From 648256880447bc1cf30be6eba77af96dee949a72 Mon Sep 17 00:00:00 2001
From: naugtur <naugtur@gmail.com>
Date: Tue, 27 Aug 2024 09:48:25 +0200
Subject: [PATCH] feat(trampoline): apply minimal defensive coding to generator
 iterations in trampoline

---
 packages/trampoline/src/trampoline.js | 29 ++++++++++++++++++---------
 1 file changed, 19 insertions(+), 10 deletions(-)

diff --git a/packages/trampoline/src/trampoline.js b/packages/trampoline/src/trampoline.js
index 228e95312d..68afa2266d 100644
--- a/packages/trampoline/src/trampoline.js
+++ b/packages/trampoline/src/trampoline.js
@@ -2,6 +2,15 @@
 /**
  * @import {AnyGenerator, SyncTrampolineGeneratorFn, AsyncTrampolineGeneratorFn } from './types.js'
  */
+const { getPrototypeOf } = Object;
+const { bind } = Function.prototype;
+const uncurryThis = bind.bind(bind.call); // eslint-disable-line @endo/no-polymorphic-call
+export const { prototype: generatorPrototype } = getPrototypeOf(
+  // eslint-disable-next-line no-empty-function, func-names
+  function* () {},
+);
+const generatorNext = uncurryThis(generatorPrototype.next);
+const generatorThrow = uncurryThis(generatorPrototype.throw);
 
 /**
  * Trampoline on {@link TrampolineGeneratorFn generatorFn} synchronously.
@@ -9,18 +18,18 @@
  * @template {readonly any[]} [TArgs=unknown[]] Parameters for `generatorFn`
  * @template [TResult=unknown] Type of the return value of the `generatorFn`
  * @template {Generator<any, any, TResult>} [TGenerator=Generator] Type of the generator function
- * @param {SyncTrampolineGeneratorFn<TGenerator, TArgs, TResult>} generatorFn Generator-returning function accepting a thunk and optionally an initial value
- * @param {TArgs} args Initial args
+ * @param {SyncTrampolineGeneratorFn<TGenerator, TArgs, TResult>} generatorFn Generator-returning function accepting any arguments
+ * @param {TArgs} args Arguments to pass to the generatorFn call
  * @returns {TResult}
  */
 export function syncTrampoline(generatorFn, ...args) {
   const iterator = generatorFn(...args);
-  let result = iterator.next();
+  let result = generatorNext(iterator);
   while (!result.done) {
     try {
-      result = iterator.next(result.value);
+      result = generatorNext(iterator, result.value);
     } catch (err) {
-      result = iterator.throw(err);
+      result = generatorThrow(iterator, err);
     }
   }
   return result.value;
@@ -32,20 +41,20 @@ export function syncTrampoline(generatorFn, ...args) {
  * @template {readonly any[]} [TArgs=unknown[]] Parameters for `generatorFn`
  * @template [TResult=unknown] Type of the return value of the `generatorFn`
  * @template {Generator<any, any, TResult>} [TGenerator=Generator] Type of the generator function
- * @param {AsyncTrampolineGeneratorFn<TGenerator, TArgs, TResult>} generatorFn Generator-returning function accepting a thunk and optionally an initial value
- * @param {TArgs} args Initial args
+ * @param {AsyncTrampolineGeneratorFn<TGenerator, TArgs, TResult>} generatorFn Generator-returning function accepting any arguments
+ * @param {TArgs} args Arguments to pass to the generatorFn call
  * @returns {Promise<TResult>}
  */
 export async function trampoline(generatorFn, ...args) {
   const iterator = generatorFn(...args);
-  let result = iterator.next();
+  let result = generatorNext(iterator);
   while (!result.done) {
     try {
       // eslint-disable-next-line no-await-in-loop
       const val = await result.value;
-      result = iterator.next(val);
+      result = generatorNext(iterator, val);
     } catch (err) {
-      result = iterator.throw(err);
+      result = generatorThrow(iterator, err);
     }
   }
   return result.value;