fix: disable server HMR before plugins read it in their config hook (#10731)

Author: sheremet-va

packages/vitest/src/node/config/resolveConfig.ts

@@ -1029,7 +1029,7 @@ export async function resolveConfig(
       mode: options.mode || 'test',
       plugins: [
         CliOverride(cliOptionsCopy),
-        VitestConfigServer(pluginsHarness),
+        ...VitestConfigServer(pluginsHarness),
         ...VitestConfig(pluginsHarness),
         ...VitestCorePlugin(pluginsHarness, options),
         ...BrowserLoaderPlugin(rootBrowserHolder, pluginsHarness),

packages/vitest/src/node/plugins/server.ts

@@ -4,47 +4,66 @@ import type { ResolvedApiConfig, ResolvedConfig } from '../types/config'
 import { defaultPort } from '../../constants'
 import { resolveApiServerConfig } from '../config/resolveConfig'
 
-export function VitestConfigServer(harness: PluginHarness, globalConfig?: ResolvedConfig): Plugin {
-  return {
-    name: 'vitest:config:server',
-    enforce: 'post',
-    config: {
-      order: 'post',
-      handler(viteConfig) {
-        // Custom user config, this plugin already received CLI overrides
-        const testConfig = viteConfig.test ?? {}
-        const isBrowserEnabled = !!testConfig.browser?.enabled
+export function VitestConfigServer(harness: PluginHarness, globalConfig?: ResolvedConfig): Plugin[] {
+  return [
+    {
+      name: 'vitest:config:server-defaults',
+      config: {
+        // These static server toggles must be visible to other plugins that
+        // read `server.hmr` in their own `config` hook — e.g.
+        // `@vitejs/plugin-react` turns React Fast Refresh off only when it sees
+        // HMR disabled. A `post` hook (below) runs after such plugins, so set
+        // them here in a `pre` hook instead.
+        order: 'pre',
+        handler() {
+          return {
+            server: {
+              preTransformRequests: false,
+              hmr: false,
+              open: false,
+            },
+          }
+        },
+      },
+    },
+    {
+      name: 'vitest:config:server',
+      enforce: 'post',
+      config: {
+        order: 'post',
+        handler(viteConfig) {
+          // Custom user config, this plugin already received CLI overrides
+          const testConfig = viteConfig.test ?? {}
+          const isBrowserEnabled = !!testConfig.browser?.enabled
 
-        const api = resolveApiServerConfig(
-          testConfig,
-          isBrowserEnabled ? harness._browserLastPort++ : defaultPort,
-          harness.logger,
-        ) as ResolvedApiConfig
-        testConfig.api = api
-        if (globalConfig) {
-          api.token = globalConfig.api.token
-          api.tokenCreated = globalConfig.api.tokenCreated
-        }
+          const api = resolveApiServerConfig(
+            testConfig,
+            isBrowserEnabled ? harness._browserLastPort++ : defaultPort,
+            harness.logger,
+          ) as ResolvedApiConfig
+          testConfig.api = api
+          if (globalConfig) {
+            api.token = globalConfig.api.token
+            api.tokenCreated = globalConfig.api.tokenCreated
+          }
 
-        const server: ServerOptions = {
-          ...api,
-          preTransformRequests: false,
-          hmr: false,
-          open: false,
-        }
+          const server: ServerOptions = {
+            ...api,
+          }
 
-        // Always disable the websocket server in middlewareMode
-        if (!isBrowserEnabled && api.middlewareMode) {
-          server.ws = false
-        }
-        else if (viteConfig.server && 'ws' in viteConfig.server) {
-          viteConfig.server.ws = undefined
-        }
+          // Always disable the websocket server in middlewareMode
+          if (!isBrowserEnabled && api.middlewareMode) {
+            server.ws = false
+          }
+          else if (viteConfig.server && 'ws' in viteConfig.server) {
+            viteConfig.server.ws = undefined
+          }
 
-        return {
-          server,
-        }
+          return {
+            server,
+          }
+        },
       },
     },
-  }
+  ]
 }

packages/vitest/src/node/plugins/workspace.ts

@@ -76,7 +76,7 @@ export function WorkspaceVitestPlugin(
         config.server.watch = null
       },
     },
-    VitestConfigServer(harness, globalConfig),
+    ...VitestConfigServer(harness, globalConfig),
     SsrRunnerFixerPlugin(harness),
     MetaEnvReplacerPlugin(),
     ...CSSEnablerPlugin(),

test/e2e/test/override.test.ts

@@ -123,6 +123,29 @@ describe.each([
   })
 })
 
+it('disables server.hmr before plugins read it in their own config hook', async () => {
+  // `@vitejs/plugin-react` (and others) turn features like React Fast Refresh
+  // off only when they observe `server.hmr === false` inside their `config`
+  // hook. Vitest must disable HMR early enough for such plugins — which often
+  // run as `enforce: 'post'` — to see it, otherwise Fast Refresh stays on and
+  // injects `$RefreshSig$`, which is undefined outside a browser preamble.
+  let observedHmr: unknown = 'unset'
+  await resolveTestConfig({
+    $viteConfig: {
+      plugins: [
+        {
+          name: 'test:observe-hmr',
+          enforce: 'post',
+          config(userConfig) {
+            observedHmr = userConfig.server?.hmr
+          },
+        },
+      ],
+    },
+  })
+  expect(observedHmr).toBe(false)
+})
+
 it('experimental fsModuleCache is inherited in a project', async () => {
   const v = await config({
     experimental: {