Feature: Ignore optional export interfaces

[jamesstocktonj1]

Description

Currently running into a little issue with an SDK I'm writing. This SDK wraps, among other things, the wasi:cli and the wasi:http interfaces. The setup is something as follows.

WIT:

package jamesstocktonj1:componentize-sdk;

world http {
  export wasi:http/incoming-handler@0.2.6;
}

world cli {
  export wasi:cli/run@0.2.6;
}

world all {
  include sdk;
  include http;
  include cli;
}

Componentize Go Toml:

wit_paths = ["./wit"]
worlds = [
    "sdk",
    "http",
    "cli"
]

Issue 1

When I import this package (for example the net/wasihttp path), it builds a component which exports BOTH wasi:http and wasi:cli and then same is true when trying to write a CLI application.

I've tried splitting the gen/wit_exports file into gen/wit_exports_cli and gen/wit_exports_http but componentize-go complains that:

Error: failed to encode component from module

Caused by:
    0: failed to decode world from module
    1: module was not valid
    2: failed to find export of interface `wasi:cli/run@0.2.6` function `run`

Issue 2

We also have a scenario where we want to export neither CLI or HTTP but instead just want to use the http.Client interface. This again causes the component to export both interface although neither are needed.

Summary

• How can we make certain wit interfaces optional?
• Would it be possible to have optional exports depending on what Go module path is imported?
  • Having a go.mod and componentize-go.toml for each path would be possible but quite wasteful
• Can this be done without having to specify a specific interface? e.g. componentize-go --world foo build ...
• Can we fix this in the Componentize Go build side?

For more context this is the SDK in question:
https://github.com/jamesstocktonj1/componentize-sdk

[jamesstocktonj1]

Potential solution

Something which could get us partway there is to use a similar go list command e.g.

$ go list -deps ./...
...
github.com/jamesstocktonj1/componentize-sdk/net/wasihttp
github.com/jamesstocktonj1/componentize-sdk/examples/hello

Then have an option something along the lines of:

[worlds.'http']
implemented_by = "github.com/jamesstocktonj1/componentize-sdk/net/wasihttp"

Allowing for more fine-grained configuration rather than just a list of worlds.

[asteurer]

Have you considered creating multiple worlds instead? You could have a world that only uses CLI, a world that only uses HTTP, and a world that uses both. Alternatively, if you don't want separate worlds, you could provide no-op/error stubs for the undesired exports so that you're not getting linker errors. Either way, based on how I'm interpreting the direction you're proposing for the tooling, I don't love the idea of trying to create a WIT feature (i.e. optional exports) that is only available in componentize-go, but not in any of the other WIT-supported languages.