Import only necessary WASI APIs

[nullpo-head]

Currently, Grain seems to emit a wasm binary that imports almost all WASI APIs, regardless of whether they are actually used or not. This means that on a WASM runtime that does not support all WASI APIs, the Grain app will not run, even if the Grain app is actually calling only the WASI APIs supported by that runtime.

Is it possible to improve Grain so that it imports only the APIs that are actually used, instead of always importing all WASI APIs?

I'd also like to note that WASI is making big changes on its API¹², so reducing imports will also benefit future compatibility.

For example,

import Process from "sys/process"
Process.exit(1)

This code only calls the proc_exit WASI API through Grain's standard library, but the emitted wasm module imports almost all WASI APIs.

  (import "wasi_snapshot_preview1" "fd_write" (func (;0;) (type 2)))
  (import "wasi_snapshot_preview1" "args_get" (func (;1;) (type 0)))
  (import "wasi_snapshot_preview1" "args_sizes_get" (func (;2;) (type 0)))
-- snip --
  (import "wasi_snapshot_preview1" "path_rename" (func (;36;) (type 11)))

Footnotes

1. FS APIs will have big changes https://github.com/WebAssembly/WASI/issues/469#issuecomment-1045251844 ↩

2. Some APIs will be removed, such as proc_raise, which Grain always imports. https://github.com/WebAssembly/WASI/issues/26 ↩