fix: warm server action modules in dev

packages/vinext/src/config/server-action-warmup.ts

@@ -0,0 +1,168 @@
+import { glob, readFile } from "node:fs/promises";
+import path from "node:path";
+import { normalizePageExtensions } from "../routing/file-matcher.js";
+
+const SERVER_ACTION_SOURCE_EXTENSIONS = ["js", "jsx", "ts", "tsx", "mjs", "mts", "cjs", "cts"];
+const SERVER_ACTION_SCAN_EXCLUDED_ROOTS = new Set([
+  ".git",
+  ".next",
+  ".output",
+  ".refs",
+  ".turbo",
+  ".vinext",
+  ".worktrees",
+  "build",
+  "coverage",
+  "dist",
+  "node_modules",
+  "out",
+]);
+
+type CollectServerActionWarmupEntriesOptions = {
+  root: string;
+  pageExtensions?: readonly string[] | null;
+};
+
+function buildExtensionGlob(extensions: readonly string[]): string {
+  return extensions.length === 1 ? extensions[0] : `{${extensions.join(",")}}`;
+}
+
+function toViteEntry(root: string, filePath: string): string {
+  return path.relative(root, filePath).split(path.sep).join("/");
+}
+
+function normalizeServerActionExtensions(pageExtensions?: readonly string[] | null): string[] {
+  return [
+    ...new Set([...SERVER_ACTION_SOURCE_EXTENSIONS, ...normalizePageExtensions(pageExtensions)]),
+  ];
+}
+
+function shouldExcludeServerActionScanPath(name: string): boolean {
+  const segments = name.split(/[\\/]+/).filter(Boolean);
+  return (
+    SERVER_ACTION_SCAN_EXCLUDED_ROOTS.has(segments[0] ?? "") || segments.includes("node_modules")
+  );
+}
+
+function skipWhitespaceAndComments(source: string, start: number): number {
+  let index = start;
+  while (index < source.length) {
+    const char = source[index];
+    const next = source[index + 1];
+
+    if (
+      char === " " ||
+      char === "\t" ||
+      char === "\n" ||
+      char === "\r" ||
+      char === "\f" ||
+      char === "\v"
+    ) {
+      index++;
+      continue;
+    }
+
+    if (char === "/" && next === "/") {
+      index += 2;
+      while (index < source.length && source[index] !== "\n" && source[index] !== "\r") {
+        index++;
+      }
+      continue;
+    }
+
+    if (char === "/" && next === "*") {
+      index += 2;
+      while (index < source.length && !(source[index] === "*" && source[index + 1] === "/")) {
+        index++;
+      }
+      index = Math.min(index + 2, source.length);
+      continue;
+    }
+
+    return index;
+  }
+
+  return index;
+}
+
+function readDirectiveLiteral(
+  source: string,
+  start: number,
+): { value: string; end: number } | null {
+  const quote = source[start];
+  if (quote !== '"' && quote !== "'") {
+    return null;
+  }
+
+  let value = "";
+  let index = start + 1;
+  while (index < source.length) {
+    const char = source[index];
+    if (char === quote) {
+      return { value, end: index + 1 };
+    }
+    if (char === "\\") {
+      const escaped = source[index + 1];
+      if (escaped === undefined) {
+        return null;
+      }
+      // This scanner only needs directive equality, not full JavaScript string semantics.
+      value += escaped;
+      index += 2;
+      continue;
+    }
+    value += char;
+    index++;
+  }
+
+  return null;
+}
+
+export function hasModuleUseServerDirective(source: string): boolean {
+  let index = source.charCodeAt(0) === 0xfeff ? 1 : 0;
+
+  while (index < source.length) {
+    index = skipWhitespaceAndComments(source, index);
+    const directive = readDirectiveLiteral(source, index);
+    if (!directive) {
+      return false;
+    }
+    if (directive.value === "use server") {
+      return true;
+    }
+    index = skipWhitespaceAndComments(source, directive.end);
+    if (source[index] === ";") {
+      index++;
+    }
+  }
+
+  return false;
+}
+
+export async function collectServerActionWarmupEntries(
+  options: CollectServerActionWarmupEntriesOptions,
+): Promise<string[]> {
+  const extensions = normalizeServerActionExtensions(options.pageExtensions);
+  const pattern = `**/*.${buildExtensionGlob(extensions)}`;
+  const entries: string[] = [];
+
+  for await (const relativeFile of glob(pattern, {
+    cwd: options.root,
+    exclude: shouldExcludeServerActionScanPath,
+  })) {
+    const filePath = path.join(options.root, relativeFile);
+    const source = await readFile(filePath, "utf8");
+    if (hasModuleUseServerDirective(source)) {
+      entries.push(toViteEntry(options.root, filePath));
+    }
+  }
+
+  return entries.sort();
+}
+
+export function mergeServerActionWarmupEntries(
+  userWarmup: readonly string[] | undefined,
+  actionWarmup: readonly string[],
+): string[] {
+  return [...new Set([...(userWarmup ?? []), ...actionWarmup])];
+}

packages/vinext/src/index.ts

@@ -43,6 +43,10 @@ import {
   type NextRewrite,
   type NextHeader,
 } from "./config/next-config.js";
+import {
+  collectServerActionWarmupEntries,
+  mergeServerActionWarmupEntries,
+} from "./config/server-action-warmup.js";
 
 import { findMiddlewareFile, runMiddleware } from "./server/middleware.js";
 import { logRequest, now } from "./server/request-log.js";
@@ -1298,6 +1302,17 @@ export default function vinext(options: VinextOptions = {}): PluginOption[] {
             instrumentationClientPath,
           ].flatMap((entry) => (entry ? [toRelativeFileEntry(root, entry)] : []));
           const optimizeEntries = [...new Set([...appEntries, ...explicitInstrumentationEntries])];
+          const actionWarmupEntries =
+            env?.command === "build"
+              ? []
+              : await collectServerActionWarmupEntries({
+                  root,
+                  pageExtensions: nextConfig?.pageExtensions,
+                });
+          const rscDevWarmup = mergeServerActionWarmupEntries(
+            config.environments?.rsc?.dev?.warmup,
+            actionWarmupEntries,
+          );
 
           viteConfig.environments = {
             rsc: {
@@ -1328,6 +1343,13 @@ export default function vinext(options: VinextOptions = {}): PluginOption[] {
                 exclude: [...new Set([...incomingExclude, "vinext", "@vercel/og"])],
                 entries: optimizeEntries,
               },
+              ...(rscDevWarmup.length > 0
+                ? {
+                    dev: {
+                      warmup: rscDevWarmup,
+                    },
+                  }
+                : {}),
               build: {
                 outDir: options.rscOutDir ?? "dist/server",
                 ...withBuildBundlerOptions(viteMajorVersion, {