feat(typescript): allow override of forced noEmit and emitDeclarationOnly compiler options

[Harris-Miller]

Rollup Plugin Name: typescript

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• no

Breaking Changes?

• yes (breaking changes will not be merged unless absolutely necessary)
• no

If yes, then include "BREAKING CHANGES:" in the first commit message body, followed by a description of what is breaking.

List any relevant issue numbers:

Description

This MR is a replacement for the closed #1206. the suggested feature of a transpilerMode option, which unfortunately was discovered to be a breaking change.

Why

Currently, this plugin forced the compilerOptions noEmit and emitDeclarationOnly to be false. There is a note // Typescript needs to emit the code for us to work with.

This is false

The way that the plugin is written, the load hook looks for if typescript did transpilation for a file and returns that if found, null otherwise. This means for emitDeclarationOnly rollup will simply load from the output of the previous plugin or from the file system. This is ideal to mimic the following:

// package.json
{
  "scripts": {
    "build": "babel src --out-dir dist" 
    "typecheck": "tsc --emitDeclarationOnly"
  }
}

Where build uses babel to do all transpilation, including typescript via @babel/preset-typescript, and tsc is used to only emit declaration files.

Currently, rollup can more or less do this by running all code though @rollup/plugin-typescript first and then @rollup/plugin-babel, however with the forced emitDeclarationOnly: false being on, all the code is run through the typescript transpiler first. If @rollup/plugin-babel is set up to do to typescript, there isn't a need to actually do this

By allowing emitDeclarationOnly: true, @rollup/plugin-typescript is drastically faster! Since it only has to emit declaration file (which are emitted by rollup separately as "asset" files in the generateBundle step). On the large projects I tested this out at my work, I say initial builds drop from 20 seconds down to 2 seconds

[NotWoods]

Thanks for the change!

[shellscape]

Looks like there are some snapshot mismatches in the tests for this change. Please see the CI output for Validate Monorepo.

[Harris-Miller]

I fixed the tests. Let me know if you need anything additional

[Harris-Miller]

Anything needed from me to get this merged?

[shellscape]

nope :)