Improved UX when closing projects with layers with unsaved changes

Previously, the unsaved layer warnings would come AFTER the
unsaved project warning. The unsaved layer warnings had no
cancel option, which meant that there was no way to cancel
a project close when unsaved layer edits exist, and you
were forced to either save these edits or discard them.

Now, the unsaved layer edits checks occur before the unsaved
project check, and you have the option now to 'Cancel' the
project close from the unsaved layer edits messagebox. This
allows users to cancel the project close operation if they
want to e.g. inspect manually unsaved layers to decide
what action is appropriate to take on these.

Also fixes the unsaved layer edits prompt sometimes didn't
appear, even though unsaved changes were present...

Author: nyalldawson

src/app/qgisapp.cpp

@@ -5218,7 +5218,7 @@ void QgisApp::fileExit()
     return;
   }
 
-  if ( saveDirty() )
+  if ( checkUnsavedLayerEdits() && saveDirty() )
   {
     closeProject();
     userProfileManager()->setDefaultFromActive();
@@ -5253,7 +5253,7 @@ bool QgisApp::fileNew( bool promptToSaveFlag, bool forceBlank )
 
   if ( promptToSaveFlag )
   {
-    if ( !saveDirty() )
+    if ( !checkUnsavedLayerEdits() || !saveDirty() )
     {
       return false; //cancel pressed
     }
@@ -5347,7 +5347,7 @@ bool QgisApp::fileNewFromTemplate( const QString &fileName )
   if ( checkTasksDependOnProject() )
     return false;
 
-  if ( !saveDirty() )
+  if ( !checkUnsavedLayerEdits() || !saveDirty() )
   {
     return false; //cancel pressed
   }
@@ -5646,7 +5646,7 @@ void QgisApp::fileOpen()
     return;
 
   // possibly save any pending work before opening a new project
-  if ( saveDirty() )
+  if ( checkUnsavedLayerEdits() && saveDirty() )
   {
     // Retrieve last used project dir from persistent settings
     QgsSettings settings;
@@ -5680,6 +5680,9 @@ void QgisApp::fileRevert()
                               QMessageBox::Yes | QMessageBox::No, QMessageBox::No ) == QMessageBox::No )
     return;
 
+  if ( !checkUnsavedLayerEdits() )
+    return;
+
   // re-open the current project
   addProject( QgsProject::instance()->fileName() );
 }
@@ -6107,7 +6110,7 @@ void QgisApp::openProject( QAction *action )
     return;
 
   QString debugme = action->data().toString();
-  if ( saveDirty() )
+  if ( checkUnsavedLayerEdits() && saveDirty() )
     addProject( debugme );
 }
 
@@ -6133,7 +6136,7 @@ void QgisApp::openProject( const QString &fileName )
     return;
 
   // possibly save any pending work before opening a different project
-  if ( saveDirty() )
+  if ( checkUnsavedLayerEdits() && saveDirty() )
   {
     // error handling and reporting is in addProject() function
     addProject( fileName );
@@ -10917,6 +10920,30 @@ bool QgisApp::saveDirty()
   return answer != QMessageBox::Cancel;
 }
 
+bool QgisApp::checkUnsavedLayerEdits()
+{
+  // check to see if there are any vector layers with unsaved provider edits
+  // to ensure user has opportunity to save any editing
+  if ( QgsProject::instance()->count() > 0 )
+  {
+    const QMap<QString, QgsMapLayer *> layers = QgsProject::instance()->mapLayers();
+    for ( auto it = layers.begin(); it != layers.end(); ++it )
+    {
+      if ( QgsVectorLayer *vl = qobject_cast<QgsVectorLayer *>( it.value() ) )
+      {
+        const bool hasUnsavedEdits = ( vl->isEditable() && vl->isModified() );
+        if ( !hasUnsavedEdits )
+          continue;
+
+        if ( !toggleEditing( vl, true ) )
+          return false;
+      }
+    }
+  }
+
+  return true;
+}
+
 bool QgisApp::checkTasksDependOnProject()
 {
   QSet< QString > activeTaskDescriptions;

src/app/qgisapp.h

@@ -1787,6 +1787,17 @@ class APP_EXPORT QgisApp : public QMainWindow, private Ui::MainWindow
      * \returns true if saved or discarded, false if canceled
      */
     bool saveDirty();
+
+    /**
+     * Checks for unsaved changes in open layers and prompts the user to save
+     * or discard these changes for each layer.
+     *
+     * Returns true if there are no unsaved layer edits remaining, or the user
+     * opted to discard them all. Returns false if the user opted to cancel
+     * on any layer.
+     */
+    bool checkUnsavedLayerEdits();
+
     //! Checks for running tasks dependent on the open project
     bool checkTasksDependOnProject();