feat: add changelog indexing to preview pipeline

src/content-indexer/preview.ts

@@ -4,8 +4,12 @@ import { config as dotenvConfig } from "dotenv";
 import fs from "fs";
 import path from "path";
 
+import { uploadChangelogFile } from "@/content-indexer/uploaders/preview-changelog.ts";
 import { uploadMdxFile } from "@/content-indexer/uploaders/preview-mdx.ts";
-import { runIndexAndUpload } from "@/content-indexer/utils/preview-index.ts";
+import {
+  runChangelogIndexAndUpload,
+  runIndexAndUpload,
+} from "@/content-indexer/utils/preview-index.ts";
 import { buildPreviewUrl } from "@/content-indexer/utils/preview-url.ts";
 import { startWatchers } from "@/content-indexer/utils/preview-watchers.ts";
 import { getRedis } from "@/content-indexer/utils/redis.ts";
@@ -87,6 +91,23 @@ const main = async () => {
     if (uploadFile) {
       const redis = getRedis();
       const filePath = uploadFile.replace(/^fern\//, "");
+
+      // Changelog files: different key prefix + reindex logic
+      if (filePath.startsWith("changelog/") && filePath.endsWith(".md")) {
+        const filename = path.basename(filePath);
+        const { reindexNeeded } = await uploadChangelogFile(
+          filename,
+          branch,
+          redis,
+        );
+        if (reindexNeeded) {
+          console.info("  🔄 New/deleted changelog file, re-indexing...");
+          await runChangelogIndexAndUpload(branch);
+        }
+        return;
+      }
+
+      // MDX files (existing behavior)
       const { reindexNeeded } = await uploadMdxFile(filePath, branch, redis);
 
       if (reindexNeeded) {

src/content-indexer/uploaders/preview-changelog.ts

@@ -0,0 +1,120 @@
+import type { Redis } from "@upstash/redis";
+import { execSync } from "child_process";
+import fs from "fs/promises";
+import path from "path";
+
+import type { PathIndex } from "@/content-indexer/types/pathIndex.ts";
+
+import { PREVIEW_TTL_SECONDS } from "./redis.ts";
+
+/**
+ * Uploads a single changelog file to Redis under a branch-scoped key.
+ * Returns whether a reindex is needed (new or deleted file).
+ *
+ * @param filename - Changelog filename (e.g., "2025-11-20.md")
+ * @param branch - Branch identifier for Redis key prefix
+ * @param redis - Redis client instance
+ */
+export const uploadChangelogFile = async (
+  filename: string,
+  branch: string,
+  redis: Redis,
+): Promise<{ reindexNeeded: boolean }> => {
+  const fullPath = path.join(process.cwd(), "fern", "changelog", filename);
+  const redisKey = `${branch}:changelog:${filename}`;
+
+  let content: string;
+  try {
+    content = await fs.readFile(fullPath, "utf-8");
+  } catch (error) {
+    if ((error as NodeJS.ErrnoException).code === "ENOENT") {
+      // File deleted — remove branch key so previewGet falls back to main:
+      await redis.del(redisKey);
+      console.info(`  🗑️ ${filename} deleted -> removed ${redisKey}`);
+      return { reindexNeeded: true };
+    }
+    throw error;
+  }
+
+  // Detect new files: no existing branch key or main key means this is new
+  const existingBranchContent = await redis.get<string>(redisKey);
+  const existingMainContent = await redis.get<string>(
+    `main:changelog:${filename}`,
+  );
+  const isNew = existingBranchContent === null && existingMainContent === null;
+
+  await redis.set(redisKey, content, { ex: PREVIEW_TTL_SECONDS });
+  console.info(`  📄 ${filename} -> ${redisKey}`);
+
+  // New files need reindex (to add the route to the index); content-only edits don't
+  // because the changelog index only stores date + filePath, not content.
+  return { reindexNeeded: isNew };
+};
+
+/**
+ * Returns changelog filenames that differ from main.
+ * Includes both committed changes (git diff) and untracked new files.
+ */
+const getChangedChangelogFiles = (): string[] => {
+  // Committed/staged changes vs main
+  const diffOutput = execSync(
+    "git diff --name-only origin/main -- fern/changelog/",
+    { encoding: "utf-8" },
+  );
+
+  // Untracked new files not yet committed
+  const untrackedOutput = execSync(
+    "git ls-files --others --exclude-standard -- fern/changelog/",
+    { encoding: "utf-8" },
+  );
+
+  const allFiles = new Set([
+    ...diffOutput.trim().split("\n"),
+    ...untrackedOutput.trim().split("\n"),
+  ]);
+
+  return [...allFiles]
+    .filter((line) => line.length > 0 && line.endsWith(".md"))
+    .map((line) => path.basename(line));
+};
+
+/**
+ * Uploads only changelog files that differ from main and exist in the path index.
+ *
+ * @param pathIndex - The changelog path index to validate against
+ * @param branch - Branch identifier for Redis key prefix
+ * @param redis - Redis client instance
+ */
+export const uploadChangedChangelogFiles = async (
+  pathIndex: PathIndex,
+  branch: string,
+  redis: Redis,
+): Promise<void> => {
+  const changedFiles = getChangedChangelogFiles();
+
+  // Only upload files that are in the path index
+  const indexedFiles = new Set(
+    Object.values(pathIndex)
+      .filter((entry) => entry.type === "changelog")
+      .map((entry) => entry.filePath),
+  );
+
+  const toUpload = changedFiles.filter((f) => indexedFiles.has(f));
+
+  if (toUpload.length === 0) {
+    console.info("\n📤 No changed changelog files to upload");
+    return;
+  }
+
+  console.info(
+    `\n📤 Uploading ${toUpload.length} changed changelog file${toUpload.length === 1 ? "" : "s"} to Redis...`,
+  );
+
+  await Promise.all(
+    toUpload.map((filename) => uploadChangelogFile(filename, branch, redis)),
+  );
+
+  console.info(
+    `✅ ${toUpload.length} changelog file${toUpload.length === 1 ? "" : "s"} uploaded`,
+  );
+};

src/content-indexer/utils/preview-index.ts

@@ -1,6 +1,8 @@
 import path from "path";
 
+import { buildChangelogIndex } from "@/content-indexer/indexers/changelog.ts";
 import { buildDocsContentIndex } from "@/content-indexer/indexers/main.ts";
+import { uploadChangedChangelogFiles } from "@/content-indexer/uploaders/preview-changelog.ts";
 import { uploadChangedMdxFiles } from "@/content-indexer/uploaders/preview-mdx.ts";
 import { uploadSpecs } from "@/content-indexer/uploaders/preview-specs.ts";
 import { storeToRedis } from "@/content-indexer/uploaders/redis.ts";
@@ -38,4 +40,31 @@ export const runIndexAndUpload = async (branch: string): Promise<void> => {
       ? uploadSpecs(specs, branch, redis)
       : Promise.resolve(),
   ]);
+
+  await runChangelogIndexAndUpload(branch);
+};
+
+/**
+ * Runs the changelog indexer in preview mode and uploads changed changelog files.
+ * Stores the changelog path index under a branch-scoped Redis key,
+ * then uploads only changelog files that differ from main.
+ */
+export const runChangelogIndexAndUpload = async (
+  branch: string,
+): Promise<void> => {
+  console.info("\n🔍 Running changelog indexer (preview mode)...\n");
+
+  const { pathIndex } = await buildChangelogIndex({
+    localBasePath: path.join(process.cwd(), "fern/changelog"),
+    branchId: branch,
+  });
+
+  await storeToRedis(pathIndex, undefined, {
+    branchId: branch,
+    indexerType: "changelog",
+    quiet: true,
+  });
+
+  const redis = getRedis();
+  await uploadChangedChangelogFiles(pathIndex, branch, redis);
 };