feat(github): support automergeStrategy (#34537)

lib/config/options/index.ts

@@ -2010,7 +2010,7 @@ const options: RenovateOptions[] = [
     type: 'string',
     allowedValues: ['auto', 'fast-forward', 'merge-commit', 'rebase', 'squash'],
     default: 'auto',
-    supportedPlatforms: ['azure', 'bitbucket', 'gitea'],
+    supportedPlatforms: ['azure', 'bitbucket', 'gitea', 'github'],
   },
   {
     name: 'automergeComment',

lib/modules/platform/github/common.ts

@@ -1,6 +1,8 @@
 import is from '@sindresorhus/is';
+import { logger } from '../../../logger';
 import { GithubHttp } from '../../../util/http/github';
 import { getPrBodyStruct } from '../pr-body';
+import type { MergePRConfig } from '../types';
 import type { GhPr, GhRestPr } from './types';
 
 export const githubApi = new GithubHttp();
@@ -57,3 +59,22 @@ export function coerceRestPr(pr: GhRestPr): GhPr {
 
   return result;
 }
+
+export function mapMergeStartegy(
+  strategy: MergePRConfig['strategy'],
+): string | undefined {
+  switch (strategy) {
+    case 'auto':
+      return undefined;
+    case 'fast-forward': {
+      logger.warn(
+        'Fast-forward merge strategy is not supported by Github. Falling back to merge strategy set for the repository.',
+      );
+      return undefined;
+    }
+    case 'merge-commit':
+      return 'merge';
+    default:
+      return strategy;
+  }
+}

lib/modules/platform/github/index.spec.ts

@@ -3640,6 +3640,7 @@ describe('modules/platform/github/index', () => {
         await github.mergePr({
           branchName: '',
           id: pr.number,
+          strategy: 'merge-commit', // for coverage - has no effect on this test
         }),
       ).toBeFalse();
     });
@@ -3661,9 +3662,52 @@ describe('modules/platform/github/index', () => {
         await github.mergePr({
           branchName: '',
           id: pr.number,
+          strategy: 'auto', // for coverage -- has not effect on this test
         }),
       ).toBeFalse();
     });
+
+    it('should warn if automergeStrategy is not supported', async () => {
+      const scope = httpMock.scope(githubApiHost);
+      initRepoMock(scope, 'some/repo');
+      scope.put('/repos/some/repo/pulls/1234/merge').reply(200);
+      await github.initRepo({ repository: 'some/repo' });
+
+      const mergeResult = await github.mergePr({
+        id: 1234,
+        branchName: 'somebranch',
+        strategy: 'fast-forward',
+      });
+
+      expect(mergeResult).toBeTrue();
+      expect(logger.logger.warn).toHaveBeenCalledWith(
+        'Fast-forward merge strategy is not supported by Github. Falling back to merge strategy set for the repository.',
+      );
+    });
+
+    it('should use configured automergeStrategy', async () => {
+      const scope = httpMock.scope(githubApiHost);
+      initRepoMock(scope, 'some/repo');
+      scope.put('/repos/some/repo/pulls/1234/merge').reply(200);
+      await github.initRepo({ repository: 'some/repo' });
+
+      const mergeResult = await github.mergePr({
+        id: 1234,
+        branchName: 'somebranch',
+        strategy: 'rebase',
+      });
+
+      expect(mergeResult).toBeTrue();
+      expect(logger.logger.debug).toHaveBeenCalledWith(
+        {
+          options: {
+            body: { merge_method: 'rebase' },
+          },
+          url: 'repos/some/repo/pulls/1234/merge',
+        },
+        'mergePr',
+      );
+    });
   });
 
   describe('massageMarkdown(input)', () => {

lib/modules/platform/github/index.ts

@@ -67,7 +67,7 @@ import { repoFingerprint } from '../util';
 import { normalizeNamePerEcosystem } from '../utils/github-alerts';
 import { smartTruncate } from '../utils/pr-body';
 import { remoteBranchExists } from './branch';
-import { coerceRestPr, githubApi } from './common';
+import { coerceRestPr, githubApi, mapMergeStartegy } from './common';
 import {
   enableAutoMergeMutation,
   getIssuesQuery,
@@ -1847,6 +1847,7 @@ export async function reattemptPlatformAutomerge({
 export async function mergePr({
   branchName,
   id: prNo,
+  strategy,
 }: MergePRConfig): Promise<boolean> {
   logger.debug(`mergePr(${prNo}, ${branchName})`);
   const url = `repos/${
@@ -1861,9 +1862,12 @@ export async function mergePr({
   }
   let automerged = false;
   let automergeResult: HttpResponse<unknown>;
-  if (config.mergeMethod) {
-    // This path is taken if we have auto-detected the allowed merge types from the repo
-    options.body.merge_method = config.mergeMethod;
+  const mergeStrategy = mapMergeStartegy(strategy) ?? config.mergeMethod;
+
+  if (mergeStrategy) {
+    // This path is taken if we have auto-detected the allowed merge types from the repo or
+    // automergeStrategy is configured by user
+    options.body.merge_method = mergeStrategy;
     try {
       logger.debug({ options, url }, `mergePr`);
       automergeResult = await githubApi.putJson(url, options);

lib/modules/platform/github/readme.md

@@ -140,7 +140,3 @@ When Renovate runs against repositories on `github.com`, and the environment var
 <!-- prettier-ignore -->
 !!! warning
     We reverted the Package Registry Credentials feature to experimental mode, because users reported it's not working correctly with app tokens.
-
-## Features awaiting implementation
-
-- The `automergeStrategy` configuration option has not been implemented for this platform, and all values behave as if the value `auto` was used. Renovate will use the merge strategy configured in the GitHub repository itself, and this cannot be overridden yet