Allow templates to be located on non-default branch (backstage#2839)

* Checkout branch if not on default

* Use checkout Ref

* Get first directory instead of relying on component_id

* Checkout branch when clonning

* Update test

* Default to empty string

* Added changeset

* Added test for Cookie Cutter installed & nothing generated

* Added comment

.changeset/happy-ads-behave.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-scaffolder-backend': patch
+---
+
+Allow templates to be located on non-default branch

plugins/scaffolder-backend/src/scaffolder/stages/prepare/github.test.ts

@@ -76,7 +76,9 @@ describe('GitHubPreparer', () => {
       1,
       'https://github.com/benjdlambert/backstage-graphql-template',
       expect.any(String),
-      {},
+      {
+        checkoutBranch: 'master',
+      },
     );
   });
   it('calls the clone command with the correct arguments for a repository when no path is provided', async () => {
@@ -87,7 +89,9 @@ describe('GitHubPreparer', () => {
       1,
       'https://github.com/benjdlambert/backstage-graphql-template',
       expect.any(String),
-      {},
+      {
+        checkoutBranch: 'master',
+      },
     );
   });
   it('return the temp directory with the path to the folder if it is specified', async () => {
@@ -107,6 +111,7 @@ describe('GitHubPreparer', () => {
       'https://github.com/benjdlambert/backstage-graphql-template',
       expect.any(String),
       {
+        checkoutBranch: 'master',
         fetchOpts: {
           callbacks: {
             credentials: expect.any(Function),

plugins/scaffolder-backend/src/scaffolder/stages/prepare/github.ts

@@ -21,7 +21,7 @@ import { parseLocationAnnotation } from '../helpers';
 import { InputError } from '@backstage/backend-common';
 import { PreparerBase } from './types';
 import GitUriParser from 'git-url-parse';
-import { Clone, Cred } from 'nodegit';
+import { Clone, CloneOptions, Cred } from 'nodegit';
 
 export class GithubPreparer implements PreparerBase {
   token?: string;
@@ -52,17 +52,22 @@ export class GithubPreparer implements PreparerBase {
       template.spec.path ?? '.',
     );
 
-    const cloneOptions = token
-      ? {
-          fetchOpts: {
-            callbacks: {
-              credentials() {
-                return Cred.userpassPlaintextNew(token, 'x-oauth-basic');
-              },
+    let cloneOptions: CloneOptions = {
+      checkoutBranch: parsedGitLocation.ref,
+    };
+
+    if (token) {
+      cloneOptions = {
+        ...cloneOptions,
+        fetchOpts: {
+          callbacks: {
+            credentials() {
+              return Cred.userpassPlaintextNew(token, 'x-oauth-basic');
             },
           },
-        }
-      : {};
+        },
+      };
+    }
 
     await Clone.clone(repositoryCheckoutUrl, tempDir, cloneOptions);
 

plugins/scaffolder-backend/src/scaffolder/stages/templater/cookiecutter.test.ts

@@ -13,16 +13,22 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-jest.mock('./helpers', () => ({ runDockerContainer: jest.fn() }));
+jest.mock('./helpers', () => ({
+  runDockerContainer: jest.fn(),
+  runCommand: jest.fn(),
+}));
+jest.mock('command-exists-promise', () => jest.fn());
 
 import { CookieCutter } from './cookiecutter';
 import fs from 'fs-extra';
 import os from 'os';
 import path from 'path';
-import { RunDockerContainerOptions } from './helpers';
+import { RunDockerContainerOptions, RunCommandOptions } from './helpers';
 import { PassThrough } from 'stream';
 import Docker from 'dockerode';
 
+const commandExists = require('command-exists-promise');
+
 describe('CookieCutter Templater', () => {
   const cookie = new CookieCutter();
   const mockDocker = {} as Docker;
@@ -32,6 +38,10 @@ describe('CookieCutter Templater', () => {
     runDockerContainer: jest.Mock<RunDockerContainerOptions>;
   } = require('./helpers');
 
+  jest
+    .spyOn(fs, 'readdir')
+    .mockImplementation(() => Promise.resolve(['newthing']));
+
   beforeEach(async () => {
     jest.clearAllMocks();
   });
@@ -174,4 +184,71 @@ describe('CookieCutter Templater', () => {
       dockerClient: mockDocker,
     });
   });
+
+  describe('when cookiecutter is available', () => {
+    beforeAll(() => {
+      commandExists.mockImplementation(() => () => true);
+    });
+
+    it('use the binary', async () => {
+      const {
+        runCommand,
+      }: {
+        runCommand: jest.Mock<RunCommandOptions>;
+      } = require('./helpers');
+
+      const stream = new PassThrough();
+
+      const tempdir = await mkTemp();
+
+      const values = {
+        owner: 'blobby',
+        storePath: 'spotify/end-repo',
+        component_id: 'newthing',
+      };
+
+      await cookie.run({
+        directory: tempdir,
+        values,
+        logStream: stream,
+        dockerClient: mockDocker,
+      });
+
+      expect(runCommand).toHaveBeenCalledWith({
+        command: 'cookiecutter',
+        args: expect.arrayContaining([
+          '--no-input',
+          '-o',
+          tempdir,
+          expect.stringContaining(`${tempdir}-result`),
+          '--verbose',
+        ]),
+        logStream: stream,
+      });
+    });
+  });
+
+  describe('when nothing was generated', () => {
+    beforeEach(() => {
+      jest.spyOn(fs, 'readdir').mockImplementation(() => Promise.resolve([]));
+    });
+
+    it('throws an error', async () => {
+      const stream = new PassThrough();
+
+      const tempdir = await mkTemp();
+
+      return expect(
+        cookie.run({
+          directory: tempdir,
+          values: {
+            owner: 'blobby',
+            storePath: 'spotify/end-repo',
+          },
+          logStream: stream,
+          dockerClient: mockDocker,
+        }),
+      ).rejects.toThrow(/Cookie Cutter did not generate anything/);
+    });
+  });
 });

plugins/scaffolder-backend/src/scaffolder/stages/templater/cookiecutter.ts

@@ -78,8 +78,16 @@ export class CookieCutter implements TemplaterBase {
       });
     }
 
+    // if cookiecutter was successful, resultDir will contain
+    // exactly one directory.
+    const [generated] = await fs.readdir(resultDir);
+
+    if (generated === undefined) {
+      throw new Error('Cookie Cutter did not generate anything');
+    }
+
     return {
-      resultDir: path.resolve(resultDir, options.values.component_id as string),
+      resultDir: path.resolve(resultDir, generated),
     };
   }
 }