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Phase 6: Mochi extern fn emitter

Phase 6 produces the Mochi-side counterpart to the Phase 5 Python wrapper. It takes the wrapper.Wrapper.Items list and emits a Mochi source file (<package>_shim.mochi) the importing program loads as if hand-written, plus a content-hash that the lockfile pins (wrapper-sha256).

Gate​

go test ./package3/python/emit/... is green. The gate covers:

  • The EmitShim entry point: validates a non-nil wrapper with a non-empty package, computes deterministic output, and reports a SHA-256 over the rendered Source.
  • Header banner: emits an auto-gen comment carrying the generator identifier, source package name, item count, skip count, and async loop mode. Can be suppressed via Options.Header = false.
  • Function emit: extern python fun <name>(P1, P2): R, with the async wrapper rendering : async R per Phase 4's lowering of Awaitable[T].
  • Record emit: typed type <Name> = { field1: t1, field2: t2 } Mochi record alias when the wrapper resolved a structural Fields list; field-less records (and any record where Phase 4 left the body opaque) surface as extern python type <Name> instead.
  • Interface emit: extern python type <Name> (Protocol semantics travel through the wrapper at call time; the .pyi carries the structural shape downstream typing needs).
  • Constant emit: extern python var <NAME>: <type>.
  • Grouping: records, opaque externs, constants, functions. Within each group, items appear in SourceName order.
  • Skip report: trailing // SKIPPED items block lists the Phase 5 / Phase 4 refusals with reason tokens; suppressible via Options.IncludeSkipReport = false.
  • Determinism: same Wrapper + Options produces the same Source and SHA-256 across calls.
  • Sentinel TestPhase6ExternEmit walks a representative .pyi end-to-end through stubs.ParsePYI -> wrapper.Synthesise -> EmitShim and asserts the emitted shim contains the expected typed record, opaque interface, extern var, async extern fn, and skip line.

Files​

  • package3/python/emit/doc.go — package overview.
  • package3/python/emit/shim.go — Shim, Decl, DeclKind, Options, EmitShim entry point + per-kind renderers (function, record, interface, constant).
  • package3/python/emit/shim_test.go, phase06_test.go — ~25 tests covering the gate above.

Fixtures​

The unit tests construct Wrapper.Items values directly and round-trip a representative .pyi through the Phase 3 -> 5 -> 6 pipeline. Corpus-wide validation against the 25-package fixture set lands with Phase 8 (build orchestration), where the shim is exercised against actual MEP-51 build flows.

Skip count​

Phase 6 does not introduce its own refusal cases; it forwards the Phase 4 / Phase 5 Wrapper.Skipped slice into the trailing comment block. The expected SkipReport count per fixture is therefore identical to Phase 5's.

Notes​

  • extern python type is the opaque marker form for both Protocols and structure-less records. The MEP-71 §3 type table notes that the wrapper carries dispatch and the .pyi carries the structural surface; the Mochi side does not need a structural form here.
  • The shim does not emit import python ... (Phase 7's surface). The importing program continues to use a regular import "./python_wrap/<pkg>_shim.mochi" as <alias> until Phase 7 lands the dedicated syntactic form.

Timestamps​

  • 2026-05-29 23:50 (GMT+7): Phase 6 started.
  • 2026-05-29 23:56 (GMT+7): Phase 6 LANDED.