(related tdf#134298) sw: layout: avoid infinite loop in InternalAction()

The condition IsInterrupt() && pPage && (m_nCheckPageNum != USHRT_MAX)
isn't handled properly and the while loop will never terminate with
the fix for tdf#134298 in several UITest_writer_tests*.

If m_nCheckPageNum is set, then it must result in a call to
CheckPageDescs() here; it's a member of SwLayAction so won't survive
until the next idle layout invocation.

There is a funny history of these loop conditions with
commit 9eff9e699e17cc5a8a25895bd28dc8e4ceb8071e
and cee296066ab780217395201ab84c2150c8840d25 so we can only hope
this time we got it right...

Change-Id: I91b63540bf4280296d747cb8e841594f8dd3b140
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/105927
Tested-by: Jenkins
Reviewed-by: Michael Stahl <michael.stahl@cib.de>

1 files changed, 12 insertions, 8 deletions

diff --git a/sw/source/core/layout/layact.cxx b/sw/source/core/layout/layact.cxx
index 2195829f06ed..45ac680c8f4f 100644
--- a/sw/source/core/layout/layact.cxx
+++ b/sw/source/core/layout/layact.cxx
@@ -447,15 +447,19 @@ void SwLayAction::InternalAction(OutputDevice* pRenderContext)
     sal_uInt16 nPercentPageNum = 0;
     while ((!IsInterrupt() && pPage) || (m_nCheckPageNum != USHRT_MAX))
     {
-        if (!pPage && m_nCheckPageNum != USHRT_MAX)
+        // note: this is the only place that consumes and resets m_nCheckPageNum
+        if ((IsInterrupt() || !pPage) && m_nCheckPageNum != USHRT_MAX)
         {
-            SwPageFrame *pPg = static_cast<SwPageFrame*>(m_pRoot->Lower());
-            while (pPg && pPg->GetPhyPageNum() < m_nCheckPageNum)
-                pPg = static_cast<SwPageFrame*>(pPg->GetNext());
-            if (pPg)
-                pPage = pPg;
-            if (!pPage)
-                break;
+            if (!pPage || m_nCheckPageNum < pPage->GetPhyPageNum())
+            {
+                SwPageFrame *pPg = static_cast<SwPageFrame*>(m_pRoot->Lower());
+                while (pPg && pPg->GetPhyPageNum() < m_nCheckPageNum)
+                    pPg = static_cast<SwPageFrame*>(pPg->GetNext());
+                if (pPg)
+                    pPage = pPg;
+                if (!pPage)
+                    break;
+            }
 
             SwPageFrame *pTmp = pPage->GetPrev() ?
                                         static_cast<SwPageFrame*>(pPage->GetPrev()) : pPage;