Wrong overload signature chosen for super class method

[jdforsythe]

TypeScript Version: 2.7.2

Search Terms:
overload signature super union
Code

class Entity {
  id: number;
}

class BaseClass {
  constructor() { }

  testMethod(single: Entity): Entity;
  testMethod(multiple: Entity[]): Entity[];
  testMethod(singleOrMultiple: Entity | Entity[]): Entity | Entity[] {
    return singleOrMultiple;
  }

  testTwo(single: Entity): Entity;
  testTwo(multiple: Entity[]): Entity[];
  testTwo(singleOrMultiple: Entity | Entity[]): Entity | Entity[] {
    return singleOrMultiple;
  }
}

class SubClass extends BaseClass {
  testMethod(single: Entity): Entity;
  testMethod(multiple: Entity[]): Entity[];
  testMethod(singleOrMultiple: Entity | Entity[]): Entity | Entity[] {
    // Argument of type 'Entity | Entity[]' is not assignable to parameter of type 'Entity[]'.
    // Type 'Entity' is not assignable to type 'Entity[]'.
    // Property 'includes' is missing in type 'Entity'.
    return super.testMethod(singleOrMultiple);
  }

  testTwo(single: Entity): Entity;
  testTwo(multiple: Entity[]): Entity[];
  testTwo(singleOrMultiple: Entity | Entity[]): Entity | Entity[] {
    // if I manually narrow to array or not, the compiler doesn't complain
    if (Array.isArray(singleOrMultiple)) {
      return super.testTwo(singleOrMultiple);
    }
    else {
      return super.testTwo(singleOrMultiple);
    }
  }
}

Expected behavior:
Since the signatures are identical, I would expect the compiler to choose the proper overload of the super method

Actual behavior:
Compiler chooses the wrong overload signature.

Playground Link:

Related Issues:

Duplicate of #14107

Note that you may manually fix this by writing:

testMethod(single: Entity): Entity;
testMethod(multiple: Entity[]): Entity[];
testMethod(singleOrMultiple: Entity | Entity[]): Entity | Entity[];
testMethod(singleOrMultiple: Entity | Entity[]): Entity | Entity[] {

The final signature is the implementation signature and isn't visible, so we have to duplicate it.

[typescript-bot]

Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.