses the right-hand side.
	// For a plain non-empty ref, that ref is translated and returned directly.
	// Empty refs and single-sided ranges ("..rev" / "rev.." / "...rev" / "rev...")
	// return "", which causes FileBlame to omit "-r" and let `jj file annotate`
	// use its default revision behavior.

[umputun]

the Go code looks solid, clean implementation following git/hg patterns. tests are good, binary diff synthesis is a nice catch. couple of things before merge:

1. rebase needed - branch is behind master (we merged a structural refactor, dep bumps, and mktemp fix since). the dep downgrades and stale switch statement changes in model.go/annotlist.go will resolve on rebase

2. runJj duplicates runVCS in jj.go:274. the only difference is extraArgs prepending. could prepend to args and call runVCS(j.workDir, "jj", fullArgs...) instead

3. skill/plugin not jj-aware - the Claude Code skill (detect-ref.sh) is entirely git-based. in a jj repo every git command in that script fails. this doesn't have to be in this PR, but I'd like to track it. could you open an issue for jj support in detect-ref.sh?

4. history module - history.Service.gitCommitHash() returns empty for jj repos since gitRoot is empty. not a blocker, just worth a comment somewhere

the .jj-before-.git detection order makes sense for colocated repos. I checked and jj does need its own backend, git diff gives wrong results in jj repos due to the detached HEAD / working-copy-as-commit model

[nvahalik]

Re: #4 (history module) — leaving this as-is for now, but here's what a fix would look like:

gitCommitHash(), gitDiff(), and filterRepoFiles() all shell out to git directly. For jj support, the cleanest path would be adding VCSType to history.Params and dispatching per-method:

method	git (current)	jj equivalent
gitCommitHash	git rev-parse --short HEAD	jj log -r @ --no-graph -T 'commit_id.short(8)'
gitDiff	git diff / git diff --cached	jj diff
filterRepoFiles	filepath.Rel(gitRoot, ...)	same logic, just needs a non-empty root

The GitRoot field in Params would become VCSRoot (or just get populated for jj repos too — the caller in history_save.go already has access to the workdir from VCS detection).

[umputun]

runJj refactor in 9cd28f8 looks clean, thx. tests pass, lint clean.

LGTM, merging. a few minor doc nits I'll clean up in a follow-up commit:

1. jjblame.go:61 - "5-way Split" comment is wrong, SplitN(row, "\t", 4) produces 4 fields (Copilot A)
2. jjblame.go:34 - blameTargetRef godoc misdescribes the mechanism. code is correct: empty/single-sided ranges return "" so FileBlame omits -r and jj defaults to working copy (Copilot C)
3. directory.go:25 - NewDirectoryReader godoc still says "must be inside a git repository", stale now that the lister is pluggable

on Copilot B (binary stdout buffering in jj.go:147) - real issue, runVCS uses cmd.Output() so a multi-MB binary gets buffered just to synthesize a one-line marker. not a blocker, will track as a follow-up issue.

thx for the jj support!