🐞 bug report

Is this a regression?

Yes, the previous version in which this bug was not present was: ^8

Description

Using a template literal expression used to work until Angular 9, for as long as the template lived in the TS source not in HTML (obviously).

Since Angular 9 that does not work any longer in one scenario. I am mostly focusing on library builds here:

Working

• build library with Angular 9 Ivy & serve the Angular 9 application
• build library with Angular 8 View Engine & serve the Angular 8 application
• build library with Angular 8 View Engine & serve the Angular 9 application (ngcc)

Not working

• build library with Angular 9 View Engine (ng build lib --prod) & serve the Angular 9 application (ngcc)

🔬 Minimal Reproduction

In any Angular workspace create a library and do the following:

const enum Demo {
  First
}

@Component({
  template: `
    Static variable: ${ Demo.First  }
  `
})
export class DemoComponent {}

🔥 Exception or Error

error NG1010: template must be a string

🌍 Your Environment

Angular Version:

Angular CLI: 9.0.3
Node: 12.15.0
OS: darwin x64

Angular: 9.0.2
... animations, common, compiler, compiler-cli, core, forms
... language-service, platform-browser, platform-browser-dynamic
... router
Ivy Workspace: Yes

Package                            Version
------------------------------------------------------------
@angular-devkit/architect          0.900.3
@angular-devkit/build-angular      0.900.3
@angular-devkit/build-ng-packagr   0.900.3
@angular-devkit/build-optimizer    0.900.3
@angular-devkit/build-webpack      0.900.3
@angular-devkit/core               9.0.3
@angular-devkit/schematics         9.0.3
@angular/cdk                       9.0.1
@angular/cli                       9.0.3
@angular/material                  9.0.1
@ngtools/webpack                   9.0.3
@schematics/angular                9.0.3
@schematics/update                 0.900.3
ng-packagr                         9.0.1
rxjs                               6.5.4
typescript                         3.7.5
webpack                            4.41.2

Anything else relevant?

I am not 100% sure this was ever officially supported, even though I would have hoped so, since it is native ES6 feature. If it wasn’t supported, please close the issue.

Interesting observation is, that View Engine compiled library from Angular 8 is correctly processed by ngcc, while View Engine from Angular 9 surprisingly fails.

---

EDIT: Seems like an easy reproduction mentioned above is not reproducible any more. I can still reproduce it, if I use literal expressions while binding to input, e.g.: [title]="${variable}".

Reproduction:

• Clone: https://github.com/klemenoslaj/template-literal-expressions-issue
• Execute: yarn && yarn reproduce

Resulting in error:

dist/example/fesm2015/example.js:29:19 - error NG1010: template must be a string

29         template: `
                     ~
30     <button [title]="${ButtonType.Button}">Button</button>
   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
31   `
   ~~~
dist/example/fesm2015/example.js:39:24 - error NG6001: The class 'ExampleComponent' is listed in the declarations of the NgModule 'ExampleModule', but is not a directive, a component, or a pipe.