Followup 73733a, fix crash when running invalid python strings

(cherry-picked from 7a8c3e0)

Author: nyalldawson

src/app/qgisapp.h

@@ -1735,6 +1735,8 @@ class APP_EXPORT QgisApp : public QMainWindow, private Ui::MainWindow
     bool gestureEvent( QGestureEvent *event );
     void tapAndHoldTriggered( QTapAndHoldGesture *gesture );
 #endif
+
+    friend class TestQgisAppPython;
 };
 
 #ifdef ANDROID

src/python/qgspythonutilsimpl.cpp

@@ -300,7 +300,7 @@ bool QgsPythonUtilsImpl::runStringUnsafe( const QString& command, bool single )
   // (non-unicode strings can be mangled)
   PyObject* obj = PyRun_String( command.toUtf8().data(), single ? Py_single_input : Py_file_input, mMainDict, mMainDict );
   bool res = nullptr == PyErr_Occurred();
-  Py_DECREF( obj );
+  Py_XDECREF( obj );
 
   // we are done calling python API, release global interpreter lock
   PyGILState_Release( gstate );

tests/src/app/CMakeLists.txt

@@ -101,6 +101,7 @@ ENDMACRO (ADD_QGIS_TEST)
 #############################################################
 # Tests:
 
+ADD_QGIS_TEST(apppythontest testqgisapppython.cpp)
 ADD_QGIS_TEST(qgisappclipboard testqgisappclipboard.cpp)
 ADD_QGIS_TEST(attributetabletest testqgsattributetable.cpp)
 ADD_QGIS_TEST(fieldcalculatortest testqgsfieldcalculator.cpp)

tests/src/app/testqgisapppython.cpp

@@ -0,0 +1,97 @@
+/***************************************************************************
+     testqgsapppython.cpp
+     --------------------
+    Date                 : May 2016
+    Copyright            : (C) 2016 by Nyall Dawson
+    Email                : nyall dot dawson at gmail dot com
+ ***************************************************************************
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU General Public License as published by  *
+ *   the Free Software Foundation; either version 2 of the License, or     *
+ *   (at your option) any later version.                                   *
+ *                                                                         *
+ ***************************************************************************/
+#include <QApplication>
+#include <QObject>
+#include <QSplashScreen>
+#include <QString>
+#include <QStringList>
+#include <QtTest/QtTest>
+
+#include <qgisapp.h>
+#include <qgsapplication.h>
+
+/** \ingroup UnitTests
+ * This is a unit test for the QgisApp python support.
+ */
+class TestQgisAppPython : public QObject
+{
+    Q_OBJECT
+
+  public:
+    TestQgisAppPython();
+
+  private slots:
+    void initTestCase();// will be called before the first testfunction is executed.
+    void cleanupTestCase();// will be called after the last testfunction was executed.
+    void init() {} // will be called before each testfunction is executed.
+    void cleanup() {} // will be called after every testfunction.
+
+    void runString();
+    void evalString();
+
+  private:
+    QgisApp * mQgisApp;
+    QString mTestDataDir;
+};
+
+TestQgisAppPython::TestQgisAppPython()
+    : mQgisApp( nullptr )
+{
+
+}
+
+//runs before all tests
+void TestQgisAppPython::initTestCase()
+{
+  // Set up the QSettings environment
+  QCoreApplication::setOrganizationName( "QGIS" );
+  QCoreApplication::setOrganizationDomain( "qgis.org" );
+  QCoreApplication::setApplicationName( "QGIS-TEST" );
+
+  qDebug() << "TestQgisAppClipboard::initTestCase()";
+  // init QGIS's paths - true means that all path will be inited from prefix
+  QgsApplication::init();
+  QgsApplication::initQgis();
+  mTestDataDir = QString( TEST_DATA_DIR ) + '/'; //defined in CmakeLists.txt
+  mQgisApp = new QgisApp();
+  mQgisApp->loadPythonSupport();
+}
+
+//runs after all tests
+void TestQgisAppPython::cleanupTestCase()
+{
+  QgsApplication::exitQgis();
+}
+
+void TestQgisAppPython::runString()
+{
+  QVERIFY( mQgisApp->mPythonUtils->runString( "a=1+1" ) );
+  QVERIFY( !mQgisApp->mPythonUtils->runString( "x" ) );
+  QVERIFY( !mQgisApp->mPythonUtils->runString( "" ) );
+}
+
+void TestQgisAppPython::evalString()
+{
+  QString result;
+  //good string
+  QVERIFY( mQgisApp->mPythonUtils->evalString( "1+1", result ) );
+  QCOMPARE( result, QString( "2" ) );
+
+  //bad string
+  QVERIFY( !mQgisApp->mPythonUtils->evalString( "1+", result ) );
+}
+
+QTEST_MAIN( TestQgisAppPython )
+#include "testqgisapppython.moc"