HTML files and fileReplacements work differently for "ng serve --prod" and "ng build --prod"

[gunsh]

🐞 Bug report

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

Is this a regression?

I recall this working prior to upgrading to v8.

Description

The section "fileReplacements" in "angular.json" works for "ng serve" and "ng serve --prod" but not for "ng build --prod".

🔬 Minimal Reproduction

Clone the repro app. There are two sets of files to observe:

• environment.ts and environment.prod.ts
• index.html and index.prod.html

File "angular.json" has the appropriate "fileReplacements" for production build for the two sets of files. The HTML files differ in the <h1> tag which clearly indicates development/production. Also, the AppComponent merely reflects "environment.production".

1. Run the app with "ng serve", both <h1> and AppComponent show "development" as expected.
2. Run the app with "ng serve --prod", both <h1> and AppComponent show "production" as expected.
3. Run the app with "ng build --prod" and run the app using e.g. "serve", the <h1> shows "development" while AppComponent shows "production". Clearly not as expected. Inspecting generated "dist/index.html" shows that the file was NOT replaced.

🔥 Exception or Error

There is no error. If this feature is not supported as some people have indicated in issue #10881, then there should definitely be an error during build that the files are skipped/ignored. There is no indication that the HTML files are skipped.

It is strange that "ng serve --prod" behaves differently to "ng build --prod".

🌍 Your Environment

Angular CLI: 8.0.6
Node: 10.16.0
OS: win32 x64
Angular: 8.0.3
... animations, common, compiler, compiler-cli, core, forms
... language-service, platform-browser, platform-browser-dynamic
... router

Package                           Version
-----------------------------------------------------------
@angular-devkit/architect         0.800.6
@angular-devkit/build-angular     0.800.6
@angular-devkit/build-optimizer   0.800.6
@angular-devkit/build-webpack     0.800.6
@angular-devkit/core              8.0.6
@angular-devkit/schematics        8.0.6
@angular/cli                      8.0.6
@ngtools/webpack                  8.0.6
@schematics/angular               8.0.6
@schematics/update                0.800.6
rxjs                              6.4.0
typescript                        3.4.5
webpack                           4.30.0

Anything else relevant?
I have tried running "ng update" to get the latest and greatest but it did not work either.

[alan-agius4]

Duplicate of #14599

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