From 306065e5c47e7f9a3b4d87c12448ed314048f8d3 Mon Sep 17 00:00:00 2001
From: Blottiere Paul <blottiere.paul@gmail.com>
Date: Fri, 8 May 2020 23:36:11 +0200
Subject: [PATCH 01/11] Update API

---
 src/core/qgslegendrenderer.cpp             | 7 +++++--
 src/core/qgslegendrenderer.h               | 2 +-
 src/server/services/wms/qgswmsrenderer.cpp | 5 +----
 3 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/src/core/qgslegendrenderer.cpp b/src/core/qgslegendrenderer.cpp
index 78637fcff39..954c6a096fe 100644
--- a/src/core/qgslegendrenderer.cpp
+++ b/src/core/qgslegendrenderer.cpp
@@ -68,14 +68,17 @@ void QgsLegendRenderer::drawLegend( QPainter *painter )
   paintAndDetermineSize( context );
 }
 
-void QgsLegendRenderer::exportLegendToJson( const QgsRenderContext &context, QJsonObject &json )
+QJsonObject QgsLegendRenderer::exportLegendToJson( const QgsRenderContext &context )
 {
+  QJsonObject json;
+
   QgsLayerTreeGroup *rootGroup = mLegendModel->rootGroup();
   if ( !rootGroup )
-    return;
+    return json;
 
   json[QStringLiteral( "title" )] = mSettings.title();
   exportLegendToJson( context, rootGroup, json );
+  return json;
 }
 
 void QgsLegendRenderer::exportLegendToJson( const QgsRenderContext &context, QgsLayerTreeGroup *nodeGroup, QJsonObject &json )
diff --git a/src/core/qgslegendrenderer.h b/src/core/qgslegendrenderer.h
index ed02ca61123..12fdbd7f55c 100644
--- a/src/core/qgslegendrenderer.h
+++ b/src/core/qgslegendrenderer.h
@@ -100,7 +100,7 @@ class CORE_EXPORT QgsLegendRenderer
      *
      * \since QGIS 3.8
      */
-    void exportLegendToJson( const QgsRenderContext &context, QJsonObject &json );
+    QJsonObject exportLegendToJson( const QgsRenderContext &context );
 
     /**
      * Sets the \a style of a \a node.
diff --git a/src/server/services/wms/qgswmsrenderer.cpp b/src/server/services/wms/qgswmsrenderer.cpp
index ba004e9913b..10a4b65c6b3 100644
--- a/src/server/services/wms/qgswmsrenderer.cpp
+++ b/src/server/services/wms/qgswmsrenderer.cpp
@@ -194,11 +194,8 @@ namespace QgsWms
     QgsLegendRenderer renderer( &model, settings );
 
     // rendering
-    QJsonObject json;
     QgsRenderContext renderContext;
-    renderer.exportLegendToJson( renderContext, json );
-
-    return json;
+    return renderer.exportLegendToJson( renderContext );
   }
 
   void QgsRenderer::runHitTest( const QgsMapSettings &mapSettings, HitTest &hitTest ) const

From 0772591784337416721b5f37281d28c286c4ebb2 Mon Sep 17 00:00:00 2001
From: Blottiere Paul <blottiere.paul@gmail.com>
Date: Fri, 8 May 2020 23:36:36 +0200
Subject: [PATCH 02/11] Update unit tests

---
 tests/src/core/testqgslegendrenderer.cpp | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/tests/src/core/testqgslegendrenderer.cpp b/tests/src/core/testqgslegendrenderer.cpp
index 696659ed38c..bccf8bf2cf1 100644
--- a/tests/src/core/testqgslegendrenderer.cpp
+++ b/tests/src/core/testqgslegendrenderer.cpp
@@ -101,10 +101,8 @@ static QJsonObject _renderJsonLegend( QgsLayerTreeModel *legendModel, const QgsL
 {
   QgsLegendRenderer legendRenderer( legendModel, settings );
 
-  QJsonObject json;
   QgsRenderContext context;
-  legendRenderer.exportLegendToJson( context, json );
-  return json;
+  return legendRenderer.exportLegendToJson( context );
 }
 
 static bool _verifyImage( const QString &testName, QString &report, int diff = 30 )

From 6550dad44987a7623b601b125e12297d8d70d7ea Mon Sep 17 00:00:00 2001
From: Blottiere Paul <blottiere.paul@gmail.com>
Date: Fri, 8 May 2020 23:36:47 +0200
Subject: [PATCH 03/11] Update sip

---
 python/core/auto_generated/qgslegendrenderer.sip.in | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/python/core/auto_generated/qgslegendrenderer.sip.in b/python/core/auto_generated/qgslegendrenderer.sip.in
index 64b0ce9188a..575cbe4f65b 100644
--- a/python/core/auto_generated/qgslegendrenderer.sip.in
+++ b/python/core/auto_generated/qgslegendrenderer.sip.in
@@ -81,7 +81,7 @@ Draws the legend using a given render ``context``. The legend will occupy the ar
 .. versionadded:: 3.6
 %End
 
-    void exportLegendToJson( const QgsRenderContext &context, QJsonObject &json );
+    QJsonObject exportLegendToJson( const QgsRenderContext &context );
 %Docstring
 Renders the legend in a ``json`` object.
 

From 2cbf4a12ea68dad9321e9380cebcc9cf983d1296 Mon Sep 17 00:00:00 2001
From: Blottiere Paul <blottiere.paul@gmail.com>
Date: Mon, 11 May 2020 11:32:45 +0200
Subject: [PATCH 04/11] Update another method

---
 src/core/qgslegendrenderer.cpp | 9 +++++----
 src/core/qgslegendrenderer.h   | 2 +-
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/src/core/qgslegendrenderer.cpp b/src/core/qgslegendrenderer.cpp
index 954c6a096fe..452eeb6a050 100644
--- a/src/core/qgslegendrenderer.cpp
+++ b/src/core/qgslegendrenderer.cpp
@@ -76,13 +76,14 @@ QJsonObject QgsLegendRenderer::exportLegendToJson( const QgsRenderContext &conte
   if ( !rootGroup )
     return json;
 
+  json = exportLegendToJson( context, rootGroup );
   json[QStringLiteral( "title" )] = mSettings.title();
-  exportLegendToJson( context, rootGroup, json );
   return json;
 }
 
-void QgsLegendRenderer::exportLegendToJson( const QgsRenderContext &context, QgsLayerTreeGroup *nodeGroup, QJsonObject &json )
+QJsonObject QgsLegendRenderer::exportLegendToJson( const QgsRenderContext &context, QgsLayerTreeGroup *nodeGroup )
 {
+  QJsonObject json;
   QJsonArray nodes;
   const QList<QgsLayerTreeNode *> childNodes = nodeGroup->children();
   for ( QgsLayerTreeNode *node : childNodes )
@@ -93,10 +94,9 @@ void QgsLegendRenderer::exportLegendToJson( const QgsRenderContext &context, Qgs
       const QModelIndex idx = mLegendModel->node2index( nodeGroup );
       const QString text = mLegendModel->data( idx, Qt::DisplayRole ).toString();
 
-      QJsonObject group;
+      QJsonObject group = exportLegendToJson( context, nodeGroup );
       group[ QStringLiteral( "type" ) ] = QStringLiteral( "group" );
       group[ QStringLiteral( "title" ) ] = text;
-      exportLegendToJson( context, nodeGroup, group );
       nodes.append( group );
     }
     else if ( QgsLayerTree::isLayer( node ) )
@@ -141,6 +141,7 @@ void QgsLegendRenderer::exportLegendToJson( const QgsRenderContext &context, Qgs
   }
 
   json[QStringLiteral( "nodes" )] = nodes;
+  return json;
 }
 
 QSizeF QgsLegendRenderer::paintAndDetermineSize( QgsRenderContext &context )
diff --git a/src/core/qgslegendrenderer.h b/src/core/qgslegendrenderer.h
index 12fdbd7f55c..e8b74cc3484 100644
--- a/src/core/qgslegendrenderer.h
+++ b/src/core/qgslegendrenderer.h
@@ -234,7 +234,7 @@ class CORE_EXPORT QgsLegendRenderer
      *
      * \since QGIS 3.8
      */
-    void exportLegendToJson( const QgsRenderContext &context, QgsLayerTreeGroup *nodeGroup, QJsonObject &json );
+    QJsonObject exportLegendToJson( const QgsRenderContext &context, QgsLayerTreeGroup *nodeGroup );
 
     /**
      * Draws the legend using the specified render \a context, and returns the actual size of the legend.

From 236db3903b139e3460eb5334f10eaa0948dd17c2 Mon Sep 17 00:00:00 2001
From: Blottiere Paul <blottiere.paul@gmail.com>
Date: Mon, 11 May 2020 11:47:32 +0200
Subject: [PATCH 05/11] Update api of exportToJson

---
 .../layertree/qgslayertreemodellegendnode.cpp     |  4 +++-
 src/core/layertree/qgslayertreemodellegendnode.h  |  2 +-
 src/core/qgslegendrenderer.cpp                    | 15 ++++++++-------
 3 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/src/core/layertree/qgslayertreemodellegendnode.cpp b/src/core/layertree/qgslayertreemodellegendnode.cpp
index f714eae01e3..2713f1b3f57 100644
--- a/src/core/layertree/qgslayertreemodellegendnode.cpp
+++ b/src/core/layertree/qgslayertreemodellegendnode.cpp
@@ -84,10 +84,12 @@ QgsLayerTreeModelLegendNode::ItemMetrics QgsLayerTreeModelLegendNode::draw( cons
   return im;
 }
 
-void QgsLayerTreeModelLegendNode::exportToJson( const QgsLegendSettings &settings, const QgsRenderContext &context, QJsonObject &json )
+QJsonObject QgsLayerTreeModelLegendNode::exportToJson( const QgsLegendSettings &settings, const QgsRenderContext &context )
 {
+  QJsonObject json;
   exportSymbolToJson( settings, context, json );
   exportSymbolTextToJson( settings, json );
+  return json;
 }
 
 QSizeF QgsLayerTreeModelLegendNode::drawSymbol( const QgsLegendSettings &settings, ItemContext *ctx, double itemHeight ) const
diff --git a/src/core/layertree/qgslayertreemodellegendnode.h b/src/core/layertree/qgslayertreemodellegendnode.h
index 662e39773ed..4b7a52582c0 100644
--- a/src/core/layertree/qgslayertreemodellegendnode.h
+++ b/src/core/layertree/qgslayertreemodellegendnode.h
@@ -223,7 +223,7 @@ class CORE_EXPORT QgsLayerTreeModelLegendNode : public QObject
      * \param json The json object to update
      * \since QGIS 3.8
      */
-    void exportToJson( const QgsLegendSettings &settings, const QgsRenderContext &context, QJsonObject &json );
+    QJsonObject exportToJson( const QgsLegendSettings &settings, const QgsRenderContext &context );
 
     /**
      * Draws symbol on the left side of the item
diff --git a/src/core/qgslegendrenderer.cpp b/src/core/qgslegendrenderer.cpp
index 452eeb6a050..a2776c83ce5 100644
--- a/src/core/qgslegendrenderer.cpp
+++ b/src/core/qgslegendrenderer.cpp
@@ -101,9 +101,6 @@ QJsonObject QgsLegendRenderer::exportLegendToJson( const QgsRenderContext &conte
     }
     else if ( QgsLayerTree::isLayer( node ) )
     {
-      QJsonObject group;
-      group[ QStringLiteral( "type" ) ] = QStringLiteral( "layer" );
-
       QgsLayerTreeLayer *nodeLayer = QgsLayerTree::toLayer( node );
 
       QString text;
@@ -120,21 +117,25 @@ QJsonObject QgsLegendRenderer::exportLegendToJson( const QgsRenderContext &conte
 
       if ( legendNodes.count() == 1 )
       {
-        legendNodes.at( 0 )->exportToJson( mSettings, context, group );
+        QJsonObject group = legendNodes.at( 0 )->exportToJson( mSettings, context );
+        group[ QStringLiteral( "type" ) ] = QStringLiteral( "layer" );
         nodes.append( group );
       }
       else if ( legendNodes.count() > 1 )
       {
+        QJsonObject group;
+        group[ QStringLiteral( "type" ) ] = QStringLiteral( "layer" );
+        group[ QStringLiteral( "title" ) ] = text;
+
         QJsonArray symbols;
         for ( int j = 0; j < legendNodes.count(); j++ )
         {
           QgsLayerTreeModelLegendNode *legendNode = legendNodes.at( j );
-          QJsonObject symbol;
-          legendNode->exportToJson( mSettings, context, symbol );
+          QJsonObject symbol = legendNode->exportToJson( mSettings, context );
           symbols.append( symbol );
         }
-        group[ QStringLiteral( "title" ) ] = text;
         group[ QStringLiteral( "symbols" ) ] = symbols;
+
         nodes.append( group );
       }
     }

From 555d8863faf06a113102e6c7b228365caa843f2d Mon Sep 17 00:00:00 2001
From: Blottiere Paul <blottiere.paul@gmail.com>
Date: Mon, 11 May 2020 11:48:03 +0200
Subject: [PATCH 06/11] Update sip binding

---
 .../auto_generated/layertree/qgslayertreemodellegendnode.sip.in | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/python/core/auto_generated/layertree/qgslayertreemodellegendnode.sip.in b/python/core/auto_generated/layertree/qgslayertreemodellegendnode.sip.in
index 9df218b7b89..20d954c3b26 100644
--- a/python/core/auto_generated/layertree/qgslayertreemodellegendnode.sip.in
+++ b/python/core/auto_generated/layertree/qgslayertreemodellegendnode.sip.in
@@ -160,7 +160,7 @@ Default implementation calls drawSymbol() and drawSymbolText() methods.
 If ctx is ``None``, this is just first stage when preparing layout - without actual rendering.
 %End
 
-    void exportToJson( const QgsLegendSettings &settings, const QgsRenderContext &context, QJsonObject &json );
+    QJsonObject exportToJson( const QgsLegendSettings &settings, const QgsRenderContext &context );
 %Docstring
 Entry point called from QgsLegendRenderer to do the rendering in a
 JSON object.

From 91a6c5601e5448ce2bf672ca8ec58f623abe2d20 Mon Sep 17 00:00:00 2001
From: Blottiere Paul <blottiere.paul@gmail.com>
Date: Mon, 11 May 2020 13:55:36 +0200
Subject: [PATCH 07/11] Update exportSymbolToJson

---
 .../layertree/qgslayertreemodellegendnode.cpp | 41 +++++++++++--------
 .../layertree/qgslayertreemodellegendnode.h   | 18 +++-----
 2 files changed, 30 insertions(+), 29 deletions(-)

diff --git a/src/core/layertree/qgslayertreemodellegendnode.cpp b/src/core/layertree/qgslayertreemodellegendnode.cpp
index 2713f1b3f57..c6af2c7296e 100644
--- a/src/core/layertree/qgslayertreemodellegendnode.cpp
+++ b/src/core/layertree/qgslayertreemodellegendnode.cpp
@@ -86,9 +86,9 @@ QgsLayerTreeModelLegendNode::ItemMetrics QgsLayerTreeModelLegendNode::draw( cons
 
 QJsonObject QgsLayerTreeModelLegendNode::exportToJson( const QgsLegendSettings &settings, const QgsRenderContext &context )
 {
-  QJsonObject json;
-  exportSymbolToJson( settings, context, json );
-  exportSymbolTextToJson( settings, json );
+  QJsonObject json = exportSymbolToJson( settings, context );
+  const QString text = data( Qt::DisplayRole ).toString();
+  json[ QStringLiteral( "title" ) ] = text;
   return json;
 }
 
@@ -132,18 +132,21 @@ QSizeF QgsLayerTreeModelLegendNode::drawSymbol( const QgsLegendSettings &setting
   return size;
 }
 
-void QgsLayerTreeModelLegendNode::exportSymbolToJson( const QgsLegendSettings &settings, const QgsRenderContext &, QJsonObject &json ) const
+QJsonObject QgsLayerTreeModelLegendNode::exportSymbolToJson( const QgsLegendSettings &settings, const QgsRenderContext & ) const
 {
   const QIcon icon = data( Qt::DecorationRole ).value<QIcon>();
   if ( icon.isNull() )
-    return;
+    return QJsonObject();
 
   const QImage image( icon.pixmap( settings.symbolSize().width(), settings.symbolSize().height() ).toImage() );
   QByteArray byteArray;
   QBuffer buffer( &byteArray );
   image.save( &buffer, "PNG" );
   const QString base64 = QString::fromLatin1( byteArray.toBase64().data() );
+
+  QJsonObject json;
   json[ "icon" ] = base64;
+  return json;
 }
 
 QSizeF QgsLayerTreeModelLegendNode::drawSymbolText( const QgsLegendSettings &settings, ItemContext *ctx, QSizeF symbolSize ) const
@@ -227,12 +230,6 @@ QSizeF QgsLayerTreeModelLegendNode::drawSymbolText( const QgsLegendSettings &set
   return labelSize;
 }
 
-void QgsLayerTreeModelLegendNode::exportSymbolTextToJson( const QgsLegendSettings &, QJsonObject &json ) const
-{
-  const QString text = data( Qt::DisplayRole ).toString();
-  json[ "title" ] = text;
-}
-
 // -------------------------------------------------------------------------
 
 QgsSymbolLegendNode::QgsSymbolLegendNode( QgsLayerTreeLayer *nodeLayer, const QgsLegendSymbolItem &item, QObject *parent )
@@ -663,12 +660,12 @@ QSizeF QgsSymbolLegendNode::drawSymbol( const QgsLegendSettings &settings, ItemC
                  std::max( height + 2 * heightOffset, static_cast< double >( desiredHeight ) ) );
 }
 
-void QgsSymbolLegendNode::exportSymbolToJson( const QgsLegendSettings &settings, const QgsRenderContext &context, QJsonObject &json ) const
+QJsonObject QgsSymbolLegendNode::exportSymbolToJson( const QgsLegendSettings &settings, const QgsRenderContext &context ) const
 {
   const QgsSymbol *s = mCustomSymbol ? mCustomSymbol.get() : mItem.symbol();
   if ( !s )
   {
-    return;
+    return QJsonObject();
   }
 
 
@@ -706,7 +703,10 @@ void QgsSymbolLegendNode::exportSymbolToJson( const QgsLegendSettings &settings,
   QBuffer buffer( &byteArray );
   img.save( &buffer, "PNG" );
   const QString base64 = QString::fromLatin1( byteArray.toBase64().data() );
+
+  QJsonObject json;
   json[ "icon" ] = base64;
+  return json;
 }
 
 void QgsSymbolLegendNode::setEmbeddedInParent( bool embedded )
@@ -864,13 +864,16 @@ QSizeF QgsImageLegendNode::drawSymbol( const QgsLegendSettings &settings, ItemCo
   return settings.wmsLegendSize();
 }
 
-void QgsImageLegendNode::exportSymbolToJson( const QgsLegendSettings &, const QgsRenderContext &, QJsonObject &json ) const
+QJsonObject QgsImageLegendNode::exportSymbolToJson( const QgsLegendSettings &, const QgsRenderContext & ) const
 {
   QByteArray byteArray;
   QBuffer buffer( &byteArray );
   mImage.save( &buffer, "PNG" );
   const QString base64 = QString::fromLatin1( byteArray.toBase64().data() );
+
+  QJsonObject json;
   json[ "icon" ] = base64;
+  return json;
 }
 
 // -------------------------------------------------------------------------
@@ -956,7 +959,7 @@ QSizeF QgsRasterSymbolLegendNode::drawSymbol( const QgsLegendSettings &settings,
   return size;
 }
 
-void QgsRasterSymbolLegendNode::exportSymbolToJson( const QgsLegendSettings &settings, const QgsRenderContext &, QJsonObject &json ) const
+QJsonObject QgsRasterSymbolLegendNode::exportSymbolToJson( const QgsLegendSettings &settings, const QgsRenderContext & ) const
 {
   QImage img = QImage( settings.symbolSize().toSize(), QImage::Format_ARGB32 );
   img.fill( Qt::transparent );
@@ -991,7 +994,10 @@ void QgsRasterSymbolLegendNode::exportSymbolToJson( const QgsLegendSettings &set
   QBuffer buffer( &byteArray );
   img.save( &buffer, "PNG" );
   const QString base64 = QString::fromLatin1( byteArray.toBase64().data() );
+
+  QJsonObject json;
   json[ "icon" ] = base64;
+  return json;
 }
 
 // -------------------------------------------------------------------------
@@ -1080,13 +1086,16 @@ QSizeF QgsWmsLegendNode::drawSymbol( const QgsLegendSettings &settings, ItemCont
   return settings.wmsLegendSize();
 }
 
-void QgsWmsLegendNode::exportSymbolToJson( const QgsLegendSettings &, const QgsRenderContext &, QJsonObject &json ) const
+QJsonObject QgsWmsLegendNode::exportSymbolToJson( const QgsLegendSettings &, const QgsRenderContext & ) const
 {
   QByteArray byteArray;
   QBuffer buffer( &byteArray );
   mImage.save( &buffer, "PNG" );
   const QString base64 = QString::fromLatin1( byteArray.toBase64().data() );
+
+  QJsonObject json;
   json[ "icon" ] = base64;
+  return json;
 }
 
 /* private */
diff --git a/src/core/layertree/qgslayertreemodellegendnode.h b/src/core/layertree/qgslayertreemodellegendnode.h
index 4b7a52582c0..fac8b070689 100644
--- a/src/core/layertree/qgslayertreemodellegendnode.h
+++ b/src/core/layertree/qgslayertreemodellegendnode.h
@@ -241,7 +241,7 @@ class CORE_EXPORT QgsLayerTreeModelLegendNode : public QObject
      * \param json The json object to update
      * \since QGIS 3.8
      */
-    virtual void exportSymbolToJson( const QgsLegendSettings &settings, const QgsRenderContext &context, QJsonObject &json ) const;
+    virtual QJsonObject exportSymbolToJson( const QgsLegendSettings &settings, const QgsRenderContext &context ) const;
 
     /**
      * Draws label on the right side of the item
@@ -252,14 +252,6 @@ class CORE_EXPORT QgsLayerTreeModelLegendNode : public QObject
      */
     virtual QSizeF drawSymbolText( const QgsLegendSettings &settings, ItemContext *ctx, QSizeF symbolSize ) const;
 
-    /**
-     * Adds a label in a JSON object with the key "title".
-     * \param settings Legend layout configuration
-     * \param json The json object to update
-     * \since QGIS 3.8
-     */
-    void exportSymbolTextToJson( const QgsLegendSettings &settings, QJsonObject &json ) const;
-
   signals:
     //! Emitted on internal data change so the layer tree model can forward the signal to views
     void dataChanged();
@@ -311,7 +303,7 @@ class CORE_EXPORT QgsSymbolLegendNode : public QgsLayerTreeModelLegendNode
 
     QSizeF drawSymbol( const QgsLegendSettings &settings, ItemContext *ctx, double itemHeight ) const override;
 
-    void exportSymbolToJson( const QgsLegendSettings &settings, const QgsRenderContext &context, QJsonObject &json ) const override;
+    QJsonObject exportSymbolToJson( const QgsLegendSettings &settings, const QgsRenderContext &context ) const override;
 
     void setEmbeddedInParent( bool embedded ) override;
 
@@ -554,7 +546,7 @@ class CORE_EXPORT QgsImageLegendNode : public QgsLayerTreeModelLegendNode
 
     QSizeF drawSymbol( const QgsLegendSettings &settings, ItemContext *ctx, double itemHeight ) const override;
 
-    void exportSymbolToJson( const QgsLegendSettings &settings, const QgsRenderContext &context, QJsonObject &json ) const override;
+    QJsonObject exportSymbolToJson( const QgsLegendSettings &settings, const QgsRenderContext &context ) const override;
 
   private:
     QImage mImage;
@@ -585,7 +577,7 @@ class CORE_EXPORT QgsRasterSymbolLegendNode : public QgsLayerTreeModelLegendNode
 
     QSizeF drawSymbol( const QgsLegendSettings &settings, ItemContext *ctx, double itemHeight ) const override;
 
-    void exportSymbolToJson( const QgsLegendSettings &settings, const QgsRenderContext &context, QJsonObject &json ) const override;
+    QJsonObject exportSymbolToJson( const QgsLegendSettings &settings, const QgsRenderContext &context ) const override;
 
   private:
     QColor mColor;
@@ -617,7 +609,7 @@ class CORE_EXPORT QgsWmsLegendNode : public QgsLayerTreeModelLegendNode
 
     QSizeF drawSymbol( const QgsLegendSettings &settings, ItemContext *ctx, double itemHeight ) const override;
 
-    void exportSymbolToJson( const QgsLegendSettings &settings, const QgsRenderContext &context, QJsonObject &json ) const override;
+    QJsonObject exportSymbolToJson( const QgsLegendSettings &settings, const QgsRenderContext &context ) const override;
 
     void invalidateMapBasedData() override;
 

From 1c28b6904441bcad983830a194d7896d9e6236d9 Mon Sep 17 00:00:00 2001
From: Blottiere Paul <blottiere.paul@gmail.com>
Date: Mon, 11 May 2020 13:55:59 +0200
Subject: [PATCH 08/11] Update sip binding

---
 .../qgslayertreemodellegendnode.sip.in        | 20 +++++--------------
 1 file changed, 5 insertions(+), 15 deletions(-)

diff --git a/python/core/auto_generated/layertree/qgslayertreemodellegendnode.sip.in b/python/core/auto_generated/layertree/qgslayertreemodellegendnode.sip.in
index 20d954c3b26..0a48977adcd 100644
--- a/python/core/auto_generated/layertree/qgslayertreemodellegendnode.sip.in
+++ b/python/core/auto_generated/layertree/qgslayertreemodellegendnode.sip.in
@@ -183,7 +183,7 @@ Draws symbol on the left side of the item
 :return: Real size of the symbol (may be bigger than "normal" symbol size from settings)
 %End
 
-    virtual void exportSymbolToJson( const QgsLegendSettings &settings, const QgsRenderContext &context, QJsonObject &json ) const;
+    virtual QJsonObject exportSymbolToJson( const QgsLegendSettings &settings, const QgsRenderContext &context ) const;
 %Docstring
 Adds a symbol in base64 string within a JSON object with the key "icon".
 
@@ -203,16 +203,6 @@ Draws label on the right side of the item
 :param symbolSize: Real size of the associated symbol - used for correct positioning when rendering
 
 :return: Size of the label (may span multiple lines)
-%End
-
-    void exportSymbolTextToJson( const QgsLegendSettings &settings, QJsonObject &json ) const;
-%Docstring
-Adds a label in a JSON object with the key "title".
-
-:param settings: Legend layout configuration
-:param json: The json object to update
-
-.. versionadded:: 3.8
 %End
 
   signals:
@@ -269,7 +259,7 @@ Constructor for QgsSymbolLegendNode.
     virtual QSizeF drawSymbol( const QgsLegendSettings &settings, ItemContext *ctx, double itemHeight ) const;
 
 
-    virtual void exportSymbolToJson( const QgsLegendSettings &settings, const QgsRenderContext &context, QJsonObject &json ) const;
+    virtual QJsonObject exportSymbolToJson( const QgsLegendSettings &settings, const QgsRenderContext &context ) const;
 
 
     virtual void setEmbeddedInParent( bool embedded );
@@ -519,7 +509,7 @@ Constructor for QgsImageLegendNode.
     virtual QSizeF drawSymbol( const QgsLegendSettings &settings, ItemContext *ctx, double itemHeight ) const;
 
 
-    virtual void exportSymbolToJson( const QgsLegendSettings &settings, const QgsRenderContext &context, QJsonObject &json ) const;
+    virtual QJsonObject exportSymbolToJson( const QgsLegendSettings &settings, const QgsRenderContext &context ) const;
 
 
 };
@@ -553,7 +543,7 @@ Constructor for QgsRasterSymbolLegendNode.
     virtual QSizeF drawSymbol( const QgsLegendSettings &settings, ItemContext *ctx, double itemHeight ) const;
 
 
-    virtual void exportSymbolToJson( const QgsLegendSettings &settings, const QgsRenderContext &context, QJsonObject &json ) const;
+    virtual QJsonObject exportSymbolToJson( const QgsLegendSettings &settings, const QgsRenderContext &context ) const;
 
 
 };
@@ -586,7 +576,7 @@ Constructor for QgsWmsLegendNode.
     virtual QSizeF drawSymbol( const QgsLegendSettings &settings, ItemContext *ctx, double itemHeight ) const;
 
 
-    virtual void exportSymbolToJson( const QgsLegendSettings &settings, const QgsRenderContext &context, QJsonObject &json ) const;
+    virtual QJsonObject exportSymbolToJson( const QgsLegendSettings &settings, const QgsRenderContext &context ) const;
 
 
     virtual void invalidateMapBasedData();

From c10169e2628c75cc3f6237c6cd28b0244697b152 Mon Sep 17 00:00:00 2001
From: Blottiere Paul <blottiere.paul@gmail.com>
Date: Tue, 12 May 2020 08:21:55 +0200
Subject: [PATCH 09/11] Use QStringLiteral

---
 src/core/layertree/qgslayertreemodellegendnode.cpp | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/src/core/layertree/qgslayertreemodellegendnode.cpp b/src/core/layertree/qgslayertreemodellegendnode.cpp
index c6af2c7296e..19e463962b4 100644
--- a/src/core/layertree/qgslayertreemodellegendnode.cpp
+++ b/src/core/layertree/qgslayertreemodellegendnode.cpp
@@ -145,7 +145,7 @@ QJsonObject QgsLayerTreeModelLegendNode::exportSymbolToJson( const QgsLegendSett
   const QString base64 = QString::fromLatin1( byteArray.toBase64().data() );
 
   QJsonObject json;
-  json[ "icon" ] = base64;
+  json[ QStringLiteral( "icon" ) ] = base64;
   return json;
 }
 
@@ -705,7 +705,7 @@ QJsonObject QgsSymbolLegendNode::exportSymbolToJson( const QgsLegendSettings &se
   const QString base64 = QString::fromLatin1( byteArray.toBase64().data() );
 
   QJsonObject json;
-  json[ "icon" ] = base64;
+  json[ QStringLiteral( "icon" ) ] = base64;
   return json;
 }
 
@@ -872,7 +872,7 @@ QJsonObject QgsImageLegendNode::exportSymbolToJson( const QgsLegendSettings &, c
   const QString base64 = QString::fromLatin1( byteArray.toBase64().data() );
 
   QJsonObject json;
-  json[ "icon" ] = base64;
+  json[ QStringLiteral( "icon" ) ] = base64;
   return json;
 }
 
@@ -996,7 +996,7 @@ QJsonObject QgsRasterSymbolLegendNode::exportSymbolToJson( const QgsLegendSettin
   const QString base64 = QString::fromLatin1( byteArray.toBase64().data() );
 
   QJsonObject json;
-  json[ "icon" ] = base64;
+  json[ QStringLiteral( "icon" ) ] = base64;
   return json;
 }
 
@@ -1094,7 +1094,7 @@ QJsonObject QgsWmsLegendNode::exportSymbolToJson( const QgsLegendSettings &, con
   const QString base64 = QString::fromLatin1( byteArray.toBase64().data() );
 
   QJsonObject json;
-  json[ "icon" ] = base64;
+  json[ QStringLiteral( "icon" ) ] = base64;
   return json;
 }
 

From 86503e53fa6369adb2e2dd85bb08ffda65780508 Mon Sep 17 00:00:00 2001
From: Blottiere Paul <blottiere.paul@gmail.com>
Date: Tue, 12 May 2020 13:16:54 +0200
Subject: [PATCH 10/11] Update doc

---
 .../auto_generated/layertree/qgslayertreemodellegendnode.sip.in | 2 --
 src/core/layertree/qgslayertreemodellegendnode.h                | 2 --
 2 files changed, 4 deletions(-)

diff --git a/python/core/auto_generated/layertree/qgslayertreemodellegendnode.sip.in b/python/core/auto_generated/layertree/qgslayertreemodellegendnode.sip.in
index 0a48977adcd..3b28e1c679a 100644
--- a/python/core/auto_generated/layertree/qgslayertreemodellegendnode.sip.in
+++ b/python/core/auto_generated/layertree/qgslayertreemodellegendnode.sip.in
@@ -167,7 +167,6 @@ JSON object.
 
 :param settings: Legend layout configuration
 :param context: Rendering context
-:param json: The json object to update
 
 .. versionadded:: 3.8
 %End
@@ -189,7 +188,6 @@ Adds a symbol in base64 string within a JSON object with the key "icon".
 
 :param settings: Legend layout configuration
 :param context: Rendering context
-:param json: The json object to update
 
 .. versionadded:: 3.8
 %End
diff --git a/src/core/layertree/qgslayertreemodellegendnode.h b/src/core/layertree/qgslayertreemodellegendnode.h
index fac8b070689..5eb35fa6169 100644
--- a/src/core/layertree/qgslayertreemodellegendnode.h
+++ b/src/core/layertree/qgslayertreemodellegendnode.h
@@ -220,7 +220,6 @@ class CORE_EXPORT QgsLayerTreeModelLegendNode : public QObject
      * JSON object.
      * \param settings Legend layout configuration
      * \param context Rendering context
-     * \param json The json object to update
      * \since QGIS 3.8
      */
     QJsonObject exportToJson( const QgsLegendSettings &settings, const QgsRenderContext &context );
@@ -238,7 +237,6 @@ class CORE_EXPORT QgsLayerTreeModelLegendNode : public QObject
      * Adds a symbol in base64 string within a JSON object with the key "icon".
      * \param settings Legend layout configuration
      * \param context Rendering context
-     * \param json The json object to update
      * \since QGIS 3.8
      */
     virtual QJsonObject exportSymbolToJson( const QgsLegendSettings &settings, const QgsRenderContext &context ) const;

From 3cfe500f35de59f2592a4097f0898e64551d1446 Mon Sep 17 00:00:00 2001
From: Blottiere Paul <blottiere.paul@gmail.com>
Date: Tue, 12 May 2020 21:07:20 +0200
Subject: [PATCH 11/11] Add Python unit test

---
 tests/src/python/CMakeLists.txt            |  1 +
 tests/src/python/test_qgslegendrenderer.py | 50 ++++++++++++++++++++++
 2 files changed, 51 insertions(+)
 create mode 100644 tests/src/python/test_qgslegendrenderer.py

diff --git a/tests/src/python/CMakeLists.txt b/tests/src/python/CMakeLists.txt
index 757cd04900a..7dd2be7f880 100644
--- a/tests/src/python/CMakeLists.txt
+++ b/tests/src/python/CMakeLists.txt
@@ -138,6 +138,7 @@ ADD_PYTHON_TEST(PyQgsLayoutUnitsComboBox test_qgslayoutunitscombobox.py)
 ADD_PYTHON_TEST(PyQgsLegendPatchShape test_qgslegendpatchshape.py)
 ADD_PYTHON_TEST(PyQgsLegendPatchShapeButton test_qgslegendpatchshapebutton.py)
 ADD_PYTHON_TEST(PyQgsLegendPatchShapeWidget test_qgslegendpatchshapewidget.py)
+ADD_PYTHON_TEST(PyQgsLegendRenderer test_qgslegendrenderer.py)
 ADD_PYTHON_TEST(PyQgsLineSegment test_qgslinesegment.py)
 ADD_PYTHON_TEST(PyQgsLineSymbolLayers test_qgslinesymbollayers.py)
 ADD_PYTHON_TEST(PyQgsLocalDefaultSettings test_qgslocaldefaultsettings.py)
diff --git a/tests/src/python/test_qgslegendrenderer.py b/tests/src/python/test_qgslegendrenderer.py
new file mode 100644
index 00000000000..0f85018772f
--- /dev/null
+++ b/tests/src/python/test_qgslegendrenderer.py
@@ -0,0 +1,50 @@
+# coding=utf-8
+""""Test QgsLegendRenderer JSON export
+
+.. note:: This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+Run with ctest -V -R PyQgsLegendRenderer
+
+"""
+
+__author__ = 'elpaso@itopen.it'
+__date__ = '2020-04-29'
+__copyright__ = 'Copyright 2020, ItOpen'
+
+import os
+
+from qgis.core import (
+    QgsProject,
+    QgsLegendModel,
+    QgsLegendSettings,
+    QgsLegendRenderer,
+    QgsRenderContext,
+)
+from qgis.testing import start_app, unittest
+from utilities import unitTestDataPath
+
+QGISAPP = start_app()
+TEST_DATA_DIR = unitTestDataPath()
+
+
+class TestPyQgsLegendRenderer(unittest.TestCase):
+
+    def test_json_export(self):
+
+        project = QgsProject()
+        self.assertTrue(project.read(os.path.join(unitTestDataPath('qgis_server'), 'test_project.qgs')))
+        model = QgsLegendModel(project.layerTreeRoot())
+        ctx = QgsRenderContext()
+        settings = QgsLegendSettings()
+        renderer = QgsLegendRenderer(model, settings)
+        nodes = renderer.exportLegendToJson(ctx)['nodes'].toVariant()
+        self.assertEqual(len(nodes), 7)
+        self.assertEqual(nodes[0]['type'], 'layer')
+        self.assertEqual(nodes[0]['title'], 'testlayer')
+
+
+if __name__ == '__main__':
+    unittest.main()