core-app-api: defaultConfigLoader no longer requires APP_CONFIG to be set

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

.changeset/sweet-pigs-pump.md

@@ -0,0 +1,6 @@
+---
+'@backstage/core-app-api': patch
+'@backstage/frontend-defaults': patch
+---
+
+The default config loader no longer requires `process.env.APP_CONFIG` to be set, allowing config to be read from other sources instead.

packages/core-app-api/src/app/defaultConfigLoader.test.tsx

@@ -29,6 +29,10 @@ describe('defaultConfigLoaderSync', () => {
     delete anyWindow.__APP_CONFIG__;
   });
 
+  it('loads nothing is config is missing', () => {
+    expect(defaultConfigLoaderSync()).toEqual([]);
+  });
+
   it('loads static config', () => {
     anyEnv.APP_CONFIG = [
       { data: { my: 'config' }, context: 'a' },
@@ -95,12 +99,6 @@ describe('defaultConfigLoaderSync', () => {
     expect(ConfigReader.fromConfigs(configs).get('my')).toBe('override-config');
   });
 
-  it('fails to load invalid missing config', () => {
-    expect(() => defaultConfigLoaderSync()).toThrow(
-      'No static configuration provided',
-    );
-  });
-
   it('fails to load invalid static config', () => {
     anyEnv.APP_CONFIG = { my: 'invalid-config' };
     expect(() => defaultConfigLoaderSync()).toThrow(

packages/core-app-api/src/app/defaultConfigLoader.ts

@@ -40,14 +40,15 @@ export function defaultConfigLoaderSync(
   // It's a param so we can test it, but at runtime this will always fall back to default.
   runtimeConfigJson: string = '__APP_INJECTED_RUNTIME_CONFIG__',
 ) {
-  const appConfig = process.env.APP_CONFIG;
-  if (!appConfig) {
-    throw new Error('No static configuration provided');
+  const configs = new Array<AppConfig>();
+
+  const staticConfig = process.env.APP_CONFIG;
+  if (staticConfig) {
+    if (!Array.isArray(staticConfig)) {
+      throw new Error('Static configuration has invalid format');
+    }
+    configs.push(...staticConfig);
   }
-  if (!Array.isArray(appConfig)) {
-    throw new Error('Static configuration has invalid format');
-  }
-  const configs = appConfig.slice() as unknown as AppConfig[];
 
   // Check if we have any config script tags, otherwise fall back to injected config
   const configScripts = document.querySelectorAll(