Add window.structuredClone

Depends on https://github.com/lightpanda-io/zig-v8-fork/pull/156

Uses V8::Serializer and V8::Deserializer which handles built-in types, e.g.
regex. But it doesn't handle Zig types by default. This is something we need
to hook in, using the delegate callbacks. Which we can do after.

Meant to replace https://github.com/lightpanda-io/browser/pull/1785

src/browser/js/Value.zig

@@ -245,6 +245,46 @@ pub fn toJson(self: Value, allocator: Allocator) ![]u8 {
     return js.String.toSliceWithAlloc(.{ .local = local, .handle = str_handle }, allocator);
 }
 
+// Currently does not support host objects (Blob, File, etc.) or transferables
+// which require delegate callbacks to be implemented.
+pub fn structuredClone(self: Value) !Value {
+    const local = self.local;
+    const v8_context = local.handle;
+    const v8_isolate = local.isolate.handle;
+
+    const size, const data = blk: {
+        const serializer = v8.v8__ValueSerializer__New(v8_isolate, null) orelse return error.JsException;
+        defer v8.v8__ValueSerializer__DELETE(serializer);
+
+        var write_result: v8.MaybeBool = undefined;
+        v8.v8__ValueSerializer__WriteHeader(serializer);
+        v8.v8__ValueSerializer__WriteValue(serializer, v8_context, self.handle, &write_result);
+        if (!write_result.has_value or !write_result.value) {
+            return error.JsException;
+        }
+
+        var size: usize = undefined;
+        const data = v8.v8__ValueSerializer__Release(serializer, &size) orelse return error.JsException;
+        break :blk .{ size, data };
+    };
+
+    defer v8.v8__ValueSerializer__FreeBuffer(data);
+
+    const cloned_handle = blk: {
+        const deserializer = v8.v8__ValueDeserializer__New(v8_isolate, data, size, null) orelse return error.JsException;
+        defer v8.v8__ValueDeserializer__DELETE(deserializer);
+
+        var read_header_result: v8.MaybeBool = undefined;
+        v8.v8__ValueDeserializer__ReadHeader(deserializer, v8_context, &read_header_result);
+        if (!read_header_result.has_value or !read_header_result.value) {
+            return error.JsException;
+        }
+        break :blk v8.v8__ValueDeserializer__ReadValue(deserializer, v8_context) orelse return error.JsException;
+    };
+
+    return .{ .local = local, .handle = cloned_handle };
+}
+
 pub fn persist(self: Value) !Global {
     return self._persist(true);
 }

src/browser/tests/window/window.html

@@ -125,6 +125,143 @@
   testing.expectEqual(screen, window.screen);
 </script>
 
+<script id=structuredClone>
+  // Basic types
+  testing.expectEqual(42, structuredClone(42));
+  testing.expectEqual('hello', structuredClone('hello'));
+  testing.expectEqual(true, structuredClone(true));
+  testing.expectEqual(null, structuredClone(null));
+  testing.expectEqual(undefined, structuredClone(undefined));
+
+  // Objects and arrays (these work with JSON too, but verify they're cloned)
+  const obj = { a: 1, b: { c: 2 } };
+  const clonedObj = structuredClone(obj);
+  testing.expectEqual(1, clonedObj.a);
+  testing.expectEqual(2, clonedObj.b.c);
+  clonedObj.b.c = 999;
+  testing.expectEqual(2, obj.b.c); // original unchanged
+
+  const arr = [1, [2, 3]];
+  const clonedArr = structuredClone(arr);
+  testing.expectEqual(1, clonedArr[0]);
+  testing.expectEqual(2, clonedArr[1][0]);
+  clonedArr[1][0] = 999;
+  testing.expectEqual(2, arr[1][0]); // original unchanged
+
+  // Date - JSON would stringify to ISO string
+  const date = new Date('2024-01-15T12:30:00Z');
+  const clonedDate = structuredClone(date);
+  testing.expectEqual(true, clonedDate instanceof Date);
+  testing.expectEqual(date.getTime(), clonedDate.getTime());
+  testing.expectEqual(date.toISOString(), clonedDate.toISOString());
+
+  // RegExp - JSON would stringify to {}
+  const regex = /test\d+/gi;
+  const clonedRegex = structuredClone(regex);
+  testing.expectEqual(true, clonedRegex instanceof RegExp);
+  testing.expectEqual(regex.source, clonedRegex.source);
+  testing.expectEqual(regex.flags, clonedRegex.flags);
+  testing.expectEqual(true, clonedRegex.test('test123'));
+
+  // Map - JSON can't handle
+  const map = new Map([['a', 1], ['b', 2]]);
+  const clonedMap = structuredClone(map);
+  testing.expectEqual(true, clonedMap instanceof Map);
+  testing.expectEqual(2, clonedMap.size);
+  testing.expectEqual(1, clonedMap.get('a'));
+  testing.expectEqual(2, clonedMap.get('b'));
+
+  // Set - JSON can't handle
+  const set = new Set([1, 2, 3]);
+  const clonedSet = structuredClone(set);
+  testing.expectEqual(true, clonedSet instanceof Set);
+  testing.expectEqual(3, clonedSet.size);
+  testing.expectEqual(true, clonedSet.has(1));
+  testing.expectEqual(true, clonedSet.has(2));
+  testing.expectEqual(true, clonedSet.has(3));
+
+  // ArrayBuffer
+  const buffer = new ArrayBuffer(8);
+  const view = new Uint8Array(buffer);
+  view[0] = 42;
+  view[7] = 99;
+  const clonedBuffer = structuredClone(buffer);
+  testing.expectEqual(true, clonedBuffer instanceof ArrayBuffer);
+  testing.expectEqual(8, clonedBuffer.byteLength);
+  const clonedView = new Uint8Array(clonedBuffer);
+  testing.expectEqual(42, clonedView[0]);
+  testing.expectEqual(99, clonedView[7]);
+
+  // TypedArray
+  const typedArr = new Uint32Array([100, 200, 300]);
+  const clonedTypedArr = structuredClone(typedArr);
+  testing.expectEqual(true, clonedTypedArr instanceof Uint32Array);
+  testing.expectEqual(3, clonedTypedArr.length);
+  testing.expectEqual(100, clonedTypedArr[0]);
+  testing.expectEqual(200, clonedTypedArr[1]);
+  testing.expectEqual(300, clonedTypedArr[2]);
+
+  // Special number values - JSON can't preserve these
+  testing.expectEqual(true, Number.isNaN(structuredClone(NaN)));
+  testing.expectEqual(Infinity, structuredClone(Infinity));
+  testing.expectEqual(-Infinity, structuredClone(-Infinity));
+
+  // Object with undefined value - JSON would omit it
+  const objWithUndef = { a: 1, b: undefined, c: 3 };
+  const clonedObjWithUndef = structuredClone(objWithUndef);
+  testing.expectEqual(1, clonedObjWithUndef.a);
+  testing.expectEqual(undefined, clonedObjWithUndef.b);
+  testing.expectEqual(true, 'b' in clonedObjWithUndef);
+  testing.expectEqual(3, clonedObjWithUndef.c);
+
+  // Error objects
+  const error = new Error('test error');
+  const clonedError = structuredClone(error);
+  testing.expectEqual(true, clonedError instanceof Error);
+  testing.expectEqual('test error', clonedError.message);
+
+  // TypeError
+  const typeError = new TypeError('type error');
+  const clonedTypeError = structuredClone(typeError);
+  testing.expectEqual(true, clonedTypeError instanceof TypeError);
+  testing.expectEqual('type error', clonedTypeError.message);
+
+  // BigInt
+  const bigInt = BigInt('9007199254740993');
+  const clonedBigInt = structuredClone(bigInt);
+  testing.expectEqual(bigInt, clonedBigInt);
+
+  // Circular references ARE supported by structuredClone (unlike JSON)
+  const circular = { a: 1 };
+  circular.self = circular;
+  const clonedCircular = structuredClone(circular);
+  testing.expectEqual(1, clonedCircular.a);
+  testing.expectEqual(clonedCircular, clonedCircular.self); // circular ref preserved
+
+  // Functions cannot be cloned - should throw
+  {
+    let threw = false;
+    try {
+      structuredClone(() => {});
+    } catch (err) {
+      threw = true;
+      // Just verify an error was thrown - V8's message format may vary
+    }
+    testing.expectEqual(true, threw);
+  }
+
+  // Symbols cannot be cloned - should throw
+  {
+    let threw = false;
+    try {
+      structuredClone(Symbol('test'));
+    } catch (err) {
+      threw = true;
+    }
+    testing.expectEqual(true, threw);
+  }
+</script>
+
 <script id=unhandled_rejection>
   {
     let unhandledCalled = 0;

src/browser/webapi/Window.zig

@@ -412,6 +412,10 @@ pub fn atob(_: *const Window, input: []const u8, page: *Page) ![]const u8 {
     return decoded;
 }
 
+pub fn structuredClone(_: *const Window, value: js.Value) !js.Value {
+    return value.structuredClone();
+}
+
 pub fn getFrame(self: *Window, idx: usize) !?*Window {
     const page = self._page;
     const frames = page.frames.items;
@@ -797,6 +801,7 @@ pub const JsApi = struct {
     pub const btoa = bridge.function(Window.btoa, .{});
     pub const atob = bridge.function(Window.atob, .{ .dom_exception = true });
     pub const reportError = bridge.function(Window.reportError, .{});
+    pub const structuredClone = bridge.function(Window.structuredClone, .{});
     pub const getComputedStyle = bridge.function(Window.getComputedStyle, .{});
     pub const getSelection = bridge.function(Window.getSelection, .{});