module: fix leak of vm.SyntheticModule

Previously we maintain a strong persistent reference to the
ModuleWrap to retrieve the ID-to-ModuleWrap mapping from
the HostImportModuleDynamicallyCallback using the number ID
stored in the host-defined options. As a result the ModuleWrap
would be kept alive until the Environment is shut down, which
would be a leak for user code. With the new symbol-based
host-defined option we can just get the ModuleWrap from the
JS-land WeakMap so there's now no need to maintain this
strong reference. This would at least fix the leak for
vm.SyntheticModule. vm.SourceTextModule is still leaking
due to the strong persistent reference to the v8::Module.

PR-URL: nodejs#48510
Refs: nodejs#44211
Refs: nodejs#42080
Refs: nodejs#47096
Refs: nodejs#43205
Refs: nodejs#38695
Reviewed-By: Antoine du Hamel <[email protected]>
Reviewed-By: Benjamin Gruenbaum <[email protected]>
Reviewed-By: Stephen Belanger <[email protected]>

src/module_wrap.cc

@@ -64,6 +64,7 @@ ModuleWrap::ModuleWrap(Environment* env,
   if (!synthetic_evaluation_step->IsUndefined()) {
     synthetic_ = true;
   }
+  MakeWeak();
 }
 
 ModuleWrap::~ModuleWrap() {

test/es-module/test-vm-synthetic-module-leak.js

@@ -0,0 +1,23 @@
+// Flags: --experimental-vm-modules --max-old-space-size=16
+'use strict';
+
+// This tests that vm.SyntheticModule does not leak.
+// See https://github.com/nodejs/node/issues/44211
+require('../common');
+const vm = require('vm');
+
+let count = 0;
+async function createModule() {
+  // Try to reach the maximum old space size.
+  const m = new vm.SyntheticModule(['bar'], () => {
+    m.setExport('bar', new Array(512).fill('----'));
+  });
+  await m.link(() => {});
+  await m.evaluate();
+  if (count++ < 4 * 1024) {
+    setTimeout(createModule, 1);
+  }
+  return m;
+}
+
+createModule();