feat(no-trapping-shim): Ponyfill and shim for noTrapping integrity level

Author: erights

packages/no-trapping-shim/package.json

@@ -35,7 +35,6 @@
     "test:c8": "c8 $C8_OPTIONS ava --config=ava-nesm.config.js",
     "test:xs": "exit 0"
   },
-  "dependencies": {},
   "devDependencies": {
     "@endo/lockdown": "workspace:^",
     "@endo/ses-ava": "workspace:^",

packages/no-trapping-shim/src/no-trapping-pony.js

@@ -0,0 +1,128 @@
+const OriginalProxy = Proxy;
+const { freeze } = Object;
+const { apply } = Reflect;
+
+const noTrappingSet = new WeakSet();
+
+const proxyHandlerMap = new WeakMap();
+
+/**
+ * In the shim, this should also be on `Reflect`.
+ * TODO always return boolean vs sometimes throw
+ *
+ * @param {any} specimen
+ * @returns {boolean}
+ */
+export const isNoTrapping = specimen => {
+  if (noTrappingSet.has(specimen)) {
+    return true;
+  }
+  if (!proxyHandlerMap.has(specimen)) {
+    return false;
+  }
+  const [target, handler] = proxyHandlerMap.get(specimen);
+  if (isNoTrapping(target)) {
+    noTrappingSet.add(specimen);
+    return true;
+  }
+  const trap = handler.isNoTrapping;
+  if (trap === undefined) {
+    return false;
+  }
+  const result = apply(trap, handler, [target]);
+  const ofTarget = isNoTrapping(target);
+  if (result !== ofTarget) {
+    throw TypeError(
+      `'isNoTrapping' proxy trap does not reflect 'isNoTrapping' of proxy target (which is '${ofTarget}')`,
+    );
+  }
+  if (result) {
+    noTrappingSet.add(specimen);
+  }
+  return result;
+};
+
+/**
+ * In the shim, this should also be on `Reflect`.
+ * TODO always return boolean vs sometimes throw
+ *
+ * @param {any} specimen
+ * @returns {boolean}
+ */
+export const suppressTrapping = specimen => {
+  if (noTrappingSet.has(specimen)) {
+    return true;
+  }
+  freeze(specimen);
+  if (!proxyHandlerMap.has(specimen)) {
+    noTrappingSet.add(specimen);
+    return true;
+  }
+  const [target, handler] = proxyHandlerMap.get(specimen);
+  if (isNoTrapping(target)) {
+    noTrappingSet.add(specimen);
+    return true;
+  }
+  const trap = handler.suppressTrapping;
+  if (trap === undefined) {
+    const result = suppressTrapping(target);
+    if (result) {
+      noTrappingSet.add(specimen);
+    }
+    return result;
+  }
+  const result = apply(trap, handler, [target]);
+  const ofTarget = isNoTrapping(target);
+  if (result !== ofTarget) {
+    throw TypeError(
+      `'suppressTrapping' proxy trap does not reflect 'isNoTrapping' of proxy target (which is '${ofTarget}')`,
+    );
+  }
+  if (result) {
+    noTrappingSet.add(specimen);
+  }
+  return result;
+};
+
+const makeMetaHandler = handler =>
+  freeze({
+    get(_, trapName, _receiver) {
+      return freeze((target, ...rest) => {
+        if (isNoTrapping(target) || handler[trapName] === undefined) {
+          return Reflect[trapName](target, ...rest);
+        } else {
+          return handler[trapName](target, ...rest);
+        }
+      });
+    },
+  });
+
+const makeSafeHandler = handler =>
+  new OriginalProxy({}, makeMetaHandler(handler));
+
+/**
+ * In the shim, `SafeProxy` should replace the global `Proxy`.
+ *
+ * @param {any} target
+ * @param {object} handler
+ */
+const SafeProxy = function Proxy(target, handler) {
+  if (new.target !== SafeProxy) {
+    if (new.target === undefined) {
+      throw TypeError('Proxy constructor requires "new"');
+    }
+    throw TypeError('Safe Proxy shim does not support subclassing');
+  }
+  const safeHandler = makeSafeHandler(handler);
+  const proxy = new OriginalProxy(target, safeHandler);
+  proxyHandlerMap.set(proxy, [target, handler]);
+  return proxy;
+};
+SafeProxy.revocable = (target, handler) => {
+  const safeHandler = makeSafeHandler(handler);
+  const { proxy, revoke } = OriginalProxy.revocable(target, safeHandler);
+  proxyHandlerMap.set(proxy, [target, handler]);
+  return { proxy, revoke };
+};
+
+export { SafeProxy };

packages/no-trapping-shim/src/no-trapping-shim.js

@@ -0,0 +1,11 @@
+/* global globalThis */
+import {
+  isNoTrapping,
+  suppressTrapping,
+  SafeProxy,
+} from './no-trapping-pony.js';
+
+Reflect.isNoTrapping = isNoTrapping;
+Reflect.suppressTrapping = suppressTrapping;
+// @ts-expect-error Something about the type of Proxy?
+globalThis.Proxy = SafeProxy;

packages/no-trapping-shim/test/index.test.js

@@ -0,0 +1,30 @@
+import test from '@endo/ses-ava/prepare-endo.js';
+import {
+  isNoTrapping,
+  SafeProxy,
+  suppressTrapping,
+} from '../src/no-trapping-pony.js';
+
+const { freeze, isFrozen } = Object;
+
+test('no-trapping-pony', async t => {
+  const specimen = { foo: 8 };
+
+  const sillyHandler = freeze({
+    get(target, prop, receiver) {
+      return [target, prop, receiver];
+    },
+  });
+
+  const safeProxy = new SafeProxy(specimen, sillyHandler);
+
+  t.false(isNoTrapping(specimen));
+  t.false(isFrozen(specimen));
+  t.deepEqual(safeProxy.foo, [specimen, 'foo', safeProxy]);
+
+  suppressTrapping(specimen);
+
+  t.true(isNoTrapping(specimen));
+  t.true(isFrozen(specimen));
+  t.deepEqual(safeProxy.foo, 8);
+});

packages/no-trapping-shim/test/no-trapping-pony.test.js

@@ -702,6 +702,19 @@ __metadata:
   languageName: unknown
   linkType: soft
 
+"@endo/no-trapping-shim@workspace:packages/no-trapping-shim":
+  version: 0.0.0-use.local
+  resolution: "@endo/no-trapping-shim@workspace:packages/no-trapping-shim"
+  dependencies:
+    "@endo/lockdown": "workspace:^"
+    "@endo/ses-ava": "workspace:^"
+    ava: "npm:^6.1.3"
+    c8: "npm:^7.14.0"
+    tsd: "npm:^0.31.2"
+    typescript: "npm:~5.6.3"
+  languageName: unknown
+  linkType: soft
+
 "@endo/pass-style@workspace:^, @endo/pass-style@workspace:packages/pass-style":
   version: 0.0.0-use.local
   resolution: "@endo/pass-style@workspace:packages/pass-style"