fix(swingset): add dummy dispatch.dropExports to liveslots

The new `dropExports()` doesn't do anything yet, but at least test that it
can be called directly in liveslots. It should be reachable through all vat
worker types, but I won't be able to test that until we have a kernel
mechanism to provoke it.

closes #2653

packages/SwingSet/docs/vat-worker.md

@@ -24,6 +24,7 @@ The `Delivery` object is a hardened Array of data (Objects, Arrays, and Strings,
 
 * `['message', targetSlot, msg]`
 * `['notify', resolutions]`
+* `['dropExports', vrefs]`
 
 In the `message` form, `targetSlot` is a object/promise reference (a string like `o+13` or `p-24`), which identifies the object or promise to which the message is being sent. This target can be a promise if the message is being pipelined to the result of some earlier message.
 

packages/SwingSet/src/kernel/liveSlots.js

@@ -611,6 +611,13 @@ function build(
     }
   }
 
+  function dropExports(vrefs) {
+    assert(Array.isArray(vrefs));
+    vrefs.map(vref => insistVatType('object', vref));
+    vrefs.map(vref => assert(parseVatSlot(vref).allocatedByVat));
+    console.log(`-- liveslots ignoring dropExports`);
+  }
+
   // TODO: when we add notifyForward, guard against cycles
 
   function exitVat(completion) {
@@ -674,7 +681,7 @@ function build(
     slotToVal.set(rootSlot, rootObject);
   }
 
-  const dispatch = harden({ deliver, notify });
+  const dispatch = harden({ deliver, notify, dropExports });
   return harden({ vatGlobals, setBuildRootObject, dispatch, m });
 }
 

packages/SwingSet/src/kernel/vatManager/supervisor-nodeworker.js

@@ -64,6 +64,11 @@ function doNotify(resolutions) {
   return doProcess(['notify', resolutions], errmsg);
 }
 
+function doDropExports(vrefs) {
+  const errmsg = `vat.doDropExport failed`;
+  return doProcess(['dropExports', vrefs], errmsg);
+}
+
 parentPort.on('message', ([type, ...margs]) => {
   workerLog(`received`, type);
   if (type === 'start') {
@@ -143,6 +148,8 @@ parentPort.on('message', ([type, ...margs]) => {
       doMessage(...dargs).then(res => sendUplink(['deliverDone', ...res]));
     } else if (dtype === 'notify') {
       doNotify(...dargs).then(res => sendUplink(['deliverDone', ...res]));
+    } else if (dtype === 'dropExports') {
+      doDropExports(...dargs).then(res => sendUplink(['deliverDone', ...res]));
     } else {
       assert.fail(X`bad delivery type ${dtype}`);
     }

packages/SwingSet/src/kernel/vatManager/supervisor-subprocess-node.js

@@ -64,6 +64,11 @@ function doNotify(resolutions) {
   return doProcess(['notify', resolutions], errmsg);
 }
 
+function doDropExports(vrefs) {
+  const errmsg = `vat.doDropExport failed`;
+  return doProcess(['dropExports', vrefs], errmsg);
+}
+
 const toParent = arrayEncoderStream();
 toParent
   .pipe(netstringEncoderStream())
@@ -163,6 +168,8 @@ fromParent.on('data', ([type, ...margs]) => {
       doMessage(...dargs).then(res => sendUplink(['deliverDone', ...res]));
     } else if (dtype === 'notify') {
       doNotify(...dargs).then(res => sendUplink(['deliverDone', ...res]));
+    } else if (dtype === 'dropExports') {
+      doDropExports(...dargs).then(res => sendUplink(['deliverDone', ...res]));
     } else {
       assert.fail(X`bad delivery type ${dtype}`);
     }

packages/SwingSet/src/kernel/vatManager/supervisor-subprocess-xsnap.js

@@ -151,6 +151,12 @@ function makeWorker(port) {
     return doProcess(['notify', resolutions], errmsg);
   }
 
+  /** @type { (rs: unknown) => Promise<Tagged> } */
+  function doDropExports(vrefs) {
+    const errmsg = `vat.dropExports failed`;
+    return doProcess(['dropExports', vrefs], errmsg);
+  }
+
   /**
    * TODO: consider other methods per SES VirtualConsole.
    * See https://github.com/Agoric/agoric-sdk/issues/2146
@@ -277,6 +283,8 @@ function makeWorker(port) {
             return doMessage(dargs[0], dargs[1]);
           case 'notify':
             return doNotify(dargs[0]);
+          case 'dropExports':
+            return doDropExports(dargs[0]);
           default:
             assert.fail(X`bad delivery type ${dtype}`);
         }

packages/SwingSet/test/test-liveslots.js

@@ -15,8 +15,17 @@ function capargs(args, slots = []) {
   return capdata(JSON.stringify(args), slots);
 }
 
-function caponeslot(slot) {
-  return capargs([{ '@qclass': 'slot', index: 0 }], [slot]);
+function capdataOneSlot(slot) {
+  return capargs({ '@qclass': 'slot', iface: 'Alleged: export', index: 0 }, [
+    slot,
+  ]);
+}
+
+function capargsOneSlot(slot) {
+  return capargs(
+    [{ '@qclass': 'slot', iface: 'Alleged: export', index: 0 }],
+    [slot],
+  );
 }
 
 function oneResolution(promiseID, rejected, data) {
@@ -639,7 +648,7 @@ test('disavow', async t => {
   const import1 = 'o-1';
 
   // root~.one(import1) // sendOnly
-  dispatch.deliver(rootA, 'one', caponeslot(import1), undefined);
+  dispatch.deliver(rootA, 'one', capargsOneSlot(import1), undefined);
   await waitUntilQuiescent();
   t.deepEqual(log.shift(), { type: 'dropImports', slots: [import1] });
   t.deepEqual(log.shift(), 'disavowed pres1');
@@ -672,3 +681,37 @@ test('disavow', async t => {
   t.deepEqual(log.shift(), 'tried to send to disavowed');
   t.deepEqual(log, []);
 });
+
+test('dropExports', async t => {
+  const { log, syscall } = buildSyscall();
+
+  function build(_vatPowers) {
+    const ex1 = Far('export', {});
+    const root = Far('root', {
+      one() {
+        return ex1;
+      },
+    });
+    return root;
+  }
+  const dispatch = makeDispatch(syscall, build, true);
+  t.deepEqual(log, []);
+  const rootA = 'o+0';
+
+  // rp1 = root~.one()
+  // ex1 = await rp1
+  const rp1 = 'p-1';
+  dispatch.deliver(rootA, 'one', capargs([]), rp1);
+  await waitUntilQuiescent();
+  const l1 = log.shift();
+  const ex1 = l1.resolutions[0][2].slots[0];
+  t.deepEqual(l1, {
+    type: 'resolve',
+    resolutions: [[rp1, false, capdataOneSlot(ex1)]],
+  });
+  t.deepEqual(log, []);
+
+  // now tell the vat to drop that export
+  dispatch.dropExports([ex1]);
+  // for now, all that we care about is that liveslots doesn't crash
+});