Drop generic option, go with custom property specific for GeoPDF exports

It's too messy to try to handle this in a format-agnostic way, as
the requirement for GeoPDF is very unique to GeoPDF (ie SVG and other
formats don't export as mini-read-only-projects with custom layer
trees like GeoPDF does)

python/PyQt6/core/auto_generated/layout/qgslayoutitem.sip.in

@@ -442,40 +442,6 @@ Returns the behavior of this item during exporting to layered exports (e.g. SVG
 .. seealso:: :py:func:`exportLayerName`
 
 .. versionadded:: 3.10
-%End
-
-    QString exportLayerName() const;
-%Docstring
-Returns the name for this item during exporting to layered exports (e.g. SVG or GeoPDF).
-
-By default this is an empty string, which indicates that the item does not need to be placed in any specific
-layer and will automatically be grouped with other items where possible.
-
-If the layer name is non-empty, then the item will be placed in a group with the corresponding name
-during layered exports.
-
-.. seealso:: :py:func:`setExportLayerName`
-
-.. seealso:: :py:func:`exportLayerBehavior`
-
-.. versionadded:: 3.40
-%End
-
-    void setExportLayerName( const QString &name );
-%Docstring
-Sets the ``name`` for this item during exporting to layered exports (e.g. SVG or GeoPDF).
-
-If ``name`` is an empty string then the item does not need to be placed in any specific
-layer and will automatically be grouped with other items where possible.
-
-If the layer ``name`` is non-empty, then the item will be placed in a group with the corresponding name
-during layered exports.
-
-.. seealso:: :py:func:`exportLayerName`
-
-.. seealso:: :py:func:`exportLayerBehavior`
-
-.. versionadded:: 3.40
 %End
 
  virtual int numberExportLayers() const /Deprecated/;

python/core/auto_generated/layout/qgslayoutitem.sip.in

@@ -442,40 +442,6 @@ Returns the behavior of this item during exporting to layered exports (e.g. SVG
 .. seealso:: :py:func:`exportLayerName`
 
 .. versionadded:: 3.10
-%End
-
-    QString exportLayerName() const;
-%Docstring
-Returns the name for this item during exporting to layered exports (e.g. SVG or GeoPDF).
-
-By default this is an empty string, which indicates that the item does not need to be placed in any specific
-layer and will automatically be grouped with other items where possible.
-
-If the layer name is non-empty, then the item will be placed in a group with the corresponding name
-during layered exports.
-
-.. seealso:: :py:func:`setExportLayerName`
-
-.. seealso:: :py:func:`exportLayerBehavior`
-
-.. versionadded:: 3.40
-%End
-
-    void setExportLayerName( const QString &name );
-%Docstring
-Sets the ``name`` for this item during exporting to layered exports (e.g. SVG or GeoPDF).
-
-If ``name`` is an empty string then the item does not need to be placed in any specific
-layer and will automatically be grouped with other items where possible.
-
-If the layer ``name`` is non-empty, then the item will be placed in a group with the corresponding name
-during layered exports.
-
-.. seealso:: :py:func:`exportLayerName`
-
-.. seealso:: :py:func:`exportLayerBehavior`
-
-.. versionadded:: 3.40
 %End
 
  virtual int numberExportLayers() const /Deprecated/;

src/core/layout/qgslayoutexporter.cpp

@@ -628,7 +628,11 @@ QgsLayoutExporter::ExportResult QgsLayoutExporter::exportToPdf( const QString &f
       p.end();
       return layerExportResult;
     };
-    result = handleLayeredExport( items, exportFunc );
+    auto getExportGroupNameFunc = []( QgsLayoutItem * item )->QString
+    {
+      return item->customProperty( QStringLiteral( "pdfExportGroup" ) ).toString();
+    };
+    result = handleLayeredExport( items, exportFunc, getExportGroupNameFunc );
     if ( result != Success )
       return result;
 
@@ -1113,7 +1117,11 @@ QgsLayoutExporter::ExportResult QgsLayoutExporter::exportToSvg( const QString &f
       {
         return renderToLayeredSvg( settings, width, height, i, bounds, fileName, layerId, layerDetail.name, svg, svgDocRoot, settings.exportMetadata );
       };
-      ExportResult res = handleLayeredExport( items, exportFunc );
+      auto getExportGroupNameFunc = []( QgsLayoutItem * )->QString
+      {
+        return QString();
+      };
+      ExportResult res = handleLayeredExport( items, exportFunc, getExportGroupNameFunc );
       if ( res != Success )
         return res;
 
@@ -1771,7 +1779,8 @@ QString nameForLayerWithItems( const QList< QGraphicsItem * > &items, unsigned i
 }
 
 QgsLayoutExporter::ExportResult QgsLayoutExporter::handleLayeredExport( const QList<QGraphicsItem *> &items,
-    const std::function<QgsLayoutExporter::ExportResult( unsigned int, const QgsLayoutItem::ExportLayerDetail & )> &exportFunc )
+    const std::function<QgsLayoutExporter::ExportResult( unsigned int, const QgsLayoutItem::ExportLayerDetail & )> &exportFunc,
+    const std::function<QString( QgsLayoutItem *item )> &getItemExportGroupFunc )
 {
   LayoutItemHider itemHider( items );
   ( void )itemHider;
@@ -1793,7 +1802,7 @@ QgsLayoutExporter::ExportResult QgsLayoutExporter::handleLayeredExport( const QL
     if ( layoutItem )
     {
       QgsLayoutItem::ExportLayerBehavior itemExportBehavior = layoutItem->exportLayerBehavior();
-      thisItemExportGroupName = layoutItem->exportLayerName();
+      thisItemExportGroupName = getItemExportGroupFunc( layoutItem );
       if ( !thisItemExportGroupName.isEmpty() )
       {
         if ( thisItemExportGroupName != previousItemGroup && !currentLayerItems.empty() )

src/core/layout/qgslayoutexporter.h

@@ -776,7 +776,10 @@ class CORE_EXPORT QgsLayoutExporter
     bool georeferenceOutputPrivate( const QString &file, QgsLayoutItemMap *referenceMap = nullptr,
                                     const QRectF &exportRegion = QRectF(), double dpi = -1, bool includeGeoreference = true, bool includeMetadata = false ) const;
 
-    ExportResult handleLayeredExport( const QList<QGraphicsItem *> &items, const std::function<QgsLayoutExporter::ExportResult( unsigned int layerId, const QgsLayoutItem::ExportLayerDetail &layerDetails )> &exportFunc );
+    ExportResult handleLayeredExport( const QList<QGraphicsItem *> &items,
+                                      const std::function<QgsLayoutExporter::ExportResult( unsigned int layerId, const QgsLayoutItem::ExportLayerDetail &layerDetails )> &exportFunc,
+                                      const std::function<QString( QgsLayoutItem *item )> &getItemExportGroupFunc
+                                    );
 
     static QgsVectorSimplifyMethod createExportSimplifyMethod();
     static QgsMaskRenderSettings createExportMaskSettings();

src/core/layout/qgslayoutitem.cpp

@@ -243,16 +243,6 @@ QgsLayoutItem::ExportLayerBehavior QgsLayoutItem::exportLayerBehavior() const
   return CanGroupWithAnyOtherItem;
 }
 
-QString QgsLayoutItem::exportLayerName() const
-{
-  return mExportLayerName;
-}
-
-void QgsLayoutItem::setExportLayerName( const QString &name )
-{
-  mExportLayerName = name;
-}
-
 int QgsLayoutItem::numberExportLayers() const
 {
   return 0;
@@ -643,7 +633,6 @@ bool QgsLayoutItem::writeXml( QDomElement &parentElement, QDomDocument &doc, con
   element.setAttribute( QStringLiteral( "size" ), mItemSize.encodeSize() );
   element.setAttribute( QStringLiteral( "itemRotation" ), QString::number( mItemRotation ) );
   element.setAttribute( QStringLiteral( "groupUuid" ), mParentGroupUuid );
-  element.setAttribute( QStringLiteral( "exportLayer" ), mExportLayerName );
 
   element.setAttribute( QStringLiteral( "zValue" ), QString::number( zValue() ) );
   element.setAttribute( QStringLiteral( "visibility" ), isVisible() );
@@ -834,7 +823,6 @@ bool QgsLayoutItem::readXml( const QDomElement &element, const QDomDocument &doc
 
   mExcludeFromExports = element.attribute( QStringLiteral( "excludeFromExports" ), QStringLiteral( "0" ) ).toInt();
   mEvaluatedExcludeFromExports = mExcludeFromExports;
-  mExportLayerName = element.attribute( QStringLiteral( "exportLayer" ) );
 
   const bool result = readPropertiesFromElement( element, doc, context );
 

src/core/layout/qgslayoutitem.h

@@ -475,36 +475,6 @@ class CORE_EXPORT QgsLayoutItem : public QgsLayoutObject, public QGraphicsRectIt
      */
     virtual ExportLayerBehavior exportLayerBehavior() const;
 
-    /**
-     * Returns the name for this item during exporting to layered exports (e.g. SVG or GeoPDF).
-     *
-     * By default this is an empty string, which indicates that the item does not need to be placed in any specific
-     * layer and will automatically be grouped with other items where possible.
-     *
-     * If the layer name is non-empty, then the item will be placed in a group with the corresponding name
-     * during layered exports.
-     *
-     * \see setExportLayerName()
-     * \see exportLayerBehavior()
-     * \since QGIS 3.40
-     */
-    QString exportLayerName() const;
-
-    /**
-     * Sets the \a name for this item during exporting to layered exports (e.g. SVG or GeoPDF).
-     *
-     * If \a name is an empty string then the item does not need to be placed in any specific
-     * layer and will automatically be grouped with other items where possible.
-     *
-     * If the layer \a name is non-empty, then the item will be placed in a group with the corresponding name
-     * during layered exports.
-     *
-     * \see exportLayerName()
-     * \see exportLayerBehavior()
-     * \since QGIS 3.40
-     */
-    void setExportLayerName( const QString &name );
-
     /**
      * Returns the number of layers that this item requires for exporting during layered exports (e.g. SVG).
      * Returns 0 if this item is to be placed on the same layer as the previous item,
@@ -1348,8 +1318,6 @@ class CORE_EXPORT QgsLayoutItem : public QgsLayoutObject, public QGraphicsRectIt
     //! Whether item should be excluded in exports
     bool mExcludeFromExports = false;
 
-    QString mExportLayerName;
-
     /**
      * Temporary evaluated item exclusion. Data defined properties may mean
      * this value differs from mExcludeFromExports.

src/gui/layout/qgslayoutitemwidget.cpp

@@ -747,7 +747,7 @@ void QgsLayoutItemPropertiesWidget::setValuesForGuiNonPositionElements()
   whileBlocking( mOpacityWidget )->setOpacity( mItem->itemOpacity() );
   whileBlocking( mItemRotationSpinBox )->setValue( mItem->itemRotation() );
   whileBlocking( mExcludeFromPrintsCheckBox )->setChecked( mItem->excludeFromExports() );
-  whileBlocking( mExportGroupNameCombo )->setCurrentText( mItem->exportLayerName() );
+  whileBlocking( mExportGroupNameCombo )->setCurrentText( mItem->customProperty( QStringLiteral( "pdfExportGroup" ) ).toString() );
 }
 
 void QgsLayoutItemPropertiesWidget::initializeDataDefinedButtons()
@@ -795,8 +795,9 @@ void QgsLayoutItemPropertiesWidget::setValuesForGuiElements()
     QStringList existingGroups;
     for ( const QgsLayoutItem *item : std::as_const( items ) )
     {
-      if ( !item->exportLayerName().isEmpty() && !existingGroups.contains( item->exportLayerName() ) )
-        existingGroups.append( item->exportLayerName() );
+      const QString groupName = item->customProperty( QStringLiteral( "pdfExportGroup" ) ).toString();
+      if ( !groupName.isEmpty() && !existingGroups.contains( groupName ) )
+        existingGroups.append( groupName );
     }
 
     std::sort( existingGroups.begin(), existingGroups.end(), [ = ]( const QString & a, const QString & b ) -> bool
@@ -852,7 +853,7 @@ void QgsLayoutItemPropertiesWidget::exportGroupNameEditingFinished()
   if ( mItem )
   {
     mItem->layout()->undoStack()->beginCommand( mItem, tr( "Change Export Group Name" ), QgsLayoutItem::UndoExportLayerName );
-    mItem->setExportLayerName( mExportGroupNameCombo->currentText() );
+    mItem->setCustomProperty( QStringLiteral( "pdfExportGroup" ), mExportGroupNameCombo->currentText() );
     mItem->layout()->undoStack()->endCommand();
   }
 }