zit

A Fossil version-control system in Zig.

zit reads and writes Fossil's artifacts and speaks Fossil's sync protocol, so it clones from, pushes to, pulls from, and serves stock fossil, and a checkout means the same thing to both tools. It is written from the specifications, not ported from C: six Internet-Drafts frozen in docs/rfcs/ are the authority, and Fossil itself appears only in the differential tests that hold the two implementations to the same answer.

The zit binary is a thin command over a library — a Zig counterpart to libfossil. No module touches ambient time, randomness, filesystem, or network; effects arrive through injected interfaces, the sync client is a pure state machine, and the whole stack runs under seeded deterministic simulation where any failure replays exactly from its seed.

Download

Release binaries for macOS ARM64 and Linux x86-64/ARM64, with checksums and a source archive, are at fossil.craftdesign.group/zit and mirrored to GitHub releases. See the 0.6.2 release notes for changes and compatibility, and the 0.1.0 notes for the basis of the conformance claim.

What it does

The everyday verbs — init, add, commit, update, merge, diff, status, timeline, branch, tag, annotate, grep, bisect, stash, undo/redo, clone, push, pull, sync, serve — with Fossil's output shapes and Fossil's settings: .fossil-settings/ is read at every tier, and ignore-glob, clean-glob, manifest, and the rest mean what they mean in Fossil. zit help lists everything; any unambiguous prefix of a verb works.

Beyond that:

• Git in both directions — import-git and export-git, each checked against a real git in the differential suites.
• Sub-manifests (draft-fossil-submanifests-00) — S-card tree manifests bound per-commit manifest size on wide repositories, with adoption tooling that replays the repository's own history to measure whether enabling pays (submanifest analyze / enable; import-git picks a k the same way). This is the one compatibility break. A repository that emits S-bearing artifacts is permanently unreadable by stock Fossil, and sync's peer-version gate refuses to send trees to a pre-S peer rather than hand it artifacts it would misread. Emission is off by default; enabling it states the spend.
• Sparse cones (draft-fossil-sparse-cone-00) — partial worktrees (open --cone, cone).
• Indexer feeds — frames and crosslink stream raw artifacts and derived per-check-in records from a cursor, for a forge or a search index; info answers many names in one call, as text or JSON.
• Store care — verify (fsck), pack, purge, shun, and a local, disposable rebuild checkpoint that keeps cache-cold opens fast on large histories. Never stored in the repository, never synced.
• Review records — landing proposes a branch to land on trunk as a reviewable record; precedent reuses a remembered conflict resolution.

What it leaves to Fossil

By decision, not omission — zit is a version-control system, not a forge.

• The collaboration layer. Wiki, tickets, forum, technotes, and attachments are carried opaquely — stored and synced by hash, never interpreted. The web UI goes with them: zit ui hands the checkout to a forge that serves it.
• Unversioned files. No uv verb and no unversioned store. The uvfile sync vocabulary is fully parsed and content-verified on the wire, and a peer's unversioned files are declined visibly — the session completes and reports how many were not transferred.
• Manifest signing. Signature wrappers are recognized and stripped on read; zit never signs what it commits.
• SHA-1 repository creation. SHA-1 history clones and reads fine; zit init writes the sha3-256 naming policy only.
• Delta-manifest authoring on fresh repositories. A repository whose history carries delta manifests keeps its dialect; a flat repository stays flat.

The specifications

The drafts are the authority, not Fossil's source. Test expectations come from the spec text and its worked examples — every normative clause a module implements gets a test citing its section. Where Fossil's implemented behaviour and an earlier draft text disagreed, the draft was corrected in place and lists the change in its Changes appendix.

Module	Draft	What it specifies
delta	draft-fossil-delta-format-00	byte-level delta encoding
artifact	draft-fossil-artifact-format-00	manifest / control-artifact card format, naming, checksums
repostate	draft-fossil-repo-state-00	derived branch / tag / leaf / current-trunk views
submanifest	draft-fossil-submanifests-00	S-card tree manifests: bounded per-commit manifest size for wide repositories
sync	draft-fossil-sync-protocol-00	HTTP sync / clone protocol
cone	draft-fossil-sparse-cone-00	sparse cones: partial worktrees, the sparse-store path for monorepos

Build

Requires Zig 0.16 or later.

zig build --release=fast   # the shipped binary, at zig-out/bin/zit
zig-out/bin/zit version
zig build test             # unit tests, one cited test per RFC clause

--release=fast is what the release builds use; a plain zig build is a Debug binary, many times slower on a real history.

Further steps: zig build e2e (spawns the real binary), smoke (interop against a fossil on PATH), muscle (differential transcript against fossil), git-import-e2e / git-export-e2e (against a real git), dst (deterministic simulation; -- --seed N replays), fuzz -- <target> --seed N, bench, and cov (kcov line coverage). zig build --help lists them all.

Source control

This project is itself under Fossil. The repository lives in .zit.fossil (ignored); open a checkout with fossil open --keep .zit.fossil. Trunk is mirrored to GitHub, where issues and CI live.