The Mizan codegen substrate moves off JavaScript template-literal emission
onto a compiled Rust binary that consumes the same OpenAPI + x-mizan-* IR
the JS substrate consumed. Three structural wins fall out of one move:
1. Moat closes. The codegen logic (how `affects` becomes auto-invalidation,
how named contexts collapse onto bundled fetches, how the registry-to-
Provider mapping is shaped) ships compiled instead of as source bytes
in every consumer's node_modules.
2. Pattern F (lines.push append-walls) becomes structurally unauthorable.
The emit substrate is askama templates in templates/<target>/*.j2 —
actual target-language files with {{ ... }} substitution markers,
syntax-highlighted natively, type-checked against the render context
structs at compile time. The Rust emit modules build typed render
contexts and call .render(); no string-builder surface exists.
3. OpenAPI `default`-bearing fields now emit as non-optional in TS / Python
/ Rust — the server always populates them, so consumer code reads them
without nullable checks. Surfaced by Blazr's typecheck on regeneration.
Layout:
frontends/mizan-rust/ — Rust port of @mizan/base; #[cfg(feature="pyo3")]
exposes PyMizanClient for the Python target.
protocol/mizan-codegen/ — codegen binary source + askama templates.
protocol/mizan-generate/ — npm-package shim. bin/launcher.mjs dispatches
to the platform-appropriate prebuilt binary.
Old generator/ JS tree deleted.
tests/rust/ — wire-parity drivers. drive_kernel exercises
raw client.call() / fetch_context(); drive_emitted
exercises the typed crate the codegen emits.
tests/afi/afi_codegen_app.py — codegen entrypoint module (imports + registers).
backends/mizan-fastapi/.../schema.py — adds outputNullable so the Rust
codegen can wrap T | None responses in Option<T>.
Verification:
- 20 mizan-codegen tests green (IR deserialization, byte-equivalent
parity vs JS baseline for stage1/rust/python/react/vue/svelte,
structural test for channels).
- tests/rust/run_wire_parity.py — 12/12 probes green via the Rust binary
driving the FastAPI fixture end-to-end.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Substrate-level gate: same @client fixture registered in both backends
emits equivalent schemas, therefore the codegen produces equivalent
TypeScript regardless of which backend the frontend is generated against.
Catches adapter symmetry problems (Pydantic→OpenAPI converter divergence,
metadata leakage, ordering non-determinism) without docker, browser, or
Playwright.
What ships:
backends/mizan-fastapi/src/mizan_fastapi/schema.py — build_schema():
- Builds OpenAPI 3.0 from registered Mizan functions, mirroring the
shape mizan-django's export emits.
- Drives FastAPI's native OpenAPI generation by registering a stub POST
endpoint per function with its Input/Output Pydantic models, then
appends x-mizan-functions and x-mizan-contexts extensions.
- Param-elevation logic mirrors mizan-django/src/mizan/export/__init__.py
exactly (sharedBy tracking, required iff every function in context has
the param).
- snake_to_camel and metadata field shapes match Django for byte-equality
on the AFI surface.
tests/afi/ — the conformance harness:
- fixture.py: 5 @client functions covering the protocol axes (plain,
context, mutation+affects). No channels/forms — those aren't AFI-common.
- django_app/: minimal Django project (settings, urls, AppConfig.ready
registers the fixture). manage.py adds tests/afi/ to sys.path so both
backends import the same fixture module.
- fastapi_app.py: thin make_app() that registers fixture and mounts router.
- schema_normalizer.py: drops backend-specific framing — Ninja-vs-FastAPI
envelope differences (info/servers/tags), Django-only function fields
(form metadata), x-mizan-channels. Plus afi_subset() and
function_io_schemas() helpers for narrower comparisons.
- test_codegen_parity.py: three gates
1. x-mizan-functions match across backends
2. x-mizan-contexts match across backends
3. Per-function Input/Output OpenAPI schemas match (what codegen feeds
to openapi-typescript for type generation)
The full normalized OpenAPI envelopes do diverge — FastAPI adds
HTTPValidationError, the two converters wrap things slightly differently
in non-AFI-essential ways. That's not in the test scope. The codegen
only consumes x-mizan-functions, x-mizan-contexts, and the per-function
type schemas; those are what the test gates.
Makefile: test-afi target added; rolls into the test aggregate.
Verified: 3/3 conformance tests pass. Other surfaces unaffected —
mizan-core 15/15, mizan-django 348 pass, mizan-fastapi 11/11.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
