process: mark process.env as side-effect-free

Read-only access to `process.env` does not have side effects.

Refs: nodejs#27523

Author: addaleax

src/node_env_var.cc

@@ -28,6 +28,7 @@ using v8::Nothing;
 using v8::Object;
 using v8::ObjectTemplate;
 using v8::PropertyCallbackInfo;
+using v8::PropertyHandlerFlags;
 using v8::String;
 using v8::Value;
 
@@ -377,7 +378,8 @@ MaybeLocal<Object> CreateEnvVarProxy(Local<Context> context,
   EscapableHandleScope scope(isolate);
   Local<ObjectTemplate> env_proxy_template = ObjectTemplate::New(isolate);
   env_proxy_template->SetHandler(NamedPropertyHandlerConfiguration(
-      EnvGetter, EnvSetter, EnvQuery, EnvDeleter, EnvEnumerator, data));
+      EnvGetter, EnvSetter, EnvQuery, EnvDeleter, EnvEnumerator, data,
+      PropertyHandlerFlags::kHasNoSideEffect));
   return scope.EscapeMaybe(env_proxy_template->NewInstance(context));
 }
 }  // namespace node

test/parallel/test-process-env-sideeffects.js

@@ -0,0 +1,24 @@
+'use strict';
+const common = require('../common');
+common.skipIfInspectorDisabled();
+
+// Test that read-only process.env access is considered to have no
+// side-effects by the insepctor.
+
+const assert = require('assert');
+const inspector = require('inspector');
+
+const session = new inspector.Session();
+session.connect();
+
+process.env.TESTVAR = 'foobar';
+
+session.post('Runtime.evaluate', {
+  expression: 'process.env.TESTVAR',
+  throwOnSideEffect: true
+}, (error, res) => {
+  assert.ifError(error);
+  assert.deepStrictEqual(res, {
+    result: { type: 'string', value: 'foobar' }
+  });
+});