[TCling] Invoke InterOp interpreter API in metacling

This uses provides InterOp with the TInterpreter instance created by ROOT in TCling.
The InterOp API can now be used without providing interpreter ownership.

core/metacling/src/CMakeLists.txt

@@ -76,7 +76,6 @@ if(MSVC)
 endif()
 
 add_dependencies(MetaCling CLING clangCppInterOp)
-# target_include_directories(MetaCling SYSTEM PUBLIC ${source_dir}/include/)
 
 ##### libCling #############################################################
 

core/metacling/src/TCling.cxx

@@ -115,6 +115,8 @@ clang/LLVM technology.
 #include "cling/Utils/SourceNormalization.h"
 #include "cling/Interpreter/Exception.h"
 
+#include "clang/Interpreter/CppInterOp.h"
+
 #include "llvm/IR/GlobalValue.h"
 #include "llvm/IR/Module.h"
 
@@ -1612,6 +1614,12 @@ TCling::TCling(const char *name, const char *title, const char* const argv[], vo
       // Initialize the dyld for AutoloadLibraryGenerator.
       DLM.initializeDyld(ShouldPermanentlyIgnore);
    }
+
+   // Tell CppInterOp that the cling::Interpreter instance is managed externally by ROOT
+   // We pass the handle so it sets the ownership flags and sets the interpreter as soon as TCling is initialized 
+   if (!Cpp::GetInterpreter()) {
+      Cpp::UseExternalInterpreter((Cpp::TInterp_t*)fInterpreter.get());
+   }
 }
 
 

core/metacling/src/TClingCallFunc.cxx

@@ -67,6 +67,8 @@ C++ interpreter and the Clang C++ compiler, not CINT.
 
 #include "clang/Sema/SemaInternal.h"
 
+#include "clang/Interpreter/CppInterOp.h"
+
 #include <map>
 #include <string>
 #include <sstream>