fix(vitest-plugin)!: disable vitest 5 export getter tracking under codspeed

Vitest 5 wraps every module export getter with a diagnostic counter (a Map
lookup and write per access) unless benchmark.suppressExportGetterWarnings
is set. That counter runs inside the measured code, inflating results: a
bench reading an export 100k times measures 109M instructions on Vitest 5
versus 38M on Vitest 4.

Default the option to true when the plugin is active, keeping any value
the user sets explicitly. Plain `vitest bench` runs are unaffected. With
this, the same bench measures the same instruction count on Vitest 4
and 5.

Drop the import hoisting from the benches and examples: it only worked
around the tracker.

Closes COD-3892
Closes #98
Co-Authored-By: Claude <noreply@anthropic.com>

Author: GuillaumeLagrange

examples/with-typescript-esm/src/fibonacci.bench.ts

@@ -1,9 +1,5 @@
 import { describe, test } from "vitest";
-import { recursiveFibonacci as recursiveFibonacciExport } from "./fibonacci";
-
-// Imports are getters under Vite's module runner; read them once, outside the
-// measured loop.
-const recursiveFibonacci = recursiveFibonacciExport;
+import { recursiveFibonacci } from "./fibonacci";
 
 describe("recursiveFibonacci", () => {
   test("fibo 30", async ({ bench }) => {

examples/with-vitest-v5/src/fibonacci.bench.ts

@@ -1,13 +1,5 @@
 import { describe, test } from "vitest";
-import {
-  iterativeFibonacci as iterativeFibonacciExport,
-  recursiveFibonacci as recursiveFibonacciExport,
-} from "./fibonacci";
-
-// Imports are getters under Vite's module runner; read them once, outside the
-// measured loop.
-const recursiveFibonacci = recursiveFibonacciExport;
-const iterativeFibonacci = iterativeFibonacciExport;
+import { iterativeFibonacci, recursiveFibonacci } from "./fibonacci";
 
 describe("fibonacci", () => {
   test("fibo 15", async ({ bench }) => {

packages/vitest-plugin/benches/flat.bench.ts

@@ -1,9 +1,5 @@
 import { describe, test } from "vitest";
-import parsePrExport from "./parsePr";
-
-// Imports are getters under Vite's module runner; read it once, outside the
-// measured loop.
-const parsePr = parsePrExport;
+import parsePr from "./parsePr";
 
 const LONG_BODY =
   new Array(1_000)

packages/vitest-plugin/benches/parsePr.bench.ts

@@ -1,9 +1,5 @@
 import { describe, test } from "vitest";
-import parsePrExport from "./parsePr";
-
-// Imports are getters under Vite's module runner; read it once, outside the
-// measured loop.
-const parsePr = parsePrExport;
+import parsePr from "./parsePr";
 
 const LONG_BODY =
   new Array(1_000)

packages/vitest-plugin/src/__tests__/index.test.ts

@@ -1,6 +1,7 @@
 import { getV8Flags } from "@codspeed/core";
 import { fromPartial } from "@total-typescript/shoehorn";
 import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { type ViteUserConfig } from "vitest/config";
 import codspeedPlugin from "../index";
 
 const coreMocks = vi.hoisted(() => {
@@ -34,10 +35,10 @@ function apply(mode: string) {
   return plugin.apply({}, fromPartial({ mode }));
 }
 
-function config() {
+function config(userConfig: ViteUserConfig = {}) {
   if (typeof plugin.config !== "function")
     throw new Error("config is not a function");
-  return plugin.config.call({} as never, {}, fromPartial({}));
+  return plugin.config.call({} as never, userConfig, fromPartial({}));
 }
 
 describe("codSpeedPlugin", () => {
@@ -148,9 +149,18 @@ describe("codSpeedPlugin", () => {
             provider: expect.stringContaining(
               "packages/vitest-plugin/src/v5/provider.ts",
             ),
+            suppressExportGetterWarnings: true,
           },
         },
       });
     });
+
+    it("should keep an explicit suppressExportGetterWarnings from the user", () => {
+      const result = config({
+        test: { benchmark: { suppressExportGetterWarnings: false } },
+      }) as ViteUserConfig;
+
+      expect(result.test?.benchmark?.suppressExportGetterWarnings).toBe(false);
+    });
   });
 });

packages/vitest-plugin/src/index.ts

@@ -37,14 +37,15 @@ export default function codspeedPlugin(): Plugin {
       return true;
     },
     enforce: "post",
-    config(): ViteUserConfig {
+    config(userConfig): ViteUserConfig {
       return {
         test: {
           pool: "forks",
           globalSetup: [resolveFile("globalSetup")],
           ...resolveVitestBackend().getBenchmarkTestConfig(
             getV8Flags(),
             resolveFile,
+            (userConfig as ViteUserConfig).test,
           ),
         },
       };

packages/vitest-plugin/src/vitestBackend.ts

@@ -10,6 +10,7 @@ export interface VitestBackend {
   getBenchmarkTestConfig(
     v8Flags: string[],
     resolveFile: (name: string) => string,
+    userTestConfig: ViteUserConfig["test"],
   ): ViteUserConfig["test"];
 }
 
@@ -36,10 +37,18 @@ class V5Backend implements VitestBackend {
   getBenchmarkTestConfig(
     v8Flags: string[],
     resolveFile: (name: string) => string,
+    userTestConfig: ViteUserConfig["test"],
   ): ViteUserConfig["test"] {
+    // Vitest's export getter tracker runs inside the measured code; keep it off
+    // unless the user explicitly configured it.
+    const suppressExportGetterWarnings =
+      userTestConfig?.benchmark?.suppressExportGetterWarnings ?? true;
     return {
       execArgv: v8Flags,
-      benchmark: { provider: resolveFile("v5/provider") },
+      benchmark: {
+        provider: resolveFile("v5/provider"),
+        suppressExportGetterWarnings,
+      },
     };
   }
 }