From bb649d43ab1535ba1b1434dd68f059a87f68a1e9 Mon Sep 17 00:00:00 2001
From: marcopiraccini <marco.piraccini@gmail.com>
Date: Sat, 7 Mar 2026 06:51:38 +0100
Subject: [PATCH] watch: strip watch flags from NODE_OPTIONS in child process

Signed-off-by: marcopiraccini <marco.piraccini@gmail.com>
---
 lib/internal/main/watch_mode.js     | 28 ++++++++++++++++++++++++
 test/sequential/test-watch-mode.mjs | 33 +++++++++++++++++++++++++++++
 2 files changed, 61 insertions(+)

diff --git a/lib/internal/main/watch_mode.js b/lib/internal/main/watch_mode.js
index 06c2c8602da444..6340bcda9460ae 100644
--- a/lib/internal/main/watch_mode.js
+++ b/lib/internal/main/watch_mode.js
@@ -7,6 +7,7 @@ const {
   ArrayPrototypePush,
   ArrayPrototypePushApply,
   ArrayPrototypeSlice,
+  RegExpPrototypeSymbolSplit,
   StringPrototypeStartsWith,
 } = primordials;
 
@@ -84,6 +85,32 @@ for (let i = 0; i < process.execArgv.length; i++) {
 
 ArrayPrototypePushApply(argsWithoutWatchOptions, kCommand);
 
+const kNodeOptions = process.env.NODE_OPTIONS;
+let cleanNodeOptions = kNodeOptions;
+if (kNodeOptions != null) {
+  const nodeOptionsArgs = [];
+  const parts = RegExpPrototypeSymbolSplit(/\s+/, kNodeOptions);
+  for (let i = 0; i < parts.length; i++) {
+    const part = parts[i];
+    if (part === '') continue;
+    if (part === '--watch' ||
+        part === '--watch-preserve-output' ||
+        StringPrototypeStartsWith(part, '--watch=') ||
+        StringPrototypeStartsWith(part, '--watch-preserve-output=') ||
+        StringPrototypeStartsWith(part, '--watch-path=') ||
+        StringPrototypeStartsWith(part, '--watch-kill-signal=')) {
+      continue;
+    }
+    if (part === '--watch-path' || part === '--watch-kill-signal') {
+      // These flags take a separate value argument
+      i++;
+      continue;
+    }
+    ArrayPrototypePush(nodeOptionsArgs, part);
+  }
+  cleanNodeOptions = ArrayPrototypeJoin(nodeOptionsArgs, ' ');
+}
+
 const watcher = new FilesWatcher({ debounce: 200, mode: kShouldFilterModules ? 'filter' : 'all' });
 ArrayPrototypeForEach(kWatchedPaths, (p) => watcher.watchPath(p));
 
@@ -99,6 +126,7 @@ function start() {
     env: {
       ...process.env,
       WATCH_REPORT_DEPENDENCIES: '1',
+      NODE_OPTIONS: cleanNodeOptions,
     },
   });
   watcher.watchChildProcessModules(child);
diff --git a/test/sequential/test-watch-mode.mjs b/test/sequential/test-watch-mode.mjs
index a5cac129ad1c21..fa2fb323565218 100644
--- a/test/sequential/test-watch-mode.mjs
+++ b/test/sequential/test-watch-mode.mjs
@@ -922,4 +922,37 @@ process.on('message', (message) => {
       await done();
     }
   });
+
+  it('should strip all watch flags from NODE_OPTIONS in child process', async () => {
+    const file = createTmpFile('console.log(process.env.NODE_OPTIONS);');
+    const nodeOptions = [
+      '--watch',                       // bare boolean
+      '--watch=true',                  // boolean with =value
+      '--watch-path=./src',            // string with =value
+      '--watch-path', './test',        // String with space-separated value
+      '--watch-preserve-output',       // bare boolean
+      '--watch-preserve-output=true',  // boolean with =value
+      '--watch-kill-signal=SIGKILL',   // string with =value
+      '--watch-kill-signal', 'SIGINT', // String with space-separated value
+      '--max-old-space-size=4096',
+      '--no-warnings',
+    ].join(' ');
+    const { done, restart } = runInBackground({
+      args: ['--watch', file],
+      options: {
+        env: { ...process.env, NODE_OPTIONS: nodeOptions },
+      },
+    });
+
+    try {
+      const { stdout, stderr } = await restart();
+
+      assert.strictEqual(stderr, '');
+      const nodeOptionsLine = stdout.find((line) => line.includes('--max-old-space-size'));
+      assert.ok(nodeOptionsLine);
+      assert.strictEqual(nodeOptionsLine, '--max-old-space-size=4096 --no-warnings');
+    } finally {
+      await done();
+    }
+  });
 });