From 3371003402df95d35bed4d7748dce55c3de139e0 Mon Sep 17 00:00:00 2001
From: Nyall Dawson <nyall.dawson@gmail.com>
Date: Thu, 9 Feb 2017 17:57:17 +1000
Subject: [PATCH] Small tweaks to property override button behavior

---
 src/gui/qgspropertyassistantwidget.cpp    |  2 +-
 src/gui/qgspropertyoverridebutton.cpp     | 15 +++++++++------
 src/gui/symbology-ng/qgssizescalewidget.h |  1 +
 3 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/src/gui/qgspropertyassistantwidget.cpp b/src/gui/qgspropertyassistantwidget.cpp
index 29186bd1738..bdcc4cccb7b 100644
--- a/src/gui/qgspropertyassistantwidget.cpp
+++ b/src/gui/qgspropertyassistantwidget.cpp
@@ -82,7 +82,7 @@ void QgsPropertyAssistantWidget::registerExpressionContextGenerator( QgsExpressi
 
 void QgsPropertyAssistantWidget::updateProperty( QgsProperty& property )
 {
-  property.setActive( true );
+  property.setActive( !mExpressionWidget->currentText().isEmpty() );
   if ( mExpressionWidget->isExpression() )
     property.setExpressionString( mExpressionWidget->currentField() );
   else
diff --git a/src/gui/qgspropertyoverridebutton.cpp b/src/gui/qgspropertyoverridebutton.cpp
index ff48af8646c..a6cabb1e04c 100644
--- a/src/gui/qgspropertyoverridebutton.cpp
+++ b/src/gui/qgspropertyoverridebutton.cpp
@@ -449,18 +449,14 @@ void QgsPropertyOverrideButton::menuActionTriggered( QAction* action )
       mExpressionString = exprString;
       mProperty.setExpressionString( mExpressionString );
       mProperty.setTransformer( nullptr );
-      setActivePrivate( mProperty.isActive() );
+      setActivePrivate( true );
       updateGui();
       emit changed();
     }
   }
   else if ( action == mActionClearExpr )
   {
-    // only deactivate if defined expression is being used
-    if ( mProperty.isActive() && mProperty.propertyType() == QgsProperty::ExpressionBasedProperty )
-    {
-      setActivePrivate( false );
-    }
+    setActivePrivate( false );
     mProperty.setStaticValue( QVariant() );
     mProperty.setTransformer( nullptr );
     mExpressionString.clear();
@@ -528,6 +524,13 @@ void QgsPropertyOverrideButton::showExpressionDialog()
 
 void QgsPropertyOverrideButton::showAssistant()
 {
+  //first step - try to convert any existing expression to a transformer if one doesn't
+  //already exist
+  if ( !mProperty.transformer() )
+  {
+    ( void )mProperty.convertToTransformer();
+  }
+
   QgsPanelWidget* panel = QgsPanelWidget::findParentPanel( this );
   if ( panel && panel->dockMode() )
   {
diff --git a/src/gui/symbology-ng/qgssizescalewidget.h b/src/gui/symbology-ng/qgssizescalewidget.h
index 339f31c774f..6f9cdace36e 100644
--- a/src/gui/symbology-ng/qgssizescalewidget.h
+++ b/src/gui/symbology-ng/qgssizescalewidget.h
@@ -22,6 +22,7 @@
 #include <QStandardItemModel>
 #include <QItemDelegate>
 #include "qgis_gui.h"
+#include "qgsproperty.h"
 
 class QgsVectorLayer;
 class QgsSymbol;