feat(gerrit): use commit message footers to store source branch name

lib/modules/platform/gerrit/client.spec.ts

@@ -98,7 +98,10 @@ describe('modules/platform/gerrit/client', () => {
       ['owner:self', { branchName: 'dependency-xyz' }],
       ['project:repo', { branchName: 'dependency-xyz' }],
       ['-is:wip', { branchName: 'dependency-xyz' }],
-      ['hashtag:sourceBranch-dependency-xyz', { branchName: 'dependency-xyz' }],
+      [
+        'footer:Renovate-Source-Branch=dependency-xyz',
+        { branchName: 'dependency-xyz' },
+      ],
       ['label:Code-Review=-2', { branchName: 'dependency-xyz', label: '-2' }],
       [
         'branch:otherTarget',

lib/modules/platform/gerrit/client.ts

@@ -232,7 +232,7 @@ class GerritClient {
     const filterState = mapPrStateToGerritFilter(searchConfig.state);
     const filters = ['owner:self', 'project:' + repository, filterState];
     if (searchConfig.branchName !== '') {
-      filters.push(`hashtag:sourceBranch-${searchConfig.branchName}`);
+      filters.push(`footer:Renovate-Source-Branch=${searchConfig.branchName}`);
     }
     if (searchConfig.targetBranch) {
       filters.push(`branch:${searchConfig.targetBranch}`);

lib/modules/platform/gerrit/scm.spec.ts

@@ -300,13 +300,20 @@ describe('modules/platform/gerrit/scm', () => {
         baseBranch: 'main',
         branchName: 'renovate/dependency-1.x',
         files: [],
-        message: ['commit msg', expect.stringMatching(/Change-Id: I.{32}/)],
+        message: [
+          'commit msg',
+          expect.stringMatching(
+            new RegExp(
+              '^Renovate-Source-Branch: renovate/dependency-1\\.x\\nChange-Id: I[a-z0-9]{40}$',
+            ),
+          ),
+        ],
         force: true,
       });
       expect(git.pushCommit).toHaveBeenCalledWith({
         files: [],
         sourceRef: 'renovate/dependency-1.x',
-        targetRef: 'refs/for/main%t=sourceBranch-renovate/dependency-1.x',
+        targetRef: 'refs/for/main',
       });
     });
 
@@ -339,7 +346,10 @@ describe('modules/platform/gerrit/scm', () => {
         baseBranch: 'main',
         branchName: 'renovate/dependency-1.x',
         files: [],
-        message: ['commit msg', 'Change-Id: ...'],
+        message: [
+          'commit msg',
+          'Renovate-Source-Branch: renovate/dependency-1.x\nChange-Id: ...',
+        ],
         force: true,
       });
       expect(git.fetchRevSpec).toHaveBeenCalledWith('refs/changes/1/2');
@@ -377,14 +387,17 @@ describe('modules/platform/gerrit/scm', () => {
         baseBranch: 'main',
         branchName: 'renovate/dependency-1.x',
         files: [],
-        message: ['commit msg', 'Change-Id: ...'],
+        message: [
+          'commit msg',
+          'Renovate-Source-Branch: renovate/dependency-1.x\nChange-Id: ...',
+        ],
         force: true,
       });
       expect(git.fetchRevSpec).toHaveBeenCalledWith('refs/changes/1/2');
       expect(git.pushCommit).toHaveBeenCalledWith({
         files: [],
         sourceRef: 'renovate/dependency-1.x',
-        targetRef: 'refs/for/main%t=sourceBranch-renovate/dependency-1.x',
+        targetRef: 'refs/for/main',
       });
       expect(clientMock.wasApprovedBy).toHaveBeenCalledWith(
         existingChange,

lib/modules/platform/gerrit/scm.ts

@@ -109,7 +109,7 @@ export class GerritScm extends DefaultGitScm {
       typeof commit.message === 'string' ? [commit.message] : commit.message;
     commit.message = [
       ...origMsg,
-      `Change-Id: ${existingChange?.change_id ?? generateChangeId()}`,
+      `Renovate-Source-Branch: ${commit.branchName}\nChange-Id: ${existingChange?.change_id ?? generateChangeId()}`,
     ];
     const commitResult = await git.prepareCommit({ ...commit, force: true });
     if (commitResult) {
@@ -123,9 +123,7 @@ export class GerritScm extends DefaultGitScm {
       if (hasChanges || commit.force) {
         const pushResult = await git.pushCommit({
           sourceRef: commit.branchName,
-          targetRef: `refs/for/${commit.baseBranch!}%t=sourceBranch-${
-            commit.branchName
-          }`,
+          targetRef: `refs/for/${commit.baseBranch!}`,
           files: commit.files,
         });
         if (pushResult) {

lib/modules/platform/gerrit/utils.spec.ts

@@ -10,6 +10,7 @@ import type {
   GerritChangeMessageInfo,
   GerritChangeStatus,
   GerritLabelTypeInfo,
+  GerritRevisionInfo,
 } from './types';
 import * as utils from './utils';
 import { mapBranchStatusToLabel } from './utils';
@@ -83,14 +84,22 @@ describe('modules/platform/gerrit/utils', () => {
       const change = partial<GerritChange>({
         _number: 123456,
         status: 'NEW',
-        hashtags: ['other', 'sourceBranch-renovate/dependency-1.x'],
         branch: 'main',
         subject: 'Fix for',
         reviewers: {
           REVIEWER: [partial<GerritAccountInfo>({ username: 'username' })],
           REMOVED: [],
           CC: [],
         },
+        current_revision: 'abc',
+        revisions: {
+          abc: partial<GerritRevisionInfo>({
+            commit: {
+              message:
+                'Some change\n\nRenovate-Source-Branch: renovate/dependency-1.x\nChange-Id: ...',
+            },
+          }),
+        },
         messages: [
           partial<GerritChangeMessageInfo>({
             id: '9d78ac236714cee8c2d86e95d638358925cf6853',
@@ -122,11 +131,10 @@ describe('modules/platform/gerrit/utils', () => {
       });
     });
 
-    it('map a gerrit change without sourceBranch-tag and reviewers to Pr', () => {
+    it('map a gerrit change without source branch footer and reviewers to Pr', () => {
       const change = partial<GerritChange>({
         _number: 123456,
         status: 'NEW',
-        hashtags: ['other'],
         branch: 'main',
         subject: 'Fix for',
       });
@@ -145,23 +153,36 @@ describe('modules/platform/gerrit/utils', () => {
   });
 
   describe('extractSourceBranch()', () => {
-    it('without hashtags', () => {
-      const change = partial<GerritChange>({
-        hashtags: undefined,
-      });
+    it('no commit message', () => {
+      const change = partial<GerritChange>();
       expect(utils.extractSourceBranch(change)).toBeUndefined();
     });
 
-    it('no hashtag with "sourceBranch-" prefix', () => {
+    it('commit message with no footer', () => {
       const change = partial<GerritChange>({
-        hashtags: ['other', 'another'],
+        current_revision: 'abc',
+        revisions: {
+          abc: partial<GerritRevisionInfo>({
+            commit: {
+              message: 'some message...',
+            },
+          }),
+        },
       });
       expect(utils.extractSourceBranch(change)).toBeUndefined();
     });
 
-    it('hashtag with "sourceBranch-" prefix', () => {
+    it('commit message with footer', () => {
       const change = partial<GerritChange>({
-        hashtags: ['other', 'sourceBranch-renovate/dependency-1.x', 'another'],
+        current_revision: 'abc',
+        revisions: {
+          abc: partial<GerritRevisionInfo>({
+            commit: {
+              message:
+                'Some change\n\nRenovate-Source-Branch: renovate/dependency-1.x\nChange-Id: ...',
+            },
+          }),
+        },
       });
       expect(utils.extractSourceBranch(change)).toBe('renovate/dependency-1.x');
     });

lib/modules/platform/gerrit/utils.ts

@@ -90,9 +90,14 @@ export function mapGerritChangeStateToPrState(
   return 'all';
 }
 export function extractSourceBranch(change: GerritChange): string | undefined {
-  return change.hashtags
-    ?.find((tag) => tag.startsWith('sourceBranch-'))
-    ?.replace('sourceBranch-', '');
+  if (change.current_revision === undefined) {
+    // This should never happen in production, but it does happen in tests
+    return undefined;
+  }
+
+  return change.revisions[change.current_revision]?.commit?.message?.match(
+    /^Renovate-Source-Branch: (.+)$/m,
+  )?.[1];
 }
 
 export function findPullRequestBody(change: GerritChange): string | undefined {