perf(plugins): cache runtime mirror file decisions

src/plugins/bundled-runtime-deps.test.ts

@@ -25,6 +25,7 @@ import {
   resolveBundledRuntimeDependencyInstallRootPlan,
   resolveBundledRuntimeDepsNpmRunner,
   scanBundledPluginRuntimeDeps,
+  shouldMaterializeBundledRuntimeMirrorDistFile,
   type BundledRuntimeDepsInstallParams,
 } from "./bundled-runtime-deps.js";
 
@@ -99,11 +100,42 @@ afterEach(() => {
   spawnMock.mockReset();
   spawnSyncMock.mockReset();
   bundledRuntimeDepsActivityTesting.resetBundledRuntimeDepsInstallActivity();
+  bundledRuntimeDepsTesting.clearBundledRuntimeMirrorMaterializeCache();
   for (const dir of tempDirs.splice(0)) {
     fs.rmSync(dir, { recursive: true, force: true });
   }
 });
 
+describe("shouldMaterializeBundledRuntimeMirrorDistFile", () => {
+  it("reuses unchanged root dist file decisions without rereading source", () => {
+    const root = makeTempDir();
+    const sourcePath = path.join(root, "shared-runtime.js");
+    fs.writeFileSync(
+      sourcePath,
+      [
+        `//#region extensions/browser/src/runtime.ts`,
+        `export const marker = "shared-runtime";`,
+        `//#endregion`,
+        "",
+      ].join("\n"),
+      "utf8",
+    );
+    const realReadFileSync = fs.readFileSync.bind(fs);
+    let sourceReads = 0;
+    vi.spyOn(fs, "readFileSync").mockImplementation(((target, options) => {
+      if (path.resolve(target.toString()) === path.resolve(sourcePath)) {
+        sourceReads += 1;
+      }
+      return realReadFileSync(target, options as never);
+    }) as typeof fs.readFileSync);
+
+    expect(shouldMaterializeBundledRuntimeMirrorDistFile(sourcePath)).toBe(true);
+    expect(shouldMaterializeBundledRuntimeMirrorDistFile(sourcePath)).toBe(true);
+
+    expect(sourceReads).toBe(1);
+  });
+});
+
 describe("resolveBundledRuntimeDepsNpmRunner", () => {
   it("ignores npm_execpath and uses the Node-adjacent npm CLI on Windows", () => {
     const execPath = "C:\\Program Files\\nodejs\\node.exe";

src/plugins/bundled-runtime-deps.ts

@@ -78,6 +78,10 @@ const BUNDLED_RUNTIME_MIRROR_IMPORT_SPECIFIER_RE =
 const NPM_EXECPATH_ENV_KEY = "npm_execpath";
 
 const registeredBundledRuntimeDepNodePaths = new Set<string>();
+const bundledRuntimeMirrorMaterializeCache = new Map<
+  string,
+  { signature: string; materialize: boolean }
+>();
 
 export type BundledRuntimeDepsNpmRunner = {
   command: string;
@@ -85,10 +89,15 @@ export type BundledRuntimeDepsNpmRunner = {
   env?: NodeJS.ProcessEnv;
 };
 
-export function shouldMaterializeBundledRuntimeMirrorDistFile(sourcePath: string): boolean {
-  if (!BUNDLED_RUNTIME_MIRROR_MATERIALIZED_EXTENSIONS.has(path.extname(sourcePath))) {
-    return false;
-  }
+function clearBundledRuntimeMirrorMaterializeCache(): void {
+  bundledRuntimeMirrorMaterializeCache.clear();
+}
+
+function statSignature(stat: Pick<fs.Stats, "dev" | "ino" | "size" | "mtimeMs">): string {
+  return `${stat.dev}:${stat.ino}:${stat.size}:${stat.mtimeMs}`;
+}
+
+function computeBundledRuntimeMirrorDistFileMaterialization(sourcePath: string): boolean {
   let source: string;
   try {
     source = fs.readFileSync(sourcePath, "utf8");
@@ -113,6 +122,27 @@ export function shouldMaterializeBundledRuntimeMirrorDistFile(sourcePath: string
   return true;
 }
 
+export function shouldMaterializeBundledRuntimeMirrorDistFile(sourcePath: string): boolean {
+  if (!BUNDLED_RUNTIME_MIRROR_MATERIALIZED_EXTENSIONS.has(path.extname(sourcePath))) {
+    return false;
+  }
+  const cacheKey = path.resolve(sourcePath);
+  let signature: string;
+  try {
+    signature = statSignature(fs.statSync(sourcePath));
+  } catch {
+    bundledRuntimeMirrorMaterializeCache.delete(cacheKey);
+    return false;
+  }
+  const cached = bundledRuntimeMirrorMaterializeCache.get(cacheKey);
+  if (cached?.signature === signature) {
+    return cached.materialize;
+  }
+  const materialize = computeBundledRuntimeMirrorDistFileMaterialization(sourcePath);
+  bundledRuntimeMirrorMaterializeCache.set(cacheKey, { signature, materialize });
+  return materialize;
+}
+
 export function materializeBundledRuntimeMirrorDistFile(
   sourcePath: string,
   targetPath: string,
@@ -404,6 +434,7 @@ function formatRuntimeDepsLockTimeoutMessage(params: {
 }
 
 export const __testing = {
+  clearBundledRuntimeMirrorMaterializeCache,
   formatRuntimeDepsLockTimeoutMessage,
   shouldRemoveRuntimeDepsLock,
 };