Fix Sequential model.summary missing layers. #960

Author: Oceania2018

src/TensorFlowNET.Keras/Engine/Layer.FlattenLayers.cs

@@ -10,7 +10,7 @@ public IEnumerable<ILayer> _flatten_layers(bool recursive = true, bool include_s
                 yield return this;
 
             var seen_object_ids = new List<int>();
-            var deque = new Queue<ILayer>(_layers);
+            var deque = new Queue<ILayer>(_self_tracked_trackables);
             while (!deque.empty())
             {
                 var layer_or_container = deque.Dequeue();

src/TensorFlowNET.Keras/Engine/Layer.Layers.cs

@@ -6,7 +6,7 @@ namespace Tensorflow.Keras.Engine
     public partial class Layer
     {
         protected List<ILayer> _layers = new List<ILayer>();
-        public List<ILayer> Layers => _layers;
+        public virtual List<ILayer> Layers => _layers;
 
         protected void StackLayers(params ILayer[] layers)
         {

src/TensorFlowNET.Keras/Engine/Model.cs

@@ -1,4 +1,5 @@
 using System.Collections.Generic;
+using System.Linq;
 using Tensorflow.Keras.ArgsDefinition;
 using Tensorflow.Keras.Engine.DataAdapters;
 using Tensorflow.Keras.Losses;
@@ -70,6 +71,9 @@ void _init_batch_counters()
                 aggregation: VariableAggregation.OnlyFirstReplica);
         }
 
+        public override List<ILayer> Layers
+            => _flatten_layers(recursive: false, include_self: false).ToList();
+
         public override List<IVariableV1> trainable_variables
         {
             get

src/TensorFlowNET.Keras/Engine/Sequential.cs

@@ -202,5 +202,8 @@ void track_nodes_created_by_last_call(ILayer layer, List<INode> created_nodes)
                 created_nodes.add(prev_layer.OutboundNodes.Last());
             }
         }
+
+        public override List<ILayer> Layers
+            => base.Layers.Where(x => x is not InputLayer).ToList();
     }
 }