no-type-alias could be helpful

[mightyiam]

https://github.com/typescript-eslint/typescript-eslint/blob/master/packages/eslint-plugin/docs/rules/no-type-alias.md

[swansontec]

After reading the docs for that, as well as the other rules in this repo, I would configure no-type-alias like this:

{
  // Enables things that are difficult to achieve in other ways:
  allowAliases: 'in-unions-and-intersections',
  allowLiterals: 'in-unions-and-intersections',
  allowMappedTypes: 'in-unions-and-intersections',

  // The `prefer-function-type` rule forces this:
  allowCallbacks: 'always'
}

[mightyiam]

@swansontec, I read the rule doc and I agree with the options suggested by you.

[LinusU]

I use case I've ran into lately is:

import firebase = require('firebase')

type DocumentReference = firebase.firestore.DocumentReference

// ...

function foo(ref: DocumentReference) {
  // ...
}

[swansontec]

@LinusU That's a valid point! Shortening long names might also be a valid use-case.

The @typescript-eslint/prefer-function-type and @typescript-eslint/prefer-interface rules already get rid of the most "wrong" uses of the type keyword, so the remaining cases would be things like intersections, unions, or your example shortening long names. In that case, maybe no-type-alias doesn't give much additional benefit?

The main benefit I can see would be banning "useless" type aliases like type Username = string. It's too bad there is no @typescript-eslint/no-useless-type rule, or at least an option to the allowAliases configuration that would trivial cases like this.

[mightyiam]

Shortening a nested type does seem like a constructive pattern. Isn't there another way to get a reference to that nested type other than with a type alias? And... did you check that this is an error according to this rule? It seems like it would be, always. I'm closing this on the count of @LinusU's shortening example. If anyone has an idea, please reopen.

[LinusU]

Shortening a nested type does seem like a constructive pattern. Isn't there another way to get a reference to that nested type other than with a type alias?

I would love to know this as well! ☺️