Avoid conflicts by reverting 1.x version num commit from last v1 release

.github/update-release-branch.py

@@ -239,24 +239,55 @@ def main():
 
   # Create the new branch and push it to the remote
   print('Creating branch ' + new_branch_name)
-  run_git('checkout', '-b', new_branch_name, ORIGIN + '/' + args.source_branch)
 
   if args.perform_v2_to_v1_backport:
+    # If we're performing a backport, start from the v1 branch
+    print(f'Creating {new_branch_name} from the {ORIGIN}/v1 branch')
+    run_git('checkout', '-b', new_branch_name, f'{ORIGIN}/v1')
+
+    # Revert the commit that we made as part of the last release that updated the version number and
+    # changelog to refer to 1.x.x variants. This avoids merge conflicts in the changelog and
+    # package.json files when we merge in the v2 branch.
+    # This commit will not exist the first time we release the v1 branch from the v2 branch, so we
+    # use `git log --grep` to conditionally revert the commit.
+    print('Reverting the 1.x.x version number and changelog updates from the last release to avoid conflicts')
+    v1_update_commits = run_git('log', '--grep', '^Update version and changelog for v', '--format=%H').split()
+
+    if len(v1_update_commits) > 0:
+      print(f'  Reverting {v1_update_commits[0]}')
+      # Only revert the newest commit as older ones will already have been reverted in previous
+      # releases.
+      run_git('revert', v1_update_commits[0], '--no-edit')
+
+      # Also revert the "Update checked-in dependencies" commit created by Actions.
+      update_dependencies_commit = run_git('log', '--grep', '^Update checked-in dependencies', '--format=%H').split()[0]
+      print(f'  Reverting {update_dependencies_commit}')
+      run_git('revert', update_dependencies_commit, '--no-edit')
+
+    else:
+      print('  Nothing to revert.')
+
+    print(f'Merging {ORIGIN}/{args.source_branch} into the release prep branch')
+    run_git('merge', f'{ORIGIN}/{args.source_branch}', '--no-edit')
+
     # Migrate the package version number from a v2 version number to a v1 version number
     print(f'Setting version number to {version}')
     subprocess.run(['npm', 'version', version, '--no-git-tag-version'])
-    run_git('reset', 'HEAD~1')
     run_git('add', 'package.json', 'package-lock.json')
 
     # Migrate the changelog notes from v2 version numbers to v1 version numbers
     print('Migrating changelog notes from v2 to v1')
-    subprocess.run(['sed', '-i', 's/## 2./## 1./g', 'CHANGELOG.md'])
+    subprocess.run(['sed', '-i', 's/## 2\./## 1\./g', 'CHANGELOG.md'])
 
     # Amend the commit generated by `npm version` to update the CHANGELOG
     run_git('add', 'CHANGELOG.md')
-    run_git('commit', '--amend', '-m', f'Update version and changelog for v{version}')
+    run_git('commit', '-m', f'Update version and changelog for v{version}')
   else:
-    # We don't need to do this for a v1 release, since the changelog has already been updated in the v2 branch.
+    # If we're performing a standard release, there won't be any new commits on the target branch,
+    # as these will have already been merged back into the source branch. Therefore we can just
+    # start from the source branch.
+    run_git('checkout', '-b', new_branch_name, f'{ORIGIN}/{args.source_branch}')
+
     print('Updating changelog')
     update_changelog(version)