less should be a peer dependency

[rjgotten]

less is currently registered as a dependency when it should be a peerDependency:

https://github.com/webpack-contrib/less-loader/blob/73740a89aef0748e27657a06b80b327c90b6f2b4/package.json#L45

Locking it as a dependency means users are not free to pick their own minimum version even though less-loader is API-compatible.

This right now creates a big problem for users that process any non-trivially sized stylesheet collection, as Less versions 3.10+ have hugely increased memory consumption after the codebase was converted to ES classes and is now being transpiled (first with Babel, now with TypeScript) down to ES5.

Seeing 500+ MB memory usage for compiling a single stylesheet is not out of the ordinary.

[alexander-akait]

Sorry, we can't put it in peerDependency, because we provide less out of box, I will reduce required less version, if you use yarn you can use https://classic.yarnpkg.com/en/docs/selective-version-resolutions/, it is acceptable?

[rjgotten]

No, it is not acceptable. less should simply not be provided out of the box.
Good loader design mandates that you use a peer dependency if you are simply wrapping another package and providing interface glue-code (which is what less-loader does).

https://webpack.js.org/contribute/writing-a-loader/#peer-dependencies

babel-loader doesn't provide Babel out of the box.
postcss-loader doesn't provide PostCSS out of the box.
sass-loader doesn't provide Sass and/or NodeSass out of the box.
less-loader didn't used to provide Less out of the box.

And it shouldn't start doing so now.

[alexander-akait]

@rjgotten Okay, I can implement the implementation option:

{
  loader: 'less-loader'
  options: {
    implementation: require.resolve('less')
  }
}

We want to improve 0CJS and reduce complex of configuraions.

[rjgotten]

That's actually even more flexible. 👍
Would allow mocking the entire compiler, in essence.

[alexander-akait]

Yep, in my TODO