zdump-rs 0.2.0

A bounded, independent Rust TZif witness/inspection companion to zic-rs — reads TZif, renders offset/is_dst/abbreviation at instants (POSIX-footer-projected beyond the last transition), lists transitions, and exposes leap records, as deterministic JSON. NOT a full zdump replacement.
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zdump-rs — a bounded, independent TZif witness (companion to zic-rs)

zic-rs is the compiler. zdump-rs is the witness/inspection companion. It is deliberately not a full zdump replacement — it is a narrow, independent Rust TZif reader that renders what a TZif file means (offset / is_dst / abbreviation) at explicit instants, as deterministic JSON witness rows, so the evidence court has a second, independently-written reader to cross-check against reference zdump.

Milestone: T23.zdump-witness.1 (Phase 1) · T23.zdump-witness.2 (Phase 2, current) — inside the zic-rs T23 evidence surface, not a new top-level milestone.

Published crate: https://crates.io/crates/zdump-rs · source: https://github.com/infinityabundance/zdump-rs (GitHub "No releases published" refers to GitHub Releases only — the crate is published on crates.io.)

Why it exists

Today zic-rs uses reference zdump as its semantic oracle (correct). A separate Rust reader adds an independent witness — sharing no code with zic-rs's own tzif module, so agreement between the two is real evidence, not a tautology. It is especially useful for right/-leap rendering, future Appendix-A microcases, golden TZif inspection, and eventual no-reference-zdump environments.

The evidence court now has four distinct roles:

compiler:                 zic-rs
format validator:         zic-rs  rfc9636::validate
oracle comparison:        reference zdump
independent Rust witness: zdump-rs   <-- this crate

What it does

Phase 1:

  • reads TZif v1/v2/v3/v4 (independent, bounds-checked reader; truncated/hostile input → Err, never a panic)
  • evaluates UT offset / is_dst / abbreviation at explicit UTC instants
  • emits deterministic JSON witness rows (fixed field order)

Phase 2:

  • interprets the POSIX footer — instants beyond the last explicit transition are projected (offset/is_dst/abbreviation), matching reference zdump far-future instead of guessing
  • lists transitions over a year window (the zdump -v analog: instant + before/after type)
  • exposes the leap-second table (--leaps), e.g. the 27 records in right/ zones
zdump-rs inspect     --tzif /usr/share/zoneinfo/America/New_York --at 2200-07-01T00:00:00Z   # footer-projected
zdump-rs inspect     --tzif fixtures/America_New_York.tzif --probe-default --json
zdump-rs transitions --tzif fixtures/America_New_York.tzif --from 2035 --to 2037 --json
zdump-rs transitions --tzif /usr/share/zoneinfo/right/Etc/UTC --leaps

Acceptance (Phase 1 + Phase 2, met)

Accepted when a Rust TZif witness can read selected TZif files, evaluate offset/is_dst/abbrev at explicit instants, project footer-governed future instants without guessing, list explicit transitions over a bounded window, render right/-leap explicit transitions + expose the leap table, cross-check against reference zdump on pinned fixtures, and continue refusing full zdump CLI/output parity.

  • tests/witness_golden.rs — pins witness + transition output to committed goldens for America/New_York, Europe/London, UTC, America/Vancouver (the real 2026a→2026b release-diff zone), and the right/ profiles (deterministic, no oracle); asserts right/UTC carries the full monotonic leap table.
  • tests/cross_check_zdump.rs — parses reference zdump -v and confirms zdump-rs agrees at probe instants including footer-projected far-future (2200) and the right/ zones (48/48 matched across 6 fixtures); auto-skips with a reason if zdump is absent.

Pinned fixtures + their sha256 in fixtures/SHA256SUMS (the America/New_York fixture is byte-identical to the matrix's New_York, e9ed07d7…).

Explicit NON-claims (guarded as hard as the capability)

not a full zdump replacement     not exact stdout/stderr parity     not all flags
not locale behaviour             not a replacement oracle           not civil-time truth

Phase-3 refinement (tracked, not claimed): for right/ zones the per-type offset/is_dst/abbreviation are reported correctly, but the TAI-scale wall-clock rendering near leap seconds (the 23:59:60 display) is not yet reproduced — only the transition/leap tables are surfaced.

Scope ladder

  • Phase 1 (done): witness reader — read TZif, evaluate at instants, emit JSON, cross-check zdump.
  • Phase 2 (done): transition listing over a window; footer-derived future projection; right/ leap-table exposure + leap-independent observation.
  • Phase 3: partial zdump CLI compatibility (-v, -c lo,hi, named zones) + TAI wall rendering near leaps — only after the witness core is correct.
  • Phase 4: full zdump replacement — only if scope is explicitly expanded.

Zero dependencies; #![forbid(unsafe_code)]; overflow-checks in release.