make typeinfo_cast<ModifyClass> error

Author: matcool

loader/include/Geode/platform/ItaniumCast.hpp

@@ -1,5 +1,7 @@
 #pragma once
 
+#include "_casts_shared.hpp"
+
 namespace geode::cast {
 
     struct DummyClass {
@@ -102,10 +104,8 @@ namespace geode::cast {
 
     template <class After, class Before>
     inline After typeinfo_cast(Before ptr) {
-        static_assert(
-            std::is_polymorphic_v<std::remove_pointer_t<Before>> && std::is_polymorphic_v<std::remove_pointer_t<After>>,
-            "Input is not a polymorphic type"
-        );
+        ::geode::geode_internal::typeinfoCastChecks<After, Before>();
+
         if (!ptr) {
             return static_cast<After>(nullptr);
         }

loader/include/Geode/platform/_casts_shared.hpp

@@ -0,0 +1,27 @@
+#pragma once
+
+#include <type_traits>
+
+namespace geode {
+    template <class Derived, class Base>
+    class Modify;
+}
+
+namespace geode::geode_internal {
+    template <class D, class B>
+    inline void dummyModifyFn(::geode::Modify<D, B> const&);
+
+    template <class T>
+    concept IsModifyClass = requires(std::remove_pointer_t<T> const& a) { ::geode::geode_internal::dummyModifyFn(a); };
+
+    template <class After, class Before>
+    inline constexpr void typeinfoCastChecks() {
+        static_assert(
+            std::is_polymorphic_v<std::remove_pointer_t<Before>> && std::is_polymorphic_v<std::remove_pointer_t<After>>,
+            "Input is not a polymorphic type"
+        );
+
+        static_assert(!geode_internal::IsModifyClass<After>,
+            "typeinfo_cast will not work with a Modify class. use static_cast<MyModifyClass*>(typeinfo_cast<Class*>(...)) instead");
+    }
+}

loader/include/Geode/platform/windows.hpp

@@ -10,6 +10,7 @@
 #include <typeinfo>
 #include <memory>
 #include <intrin.h>  // for _ReadWriteBarrier
+#include "_casts_shared.hpp"
 
 namespace geode {
     struct PlatformInfo {
@@ -121,9 +122,7 @@ namespace geode::cast {
 
     template <class After, class Before>
     inline After typeinfo_cast(Before ptr) {
-        static_assert(
-            std::is_polymorphic_v<std::remove_pointer_t<Before>>, "Input is not a polymorphic type"
-        );
+        ::geode::geode_internal::typeinfoCastChecks<After, Before>();
 
         if (!ptr) {
             return After();