One generated wasm to rule them all

[jordy25519]

Motivation

Create a single, isomorphic JS package using wasm-bindgen and tooling.

Proposed Solution

Generate the wasm import table in a consistent or configurable way so that the wasm binary may be used by any JS target runtime.

Maybe there is a way to provide a core wasm file with the main logic and generate only "glue" wasm files for each target which provide the right import shims.

Alternatives

It is possible to do this using wasm-pack or manual build scripts and other glue code the downside of this, in my understanding, is it requires multiple wasm binaries, one for each target, which unnecessarily bloats the final package size.

Additional Context

Idea came from the observation that the generated wasm for --target=node and --target=browser produce
the same binary apart from imports table (converted to wat):

I don't know dark js arts so maybe there's any easier way to do this from js glue code only but I could not find / comprehend that during my research into this.

[alexcrichton]

This is theoretically possible but not a lot of effort has gone into this. There's various subtle interactions with how the target and the generated JS affects the resulting wasm module, for example precisely what intrinsics are exported and not. Currently there's not a pass in wasm-bindgen that attempts to export everything it would need for all targets, so support would need to be added for that.

[torfmaster]

FYI: I created a draft PR here which might touch this issue: #4065