chore: make GC tools optional to support Node.js v12

Node.js v14 provides `WeakRef` and `FinalizationRegistry` as globals. Node.js
v12 does not (there might be a command-line flag to enable it, but I think
it's marked as experimental).

Rather than require all users upgrade to v14, we elect to disable GC when
running on v12. This change attempts to pull `WeakRef` and
`FinalizationRegistry` from the global, and deliver either the real
constructors or `undefined` to the liveslots code that uses it. We'll write
that liveslots code to tolerate their lack.

refs #1872
refs #1925

packages/SwingSet/src/controller.js

@@ -1,4 +1,4 @@
-/* global Compartment WeakRef FinalizationRegistry */
+/* global Compartment */
 
 import fs from 'fs';
 import path from 'path';
@@ -18,6 +18,7 @@ import { makeMeteringTransformer } from '@agoric/transform-metering';
 import { makeTransform } from '@agoric/transform-eventual-send';
 import { locateWorkerBin } from '@agoric/xs-vat-worker';
 
+import { WeakRef, FinalizationRegistry } from './optional-weakref';
 import { startSubprocessWorker } from './spawnSubprocessWorker';
 import { waitUntilQuiescent } from './waitUntilQuiescent';
 import { insistStorageAPI } from './storageAPI';

packages/SwingSet/src/kernel/vatManager/nodeWorkerSupervisor.js

@@ -1,13 +1,13 @@
 // this file is loaded at the start of a new Worker, which makes it a new JS
 // environment (with it's own Realm), so we must install-ses too.
-/* global WeakRef FinalizationRegistry */
 import '@agoric/install-ses';
 import { parentPort } from 'worker_threads';
 import anylogger from 'anylogger';
 
 import { assert } from '@agoric/assert';
 import { importBundle } from '@agoric/import-bundle';
 import { Remotable, getInterfaceOf, makeMarshal } from '@agoric/marshal';
+import { WeakRef, FinalizationRegistry } from '../../optional-weakref';
 import { waitUntilQuiescent } from '../../waitUntilQuiescent';
 import { makeLiveSlots } from '../liveSlots';
 

packages/SwingSet/src/kernel/vatManager/subprocessSupervisor.js

@@ -1,5 +1,4 @@
 // this file is loaded at the start of a new subprocess
-/* global WeakRef FinalizationRegistry */
 import '@agoric/install-ses';
 
 import anylogger from 'anylogger';
@@ -8,6 +7,7 @@ import fs from 'fs';
 import { assert } from '@agoric/assert';
 import { importBundle } from '@agoric/import-bundle';
 import { Remotable, getInterfaceOf, makeMarshal } from '@agoric/marshal';
+import { WeakRef, FinalizationRegistry } from '../../optional-weakref';
 import { arrayEncoderStream, arrayDecoderStream } from '../../worker-protocol';
 import {
   netstringEncoderStream,

packages/SwingSet/src/optional-weakref.js

@@ -0,0 +1,17 @@
+/* global globalThis */
+
+/*
+ * We retain a measure of compatibility with Node.js v12, which does not
+ * expose WeakRef or FinalizationRegistry (there is a --flag for it, but it's
+ * not clear how stable it is). When running on a platform without these
+ * tools, vats cannot do GC.
+ *
+ * Modules should do:
+ *
+ *  import { WeakRef, FinalizationRegistry } from '.../optional-weakref';
+ *
+ * and refrain from GC if `WeakRef === undefined`
+ */
+
+export const WeakRef = globalThis.WeakRef;
+export const FinalizationRegistry = globalThis.FinalizationRegistry;

packages/SwingSet/test/test-kernel.js

@@ -1,8 +1,8 @@
-/* global WeakRef FinalizationRegistry */
 import '@agoric/install-ses';
 import test from 'ava';
 import anylogger from 'anylogger';
 import { initSwingStore } from '@agoric/swing-store-simple';
+import { WeakRef, FinalizationRegistry } from '../src/optional-weakref';
 import { waitUntilQuiescent } from '../src/waitUntilQuiescent';
 
 import buildKernel from '../src/kernel/index';

packages/SwingSet/test/test-liveslots.js

@@ -1,7 +1,7 @@
-/* global WeakRef FinalizationRegistry */
 import '@agoric/install-ses';
 import test from 'ava';
 import { E } from '@agoric/eventual-send';
+import { WeakRef, FinalizationRegistry } from '../src/optional-weakref';
 import { waitUntilQuiescent } from '../src/waitUntilQuiescent';
 import { makeLiveSlots } from '../src/kernel/liveSlots';
 

packages/SwingSet/test/test-marshal.js

@@ -1,8 +1,8 @@
-/* global WeakRef FinalizationRegistry */
 import '@agoric/install-ses';
 import test from 'ava';
 import { makePromiseKit } from '@agoric/promise-kit';
 
+import { WeakRef, FinalizationRegistry } from '../src/optional-weakref';
 import { makeMarshaller } from '../src/kernel/liveSlots';
 
 import { buildVatController } from '../src/index';

packages/SwingSet/test/test-vpid-kernel.js

@@ -1,10 +1,8 @@
-/* global WeakRef FinalizationRegistry */
-// eslint-disable-next-line no-redeclare
-
 import '@agoric/install-ses';
 import test from 'ava';
 import anylogger from 'anylogger';
 import { initSwingStore } from '@agoric/swing-store-simple';
+import { WeakRef, FinalizationRegistry } from '../src/optional-weakref';
 import { waitUntilQuiescent } from '../src/waitUntilQuiescent';
 
 import buildKernel from '../src/kernel/index';

packages/SwingSet/test/test-vpid-liveslots.js

@@ -1,11 +1,12 @@
 // eslint-disable-next-line no-redeclare
-/* global setImmediate WeakRef FinalizationRegistry */
+/* global setImmediate */
 
 import '@agoric/install-ses';
 import test from 'ava';
 
 import { E } from '@agoric/eventual-send';
 import { makePromiseKit } from '@agoric/promise-kit';
+import { WeakRef, FinalizationRegistry } from '../src/optional-weakref';
 import { makeLiveSlots } from '../src/kernel/liveSlots';
 
 const RETIRE_VPIDS = true;