Expose layers field names to expression widget

Fixes #37544

python/gui/auto_generated/qgsexpressiontreeview.sip.in

@@ -68,6 +68,7 @@ Gets the type of expression item, e.g., header, field, ExpressionNode.
     static const int ITEM_TYPE_ROLE;
     static const int SEARCH_TAGS_ROLE;
     static const int ITEM_NAME_ROLE;
+    static const int LAYER_ID_ROLE;
 
 };
 

src/gui/qgsexpressionbuilderwidget.cpp

@@ -507,16 +507,16 @@ void QgsExpressionBuilderWidget::loadFieldsAndValues( const QMap<QString, QStrin
   // This is not maintained and setLayer() should be used instead.
 }
 
-void QgsExpressionBuilderWidget::fillFieldValues( const QString &fieldName, int countLimit, bool forceUsedValues )
+void QgsExpressionBuilderWidget::fillFieldValues( const QString &fieldName, QgsVectorLayer *layer, int countLimit, bool forceUsedValues )
 {
   // TODO We should really return a error the user of the widget that
   // the there is no layer set.
-  if ( !mLayer )
+  if ( !layer )
     return;
 
   // TODO We should thread this so that we don't hold the user up if the layer is massive.
 
-  const QgsFields fields = mLayer->fields();
+  const QgsFields fields = layer->fields();
   int fieldIndex = fields.lookupField( fieldName );
 
   if ( fieldIndex < 0 )
@@ -534,7 +534,7 @@ void QgsExpressionBuilderWidget::fillFieldValues( const QString &fieldName, int
   }
   else
   {
-    values = qgis::setToList( mLayer->uniqueValues( fieldIndex, countLimit ) );
+    values = qgis::setToList( layer->uniqueValues( fieldIndex, countLimit ) );
   }
   std::sort( values.begin(), values.end() );
 
@@ -564,7 +564,7 @@ void QgsExpressionBuilderWidget::fillFieldValues( const QString &fieldName, int
     else
       strValue = '\'' + value.toString().replace( '\'', QLatin1String( "''" ) ) + '\'';
 
-    QString representedValue = formatter->representValue( mLayer, fieldIndex, setup.config(), QVariant(), value );
+    QString representedValue = formatter->representValue( layer, fieldIndex, setup.config(), QVariant(), value );
     if ( forceRepresentedValue || representedValue != value.toString() )
       representedValue = representedValue + QStringLiteral( " [" ) + strValue + ']';
 
@@ -852,11 +852,20 @@ void QgsExpressionBuilderWidget::loadSampleValues()
   QgsExpressionItem *item = mExpressionTreeView->currentItem();
   // TODO We should really return a error the user of the widget that
   // the there is no layer set.
-  if ( !mLayer || !item )
+  QgsVectorLayer *layer = nullptr;
+  if ( ! item->data( QgsExpressionItem::LAYER_ID_ROLE ).isNull() )
+  {
+    layer = qobject_cast<QgsVectorLayer *>( QgsProject::instance()->mapLayer( item->data( QgsExpressionItem::LAYER_ID_ROLE ).toString() ) );
+  }
+  else
+  {
+    layer = mLayer;
+  }
+  if ( !layer || !item )
     return;
 
   mValueGroupBox->show();
-  fillFieldValues( item->data( QgsExpressionItem::ITEM_NAME_ROLE ).toString(), 10 );
+  fillFieldValues( item->data( QgsExpressionItem::ITEM_NAME_ROLE ).toString(), layer, 10 );
 }
 
 void QgsExpressionBuilderWidget::loadAllValues()
@@ -864,11 +873,20 @@ void QgsExpressionBuilderWidget::loadAllValues()
   QgsExpressionItem *item = mExpressionTreeView->currentItem();
   // TODO We should really return a error the user of the widget that
   // the there is no layer set.
-  if ( !mLayer || !item )
+  QgsVectorLayer *layer = nullptr;
+  if ( ! item->data( QgsExpressionItem::LAYER_ID_ROLE ).isNull() )
+  {
+    layer = qobject_cast<QgsVectorLayer *>( QgsProject::instance()->mapLayer( item->data( QgsExpressionItem::LAYER_ID_ROLE ).toString() ) );
+  }
+  else
+  {
+    layer = mLayer;
+  }
+  if ( !layer || !item )
     return;
 
   mValueGroupBox->show();
-  fillFieldValues( item->data( QgsExpressionItem::ITEM_NAME_ROLE ).toString(), -1 );
+  fillFieldValues( item->data( QgsExpressionItem::ITEM_NAME_ROLE ).toString(), layer, -1 );
 }
 
 void QgsExpressionBuilderWidget::loadSampleUsedValues()
@@ -876,11 +894,20 @@ void QgsExpressionBuilderWidget::loadSampleUsedValues()
   QgsExpressionItem *item = mExpressionTreeView->currentItem();
   // TODO We should really return a error the user of the widget that
   // the there is no layer set.
-  if ( !mLayer || !item )
+  QgsVectorLayer *layer = nullptr;
+  if ( ! item->data( QgsExpressionItem::LAYER_ID_ROLE ).isNull() )
+  {
+    layer = qobject_cast<QgsVectorLayer *>( QgsProject::instance()->mapLayer( item->data( QgsExpressionItem::LAYER_ID_ROLE ).toString() ) );
+  }
+  else
+  {
+    layer = mLayer;
+  }
+  if ( !layer || !item )
     return;
 
   mValueGroupBox->show();
-  fillFieldValues( item->data( QgsExpressionItem::ITEM_NAME_ROLE ).toString(), 10, true );
+  fillFieldValues( item->data( QgsExpressionItem::ITEM_NAME_ROLE ).toString(), layer, 10, true );
 }
 
 void QgsExpressionBuilderWidget::loadAllUsedValues()
@@ -888,11 +915,20 @@ void QgsExpressionBuilderWidget::loadAllUsedValues()
   QgsExpressionItem *item = mExpressionTreeView->currentItem();
   // TODO We should really return a error the user of the widget that
   // the there is no layer set.
-  if ( !mLayer || !item )
+  QgsVectorLayer *layer = nullptr;
+  if ( ! item->data( QgsExpressionItem::LAYER_ID_ROLE ).isNull() )
+  {
+    layer = qobject_cast<QgsVectorLayer *>( QgsProject::instance()->mapLayer( item->data( QgsExpressionItem::LAYER_ID_ROLE ).toString() ) );
+  }
+  else
+  {
+    layer = mLayer;
+  }
+  if ( !layer || !item )
     return;
 
   mValueGroupBox->show();
-  fillFieldValues( item->data( QgsExpressionItem::ITEM_NAME_ROLE ).toString(), -1, true );
+  fillFieldValues( item->data( QgsExpressionItem::ITEM_NAME_ROLE ).toString(), layer, -1, true );
 }
 
 void QgsExpressionBuilderWidget::txtPython_textChanged()

src/gui/qgsexpressionbuilderwidget.h

@@ -419,7 +419,7 @@ class GUI_EXPORT QgsExpressionBuilderWidget : public QWidget, private Ui::QgsExp
     void clearFunctionMarkers();
     void clearErrors();
     void runPythonCode( const QString &code );
-    void fillFieldValues( const QString &fieldName, int countLimit, bool forceUsedValues = false );
+    void fillFieldValues( const QString &fieldName, QgsVectorLayer *layer, int countLimit, bool forceUsedValues = false );
     QString getFunctionHelp( QgsExpressionFunction *function );
     QString loadFunctionHelp( QgsExpressionItem *functionName );
     QString helpStylesheet() const;

src/gui/qgsexpressiontreeview.cpp

@@ -323,7 +323,7 @@ void QgsExpressionTreeView::updateFunctionTree()
   loadExpressionContext();
 }
 
-void QgsExpressionTreeView::registerItem( const QString &group,
+QgsExpressionItem *QgsExpressionTreeView::registerItem( const QString &group,
     const QString &label,
     const QString &expressionText,
     const QString &helpText,
@@ -366,6 +366,7 @@ void QgsExpressionTreeView::registerItem( const QString &group,
     topLevelItem->setFont( font );
     mModel->appendRow( topLevelItem );
   }
+  return item;
 }
 
 void QgsExpressionTreeView::registerItemForAllGroups( const QStringList &groups, const QString &label, const QString &expressionText, const QString &helpText, QgsExpressionItem::ItemType type, bool highlightedItem, int sortOrder, const QStringList &tags )
@@ -414,7 +415,28 @@ void QgsExpressionTreeView::loadLayers()
   for ( ; layerIt != layers.constEnd(); ++layerIt )
   {
     QIcon icon = QgsIconUtils::iconForLayer( layerIt.value() );
-    registerItem( QStringLiteral( "Map Layers" ), layerIt.value()->name(), QStringLiteral( "'%1'" ).arg( layerIt.key() ), formatLayerHelp( layerIt.value() ), QgsExpressionItem::ExpressionNode, false, 99, icon );
+    QgsExpressionItem *parentItem = registerItem( QStringLiteral( "Map Layers" ), layerIt.value()->name(), QStringLiteral( "'%1'" ).arg( layerIt.key() ), formatLayerHelp( layerIt.value() ), QgsExpressionItem::ExpressionNode, false, 99, icon );
+    loadLayerFields( qobject_cast<QgsVectorLayer *>( layerIt.value() ), parentItem );
+  }
+
+}
+
+void QgsExpressionTreeView::loadLayerFields( QgsVectorLayer *layer, QgsExpressionItem *parentItem )
+{
+  const QgsFields fields { layer->fields() };
+  for ( int fieldIdx = 0; fieldIdx < layer->fields().count(); ++fieldIdx )
+  {
+    const QgsField field = fields.at( fieldIdx );
+    QIcon icon = fields.iconForField( fieldIdx );
+    const QString label { field.displayNameWithAlias() };
+    QgsExpressionItem *item = new QgsExpressionItem( label, " '" + field.name() + "' ", QString(), QgsExpressionItem::Field );
+    item->setData( label, Qt::UserRole );
+    item->setData( 99, QgsExpressionItem::CUSTOM_SORT_ROLE );
+    item->setData( QStringList(), QgsExpressionItem::SEARCH_TAGS_ROLE );
+    item->setData( field.name(), QgsExpressionItem::ITEM_NAME_ROLE );
+    item->setData( layer->id(), QgsExpressionItem::LAYER_ID_ROLE );
+    item->setIcon( icon );
+    parentItem->appendRow( item );
   }
 }
 

src/gui/qgsexpressiontreeview.h

@@ -98,6 +98,8 @@ class GUI_EXPORT QgsExpressionItem : public QStandardItem
     static const int SEARCH_TAGS_ROLE = Qt::UserRole + 3;
     //! Item name role
     static const int ITEM_NAME_ROLE = Qt::UserRole + 4;
+    //! Layer ID role \since QGIS 3.24
+    static const int LAYER_ID_ROLE = Qt::UserRole + 5;
 
   private:
     QString mExpressionText;
@@ -318,13 +320,13 @@ class GUI_EXPORT QgsExpressionTreeView : public QTreeView
      * \param tags tags to find function
      * \param name name of the item
      */
-    void registerItem( const QString &group, const QString &label, const QString &expressionText,
+    QgsExpressionItem *registerItem( const QString &group, const QString &label, const QString &expressionText,
-                       const QString &helpText = QString(),
+                                     const QString &helpText = QString(),
-                       QgsExpressionItem::ItemType type = QgsExpressionItem::ExpressionNode,
+                                     QgsExpressionItem::ItemType type = QgsExpressionItem::ExpressionNode,
-                       bool highlightedItem = false, int sortOrder = 1,
+                                     bool highlightedItem = false, int sortOrder = 1,
-                       const QIcon &icon = QIcon(),
+                                     const QIcon &icon = QIcon(),
-                       const QStringList &tags = QStringList(),
+                                     const QStringList &tags = QStringList(),
-                       const QString &name = QString() );
+                                     const QString &name = QString() );
 
     /**
      * Registers a node item for the expression builder, adding multiple items when the function exists in multiple groups
@@ -345,6 +347,7 @@ class GUI_EXPORT QgsExpressionTreeView : public QTreeView
     void loadExpressionContext();
     void loadRelations();
     void loadLayers();
+    void loadLayerFields( QgsVectorLayer *layer, QgsExpressionItem *parentItem );
     void loadFieldNames();
 
     /**