From 94389ad75ed5a0ede88b0a7cd862ab29f870feb3 Mon Sep 17 00:00:00 2001
From: "Mark S. Miller" <erights@gmail.com>
Date: Wed, 1 Nov 2023 18:15:54 -0700
Subject: [PATCH] fix: review suggestions

---
 packages/exo/src/exo-tools.js                | 10 ++++++++--
 packages/exo/src/get-interface.js            |  7 ++++---
 packages/exo/test/test-exo-class-js-class.js |  2 --
 packages/exo/test/test-heap-classes.js       |  4 +---
 4 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/packages/exo/src/exo-tools.js b/packages/exo/src/exo-tools.js
index 7358ca083a..427f4f672b 100644
--- a/packages/exo/src/exo-tools.js
+++ b/packages/exo/src/exo-tools.js
@@ -426,9 +426,10 @@ export const defendPrototype = (
     );
   }
 
-  if (interfaceGuard) {
+  if (!hasOwnPropertyOf(prototype, GET_INTERFACE_GUARD)) {
     const getInterfaceGuardMethod = {
       [GET_INTERFACE_GUARD]() {
+        // Note: May be `undefined`
         return interfaceGuard;
       },
     }[GET_INTERFACE_GUARD];
@@ -441,7 +442,12 @@ export const defendPrototype = (
     );
   }
 
-  return Far(tag, /** @type {T} */ (prototype));
+  return Far(
+    tag,
+    /** @type {T & import('./get-interface.js').GetInterfaceGuard<T>} */ (
+      prototype
+    ),
+  );
 };
 harden(defendPrototype);
 
diff --git a/packages/exo/src/get-interface.js b/packages/exo/src/get-interface.js
index 9fd4baf9d0..1d1d894d36 100644
--- a/packages/exo/src/get-interface.js
+++ b/packages/exo/src/get-interface.js
@@ -15,8 +15,9 @@ export const GET_INTERFACE_GUARD = Symbol.for('getInterfaceGuard');
 /**
  * @template {Record<PropertyKey, CallableFunction>} M
  * @typedef {{
- *   [GET_INTERFACE_GUARD]: () => import('@endo/patterns').InterfaceGuard<{
- *     [K in keyof M]: import('@endo/patterns').MethodGuard
- *   }>
+ *   [GET_INTERFACE_GUARD]: () =>
+ *     import('@endo/patterns').InterfaceGuard<{
+ *       [K in keyof M]: import('@endo/patterns').MethodGuard
+ *     }> | undefined
  * }} GetInterfaceGuard
  */
diff --git a/packages/exo/test/test-exo-class-js-class.js b/packages/exo/test/test-exo-class-js-class.js
index 697ece1922..8cc19eae56 100644
--- a/packages/exo/test/test-exo-class-js-class.js
+++ b/packages/exo/test/test-exo-class-js-class.js
@@ -4,8 +4,6 @@
 import { test } from './prepare-test-env-ava.js';
 
 import { passStyleOf } from '@endo/pass-style';
-// import { M, getInterfaceGuardPayload } from '@endo/patterns';
-// import { defineExoClass, makeExo } from '../src/exo-makers.js';
 import { M, getInterfaceGuardPayload } from '@endo/patterns';
 import { makeExo, defineExoClass } from '../src/exo-makers.js';
 
diff --git a/packages/exo/test/test-heap-classes.js b/packages/exo/test/test-heap-classes.js
index a5ef1346a5..91ff0a1ee3 100644
--- a/packages/exo/test/test-heap-classes.js
+++ b/packages/exo/test/test-heap-classes.js
@@ -172,9 +172,7 @@ test('missing interface', t => {
     message:
       'In "makeSayHello" method of (greeterMaker): result: "[Symbol(passStyle)]" property expected: "[Function <anon>]"',
   });
-  t.throws(() => greeterMaker[GET_INTERFACE_GUARD](), {
-    message: 'greeterMaker[GET_INTERFACE_GUARD] is not a function',
-  });
+  t.is(greeterMaker[GET_INTERFACE_GUARD](), undefined);
 });
 
 const SloppyGreeterI = M.interface('greeter', {}, { sloppy: true });