[Ivy] Subclass/component now inheriting `@Component({ host: {} })` properties from superclass.

🐞 bug report

Affected Package

The issue is caused by package @angular/core

Is this a regression?

Yes, the previous version in which this bug was not present was: 8 or 9 with Ivy disabled

Description

With Ivy enabled, subclasses extending a superclass now inherit properties from @Component({}). More specifically, subclasses now inherit host properties such as (click) and (keydown). In previous versions and Angular 9 with Ivy disabled, this does not happen.

🔬 Minimal Reproduction

https://stackblitz.com/edit/angular9-class-inheritance

Note: Open the console and click on either Foo or Bar. Then, change the ‘enableIvy’ value in the ‘tsconfig.json’ file or in the StackBlitz settings menu on the left, rerun, and you’ll see a difference in what’s outputted to the console.

🌍 Your Environment

Angular Version:

9.1.1

[kara]

@nbeekman This is actually an intentional change (see the first entry under “less common changes” in the Ivy compatibility guide.

Background: In View Engine (e.g. v8), @HostBinding would be inherited by subclasses, but equivalent bindings in host would not be, which could be confusing. In Ivy, we made it consistent so @HostBinding and host were actually equivalent.

That said, having a way to override host bindings sounds like an interesting use case, so I’ll keep this issue open for discussion.

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