cli: add isMonoRepo helper

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

packages/cli/src/lib/monorepo/isMonoRepo.ts

@@ -0,0 +1,28 @@
+/*
+ * Copyright 2022 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { paths } from '../paths';
+import fs from 'fs-extra';
+
+export async function isMonoRepo(): Promise<boolean> {
+  const rootPackageJsonPath = paths.resolveTargetRoot('package.json');
+  try {
+    const pkg = await fs.readJson(rootPackageJsonPath);
+    return Boolean(pkg?.workspaces?.packages);
+  } catch (error) {
+    return false;
+  }
+}

packages/cli/src/lib/monorepo/isMonorepo.test.ts

@@ -0,0 +1,50 @@
+/*
+ * Copyright 2022 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { isMonoRepo } from './isMonoRepo';
+import mockFs from 'mock-fs';
+
+describe('isMonoRepo', () => {
+  afterEach(() => {
+    mockFs.restore();
+  });
+
+  it('should detect a monorepo', async () => {
+    mockFs({
+      'package.json': JSON.stringify({
+        name: 'foo',
+        workspaces: {
+          packages: ['packages/*'],
+        },
+      }),
+    });
+    await expect(isMonoRepo()).resolves.toBe(true);
+  });
+
+  it('should detect a non- monorepo', async () => {
+    mockFs({
+      'package.json': JSON.stringify({
+        name: 'foo',
+      }),
+    });
+    await expect(isMonoRepo()).resolves.toBe(false);
+  });
+
+  it('should return false if package.json is missing', async () => {
+    mockFs({});
+    await expect(isMonoRepo()).resolves.toBe(false);
+  });
+});