Fix handling generic type in MethodDef instance

- Hardned check for generic type when using MethodDef.
- Simplified getting and setting TypeSpec for generic type.
- Now using pointers all the way instead of creating new TypeSpecs along the path.
- Remove wrong this accessor.

Author: josesimoes

src/CLR/Core/Execution.cpp

@@ -2032,7 +2032,8 @@ HRESULT CLR_RT_ExecutionEngine::InitializeLocals(
 
                     CLR_RT_TypeSpec_Index genericTSIndex = {};
 
-                    if (methodDefInstance.genericType && methodDefInstance.genericType->data != 0)
+                    if (methodDefInstance.genericType && NANOCLR_INDEX_IS_VALID(*methodDefInstance.genericType) &&
+                        methodDefInstance.genericType->data != CLR_EmptyToken)
                     {
                         // method is generic, it can only use class from method's class generic parameters
                         genericInstance.InitializeFromIndex(*methodDefInstance.genericType);
@@ -2093,7 +2094,8 @@ HRESULT CLR_RT_ExecutionEngine::InitializeLocals(
                     // type-level generic parameter in a locals signature (e.g. 'T' inside a generic type)
                     CLR_INT8 genericParamPosition = *sig++;
 
-                    if (methodDefInstance.genericType && methodDefInstance.genericType->data != 0)
+                    if (methodDefInstance.genericType && NANOCLR_INDEX_IS_VALID(*methodDefInstance.genericType) &&
+                        methodDefInstance.genericType->data != CLR_EmptyToken)
                     {
                         CLR_RT_TypeSpec_Instance typeSpec{};
                         typeSpec.InitializeFromIndex(

src/CLR/Core/Interpreter.cpp

@@ -2211,7 +2211,16 @@ HRESULT CLR_RT_Thread::Execute_IL(CLR_RT_StackFrame &stackArg)
                                             NANOCLR_SET_AND_LEAVE(CLR_E_WRONG_TYPE);
                                         }
 
-                                        calleeInst.InitializeFromIndex(calleeReal);
+                                        if (calleeInst.genericType && NANOCLR_INDEX_IS_VALID(*calleeInst.genericType) &&
+                                            calleeInst.genericType->data != CLR_EmptyToken)
+                                        {
+                                            // store the current generic context (if any)
+                                            calleeInst.InitializeFromIndex(calleeReal, *calleeInst.genericType);
+                                        }
+                                        else
+                                        {
+                                            calleeInst.InitializeFromIndex(calleeReal);
+                                        }
                                     }
 
 #if defined(NANOCLR_APPDOMAINS)

src/CLR/Core/TypeSystem.cpp

@@ -1597,7 +1597,7 @@ bool CLR_RT_MethodDef_Instance::InitializeFromIndex(
     }
 
     // remember the TypeSpec so this is available when needed
-    this->genericType = &typeSpec;
+    genericType = &typeSpec;
 
     return true;
 }
@@ -1695,9 +1695,8 @@ bool CLR_RT_MethodDef_Instance::ResolveToken(
                         }
                     }
 
-                    // Pick the “winner” between methodOwnerTS or callerGeneric:
-                    const CLR_RT_TypeSpec_Index *definitiveTypeSpec = useCaller ? callerGeneric : methodOwnerTS;
-                    genericType = (CLR_RT_TypeSpec_Index *)definitiveTypeSpec;
+                    // Pick the "winner" between methodOwnerTS or callerGeneric:
+                    genericType = useCaller ? callerGeneric : methodOwnerTS;
 
                     CLR_RT_Assembly *methodAssembly = g_CLR_RT_TypeSystem.m_assemblies[methodOwnerTS->Assembly() - 1];
 
@@ -6772,7 +6771,7 @@ HRESULT CLR_RT_TypeSystem::BuildMethodName(
 
     declTypeIdx.Set(md.Assembly(), declTypeInst.assembly->crossReferenceMethodDef[md.Method()].GetOwner());
 
-    if (genericType != nullptr && genericType->data != 0xffffffff)
+    if (genericType != nullptr && NANOCLR_INDEX_IS_VALID(*genericType) && genericType->data != CLR_EmptyToken)
     {
         // parse TypeSpec to get its TypeDef
         CLR_RT_TypeSpec_Instance tsInst = {};

src/CLR/Diagnostics/Info.cpp

@@ -481,7 +481,8 @@ void CLR_RT_Assembly::DumpToken(CLR_UINT32 token, const CLR_RT_MethodDef_Instanc
             //    use that, so ResizeArray prints as SimpleList<I4>::ResizeArray.
             // 2) Otherwise, fall back to xref.genericType (the raw MethodRef own owner).
             const CLR_RT_TypeSpec_Index *ownerTypeSpec;
-            if (methodDefInstance.genericType != nullptr && NANOCLR_INDEX_IS_VALID(*methodDefInstance.genericType))
+            if (methodDefInstance.genericType != nullptr && NANOCLR_INDEX_IS_VALID(*methodDefInstance.genericType) &&
+                methodDefInstance.genericType->data != CLR_EmptyToken)
             {
                 ownerTypeSpec = methodDefInstance.genericType;
             }