QMake: Make signalling of parsing state more robust

Move the emitParsingStarted into a location that is called
from both methods that had it before.

Also add an QTC_ASSERT into incrementPending, which is
triggered by the qmake parsing code directly. If something went
wrong before, then the signal will be sent anyway and in the
right sequence -- although the start signal is a bit late at
that point.

Task-number: QTCREATORBUG-20203
Change-Id: I64611e471d1e4959d5cfe0118223594a04238433
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/qmakeprojectmanager/qmakeproject.cpp

@@ -421,7 +421,6 @@ void QmakeProject::scheduleAsyncUpdate(QmakeProFile *file, QmakeProFile::AsyncUp
         return;
     }
 
-    emitParsingStarted();
     file->setParseInProgressRecursive(true);
     setAllBuildConfigurationsEnabled(false);
 
@@ -478,7 +477,6 @@ void QmakeProject::scheduleAsyncUpdate(QmakeProFile::AsyncUpdateDelay delay)
         return;
     }
 
-    emitParsingStarted();
     rootProFile()->setParseInProgressRecursive(true);
     setAllBuildConfigurationsEnabled(false);
 
@@ -501,12 +499,15 @@ void QmakeProject::startAsyncTimer(QmakeProFile::AsyncUpdateDelay delay)
     m_asyncUpdateTimer.stop();
     m_asyncUpdateTimer.setInterval(qMin(m_asyncUpdateTimer.interval(),
                                         delay == QmakeProFile::ParseLater ? UPDATE_INTERVAL : 0));
+    if (!isParsing())
+        emitParsingStarted();
     m_asyncUpdateTimer.start();
 }
 
 void QmakeProject::incrementPendingEvaluateFutures()
 {
     ++m_pendingEvaluateFuturesCount;
+    QTC_ASSERT(isParsing(), emitParsingStarted());
     m_asyncUpdateFutureInterface->setProgressRange(m_asyncUpdateFutureInterface->progressMinimum(),
                                                    m_asyncUpdateFutureInterface->progressMaximum() + 1);
 }