Deprecate vector layer setter/getter within QgsSymbol

It's not used, and potentially very dangerous

python/core/auto_generated/symbology/qgssymbol.sip.in

@@ -387,14 +387,21 @@ Returns whether the symbol utilizes any data defined properties.
 .. versionadded:: 2.12
 %End
 
-    void setLayer( const QgsVectorLayer *layer );
+ void setLayer( const QgsVectorLayer *layer ) /Deprecated/;
 %Docstring
 
 .. note::
 
    the layer will be NULL after stopRender
+
+.. deprecated:: Will be removed in QGIS 4.0
+%End
+
+ const QgsVectorLayer *layer() const /Deprecated/;
+%Docstring
+
+.. deprecated:: Will be removed in QGIS 4.0
 %End
-    const QgsVectorLayer *layer() const;
 
     void renderFeature( const QgsFeature &feature, QgsRenderContext &context, int layer = -1, bool selected = false, bool drawVertexMarker = false, int currentVertexMarkerType = 0, int currentVertexMarkerSize = 0 );
 %Docstring

src/core/symbology/qgssymbol.cpp

@@ -78,6 +78,7 @@ QgsProperty scaleWholeSymbol( double scaleFactorX, double scaleFactorY, const Qg
 
 ////////////////////
 
+Q_NOWARN_DEPRECATED_PUSH // because of deprecated mLayer
 QgsSymbol::QgsSymbol( SymbolType type, const QgsSymbolLayerList &layers )
   : mType( type )
   , mLayers( layers )
@@ -97,6 +98,7 @@ QgsSymbol::QgsSymbol( SymbolType type, const QgsSymbolLayerList &layers )
     }
   }
 }
+Q_NOWARN_DEPRECATED_POP
 
 QPolygonF QgsSymbol::_getLineString( QgsRenderContext &context, const QgsCurve &curve, bool clipToExtent )
 {
@@ -434,7 +436,9 @@ void QgsSymbol::stopRender( QgsRenderContext &context )
 
   mSymbolRenderContext.reset( nullptr );
 
+  Q_NOWARN_DEPRECATED_PUSH
   mLayer = nullptr;
+  Q_NOWARN_DEPRECATED_POP
 }
 
 void QgsSymbol::setColor( const QColor &color )
@@ -669,6 +673,20 @@ bool QgsSymbol::hasDataDefinedProperties() const
   return false;
 }
 
+void QgsSymbol::setLayer( const QgsVectorLayer *layer )
+{
+  Q_NOWARN_DEPRECATED_PUSH
+  mLayer = layer;
+  Q_NOWARN_DEPRECATED_POP
+}
+
+const QgsVectorLayer *QgsSymbol::layer() const
+{
+  Q_NOWARN_DEPRECATED_PUSH
+  return mLayer;
+  Q_NOWARN_DEPRECATED_POP
+}
+
 ///@cond PRIVATE
 
 /**
@@ -1554,7 +1572,9 @@ QgsMarkerSymbol *QgsMarkerSymbol::clone() const
 {
   QgsMarkerSymbol *cloneSymbol = new QgsMarkerSymbol( cloneLayers() );
   cloneSymbol->setOpacity( mOpacity );
+  Q_NOWARN_DEPRECATED_PUSH
   cloneSymbol->setLayer( mLayer );
+  Q_NOWARN_DEPRECATED_POP
   cloneSymbol->setClipFeaturesToExtent( mClipFeaturesToExtent );
   return cloneSymbol;
 }
@@ -1771,7 +1791,9 @@ QgsLineSymbol *QgsLineSymbol::clone() const
 {
   QgsLineSymbol *cloneSymbol = new QgsLineSymbol( cloneLayers() );
   cloneSymbol->setOpacity( mOpacity );
+  Q_NOWARN_DEPRECATED_PUSH
   cloneSymbol->setLayer( mLayer );
+  Q_NOWARN_DEPRECATED_POP
   cloneSymbol->setClipFeaturesToExtent( mClipFeaturesToExtent );
   return cloneSymbol;
 }
@@ -1889,7 +1911,9 @@ QgsFillSymbol *QgsFillSymbol::clone() const
 {
   QgsFillSymbol *cloneSymbol = new QgsFillSymbol( cloneLayers() );
   cloneSymbol->setOpacity( mOpacity );
+  Q_NOWARN_DEPRECATED_PUSH
   cloneSymbol->setLayer( mLayer );
+  Q_NOWARN_DEPRECATED_POP
   cloneSymbol->setClipFeaturesToExtent( mClipFeaturesToExtent );
   return cloneSymbol;
 }

src/core/symbology/qgssymbol.h

@@ -394,9 +394,16 @@ class CORE_EXPORT QgsSymbol
      */
     bool hasDataDefinedProperties() const;
 
-    //! \note the layer will be NULL after stopRender
+    /**
-    void setLayer( const QgsVectorLayer *layer ) { mLayer = layer; }
+     * \note the layer will be NULL after stopRender
-    const QgsVectorLayer *layer() const { return mLayer; }
+     * \deprecated Will be removed in QGIS 4.0
+     */
+    Q_DECL_DEPRECATED void setLayer( const QgsVectorLayer *layer ) SIP_DEPRECATED;
+
+    /**
+     * \deprecated Will be removed in QGIS 4.0
+     */
+    Q_DECL_DEPRECATED const QgsVectorLayer *layer() const SIP_DEPRECATED;
 
     /**
      * Render a feature. Before calling this the startRender() method should be called to initialize
@@ -483,7 +490,7 @@ class CORE_EXPORT QgsSymbol
     RenderHints mRenderHints = nullptr;
     bool mClipFeaturesToExtent = true;
 
-    const QgsVectorLayer *mLayer = nullptr; //current vectorlayer
+    Q_DECL_DEPRECATED const QgsVectorLayer *mLayer = nullptr; //current vectorlayer
 
   private:
 #ifdef SIP_RUN

src/gui/symbology/qgssymbolselectordialog.cpp

@@ -472,7 +472,9 @@ void QgsSymbolSelectorWidget::layerChanged()
   {
     mDataDefineRestorer.reset();
     // then it must be a symbol
+    Q_NOWARN_DEPRECATED_PUSH
     currentItem->symbol()->setLayer( mVectorLayer );
+    Q_NOWARN_DEPRECATED_POP
     // Now populate symbols of that type using the symbols list widget:
     QgsSymbolsListWidget *symbolsList = new QgsSymbolsListWidget( currentItem->symbol(), mStyle, mAdvancedMenu, this, mVectorLayer );
     symbolsList->setContext( mContext );