Integrate WASM with Scala CLI

[Gedochao]

Is your feature request related to a problem? Please describe.
We currently support emitting Wasm via Scala.js, but we do not yet integrate it with Scala CLI features.

Describe the solution you'd like
I'd like to be able to run Scala code with Wasm directly from Scala CLI.
Unsure which runtimes should be supported, + we should likely have a default.

• support running Wasm from Scala CLI
  • a CLI flag --wasm
  • a corresponding directive, likely a wasm param for the platform directive
• allow to pick a Wasm runtime + have a default
  • command line option
  • directive
• consider Wasm for other Scala CLI features (likely out of scope) and create follow-up issues

Additional context

• initial support for WASM: Support Scala.js 1.17.0 and targeting WASM #3213

cc @sjrd @tanishiking

[sjrd]

Note that currently, the Wasm support of Scala.js always emits JS+Wasm files. So you need a JS runtime to run it, like the existing Scala.js-on-JS.

In addition, one may need to provide specific flags to the engine, in order to enable experimental Wasm features that Scala.js-on-Wasm needs. See https://www.scala-js.org/doc/project/webassembly.html

[He-Pin]

It would be nice to have this, then can use it in https://github.com/bddicken/languages :)

[lostflydev]

Hi @Gedochao ,

I'm interested in contributing to this issue. I've been researching WebAssembly support for Scala CLI and would like to clarify some points before proposing a solution. Could you please help with the following questions?

1. Target Runtime Environment
   Which WebAssembly runtimes do you primarily want to target?
   Standalone runtimes (wasmtime, wasmer) or Node.js and other JS based with WASM support ?

2. Component Model & Interoperability
   Do you need WebAssembly Component Model support for language interoperability?

3. scala-wasm fork: Is integrating scala-wasm acceptable, or should we wait for upstream Scala.js support (#4991)?

@sjrd @tanishiking Could you please share any updates on Scala.js / scala-wasm related to standalone WASM support?

[tanishiking]

Hi @lostflydev thank you for your interest :)

• (1) Target Runtime Environment
  • Current Scala.js (and ScalaCLI) already supports JS-based Wasm environments. As you may realized, scala-wasm is specifically about supporting standalone Wasm generation. IIUC the only Wasm runtime that currently supports all the necessary features (GC, Exception Handling, Component Model) is wasmtime.
• (2) Component Model & Interoperability
  • This depends on what kind of language interoperability you're referring to. The Component Model provides
    • language-agnostic high-level data types defined via WIT
    • safe shared-nothing interoperation (slower though).
  • While the Component Model makes language interoperability on Wasm easier, noting that interoperation with host environments (such as JavaScript) is still possible without it.
• (3) scala-wasm Fork
  • I don't know Scala CLI's policy, but personally I think it would be better to wait for upstream integration. The scala-wasm APIs are still unstable at this point.

Regarding updates: the remaining tasks are listed in the issues in scala-wasm repo. but I'm going to eventually prepare for upstream integration into Scala.js 👍