ziguard-rs

A faithful Rust port of upstream ziguard.awk — the IANA tzdb source-profile transformer that converts the tz source files into main, vanguard, and rearguard form.

zic-rs       compiles the source profiles correctly   (already proven, SOURCE-VARIANT.1)
ziguard-rs   reproduces the profile transformer itself (this crate, ZIGUARD-RS.1)

ziguard-rs is a companion to the Rust tzdb tooling ecosystem — especially zic-rs, which consumes these profiles and compiles them to TZif, and it sits alongside the witness tooling zdump / zdump-rs. ziguard-rs is the source-profile transformation layer — not part of the compiler core, but the producer-side step that makes the profiles in the first place, so that layer is Rust-native too. It does not redefine tzdb source policy; it reproduces the upstream transform.

The three roles form the source-profile loop:

ziguard-rs   source-profile transformation        (this crate — produce main/vanguard/rearguard)
zic-rs       source profile -> TZif compilation    (consume + compile)
zdump / zdump-rs   behaviour witness               (verify the result)

Install / use

cargo install ziguard-rs

Usage mirrors the upstream AWK-style stream model:

# with file arguments (as `awk -f ziguard.awk f1 f2 …` does), in $(TDATA) order:
ziguard-rs --format main      africa antarctica asia australasia europe \
                              northamerica southamerica etcetera factory backward > main.zi
ziguard-rs --format vanguard  africa … backward > vanguard.zi
ziguard-rs --format rearguard africa … backward > rearguard.zi

# or as a stdin filter:
cat africa … backward | ziguard-rs --format rearguard > rearguard.zi

--format is required (main | vanguard | rearguard). With no file arguments it reads stdin.

Correctness — how it's proven

Correctness is not asserted from the code; it is the byte-identical match against the real awk oracle and the upstream-distributed profiles.

• Full-source oracle (tests/oracle.rs): over the complete pinned tzdb-2026b source set, the three outputs match the upstream-distributed SHA-256 exactly: main e0225823…, vanguard 49e16da4…, rearguard 91c4f362… — the same hashes IANA ships and that zic-rs independently pins. The source is admitted with sha256 ffad46a0… + OpenPGP GOODSIG (Paul Eggert, 7E37…7E34).
• Upstream's own ziguard.ck: round-tripping the forms (rearguard∘vanguard = rearguard, vanguard∘rearguard = vanguard) reproduces upstream's consistency check.
• All IANA releases (reports/release-all/): across 48 signed release bundles (2016g→2026b), ziguard-rs is byte-identical to the 2026b ziguard.awk it ports over all 38 releases that ship the script — zero port bugs; and reproduces the 6 releases (2024b→2026b) whose shipped script is unchanged exactly. Older releases differ only by the script's own evolution (recorded, not hidden).
• Per-rule fixtures (tests/rules.rs): each transform class (Czechoslovakia / Ireland / Namibia / Portugal / Morocco / Japan / Etc/GMT↔GMT / %z↔explicit-abbr / link dedup / link-chain shortening / #STDOFF) localised to an awk-derived golden.
• Kani (#[cfg(kani)]): 3 bounded proofs on the pure arithmetic helpers (numeric-prefix slice bounds, abbreviation-arithmetic non-overflow, field-index bounds) — see reports/kani/.
• Fuzzing (fuzz/): transform + the helpers; one hostile-input overflow found, fixed (saturating arithmetic — byte-identical on real data), and re-verified clean — see reports/fuzz/.

cargo fmt --check && cargo clippy --all-targets -- -D warnings && cargo test   # the gate

What this does and does not claim

It claims: to reproduce the 2026b ziguard.awk transformation byte-for-byte for admitted tzdb releases, and to reproduce the distributed main/vanguard/rearguard profiles where the upstream script is unchanged.

It does not claim:

• to redefine or own tzdb source policy, or to be a new profile standard;
• civil-time truth, or to replace upstream IANA authority;
• to reproduce older releases' shipped profiles — those used an earlier ziguard.awk (the difference is the script's, recorded in the campaign receipt, not a port error);
• all future ziguard.awk behaviour forever, or correctness beyond the pinned admitted releases.

Single dependency: regex (an AWK port is fundamentally an ERE transformer). The crate's own code is #![forbid(unsafe_code)].

License

Apache-2.0. Upstream ziguard.awk is in the public domain (Paul Eggert); this is an independent Rust reimplementation.