cli: stop requiring config for the frontend build

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

.changeset/poor-jeans-rescue.md

@@ -0,0 +1,5 @@
+---
+'@backstage/cli': patch
+---
+
+Make `http://localhost:3000` the default base URL for serving locally, and `/` the default public path for built apps. The app build no longer requires any configuration values to be present.

packages/cli/src/lib/bundler/bundle.ts

@@ -23,7 +23,7 @@ import {
   printFileSizesAfterBuild,
 } from 'react-dev-utils/FileSizeReporter';
 import formatWebpackMessages from 'react-dev-utils/formatWebpackMessages';
-import { createConfig, resolveBaseUrl } from './config';
+import { createConfig } from './config';
 import { BuildOptions } from './types';
 import { resolveBundlingPaths, resolveOptionalBundlingPaths } from './paths';
 import chalk from 'chalk';
@@ -51,7 +51,6 @@ export async function buildBundle(options: BuildOptions) {
     ...options,
     checksEnabled: false,
     isDev: false,
-    baseUrl: resolveBaseUrl(options.frontendConfig),
     getFrontendAppConfigs: () => options.frontendAppConfigs,
   };
   const configs = [

packages/cli/src/lib/bundler/config.ts

@@ -44,9 +44,9 @@ import { hasReactDomClient } from './hasReactDomClient';
 const BUILD_CACHE_ENV_VAR = 'BACKSTAGE_CLI_EXPERIMENTAL_BUILD_CACHE';
 
 export function resolveBaseUrl(config: Config): URL {
-  const baseUrl = config.getString('app.baseUrl');
+  const baseUrl = config.getOptionalString('app.baseUrl');
   try {
-    return new URL(baseUrl);
+    return new URL(baseUrl ?? '/', 'http://localhost:3000');
   } catch (error) {
     throw new Error(`Invalid app.baseUrl, ${error}`);
   }
@@ -100,8 +100,7 @@ export async function createConfig(
   const { packages } = await getPackages(cliPaths.targetDir);
   const externalPkgs = packages.filter(p => !isChildPath(paths.root, p.dir));
 
-  const baseUrl = frontendConfig.getString('app.baseUrl');
-  const validBaseUrl = new URL(baseUrl);
+  const validBaseUrl = resolveBaseUrl(frontendConfig);
   let publicPath = validBaseUrl.pathname.replace(/\/$/, '');
   if (publicSubPath) {
     publicPath = `${publicPath}${publicSubPath}`.replace('//', '/');

packages/cli/src/lib/bundler/server.ts

@@ -110,9 +110,10 @@ DEPRECATION WARNING: React Router Beta is deprecated and support for it will be
   });
   latestFrontendAppConfigs = cliConfig.frontendAppConfigs;
 
-  const appBaseUrl = cliConfig.frontendConfig.getString('app.baseUrl');
-  const backendBaseUrl = cliConfig.frontendConfig.getString('backend.baseUrl');
-  if (appBaseUrl === backendBaseUrl) {
+  const appBaseUrl = cliConfig.frontendConfig.getOptionalString('app.baseUrl');
+  const backendBaseUrl =
+    cliConfig.frontendConfig.getOptionalString('backend.baseUrl');
+  if (appBaseUrl && appBaseUrl === backendBaseUrl) {
     console.log(
       chalk.yellow(
         `⚠️   Conflict between app baseUrl and backend baseUrl:

packages/cli/src/lib/bundler/types.ts

@@ -23,7 +23,6 @@ export type BundlingOptions = {
   isDev: boolean;
   frontendConfig: Config;
   getFrontendAppConfigs(): AppConfig[];
-  baseUrl: URL;
   parallelism?: number;
   additionalEntryPoints?: string[];
   // Path to append to the detected public path, e.g. '/public'