From 806264ac3894ba78acb09fbf08bef17e00311c4d Mon Sep 17 00:00:00 2001
From: "Mark S. Miller" <erights@gmail.com>
Date: Mon, 3 Jul 2023 23:40:31 -0700
Subject: [PATCH] feat(exo): revocables

---
 packages/exo/src/exo-makers.js              | 37 ++++++++-
 packages/exo/test/test-revoke-heap-class.js | 89 +++++++++++++++++++++
 2 files changed, 122 insertions(+), 4 deletions(-)
 create mode 100644 packages/exo/test/test-revoke-heap-class.js

diff --git a/packages/exo/src/exo-makers.js b/packages/exo/src/exo-makers.js
index 94f42706ab..8b18d64b6a 100644
--- a/packages/exo/src/exo-makers.js
+++ b/packages/exo/src/exo-makers.js
@@ -62,11 +62,28 @@ export const initEmpty = () => emptyRecord;
  * Each property is distinct, is checked and changed separately.
  */
 
+/**
+ * @callback Revoker
+ * @param {object} exo
+ * @returns {boolean}
+ */
+
+/**
+ * @typedef {Record<FacetName, Revoker>} RevokerKit
+ */
+
+/**
+ * @callback GetRevoker
+ * @param {Revoker | RevokerKit} revoke
+ * @returns {void}
+ */
+
 /**
  * @template C
  * @typedef {object} FarClassOptions
  * @property {(context: C) => void} [finish]
  * @property {StateShape} [stateShape]
+ * @property {GetRevoker} [getRevoker]
  */
 
 /**
@@ -81,7 +98,7 @@ export const initEmpty = () => emptyRecord;
  */
 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(
@@ -91,6 +108,11 @@ export const defineExoClass = (tag, interfaceGuard, init, methods, options) => {
     true,
     interfaceGuard,
   );
+  if (getRevoker) {
+    const revoke = self => contextMap.delete(self);
+    harden(revoke);
+    getRevoker(revoke);
+  }
   let instanceCount = 0;
   /**
    * @param  {Parameters<I>} args
@@ -135,11 +157,11 @@ export const defineExoClassKit = (
   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,
@@ -148,6 +170,13 @@ export const defineExoClassKit = (
     true,
     interfaceGuardKit,
   );
+  if (getRevoker) {
+    const revokerKit = objectMap(
+      contextMapKit,
+      contextMap => facet => contextMap.delete(facet),
+    );
+    getRevoker(revokerKit);
+  }
   let instanceCount = 0;
   /**
    * @param {Parameters<I>} args
diff --git a/packages/exo/test/test-revoke-heap-class.js b/packages/exo/test/test-revoke-heap-class.js
new file mode 100644
index 0000000000..7d1b8b9087
--- /dev/null
+++ b/packages/exo/test/test-revoke-heap-class.js
@@ -0,0 +1,89 @@
+// 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 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 revokerKit;
+  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) {
+        revokerKit = r;
+      },
+    },
+  );
+  const { up: upCounter, down: downCounter } = makeCounterKit(3);
+  t.is(upCounter.incr(5), 8);
+  t.is(downCounter.decr(), 7);
+  t.is(revokerKit.up(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(downCounter.decr(), 6);
+});