Fix empty TypedArray creation

Runtime/src/index.ts

@@ -536,6 +536,15 @@ export class SwiftRuntime {
             ) => {
                 const ArrayType: TypedArray =
                     this.memory.getObject(constructor_ref);
+                if (length == 0) {
+                    // The elementsPtr can be unaligned in Swift's Array
+                    // implementation when the array is empty. However,
+                    // TypedArray requires the pointer to be aligned.
+                    // So, we need to create a new empty array without
+                    // using the elementsPtr.
+                    // See https://github.com/swiftwasm/swift/issues/5599
+                    return this.memory.retain(new ArrayType());
+                }
                 const array = new ArrayType(
                     this.memory.rawMemory.buffer,
                     elementsPtr,

Tests/JavaScriptKitTests/JSTypedArrayTests.swift

@@ -0,0 +1,18 @@
+import XCTest
+import JavaScriptKit
+
+final class JSTypedArrayTests: XCTestCase {
+    func testEmptyArray() {
+        _ = JSTypedArray<Int>([])
+        _ = JSTypedArray<UInt>([])
+        _ = JSTypedArray<Int8>([Int8]())
+        _ = JSTypedArray<UInt8>([UInt8]())
+        _ = JSUInt8ClampedArray([UInt8]())
+        _ = JSTypedArray<Int16>([Int16]())
+        _ = JSTypedArray<UInt16>([UInt16]())
+        _ = JSTypedArray<Int32>([Int32]())
+        _ = JSTypedArray<UInt32>([UInt32]())
+        _ = JSTypedArray<Float32>([Float32]())
+        _ = JSTypedArray<Float64>([Float64]())
+    }
+}