Merge latest changes from origin before rebuilding docs (#2117)

* Added missing tests and make sure we merge latest changes before building docs from a repo

* Removed flaky test

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

@@ -0,0 +1,56 @@
+/*
+ * Copyright 2020 Spotify AB
+ *
+ * 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 { getVoidLogger } from '@backstage/backend-common';
+import { GithubPreparer } from './github';
+import { checkoutGitRepository } from './helpers';
+
+jest.mock('./helpers', () => ({
+  ...jest.requireActual<{}>('./helpers'),
+  checkoutGitRepository: jest.fn(() => '/tmp/backstage-repo/org/name/branch'),
+}));
+
+const createMockEntity = (annotations = {}) => {
+  return {
+    apiVersion: 'version',
+    kind: 'TestKind',
+    metadata: {
+      name: 'test-component-name',
+      annotations: {
+        ...annotations,
+      },
+    },
+  };
+};
+
+const logger = getVoidLogger();
+
+describe('github preparer', () => {
+  it('should prepare temp docs path from github repo', async () => {
+    const preparer = new GithubPreparer(logger);
+
+    const mockEntity = createMockEntity({
+      'backstage.io/techdocs-ref':
+        'github:https://github.com/spotify/backstage/blob/master/plugins/techdocs-backend/examples/documented-component',
+    });
+
+    const tempDocsPath = await preparer.prepare(mockEntity);
+    expect(checkoutGitRepository).toHaveBeenCalledTimes(1);
+    expect(tempDocsPath).toEqual(
+      '/tmp/backstage-repo/org/name/branch/plugins/techdocs-backend/examples/documented-component',
+    );
+  });
+});

plugins/techdocs-backend/src/techdocs/stages/prepare/helpers.ts

@@ -17,7 +17,7 @@ import { Entity } from '@backstage/catalog-model';
 import { InputError } from '@backstage/backend-common';
 import { RemoteProtocol } from './types';
 import parseGitUrl from 'git-url-parse';
-import { Clone } from 'nodegit';
+import { Clone, Repository } from 'nodegit';
 import fs from 'fs-extra';
 import os from 'os';
 import path from 'path';
@@ -78,8 +78,14 @@ export const checkoutGitRepository = async (
   );
 
   if (fs.existsSync(repositoryTmpPath)) {
+    const repository = await Repository.open(repositoryTmpPath);
+    await repository.mergeBranches(
+      parsedGitLocation.ref,
+      `origin/${parsedGitLocation.ref}`,
+    );
     return repositoryTmpPath;
   }
+
   const repositoryCheckoutUrl = parsedGitLocation.toString('https');
 
   fs.mkdirSync(repositoryTmpPath, { recursive: true });