Remove ctx argument on imported functions and allow closures.

[lachlansneff]

This allows you to use fully-fledged closures for imported functions.

let a_str = "this is a str";

let import_object = imports! {
    "env" => {
        "foo_bar" => Func::new(|other_thing| {
            println!("{}: {}", a_str, other_thing);
        },
    },
};

@evgenykuzyakov Does this fix the data initialization issue you were having?

[CryZe]

This might indirectly also work around #188

[lachlansneff]

@CryZe Could you elaborate? I didn't really change how imported function calling worked on windows.

[CryZe]

Oh yeah, if ctx / some env internally is still used as the first argument, then this still happens.

[lachlansneff]

Oh, that's a shame. I haven't had time to look into fixing the issues you found; been working on some stuff that we're not ready to show yet.

[evgenykuzyakov]

Yes. This should fix #169

[bjfish]

Adding closures would be nice, I think whatever is done should be compatible with our current ctx usage in emscripten/C API/etc.

It's not a big deal but this PR would be a little easier to read if the renaming of ctx to env was split into a new PR. Plus we should update the naming in the example repos/blog posts/documentation to env if this is changed.

[Hywan]

Why do you want to remove the context argument?

[lachlansneff]

This doesn't remove per-say, but really just repurposes it to hold some environmental data, whether that's the vm ctx or not. Then it adds some convenient sugar around that to make it easy to use closures as imported functions.

[Hywan]

LGTM!

[syrusakbary]

Closing this PR in favor of the Import State changes from #299: 7b0992e.

This new API let the user establish the context data very easily.
See example in WASI API:

wasmer/lib/wasi/src/lib.rs

Lines 33 to 53 in 2aefa73

	let state_gen = move || {
	fn state_destructor(data: *mut c_void) {
	unsafe {
	drop(Box::from_raw(data as *mut WasiState));
	}
	}
	let state = Box::new(WasiState {
	fs: WasiFs::new(&preopened_files).unwrap(),
	args: &args[..],
	envs: &envs[..],
	});
	(
	Box::leak(state) as *mut WasiState as *mut c_void,
	state_destructor as fn(*mut c_void),
	)
	};
	imports! {
	// This generates the wasi state.
	state_gen,

[Hywan]

The C code doesn't handle the Option correctly I guess (it expects a pointer).