Architecture

Three sub-projects (interp, wasi, cli) so the published libraries stay dependency-free, with platform shims confined to thin per-target source roots.

Three sub-projects

The repo splits into three sub-projects so the published libraries stay dependency-free:

Sub-project	Published as	Depends on	External runtime deps
`interp/`	`wasm`	Scala stdlib only	None
`wasi/`	`wasm-wasi`	`interp`	None
`cli/`	(not published)	`interp` + `wasi`	`scopt`

interp/ — the interpreter itself: parser, validator, runtime, interpreter loop, host-import surface. Cross-built on JVM / Scala.js / Scala Native; the same shared/ sources compile for every backend.
wasi/ — the WASI Preview 1 host shim (29 syscalls). Also zero external deps. Pulls interp in transitively.
cli/ — a small command-line runner. Depends on scopt for argument parsing; not published because it’s a runnable example, not a library. JVM / Scala.js (Node) / Scala Native builds are all wired up.

Source-tree layout

build.sbt                              three crossProjects + Fixtures.scala generator
project/
interp/                                cross-platform interpreter library (zero deps)
  shared/src/
    main/scala/io/github/edadma/wasm/  types, parser, validator, interpreter, runtime, host
    test/scala/io/github/edadma/wasm/  category-split tests + zero-dep runner
    test/resources/fixtures/           .wat sources + wat2wasm-produced .wasm
  jvm/  js/  native/                   empty platform shells
wasi/                                  cross-platform WASI Preview 1 shim (zero deps)
  shared/src/main/scala/.../wasi/      Wasi.preview1 + WasiContext + HostBackedPreopen
  jvm/    src/main/scala/.../wasi/     HostPreopen.fromDir   (java.nio.file + FileChannel)
  native/ src/main/scala/.../wasi/     HostPreopen.fromDir   (same surface as JVM)
  js/     src/main/scala/.../wasi/     HostPreopen.fromDir   (Node fs.*Sync)
  shared/src/test/                     WasiFd / WasiArgs / WasiClock / WasiFs / WasiHostFs / WasiRealRust tests
cli/                                   cross-platform CLI (depends on interp + wasi + scopt)
  shared/src/main/scala/.../cli/       Cli.scala (scopt config + dispatch)
  jvm/    src/main/scala/.../cli/      Main.scala (java.nio file read + HostPreopen plumbing)
  js/     src/main/scala/.../cli/      Main.scala (Node fs + process.argv + HostPreopen plumbing)
  native/ src/main/scala/.../cli/      Main.scala (java.nio + HostPreopen plumbing)
examples/
  hello.wat / hello.wasm               canonical Hello, world! module

How fixtures get into the test suite

Fixtures.scala is a generated Scala object exposing each committed .wasm binary as an Array[Byte]. It’s regenerated into each platform’s target/.../src_managed/test/ on every compile by a sourceGenerator in build.sbt, so it always derives from the committed binaries — no committed copy to drift.

Fixtures are base64-encoded string constants decoded once at class init. The previous Array[Byte](b0, b1, ...) literal form trips the JVM 64KB method-size limit on real-world fixtures like rustc-built wasi binaries; the base64 form sidesteps it.

To refresh a fixture from its .wat source, see Testing → Regenerating fixtures.