New hint for comparer

Author: alex-kulakov

Orm/Xtensive.Orm/Modelling/Comparison/Comparer.cs

@@ -228,6 +228,10 @@ protected virtual MovementInfo BuildMovementInfo(Node source, Node target)
         return movementInfo;
       }
 
+      var recreateHint = Hints.GetHint<RecreateTableHint>(source);
+      if (recreateHint != null) {
+        movementInfo |= MovementInfo.Removed | MovementInfo.Created;// recreated;
+      }
       var sc = StringComparer.OrdinalIgnoreCase;
 
       // both source!=null && target!=null
@@ -611,9 +615,9 @@ protected bool HasDataChangeHint(Node source)
         return false;
 
       return 
-        Hints.GetHints<CopyDataHint>(source).Any()
-        || Hints.GetHints<DeleteDataHint>(source).Any()
-        || Hints.GetHints<UpdateDataHint>(source).Any();
+        Hints.HasHints<CopyDataHint>(source)
+        || Hints.HasHints<DeleteDataHint>(source)
+        || Hints.HasHints<UpdateDataHint>(source);
     }
 
     /// <summary>

Orm/Xtensive.Orm/Modelling/Comparison/Hints/HintSet.cs

@@ -188,6 +188,19 @@ public bool HasHints(Node node)
       return nodeHintMap.Values.Count > 0;
     }
 
+    public bool HasHints<THint>(Node node)
+      where THint : Hint
+    {
+      ArgumentValidator.EnsureArgumentNotNull(node, "node");
+
+      if (!hintMap.ContainsKey(node))
+        hintMap.Add(node, new Dictionary<Type, object>());
+      var nodeHintMap = hintMap.GetValueOrDefault(node);
+      if (nodeHintMap == null)
+        return false;
+      return nodeHintMap.ContainsKey(typeof(THint));
+    }
+
     #region IEnumerable<...> methods
 
     /// <inheritdoc/>

Orm/Xtensive.Orm/Modelling/Comparison/Hints/RecreateTableHint.cs

@@ -0,0 +1,37 @@
+// Copyright (C) 2021 Xtensive LLC.
+// This code is distributed under MIT license terms.
+// See the License.txt file in the project root for more information.
+
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace Xtensive.Modelling.Comparison.Hints
+{
+  /// <summary>
+  /// Hints comparer that the table is recreated.
+  /// How to treat it is up to comparer.
+  /// </summary>
+  [Serializable]
+  public sealed class RecreateTableHint : Hint
+  {
+    /// <summary>
+    /// Path to the table.
+    /// </summary>
+    public string Path { get; private set; }
+
+    /// <inheritdoc/>
+    public override IEnumerable<HintTarget> GetTargets()
+    {
+      yield return new HintTarget(ModelType.Source, Path);
+      yield return new HintTarget(ModelType.Target, Path);
+    }
+
+    public override string ToString() => $"Recreate '{Path}'";
+
+    public RecreateTableHint(string path)
+    {
+      Path = path;
+    }
+  }
+}