swc transpiler and new --transpiler option to use third-party transpilers

[cspotcode]

Implements #779

Usage information is at the top of this description. Below are design questions and development to-dos.

Usage

// tsconfig.json
{
  "ts-node": {
    "transpiler": "ts-node/transpilers/swc-experimental",
    "transpileOnly": true
  }
}

# Can substitute @swc/wasm if you are unable to use native modules
npm install --save-dev typescript @swc/core @swc/helpers github:TypeStrong/ts-node#main

# should be very fast via swc
ts-node ./index.ts

Gotchas

swc uses a different helpers library, @swc/helpers instead of tslib. If you have importHelpers enabled, you will also need to install @swc/helpers in all the places where you would normally install tslib. When in doubt, there is no harm installing both.

---

Implementation notes, design questions

This is incomplete. To be a proper drop-in compiler I think it will need to implement additional parts of the TsCommon interface. It can pull these from require('typescript') <--this much has been implemented.

But ideally our compiler option supports composable compilers, so you can specify "compiler": ["ntypescript", "ts-node/compilers/swc"] and the swc wrapper will defer to ntypescript for things it does not implement itself. This has not been implemented yet.

Still, it might be cool for users to specify "transpileOnly": true, "compiler": "ts-node/compilers/swc" and get a performance boost.

Other compilers: (note they are only worth considering if they're noticeably faster than ts.transpileModule)

• https://github.com/alangpierce/sucrase
• https://github.com/evanw/esbuild
  • https://esbuild.github.io/api/#transform-api
  • Faster sync API via worker_thread evanw/esbuild#590

Configuration with options: bike-shedding

How should we allow passing configuration options to the transpiler?

"transpiler": "ts-node/transpilers/swc-experimental",
"transpilerOptions": {
  "swc": "@swc/wasm"
}

"transpiler": {
  "name": "ts-node/transpilers/swc-experimental",
  "swc": "@swc/wasm"
}

"transpiler": ["name", { "swc": "@swc/wasm"}]

TODO

• use peerDependenciesMeta
  https://yarnpkg.com/configuration/manifest/#peerDependenciesMeta
  https://blog.npmjs.org/post/186983646370/npm-cli-roadmap-summer-2019
• expose as factory which accepts options, so it can be customized (use @swc/wasm vs @swc/core)
• update ts-node logic to invoke factory when detected
• warn when transpileOnly turned off, since you won't get the speed benefit of swc?
• warn when createTypescriptCompiler is misspelled by detecting when compiler instance doesn't have well-known compiler APIs such as transpileModule or createProgram Instead, I've switched to a proper transpiler API that does not need to mimic TS compiler API
• investigate weird WASM shutdown slowness: when using @swc/wasm, there is a delay in node process shutdown once code has finished running. Does not happen with @swc/core
• Compare against https://github.com/Brooooooklyn/swc-node/blob/master/packages/register/register.ts#L9; see if there are any lessons to be learned or additional work for us to achieve feature parity
• remove TODOs from comments

[codecov]

Codecov Report

Merging #1160 (1a06089) into master (3b5b9c2) will decrease coverage by 0.28%.
The diff coverage is 73.07%.

Impacted Files	Coverage Δ
src/index.ts	80.56% <68.75%> (-0.02%)	⬇️
src/transpilers/swc.ts	73.52% <73.52%> (ø)
src/bin.ts	91.17% <100.00%> (+0.08%)	⬆️
transpilers/swc-experimental.js	100.00% <100.00%> (ø)

[Gerrit0]

From someone fairly unfamiliar with ts-node's architecture, looks good! As a user, I would definitely want a warning for ts-node failing to use the specified compiler.

[Gerrit0]

99 is set twice - intentional?

[cspotcode]

Thinking about this, I see some problems:

• With the current design, I'm not sure there's a clean way to warn the user when they use swc without transpileOnly, but I agree we should have such a warning.

• I was hoping to avoid adding complexity to ts-node's core by doing this via the existing --compiler option , but then I ended up changing the compiler loader anyway to support factories.

• It's unfortunate that every call to transpileModule needs to re-create the swc options.

Given the above problems, perhaps it is better to introduce a proper --transformer option, similar to --compiler. When this option is used, it provides the --transpileModule implementation and throws an error when used without --transpileOnly. This also allows us to enforce a very clean create() factory API, so compiler options can be parsed and established only once, and then all subsequent calls simply invoke the transformer.

--transformer? --transpiler? --transpileModuleProvider? --transpileOnlyCompiler? Not sure what to call it.

[klesun]

It shortens ts-node compilation delay about 3-6 times, thanks so much for this PR!

[QuentinFarizon]

When using yarn one should use yarn add --dev https://github.com/TypeStrong/ts-node#main typescript @swc/core @swc/helpers

Thanks for the 3x launch time improvement !