Not working yet

python/core/auto_generated/layertree/qgslayertreemodel.sip.in

@@ -82,7 +82,6 @@ The root node is not transferred by the model.
       DeferredLegendInvalidation,
       UseEmbeddedWidgets,
       UseTextFormatting,
-      ShowHidden,
 
       // behavioral flags
       AllowNodeReorder,

python/gui/auto_generated/layertree/qgslayertreeview.sip.in

@@ -39,6 +39,10 @@ the Free Software Foundation; either version 2 of the License, or     *
 
     void setFilterText( const QString &filterText = QString() );
 
+    bool showHidden() const;
+
+    void setShowHidden( bool showHidden );
+
   protected:
 
     virtual bool filterAcceptsRow( int sourceRow, const QModelIndex &sourceParent ) const;
@@ -307,6 +311,13 @@ Set width of contextual menu mark, at right of layer node items.
 Set the message bar to display messages from the layer tree
 
 .. versionadded:: 3.14
+%End
+
+    void setShowHidden( bool showHidden );
+%Docstring
+Set the show hidden layers to ``showHidden``
+
+.. versionadded:: 3.18
 %End
 
   signals:

src/app/qgsprojectproperties.cpp

@@ -1193,7 +1193,6 @@ void QgsProjectProperties::apply()
     else
       flags &= ~QgsMapLayer::Hidden;
 
-
     layer->setFlags( flags );
 
     QgsVectorLayer *vl = qobject_cast<QgsVectorLayer *>( layer );

src/core/layertree/qgslayertreemodel.h

@@ -98,7 +98,6 @@ class CORE_EXPORT QgsLayerTreeModel : public QAbstractItemModel
       DeferredLegendInvalidation = 0x0008,  //!< Defer legend model invalidation
       UseEmbeddedWidgets         = 0x0010,  //!< Layer nodes may optionally include extra embedded widgets (if used in QgsLayerTreeView). Added in 2.16
       UseTextFormatting          = 0x0020,  //!< Layer nodes will alter text appearance based on layer properties, such as scale based visibility
-      ShowHidden                 = 0x0020,  //!< Display hidden layers
 
       // behavioral flags
       AllowNodeReorder           = 0x1000,  //!< Allow reordering with drag'n'drop

src/gui/layertree/qgslayertreeview.cpp

@@ -95,6 +95,7 @@ void QgsLayerTreeView::setModel( QAbstractItemModel *model )
          );
 
   mProxyModel = new QgsLayerTreeProxyModel( treeModel, this );
+  mProxyModel->setShowHidden( false );
   QTreeView::setModel( mProxyModel );
 
   connect( treeModel->rootGroup(), &QgsLayerTreeNode::expandedChanged, this, &QgsLayerTreeView::onExpandedChanged );
@@ -536,6 +537,12 @@ void QgsLayerTreeView::setMessageBar( QgsMessageBar *messageBar )
          );
 }
 
+void QgsLayerTreeView::setShowHidden( bool showHidden )
+{
+  mShowHidden = true;
+  mProxyModel->setShowHidden( showHidden );
+}
+
 void QgsLayerTreeView::mouseReleaseEvent( QMouseEvent *event )
 {
   // we need to keep last mouse position in order to know whether to emit an indicator's clicked() signal
@@ -684,7 +691,19 @@ bool QgsLayerTreeProxyModel::nodeShown( QgsLayerTreeNode *node ) const
       return true;
     if ( !mFilterText.isEmpty() && !layer->name().contains( mFilterText, Qt::CaseInsensitive ) )
       return false;
-
+    if ( ! mShowHidden && layer->flags().testFlag( QgsMapLayer::LayerFlag::Hidden ) )
+      return false;
     return true;
   }
 }
+
+bool QgsLayerTreeProxyModel::showHidden() const
+{
+  return mShowHidden;
+}
+
+void QgsLayerTreeProxyModel::setShowHidden( bool showHidden )
+{
+  mShowHidden = showHidden;
+  invalidateFilter();
+}

src/gui/layertree/qgslayertreeview.h

@@ -43,6 +43,10 @@ class GUI_EXPORT QgsLayerTreeProxyModel : public QSortFilterProxyModel
 
     void setFilterText( const QString &filterText = QString() );
 
+    bool showHidden() const;
+
+    void setShowHidden( bool showHidden );
+
   protected:
 
     bool filterAcceptsRow( int sourceRow, const QModelIndex &sourceParent ) const override;
@@ -53,6 +57,7 @@ class GUI_EXPORT QgsLayerTreeProxyModel : public QSortFilterProxyModel
 
     QgsLayerTreeModel *mLayerTreeModel = nullptr;
     QString mFilterText;
+    bool mShowHidden = false;
 };
 
 
@@ -289,6 +294,12 @@ class GUI_EXPORT QgsLayerTreeView : public QTreeView
      */
     void setMessageBar( QgsMessageBar *messageBar );
 
+    /**
+     * Set the show hidden layers to \a showHidden
+     * \since QGIS 3.18
+     */
+    void setShowHidden( bool showHidden );
+
   signals:
     //! Emitted when a current layer is changed
     void currentLayerChanged( QgsMapLayer *layer );
@@ -345,6 +356,8 @@ class GUI_EXPORT QgsLayerTreeView : public QTreeView
 
     QgsMessageBar *mMessageBar = nullptr;
 
+    bool mShowHidden = false;
+
     // friend so it can access viewOptions() method and mLastReleaseMousePos without making them public
     friend class QgsLayerTreeViewItemDelegate;
 };