wasm-tools parse support for .wast file.

[doehyunbaek]

From current README, I got the impression that both wat and wast crates are accessible from subcommand parse:

wasm-tools/README.md

Line 128 in d15fda3

| `wasm-tools parse` | [wat] and [wast] | Translate the WebAssembly text format to binary |

But as I try out the command from the shell and also looking through the code, this doesn't seem currently possible:

wasm-tools/src/lib.rs

Lines 67 to 72 in 4975360

	if let Some(path) = &self.input {
	if path != Path::new("-") {
	let bytes = wat::parse_file(path)?;
	return Ok(bytes);
	}
	}

Is it intended? If not, may I contribute a feature addition?

[alexcrichton]

Ah yes so *.wast support isn't surfaced in the CLI at this time. The wat crate is itself built on the wast crate (it's a very small shim) and the wast crate has support for both the text syntax and the *.wast assertion syntax. (sorry if that's confusingly named)

I'd be happy to see *.wast support in the CLI, but I'm not entirely sure what that might look like. Do you have an idea in mind though of what wasm-tools parse foo.wast might do?

[doehyunbaek]

I did not have particular output format in mind, but I found that our team uses wast2json tool from wabt.

What do you think about implementing wast support as a drop-in replacement for wast2json? Pro would be that it would be really useful for the migration of the users.

[alexcrichton]

Sounds reasonable to me! If you're up for making a PR that'd be most welcome as well, I'd be happy to review.

If I might throw out an initial idea to help shape this a bit:

• I can't think of a better name than wasm-tools wast2json myself
• Perhaps the output is JSON to stdout by default, -o outputs the JSON to a file, and --module-dir is a required argument of where to put all the modules?
• I'd recommend using serde_json and serde::{Deserialize,Serialize} for JSON things in Rust
• I'd prefer to keep the serde bits out of wast if possible (keeps its dependencies slim), so what I'd recommend is a src/bin/wasm-tools/wast2json.rs which has all the serde bits. That'd use Wast to convert to a structure which has #[derive(Serialize)] and then it could all be emitted as JSON.

Please feel free of course to change any details as well, just some initial suggestions!

[doehyunbaek]

I'll try to follow up with a PR with respect to your suggestion. Thanks!

[doehyunbaek]

Oh @alexcrichton thanks for implementing this. I thought about doing thsis early April because I have some important due date in a few weeks. Maybe I should have communicated it.

Again thanks for your help!

[alexcrichton]

Oh I'm so sorry! I was feeling inspired the other night, but I also should have checked in here first before going ahead.

[doehyunbaek]

No I am really grateful that you did it! No need to be sorry!