## Inheritance Semantics:
Decorators:
1) list the decorators of the class and its parents in the ancestor first order
2) only use the last decorator of each kind (e.g. @Component / ...)
Constructor parameters:
If a class inherits from a parent class and does not declare
a constructor, it inherits the parent class constructor,
and with it the parameter metadata of that parent class.
Lifecycle hooks:
Follow the normal class inheritance model,
i.e. lifecycle hooks of parent classes will be called
even if the method is not overwritten in the child class.
## Example
E.g. the following is a valid use of inheritance and it will
also inherit all metadata:
```
@Directive({selector: 'someDir'})
class ParentDirective {
constructor(someDep: SomeDep) {}
ngOnInit() {}
}
class ChildDirective extends ParentDirective {}
```
Closes#11606Closes#12892
This is needed to resolve symbols without `.d.ts` files.
This bumps the version of the metadata from 1 to 2.
This adds logic into `ng_host.ts` to automatically upgrade
version 1 to version 2 metadata by adding the exported symbols
from the `.d.ts` file.
ngc can now validate metadata before emitting to verify it doesn't
contain an error symbol that will result in a runtime error if
it is used by the StaticReflector.
To enable this add the section,
"angularCompilerOptions": {
"strictMetadataEmit": true
}
to the top level of the tsconfig.json file passed to ngc.
Enabled metadata validation for packages that are intended to be
used statically.
Victor Berchet
Bowen Ni
Tobias Bosch
Bowen Ni
Alex Eagle
Chuck Jazdzewski
Joao Dias
Igor Minar
Miško Hevery
Marc Laval
Alex Eagle
Matias Niemelä
Hans