ngcc generates invalid property metadata

🐞 bug report

Affected Package

@angular/compiler-cli / ngcc

Description

Currently when compiling @angular/cdk/a11y with ngcc, the generated property metadata call (setClassMetadata) incorrectly sets metadata for the autoCapture property within the FocusTrap twice.

ɵngcc0.ɵsetClassMetadata(..., {
  autoCapture: [{
      type: Input,
      args: ['cdkTrapFocusAutoCapture']
    }], 
  autoCapture: [], 
});

This means that the first occurrence will be accidentally overwritten and the metadata is discarded. The duplication seems to happen because autoCapture declares a getter and a setter.

As far as I could tell the issue is that ngcc returns the getter and setter for reflection.getMembersOfClass(FocusTrap) but sets decorators that are either defined on getter or setter as decorators for both members. This then results in two properties with the same name in the setClassMetadata call.

https://github.com/angular/angular/blob/master/packages/compiler-cli/src/ngtsc/annotations/src/metadata.ts#L59-L62

🔬 Minimal Reproduction

https://github.com/devversion/ivy-ngcc-generates-duplicate-prop-metadata

🔥 Exception or Error

See: https://github.com/angular/components/issues/16066

Defining the same property multiple times seems to cause an exception in IE11 with use strict mode. This is actually reasonable as the first declaration is accidentally overwritten in an object literal.

🌍 Your Environment

Angular Version:

@angular/*: 8.0.0-rc.4
@angular/cdk: 8.0.0-rc.1

[Splaktar]

Is freq1: low correct for this issue? It seems a little low for an issue that breaks apps on an entire, supported, browser?

[M4R1KU]

@nmainardi It is fixed in 9.0.0-rc.3. You have to upgrade to atleast this version.