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 this repository 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 — whose modules take no ambient time, randomness, filesystem, or network, so the whole stack runs under seeded deterministic simulation.

Download

Download Zit 0.3.35 for macOS ARM64 or Linux x86-64/ARM64, or get the source archive, or read the release notes.

Releases are also mirrored to GitHub.

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, ignore-glob, clean-glob, manifest, and the rest mean what they mean in Fossil.

Beyond that:

• Git in both directions — import-git and export-git.
• Sub-manifests — bounded per-commit manifest size for wide repositories (submanifest analyze / enable). Off by default; a repository that turns them on is no longer readable by stock Fossil, and sync refuses to hand such artifacts to a peer that would misread them.
• Sparse cones — 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 search index.
• Store care — verify, pack, purge, shun, and a local rebuild checkpoint that keeps cache-cold opens fast on large histories.
• Sync at Fossil's scale — clusters are indexed, announced bounded, and minted at Fossil's own thresholds, so a no-op pull of a million-artifact repository sends kilobytes, not the whole inventory; clone streams to disk as it arrives.
• A write plane for forges — the machine verbs wiki, ticket, forum, technote, and attach author Fossil's collaboration artifacts, landing proposes and lands a branch as an ordinary forum thread, and attach list reads attachments back. Each is one line of stdout, exact exit codes, and works against a bare store with -R — the seam quarry writes through.
• Signed check-ins — commit --sign clearsigns the manifest through Fossil's own pgp-command contract, and the signature survives pack, verify, and sync byte-exact.

What it leaves to Fossil

By decision, not omission. zit authors and syncs the collaboration artifacts but renders none of them: the web UI belongs to a forge (zit ui hands off to one that serves the repository), and wiki, tickets, forum threads, and technotes are read there rather than here. There is no unversioned-file store; a peer's unversioned files are declined visibly. zit never creates a SHA-1 repository, though it reads one.

The specifications

The drafts under docs/rfcs are the sole authority. Expected values in tests come from the spec text and its worked examples, never from observing another implementation; where the code follows Fossil's implemented behaviour against the published text, the divergence is recorded in docs/rfcs/erratum.

Layer	Draft	Specifies
delta	draft-fossil-delta-format-00	byte-level delta encoding: copy/literal segments, base-64 integers, mod-2³² checksum
artifact	draft-fossil-artifact-format-00	card-structured manifests and control artifacts, content addressing (SHA-1 / SHA3-256), checksums
repostate	draft-fossil-repo-state-00	branch, tag, and leaf state derived from the append-only artifact set
submanifest	draft-fossil-submanifests-00	S-card tree manifests: bounded per-commit manifest size for wide repositories
sync	draft-fossil-sync-protocol-00	HTTP replication of the artifact set between repositories
cone	draft-fossil-sparse-cone-00	sparse cones: partial worktrees and the sparse-store path for monorepos

Building

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
zig build smoke            # interop check against a fossil binary on PATH

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

Finding your way

• Timeline — current activity and history
• Source tree — browse the code at trunk
• README — design notes, scope, and build steps
• Release notes — every release, oldest to newest
• Technotes — engineering notes on how and why things changed
• docs/rfcs — the six frozen drafts
• GitHub mirror — issues and CI