noImplicitOverride doesn't work if member is defined in multiple interfaces

[frigus02]

Bug Report

The --noImplicitOverride check doesn't catch the case where an overridden member is defined in multiple interfaces.

We found this in code using Polymer. Compiling the following example with tsc file.ts --target esnext --moduleResolution node --noImplicitOverride gives the inlined error. But I would have expected the error as well for connectedCallback.

class XCustom extends PolymerElement {
    connectedCallback() { super.connectedCallback(); }
    disconnectedCallback() {  super.disconnectedCallback();  }
 // ~~~~~~~~~~~~~~~~~~~~ This member must have an 'override' modifier because it overrides a member in the base class 'PolymerElement'.
}

I boiled it down to the minimal example below.

🔎 Search Terms

noImplicitOverride, override, interface, multiple

🕗 Version & Regression Information

This is the behavior in every version I tried: 4.3.5, 4.4.0-beta

⏯ Playground Link

Playground link with relevant code

💻 Code

const ElementMixin: ElementMixinConstructor & PropertiesMixinConstructor = class {
  connectedCallback() {}
  disconnectedCallback() {}
};

interface ElementMixinConstructor {
  new(...args: any[]): ElementMixin;
}

interface ElementMixin {
  connectedCallback(): void;
}

interface PropertiesMixinConstructor {
  new(...args: any[]): PropertiesMixin;
}

interface PropertiesMixin {
  connectedCallback(): void;
  disconnectedCallback(): void;
}

export class TestElement extends ElementMixin {
  connectedCallback() {
    super.connectedCallback();
  }

  disconnectedCallback() {
    super.disconnectedCallback();
  }
}

🙁 Actual behavior

Compiled with --noImplicitOverride, this only requires override for disconnectedCallback but not for connectedCallback.

As soon as I remove connectedCallback from either the ElementMixin or PropertiesMixin interface, TypeScript requires override for it as well.

The behavior is the same for property members.

🙂 Expected behavior

I would expect TypeScript to require override for both disconnectedCallback and connectedCallback.