Do not do threaded group calc if...

the dependency computation resulted in a breach of
recursion limit of MAXRECURSION. In such a case,
the formula-group we are trying to thread is at the
bottom of recursion guard stack and the dependencies
(up the recursion guard stack) are yet to be computed,
so the formula-group is not safe for threading.

This patch fixes a crash in tdf#115034/1 when threading
is enabled.

Change-Id: I81737d3dd00f4e5cc782e9f030c18e36f6337a1b
Reviewed-on: https://gerrit.libreoffice.org/54789Reviewed-by: Michael Meeks <michael.meeks@collabora.com>
Tested-by: Jenkins

sc/source/core/data/formulacell.cxx

@@ -4405,8 +4405,9 @@ bool ScFormulaCell::InterpretFormulaGroup()
         return false;
 
     auto aScope = sc::FormulaLogger::get().enterGroup(*pDocument, *this);
+    ScRecursionHelper& rRecursionHelper = pDocument->GetRecursionHelper();
 
-    if (pDocument->GetRecursionHelper().GetRecursionCount())
+    if (rRecursionHelper.GetRecursionCount())
     {
         // Do not attempt to interpret a group when calculations are already
         // running, otherwise we may run into a circular reference hell. See
@@ -4441,7 +4442,7 @@ bool ScFormulaCell::InterpretFormulaGroup()
     // ScFormulaCell::InterpretFormulaGroup() must never be called through
     // anything else than ScFormulaCell::Interpret(), same as
     // ScFormulaCell::InterpretTail()
-    RecursionCounter aRecursionCounter( pDocument->GetRecursionHelper(), this);
+    RecursionCounter aRecursionCounter( rRecursionHelper, this);
 
     // Preference order:
     // First try OpenCL, but only if actual OpenCL is available (i.e. no SwInterpreter).
@@ -4473,7 +4474,16 @@ bool ScFormulaCell::InterpretFormulaGroupThreading(sc::FormulaLogger::GroupScope
         // Disable or hugely enlarge subset for S/W group
         // threading interpreter
 
-        if (!aCalculator.DoIt())
+        bool bOKToThread = aCalculator.DoIt();
+
+        if (pDocument->GetRecursionHelper().IsInRecursionReturn())
+        {
+            mxGroup->meCalcState = sc::GroupCalcDisabled;
+            aScope.addMessage("Recursion limit reached, cannot thread this formula group now");
+            return false;
+        }
+
+        if (!bOKToThread)
         {
             mxGroup->meCalcState = sc::GroupCalcDisabled;
             aScope.addMessage("could not do new dependencies calculation thing");
@@ -4535,7 +4545,6 @@ bool ScFormulaCell::InterpretFormulaGroupThreading(sc::FormulaLogger::GroupScope
             nThreadCount /= 2;
 
         SAL_INFO("sc.threaded", "Running " << nThreadCount << " threads");
-
         {
             assert(!pDocument->IsThreadedGroupCalcInProgress());
             pDocument->SetThreadedGroupCalcInProgress(true);

sc/source/core/tool/recursionhelper.cxx

@@ -16,7 +16,7 @@ void ScRecursionHelper::Init()
     bInRecursionReturn = bDoingRecursion = bInIterationReturn = false;
     aInsertPos = GetIterationEnd();
     ResetIteration();
-    aFGList.clear();
+    // Must not force clear aFGList ever.
 }
 
 void ScRecursionHelper::ResetIteration()