[no-type-alias] False positive with constructor aliases

[mdouglass]

Repro

{
  "parser": "@typescript-eslint/parser",
  "parserOptions": { "project": "./tsconfig.json", "sourceType": "module" },
  "plugins": ["@typescript-eslint"],
  "rules": {
    "@typescript-eslint/no-type-alias": ["error", { "allowCallbacks": "always" }]
  }
}

type ConstructorFunction = new (port: string) => any

Expected Result
No warning because allowCallbacks is set to always

Actual Result
1:26 error Type unhandled are not allowed @typescript-eslint/no-type-alias

Additional Info
If the new is removed then this code passes without errors, so I presume it is because constructors are not handled. It is possible that this should be a new option (allowConstructors) rather than rolled into allowCallbacks.

Versions

package	version
@typescript-eslint/eslint-plugin	2.6.1
@typescript-eslint/parser	2.6.1
TypeScript	3.7.2
ESLint	6.6.0
node	13.1.0
npm	6.12.1

[a-tarasyuk]

@bradzacher Is it a bug? Or need to add the new option allowConstructors?

[bradzacher]

It's a bit of both.

It's a case that was never thought of, hence it's marked as "unhandled"

typescript-eslint/packages/eslint-plugin/src/rules/no-type-alias.ts

Lines 239 to 240 in 96d1cc3

	// unhandled type - shouldn't happen
	reportError(type.node, type.compositionType, isTopLevel, 'Unhandled');

But it also doesn't really fit into any of the existing options. The closest would probably be allowCallbacks, but it's still not quite right.

So it's a bug that needs to be handled with a new option.