feat: support postcss.config.ts

[G-Rath]

Notable Changes

This lands support for postcss.config.ts 🎉

Commit Message Summary (CHANGELOG)

feat: support `postcss.config.ts`

Type

• Feature

SemVer

• Fix (:label: Patch)
• Feature (:label: Minor)
• Breaking Change (:label: Major)

Issues

• Fixes Allow typescript config #189

Checklist

• Lint and unit tests pass with my changes
• I have added tests that prove my fix is effective/works
• I have added necessary documentation (if appropriate)
• Any dependent changes are merged and published in downstream modules

[G-Rath]

The types should be mostly correct, but plugins & other dependencies require some upstream updates to be v8 compatiable i.e. DefinitelyTyped/DefinitelyTyped#53003

[ai]

Thanks. Looks great.

But can I also ask you to add ESM export test for postcss.config.ts with "module": "esnext" in tsconfig.json?

[G-Rath]

@ai I can do an approximation of that, but it won't be completely possible without upgrading jest and configuring module support (i.e you need to run node with --experimental-vm-modules) since using esnext means that the test suite has to be able to use import/export.

I can implement the use of interopRequireDefault which should be the key thing required to provide nice support for both modules & commonjs.

[ai]

Yeap, you can update Jest and change how we run tests

[G-Rath]

I don't think this is possible without making a breaking change, as you have to set "type": "module" in the root package.json, which means require cannot be used anywhere (not to mention iirc this impacts downstream users on the module).

I'm happy to explore this, but think it would be better to land support for this as is (as that matches how other libraries like jest, webpack, karma, ajv, etc are supporting it), and then look at refactoring the codebase for native ESM support as a follow up.

[ai]

I asked this, because I'm afraid that ts-node is a bad solution.

A few months ago, there was no way to use ts-node with ESM in TS. If it is still a problem, can we switch to another method?

[G-Rath]

I'm afraid that ts-node is a bad solution.

Is that a statement or a concern? My experience with ts-node so far (which includes my using it to implement support for configs written in TypeScript for a number of tools) has been pleasant and I don't know of any other solution that's as light weight or universal (i.e you could do it with babel, but that's a huge dependency to have for this feature; you could also probably do it with something like esbuild, but then that means you're pulling in binaries that have OS requirements as well as not having type-checking).

My understanding is that ESM is now supported at a similar level to Node.

I can confirm I've been able to create a project with module set to esnext which ts-node is able to correctly execute.

[ai]

Great news. Yeap, let’s do it this way (I will need a day to merge and release it).

[ai]

I will play with ts-node and ESM support on my hobby project first. I hope to release it next week.

[G-Rath]

Awesome - let me know if there's anything I can help with :)

[ai]

Can we call require('ts-node') only if .ts file as found?

I do not want to load heavy TypeScript for the projects with .js configs, but with ts-node in the system.

[G-Rath]

I'll have a look, but this doesn't actually load the heavy side of the TypeScript compiler until it's actually needed, making it a very cheap call.

[ai]

Am I right that we are calling require('ts-node').register() on any config loading?

(I may be wrong, I am not sure)

[G-Rath]

Yes; like I said the require cost is negligible since it doesn't actually do any work (including creating the TypeScript compiler, and compiling code, which are the expensive operations) until a .ts file is required.

However I think we might be able to move it into the loader function.

[ai]

Sorry, for the delay. I am back to review the PR.

[ai]

LGTM. Hope to merge and release it tomorrow (sorry, I am moving from one country to another, don’t have a lot of time for open source this month).

[ai]

Thanks. Released in 3.1.