Experiment with always using parameters from base types for derived methods

Note some related issues for doing this with properties rather than methods: #3667, #6118, #1373.

Goal

We want to make it easier for users to derive types without rewriting the same parameter signature every time

class Base {
  method(x: number) {
    // ...
  }
}

class Derived extends Base {
  method(x) {
    // 'x' should have the type 'number' here.
  }
}

Potential ideas

• Only enable in noImplicitAny (doesn't work for default initializers 😞)
• Revert to any in all locations, opt in with another strictness flag (😞)
• Something else? 😕

Potential issues

Default initializers with more capable derived types

class A {
  a = 1;
}

class B extends A {
  b = 2;
}

class Base {
  method(x: A) {
    // ...
  }
}

class Derived extends Base {
  method(x = new B) {
    x.b;
    // Today, 'x' has type 'B' which is technically unsound
    // but that's just what we do. Does changing this to 'A' break things?
  }
}

Default initializers that become less-capable via contextual types

class Base {
  method(x: "a" | "b") {
    // ...
  }
}

class Derived extends Base {
  method(x = "a") {
    // We have to make sure 'x' doesn't have type '"a"'
    // which is both unsound and less useful.
  }
}

Distinction between properties and methods

Would this work?

class Base {
  method = (x: number) => {
    // ...
  }
}

class Derived extends Base {
  method(x) {
    // Does 'x' have the type 'number' here?
  }
}

What about this?

class Base {
  method(x: number) {
    // ...
  }
}

class Derived extends Base {
  method = (x) => {
    // Does 'x' have the type 'number' here?
  }
}

Keywords: base type derived contextual contextually inherit methods implicit any

この issue の目的と例から始め、その後、関連するプロパティの issue #3667、#6118、#1373 と比較してください。派生メソッド、デフォルト初期化子、メソッドプロパティをどのように文脈化すべきかを調査してください。完了とは、すべての例について動作と strictness への影響が解決されていることを意味します。