Expand StartParsingRAII

In particular the CachedTokens need to be pushed/pop or otherwise
give misleading information.

This fixes ROOT-10224.

interpreter/cling/include/cling/Utils/ParserStateRAII.h

@@ -47,6 +47,9 @@ namespace cling {
     ParserStateRAII(clang::Parser& p, bool skipToEOF);
     ~ParserStateRAII();
 
+    void SetSkipToEOF(bool newvalue) {
+      SkipToEOF = newvalue;
+    }
 };
 
 } // end namespace cling

interpreter/cling/lib/Interpreter/LookupHelper.cpp

@@ -38,16 +38,25 @@ namespace cling {
   class StartParsingRAII {
     LookupHelper& m_LH;
     llvm::SaveAndRestore<bool> SaveIsRecursivelyRunning;
+    // Save and restore the state of the Parser and lexer.
+    // Note: ROOT::Internal::ParsingStateRAII also save and restore the state of Sema,
+    // including pending instantiation for example.  It is not clear whether we need
+    // to do so here too or whether we need to also see the "on-going" semantic information ...
+    // For now, we leave Sema untouched.
+    clang::Preprocessor::CleanupAndRestoreCacheRAII fCleanupRAII;
+    clang::Parser::ParserCurTokRestoreRAII fSavedCurToken;
     ParserStateRAII ResetParserState;
     void prepareForParsing(llvm::StringRef code, llvm::StringRef bufferName,
                            LookupHelper::DiagSetting diagOnOff);
   public:
     StartParsingRAII(LookupHelper& LH, llvm::StringRef code,
                      llvm::StringRef bufferName,
                      LookupHelper::DiagSetting diagOnOff)
-        : m_LH(LH), SaveIsRecursivelyRunning(LH.IsRecursivelyRunning),
-          ResetParserState(*LH.m_Parser.get(),
-                           !LH.IsRecursivelyRunning /*skipToEOF*/) {
+        : m_LH(LH), SaveIsRecursivelyRunning(LH.IsRecursivelyRunning)
+          , fCleanupRAII(LH.m_Parser.get()->getPreprocessor())
+          , fSavedCurToken(*LH.m_Parser.get())
+          , ResetParserState(*LH.m_Parser.get(), !LH.IsRecursivelyRunning /*skipToEOF*/)
+    {
       LH.IsRecursivelyRunning = true;
       prepareForParsing(code, bufferName, diagOnOff);
     }
@@ -1237,7 +1246,8 @@ namespace cling {
                                  llvm::StringRef funcName,
                                  Interpreter* Interp,
                                  UnqualifiedId &FuncId,
-                                 LookupHelper::DiagSetting diagOnOff) {
+                                 LookupHelper::DiagSetting diagOnOff,
+                                 ParserStateRAII &ResetParserState) {
 
     // Use a very simple parse step that dectect whether the name search (which
     // is already supposed to be an unqualified name) is a simple identifier,
@@ -1336,6 +1346,7 @@ namespace cling {
     //  Create a fake file to parse the function name.
     //
     // FIXME:, TODO: Cleanup that complete mess.
+    ResetParserState.SetSkipToEOF(true);
     {
       PP.getDiagnostics().setSuppressAllDiagnostics(diagOnOff ==
                                                    LookupHelper::NoDiagnostics);
@@ -1410,9 +1421,9 @@ namespace cling {
     S.EnterDeclaratorContext(P.getCurScope(), foundDC);
 
     UnqualifiedId FuncId;
-    ParserStateRAII ResetParserState(P, true /*skipToEOF*/);
+    ParserStateRAII ResetParserState(P, false /*skipToEOF*/);
     if (!ParseWithShortcuts(foundDC, Context, funcName, Interp,
-                            FuncId, diagOnOff)) {
+                            FuncId, diagOnOff, ResetParserState)) {
       // Failed parse, cleanup.
       // Destroy the scope we created first, and
       // restore the original.