[bugfix] Add dirty bit to attribute form

In some cases it is difficult to prevent that an edit widget doesn't
return the original value, even if the user didn't change anything.
So rather than just comparing values to check if they have been
modified, a dirty bit has been added which is set whenever the user
actually edits the data in an edit widget. This is part of the fix
for #17878.

Author: dgoedkoop

src/gui/qgsattributeform.cpp

@@ -565,7 +565,7 @@ bool QgsAttributeForm::saveMultiEdits()
 
 bool QgsAttributeForm::save()
 {
-  if ( mIsSaving )
+  if ( mIsSaving || !mDirty )
     return true;
 
   mIsSaving = true;
@@ -594,16 +594,20 @@ bool QgsAttributeForm::save()
 
   mIsSaving = false;
   mUnsavedMultiEditChanges = false;
+  mDirty = false;
 
   return success;
 }
 
 void QgsAttributeForm::resetValues()
 {
+  mValuesInitialized = false;
   Q_FOREACH ( QgsWidgetWrapper *ww, mWidgets )
   {
     ww->setFeature( mFeature );
   }
+  mValuesInitialized = true;
+  mDirty = false;
 }
 
 void QgsAttributeForm::resetSearch()
@@ -658,6 +662,9 @@ void QgsAttributeForm::onAttributeChanged( const QVariant &value )
   if ( oldValue == value && oldValue.isNull() == value.isNull() )
     return;
 
+  if ( mValuesInitialized )
+    mDirty = true;
+
   switch ( mMode )
   {
     case SingleEditMode:

src/gui/qgsattributeform.h

@@ -364,6 +364,8 @@ class GUI_EXPORT QgsAttributeForm : public QWidget
     QList< QgsAttributeFormWidget *> mFormWidgets;
     QgsExpressionContext mExpressionContext;
     QMap<const QgsVectorLayerJoinInfo *, QgsFeature> mJoinedFeatures;
+    bool mValuesInitialized = false;
+    bool mDirty = false;
 
     struct ContainerInformation
     {