spec/vectors/decode_vectors.txt -- 37 committed byte strings across five
surfaces, each with its normative accept/reject verdict. The reference
implementation's fuzzers prove its own decoders self-consistent, which says
nothing about whether a foreign decoder agrees with the format. This is what one
is checked against. Gated in the conformance suite as [7d], and drift-locked:
the committed file must equal vectors::render(), so a wire-format change lands
in the diff.
It found a real defect on its first run. OperationKindTag::TransposeInterval
encoded to [30] and its own decoder REJECTED it -- Push 4a added the variant to
discriminant() and never to decode_canonical. OperationKindTag is what edit
barriers persist, so a barrier prohibiting TransposeInterval could be written and
never read back. Silent data loss on reopen.
Four things should have caught it. None did, and two made it worse:
The round-trip test enumerated DISCRIMINANTS -- (0u8..30).map(decode_canonical)
-- starting from bytes the decoder already knew, so it structurally could not
notice a variant the decoder was missing. It now enumerates VARIANTS from one
all_tags() list, with a completeness check in both directions.
The distinctness test's hand-written variant list omitted it too. Same list now.
operation_kind_tag_decode_rejects_malformed_bytes asserted that tag 30 is
REJECTED, and layout-ir's decode_rejects_unknown_discriminants asserted the
same at the barrier surface. Both were locking the bug in place and made it
look deliberate. Both now name 31, and a new barrier test round-trips a barrier
prohibiting every tag -- the persistence surface where this actually bites.
The P2 decode fuzzer fed valid corpus bytes to the tag decoder and tallied the
failure as a REJECTION, like any garbage input. It never asserted that an
unmutated corpus entry decodes. Both fuzzers now do, as a pre-pass.
The harness had the same disease as the code. `check` collapsed "rejected" with
"accepted but does not re-encode", so a decoder that silently normalizes
non-canonical bytes PASSED the reject vectors it was written to catch. Verified:
removing the whole-state guard, and restoring the lenient compression codec, both
left the corpus green. `check` now returns Ok(injective) for accept and Err for
reject and never conflates them -- silently normalizing non-canonical bytes IS
accepting them. With that fixed, all four defect mutations fail the corpus, each
naming its class.
The corpus pins one vector per class this repo has shipped a bug in:
non-canonical-map-order (a guard catches it; no per-site check exists),
non-canonical-vec-order (only a per-site check catches it; a guard is blind),
lenient-sub-codec (a guard masked it in the manifest; the index had none), plus
trailing-bytes, truncated, unknown-discriminant, count-exceeds-remaining. A test
fails if one goes missing.
Gate: fmt clean, clippy 0, 30 targets / 1024 passed / 0 failed, docs 0 under
-D warnings, conformance 8/8 (now including [7d]), zero golden churn.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Levi Neuwirth
a41596d329