Angular-cli: `const enum` breaks when running production build/serve

[ericzhangjx]

🐞 Bug report

Command (mark with an x)

- [ ] new
- [x] build
- [x] serve
- [ ] test
- [ ] e2e
- [ ] generate
- [ ] add
- [ ] update
- [ ] lint
- [ ] xi18n
- [ ] run
- [ ] config
- [ ] help
- [ ] version
- [ ] doc

Is this a regression?

Not sure about this. This seems to be a reappearance of #9571.

Description

For a const enum of type number, like const enum TestEnum { DESC = 2, }, usage of this kind TestEnum.DESC.toString(10) breaks on ng serve/build --prod.

🔬 Minimal Reproduction

My global environments:
node --version // v11.10.1
npm --version // 6.9.0
npm list -g --depth=0 | grep angular // @angular/[email protected]

1. On Desktop, run ng new prod-build-test-proj;
   1.1 ? Would you like to add Angular routing? No
   1.2 ? Which stylesheet format would you like to use? CSS (.css )
2. cd prod-build-test-proj/;
3. Add following code to the bottom of file src/app/app.component.ts:

const enum TestBuildProd {
  OPT1 = 1,
  OPT2 = 2,
}

console.log(TestBuildProd.OPT1.toString(10));

1. Run npx ng build, success;
2. Run npx ng build --prod, fail;

🔥 Exception or Error

ERROR in ./src/app/app.component.ts 8:25
Module parse failed: Unexpected token (8:25)
You may need an appropriate loader to handle this file type.
| }());
| export { AppComponent };
> console.log(1 /* OPT1 */..toString(10));
| 

🌍 Your Environment

Angular CLI: 7.3.5
Node: 11.10.1
OS: darwin x64
Angular: 
... 

Package                      Version
------------------------------------------------------
@angular-devkit/architect    0.13.5
@angular-devkit/core         7.3.5
@angular-devkit/schematics   7.3.5
@schematics/angular          7.3.5
@schematics/update           0.13.5
rxjs                         6.3.3
typescript                   3.2.4

Anything else relevant?

If the code was appended to main.ts then everything works normally, this error only occurs when it was appended to *.service.ts or *.component.ts;

[alan-agius4]

Hi, I am sorry but this is not caused by Angular CLI, the issue here is a bug in TypeScript.

Build Optimizer use TypeScript to transform source files, and unfortunately when TypeScript encounters 1 /* OPT1 */.toString(10); it will add an addition dot.

This issue should be resolved with TypeScript 3.3.X.

[alan-agius4]

Related TypeScript issue https://github.com/Microsoft/TypeScript/issues/28868

[ericzhangjx]

Thanks for your quick reply, I just used template string as a workaround until TS 3.3 is supported.

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