perf(build): improve tree shaking with purity annotations

packages/vinext/src/plugins/dynamic-preload-metadata.ts

@@ -1,4 +1,4 @@
-import type { Plugin } from "vite";
+import type { ESTree, Plugin } from "vite";
 import { parseAst } from "vite";
 import MagicString from "magic-string";
 import path, { toSlash } from "pathslash";
@@ -10,6 +10,7 @@ import { getAstName, stringLiteralValue, walkAst } from "./ast-utils.js";
 import { magicStringTransformResult } from "./transform-result.js";
 
 type AstRecord = Record<string, unknown>;
+type AstCallExpression = ESTree.CallExpression & AstRecord;
 
 type TransformResult = {
   code: string;
@@ -72,7 +73,7 @@ function isIdentifierNameInSet(node: unknown, names: Set<string>): boolean {
   return getString(node, "type") === "Identifier" && names.has(getString(node, "name") ?? "");
 }
 
-function isDynamicCall(node: AstRecord, dynamicLocals: Set<string>): boolean {
+function isDynamicCall(node: AstRecord, dynamicLocals: Set<string>): node is AstCallExpression {
   if (getString(node, "type") !== "CallExpression") return false;
   return isIdentifierNameInSet(node.callee, dynamicLocals);
 }
@@ -227,7 +228,7 @@ function withoutBindings(activeNames: Set<string>, localNames: Set<string>): Set
 function visitChildren(
   node: AstRecord,
   dynamicLocals: Set<string>,
-  visitor: (node: AstRecord) => void,
+  visitor: (node: AstCallExpression) => void,
 ): void {
   for (const [key, child] of Object.entries(node)) {
     if (key === "parent") continue;
@@ -244,7 +245,7 @@ function visitChildren(
 function visitDynamicCalls(
   value: unknown,
   dynamicLocals: Set<string>,
-  visitor: (node: AstRecord) => void,
+  visitor: (node: AstCallExpression) => void,
 ): void {
   if (!isRecord(value) || dynamicLocals.size === 0) return;
 
@@ -381,6 +382,58 @@ function dynamicLoaderNode(firstArg: unknown): unknown {
   return loaderProperty?.value;
 }
 
+function dynamicLoaderArgument(firstArg: ESTree.Argument | undefined): ESTree.Argument | undefined {
+  if (firstArg?.type !== "ObjectExpression") return firstArg;
+
+  const loaderProperty = firstArg.properties.find(
+    (property): property is ESTree.ObjectProperty =>
+      property.type === "Property" &&
+      (propertyKeyName(property) === "loader" || propertyKeyName(property) === "modules"),
+  );
+  return loaderProperty?.value;
+}
+
+function isFunctionOrImportLoader(node: ESTree.Argument | undefined): boolean {
+  return (
+    node?.type === "ArrowFunctionExpression" ||
+    node?.type === "FunctionExpression" ||
+    node?.type === "ImportExpression"
+  );
+}
+
+function hasObjectAccessor(node: ESTree.Argument | undefined): boolean {
+  return (
+    node?.type === "ObjectExpression" &&
+    node.properties.some((property) => property.type === "Property" && property.kind !== "init")
+  );
+}
+
+/**
+ * A pure annotation suppresses effects from inside `dynamic()`, while argument
+ * evaluation remains observable. Limit the hint to loader shapes that
+ * `dynamic()` does not execute eagerly and plain options whose property reads
+ * cannot invoke accessors.
+ */
+function canAnnotateDynamicCallAsPure(callNode: AstCallExpression): boolean {
+  const [firstArg, secondArg] = callNode.arguments;
+  if (!isFunctionOrImportLoader(dynamicLoaderArgument(firstArg))) return false;
+  if (hasObjectAccessor(firstArg)) return false;
+  return secondArg === undefined || !hasObjectAccessor(secondArg);
+}
+
+function annotateCallAsPure(
+  output: MagicString,
+  code: string,
+  callNode: AstCallExpression,
+): boolean {
+  // Avoid stacking our hint on top of a user/compiler-provided annotation.
+  const prefix = code.slice(Math.max(0, callNode.start - 80), callNode.start);
+  if (/\/\*\s*[#@]__PURE__\s*\*\/\s*$/.test(prefix)) return false;
+
+  output.prependLeft(callNode.start, "/* @__PURE__ */ ");
+  return true;
+}
+
 function findLastEndedProperty(node: AstRecord): AstRecord | null {
   const properties = objectProperties(node);
   for (let index = properties.length - 1; index >= 0; index -= 1) {
@@ -622,6 +675,9 @@ export async function transformNextDynamicPreloadMetadata(
       resolveManifestModuleIds(specifiers, id, root, resolveDynamicImport).then((moduleIds) => {
         if (moduleIds.length === 0) return;
         if (applyLoadableGenerated(output, code, node, moduleIds)) {
+          if (canAnnotateDynamicCallAsPure(node)) {
+            annotateCallAsPure(output, code, node);
+          }
           changed = true;
         }
       }),

packages/vinext/src/shims/script-nonce-context.tsx

@@ -24,6 +24,7 @@ export function withScriptNonce(element: React.ReactElement, nonce?: string): Re
   return React.createElement(ScriptNonceProvider, { nonce }, element);
 }
 
+/* @__NO_SIDE_EFFECTS__ */
 function createScriptNonceHook(context: typeof ScriptNonceContext): () => string | undefined {
   if (!context || typeof React.useContext !== "function") {
     return function useScriptNonceFromContext(): string | undefined {

tests/build-optimization.test.ts

@@ -1248,6 +1248,97 @@ export default function Page() {
 
 // ─── Remaining treeshake config integration ─────────────────────────────
 
+describe("no-side-effect annotations", () => {
+  it("tree-shakes unused transformed dynamic calls", async () => {
+    const tmpDir = await fsp.mkdtemp(path.join(os.tmpdir(), "vinext-dynamic-dce-"));
+    const entryPath = path.join(tmpDir, "entry.js");
+    const widgetPath = path.join(tmpDir, "widget.js");
+    const outDir = path.join(tmpDir, "dist");
+    const source = [
+      `import dynamic from "next/dynamic";`,
+      `const Unused = dynamic(() => import("./widget.js"));`,
+      `globalThis.__entryMarker = true;`,
+    ].join("\n");
+    const transformed = await _transformNextDynamicPreloadMetadata(
+      source,
+      entryPath,
+      tmpDir,
+      async (specifier) => (specifier === "./widget.js" ? widgetPath : null),
+    );
+    expect(transformed?.code).toContain("/* @__PURE__ */ dynamic(");
+
+    await fsp.writeFile(
+      path.join(tmpDir, "dynamic.js"),
+      `export default function dynamic(loader) { globalThis.__dynamicCallMarker = loader; return loader; }\n`,
+    );
+    await fsp.writeFile(widgetPath, `globalThis.__widgetMarker = true;\n`);
+    await fsp.writeFile(entryPath, transformed!.code.replace(`"next/dynamic"`, `"./dynamic.js"`));
+
+    try {
+      const builder = await createBuilder({
+        root: tmpDir,
+        configFile: false,
+        logLevel: "silent",
+        build: {
+          outDir,
+          minify: false,
+          rolldownOptions: {
+            input: entryPath,
+            output: { entryFileNames: "entry.js" },
+          },
+        },
+      });
+      await builder.buildApp();
+
+      const output = await fsp.readFile(path.join(outDir, "entry.js"), "utf8");
+      expect(output).toContain("__entryMarker");
+      expect(output).not.toContain("__dynamicCallMarker");
+      expect(output).not.toContain("__widgetMarker");
+    } finally {
+      await fsp.rm(tmpDir, { recursive: true, force: true }).catch(() => {});
+    }
+  }, 15_000);
+
+  it("tree-shakes unused script nonce hook setup", async () => {
+    const tmpDir = await fsp.mkdtemp(path.join(os.tmpdir(), "vinext-script-nonce-dce-"));
+    const entryPath = path.join(tmpDir, "entry.js");
+    const outDir = path.join(tmpDir, "dist");
+    const scriptNonceContextPath = path.resolve(
+      import.meta.dirname,
+      "../packages/vinext/src/shims/script-nonce-context.tsx",
+    );
+    await fsp.writeFile(
+      entryPath,
+      `import { withScriptNonce } from ${JSON.stringify(scriptNonceContextPath)};\nglobalThis.__withScriptNonce = withScriptNonce;\n`,
+    );
+
+    try {
+      const builder = await createBuilder({
+        root: tmpDir,
+        configFile: false,
+        logLevel: "silent",
+        build: {
+          outDir,
+          minify: false,
+          rolldownOptions: {
+            input: entryPath,
+            external: ["react"],
+            output: { entryFileNames: "entry.js" },
+          },
+        },
+      });
+      await builder.buildApp();
+
+      const output = await fsp.readFile(path.join(outDir, "entry.js"), "utf8");
+      expect(output).toContain("withScriptNonce");
+      expect(output).not.toContain("createScriptNonceHook");
+      expect(output).not.toContain("useScriptNonceFromContext");
+    } finally {
+      await fsp.rm(tmpDir, { recursive: true, force: true }).catch(() => {});
+    }
+  }, 15_000);
+});
+
 describe("treeshake config integration", () => {
   it("plugin config hook applies treeshake to non-SSR builds", async () => {
     const vinext = (await import("../packages/vinext/src/index.js")).default;
@@ -2048,6 +2139,39 @@ describe("next/dynamic preload metadata transform", () => {
     );
 
     expect(result?.code).toContain(`loadableGenerated: { modules: ["app/dynamic-widget.tsx"] }`);
+    expect(result?.code).toContain(`const Widget = /* @__PURE__ */ dynamic(`);
+  });
+
+  it("does not duplicate an existing pure annotation", async () => {
+    const result = await _transformNextDynamicPreloadMetadata(
+      [
+        `import dynamic from "next/dynamic";`,
+        `const Widget = /*#__PURE__*/ dynamic(() => import("./dynamic-widget"));`,
+      ].join("\n"),
+      importer,
+      root,
+      resolveDynamicImport,
+    );
+
+    expect(result?.code.match(/__PURE__/g)).toHaveLength(1);
+    expect(result?.code).toContain(`loadableGenerated: { modules: ["app/dynamic-widget.tsx"] }`);
+  });
+
+  it("does not mark dynamic calls with accessor options as pure", async () => {
+    const result = await _transformNextDynamicPreloadMetadata(
+      [
+        `import dynamic from "next/dynamic";`,
+        `const Widget = dynamic(() => import("./dynamic-widget"), {`,
+        `  get loading() { recordOptionRead(); return Loading; },`,
+        `});`,
+      ].join("\n"),
+      importer,
+      root,
+      resolveDynamicImport,
+    );
+
+    expect(result?.code).not.toContain("__PURE__");
+    expect(result?.code).toContain(`loadableGenerated: { modules: ["app/dynamic-widget.tsx"] }`);
   });
 
   it("preserves existing explicit loadableGenerated metadata", async () => {
@@ -2391,7 +2515,7 @@ describe("next/dynamic preload metadata transform", () => {
     expect(result?.code).toBe(
       [
         `import dynamic from "next/dynamic";`,
-        `const W = dynamic(() => import("./dynamic-widget"), { loadableGenerated: { modules: ["app/dynamic-widget.tsx"] } });`,
+        `const W = /* @__PURE__ */ dynamic(() => import("./dynamic-widget"), { loadableGenerated: { modules: ["app/dynamic-widget.tsx"] } });`,
       ].join("\n"),
     );
     expect(firstDynamicCallArgTypes(result!.code)).toEqual([