Avoid pre-allocating custom attributes for managed types

Source/Engine/Engine/NativeInterop.cs

@@ -1365,6 +1365,18 @@ namespace FlaxEngine
             *classAttributesCount = attributeTypes.Length;
         }
 
+        [UnmanagedCallersOnly]
+        internal static IntPtr GetCustomAttribute(IntPtr typeHandle, IntPtr attribHandle)
+        {
+            Type type = (Type)GCHandle.FromIntPtr(typeHandle).Target;
+            Type attribType = (Type)GCHandle.FromIntPtr(attribHandle).Target;
+            object attrib = type.GetCustomAttributes(false).FirstOrDefault(x => x.GetType() == attribType);
+
+            if (attrib != null)
+                return GCHandle.ToIntPtr(GCHandle.Alloc(attrib, GCHandleType.Weak));
+            return IntPtr.Zero;
+        }
+
         [UnmanagedCallersOnly]
         internal static void GetClassInterfaces(IntPtr typeHandle, IntPtr* classInterfaces, int* classInterfacesCount)
         {

Source/Engine/Scripting/DotNet/CoreCLR.h

@@ -4,6 +4,7 @@
 #include <ThirdParty/mono-2.0/mono/metadata/blob.h>
 
 #include "Engine/Core/Types/String.h"
+#include "Engine/Core/Collections/Array.h"
 #include "Engine/Scripting/Types.h"
 
 #if defined(_WIN32)
@@ -46,4 +47,9 @@ public:
     static gchandle NewGCHandleWeakref(void* obj, bool track_resurrection);
     static void* GetGCHandleTarget(const gchandle& gchandle);
     static void FreeGCHandle(const gchandle& gchandle);
+    
+    static bool HasCustomAttribute(void* klass, void* attribClass);
+    static bool HasCustomAttribute(void* klass);
+    static void* GetCustomAttribute(void* klass, void* attribClass);
+    static Array<void*> GetCustomAttributes(void* klass);
 };

Source/Engine/Scripting/DotNet/MonoApi.cpp

@@ -587,6 +587,30 @@ const char* CoreCLR::GetClassFullname(void* klass)
     return ((CoreCLRClass*)klass)->GetFullname().Get();
 }
 
+bool CoreCLR::HasCustomAttribute(void* klass, void* attribClass)
+{
+    return CoreCLR::GetCustomAttribute(klass, attribClass) != nullptr;
+}
+bool CoreCLR::HasCustomAttribute(void* klass)
+{
+    return CoreCLR::GetCustomAttribute(klass, nullptr) != nullptr;
+}
+void* CoreCLR::GetCustomAttribute(void* klass, void* attribClass)
+{
+    return CoreCLR::CallStaticMethodInternal<void*, void*, void*>(TEXT("GetCustomAttribute"), ((CoreCLRClass*)klass)->GetTypeHandle(), ((CoreCLRClass*)attribClass)->GetTypeHandle());
+}
+Array<void*> CoreCLR::GetCustomAttributes(void* klass)
+{
+    Array<CoreCLRCustomAttribute*> attrib = ((CoreCLRClass*)klass)->GetCustomAttributes();
+
+    Array<void*> attributes;
+    attributes.Resize(attrib.Count(), false);
+    for (int i = 0; i < attrib.Count(); i++)
+        attributes.Add(attrib[i]->GetHandle());
+
+    return attributes;
+}
+
 /*
  * loader.h
 */

Source/Engine/Scripting/ManagedCLR/MClass.cpp

@@ -14,6 +14,9 @@
 #include <ThirdParty/mono-2.0/mono/metadata/attrdefs.h>
 #define GET_CUSTOM_ATTR() (MonoCustomAttrInfo*)(_attrInfo ? _attrInfo : _attrInfo = mono_custom_attrs_from_class(_monoClass))
 #endif
+#if USE_NETCORE
+#include "Engine/Scripting/DotNet/CoreCLR.h"
+#endif
 
 #if USE_MONO
 MClass::MClass(const MAssembly* parentAssembly, MonoClass* monoClass, const MString& fullname)
@@ -375,7 +378,9 @@ MObject* MClass::CreateInstance(void** params, uint32 numParams)
 
 bool MClass::HasAttribute(const MClass* monoClass) const
 {
-#if USE_MONO
+#if USE_NETCORE
+    return CoreCLR::HasCustomAttribute(_monoClass, monoClass->GetNative());
+#elif USE_MONO
     MonoCustomAttrInfo* attrInfo = GET_CUSTOM_ATTR();
     return attrInfo != nullptr && mono_custom_attrs_has_attr(attrInfo, monoClass->GetNative()) != 0;
 #else
@@ -385,7 +390,9 @@ bool MClass::HasAttribute(const MClass* monoClass) const
 
 bool MClass::HasAttribute() const
 {
-#if USE_MONO
+#if USE_NETCORE
+    return CoreCLR::HasCustomAttribute(_monoClass);
+#elif USE_MONO
     MonoCustomAttrInfo* attrInfo = GET_CUSTOM_ATTR();
     return attrInfo && attrInfo->num_attrs > 0;
 #else
@@ -395,7 +402,9 @@ bool MClass::HasAttribute() const
 
 MObject* MClass::GetAttribute(const MClass* monoClass) const
 {
-#if USE_MONO
+#if USE_NETCORE
+    return (MObject*)CoreCLR::GetCustomAttribute(_monoClass, monoClass->GetNative());
+#elif USE_MONO
     MonoCustomAttrInfo* attrInfo = GET_CUSTOM_ATTR();
     return attrInfo ? mono_custom_attrs_get_attr(attrInfo, monoClass->GetNative()) : nullptr;
 #else
@@ -409,7 +418,9 @@ const Array<MObject*>& MClass::GetAttributes()
         return _attributes;
 
     _hasCachedAttributes = true;
-#if USE_MONO
+#if USE_NETCORE
+    _attributes = *(Array<MObject*>*)(&CoreCLR::GetCustomAttributes(_monoClass));
+#elif USE_MONO
     MonoCustomAttrInfo* attrInfo = GET_CUSTOM_ATTR();
     if (attrInfo == nullptr)
         return _attributes;