src: make global non-enumerable

Per https://github.com/tc39/proposal-global, the global value `global`
should be configurable, writable, and non-enumerable. `node` has always
provided it as configurable, writable, and enumerable.

The plan is to make it non-enumerable, and barring strong evidence that
node can not ship `global` as non-enumerable, this will be how it lands
as stage 4 (in the spec).

src/node.cc

@@ -2983,6 +2983,13 @@ void StopProfilerIdleNotifier(const FunctionCallbackInfo<Value>& args) {
   env->StopProfilerIdleNotifier();
 }
 
+#define NONENUMERABLE_PROPERTY(obj, str, var)                                 \
+  do {                                                                        \
+    obj->DefineOwnProperty(env->context(),                                    \
+                           OneByteString(env->isolate(), str),                \
+                           var,                                               \
+                           v8::DontEnum).FromJust();                          \
+  } while (0)
 
 #define READONLY_PROPERTY(obj, str, var)                                      \
   do {                                                                        \
@@ -3450,9 +3457,9 @@ void LoadEnvironment(Environment* env) {
 
   env->SetMethod(env->process_object(), "_rawDebug", RawDebug);
 
-  // Expose the global object as a property on itself
+  // Expose the global object as a non-enumerable property on itself
   // (Allows you to set stuff on `global` from anywhere in JavaScript.)
-  global->Set(FIXED_ONE_BYTE_STRING(env->isolate(), "global"), global);
+  NONENUMERABLE_PROPERTY(global, "global", global);
 
   // Now we call 'f' with the 'process' variable that we've built up with
   // all our bindings. Inside bootstrap_node.js and internal/process we'll

test/parallel/test-global-descriptors.js

@@ -0,0 +1,18 @@
+'use strict';
+require('../common');
+
+const assert = require('assert');
+
+const {
+  value,
+  configurable,
+  enumerable,
+  writable
+} = Object.getOwnPropertyDescriptor(global, 'global');
+
+const actualGlobal = Function('return this')();
+assert.strictEqual(value, actualGlobal, 'global should be global object');
+
+assert.strictEqual(configurable, true, 'global should be configurable');
+assert.strictEqual(enumerable, false, 'global should be non-enumerable');
+assert.strictEqual(writable, true, 'global should be writable');