Improve Cpp::Construct pointer logic for memory arena flags

Also handle both ctors and class scopes

Author: aaronj0

include/CppInterOp/CppInterOp.h

@@ -849,7 +849,7 @@ CPPINTEROP_API void Deallocate(TCppScope_t scope, TCppObject_t address,
 
 /// Creates one or more objects of class \c scope by calling its default
 /// constructor.
-/// \param[in] scope Class to construct
+/// \param[in] scope Class to construct, or handle to Constructor
 /// \param[in] arena If set, this API uses placement new to construct at this
 /// address.
 /// \param[in] is used to indicate the number of objects to construct.

lib/CppInterOp/CppInterOp.cpp

@@ -3783,22 +3783,26 @@ void Deallocate(TCppScope_t scope, TCppObject_t address, TCppIndex_t count) {
 // FIXME: Add optional arguments to the operator new.
 TCppObject_t Construct(compat::Interpreter& interp, TCppScope_t scope,
                        void* arena /*=nullptr*/, TCppIndex_t count /*=1UL*/) {
-  auto* Class = (Decl*)scope;
-  // FIXME: Diagnose.
-  if (!HasDefaultConstructor(Class))
-    return nullptr;
 
-  auto* const Ctor = GetDefaultConstructor(interp, Class);
-  if (JitCall JC = MakeFunctionCallable(&interp, Ctor)) {
-    if (arena) {
-      JC.InvokeConstructor(&arena, count, {},
-                           (void*)~0); // Tell Invoke to use placement new.
-      return arena;
-    }
+  TCppFunction_t ctor;
+  if (Cpp::IsConstructor(scope))
+    ctor = scope;
+  else if (Cpp::IsClass(scope)) {
+    if (!HasDefaultConstructor(scope))
+      return nullptr;
+    ctor = Cpp::GetDefaultConstructor(scope);
+  } else
+    return nullptr;
 
-    void* obj = nullptr;
-    JC.InvokeConstructor(&obj, count, {}, nullptr);
-    return obj;
+  if (JitCall JC = MakeFunctionCallable(&interp, ctor)) {
+    if (JC.getKind() != Cpp::JitCall::kConstructorCall)
+      return nullptr;
+    // invoke the constructor (placement/heap) in one shot
+    // flag is non-null for placement new, null for normal new
+    void* flag = arena ? reinterpret_cast<void*>(1) : nullptr;
+    void* result = arena;
+    JC.InvokeConstructor(&result, count, {}, flag);
+    return result;
   }
   return nullptr;
 }