fix: use WeakSet for disavowals, improve comments, tidy vatPowers

Author: warner

packages/SwingSet/src/kernel/liveSlots.js

@@ -70,9 +70,10 @@ function build(
   /** Map vat slot strings -> in-vat object references. */
   const slotToVal = new Map();
 
-  /** Map disavowed Presences to the Error which kills the vat if you try to
-   * talk to them */
-  const disavowedPresences = new WeakMap();
+  /** Remember disavowed Presences which will kill the vat if you try to talk
+   * to them */
+  const disavowedPresences = new WeakSet();
+  const disavowalError = harden(Error(`this Presence has been disavowed`));
 
   const importedPromisesByPromiseID = new Map();
   let nextExportID = 1;
@@ -89,11 +90,10 @@ function build(
       applyMethod(o, prop, args, returnedP) {
         // Support: o~.[prop](...args) remote method invocation
         lsdebug(`makeImportedPresence handler.applyMethod (${slot})`);
-        const err = disavowedPresences.get(o);
-        if (err) {
+        if (disavowedPresences.has(o)) {
           // eslint-disable-next-line no-use-before-define
-          exitVatWithFailure(err);
-          throw err;
+          exitVatWithFailure(disavowalError);
+          throw disavowalError;
         }
         // eslint-disable-next-line no-use-before-define
         return queueMessage(slot, prop, args, returnedP);
@@ -273,11 +273,10 @@ function build(
       if (isPromise(val)) {
         slot = exportPromise(val);
       } else {
-        const err = disavowedPresences.get(val);
-        if (err) {
+        if (disavowedPresences.has(val)) {
           // eslint-disable-next-line no-use-before-define
-          exitVatWithFailure(err);
-          throw err; // cannot reference a disavowed object
+          exitVatWithFailure(disavowalError);
+          throw disavowalError; // cannot reference a disavowed object
         }
         assert.equal(passStyleOf(val), REMOTE_STYLE);
         slot = exportPassByPresence();
@@ -641,8 +640,7 @@ function build(
     assert.equal(allocatedByVat, false, X`attempt to disavow an export`);
     valToSlot.delete(presence);
     slotToVal.delete(slot);
-    const err = harden(Error(`this Presence has been disavowed`));
-    disavowedPresences.set(presence, err);
+    disavowedPresences.add(presence);
 
     syscall.dropImports([slot]);
   }
@@ -659,22 +657,18 @@ function build(
     assert(!didRoot);
     didRoot = true;
 
-    const disavowPowers = {};
+    const vpow = {
+      D,
+      exitVat,
+      exitVatWithFailure,
+      ...vatPowers,
+    };
     if (enableDisavow) {
-      disavowPowers.disavow = disavow;
+      vpow.disavow = disavow;
     }
 
     // here we finally invoke the vat code, and get back the root object
-    const rootObject = buildRootObject(
-      harden({
-        D,
-        exitVat,
-        exitVatWithFailure,
-        ...disavowPowers,
-        ...vatPowers,
-      }),
-      harden(vatParameters),
-    );
+    const rootObject = buildRootObject(harden(vpow), harden(vatParameters));
     assert.equal(passStyleOf(rootObject), REMOTE_STYLE);
 
     const rootSlot = makeVatSlot('object', true, 0n);

packages/SwingSet/src/kernel/vatTranslator.js

@@ -184,10 +184,10 @@ function makeTranslateVatSyscallToKernelSyscall(vatID, kernelKeeper) {
 
   function translateDropImports(vrefs) {
     assert(Array.isArray(vrefs), X`dropImport() given non-Array ${vrefs}`);
-    // We delete clist entries as we translate, which will decref the krefs.
-    // When we're done with that loop, we hand the set of krefs to
-    // kernelSyscall so it can check newly-decremented refcounts against zero,
-    // and maybe delete even more.
+    // We delete clist entries as we translate, which will (TODO) decref the
+    // krefs. When we're done with that loop, we hand the set of krefs to
+    // kernelSyscall so it can (TODO) check newly-decremented refcounts
+    // against zero, and maybe delete even more.
     const krefs = vrefs.map(vref => {
       insistVatType('object', vref);
       const kref = mapVatSlotToKernelSlot(vref);