[BUG][PWA] Url error in the "ngsw.json" file with a "baseHref" pointing to a file (eg: "/index.html")

Reproduce the PWA build using the baseHref values in angular.json and inspect the generated ngsw.json. Start with the build path that constructs service-worker URLs; done means a file-valued baseHref keeps index.html as the index while asset URLs use its containing path, without the duplicated /index.html/ segment.

Bug Report or Feature Request

- [X] bug report -> please search issues before submitting
- [ ] feature request

From here: https://github.com/angular/angular/issues/26917

Command

- [X] build

Versions

Angular CLI: 7.0.4
Node: 10.8.0 (npm: 6.3.0)
OS: win32 x64
Angular: 7.0.2
... animations, cdk, common, compiler, compiler-cli, core, forms
... http, language-service, material, platform-browser
... platform-browser-dynamic, router, service-worker

Package                           Version
-----------------------------------------------------------
@angular-devkit/architect         0.10.4
@angular-devkit/build-angular     0.10.4
@angular-devkit/build-optimizer   0.10.4
@angular-devkit/build-webpack     0.10.4
@angular-devkit/core              7.0.4
@angular-devkit/schematics        7.0.4
@angular/cli                      7.0.4
@angular/pwa                      0.10.4
@ngtools/webpack                  7.0.4
@schematics/angular               7.0.4
@schematics/update                0.10.4
rxjs                              6.3.3
typescript                        3.1.6
webpack                           4.19.1

Current behavior

I have a problem with the file ngsw.json (dist/xxx/ngsw.json), when I build my application.
Here is the configuration of my file angular.json:

{
  "$schema": "./node_modules/@angular/cli/lib/config/schema.json",
  "version": 1,
  "newProjectRoot": "projects",
  "projects": {
    "xxxxxx-xxxxxx-web": {
      ...
      "architect": {
        "build": {
          "builder": "@angular-devkit/build-angular:browser",
          "options": {
            "baseHref": "/index.html",   <-- baseHref with path to a file
            ...
          },
          "configurations": {
            "develop": {
              ...
              "baseHref": "/dev-web-xxxxxx-xxxxxx/index.html",   <-- baseHref with path to a file
              "fileReplacements": [
                {
                  "replace": "src/environments/environment.ts",
                  "with": "src/environments/environment.develop.ts"
                }
              ],
              "optimization": true,
              "outputHashing": "all",
              "sourceMap": true,
              "extractCss": true,
              "namedChunks": false,
              "aot": true,
              "extractLicenses": true,
              "vendorChunk": false,
              "buildOptimizer": true,
              "serviceWorker": true
            }
            ...

As you can see, my baseHref points to a file (index.html). And when I compile, here is the result of the file ngsw.json:

{
  "configVersion": 1,
  "index": "/dev-web-xxxxxx-xxxxxx/index.html/index.html",
  "assetGroups": [                 ^^^^^^^^^^
    {
      "name": "app",
      "installMode": "prefetch",
      "updateMode": "prefetch",
      "urls": [                 vvvvvvvvvv
        "/dev-web-xxxxxx-xxxxxx/index.html/4.459d2c031076fa54578c.js",
        "/dev-web-xxxxxx-xxxxxx/index.html/5.b0a92526f07730e41004.js",
        "/dev-web-xxxxxx-xxxxxx/index.html/index.html",
        "/dev-web-xxxxxx-xxxxxx/index.html/main.284d15247a9766d625e1.js",
        "/dev-web-xxxxxx-xxxxxx/index.html/polyfills.f8bea440aac573c30541.js",
        "/dev-web-xxxxxx-xxxxxx/index.html/runtime.e04cbf91ceee4f9b3494.js",
        "/dev-web-xxxxxx-xxxxxx/index.html/styles.380a38f67b77a997829f.css"
      ],                        ^^^^^^^^^^
      "patterns": []
    },
    {
      "name": "assets",
      "installMode": "lazy",
      "updateMode": "prefetch",
      "urls": [                 vvvvvvvvvv
        "/dev-web-xxxxxx-xxxxxx/index.html/assets/icons/icon-128x128.png",
        "/dev-web-xxxxxx-xxxxxx/index.html/assets/icons/icon-144x144.png",
        ...                     ^^^^^^^^^^

As you can see, it generates all the urls of the file with the .../index.html/..., as if it were a folder. As this file is used for the cache of the application, the cache does not work since it is not the right url...

Expected behavior

I think the file should have looked like this:

{
  "configVersion": 1,
  "index": "/dev-web-xxxxxx-xxxxxx/index.html",
  "assetGroups": [
    {
      "name": "app",
      "installMode": "prefetch",
      "updateMode": "prefetch",
      "urls": [
        "/dev-web-xxxxxx-xxxxxx/4.459d2c031076fa54578c.js",
        "/dev-web-xxxxxx-xxxxxx/5.b0a92526f07730e41004.js",
        "/dev-web-xxxxxx-xxxxxx/index.html",
        "/dev-web-xxxxxx-xxxxxx/main.284d15247a9766d625e1.js",
        "/dev-web-xxxxxx-xxxxxx/polyfills.f8bea440aac573c30541.js",
        "/dev-web-xxxxxx-xxxxxx/runtime.e04cbf91ceee4f9b3494.js",
        "/dev-web-xxxxxx-xxxxxx/styles.380a38f67b77a997829f.css"
      ],
      "patterns": []
    },
    {
      "name": "assets",
      "installMode": "lazy",
      "updateMode": "prefetch",
      "urls": [
        "/dev-web-xxxxxx-xxxxxx/assets/icons/icon-128x128.png",
        "/dev-web-xxxxxx-xxxxxx/assets/icons/icon-144x144.png",
        ...

Minimal reproduction of the problem with instructions

You just have to create an application (which uses PWA) and have a baseHref that points to a file (eg: index.html). And when you compile your application, the url generated in the ngsw.json file will be wrong.

What is the motivation / use case for changing the behavior?

I think it would just take into account when the "baseHref" to deal with a file, take the root of the file (and not take the file for a folder).

For information, I use a baseHref to a file, because I use the system of route of Angular with the hash and that the url https://storage.googleapis.com/dev-web-xxxxxx-xxxxxx/ does not point towards my file index.html. As the project is hosted on a Google Cloud Storage, when we update the application (CTRL+F5, ...) with a url of this type ...-xxxxxx/#/user/login, I end up with a 404 error (because the url in ...-xxxxxx/ does not point to the file index.html). To solve this problem, I force Angular to keep the index.html in the URL (eg: ...-xxxxxx/index.html#/user/login), through baseHref with the index.html in it.

For now, I make the corrections of the url in the file ngsw.json manually, so that the cache of the application works...