Element error event handler

[cosmic-pixel-painter]

This PR fixes microsoft/TypeScript#62075. and is a result of the comment left on the PR over here, which I closed. Thanks for the advice on that 🙏 . I re-read your comment and figured out a path forward. I also dropped UIEvent from this PR.

Recap

As a recap, this handles this bug report here. The issue is that HTMLElement.onerror (and other element onerror handlers) uses the incorrect interface OnErrorEventHandler, which has the signature:

type OnErrorEventHandler = (
  event: Event | string,
  source?: string,
  lineno?: number,
  colno?: number,
  error?: Error
) => any;

This causes a type error when assigning a Event-based handler:

const div = document.createElement("div");
div.onerror = (event: Event) => {  // TS Error!
  // Type '(event: Event) => void' is not assignable to type 'OnErrorEventHandler'.
  // Types of parameters 'event' and 'event' are incompatible.
  // Type 'string | Event' is not assignable to type 'Event'.
};

It should be that window.onerror uses OnErrorEventHandler and elements uses the Event object.

Changes

• I ended up changing GlobalEventHandlers.onerror to use an event-based handler instead of OnErrorEventHandler. I did this by updating events.kdl to use Event instead of ErrorEvent.
• I then overrode window.onerror to keep using OnErrorEventHandler since Window is the only place where this handler signature is expected. The change is in overridingTypes.jsonc.
• This caused duplicate declarations since Window extends GlobalEventHandlers and both define onerror differently. This was happening in the global scope "polluter". I fixed this by tracking already emitted members in emitAllMembers.
• I then updated isCovariantEventHandler to not skip properties that have an explicit overrideType. This was need to handle Window's onerror override.

Before/After

Before:

interface GlobalEventHandlers {
  onerror: OnErrorEventHandler;
}
// Window inherits OnErrorEventHandler from GlobalEventHandlers

After:

interface GlobalEventHandlers {
  onerror: ((this: GlobalEventHandlers, ev: Event) => any) | null;
}

interface Window extends GlobalEventHandlers {
  onerror: OnErrorEventHandler;  // Explicit override
}

Testing

I added the onerror.ts test file and updated the eventlistener.ts test file.

Other Thoughts

This has been a crazy and fun bug to hunt down. I think I nailed it this time 😂

[github-actions]

Thanks for the PR!

This section of the codebase is owned by @saschanaz - if they write a comment saying "LGTM" then it will be merged.

[cosmic-pixel-painter]

@saschanaz I was able to fix it using the KDL file and didn't need to touch the overrideType 🎉 . I think this nails it 🔨