[8.2.x][ES2015][prod] custom decorators on inputs are ignored when used inside lib

[jlowcs]

🐞 bug report

Affected Package

I'd assume @angular-devkit/[email protected]

Is this a regression?

Yes, the issue was not present in Angular 8.1.x or 8.0.x, or even previous majors.

Description

When running in prod mode, with a ES2015 target, any custom decorator that is used in a library used by the app will simply be ignored.

🔬 Minimal Reproduction

I made a small repository that reproduces the issue. You can follow the README.

Basically, what it does is:

• build a library that uses a custom decorator on a component's input
• use the component from that built library in an app, in prod mode, with a ES2015 target

=> the decorator is ignored

🌍 Your Environment

Angular Version:

Angular CLI: 8.2.1
Node: 10.15.3
OS: win32 x64
Angular: 8.2.1
... cli, common, compiler, compiler-cli, core, platform-browser
... platform-browser-dynamic

Package                            Version
------------------------------------------------------------
@angular-devkit/architect          0.802.1
@angular-devkit/build-angular      0.802.1
@angular-devkit/build-ng-packagr   0.802.1
@angular-devkit/build-optimizer    0.802.1
@angular-devkit/build-webpack      0.802.1
@angular-devkit/core               8.2.1
@angular-devkit/schematics         8.2.1
@ngtools/webpack                   8.2.1
@schematics/angular                8.2.1
@schematics/update                 0.802.1
ng-packagr                         5.4.3
rxjs                               6.5.2
typescript                         3.5.3
webpack                            4.38.0

Anything else relevant?

The issue is only present when targetting ES2015 and in prod mode.

[clydin]

Duplicate of #15301

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