Hide contextual functions from builder unless provided by context

python/core/qgsexpression.sip

@@ -247,7 +247,8 @@ class QgsExpression
                   bool usesGeometry = false,
                   QStringList referencedColumns = QStringList(),
                   bool lazyEval = false,
-                  bool handlesNull = false );
+                  bool handlesNull = false,
+                  bool isContextual = false );
 
         virtual ~Function();
 
@@ -272,6 +273,11 @@ class QgsExpression
 
         virtual QStringList referencedColumns() const;
 
+        /** Returns whether the function is only available if provided by a QgsExpressionContext object.
+         * @note added in QGIS 2.12
+         */
+        bool isContextual() const;
+
         /** The group the function belongs to. */
         QString group();
         /** The help text for the function. */

python/core/qgsexpressioncontext.sip

@@ -19,7 +19,8 @@ class QgsScopedExpressionFunction : QgsExpression::Function
                                  bool usesGeometry = false,
                                  QStringList referencedColumns = QStringList(),
                                  bool lazyEval = false,
-                                 bool handlesNull = false );
+                                 bool handlesNull = false,
+                                 bool isContextual = true );
 
     virtual ~QgsScopedExpressionFunction();
 

src/core/qgsexpression.h

@@ -341,7 +341,8 @@ class CORE_EXPORT QgsExpression
                   bool usesGeometry = false,
                   QStringList referencedColumns = QStringList(),
                   bool lazyEval = false,
-                  bool handlesNull = false )
+                  bool handlesNull = false,
+                  bool isContextual = false )
             : mName( fnname )
             , mParams( params )
             , mUsesGeometry( usesGeometry )
@@ -350,6 +351,7 @@ class CORE_EXPORT QgsExpression
             , mReferencedColumns( referencedColumns )
             , mLazyEval( lazyEval )
             , mHandlesNull( handlesNull )
+            , mIsContextual( isContextual )
         {}
 
         virtual ~Function() {}
@@ -375,6 +377,11 @@ class CORE_EXPORT QgsExpression
 
         virtual QStringList referencedColumns() const { return mReferencedColumns; }
 
+        /** Returns whether the function is only available if provided by a QgsExpressionContext object.
+         * @note added in QGIS 2.12
+         */
+        bool isContextual() const { return mIsContextual; }
+
         /** The group the function belongs to. */
         QString group() { return mGroup; }
         /** The help text for the function. */
@@ -409,6 +416,7 @@ class CORE_EXPORT QgsExpression
         QStringList mReferencedColumns;
         bool mLazyEval;
         bool mHandlesNull;
+        bool mIsContextual; //if true function is only available through an expression context
     };
 
     class StaticFunction : public Function

src/core/qgsexpressioncontext.h

@@ -46,8 +46,9 @@ class CORE_EXPORT QgsScopedExpressionFunction : public QgsExpression::Function
                                  bool usesGeometry = false,
                                  QStringList referencedColumns = QStringList(),
                                  bool lazyEval = false,
-                                 bool handlesNull = false )
+                                 bool handlesNull = false,
-        : QgsExpression::Function( fnname, params, group, helpText, usesGeometry, referencedColumns, lazyEval, handlesNull )
+                                 bool isContextual = true )
+        : QgsExpression::Function( fnname, params, group, helpText, usesGeometry, referencedColumns, lazyEval, handlesNull, isContextual )
     {}
 
     virtual ~QgsScopedExpressionFunction() {}

src/gui/qgsexpressionbuilderwidget.cpp

@@ -445,6 +445,12 @@ void QgsExpressionBuilderWidget::updateFunctionTree()
     QString name = func->name();
     if ( name.startsWith( "_" ) ) // do not display private functions
       continue;
+    if ( func->isContextual() )
+    {
+      //don't show contextual functions by default - it's up the the QgsExpressionContext
+      //object to provide them if supported
+      continue;
+    }
     if ( func->params() != 0 )
       name += "(";
     else if ( !name.startsWith( "$" ) )