fix(devserver) Remove "prod" requirement for using publicPath (#4962)

* add option to force publicPath in 'dev' builds

* Update quasar-conf-js.md

app/lib/quasar-config.js

@@ -376,6 +376,7 @@ class QuasarConfig {
       webpackManifest: this.ctx.prod,
       vueRouterMode: 'hash',
       preloadChunks: true,
+      forceDevPublicPath: false,
       // transpileDependencies: [], // leaving here for completeness
       devtool: this.ctx.dev
         ? '#cheap-module-eval-source-map'
@@ -474,7 +475,7 @@ class QuasarConfig {
     }
 
     cfg.build.publicPath =
-      this.ctx.prod && cfg.build.publicPath && ['spa', 'pwa'].includes(this.ctx.modeName)
+      (this.ctx.prod || cfg.build.forceDevPublicPath) && cfg.build.publicPath && ['spa', 'pwa'].includes(this.ctx.modeName)
         ? formatPublicPath(cfg.build.publicPath)
         : (cfg.build.vueRouterMode !== 'hash' ? '/' : '')
 
@@ -711,7 +712,7 @@ class QuasarConfig {
       }
     }
     else {
-      cfg.build.env.__statics = `"${this.ctx.dev ? '/' : cfg.build.publicPath || '/'}statics"`
+      cfg.build.env.__statics = `"${((this.ctx.prod || cfg.build.forceDevPublicPath) && cfg.build.publicPath) ? cfg.build.publicPath : '/' }statics"`
     }
 
     appFilesValidations(cfg)

docs/src/pages/quasar-cli/quasar-conf-js.md

@@ -209,6 +209,7 @@ devServer: {
 | afterBuild({ quasarConf }) | Function | Run hook after Quasar built app for production (`$ quasar build`). At this point, the distributables folder has been created and is available should you wish to do something with it. Can use async/await or directly return a Promise. |
 | onPublish(opts) | Function | Run hook if publishing was requested (`$ quasar build -P`), after Quasar built app for production and the afterBuild hook (if specified) was executed. Can use async/await or directly return a Promise. `opts` is Object of form `{arg, distDir}`, where "arg" is the argument supplied (if any) to -P parameter. |
 | publicPath | String | Public path of your app. By default, it uses the root. Use it when your public path is something else, like "<protocol>://<domain>/some/nested/folder" -- in this case, it means the distributables are in "some/nested/folder" on your webserver. |
+| forceDevPublicPath | Boolean | Force use of the custom publicPath in dev builds also (only for SPA and PWA modes). Make sure that you know what you are doing. |
 | vueRouterMode | String | Sets [Vue Router mode](https://router.vuejs.org/en/essentials/history-mode.html): 'hash' or 'history'. Pick wisely. History mode requires configuration on your deployment web server too. |
 | htmlFilename | String | Default is 'index.html'. |
 | productName | String | Default value is taken from package.json > productName field. |