Moved form feature to private and added setters/getters

plus other minor style changes as suggested by m-kuhn
in his PR review

python/core/auto_generated/fieldformatter/qgsvaluerelationfieldformatter.sip.in

@@ -118,7 +118,7 @@ Return a list of variables required by the form context ``expression``
 
     static bool expressionIsUsable( const QString &expression, const QgsFeature &feature );
 %Docstring
-Check wether the ``feature`` has all values required by the ``expression``
+Check whether the ``feature`` has all values required by the ``expression``
 
 @return True if the expression can be used
 

python/gui/auto_generated/editorwidgets/core/qgseditorwidgetwrapper.sip.in

@@ -213,6 +213,7 @@ This will be disabled when the form is not editable.
 .. versionadded:: 3.0
 %End
 
+
   signals:
 
     void valueChanged( const QVariant &value );
@@ -279,8 +280,32 @@ change the visual cue.
 .. versionadded:: 2.16
 %End
 
-  protected:
 
+    QgsFeature formFeature() const;
+%Docstring
+The feature currently being edited, in its current state
+
+:return: the feature currently being edited, in its current state
+
+.. versionadded:: 3.2
+%End
+
+    void setFormFeature( const QgsFeature &feature );
+%Docstring
+Set the feature currently being edited to ``feature``
+
+.. versionadded:: 3.2
+%End
+
+    bool setFormFeatureAttribute( const QString &attributeName, const QVariant &attributeValue );
+%Docstring
+Update the feature currently being edited by changing its
+attribute ``attributeName`` to ``attributeValue``
+
+:return: bool true on success
+
+.. versionadded:: 3.2
+%End
 
 
 };

python/gui/auto_generated/qgsattributeeditorcontext.sip.in

@@ -180,7 +180,7 @@ QGIS forms
 
     const QgsAttributeEditorContext *parentContext() const;
 
-    const QgsFeature formFeature() const;
+    QgsFeature formFeature() const;
 %Docstring
 Return current feature from the currently edited form or table row
 

src/core/fieldformatter/qgsvaluerelationfieldformatter.cpp

@@ -179,11 +179,11 @@ QSet<QString> QgsValueRelationFieldFormatter::expressionFormVariables( const QSt
   const QStringList formVariables( QgsExpressionContextUtils::formScope()->variableNames() );
   QSet<QString> variables;
 
-  for ( auto it = formVariables.constBegin(); it != formVariables.constEnd(); it++ )
+  for ( auto const &variable : formVariables )
   {
-    if ( expression.contains( *it ) )
+    if ( expression.contains( variable ) )
     {
-      variables.insert( *it );
+      variables.insert( variable );
     }
   }
   return variables;

src/core/fieldformatter/qgsvaluerelationfieldformatter.h

@@ -115,7 +115,7 @@ class CORE_EXPORT QgsValueRelationFieldFormatter : public QgsFieldFormatter
     static QSet<QString> expressionFormVariables( const QString &expression );
 
     /**
-     * Check wether the \a feature has all values required by the \a expression
+     * Check whether the \a feature has all values required by the \a expression
      *
      * @return True if the expression can be used
      * \since QGIS 3.2

src/gui/editorwidgets/core/qgseditorwidgetwrapper.cpp

@@ -25,9 +25,9 @@
 
 QgsEditorWidgetWrapper::QgsEditorWidgetWrapper( QgsVectorLayer *vl, int fieldIdx, QWidget *editor, QWidget *parent )
   : QgsWidgetWrapper( vl, editor, parent )
+  , mFieldIdx( fieldIdx )
   , mValidConstraint( true )
   , mIsBlockingCommit( false )
-  , mFieldIdx( fieldIdx )
 {
 }
 
@@ -68,7 +68,7 @@ void QgsEditorWidgetWrapper::setEnabled( bool enabled )
 
 void QgsEditorWidgetWrapper::setFeature( const QgsFeature &feature )
 {
-  mFeature = feature;
+  mFormFeature = feature;
   setValue( feature.attribute( mFieldIdx ) );
 }
 
@@ -102,6 +102,11 @@ void QgsEditorWidgetWrapper::updateConstraintWidgetStatus()
   }
 }
 
+bool QgsEditorWidgetWrapper::setFormFeatureAttribute( const QString &attributeName, const QVariant &attributeValue )
+{
+  return mFormFeature.setAttribute( attributeName, attributeValue );
+}
+
 QgsEditorWidgetWrapper::ConstraintResult QgsEditorWidgetWrapper::constraintResult() const
 {
   return mConstraintResult;

src/gui/editorwidgets/core/qgseditorwidgetwrapper.h

@@ -213,6 +213,7 @@ class GUI_EXPORT QgsEditorWidgetWrapper : public QgsWidgetWrapper
      */
     void setConstraintResultVisible( bool constraintResultVisible );
 
+
   signals:
 
     /**
@@ -277,20 +278,44 @@ class GUI_EXPORT QgsEditorWidgetWrapper : public QgsWidgetWrapper
      */
     virtual void updateConstraintWidgetStatus();
 
-  protected:
 
     /**
-     * mFieldIdx the widget feature field id
+     * The feature currently being edited, in its current state
+     *
+     * \return the feature currently being edited, in its current state
+     * \since QGIS 3.2
      */
-    int mFieldIdx;
+    QgsFeature formFeature() const { return mFormFeature; }
 
     /**
-     * mFeature the current feature
+     * Set the feature currently being edited to \a feature
+     *
+     * \since QGIS 3.2
+     */
+    void setFormFeature( const QgsFeature &feature ) { mFormFeature = feature; }
+
+    /**
+     * Update the feature currently being edited by changing its
+     * attribute \a attributeName to \a attributeValue
+     *
+     * \return bool true on success
+     * \since QGIS 3.2
      */
-    QgsFeature mFeature;
+    bool setFormFeatureAttribute( const QString &attributeName, const QVariant &attributeValue );
+
 
   private:
 
+    /**
+     * mFieldIdx the widget feature field id
+     */
+    int mFieldIdx;
+
+    /**
+     * The feature currently being edited, in its current state
+     */
+    QgsFeature mFormFeature;
+
     /**
      * Boolean storing the current validity of the constraint for this widget.
      */

src/gui/editorwidgets/qgsvaluerelationwidgetwrapper.cpp

@@ -87,7 +87,7 @@ QVariant QgsValueRelationWidgetWrapper::value() const
 
 QWidget *QgsValueRelationWidgetWrapper::createWidget( QWidget *parent )
 {
-  QgsAttributeForm *form = dynamic_cast<QgsAttributeForm *>( parent );
+  QgsAttributeForm *form = qobject_cast<QgsAttributeForm *>( parent );
   if ( form )
     connect( form, &QgsAttributeForm::widgetValueChanged, this, &QgsValueRelationWidgetWrapper::widgetValueChanged );
 
@@ -195,7 +195,7 @@ void QgsValueRelationWidgetWrapper::widgetValueChanged( const QString &attribute
   // Do nothing if the value has not changed
   if ( attributeChanged )
   {
-    mFeature.setAttribute( attribute, newValue );
+    setFormFeatureAttribute( attribute, newValue );
     // Update combos if the value used in the filter expression has changed
     if ( QgsValueRelationFieldFormatter::expressionRequiresFormScope( mExpression )
          && QgsValueRelationFieldFormatter::expressionFormAttributes( mExpression ).contains( attribute ) )
@@ -210,14 +210,14 @@ void QgsValueRelationWidgetWrapper::widgetValueChanged( const QString &attribute
 
 void QgsValueRelationWidgetWrapper::setFeature( const QgsFeature &feature )
 {
-  mFeature = feature;
+  setFormFeature( feature );
   whileBlocking( this )->populate();
-  whileBlocking( this )->setValue( feature.attribute( mFieldIdx ) );
+  whileBlocking( this )->setValue( feature.attribute( fieldIdx() ) );
   // A bit of logic to set the default value if AllowNull is false and this is a new feature
   // Note that this needs to be here after the cache has been created/updated by populate()
   // and signals unblocked (we want this to propagate to the feature itself)
-  if ( mFeature.isValid()
-       && ! mFeature.attribute( mFieldIdx ).isValid()
+  if ( formFeature().isValid()
+       && ! formFeature().attribute( fieldIdx() ).isValid()
        && mCache.size() > 0
        && ! config( QStringLiteral( "AllowNull" ) ).toBool( ) )
   {
@@ -236,7 +236,7 @@ void QgsValueRelationWidgetWrapper::populate( )
   // Initialize, note that signals are blocked, to avoid double signals on new features
   if ( QgsValueRelationFieldFormatter::expressionRequiresFormScope( mExpression ) )
   {
-    mCache = QgsValueRelationFieldFormatter::createCache( config( ), mFeature );
+    mCache = QgsValueRelationFieldFormatter::createCache( config( ), formFeature() );
   }
   else if ( mCache.isEmpty() )
   {