Don't return const references to implicitly shared Qt classes

Instead return the inexpensive copies. Should provide extra safety
against issues like #14822

(refs #14822)

Author: nyalldawson

python/analysis/raster/qgsrelief.sip

@@ -26,7 +26,7 @@ class QgsRelief
 
     void clearReliefColors();
     void addReliefColorClass( const QgsRelief::ReliefColor& color );
-    const QList< QgsRelief::ReliefColor >& reliefColors() const;
+    QList< QgsRelief::ReliefColor > reliefColors() const;
     void setReliefColors( const QList< QgsRelief::ReliefColor >& c );
 
     /** Calculates class breaks according with the method of Buenzli (2011) using an iterative algorithm for segmented regression

python/core/composer/qgsatlascomposition.sip

@@ -145,7 +145,7 @@ public:
      * @see setPredefinedScales
      * @see QgsComposerMap::atlasScalingMode
      */
-    const QVector<qreal>& predefinedScales() const;
+    QVector<qreal> predefinedScales() const;
 
     /** Sets the list of predefined scales for the atlas. This is used
      * for maps which are set to the predefined atlas scaling mode.

python/core/composer/qgscomposerhtml.sip

@@ -51,7 +51,7 @@ class QgsComposerHtml: QgsComposerMultiFrame
      * @see setUrl
      * @see contentMode
      */
-    const QUrl& url() const;
+    QUrl url() const;
 
     /** Sets the HTML to display in the item when the item is using
      * the QgsComposerHtml::ManualHtml mode. Setting the HTML using this function

python/core/composer/qgscomposition.sip

@@ -235,7 +235,7 @@ class QgsComposition : QGraphicsScene, QgsExpressionContextGenerator
     double snapGridOffsetY() const;
 
     void setGridPen( const QPen& p );
-    const QPen& gridPen() const;
+    QPen gridPen() const;
 
     void setGridStyle( const GridStyle s );
     GridStyle gridStyle() const;

python/core/layertree/qgslayertreemodel.sip

@@ -228,7 +228,7 @@ class QgsLayerTreeModel : QAbstractItemModel
      */
     void refreshScaleBasedLayers( const QModelIndex& index = QModelIndex() );
 
-    static const QIcon& iconGroup();
+    static QIcon iconGroup();
 
     //! Filter nodes from QgsMapLayerLegend according to the current filtering rules
     QList<QgsLayerTreeModelLegendNode*> filterLegendNodes( const QList<QgsLayerTreeModelLegendNode*>& nodes );

python/core/qgsdataitem.sip

@@ -308,12 +308,12 @@ class QgsLayerItem : QgsDataItem
     virtual QString comments() const;
 
   public:
-    static const QIcon &iconPoint();
-    static const QIcon &iconLine();
-    static const QIcon &iconPolygon();
-    static const QIcon &iconTable();
-    static const QIcon &iconRaster();
-    static const QIcon &iconDefault();
+    static QIcon iconPoint();
+    static QIcon iconLine();
+    static QIcon iconPolygon();
+    static QIcon iconTable();
+    static QIcon iconRaster();
+    static QIcon iconDefault();
 
     virtual QString layerName() const;
 };
@@ -331,8 +331,8 @@ class QgsDataCollectionItem : QgsDataItem
 
     void addChild( QgsDataItem *item /Transfer/ );
 
-    static const QIcon &iconDir(); // shared icon: open/closed directory
-    static const QIcon &iconDataCollection(); // default icon for data collection
+    static QIcon iconDir(); // shared icon: open/closed directory
+    static QIcon iconDataCollection(); // default icon for data collection
 };
 
 /** A directory: contains subdirectories and layers */
@@ -477,7 +477,7 @@ class QgsFavoritesItem : QgsDataCollectionItem
     void removeDirectory( QgsDirectoryItem *item );
 
     //! Icon for favorites group
-    static const QIcon &iconFavorites();
+    static QIcon iconFavorites();
 };
 
 /** A zip file: contains layers, using GDAL/OGR VSIFILE mechanism */
@@ -492,7 +492,7 @@ class QgsZipItem : QgsDataCollectionItem
     ~QgsZipItem();
 
     QVector<QgsDataItem*> createChildren();
-    const QStringList & getZipFileList();
+    QStringList getZipFileList();
 
     //! @note not available via python bindings
     // static QVector<dataItem_t *> mDataItemPtr;
@@ -504,6 +504,6 @@ class QgsZipItem : QgsDataCollectionItem
     //! @note available in python as itemFromFilePath
     static QgsDataItem* itemFromPath( QgsDataItem* parent, const QString& filePath, const QString& name, const QString& path ) /Factory,PyName=itemFromFilePath/;
 
-    static const QIcon &iconZip();
+    static QIcon iconZip();
 
 };

python/core/qgsexpressionfieldbuffer.sip

@@ -64,5 +64,5 @@ class QgsExpressionFieldBuffer
      */
     void updateFields( QgsFields& flds );
 
-    const QList<QgsExpressionFieldBuffer::ExpressionField>& expressions() const;
+    QList<QgsExpressionFieldBuffer::ExpressionField> expressions() const;
 };

python/core/qgsnetworkaccessmanager.sip

@@ -46,7 +46,7 @@ class QgsNetworkAccessManager : QNetworkAccessManager
     const QNetworkProxy &fallbackProxy() const;
 
     //! retrieve exclude list (urls shouldn't use the fallback proxy)
-    const QStringList &excludeList() const;
+    QStringList excludeList() const;
 
     //! set fallback proxy and URL that shouldn't use it.
     void setFallbackProxyAndExcludes( const QNetworkProxy &proxy, const QStringList &excludes );

python/core/qgsproviderregistry.sip

@@ -29,7 +29,7 @@ class QgsProviderRegistry
     QString pluginList( bool asHtml = false ) const;
 
     /** Return library directory where plugins are found */
-    const QDir & libraryDirectory() const;
+    QDir libraryDirectory() const;
 
     /** Set library directory where to search for plugins */
     void setLibraryDirectory( const QDir & path );

python/core/qgsrelationmanager.sip

@@ -25,7 +25,7 @@ class QgsRelationManager : QObject
      *
      * @return A QMap where the key is the relation id, the value the relation object.
      */
-    const QMap<QString, QgsRelation>& relations() const;
+    QMap<QString, QgsRelation> relations() const;
 
     /**
      * Add a relation.