DRAFT: Adding JSPI and Asyncify

[calvinrp]

Adds options to jco transpile and jco types:

.addOption(new Option('--async-mode [mode]', 'use async imports and exports').choices(['sync', 'jspi', 'asyncify']).preset('sync'))
.option('--default-async-imports', 'default async component imports from WASI interfaces')
.option('--default-async-exports', 'default async component exports from WASI interfaces')
.option('--async-imports <imports...>', 'async component imports (examples: "wasi:io/[email protected]#poll", "wasi:io/poll#[method]pollable.block")')
.option('--async-exports <exports...>', 'async component exports (examples: "wasi:cli/run@#run", "handle")')

Which treats the specified imports and exports as async using either JSPI or Asyncify.

JSPI is behind a feature flag in Chrome, Deno and NodeJS. Can run via:

DENO_V8_FLAGS="--experimental-wasm-jspi" deno

node --experimental-wasm-jspi

From my understanding, Asyncify does not support reentrancy (so it throws an error) but JSPI does.

[guybedford]

Very exciting to see this, thank you.

Left some initial comments.

[guybedford]

Since components can contain multiple sub-components, this is currently joining imports and exports across all sub-components.

If we only consider the outer component import and exports, then we should restrict to that, but we can't do that either since internal components must be async if the outer component is!

Therefore I think we should probably restrict this to outer component imports only

And we should make exports all async as soon as we go into asyncify mode. This also will then help avoid the easy footgun of inadvertantly not making an export async, and then finding it calls an async import down the line which would trap.

[guybedford]

It could be nice to automatically include a preview2 implementation designed for async now, and run the preview2 tests against that.

One issue here is how to get the async imports, but an easy option might be to just use a convention like:

import ... from '@bytecodealliance/preview2-shims/async/io'`;

This would be amazing to explore further...

[calvinrp]

Yep, I have a working draft of WASI P2 shims that I have been testing against. But was thinking of breaking into a separate PR.