QbsProjectManager: Fix handling of overlapping parse requests.

The current code simply asserts when a new parse request comes in while
parsing. However, that condition is easily triggered, for instance if a
project file is saved to disk during a parse operation. Such updates
currently have no effect at all (other than triggering an error
message).
Instead, we now cancel the old parse job and start a new one.

Change-Id: If2eeb93b85b5163dcea99785a0fc89a254d082db
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>

src/plugins/qbsprojectmanager/qbsproject.cpp

@@ -102,6 +102,7 @@ QbsProject::QbsProject(QbsManager *manager, const QString &fileName) :
     m_qbsUpdateFutureInterface(0),
     m_forceParsing(false),
     m_parsingScheduled(false),
+    m_cancelingParsing(false),
     m_currentBc(0)
 {
     m_parsingDelay.setInterval(1000); // delay parsing by 1s.
@@ -275,12 +276,23 @@ void QbsProject::handleQbsParsingDone(bool success)
 {
     QTC_ASSERT(m_qbsProjectParser, return);
 
+    // If this parse operation was canceled, start a new one right away, ignoring the old result.
+    if (m_cancelingParsing) {
+        m_cancelingParsing = false;
+        m_qbsProjectParser->deleteLater();
+        m_qbsProjectParser = 0;
+        parseCurrentBuildConfiguration(m_forceParsing);
+        return;
+    }
+
     generateErrors(m_qbsProjectParser->error());
 
     if (success) {
         m_qbsProject = m_qbsProjectParser->qbsProject();
         QTC_CHECK(m_qbsProject.isValid());
         readQbsData();
+    } else {
+        m_qbsUpdateFutureInterface->reportCanceled();
     }
 
     m_qbsProjectParser->deleteLater();
@@ -369,12 +381,27 @@ void QbsProject::parseCurrentBuildConfiguration(bool force)
     m_parsingScheduled = false;
     if (!m_forceParsing)
         m_forceParsing = force;
+    if (m_cancelingParsing)
+        return;
 
     if (!activeTarget())
         return;
     QbsBuildConfiguration *bc = qobject_cast<QbsBuildConfiguration *>(activeTarget()->activeBuildConfiguration());
     if (!bc)
         return;
+
+    // New parse requests override old ones.
+    // NOTE: We need to wait for the current operation to finish, since otherwise there could
+    //       be a conflict. Consider the case where the old qbs::ProjectSetupJob is writing
+    //       to the build graph file when the cancel request comes in. If we don't wait for
+    //       acknowledgment, it might still be doing that when the new one already reads from the
+    //       same file.
+    if (m_qbsProjectParser) {
+        m_cancelingParsing = true;
+        m_qbsProjectParser->cancel();
+        return;
+    }
+
     parse(bc->qbsConfiguration(), bc->environment(), bc->buildDirectory().toString());
 }
 

src/plugins/qbsprojectmanager/qbsproject.h

@@ -153,6 +153,7 @@ private:
     QFutureInterface<bool> *m_qbsUpdateFutureInterface;
     bool m_forceParsing;
     bool m_parsingScheduled;
+    bool m_cancelingParsing;
 
     QFuture<void> m_codeModelFuture;
 

src/plugins/qbsprojectmanager/qbsprojectparser.cpp

@@ -136,6 +136,12 @@ bool QbsProjectParser::parse(const QVariantMap &config, const Environment &env,
     return true;
 }
 
+void QbsProjectParser::cancel()
+{
+    QTC_ASSERT(m_qbsSetupProjectJob, return);
+    m_qbsSetupProjectJob->cancel();
+}
+
 qbs::Project QbsProjectParser::qbsProject() const
 {
     return m_project;
@@ -153,8 +159,8 @@ void QbsProjectParser::handleQbsParsingDone(bool success)
     m_project = m_qbsSetupProjectJob->project();
     m_error = m_qbsSetupProjectJob->error();
 
-    if (!success)
+    // Do not report the operation as canceled here, as we might want to make overlapping
-        m_fi->reportCanceled();
+    // parses appear atomic to the user.
 
     emit done(success);
 }

src/plugins/qbsprojectmanager/qbsprojectparser.h

@@ -54,6 +54,7 @@ public:
     void setForced(bool);
 
     bool parse(const QVariantMap &config, const Utils::Environment &env, const QString &dir);
+    void cancel();
 
     qbs::Project qbsProject() const;
     qbs::ErrorInfo error();