fix(forks): wrap defines to support undefined values

packages/vitest/src/node/pools/forks.ts

@@ -8,6 +8,7 @@ import type { ContextRPC, ContextTestEnvironment, ResolvedConfig, RunnerRPC, Run
 import type { PoolProcessOptions, ProcessPool, RunWithFiles } from '../pool'
 import type { WorkspaceProject } from '../workspace'
 import { envsOrder, groupFilesByEnv } from '../../utils/test-helpers'
+import { wrapSerializableConfig } from '../../utils/config-helpers'
 import { groupBy, resolve } from '../../utils'
 import { createMethodsRPC } from './rpc'
 
@@ -44,12 +45,6 @@ function createChildProcessChannel(project: WorkspaceProject) {
   return { channel, cleanup }
 }
 
-function stringifyRegex(input: RegExp | string): string {
-  if (typeof input === 'string')
-    return input
-  return `$$vitest:${input.toString()}`
-}
-
 export function createForksPool(ctx: Vitest, { execArgv, env }: PoolProcessOptions): ProcessPool {
   const numCpus
     = typeof nodeos.availableParallelism === 'function'
@@ -144,14 +139,7 @@ export function createForksPool(ctx: Vitest, { execArgv, env }: PoolProcessOptio
           return configs.get(project)!
 
         const _config = project.getSerializableConfig()
-
-        const config = {
-          ..._config,
-          // v8 serialize does not support regex
-          testNamePattern: _config.testNamePattern
-            ? stringifyRegex(_config.testNamePattern)
-            : undefined,
-        } as ResolvedConfig
+        const config = wrapSerializableConfig(_config)
 
         configs.set(project, config)
         return config

packages/vitest/src/node/pools/vmForks.ts

@@ -12,6 +12,7 @@ import { groupFilesByEnv } from '../../utils/test-helpers'
 import { AggregateError } from '../../utils/base'
 import type { WorkspaceProject } from '../workspace'
 import { getWorkerMemoryLimit, stringToBytes } from '../../utils/memory-limit'
+import { wrapSerializableConfig } from '../../utils/config-helpers'
 import { createMethodsRPC } from './rpc'
 
 const suppressWarningsPath = resolve(rootDir, './suppress-warnings.cjs')
@@ -49,12 +50,6 @@ function createChildProcessChannel(project: WorkspaceProject) {
   return { channel, cleanup }
 }
 
-function stringifyRegex(input: RegExp | string): string {
-  if (typeof input === 'string')
-    return input
-  return `$$vitest:${input.toString()}`
-}
-
 export function createVmForksPool(ctx: Vitest, { execArgv, env }: PoolProcessOptions): ProcessPool {
   const numCpus
     = typeof nodeos.availableParallelism === 'function'
@@ -149,14 +144,8 @@ export function createVmForksPool(ctx: Vitest, { execArgv, env }: PoolProcessOpt
           return configs.get(project)!
 
         const _config = project.getSerializableConfig()
+        const config = wrapSerializableConfig(_config)
 
-        const config = {
-          ..._config,
-          // v8 serialize does not support regex
-          testNamePattern: _config.testNamePattern
-            ? stringifyRegex(_config.testNamePattern)
-            : undefined,
-        } as ResolvedConfig
         configs.set(project, config)
         return config
       }

packages/vitest/src/runtime/workers/forks.ts

@@ -1,6 +1,6 @@
 import v8 from 'node:v8'
 import type { WorkerGlobalState } from '../../types/worker'
-import { createForksRpcOptions, unwrapForksConfig } from './utils'
+import { createForksRpcOptions, unwrapSerializableConfig } from './utils'
 import { runBaseTests } from './base'
 import type { VitestWorker } from './types'
 
@@ -13,7 +13,7 @@ class ForksBaseWorker implements VitestWorker {
     // TODO: don't rely on reassigning process.exit
     // https://github.com/vitest-dev/vitest/pull/4441#discussion_r1443771486
     const exit = process.exit
-    state.ctx.config = unwrapForksConfig(state.ctx.config)
+    state.ctx.config = unwrapSerializableConfig(state.ctx.config)
 
     try {
       await runBaseTests(state)

packages/vitest/src/runtime/workers/utils.ts

@@ -4,6 +4,8 @@ import type { WorkerContext } from '../../types/worker'
 import type { ResolvedConfig } from '../../types/config'
 import type { WorkerRpcOptions } from './types'
 
+const REGEXP_WRAP_PREFIX = '$$vitest:'
+
 export function createThreadsRpcOptions({ port }: WorkerContext): WorkerRpcOptions {
   return {
     post: (v) => { port.postMessage(v) },
@@ -28,15 +30,27 @@ export function createForksRpcOptions(nodeV8: typeof import('v8')): WorkerRpcOpt
   }
 }
 
-function parsePossibleRegexp(str: string | RegExp) {
-  const prefix = '$$vitest:'
-  if (typeof str === 'string' && str.startsWith(prefix))
-    return parseRegexp(str.slice(prefix.length))
-  return str
-}
+/**
+ * Reverts the wrapping done by `utils/config-helpers.ts`'s `wrapSerializableConfig`
+ */
+export function unwrapSerializableConfig(config: ResolvedConfig) {
+  if (config.testNamePattern && typeof config.testNamePattern === 'string') {
+    const testNamePattern = config.testNamePattern as string
+
+    if (testNamePattern.startsWith(REGEXP_WRAP_PREFIX))
+      config.testNamePattern = parseRegexp(testNamePattern.slice(REGEXP_WRAP_PREFIX.length))
+  }
+
+  if (config.defines && Array.isArray(config.defines.keys) && config.defines.original) {
+    const { keys, original } = config.defines
+    const defines: ResolvedConfig['defines'] = {}
+
+    // Apply all keys from the original. Entries which had undefined value are missing from original now
+    for (const key of keys)
+      defines[key] = original[key]
+
+    config.defines = defines
+  }
 
-export function unwrapForksConfig(config: ResolvedConfig) {
-  if (config.testNamePattern)
-    config.testNamePattern = parsePossibleRegexp(config.testNamePattern) as RegExp
   return config
 }

packages/vitest/src/runtime/workers/vmForks.ts

@@ -1,6 +1,6 @@
 import v8 from 'node:v8'
 import type { WorkerGlobalState } from '../../types/worker'
-import { createForksRpcOptions, unwrapForksConfig } from './utils'
+import { createForksRpcOptions, unwrapSerializableConfig } from './utils'
 import type { VitestWorker } from './types'
 import { runVmTests } from './vm'
 
@@ -11,7 +11,7 @@ class ForksVmWorker implements VitestWorker {
 
   async runTests(state: WorkerGlobalState) {
     const exit = process.exit
-    state.ctx.config = unwrapForksConfig(state.ctx.config)
+    state.ctx.config = unwrapSerializableConfig(state.ctx.config)
 
     try {
       await runVmTests(state)

packages/vitest/src/utils/config-helpers.ts

@@ -1,5 +1,8 @@
+import type { ResolvedConfig } from '../types/config'
 import type { BenchmarkBuiltinReporters, BuiltinReporters } from '../node/reporters'
 
+const REGEXP_WRAP_PREFIX = '$$vitest:'
+
 interface PotentialConfig {
   outputFile?: string | Partial<Record<string, string>>
 }
@@ -13,3 +16,25 @@ export function getOutputFile(config: PotentialConfig | undefined, reporter: Bui
 
   return config.outputFile[reporter]
 }
+
+/**
+ * Prepares `ResolvedConfig` for serialization, e.g. `node:v8.serialize`
+ */
+export function wrapSerializableConfig(config: ResolvedConfig) {
+  let testNamePattern = config.testNamePattern
+  let defines = config.defines
+
+  // v8 serialize does not support regex
+  if (testNamePattern && typeof testNamePattern !== 'string')
+    testNamePattern = `${REGEXP_WRAP_PREFIX}${testNamePattern.toString()}` as unknown as RegExp
+
+  // v8 serialize drops properties with undefined value
+  if (defines)
+    defines = { keys: Object.keys(defines), original: defines }
+
+  return {
+    ...config,
+    testNamePattern,
+    defines,
+  } as ResolvedConfig
+}

packages/vitest/src/workers.ts

@@ -1,4 +1,4 @@
-export { createForksRpcOptions, createThreadsRpcOptions, unwrapForksConfig } from './runtime/workers/utils'
+export { createForksRpcOptions, createThreadsRpcOptions, unwrapSerializableConfig } from './runtime/workers/utils'
 export { provideWorkerState } from './utils/global'
 export { run as runVitestWorker } from './runtime/worker'
 export { runVmTests } from './runtime/workers/vm'

test/core/test/define-ssr.test.ts

@@ -3,6 +3,10 @@ import { afterAll, expect, test } from 'vitest'
 declare let __DEFINE__: string
 declare let __JSON__: any
 declare let __MODE__: string
+declare let __UNDEFINED__: undefined
+declare let __NULL__: null
+declare let __ZERO__: 0
+declare let __FALSE__: false
 declare let SOME: {
   VARIABLE: string
   SOME: {
@@ -64,3 +68,10 @@ test('dotted defines are processed by Vite, but cannot be reassigned', () => {
   SOME.VARIABLE = 'new variable'
   expect(SOME.VARIABLE).not.toBe('new variable')
 })
+
+test('falsy defines are passed', () => {
+  expect(__UNDEFINED__).toBe(undefined)
+  expect(__NULL__).toBe(null)
+  expect(__ZERO__).toBe(0)
+  expect(__FALSE__).toBe(false)
+})

test/core/test/define-web.test.ts

@@ -5,6 +5,10 @@ import { afterAll, expect, test } from 'vitest'
 declare let __DEFINE__: string
 declare let __JSON__: any
 declare let __MODE__: string
+declare let __UNDEFINED__: undefined
+declare let __NULL__: null
+declare let __ZERO__: 0
+declare let __FALSE__: false
 declare let SOME: {
   VARIABLE: string
   SOME: {
@@ -61,3 +65,10 @@ test('dotted defines can be reassigned', () => {
   SOME.VARIABLE = 'new variable'
   expect(SOME.VARIABLE).toBe('new variable')
 })
+
+test('falsy defines are passed', () => {
+  expect(__UNDEFINED__).toBe(undefined)
+  expect(__NULL__).toBe(null)
+  expect(__ZERO__).toBe(0)
+  expect(__FALSE__).toBe(false)
+})

test/core/vite.config.ts

@@ -32,6 +32,10 @@ export default defineConfig({
     '__MODE__': 'process.env.MODE',
     'SOME.VARIABLE': '"variable"',
     'SOME.SOME.VARIABLE': '"nested variable"',
+    '__UNDEFINED__': undefined,
+    '__NULL__': null,
+    '__ZERO__': 0,
+    '__FALSE__': false,
   },
   resolve: {
     alias: [