Support to parse WIT files from multiple paths

[iawia002]

Background information reference: bytecodealliance/wasmtime#8939 (comment)

This patch allows us to parse WIT files from multiple paths, which is often useful in testing. We can unify all the generated code into a single mod. For example, for Wasmtime's case, we can do it like this:

before:

wit_bindgen::generate!({
    world: "test-command",
    path: "../wasi/wit",
    generate_all,
});

pub mod config {
    wit_bindgen::generate!({
        path: "../wasi-runtime-config/wit",
        world: "wasi:config/imports",
    });
}

// use the generated code:

use test_programs::wasi::sockets;
use test_programs::config::wasi::config;

after:

wit_bindgen::generate!({
    inline: "
        package wasmtime:test;

        world test {
            include wasi:cli/imports@0.2.0;
            include wasi:config/imports@0.2.0-draft;
            import wasi:http/types@0.2.0;
            import wasi:http/outgoing-handler@0.2.0;
        }
    ",
    paths: ["../wasi/wit", "../wasi-runtime-config/wit"],
    generate_all,
});

// use the generated code:

use test_programs::wasi::sockets;
use test_programs::wasi::config;

I am not familiar with the whole process of wit parsing, so I am not sure if there will be any side effects of doing this. I have tested the wasmtime case locally and it does work.

cc @alexcrichton

[alexcrichton]

Thanks for this!

[alexcrichton]

Instead of using a new key for this could this syntax be folded into the previous key? For example path: "..." or path: [...] would be supported

[alexcrichton]

Adding a runtime test for this is pretty heavyweight and not much runtime functionality is tested here, so could this be added to crates/rust/tests/* instead?

[alexcrichton]

Can this be &[PathBuf] instead of &Vec<String>? That keeps the type-level annotation that these are paths and additionally avoids the dance of into_os_string().into_string().unwrap() below too

[iawia002]

Thanks for the review, All comments addressed, PTAL

[alexcrichton]

Thanks!