From d8fa9b8c4f03332d302d05631d514590c737cea7 Mon Sep 17 00:00:00 2001
From: Karl Seguin <k@openmymind.io>
Date: Sun, 20 Apr 2025 12:47:28 +0800
Subject: [PATCH] Return TypeError if trying to turn an unknown v8.Object into
 a toa

---
 src/runtime/js.zig | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/runtime/js.zig b/src/runtime/js.zig
index 4a267e75..ab540696 100644
--- a/src/runtime/js.zig
+++ b/src/runtime/js.zig
@@ -1340,6 +1340,13 @@ pub fn Env(comptime S: type, comptime types: anytype) type {
                 return @constCast(@as(*const T, &.{}));
             }
 
+            // if it isn't an empty struct, then the v8.Object should have an
+            // InternalFieldCount > 0, since our toa pointer should be embedded
+            // at index 0 of the internal field count.
+            if (js_obj.internalFieldCount() == 0) {
+                return error.InvalidArgument;
+            }
+
             const type_name = @typeName(T);
             if (@hasField(TypeLookup, type_name) == false) {
                 @compileError(std.fmt.comptimePrint(