feat(exo): revocables

Author: erights

packages/exo/src/exo-makers.js

@@ -5,7 +5,8 @@ import { objectMap } from '@endo/patterns';
 
 import { defendPrototype, defendPrototypeKit } from './exo-tools.js';
 
-const { create, seal, freeze, defineProperty } = Object;
+const { Fail, quote: q } = assert;
+const { create, seal, freeze, defineProperty, entries, values } = Object;
 
 const { getEnvironmentOption } = makeEnvironmentCaptor(globalThis);
 const DEBUG = getEnvironmentOption('DEBUG', '');
@@ -62,11 +63,24 @@ export const initEmpty = () => emptyRecord;
  * Each property is distinct, is checked and changed separately.
  */
 
+/**
+ * @callback Revoker
+ * @param {object} exo
+ * @returns {boolean}
+ */
+
+/**
+ * @callback GetRevoker
+ * @param {Revoker} revoke
+ * @returns {void}
+ */
+
 /**
  * @template C
  * @typedef {object} FarClassOptions
  * @property {(context: C) => void} [finish]
  * @property {StateShape} [stateShape]
+ * @property {GetRevoker} [getRevoker]
  */
 
 /**
@@ -79,9 +93,15 @@ export const initEmpty = () => emptyRecord;
  * @param {FarClassOptions<ClassContext<ReturnType<I>, M>>} [options]
  * @returns {(...args: Parameters<I>) => (M & import('@endo/eventual-send').RemotableBrand<{}, M>)}
  */
-export const defineExoClass = (tag, interfaceGuard, init, methods, options) => {
+export const defineExoClass = (
+  tag,
+  interfaceGuard,
+  init,
+  methods,
+  options = {},
+) => {
   harden(methods);
-  const { finish = undefined } = options || {};
+  const { finish = undefined, getRevoker = undefined } = options;
   /** @type {WeakMap<M,ClassContext<ReturnType<I>, M>>} */
   const contextMap = new WeakMap();
   const proto = defendPrototype(
@@ -113,6 +133,13 @@ export const defineExoClass = (tag, interfaceGuard, init, methods, options) => {
       self
     );
   };
+
+  if (getRevoker) {
+    const revoke = self => contextMap.delete(self);
+    harden(revoke);
+    getRevoker(revoke);
+  }
+
   return harden(makeInstance);
 };
 harden(defineExoClass);
@@ -132,14 +159,14 @@ export const defineExoClassKit = (
   interfaceGuardKit,
   init,
   methodsKit,
-  options,
+  options = {},
 ) => {
   harden(methodsKit);
-  const { finish = undefined } = options || {};
+  const { finish = undefined, getRevoker = undefined } = options;
   const contextMapKit = objectMap(methodsKit, () => new WeakMap());
   const getContextKit = objectMap(
-    methodsKit,
-    (_v, name) => facet => contextMapKit[name].get(facet),
+    contextMapKit,
+    contextMap => facet => contextMap.get(facet),
   );
   const prototypeKit = defendPrototypeKit(
     tag,
@@ -172,6 +199,34 @@ export const defineExoClassKit = (
     }
     return context.facets;
   };
+
+  if (getRevoker) {
+    const revoke = aFacet => {
+      let seenTrue = false;
+      let facets;
+      for (const contextMap of values(contextMapKit)) {
+        if (contextMap.has(aFacet)) {
+          seenTrue = true;
+          facets = contextMap.get(aFacet).facets;
+          break;
+        }
+      }
+      if (!seenTrue) {
+        return false;
+      }
+      // eslint-disable-next-line no-use-before-define
+      for (const [facetName, facet] of entries(facets)) {
+        const seen = contextMapKit[facetName].delete(facet);
+        if (seen === false) {
+          Fail`internal: inconsistent facet revocation ${q(facetName)}`;
+        }
+      }
+      return seenTrue;
+    };
+    harden(revoke);
+    getRevoker(revoke);
+  }
+
   return harden(makeInstanceKit);
 };
 harden(defineExoClassKit);

packages/exo/test/test-revoke-heap-classes.js

@@ -0,0 +1,125 @@
+// eslint-disable-next-line import/order
+import { test } from './prepare-test-env-ava.js';
+
+// eslint-disable-next-line import/order
+import { M } from '@endo/patterns';
+import { defineExoClass, defineExoClassKit } from '../src/exo-makers.js';
+
+const { apply } = Reflect;
+
+const UpCounterI = M.interface('UpCounter', {
+  incr: M.call()
+    // TODO M.number() should not be needed to get a better error message
+    .optional(M.and(M.number(), M.gte(0)))
+    .returns(M.number()),
+});
+
+const DownCounterI = M.interface('DownCounter', {
+  decr: M.call()
+    // TODO M.number() should not be needed to get a better error message
+    .optional(M.and(M.number(), M.gte(0)))
+    .returns(M.number()),
+});
+
+test('test revoke defineExoClass', t => {
+  let revoke;
+  const makeUpCounter = defineExoClass(
+    'UpCounter',
+    UpCounterI,
+    /** @param {number} x */
+    (x = 0) => ({ x }),
+    {
+      incr(y = 1) {
+        const { state } = this;
+        state.x += y;
+        return state.x;
+      },
+    },
+    {
+      getRevoker(r) {
+        revoke = r;
+      },
+    },
+  );
+  const upCounter = makeUpCounter(3);
+  t.is(upCounter.incr(5), 8);
+  t.is(revoke(upCounter), true);
+  t.throws(() => upCounter.incr(1), {
+    message:
+      '"In \\"incr\\" method of (UpCounter)" may only be applied to a valid instance: "[Alleged: UpCounter]"',
+  });
+});
+
+test('test revoke defineExoClassKit', t => {
+  let revoke;
+  const makeCounterKit = defineExoClassKit(
+    'Counter',
+    { up: UpCounterI, down: DownCounterI },
+    /** @param {number} x */
+    (x = 0) => ({ x }),
+    {
+      up: {
+        incr(y = 1) {
+          const { state } = this;
+          state.x += y;
+          return state.x;
+        },
+      },
+      down: {
+        decr(y = 1) {
+          const { state } = this;
+          state.x -= y;
+          return state.x;
+        },
+      },
+    },
+    {
+      getRevoker(r) {
+        revoke = r;
+      },
+    },
+  );
+  const { up: upCounter, down: downCounter } = makeCounterKit(3);
+  t.is(upCounter.incr(5), 8);
+  t.is(downCounter.decr(), 7);
+  t.is(revoke(upCounter), true);
+  t.throws(() => upCounter.incr(3), {
+    message:
+      '"In \\"incr\\" method of (Counter up)" may only be applied to a valid instance: "[Alleged: Counter up]"',
+  });
+  t.is(revoke(downCounter), false);
+  t.throws(() => downCounter.decr(), {
+    message:
+      '"In \\"decr\\" method of (Counter down)" may only be applied to a valid instance: "[Alleged: Counter down]"',
+  });
+});
+
+test('test facet cross-talk', t => {
+  const makeCounterKit = defineExoClassKit(
+    'Counter',
+    { up: UpCounterI, down: DownCounterI },
+    /** @param {number} x */
+    (x = 0) => ({ x }),
+    {
+      up: {
+        incr(y = 1) {
+          const { state } = this;
+          state.x += y;
+          return state.x;
+        },
+      },
+      down: {
+        decr(y = 1) {
+          const { state } = this;
+          state.x -= y;
+          return state.x;
+        },
+      },
+    },
+  );
+  const { up: upCounter, down: downCounter } = makeCounterKit(3);
+  t.throws(() => apply(upCounter.incr, downCounter, [2]), {
+    message:
+      '"In \\"incr\\" method of (Counter up)" may only be applied to a valid instance: "[Alleged: Counter down]"',
+  });
+});