question: wit-bindgen lack of host generation

[chaynabors]

The README states:

The wit-bindgen project is intended to facilitate in generating a component, but once a component is in your hands the next thing to do is to actually execute that somewhere. This is not under the purview of wit-bindgen itself[...]

I wrote host side bindgen for wasmtime-py and I'm vending it locally right now. A lot of the code feels shareable, and I'm trying to understand the justification for this. Is there any appetite to increase scope in this repo?

The readme does a fine job pointing me to host side bindgen, except for languages like python whose host bindgen doesn't actually exist, and that desync is probably at least a little confusing for people like myself. The state of the art is that I have to lower my types to wire manually. That's arguably a problem for wasmtime-py, but referencing wit-bindgen for half of my codegen makes me want to ask the question at least.

[pchickey]

The host side bindgen for wasmtime was originally part of this same codebase. There were at least 2 big problems that led us to separate them, and limit this repository to only guest language generation.

1. Guest languages are typically pretty stable targets for code generation, but engine implementations and their interfaces change all the time. The binding generation for the engine was tightly coupled to the engine version itself, and so would need to be versioned in lockstep with the engine, with no compatibility guarantees once out of step. This means it makes more sense to ship host side bindings generation as part of the engine itself.
2. To write test programs for engines, we frequently need guest side generation, but changes to the generated bindings of those test programs need to be treated separately from the changes to the engine itself. So, we still need a dependency on wit-bindgen in wasmtime, but we need those releases to happen on a separate cadence from wasmtime itself.

Both of these problems would affect wasmtime-py just like they historically did with wasmtime. At one point there was a bindings generator in wasmtime-py based off the same rough design of jco, but I'm not sure what the status of that is currently - I don't maintain that package but the maintainers would be able to help you in the wasmtime-py issue tracker. Either way, bindings generation for the wasmtime-py project will happen in that project, and not in this one.

[chaynabors]

Thanks @pchickey. Will close and open there.