fix(core): migrate using yarn when nxJson has another package manager…

… configured (#16844)

(cherry picked from commit 0654776)

packages/nx/src/utils/package-manager.spec.ts

@@ -0,0 +1,43 @@
+jest.mock('fs');
+import * as fs from 'fs';
+import * as configModule from 'nx/src/config/configuration';
+import { detectPackageManager } from 'nx/src/utils/package-manager';
+
+describe('package-manager', () => {
+  it('should detect package manager in nxJson', () => {
+    jest.spyOn(configModule, 'readNxJson').mockReturnValueOnce({
+      cli: {
+        packageManager: 'pnpm',
+      },
+    });
+    const packageManager = detectPackageManager();
+    expect(packageManager).toEqual('pnpm');
+    expect(fs.existsSync).not.toHaveBeenCalled();
+  });
+
+  it('should detect yarn package manager from yarn.lock', () => {
+    jest.spyOn(configModule, 'readNxJson').mockReturnValueOnce({});
+    (fs.existsSync as jest.Mock).mockReturnValueOnce(true);
+    const packageManager = detectPackageManager();
+    expect(packageManager).toEqual('yarn');
+    expect(fs.existsSync).toHaveBeenNthCalledWith(1, 'yarn.lock');
+  });
+
+  it('should detect pnpm package manager from pnpm-lock.yaml', () => {
+    jest.spyOn(configModule, 'readNxJson').mockReturnValueOnce({});
+    (fs.existsSync as jest.Mock).mockImplementation((path) => {
+      return path === 'pnpm-lock.yaml';
+    });
+    const packageManager = detectPackageManager();
+    expect(packageManager).toEqual('pnpm');
+    expect(fs.existsSync).toHaveBeenCalledTimes(3);
+  });
+
+  it('should use npm package manager as default', () => {
+    jest.spyOn(configModule, 'readNxJson').mockReturnValueOnce({});
+    (fs.existsSync as jest.Mock).mockReturnValue(false);
+    const packageManager = detectPackageManager();
+    expect(packageManager).toEqual('npm');
+    expect(fs.existsSync).toHaveBeenCalledTimes(5);
+  });
+});

packages/nx/src/utils/package-manager.ts

@@ -30,11 +30,14 @@ export interface PackageManagerCommands {
  */
 export function detectPackageManager(dir: string = ''): PackageManager {
   const nxJson = readNxJson();
-  return nxJson.cli?.packageManager ?? existsSync(join(dir, 'yarn.lock'))
-    ? 'yarn'
-    : existsSync(join(dir, 'pnpm-lock.yaml'))
-    ? 'pnpm'
-    : 'npm';
+  return (
+    nxJson.cli?.packageManager ??
+    (existsSync(join(dir, 'yarn.lock'))
+      ? 'yarn'
+      : existsSync(join(dir, 'pnpm-lock.yaml'))
+      ? 'pnpm'
+      : 'npm')
+  );
 }
 
 /**