Add downgrade logic for branch in DocLinkService

CHANGELOG.md

@@ -200,6 +200,7 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 - Add path ignore for markdown files for CI ([#2312](https://github.com/opensearch-project/OpenSearch-Dashboards/pull/2312))
 - Updating WS scans to ignore BWC artifacts in `cypress` ([#2408](https://github.com/opensearch-project/OpenSearch-Dashboards/pull/2408))
 - [CI] Run functional test repo as workflow ([#2503](https://github.com/opensearch-project/OpenSearch-Dashboards/pull/2503))
+- [CI] Patch pkg.branch according to pkg.version when build ([#3483](https://github.com/opensearch-project/OpenSearch-Dashboards/pull/3483))
 
 ### 📝 Documentation
 

src/dev/build/tasks/create_package_json_task.ts

@@ -29,6 +29,7 @@
  */
 
 import { copyWorkspacePackages } from '@osd/pm';
+import { parse } from 'semver';
 
 import { read, write, Task } from '../lib';
 
@@ -37,14 +38,40 @@ export const CreatePackageJson: Task = {
 
   async run(config, log, build) {
     const pkg = config.getOpenSearchDashboardsPkg();
+    /**
+     * OpenSearch server uses the `branch` property from `package.json` to
+     * build links to the documentation. If set to `main`, it would use `/latest`
+     * and if not, it would use the `version` to construct URLs.
+     */
+    const buildVersion = config.getBuildVersion();
+    let branch;
+    if (pkg.branch === 'main') {
+      branch = pkg.branch;
+    } else {
+      const parsedBuildVersion = parse(buildVersion);
+      if (parsedBuildVersion) {
+        branch = `${parsedBuildVersion.major}.${parsedBuildVersion.minor}`;
+        log.info(`Updating package.branch to ${branch}`);
+      } else {
+        const validDocPathsPattern = /^\d+\.\d+$/;
+        if (validDocPathsPattern.test(pkg.branch as string)) {
+          branch = pkg.branch;
+        } else {
+          // package version was not parsable and branch is unusable
+          throw new Error(
+            `Failed to identify documentation path while generating package.json: encountered invalid build version (${buildVersion}) and branch property (${pkg.branch}).`
+          );
+        }
+      }
+    }
 
     const newPkg = {
       name: pkg.name,
       private: true,
       description: pkg.description,
       keywords: pkg.keywords,
-      version: config.getBuildVersion(),
-      branch: pkg.branch,
+      version: buildVersion,
+      branch,
       build: {
         number: config.getBuildNumber(),
         sha: config.getBuildSha(),