Have PropertyDictionary and ItemDictionary implement ICollection<T>

src/Build/Collections/ItemDictionary.cs

@@ -29,7 +29,7 @@ namespace Microsoft.Build.Collections
     /// </remarks>
     /// <typeparam name="T">Item class type to store</typeparam>
     [DebuggerDisplay("#Item types={ItemTypes.Count} #Items={Count}")]
-    internal sealed class ItemDictionary<T> : IItemDictionary<T>
+    internal sealed class ItemDictionary<T> : ICollection<T>, IItemDictionary<T>
         where T : class, IKeyed, IItem
     {
         /// <summary>
@@ -102,6 +102,8 @@ public ICollection<string> ItemTypes
             }
         }
 
+        public bool IsReadOnly => false;
+
         /// <summary>
         /// Returns the item list for a particular item type,
         /// creating and adding a new item list if necessary.
@@ -403,6 +405,20 @@ private void AddProjectItem(T projectItem)
             _nodes.Add(projectItem, node);
         }
 
+        public void CopyTo(T[] array, int arrayIndex)
+        {
+            if (Count > array.Length - arrayIndex)
+            {
+                throw new ArgumentException(nameof(array));
+            }
+
+            foreach (T item in this)
+            {
+                array[arrayIndex] = item;
+                ++arrayIndex;
+            }
+        }
+
         /// <summary>
         /// Custom enumerator that allows enumeration over all the items in the collection
         /// as though they were in a single list.

src/Build/Collections/PropertyDictionary.cs

@@ -36,7 +36,7 @@ namespace Microsoft.Build.Collections
     /// </remarks>
     /// <typeparam name="T">Property or Metadata class type to store</typeparam>
     [DebuggerDisplay("#Entries={Count}")]
-    internal sealed class PropertyDictionary<T> : IEnumerable<T>, IEquatable<PropertyDictionary<T>>, IPropertyProvider<T>, IDictionary<string, T>, IConstrainableDictionary<T>
+    internal sealed class PropertyDictionary<T> : IEnumerable<T>, ICollection<T>, IEquatable<PropertyDictionary<T>>, IPropertyProvider<T>, IDictionary<string, T>, IConstrainableDictionary<T>
         where T : class, IKeyed, IValued, IEquatable<T>
     {
         /// <summary>
@@ -163,6 +163,8 @@ public int Count
             }
         }
 
+        bool ICollection<T>.IsReadOnly => false;
+
         /// <summary>
         /// Get the property with the specified name, or null if none exists.
         /// Sets the property with the specified name, overwriting it if already exists.
@@ -451,6 +453,28 @@ bool ICollection<KeyValuePair<string, T>>.Remove(KeyValuePair<string, T> item)
             return ((IDictionary<string, T>)this).Remove(item.Key);
         }
 
+        /// <inheritdoc/>
+        void ICollection<T>.Add(T item) => Set(item);
+
+        /// <inheritdoc/>
+        bool ICollection<T>.Contains(T item)
+        {
+            return ((IDictionary<string, T>)this).TryGetValue(item.Key, out T existingItem) &&
+                EqualityComparer<T>.Default.Equals(existingItem, item);
+        }
+
+        /// <inheritdoc/>
+        void ICollection<T>.CopyTo(T[] array, int arrayIndex)
+        {
+            using (_lock.EnterDisposableWriteLock())
+            {
+                _properties.CopyTo(array, arrayIndex);
+            }
+        }
+
+        /// <inheritdoc/>
+        bool ICollection<T>.Remove(T item) => Remove(item.Key);
+
         #endregion
 
         #region IEnumerable<KeyValuePair<string,T>> Members
@@ -471,6 +495,7 @@ IEnumerator<KeyValuePair<string, T>> IEnumerable<KeyValuePair<string, T>>.GetEnu
 
         #endregion
 
+
         /// <summary>
         /// Removes any property with the specified name.
         /// Returns true if the property was in the collection, otherwise false.