refactor(runner): limit max concurrency without p-limit as a dependen…

…cy (#5980)

packages/browser/src/node/plugin.ts

@@ -188,7 +188,6 @@ export default (browserServer: BrowserServer, base = '/'): Plugin[] => {
               'vitest > pretty-format > ansi-regex',
               'vitest > chai',
               'vitest > chai > loupe',
-              'vitest > @vitest/runner > p-limit',
               'vitest > @vitest/utils > diff-sequences',
               'vitest > @vitest/utils > loupe',
               '@vitest/browser > @testing-library/user-event',

packages/runner/package.json

@@ -43,7 +43,6 @@
   },
   "dependencies": {
     "@vitest/utils": "workspace:*",
-    "p-limit": "^5.0.0",
     "pathe": "^1.1.2"
   }
 }

packages/runner/src/run.ts

@@ -1,4 +1,3 @@
-import limit from 'p-limit'
 import type { Awaitable } from '@vitest/utils'
 import { getSafeTimers, shuffle } from '@vitest/utils'
 import { processError } from '@vitest/utils/error'
@@ -20,6 +19,7 @@ import type {
   Test,
 } from './types'
 import { partitionSuiteChildren } from './utils/suite'
+import { limitConcurrency } from './utils/limit-concurrency'
 import { getFn, getHooks } from './map'
 import { collectTests } from './collect'
 import { setCurrentTest } from './test-state'
@@ -466,7 +466,7 @@ export async function runSuite(suite: Suite, runner: VitestRunner) {
   }
 }
 
-let limitMaxConcurrency: ReturnType<typeof limit>
+let limitMaxConcurrency: ReturnType<typeof limitConcurrency>
 
 async function runSuiteChild(c: Task, runner: VitestRunner) {
   if (c.type === 'test' || c.type === 'custom') {
@@ -478,7 +478,7 @@ async function runSuiteChild(c: Task, runner: VitestRunner) {
 }
 
 export async function runFiles(files: File[], runner: VitestRunner) {
-  limitMaxConcurrency ??= limit(runner.config.maxConcurrency)
+  limitMaxConcurrency ??= limitConcurrency(runner.config.maxConcurrency)
 
   for (const file of files) {
     if (!file.tasks.length && !runner.config.passWithNoTests) {

packages/runner/src/utils/index.ts

@@ -2,3 +2,4 @@ export * from './collect'
 export * from './suite'
 export * from './tasks'
 export * from './chain'
+export * from './limit-concurrency'

packages/runner/src/utils/limit-concurrency.ts

@@ -0,0 +1,57 @@
+// A compact (code-wise, probably not memory-wise) singly linked list node.
+type QueueNode<T> = [value: T, next?: QueueNode<T>]
+
+/**
+ * Return a function for running multiple async operations with limited concurrency.
+ */
+export function limitConcurrency(concurrency = Infinity): <Args extends unknown[], T>(func: (...args: Args) => PromiseLike<T> | T, ...args: Args) => Promise<T> {
+  // The number of currently active + pending tasks.
+  let count = 0
+
+  // The head and tail of the pending task queue, built using a singly linked list.
+  // Both head and tail are initially undefined, signifying an empty queue.
+  // They both become undefined again whenever there are no pending tasks.
+  let head: undefined | QueueNode<() => void>
+  let tail: undefined | QueueNode<() => void>
+
+  // A bookkeeping function executed whenever a task has been run to completion.
+  const finish = () => {
+    count--
+
+    // Check if there are further pending tasks in the queue.
+    if (head) {
+      // Allow the next pending task to run and pop it from the queue.
+      head[0]()
+      head = head[1]
+
+      // The head may now be undefined if there are no further pending tasks.
+      // In that case, set tail to undefined as well.
+      tail = head && tail
+    }
+  }
+
+  return (func, ...args) => {
+    // Create a promise chain that:
+    //  1. Waits for its turn in the task queue (if necessary).
+    //  2. Runs the task.
+    //  3. Allows the next pending task (if any) to run.
+    return new Promise<void>((resolve) => {
+      if (count++ < concurrency) {
+        // No need to queue if fewer than maxConcurrency tasks are running.
+        resolve()
+      }
+      else if (tail) {
+        // There are pending tasks, so append to the queue.
+        tail = tail[1] = [resolve]
+      }
+      else {
+        // No other pending tasks, initialize the queue with a new tail and head.
+        head = tail = [resolve]
+      }
+    }).then(() => {
+      // Running func here ensures that even a non-thenable result or an
+      // immediately thrown error gets wrapped into a Promise.
+      return func(...args)
+    }).finally(finish)
+  }
+}

test/cli/test/console.test.ts

@@ -41,8 +41,8 @@ test('can run custom pools with Vitest', async () => {
   `)
   const stderrArray = vitest.stderr.split('\n')
   // remove stack trace
-  const stderr = stderrArray.slice(0, -9).join('\n')
-  const stackStderr = stderrArray.slice(-9).join('\n')
+  const stderr = stderrArray.slice(0, -14).join('\n')
+  const stackStderr = stderrArray.slice(-14).join('\n')
   expect(stderr).toMatchInlineSnapshot(`
     "stderr | trace.test.ts > logging to stdout
     warn with trace
@@ -64,14 +64,19 @@ test('can run custom pools with Vitest', async () => {
   expect(stackStderr).not.toMatch('❯ ')
   if (process.platform !== 'win32') {
     const root = resolve(process.cwd(), '../..')
-    expect(stackStderr.replace(new RegExp(root, 'g'), '<root>').replace(/\d+:\d+/g, 'ln:cl')).toMatchInlineSnapshot(`
+    expect(stackStderr.replace(new RegExp(root, 'g'), '<root>').replace(/\d+:\d+/g, 'ln:cl').replace(/\.\w+\.js:/g, '.<chunk>.js:')).toMatchInlineSnapshot(`
       "stderr | trace.test.ts > logging to stdout
       Trace: trace with trace
           at <root>/test/cli/fixtures/console/trace.test.ts:ln:cl
           at file://<root>/packages/runner/dist/index.js:ln:cl
           at file://<root>/packages/runner/dist/index.js:ln:cl
           at runTest (file://<root>/packages/runner/dist/index.js:ln:cl)
           at processTicksAndRejections (node:internal/process/task_queues:ln:cl)
+          at runSuite (file://<root>/packages/runner/dist/index.js:ln:cl)
+          at runFiles (file://<root>/packages/runner/dist/index.js:ln:cl)
+          at startTests (file://<root>/packages/runner/dist/index.js:ln:cl)
+          at file://<root>/packages/vitest/dist/chunks/runtime-runBaseTests.<chunk>.js:ln:cl
+          at withEnv (file://<root>/packages/vitest/dist/chunks/runtime-runBaseTests.<chunk>.js:ln:cl)
 
       "
     `)