[QgsFilterLineEdit] disable clear action when read only

python/gui/qgsfilterlineedit.sip.in

@@ -213,6 +213,15 @@ Will select all text when this widget receives the focus.
 .. versionadded:: 3.0
 %End
 
+
+    virtual bool event( QEvent *event );
+%Docstring
+Reimplemented to enable/disable the clear action
+depending on read-only status
+
+.. versionadded:: 3.0.1
+%End
+
   public slots:
 
     virtual void clearValue();

src/gui/qgsfilterlineedit.cpp

@@ -178,3 +178,11 @@ bool QgsFilterLineEdit::shouldShowClear() const
   }
   return false; //avoid warnings
 }
+
+bool QgsFilterLineEdit::event( QEvent *event )
+{
+  if ( event->type() == QEvent::ReadOnlyChange )
+    updateClearIcon();
+
+  return QLineEdit::event( event );;
+}

src/gui/qgsfilterlineedit.h

@@ -213,6 +213,15 @@ class GUI_EXPORT QgsFilterLineEdit : public QLineEdit
      */
     void setSelectOnFocus( bool selectOnFocus );
 
+
+    /**
+     * Reimplemented to enable/disable the clear action
+     * depending on read-only status
+     *
+     * \since QGIS 3.0.1
+     */
+    virtual bool event( QEvent *event ) override;
+
   public slots:
 
     /**