Add OrderedDictionary

src/libraries/Common/src/System/Collections/Generic/EnumerableHelpers.cs

@@ -8,6 +8,10 @@ namespace System.Collections.Generic
     /// </summary>
     internal static partial class EnumerableHelpers
     {
+        /// <summary>Calls Reset on an enumerator instance.</summary>
+        /// <remarks>Enables Reset to be called without boxing on a struct enumerator that lacks a public Reset.</remarks>
+        internal static void Reset<T>(ref T enumerator) where T : IEnumerator => enumerator.Reset();
+
         /// <summary>Gets an enumerator singleton for an empty collection.</summary>
         internal static IEnumerator<T> GetEmptyEnumerator<T>() =>
             ((IEnumerable<T>)Array.Empty<T>()).GetEnumerator();

src/libraries/Common/tests/System/Collections/IDictionary.NonGeneric.Tests.cs

@@ -491,7 +491,6 @@ public virtual void IDictionary_NonGeneric_Values_Enumeration_ParentDictionaryMo
                 {
                     Assert.Throws<InvalidOperationException>(() => valuesEnum.MoveNext());
                     Assert.Throws<InvalidOperationException>(() => valuesEnum.Reset());
-                    Assert.Throws<InvalidOperationException>(() => valuesEnum.Current);
                 }
                 else
                 {
@@ -832,7 +831,7 @@ public virtual void IDictionary_NonGeneric_IDictionaryEnumerator_Current_AfterEn
             object current, key, value, entry;
             IDictionaryEnumerator enumerator = NonGenericIDictionaryFactory(count).GetEnumerator();
             while (enumerator.MoveNext()) ;
-            if (Enumerator_Current_UndefinedOperation_Throws)
+            if (count == 0 ? Enumerator_Empty_Current_UndefinedOperation_Throw : Enumerator_Current_UndefinedOperation_Throws)
             {
                 Assert.Throws<InvalidOperationException>(() => enumerator.Current);
                 Assert.Throws<InvalidOperationException>(() => enumerator.Key);

src/libraries/Common/tests/System/Collections/IEnumerable.NonGeneric.Tests.cs

@@ -60,6 +60,18 @@ public abstract partial class IEnumerable_NonGeneric_Tests : TestBase
         /// </summary>
         protected virtual bool Enumerator_Current_UndefinedOperation_Throws => false;
 
+        /// <summary>
+        /// When calling Current of the empty enumerator before the first MoveNext, after the end of the collection,
+        /// or after modification of the enumeration, the resulting behavior is undefined. Tests are included
+        /// to cover two behavioral scenarios:
+        ///   - Throwing an InvalidOperationException
+        ///   - Returning an undefined value.
+        ///
+        /// If this property is set to true, the tests ensure that the exception is thrown. The default value is
+        /// false.
+        /// </summary>
+        protected virtual bool Enumerator_Empty_Current_UndefinedOperation_Throw => Enumerator_Current_UndefinedOperation_Throws;
+
         /// <summary>
         /// When calling MoveNext or Reset after modification of the enumeration, the resulting behavior is
         /// undefined. Tests are included to cover two behavioral scenarios:
@@ -305,7 +317,7 @@ public virtual void Enumerator_Current_BeforeFirstMoveNext_UndefinedBehavior(int
             object current;
             IEnumerable enumerable = NonGenericIEnumerableFactory(count);
             IEnumerator enumerator = enumerable.GetEnumerator();
-            if (Enumerator_Current_UndefinedOperation_Throws)
+            if (count == 0 ? Enumerator_Empty_Current_UndefinedOperation_Throw : Enumerator_Current_UndefinedOperation_Throws)
                 Assert.Throws<InvalidOperationException>(() => enumerator.Current);
             else
                 current = enumerator.Current;
@@ -319,7 +331,7 @@ public virtual void Enumerator_Current_AfterEndOfEnumerable_UndefinedBehavior(in
             IEnumerable enumerable = NonGenericIEnumerableFactory(count);
             IEnumerator enumerator = enumerable.GetEnumerator();
             while (enumerator.MoveNext()) ;
-            if (Enumerator_Current_UndefinedOperation_Throws)
+            if (count == 0 ? Enumerator_Empty_Current_UndefinedOperation_Throw : Enumerator_Current_UndefinedOperation_Throws)
                 Assert.Throws<InvalidOperationException>(() => enumerator.Current);
             else
                 current = enumerator.Current;
@@ -336,7 +348,7 @@ public virtual void Enumerator_Current_ModifiedDuringEnumeration_UndefinedBehavi
                 IEnumerator enumerator = enumerable.GetEnumerator();
                 if (ModifyEnumerable(enumerable))
                 {
-                    if (Enumerator_Current_UndefinedOperation_Throws)
+                    if (count == 0 ? Enumerator_Empty_Current_UndefinedOperation_Throw : Enumerator_Current_UndefinedOperation_Throws)
                         Assert.Throws<InvalidOperationException>(() => enumerator.Current);
                     else
                         current = enumerator.Current;

src/libraries/Common/tests/System/Collections/IList.Generic.Tests.cs

@@ -103,17 +103,31 @@ protected override IEnumerable<ModifyEnumerable> GetModifyEnumerables(ModifyOper
         public void IList_Generic_ItemGet_NegativeIndex_ThrowsException(int count)
         {
             IList<T> list = GenericIListFactory(count);
+
             Assert.Throws(IList_Generic_Item_InvalidIndex_ThrowType, () => list[-1]);
             Assert.Throws(IList_Generic_Item_InvalidIndex_ThrowType, () => list[int.MinValue]);
+
+            if (list is IReadOnlyList<T> rol)
+            {
+                Assert.Throws(IList_Generic_Item_InvalidIndex_ThrowType, () => rol[-1]);
+                Assert.Throws(IList_Generic_Item_InvalidIndex_ThrowType, () => rol[int.MinValue]);
+            }
         }
 
         [Theory]
         [MemberData(nameof(ValidCollectionSizes))]
         public void IList_Generic_ItemGet_IndexGreaterThanListCount_ThrowsException(int count)
         {
             IList<T> list = GenericIListFactory(count);
+
             Assert.Throws(IList_Generic_Item_InvalidIndex_ThrowType, () => list[count]);
             Assert.Throws(IList_Generic_Item_InvalidIndex_ThrowType, () => list[count + 1]);
+
+            if (list is IReadOnlyList<T> rol)
+            {
+                Assert.Throws(IList_Generic_Item_InvalidIndex_ThrowType, () => rol[count]);
+                Assert.Throws(IList_Generic_Item_InvalidIndex_ThrowType, () => rol[count + 1]);
+            }
         }
 
         [Theory]
@@ -122,7 +136,15 @@ public void IList_Generic_ItemGet_ValidGetWithinListBounds(int count)
         {
             IList<T> list = GenericIListFactory(count);
             T result;
+
             Assert.All(Enumerable.Range(0, count), index => result = list[index]);
+            Assert.All(Enumerable.Range(0, count), index => Assert.Equal(list[index], list[index]));
+
+            if (list is IReadOnlyList<T> rol)
+            {
+                Assert.All(Enumerable.Range(0, count), index => result = rol[index]);
+                Assert.All(Enumerable.Range(0, count), index => Assert.Equal(rol[index], rol[index]));
+            }
         }
 
         #endregion
@@ -369,7 +391,7 @@ public void IList_Generic_IndexOf_InvalidValue(int count)
         [MemberData(nameof(ValidCollectionSizes))]
         public void IList_Generic_IndexOf_ReturnsFirstMatchingValue(int count)
         {
-            if (!IsReadOnly && !AddRemoveClear_ThrowsNotSupported)
+            if (!IsReadOnly && !AddRemoveClear_ThrowsNotSupported && DuplicateValuesAllowed)
             {
                 IList<T> list = GenericIListFactory(count);
                 foreach (T duplicate in list.ToList()) // hard copies list to circumvent enumeration error

src/libraries/Common/tests/System/Collections/IList.NonGeneric.Tests.cs

@@ -83,6 +83,17 @@ protected virtual object CreateT(int seed)
         /// </summary>
         protected virtual bool IList_CurrentAfterAdd_Throws => Enumerator_Current_UndefinedOperation_Throws;
 
+        /// <summary>
+        /// When calling Current of the empty enumerator after the end of the list and list is extended by new items.
+        /// Tests are included to cover two behavioral scenarios:
+        ///   - Throwing an InvalidOperationException
+        ///   - Returning an undefined value.
+        ///
+        /// If this property is set to true, the tests ensure that the exception is thrown. The default value is
+        /// the same as Enumerator_Current_UndefinedOperation_Throws.
+        /// </summary>
+        protected virtual bool IList_Empty_CurrentAfterAdd_Throws => Enumerator_Empty_Current_UndefinedOperation_Throw;
+
         #endregion
 
         #region ICollection Helper Methods
@@ -697,7 +708,7 @@ public void IList_NonGeneric_IndexOf_InvalidValue(int count)
         [MemberData(nameof(ValidCollectionSizes))]
         public void IList_NonGeneric_IndexOf_ReturnsFirstMatchingValue(int count)
         {
-            if (!IsReadOnly && !ExpectedFixedSize)
+            if (!IsReadOnly && !ExpectedFixedSize && DuplicateValuesAllowed)
             {
                 IList list = NonGenericIListFactory(count);
 
@@ -1084,7 +1095,7 @@ public void IList_NonGeneric_CurrentAtEnd_AfterAdd(int count)
                 IEnumerator enumerator = collection.GetEnumerator();
                 while (enumerator.MoveNext()) ; // Go to end of enumerator
 
-                if (Enumerator_Current_UndefinedOperation_Throws)
+                if (count == 0 ? Enumerator_Empty_Current_UndefinedOperation_Throw : Enumerator_Current_UndefinedOperation_Throws)
                 {
                     Assert.Throws<InvalidOperationException>(() => enumerator.Current); // Enumerator.Current should fail
                 }
@@ -1099,7 +1110,7 @@ public void IList_NonGeneric_CurrentAtEnd_AfterAdd(int count)
                 {
                     collection.Add(CreateT(seed++));
 
-                    if (IList_CurrentAfterAdd_Throws)
+                    if (count == 0 ? IList_Empty_CurrentAfterAdd_Throws : IList_CurrentAfterAdd_Throws)
                     {
                         Assert.Throws<InvalidOperationException>(() => enumerator.Current); // Enumerator.Current should fail
                     }