Revert "Remove no longer required hack to get composer maps to render"

Because... server

src/app/composer/qgscomposer.cpp

@@ -934,6 +934,23 @@ bool QgsComposer::loadFromTemplate( const QDomDocument &templateDoc, bool clearE
   return result;
 }
 
+void QgsComposer::onCanvasLayersChanged( const QList<QgsMapLayer *> &layers )
+{
+  if ( !mComposition )
+    return;
+
+  QList< QgsComposerMap * > maps;
+  mComposition->composerItems( maps );
+
+  Q_FOREACH ( QgsComposerMap *map, maps )
+  {
+    if ( map->keepLayerSet() )
+      continue;
+
+    map->setLayers( layers );
+  }
+}
+
 void QgsComposer::updateStatusCursorPos( QPointF cursorPosition )
 {
   if ( !mComposition )

src/app/composer/qgscomposer.h

@@ -114,6 +114,16 @@ class QgsComposer: public QMainWindow, private Ui::QgsComposerBase
      */
     bool loadFromTemplate( const QDomDocument &templateDoc, bool clearExisting );
 
+  public slots:
+
+    /**
+     * Should be called whenever the app's canvas layers change (or layer order
+     * changes). Required to update composer maps which are synced to the canvas
+     * layer set with the new canvas layer set.
+     * @note added in QGIS 3.0
+     */
+    void onCanvasLayersChanged( const QList< QgsMapLayer * > &layers );
+
   protected:
     //! Move event
     virtual void moveEvent( QMoveEvent * ) override;

src/app/qgisapp.cpp

@@ -6828,6 +6828,7 @@ QgsComposer *QgisApp::createNewComposer( QString title )
   connect( newComposerObject, &QgsComposer::composerAdded, this, &QgisApp::composerAdded );
   connect( newComposerObject, &QgsComposer::composerWillBeRemoved, this, &QgisApp::composerWillBeRemoved );
   connect( newComposerObject, &QgsComposer::atlasPreviewFeatureChanged, this, &QgisApp::refreshMapCanvas );
+  connect( mLayerTreeCanvasBridge, &QgsLayerTreeMapCanvasBridge::canvasLayersChanged, newComposerObject, &QgsComposer::onCanvasLayersChanged );
 
   markDirty();
   return newComposerObject;
@@ -6931,6 +6932,7 @@ bool QgisApp::loadComposersFromProject( const QDomDocument &doc )
     connect( composer, &QgsComposer::composerAdded, this, &QgisApp::composerAdded );
     connect( composer, &QgsComposer::composerWillBeRemoved, this, &QgisApp::composerWillBeRemoved );
     connect( composer, &QgsComposer::atlasPreviewFeatureChanged, this, &QgisApp::refreshMapCanvas );
+    connect( mLayerTreeCanvasBridge, &QgsLayerTreeMapCanvasBridge::canvasLayersChanged, composer, &QgsComposer::onCanvasLayersChanged );
 
     QgsDebugMsg( QString( "Loaded composer %1: %2ms" ).arg( title ).arg( t.elapsed() ) );
   }

src/core/composer/qgscomposermap.cpp

@@ -475,15 +475,11 @@ QList<QgsMapLayer *> QgsComposerMap::layersToRender( const QgsExpressionContext
     if ( mComposition->project()->mapThemeCollection()->hasMapTheme( presetName ) )
       renderLayers = mComposition->project()->mapThemeCollection()->mapThemeVisibleLayers( presetName );
     else  // fallback to using map canvas layers
-      renderLayers =  mComposition->project()->mapThemeCollection()->masterVisibleLayers();
-  }
-  else if ( mKeepLayerSet )
-  {
-    renderLayers = layers();
+      renderLayers = layers();
   }
   else
   {
-    renderLayers =  mComposition->project()->mapThemeCollection()->masterVisibleLayers();
+    renderLayers = layers();
   }
 
   bool ok = false;
@@ -1500,7 +1496,6 @@ QList<QgsMapLayer *> QgsComposerMap::layers() const
 
 void QgsComposerMap::setLayers( const QList<QgsMapLayer *> &layers )
 {
-  mKeepLayerSet = true;
   mLayers = _qgis_listRawToQPointer( layers );
 }
 

src/core/composer/qgscomposermap.h

@@ -220,16 +220,16 @@ class CORE_EXPORT QgsComposerMap : public QgsComposerItem
     void setKeepLayerSet( bool enabled ) {mKeepLayerSet = enabled;}
 
     /**
-     * Getter for stored layer set. This will only be used if the
-     * keepLayerSet() flag is true.
+     * Getter for stored layer set. This will usually be synchronized with the main app canvas
+     * layer set (and layer order), unless the keepLayerSet() flag is true.
      * @see setLayers()
      * @see keepLayerSet()
      */
     QList<QgsMapLayer *> layers() const;
 
     /**
-     * Setter for stored layer set. Calling this will automatically set
-     * keepLayerSet() to true.
+     * Setter for stored layer set.  This will usually be synchronized with the main app canvas
+     * layer set (and layer order), unless the keepLayerSet() flag is true.
      * @see layers()
      * @see keepLayerSet()
      */

src/gui/qgscomposerview.cpp

@@ -1001,6 +1001,7 @@ void QgsComposerView::mouseReleaseEvent( QMouseEvent *e )
         if ( mCanvas )
         {
           composerMap->zoomToExtent( mCanvas->mapSettings().visibleExtent() );
+          composerMap->setLayers( mCanvas->mapSettings().layers() );
         }
 
         composition()->addComposerMap( composerMap );