# Changelog

All notable changes to this crate are documented here. The format is
based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/), and
this crate adheres to [Semantic Versioning](https://semver.org/).

## [0.2.0] - 2026-08-17

A breaking release that replaces the v0.1.0 `AlkType:*` custom-keyword
JSON Schema format with BAST (Binary Abstract Syntax Tree) — a JSON
document that describes binary layouts using a `kind`-based vocabulary
with `$defs`/`$ref` for composition. BAST is itself a valid JSON Schema
instance (it has a meta-schema), making it self-validating,
editor-friendly, and trivially consumable from any language with a JSON
parser. The engine works the same way as before: compile a document
once into an `AlkTypeEngine`, then read/write fields at computed offsets
and validate bytes/JSON. The pivot was made now because v0.1.0 has no
real consumers (≈15 crates.io downloads, mostly bots/scanners), so the
custom-keyword wart could be removed cleanly.

### Breaking changes

- **Schema format.** The v0.1.0 `AlkType:*` custom-keyword JSON Schema
  format (`{ "AlkType:Struct": true, "fields": [...] }`) is removed.
  Schemas are now BAST documents:
  `{ "$defs": { "<TypeName>": { "kind": "struct", "fields": [...] } } }`.
  The `kind`-based vocabulary covers 18 binary kinds (integers, floats,
  bytes, string, struct, union, enum, array, etc.).
- **`AlkTypeEngine::compile` signature.** Now takes
  `(bast_doc: &Value, root_name: &str, mode: LayoutMode, json_schema: Option<&Value>)`.
  The root type name is a required parameter — it selects which `$defs`
  entry is the top-level type (previously the root was implicit from the
  single top-level schema object).
- **Builder API output.** `Definitions`/`Schema`/`Discriminator` now
  produce BAST JSON via `Definitions::build_doc(name, schema)`. The
  builder method names are unchanged; only the emitted JSON shape
  changed. `Schema::struct_()` produces a BAST struct;
  `Schema::object()` produces a standard JSON Schema (for the
  `validate_json` path).
- **Validation split.** v0.1.0 used a single `jsonschema` validator
  with 19 custom `AlkType:*` keywords for both bytes and JSON
  validation. 0.2.0 splits this into two independent paths:
  - `validate_bytes` uses a new BAST-native validator
    (`bast_validation`) — a recursive walker over the BAST type tree.
  - `validate_json` / `is_valid_json` use a standard
    `jsonschema::Validator` built from a consumer-provided JSON Schema
    (passed to `compile` as the `json_schema` parameter). No custom
    keywords; BAST is not involved — BAST describes bytes, not JSON
    shape.
  Both paths return `AlkTypeError::Validation` with a uniform
  `jsonschema::ValidationError<'static>` payload.
- **Removed.** The v0.1.0 custom-keyword accessor layer
  (`AlkTypeKind::FromStr`, `parse_*`, `resolve_ref*`,
  `DiscriminatorKind`) is removed. The BAST parser (`bast` module)
  exposes a cleaner typed surface (`BastDoc`/`BastDef`/`BastStruct`/
  `BastField`/`BastType`/etc.) that borrows from the source
  `serde_json::Value` without cloning field data.
- **Public module surface.** New public modules: `bast`, `bast_meta`,
  `bast_validation`, `builder`, `materialize`. The `schema` module is
  retained but now holds only `Endian`/`AlkTypeKind`/`VariableEncoding`
  (the binary-kind vocabulary); the v0.1.0 custom-keyword machinery is
  gone.

### Additions

- **BAST meta-schema.** Embedded in the crate as
  `BAST_META_SCHEMA` (re-exported from the crate root) and published at
  `https://alk.dev/bast/v1/schema`. BAST documents are validated against
  it at compile time (`AlkTypeEngine::compile` calls
  `validate_bast_doc` before parsing).
- **`materialize` module.** Materializes a `serde_json::Value` tree from
  a binary buffer by walking the BAST typed tree. Used by
  `AlkTypeEngine::validate_bytes` (ADR-010).
- **Builder for JSON Schemas.** `Schema::object()` produces a standard
  JSON Schema object (for the `validate_json` path), complementing
  `Schema::struct_()` which produces a BAST struct (for the bytes path).
  One builder, two output shapes — the method name selects which.

### Bug fixes vs v0.1.0

- **Enum index bounds are now checked.** The v0.1.0 validator had a
  dead constraint: enum variant indices were never bounds-checked
  against `values.len()`. The BAST-native validator enforces it
  (`validate_enum` checks `idx < values.len()`).
- **Offset-indirect, field-level endian, and aligned materialization**
  bugs found during review #003 are fixed.

### Non-breaking improvements

- `$ref` is restricted to `#/$defs/<name>` — one hash lookup, no
  `normalize_refs` pass (the v0.1.0 engine needed one).
- Schemas remain untrusted input: every engine path that walks a BAST
  document returns `Err` on a malformed document, never `panic!`/
  `unreachable!`. Overflow-safe arithmetic (`checked_add`,
  `usize::try_from`) on all offset/count casts.
- Still two dependencies (`jsonschema` with `default-features = false`,
  `serde_json` with `preserve_order`), no `async`, no `unsafe`, no
  platform deps, no feature flags. Compiles to
  `wasm32-unknown-unknown`.

### Upgrade notes

There is no migration path from v0.1.0 `AlkType:*` schemas — the format
is incompatible. Rewrite schemas as BAST documents (the `builder` API
produces them; see the README usage example) and update `compile` calls
to pass the root type name and the optional JSON Schema. The
read/write/validate API surface (`read_field`, `write_field`,
`sequential_reader`, `validate_bytes`, `validate_json`,
`is_valid_json`) is unchanged.

## [0.1.0] - 2025-11-10

Initial crates.io release. Custom-keyword JSON Schema format
(`AlkType:*`), single `jsonschema` validator for both bytes and JSON,
`AlkTypeEngine` with packed/aligned layout modes, builder API producing
`serde_json::Value`.

[0.2.0]: https://git.alk.dev/alkdev/alktype/releases/tag/v0.2.0
[0.1.0]: https://git.alk.dev/alkdev/alktype/releases/tag/v0.1.0