[TCling] Allow InterOp to access ROOT's interpreter

by linking clangCppInterOp in libCling

core/metacling/src/CMakeLists.txt

@@ -44,6 +44,7 @@ target_include_directories(MetaCling SYSTEM PRIVATE
   ${CLANG_INCLUDE_DIRS}
   ${LLVM_INCLUDE_DIRS}
   ${CLAD_INCLUDE_DIRS}
+  ${CPPINTEROP_INCLUDE_DIRS}
 )
 
 target_include_directories(MetaCling PRIVATE
@@ -74,7 +75,7 @@ if(MSVC)
    set_source_files_properties(TCling.cxx COMPILE_FLAGS /bigobj)
 endif()
 
-add_dependencies(MetaCling CLING)
+add_dependencies(MetaCling CLING clangCppInterOp)
 
 ##### libCling #############################################################
 
@@ -113,11 +114,15 @@ ROOT_LINKER_LIBRARY(Cling
         $<TARGET_OBJECTS:ClingUtils>
         $<TARGET_OBJECTS:Dictgen>
         $<TARGET_OBJECTS:MetaCling>
-        LIBRARIES ${CLING_LIBRARIES} ${LINK_LIBS} ${CLING_PLUGIN_LINK_LIBS})
+        LIBRARIES ${CLING_LIBRARIES} clangCppInterOp ${LINK_LIBS} ${CLING_PLUGIN_LINK_LIBS})
 
 # When these two link at the same time, they can exhaust the RAM on many machines, since they both link against llvm.
 add_dependencies(Cling rootcling_stage1)
 
+if(testing)
+  add_dependencies(Cling CppInterOpUnitTests)
+endif()
+
 if(MSVC)
   set_target_properties(Cling PROPERTIES WINDOWS_EXPORT_ALL_SYMBOLS TRUE)
   set(cling_exports ${cling_exports}

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"
 
@@ -1539,6 +1541,11 @@ TCling::TCling(const char *name, const char *title, const char* const argv[], vo
    if (!fInterpreter->getCI()) { // Compiler instance could not be created. See https://its.cern.ch/jira/browse/ROOT-10239
       return;
    }
+
+   // Tell CppInterOp that the cling::Interpreter instance is managed externally by ROOT
+   // Sets the interpreter by passing the fInterpreter handle as soon as TCling is initialized
+   Cpp::UseExternalInterpreter((Cpp::TInterp_t*)fInterpreter.get());
+
    // Don't check whether modules' files exist.
    fInterpreter->getCI()->getPreprocessorOpts().DisablePCHOrModuleValidation =
       DisableValidationForModuleKind::All;