Schema validation fails when replacing `.mts` file with another one

[demurgos]

Command

build, serve

Is this a regression?

• Yes, this behavior used to work in the previous version

The previous version in which this bug was not present was

No response

Description

I have an Angular 17 project using .mts files. It's working perfectly, both with ng build and ng serve. It uses the @angular-devkit/build-angular:application builder. To support a new feature, I needed to swap a file when running the live-reload mode with ng serve. Following the documentation for fileReplacements, I added:

            "serve": {
              "fileReplacements": [
                {
                  "replace": "src/environments/environment.mts",
                  "with": "src/environments/environment.serve.mts"
                }
              ],
              "ssr": false
            },

I now get the following error when running ng serve:

Error: Schema validation failed with the following errors:
  Data path "/fileReplacements/0/replace" must match pattern "\.(([cm]?j|t)sx?|json)$".

The regex pattern does not match what builds without replacement are actually using. Regular builds support "\.(([cm]?[jt])sx?|json)$". However, the pattern itself is questionable: why even limit the file extensions here? I don't need it right now, but what if I wanted to swap a .wasm file or any other kind of file? If a regular build works, adding a file replacement rule should never restrict it more.

Minimal Reproduction

Add a file replacement rule targeting an mts file. Example:

              "fileReplacements": [
                {
                  "replace": "src/environments/environment.mts",
                  "with": "src/environments/environment.serve.mts"
                }
              ],

Run the corresponding command (ng build, ng serve)

Exception or Error

Error: Schema validation failed with the following errors:
  Data path "/fileReplacements/0/replace" must match pattern "\.(([cm]?j|t)sx?|json)$".

### Your Environment

```text
$ ng version
Node.js version v21.6.1 detected.
Odd numbered Node.js versions will not enter LTS status and should not be used for production. For more information, please see https://nodejs.org/en/about/previous-releases/.

     _                      _                 ____ _     ___
    / \   _ __   __ _ _   _| | __ _ _ __     / ___| |   |_ _|
   / △ \ | '_ \ / _` | | | | |/ _` | '__|   | |   | |    | |
  / ___ \| | | | (_| | |_| | | (_| | |      | |___| |___ | |
 /_/   \_\_| |_|\__, |\__,_|_|\__,_|_|       \____|_____|___|
                |___/
    

Angular CLI: 17.1.3
Node: 21.6.1 (Unsupported)
Package Manager: yarn 4.1.0
OS: linux x64

Angular: 17.1.3
... animations, cli, common, compiler, compiler-cli, core, forms
... language-service, localize, platform-browser
... platform-browser-dynamic, platform-server, router, ssr

Package                         Version
---------------------------------------------------------
@angular-devkit/architect       0.1701.3
@angular-devkit/build-angular   17.1.3
@angular-devkit/core            17.1.3
@angular-devkit/schematics      17.1.3
@schematics/angular             17.1.3
rxjs                            7.8.1
typescript                      5.3.3
zone.js                         0.14.3
    
Warning: The current version of Node (21.6.1) is not supported by Angular.

### Anything else relevant?

_No response_

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