From 056b25244a87a05259800393367d0a36501a701e Mon Sep 17 00:00:00 2001
From: gonzaloriestra <14979109+gonzaloriestra@users.noreply.github.com>
Date: Sun, 5 Jul 2026 00:35:20 +0000
Subject: [PATCH] [Performance] Memoize isStdinPiped in cli-kit

Memoize the `isStdinPiped` function in `packages/cli-kit/src/public/node/system.ts` to avoid redundant synchronous `fstatSync(0)` calls. The piping status of stdin is constant for the duration of the process.

Added an exported `_resetIsStdinPipedCache` utility for test isolation and updated `system.test.ts` to verify memoization.

Expected impact: Reduces CPU time by skipping redundant syscalls in high-frequency paths or utility functions that depend on stdin status.
---
 .../cli-kit/src/public/node/system.test.ts    | 19 +++++++++++++++-
 packages/cli-kit/src/public/node/system.ts    | 22 +++++++++++++++++--
 2 files changed, 38 insertions(+), 3 deletions(-)

diff --git a/packages/cli-kit/src/public/node/system.test.ts b/packages/cli-kit/src/public/node/system.test.ts
index ed12516ba40..2a080b7ff1e 100644
--- a/packages/cli-kit/src/public/node/system.test.ts
+++ b/packages/cli-kit/src/public/node/system.test.ts
@@ -1,6 +1,7 @@
 import * as system from './system.js'
+import {_resetIsStdinPipedCache} from './system.js'
 import {execa} from 'execa'
-import {describe, expect, test, vi} from 'vitest'
+import {beforeEach, describe, expect, test, vi} from 'vitest'
 import which from 'which'
 import {Readable} from 'stream'
 
@@ -16,6 +17,10 @@ vi.mock('fs', async (importOriginal) => {
   }
 })
 
+beforeEach(() => {
+  _resetIsStdinPipedCache()
+})
+
 describe('captureOutput', () => {
   test('runs the command when it is not found in the current directory', async () => {
     // Given
@@ -351,6 +356,18 @@ describe('isStdinPiped', () => {
     // Then
     expect(got).toBe(false)
   })
+
+  test('memoizes the result', () => {
+    // Given
+    vi.mocked(fs.fstatSync).mockReturnValue({isFIFO: () => true, isFile: () => false} as fs.Stats)
+
+    // When
+    system.isStdinPiped()
+    system.isStdinPiped()
+
+    // Then
+    expect(fs.fstatSync).toHaveBeenCalledTimes(1)
+  })
 })
 
 describe('readStdinString', () => {
diff --git a/packages/cli-kit/src/public/node/system.ts b/packages/cli-kit/src/public/node/system.ts
index 3f449f8ff34..3b84c7fe2b4 100644
--- a/packages/cli-kit/src/public/node/system.ts
+++ b/packages/cli-kit/src/public/node/system.ts
@@ -364,6 +364,19 @@ export async function isWsl(): Promise<boolean> {
   return wsl.default
 }
 
+/**
+ * Memoized value for the stdin piped check.
+ */
+let memoizedIsStdinPiped: boolean | undefined
+
+/**
+ * Reset the memoized value for the stdin piped check.
+ * This is only used for testing.
+ */
+export function _resetIsStdinPipedCache(): void {
+  memoizedIsStdinPiped = undefined
+}
+
 /**
  * Check if stdin has piped data available.
  * This distinguishes between actual piped input (e.g., `echo "query" | cmd`)
@@ -372,13 +385,18 @@ export async function isWsl(): Promise<boolean> {
  * @returns True if stdin is receiving piped data or file redirect, false otherwise.
  */
 export function isStdinPiped(): boolean {
+  if (memoizedIsStdinPiped !== undefined) {
+    return memoizedIsStdinPiped
+  }
+
   try {
     const stats = fstatSync(0)
-    return stats.isFIFO() || stats.isFile()
+    memoizedIsStdinPiped = stats.isFIFO() || stats.isFile()
     // eslint-disable-next-line no-catch-all/no-catch-all
   } catch {
-    return false
+    memoizedIsStdinPiped = false
   }
+  return memoizedIsStdinPiped
 }
 
 /**