Fix cling::Interpreter::compileFunction getting confused by trailing transactions.

This fixes https://sft.its.cern.ch/jira/browse/ROOT-9672 by having
cling::Interpreter::DeclareCFunction return the transaction containing the
compiled code.

With the previous code, cling::Interpreter::compileFunction will get confused by
transaction created during the callbacks executed during the
cling::IncrementalParser::commitTransaction of the main transaction.

Reproducer:

With a main composed of 'only':

int main(int argc, char ** argv)
{
  char const * class_string = (argc == 2) ? argv[1] : "std::vector<int>";
  auto const result [[gnu::unused]] = TClass::GetClass(class_string);
  return 0;
}

which is a representation of real use case (in a more complex setup) in ART.
We were getting:

Error in <TClingCallFunc::make_wrapper>: Failed to compile
  ==== SOURCE BEGIN ====
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wformat-security"
__attribute__((used)) extern "C" void __cf_0(void* obj, int nargs, void** args, void* ret)
{
   if (ret) {
      (*(TStreamerInfo**)ret) = new TStreamerInfo();
      return;
   }
   else {
      new TStreamerInfo();
      return;
   }
}
#pragma clang diagnostic pop
  ==== SOURCE END ====
Error in <TClingCallFunc::ExecT>: Called with no wrapper, not implemented!
Error in <TVirtualStreamerInfo::Factory>: The plugin handler for TVirtualStreamerInfo was found but failed to create the factory object!

The reason is that during TClingCallFunc::make_wrapper, the call to cling::Interpreter::compileFunction ends with:

    if (const llvm::GlobalValue* GV
        = getLastTransaction()->getModule()->getNamedValue(name))

However in the 'broken' case, the getLastTransaction does not return the transaction for the code being compiled by DeclareCFunction but instead the one used/created at:

#0  cling::IncrementalParser::endTransaction (this=0x4a2980, T=0x8c0fb0) at /local2/pcanal/cint_working/rootcling/v6-14-00-patches/interpreter/cling/lib/Interpreter/IncrementalParser.cpp:345
#1  0x00007fffeebc7899 in cling::Interpreter::PushTransactionRAII::pop (this=0x7fffffffcb00) at /local2/pcanal/cint_working/rootcling/v6-14-00-patches/interpreter/cling/lib/Interpreter/Interpreter.cpp:111
#2  0x00007fffeebc785e in cling::Interpreter::PushTransactionRAII::~PushTransactionRAII (this=0x7fffffffcb00, __in_chrg=<optimized out>)
    at /local2/pcanal/cint_working/rootcling/v6-14-00-patches/interpreter/cling/lib/Interpreter/Interpreter.cpp:106
#3  0x00007fffeebeb659 in cling::LookupHelper::findScope (this=0x4a9dd0, className=..., diagOnOff=cling::LookupHelper::NoDiagnostics, resultType=0x7fffffffcd08, instantiateTemplate=false)
    at /local2/pcanal/cint_working/rootcling/v6-14-00-patches/interpreter/cling/lib/Interpreter/LookupHelper.cpp:466
#4  0x00007fffeeabe0df in TCling::CheckClassInfo (this=0x4a0550, name=<optimized out>, autoload=<optimized out>, isClassOrNamespaceOnly=<optimized out>)
    at /local2/pcanal/cint_working/rootcling/v6-14-00-patches/core/metacling/src/TCling.cxx:3630
#5  0x00007ffff7c3040d in TClass::Init (this=this@entry=0xdafd20, name=name@entry=0x7ffff7cb7638 "TGlobal", cversion=cversion@entry=2, typeinfo=typeinfo@entry=0x7ffff7d8b6d8 <typeinfo for TGlobal>, isa=isa@entry=0x477430,
    dfil=dfil@entry=0x7ffff7cb8cab "TGlobal.h", ifil=<optimized out>, dl=<optimized out>, il=<optimized out>, givenInfo=<optimized out>, silent=<optimized out>)
    at /local2/pcanal/cint_working/rootcling/v6-14-00-patches/core/meta/src/TClass.cxx:1431
#6  0x00007ffff7c3a1b8 in TClass::TClass (this=0xdafd20, name=0x7ffff7cb7638 "TGlobal", cversion=<optimized out>, info=..., isa=0x477430, dfil=0x7ffff7cb8cab "TGlobal.h",
    ifil=0x7ffff7cccf88 "/local2/pcanal/cint_working/rootcling/v6-14-00-patches/core/meta/src/TGlobal.cxx", dl=27, il=25, silent=false) at /local2/pcanal/cint_working/rootcling/v6-14-00-patches/core/meta/src/TClass.cxx:1273
#7  0x00007ffff7c3a72a in ROOT::CreateClass (cname=0x7ffff7cb7638 "TGlobal", id=id@entry=2, info=..., isa=isa@entry=0x477430, dfil=dfil@entry=0x7ffff7cb8cab "TGlobal.h",
    ifil=ifil@entry=0x7ffff7cccf88 "/local2/pcanal/cint_working/rootcling/v6-14-00-patches/core/meta/src/TGlobal.cxx", dl=27, il=25) at /local2/pcanal/cint_working/rootcling/v6-14-00-patches/core/meta/src/TClass.cxx:5607
#8  0x00007ffff7c4b552 in ROOT::Internal::TDefaultInitBehavior::CreateClass (il=25, dl=27, ifil=0x7ffff7cccf88 "/local2/pcanal/cint_working/rootcling/v6-14-00-patches/core/meta/src/TGlobal.cxx", dfil=0x7ffff7cb8cab "TGlobal.h",
    isa=0x477430, info=..., id=2, cname=<optimized out>, this=0x7ffff7da7508 <ROOT::Internal::DefineBehavior(void*, void*)::theDefault>) at /home/pcanal/root_builds/v6-14-00-patches/opt/include/Rtypes.h:176
#9  ROOT::TGenericClassInfo::GetClass (this=0x7ffff7dab660 <ROOT::GenerateInitInstanceLocal(TGlobal const*)::instance>) at /local2/pcanal/cint_working/rootcling/v6-14-00-patches/core/meta/src/TGenericClassInfo.cxx:250
#10 0x00007ffff7b1a2d8 in TGlobal::Class () at /home/pcanal/root_builds/v6-14-00-patches/opt/core/base/G__Core.cxx:17156
#11 0x00007ffff7ac01de in TGlobal::IsA (this=0xee3bc0) at /home/pcanal/root_builds/v6-14-00-patches/opt/include/TGlobal.h:48
#12 TGlobal::CheckTObjectHashConsistency (this=0xee3bc0) at /home/pcanal/root_builds/v6-14-00-patches/opt/include/TGlobal.h:48
#13 0x00007ffff7be9dcd in TObject::CheckedHash (this=0xee3bc0) at /home/pcanal/root_builds/v6-14-00-patches/opt/include/TObject.h:314
#14 THashTable::GetCheckedHashValue (this=0xe65a20, obj=0xee3bc0) at /home/pcanal/root_builds/v6-14-00-patches/opt/include/THashTable.h:94
#15 THashTable::Add (this=0xe65a20, obj=0xee3bc0) at /local2/pcanal/cint_working/rootcling/v6-14-00-patches/core/cont/src/THashTable.cxx:96
#16 0x00007ffff7be6bf1 in THashList::AddLast (this=this@entry=0x5be690, obj=obj@entry=0xee3bc0) at /local2/pcanal/cint_working/rootcling/v6-14-00-patches/core/cont/src/THashList.cxx:100
#17 0x00007ffff7c4e0d1 in TListOfDataMembers::AddLast (this=0x5be690, obj=0xee3bc0) at /local2/pcanal/cint_working/rootcling/v6-14-00-patches/core/meta/src/TListOfDataMembers.cxx:103
#18 0x00007ffff7ab8785 in TList::Add (obj=0xee3bc0, this=0x5be690) at /home/pcanal/root_builds/v6-14-00-patches/opt/include/TList.h:87
#19 TROOT::GetListOfGlobals (this=0x7ffff7da7a60 <ROOT::Internal::GetROOT1()::alloc>, load=load@entry=false) at /local2/pcanal/cint_working/rootcling/v6-14-00-patches/core/base/src/TROOT.cxx:1767
#20 0x00007fffeeab1058 in TCling::HandleNewDecl (this=0x4a0550, DV=0xedf238, isDeserialized=isDeserialized@entry=true, modifiedTClasses=...) at /local2/pcanal/cint_working/rootcling/v6-14-00-patches/core/metacling/src/TCling.cxx:555
#21 0x00007fffeeabb785 in TCling::UpdateListsOnCommitted (this=0x4a0550, T=...) at /local2/pcanal/cint_working/rootcling/v6-14-00-patches/core/metacling/src/TCling.cxx:6115
#22 0x00007fffeebd0103 in cling::MultiplexInterpreterCallbacks::TransactionCommitted (this=0x57fe20, T=...) at /local2/pcanal/cint_working/rootcling/v6-14-00-patches/interpreter/cling/lib/Interpreter/MultiplexInterpreterCallbacks.h:76
#23 0x00007fffeed05d71 in cling::IncrementalParser::commitTransaction (this=0x4a2980, PRT=..., ClearDiagClient=true) at /local2/pcanal/cint_working/rootcling/v6-14-00-patches/interpreter/cling/lib/Interpreter/IncrementalParser.cpp:532
#24 0x00007fffeed06399 in cling::IncrementalParser::Compile (this=0x4a2980, input=..., Opts=...) at /local2/pcanal/cint_working/rootcling/v6-14-00-patches/interpreter/cling/lib/Interpreter/IncrementalParser.cpp:663
#25 0x00007fffeebcbc4e in cling::Interpreter::DeclareInternal (this=0x4a0f30, input=..., CO=..., T=0x7fffffffd680) at /local2/pcanal/cint_working/rootcling/v6-14-00-patches/interpreter/cling/lib/Interpreter/Interpreter.cpp:1195
#26 0x00007fffeebca8e8 in cling::Interpreter::declare (this=0x4a0f30, input=..., T=0x7fffffffd680) at /local2/pcanal/cint_working/rootcling/v6-14-00-patches/interpreter/cling/lib/Interpreter/Interpreter.cpp:823
#27 0x00007fffeebcb560 in cling::Interpreter::DeclareCFunction (this=0x4a0f30, name=..., code=..., withAccessControl=true) at /local2/pcanal/cint_working/rootcling/v6-14-00-patches/interpreter/cling/lib/Interpreter/Interpreter.cpp:1096
#28 0x00007fffeebcb862 in cling::Interpreter::compileFunction (this=0x4a0f30, name=..., code=..., ifUnique=false, withAccessControl=true)
    at /local2/pcanal/cint_working/rootcling/v6-14-00-patches/interpreter/cling/lib/Interpreter/Interpreter.cpp:1140
#29 0x00007fffeeafb83c in TClingCallFunc::compile_wrapper (withAccessControl=true, wrapper=..., wrapper_name=..., this=0xcf3c10) at /local2/pcanal/cint_working/rootcling/v6-14-00-patches/core/metacling/src/TClingCallFunc.cxx:270
#30 TClingCallFunc::make_wrapper (this=this@entry=0xcf3c10) at /local2/pcanal/cint_working/rootcling/v6-14-00-patches/core/metacling/src/TClingCallFunc.cxx:1096
#31 0x00007fffeeafbcb8 in TClingCallFunc::IFacePtr (this=this@entry=0xcf3c10) at /local2/pcanal/cint_working/rootcling/v6-14-00-patches/core/metacling/src/TClingCallFunc.cxx:2233
#32 0x00007fffeeafbe83 in TClingCallFunc::ExecT<long> (address=0x0, this=0xcf3c10) at /local2/pcanal/cint_working/rootcling/v6-14-00-patches/core/metacling/src/TClingCallFunc.cxx:2045
#33 TClingCallFunc::ExecInt (this=0xcf3c10, address=0x0) at /local2/pcanal/cint_working/rootcling/v6-14-00-patches/core/metacling/src/TClingCallFunc.cxx:2065
#34 0x00007ffff7c56e8d in TMethodCall::Execute (this=0xd97710, object=<optimized out>, retLong=@0x7fffffffd958: 0) at /local2/pcanal/cint_working/rootcling/v6-14-00-patches/core/meta/src/TMethodCall.cxx:457
#35 0x0000000000401009 in TMethodCall::Execute(long&) ()
#36 0x00000000004010ea in long TPluginHandler::ExecPluginImpl<>() ()
#37 0x000000000040106d in long TPluginHandler::ExecPlugin<>(int) ()
#38 0x0000000000400e21 in mytest() ()
#39 0x0000000000400e92 in main ()

Author: pcanal

interpreter/cling/include/cling/Interpreter/Interpreter.h

@@ -282,9 +282,11 @@ namespace cling {
     ///\param[in] name - name of the function, used to find its Decl.
     ///\param[in] code - function definition, starting with 'extern "C"'.
     ///\param[in] withAccessControl - whether to enforce access restrictions.
+    ///\param[out] T - The cling::Transaction of the input
     const clang::FunctionDecl* DeclareCFunction(llvm::StringRef name,
                                                 llvm::StringRef code,
-                                                bool withAccessControl);
+                                                bool withAccessControl,
+                                                Transaction*& T);
 
     ///\brief Initialize runtime and C/C++ level overrides
     ///

interpreter/cling/lib/Interpreter/Interpreter.cpp

@@ -1003,7 +1003,8 @@ namespace cling {
 
   const FunctionDecl* Interpreter::DeclareCFunction(StringRef name,
                                                     StringRef code,
-                                                    bool withAccessControl) {
+                                                    bool withAccessControl,
+                                                    Transaction*& T) {
     /*
     In CallFunc we currently always (intentionally and somewhat necessarily)
     always fully specify member function template, however this can lead to
@@ -1092,7 +1093,7 @@ namespace cling {
     LangOptions& LO = const_cast<LangOptions&>(getCI()->getLangOpts());
     bool savedAccessControl = LO.AccessControl;
     LO.AccessControl = withAccessControl;
-    cling::Transaction* T = 0;
+    T = nullptr;
     cling::Interpreter::CompilationResult CR = declare(code, &T);
     LO.AccessControl = savedAccessControl;
 
@@ -1137,15 +1138,16 @@ namespace cling {
       }
     }
 
-    const FunctionDecl* FD = DeclareCFunction(name, code, withAccessControl);
-    if (!FD)
+    Transaction* T = nullptr;
+    const FunctionDecl* FD = DeclareCFunction(name, code, withAccessControl, T);
+    if (!FD || !T)
       return 0;
     //
     //  Get the wrapper function pointer
     //  from the ExecutionEngine (the JIT).
     //
     if (const llvm::GlobalValue* GV
-        = getLastTransaction()->getModule()->getNamedValue(name))
+        = T->getModule()->getNamedValue(name))
       return m_Executor->getPointerToGlobalFromJIT(*GV);
 
     return 0;