Push HMR updates before the SSR rebuild in dev

Client-only edits are sent to the browser right after the hydration build,
without re-running server functions; SSR rebuilds afterwards and props are
re-fetched only when a .server.ts output changed or after fullRebuild. Page
requests wait for an in-flight SSR rebuild. The SSR build no longer runs
Tailwind, the PostCSS processor is reused across rebuilds, and the watcher
debounce drops from 200ms to 50ms.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/functions/bundler/plugins/esbuild-ctx-artifact-tracker.ts

@@ -15,6 +15,7 @@ import path from "path";
 import cleanupLogsDirs from "../../cleanup-logs-dir";
 import grabRelativePath from "../../../utils/grab-relative-path";
 import cleanupArtifacts from "../../server/cleanup-artifacts";
+import { pushClientUpdate } from "../../server/server-post-build-fn";
 
 const { BUNX_BUNDLER_ERROR_EXIT_FILE, BUNX_ERROR_LOGS_DIR } = grabDirNames();
 
@@ -32,13 +33,22 @@ type Params = {
         changed_pages?: string[];
     }) => Promise<void> | void;
     build_only?: boolean;
+    /**
+     * Always re-fetch server props after this context's first build, even
+     * when only client code changed (set by `fullRebuild`, e.g. after a
+     * config change).
+     */
+    refresh_props_on_first_build?: boolean;
 };
 
 export default function esbuildCTXArtifactTracker({
     entryToPage,
     post_build_fn,
     build_only,
+    refresh_props_on_first_build,
 }: Params) {
+    let force_props_refresh = Boolean(refresh_props_on_first_build);
+
     const artifactTracker: Plugin = {
         name: "artifact-tracker",
         setup(build) {
@@ -135,12 +145,16 @@ export default function esbuildCTXArtifactTracker({
                 global.BUNEXT_BUILD_FAILED = false;
                 global.BUNEXT_BUNDLER_CTX_DISPOSED = false;
 
+                const props_refresh_forced = force_props_refresh;
+                force_props_refresh = false;
+
                 const does_error_file_exist = existsSync(
                     BUNX_BUNDLER_ERROR_EXIT_FILE,
                 );
 
-                // SSR must finish before HMR so server props are fresh.
-                // The rebuild is single-flighted: concurrent hydration
+                // Client-only changes are pushed before the SSR rebuild;
+                // anything that may change server props waits for SSR so
+                // props are fresh. The rebuild is single-flighted: concurrent hydration
                 // rebuilds join the in-flight SSR rebuild instead of
                 // starting overlapping ones.
                 if (build_only) {
@@ -158,6 +172,37 @@ export default function esbuildCTXArtifactTracker({
                     rmSync(BUNX_BUNDLER_ERROR_EXIT_FILE, { force: true });
                     cleanupLogsDirs();
                     await fullRebuild();
+                } else if (
+                    changed_pages.length > 0 &&
+                    post_build_fn &&
+                    !props_refresh_forced
+                ) {
+                    // Client graph changed: push the new bundle right away.
+                    // Server functions live in `.server.ts` files, outside
+                    // the client graph, so the browser's current props are
+                    // still valid and it needn't wait for the SSR rebuild.
+                    pushClientUpdate(changed_pages);
+
+                    const server_hashes_before = grabServerEntryPaths();
+
+                    try {
+                        await enqueueSSRRebuild();
+                    } catch (error) {
+                        log.error(`SSR Bundler Error: ${error}`);
+                    }
+
+                    // A module shared by a page and its server file changed:
+                    // props may differ, so re-fetch them for every tab.
+                    if (server_hashes_before !== grabServerEntryPaths()) {
+                        try {
+                            await post_build_fn({
+                                artifacts: artifacts || [],
+                                changed_pages: [],
+                            });
+                        } catch (error) {
+                            log.error(`Post-build Error: ${error}`);
+                        }
+                    }
                 } else {
                     try {
                         await enqueueSSRRebuild();
@@ -188,3 +233,19 @@ export default function esbuildCTXArtifactTracker({
 
     return artifactTracker;
 }
+
+/**
+ * Fingerprint of the SSR outputs of all `.server.ts(x)` entries. Outputs are
+ * content-hashed, so a changed fingerprint means some server function's code
+ * (or a module it imports) changed.
+ */
+function grabServerEntryPaths(): string {
+    const map = global.BUNEXT_SSR_BUNDLER_CTX_MAP;
+    if (!map) return "";
+
+    return Object.keys(map)
+        .filter((key) => key.match(/\.server\.tsx?$/))
+        .sort()
+        .map((key) => `${key}:${map[key]?.path || ""}`)
+        .join("\n");
+}