process: deprecate toStringTag assignment

doc/api/deprecations.md

@@ -2361,6 +2361,15 @@ changes:
     description: Runtime deprecation.
 -->
 
+<a id="DEP0126"></a>
+### DEP0126: writing to process[Symbol.toStringTag]
+<!-- YAML
+changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/26715
+    description: Runtime deprecation.
+-->
+
 Type: Runtime
 
 The `_stream_wrap` module is deprecated.

lib/internal/bootstrap/node.js

@@ -279,11 +279,16 @@ function setupProcessObject() {
   const origProcProto = Object.getPrototypeOf(process);
   Object.setPrototypeOf(origProcProto, EventEmitter.prototype);
   EventEmitter.call(process);
+  let toStringTag = 'process';
   Object.defineProperty(process, Symbol.toStringTag, {
     enumerable: false,
-    writable: true,
     configurable: false,
-    value: 'process'
+    get() {
+      return toStringTag;
+    },
+    set: deprecate((value) => toStringTag = value,
+                   'Setting \'process[Symbol.toStringTag]\' is deprecated',
+                   'DEP0126')
   });
   // Make process globally available to users by putting it on the global proxy
   Object.defineProperty(global, 'process', {

test/es-module/test-esm-process.mjs

@@ -1,7 +1,13 @@
 // Flags: --experimental-modules
 import '../common';
+import { expectWarning } from '../common/index.mjs';
 import assert from 'assert';
 import process from 'process';
 
 assert.strictEqual(Object.prototype.toString.call(process), '[object process]');
-assert(Object.getOwnPropertyDescriptor(process, Symbol.toStringTag).writable);
+process[Symbol.toStringTag] = 'custom process';
+expectWarning('DeprecationWarning',
+              'Setting \'process[Symbol.toStringTag]\' is deprecated',
+              'DEP0126');
+assert.strictEqual(Object.prototype.toString.call(process),
+                   '[object custom process]');