bug(datepicker): mat-calendar ngOnChanges incorrectly optimized by Closure compiler

[rslawik]

Reproduction

1. Click on the mont-year button.
2. Click on the year.
3. Error is logged in the console.
4. Click on the month.
5. Another error logged.

The date picker calendar has code like:

const view = this._getCurrentViewComponent();
if (view) {
  view._init();
}

where the getCurrentViewComponent is:

private _getCurrentViewComponent() {
  return this.monthView || this.yearView || this.multiYearView;
}

Each view is a non-null property on the class, so TypeScript infers that the return type is typeof this.monthView and tsickle propagates that to calendar.closure.js. Then the JavaScript compiler assumes that view._init call is always the function from monthView and optimizes code to only that.

Expected Behavior

No errors.

Actual Behavior

Errors are logged to the console:

• RangeError: Invalid time value
• TypeError: a.v is not a function

Environment

• Angular: n/a
• CDK/Material: n/a
• Browser(s): n/a
• Operating System (e.g. Windows, macOS, Ubuntu): n/a

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