Make `Base.plugin()` accept an array of plugins instead of requiring the plugins to be spread

[gr2m]

The current implementation of plugin is a result of quite a long research when we first created it. The only way we got it to work is by creating an interface Base.plugin() which requires at least one parameter, but also accepts an unlimited amount of parameters, each one being a plugin function.

The preferable API signature is

Base.withPlugins([plugin1, plugin2, ...])

Lots of things changed since the initial implementation.

@JoshuaKGoldberg maybe the improvements you too advantage of here will make this possible? Would that be something that you know is possible now or that you'd like to explore?

[JoshuaKGoldberg]

Sure! I think that's reasonable. At first glance, it looks like these rough changes would get most or all of the way there:

index.js:

- static plugin(...newPlugins) {
+ static plugin(newPlugins) {
    const currentPlugins = this.plugins;
    return class extends this {
      static plugins = currentPlugins.concat(
        newPlugins.filter((plugin) => !currentPlugins.includes(plugin))
      );
    };
  }

index.d.ts:

  static plugin<
    Class extends ClassWithPlugins,
    Plugins extends [Plugin, ...Plugin[]],
  >(
    this: Class,
-   ...plugins: Plugins,
+   plugins: Plugins,
  ): Class & {
    plugins: [...Class['plugins'], ...Plugins];
  } & Constructor<UnionToIntersection<ReturnTypeOf<Plugins>>>;

If backwards compatibility is of concern, it could instead take in a Plugins extends [(Plugin | Plugin[]), ...(Plugin | Plugin[])[] in the definition and use Array.flat in the implementation. Either works!

[gr2m]

At first glance, it looks like these rough changes would get most or all of the way there

Awesome, thank you!

I'll give this a try myself and reach out if I get stuck with specific questions and failing tests

If backwards compatibility is of concern

it's not a concern here because this is just a demo/reference project. But it might become a concern for Octokit, so that's great to know

[gr2m]

that's done now 👍🏼