Possibility of compiling on stable Rust?

[alexcrichton]

Hello! Over in the wasm-bindgen project we've got a new proposal which partly entails eventually having a JS parser built into our tooling. The JS parser would need to basically compile ES module syntax to either CommonJS or "linked manually with no modules" style syntax. The swc project seems like it perfectly fits the bill in terms of use cases here!

One hesitation that we'd currently have from using swc is that it looks like it currently requires nightly Rust and also isn't published much on crates.io. I'm curious if y'all have an idea about whether it's feasible in the near-term to compile on stable (and as a bit of a stretch goal publish on crates.io too). That'd make swc a strong possibility for us to use in wasm-bindgen as a dependency!

We're mostly just evaluating our options right now, so "not any time soon" is a totally valid answer too!

[kdy1]

I removed some unused features and checked which crate depends on which feature.

swc_common:

• specialization

swc_ecma_parser:

• box_syntax
• box_patterns
• specialization
• never_type

---

• Removing uses of never_type will be easy
• Removing box_syntax will be easy
• Removing box_pattern may be tricky, but possible
• Specialization can be replaced with hand-written folder / visitor.
  But lots of work is required

So I think it's possible and I'd like to do it, but I'm not sure how much time it would take.

[kdy1]

cc @alexcrichton
Currently swc depends on rustc-ap-* crates, but I think those crates will never be stabilized, is this correct? Then we should copy some code into swc..

Only hygiene and error reporting is used by swc, so it would not be too hard.

[alexcrichton]

Oh wow thanks for the speedy responses, this looks great!

I was trying to give this a spin locally with a few path dependencies, but it looks like dependencies like scoped-tls still have the nightly feature enabled. Do I need to disabled some features of swc or something like that though?

[kdy1]

@alexcrichton Fixed it. I made a mistake while inlining rustc-ap crates.
It would work after a cargo update

[alexcrichton]

It got farther! I think though swc_macros_common still uses some nightly features?

[kdy1]

Oh, my mistake..
I fixed and verified that stable rustc can build swc_ecma_parser

I guess you should run cargo update.

https://github.com/kdy1/swc-stable-rust

[alexcrichton]

Ok great, thanks! Our use case will also need to write out the JS file after transforming it, does that mean that we would need the swc_ecma_codegen crate as well?

[kdy1]

@alexcrichton Yes. I published swc_ecma_codgen v0.5.1 which can be built with stable rustc.

[alexcrichton]

Awesome, thanks again so much for your help!

[swc-bot]

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