[needs-docs] Use an indicator icon for embedded layers

The previous approach of showing these layers with italic
text is not obvious for users to understand, and the
interface gives little clues as to why a layer cannot
be edited. There's also no way to see what project
a layer has been embedded from!

So use a new indicator icon in the layer tree to
flag embedded layers, with a tooltip showing the path
to the embedded project location.

src/app/CMakeLists.txt

@@ -52,6 +52,7 @@ SET(QGIS_APP_SRCS
   qgslabelengineconfigdialog.cpp
   qgslabelinggui.cpp
   qgslabelingwidget.cpp
+  qgslayertreeviewembeddedindicator.cpp
   qgslayertreeviewfilterindicator.cpp
   qgsloadstylefromdbdialog.cpp
   qgsmapcanvasdockwidget.cpp
@@ -263,6 +264,7 @@ SET (QGIS_APP_MOC_HDRS
   qgslabelinggui.h
   qgslabelingwidget.h
   qgslabelpropertydialog.h
+  qgslayertreeviewembeddedindicator.h
   qgslayertreeviewfilterindicator.h
   qgsloadstylefromdbdialog.h
   qgsmapcanvasdockwidget.h

src/app/qgisapp.cpp

@@ -202,6 +202,7 @@ Q_GUI_EXPORT extern int qt_defaultDpiX();
 #include "qgslayertreeutils.h"
 #include "qgslayertreeview.h"
 #include "qgslayertreeviewdefaultactions.h"
+#include "qgslayertreeviewembeddedindicator.h"
 #include "qgslayertreeviewfilterindicator.h"
 #include "qgslayout.h"
 #include "qgslayoutatlas.h"
@@ -3726,6 +3727,7 @@ void QgisApp::initLayerTreeView()
   mLayerTreeView->setModel( model );
   mLayerTreeView->setMenuProvider( new QgsAppLayerTreeViewMenuProvider( mLayerTreeView, mMapCanvas ) );
   new QgsLayerTreeViewFilterIndicatorProvider( mLayerTreeView );  // gets parented to the layer view
+  new QgsLayerTreeViewEmbeddedIndicatorProvider( mLayerTreeView );  // gets parented to the layer view
 
   setupLayerTreeViewFromSettings();
 

src/app/qgslayertreeviewembeddedindicator.cpp

@@ -0,0 +1,77 @@
+/***************************************************************************
+  qgslayertreeviewembeddedindicator.h
+  --------------------------------------
+  Date                 : June 2018
+  Copyright            : (C) 2018 by Nyall Dawson
+  Email                : nyall dot dawson at gmail dot com
+ ***************************************************************************
+ *                                                                         *
+ *   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.                                   *
+ *                                                                         *
+ ***************************************************************************/
+
+#include "qgslayertreeviewembeddedindicator.h"
+#include "qgslayertree.h"
+#include "qgslayertreemodel.h"
+#include "qgslayertreeview.h"
+
+QgsLayerTreeViewEmbeddedIndicatorProvider::QgsLayerTreeViewEmbeddedIndicatorProvider( QgsLayerTreeView *view )
+  : QObject( view )
+  , mLayerTreeView( view )
+{
+  mIcon = QgsApplication::getThemeIcon( QStringLiteral( "/mIndicatorFilter.svg" ) );
+
+  QgsLayerTree *tree = mLayerTreeView->layerTreeModel()->rootGroup();
+  onAddedChildren( tree, 0, tree->children().count() - 1 );
+
+  connect( tree, &QgsLayerTree::addedChildren, this, &QgsLayerTreeViewEmbeddedIndicatorProvider::onAddedChildren );
+}
+
+void QgsLayerTreeViewEmbeddedIndicatorProvider::onAddedChildren( QgsLayerTreeNode *node, int indexFrom, int indexTo )
+{
+  // recursively populate indicators
+  QList<QgsLayerTreeNode *> children = node->children();
+  for ( int i = indexFrom; i <= indexTo; ++i )
+  {
+    QgsLayerTreeNode *childNode = children[i];
+
+    if ( QgsLayerTree::isGroup( childNode ) )
+    {
+      onAddedChildren( childNode, 0, childNode->children().count() - 1 );
+    }
+    else if ( QgsLayerTree::isLayer( childNode ) && childNode->customProperty( QStringLiteral( "embedded" ) ).toInt() )
+    {
+      QgsLayerTreeLayer *childLayerNode = QgsLayerTree::toLayer( childNode );
+      addIndicatorForEmbeddedLayer( childLayerNode );
+    }
+  }
+}
+
+QgsLayerTreeViewIndicator *QgsLayerTreeViewEmbeddedIndicatorProvider::newIndicator( const QString &project )
+{
+  QgsLayerTreeViewIndicator *indicator = new QgsLayerTreeViewIndicator( this );
+  indicator->setIcon( mIcon );
+  indicator->setToolTip( tr( "Embedded from <b>%1</b>" ).arg( project ) );
+  mIndicators.insert( indicator );
+  return indicator;
+}
+
+void QgsLayerTreeViewEmbeddedIndicatorProvider::addIndicatorForEmbeddedLayer( QgsLayerTreeNode *node )
+{
+  const QList<QgsLayerTreeViewIndicator *> nodeIndicators = mLayerTreeView->indicators( node );
+
+  // maybe the indicator exists already
+  for ( QgsLayerTreeViewIndicator *indicator : nodeIndicators )
+  {
+    if ( mIndicators.contains( indicator ) )
+    {
+      return;
+    }
+  }
+
+  // it does not exist: need to create a new one
+  mLayerTreeView->addIndicator( node, newIndicator( node->customProperty( QStringLiteral( "embedded_project" ) ).toString() ) );
+}

src/app/qgslayertreeviewembeddedindicator.h

@@ -0,0 +1,47 @@
+/***************************************************************************
+  qgslayertreeviewembeddedindicator.h
+  --------------------------------------
+  Date                 : June 2018
+  Copyright            : (C) 2018 by Nyall Dawson
+  Email                : nyall dot dawson at gmail dot com
+ ***************************************************************************
+ *                                                                         *
+ *   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.                                   *
+ *                                                                         *
+ ***************************************************************************/
+
+#ifndef QGSLAYERTREEVIEWEMBEDDEDINDICATOR_H
+#define QGSLAYERTREEVIEWEMBEDDEDINDICATOR_H
+
+#include "qgslayertreeviewindicator.h"
+
+#include <QSet>
+
+class QgsLayerTreeNode;
+class QgsLayerTreeView;
+
+//! Adds indicators showing whether layers are embedded.
+class QgsLayerTreeViewEmbeddedIndicatorProvider : public QObject
+{
+    Q_OBJECT
+  public:
+    explicit QgsLayerTreeViewEmbeddedIndicatorProvider( QgsLayerTreeView *view );
+
+  private slots:
+    //! Connects to signals of layers newly added to the tree
+    void onAddedChildren( QgsLayerTreeNode *node, int indexFrom, int indexTo );
+
+  private:
+    QgsLayerTreeViewIndicator *newIndicator( const QString &project );
+    void addIndicatorForEmbeddedLayer( QgsLayerTreeNode *node );
+
+  private:
+    QgsLayerTreeView *mLayerTreeView = nullptr;
+    QIcon mIcon;
+    QSet<QgsLayerTreeViewIndicator *> mIndicators;
+};
+
+#endif // QGSLAYERTREEVIEWEMBEDDEDINDICATOR_H