[Refactor] empty out DisposableStack slot on dispose

See tc39/proposal-explicit-resource-management#194

aos/AddDisposableResource.js

@@ -23,22 +23,26 @@ module.exports = function AddDisposableResource(disposeCapability, V, hint) {
 		throw new $TypeError('Assertion failed: `method`, when present, must be a function');
 	}
 
+	if (!disposeCapability['[[DisposableResourceStack]]']) {
+		throw new $TypeError('Assertion failed: `disposeCapability.[[DisposableResourceStack]]` must not be ~empty~');
+	}
+
 	var resource;
-	if (arguments.length < 4) {
+	if (arguments.length < 4) { // step 2
 		if (V == null) {
-			return 'unused'; // step 1.a
+			return 'unused'; // step 2.a
 		}
 		if (Type(V) !== 'Object') {
-			throw new $TypeError('`V` must be an Object'); // step 1.b
+			throw new $TypeError('`V` must be an Object'); // step 2.b
 		}
-		resource = CreateDisposableResource(V, hint); // step 1.c
-	} else { // step 2
+		resource = CreateDisposableResource(V, hint); // step 2.c
+	} else { // step 3
 		if (typeof V !== 'undefined') {
-			throw new $TypeError('Assertion failed: `V` must be undefined when `method` is present'); // step 2.a
+			throw new $TypeError('Assertion failed: `V` must be undefined when `method` is present'); // step 3.a
 		}
-		resource = CreateDisposableResource(void undefined, hint, method); // step 2.b
+		resource = CreateDisposableResource(void undefined, hint, method); // step 3.b
 	}
-	$push(disposeCapability['[[DisposableResourceStack]]'], resource); // step 3
+	$push(disposeCapability['[[DisposableResourceStack]]'], resource); // step 4
 
-	return 'unused'; // step 4
+	return 'unused'; // step 5
 };

aos/DisposeResources.js

@@ -25,6 +25,10 @@ module.exports = function DisposeResources(disposeCapability, completion) {
 
 	var stack = disposeCapability['[[DisposableResourceStack]]'];
 
+	if (!stack) {
+		throw new $TypeError('Assertion failed: `disposeCapability.[[DisposableResourceStack]]` must not be ~empty~'); // step 1
+	}
+
 	// for DisposableStack or AsyncDisposableStack, all are sync, or all are async.
 	// Only an environment record, via `using` and `await using`, can mix sync and async.
 	var actualHint;
@@ -40,22 +44,22 @@ module.exports = function DisposeResources(disposeCapability, completion) {
 	var promise = actualHint === 'async-dispose' && PromiseResolve($Promise, completion);
 
 	var rejecter = function (e) {
-		if (completion.type() === 'throw') { // step 1.b.i
-			var suppressed = completion.value(); // step 1.b.i.2
-			var error = new SuppressedError(e, suppressed); // steps 1.b.i.1, 1.b.i.3 - 1.b.i.5
+		if (completion.type() === 'throw') { // step 2.b.i
+			var suppressed = completion.value(); // step 2.b.i.2
+			var error = new SuppressedError(e, suppressed); // steps 2.b.i.1, 2.b.i.3 - 2.b.i.5
 			// eslint-disable-next-line no-param-reassign
-			completion = ThrowCompletion(error); // step 1.b.i.6
-		} else { // step 1.b.ii
+			completion = ThrowCompletion(error); // step 2.b.i.6
+		} else { // step 2.b.ii
 			// eslint-disable-next-line no-param-reassign
-			completion = ThrowCompletion(e); // step 1.b.ii.1
+			completion = ThrowCompletion(e); // step 2.b.ii.1
 		}
 	};
 
 	var getPromise = actualHint === 'async-dispose' && function getPromise(resource) {
 		return $then(
 			promise,
 			function () {
-				var result = Dispose( // step 1.a
+				var result = Dispose( // step 2.a
 					resource['[[ResourceValue]]'],
 					resource['[[Hint]]'],
 					resource['[[DisposeMethod]]']
@@ -69,13 +73,13 @@ module.exports = function DisposeResources(disposeCapability, completion) {
 		);
 	};
 
-	for (var i = stack.length - 1; i >= 0; i -= 1) { // step 1
+	for (var i = stack.length - 1; i >= 0; i -= 1) { // step 2
 		if (actualHint === 'async-dispose') {
 			promise = getPromise(stack[i]);
 		} else {
 			var resource = stack[i];
 			try {
-				var result = Dispose( // step 1.a
+				var result = Dispose( // step 2.a
 					resource['[[ResourceValue]]'],
 					resource['[[Hint]]'],
 					resource['[[DisposeMethod]]']
@@ -89,5 +93,8 @@ module.exports = function DisposeResources(disposeCapability, completion) {
 		}
 	}
 
-	return actualHint === 'async-dispose' ? promise : completion; // step 2
+	// eslint-disable-next-line no-param-reassign
+	disposeCapability['[[DisposableResourceStack]]'] = null; // step 3
+
+	return actualHint === 'async-dispose' ? promise : completion; // step 4
 };