nim/TODO.md

Known limitations

zap.nim is a complete Nim implementation of the ZAP serialization scheme; the RPC layer is useful but does not cover the whole protocol. The serialization layer is production ready. The items below are the parts of the upstream wire and code generator that are intentionally not yet implemented. They are scoped here precisely (with source anchors) rather than left as inline placeholders.

Toolchain

This port targets the Nim 0.18.x compiler era. build.sh/nimenv.cfg originally pinned Nim 0.15.2 with exact 2017 dependency commits; the closest toolchain that is still buildable and runnable on current CI is Nim 0.18.0, against which CI and nimble test are verified green.

The serialization layer (and the zapc code generator) builds against collections == 0.3.4 and needs nothing else. zap.nimble pins that version by git ref (the 0.18 nimble predates == version ranges) and nimble test runs the round-trip suite plus a zapc compile. CI runs inside the official nimlang/nim:0.18.0 image so the environment is deterministic.

Newer Nim breaks the dependency closure, not this repository's code:

• Nim >= 2.0 rejects collections/iface.nim — object {.inheritable.} (the pragma-after-object form was removed in Nim 2.0).
• Nim >= 0.19 rejects collections/iface.nim — newIdentNode(!"…") (!/toNimIdent was removed in Nim 0.19).

These are upstream dependency limitations (zielmicha/collections, zielmicha/reactor), not ZAP serialization defects.

Serialization (zap/)

• Two-word (intersegment / far) pointers are not decoded. zap/unpack.nim raises ZapFormatError "two-word pointers not implemented" on encounter, and getPointerField raises on an intersegment target. Single-segment messages — the form produced by this library's packer — are fully supported; cross-segment far pointers from other encoders are rejected explicitly rather than misread.

Code generator (zap/compiler.nim)

• Unions nested inside a group are not emitted.
• Named unions are not emitted.

RPC (caprpc/)

• Interface inheritance (superclasses) is not generated; compiler.nim walks methods of the declared interface only.
• The RPC layer is not covered by CI and is not built by nimble test. It depends on zielmicha/reactor (a libuv async engine), which is caught in a version vise against the Nim 0.18.x toolchain:
  • reactor's Future/Result compat shim that caprpc/common.nim:41 (proc(x: R): Future[T] = catchError(castAs(x, T))) relies on lives in the 2017 reactor commit the original build.sh pinned (b1875cd), but that commit's reactor/ipaddress.nim no longer compiles on Nim 0.18 (an Ip4Address array-type change).
  • The reactor 0.4.x tags that do compile on Nim 0.18 changed catchError to return Result[T] without the implicit Future[T] conversion, so caprpc/common.nim:41 fails to type-check. Restoring RPC CI requires either a reactor build that satisfies both constraints on a runnable Nim, or porting the caprpc/ async glue to a modern reactor. Scoped here rather than shipped as a red CI badge.

The ZAP schema text front-end (brace and whitespace-significant .zap syntax) is not part of this repository: zap/zapc is a code-generation backend that reads a binary CodeGeneratorRequest on stdin (zap/zapc.nim) emitted by the shared ZAP schema compiler. Whitespace/brace handling and desugaring live in that compiler, not here.