cli: allow running with no configuration files

Co-authored-by: Patrik Oldsberg <poldsberg@gmail.com>
Signed-off-by: MT Lewis <mtlewis@users.noreply.github.com>

packages/config-loader/api-report.md

@@ -21,6 +21,7 @@ export type AsyncConfigSourceGenerator = AsyncGenerator<
 
 // @public
 export interface BaseConfigSourcesOptions {
+  allowMissingDefaultConfig?: boolean;
   // (undocumented)
   remote?: Pick<RemoteConfigSourceOptions, 'reloadInterval'>;
   // (undocumented)

packages/config-loader/src/sources/ConfigSources.test.ts

@@ -69,13 +69,18 @@ describe('ConfigSources', () => {
   });
 
   it('should create default sources for targets', () => {
+    const fsSpy = jest.spyOn(fs, 'pathExistsSync').mockImplementation(path => {
+      return path === `${root}app-config.yaml`;
+    });
+
     expect(
       mergeSources(
         ConfigSources.defaultForTargets({ rootDir: '/', targets: [] }),
       ),
     ).toEqual([{ name: 'FileConfigSource', path: `${root}app-config.yaml` }]);
 
-    const fsSpy = jest.spyOn(fs, 'pathExistsSync').mockReturnValue(true);
+    fsSpy.mockReturnValue(true);
+
     expect(
       mergeSources(
         ConfigSources.defaultForTargets({ rootDir: '/', targets: [] }),
@@ -159,6 +164,10 @@ describe('ConfigSources', () => {
   });
 
   it('should create a default source', () => {
+    const fsSpy = jest.spyOn(fs, 'pathExistsSync').mockImplementation(path => {
+      return path === `${root}app-config.yaml`;
+    });
+
     expect(
       mergeSources(
         ConfigSources.default({
@@ -184,6 +193,8 @@ describe('ConfigSources', () => {
       { name: 'FileConfigSource', path: resolvePath('b.yaml') },
       { name: 'EnvConfigSource', env: { HOME: '/' } },
     ]);
+
+    fsSpy.mockRestore();
   });
 
   it('should merge sources', () => {

packages/config-loader/src/sources/ConfigSources.ts

@@ -74,6 +74,11 @@ export interface BaseConfigSourcesOptions {
   watch?: boolean;
   rootDir?: string;
   remote?: Pick<RemoteConfigSourceOptions, 'reloadInterval'>;
+  /**
+   * Allow the default app-config.yaml to be missing, in which case the source
+   * will not be created.
+   */
+  allowMissingDefaultConfig?: boolean;
 
   /**
    * A custom substitution function that overrides the default one.
@@ -177,14 +182,19 @@ export class ConfigSources {
     if (argSources.length === 0) {
       const defaultPath = resolvePath(rootDir, 'app-config.yaml');
       const localPath = resolvePath(rootDir, 'app-config.local.yaml');
+      const alwaysIncludeDefaultConfigSource =
+        !options.allowMissingDefaultConfig;
+
+      if (alwaysIncludeDefaultConfigSource || fs.pathExistsSync(defaultPath)) {
+        argSources.push(
+          FileConfigSource.create({
+            watch: options.watch,
+            path: defaultPath,
+            substitutionFunc: options.substitutionFunc,
+          }),
+        );
+      }
 
-      argSources.push(
-        FileConfigSource.create({
-          watch: options.watch,
-          path: defaultPath,
-          substitutionFunc: options.substitutionFunc,
-        }),
-      );
       if (fs.pathExistsSync(localPath)) {
         argSources.push(
           FileConfigSource.create({