feat(ng-dev): update renovate.json baseBranches when creating a new branch

Adds support for automatically modifying `renovate.json` to include newly created branches in the `baseBranches` array, when `updateRenovateConfig` is enabled.

Author: alan-agius4

ng-dev/release/publish/actions/renovate-config-updates.ts

@@ -0,0 +1,41 @@
+import {existsSync} from 'node:fs';
+import {green, Log} from '../../../utils/logging.js';
+import {join} from 'node:path';
+import {writeFile, readFile} from 'node:fs/promises';
+
+/**
+ * Updates the `renovate.json` configuration file to include a new base branch.
+ *
+ * @param projectDir - The project directory path.
+ * @param newBranchName - The name of the new branch to add to the base branches list.
+ * @returns A promise that resolves to an string containing the path to the modified `renovate.json` file,
+ *          or null if config updating is disabled.
+ */
+export async function updateRenovateConfig(
+  projectDir: string,
+  newBranchName: string,
+): Promise<string | null> {
+  const renovateConfigPath = join(projectDir, 'renovate.json');
+  if (!existsSync(renovateConfigPath)) {
+    Log.warn(`  ✘   Skipped updating Renovate config as it was not found.`);
+
+    return null;
+  }
+
+  const config = await readFile(renovateConfigPath, 'utf-8');
+  const configJson = JSON.parse(config) as Record<string, unknown>;
+  const baseBranches = configJson.baseBranches;
+  if (!Array.isArray(baseBranches) || baseBranches.length !== 2) {
+    Log.warn(
+      `  ✘   Skipped updating Renovate config: "baseBranches" must contain exactly 2 branches.`,
+    );
+
+    return null;
+  }
+
+  configJson.baseBranches = ['main', newBranchName];
+  await writeFile(renovateConfigPath, JSON.stringify(configJson, undefined, 2));
+  Log.info(green(`  ✓   Updated Renovate config.`));
+
+  return renovateConfigPath;
+}

ng-dev/release/publish/actions/shared/branch-off-next-branch.ts

@@ -19,6 +19,7 @@ import {
 import {CutNpmNextPrereleaseAction} from '../cut-npm-next-prerelease.js';
 import {CutNpmNextReleaseCandidateAction} from '../cut-npm-next-release-candidate.js';
 import {ActiveReleaseTrains} from '../../../versioning/active-release-trains.js';
+import {updateRenovateConfig} from '../renovate-config-updates.js';
 
 /**
  * Base action that can be used to move the next release-train into the dedicated FF/RC
@@ -139,11 +140,17 @@ export abstract class BranchOffNextBranchBaseAction extends CutNpmNextPrerelease
 
     // Create an individual commit for the next version bump. The changelog should go into
     // a separate commit that makes it clear where the changelog is cherry-picked from.
-    await this.createCommit(bumpCommitMessage, [
+    const filesToCommit: string[] = [
       workspaceRelativePackageJsonPath,
       ...this.getAspectLockFiles(),
-    ]);
+    ];
 
+    const renovateConfigPath = await updateRenovateConfig(this.projectDir, nextBranch);
+    if (renovateConfigPath) {
+      filesToCommit.push(renovateConfigPath);
+    }
+
+    await this.createCommit(bumpCommitMessage, filesToCommit);
     await this.prependReleaseNotesToChangelog(releaseNotes);
 
     const commitMessage = getReleaseNoteCherryPickCommitMessage(releaseNotes.version);