Make mutable generic collection interfaces implement read-only collection interfaces

src/coreclr/System.Private.CoreLib/src/System/Array.CoreCLR.cs

@@ -399,7 +399,7 @@ public ArrayInitializeCache(RuntimeType arrayType)
     // it for type <T> and executes it.
     //
     // The "T" will reflect the interface used to invoke the method. The actual runtime "this" will be
-    // array that is castable to "T[]" (i.e. for primitivs and valuetypes, it will be exactly
+    // array that is castable to "T[]" (i.e. for primitives and valuetypes, it will be exactly
     // "T[]" - for orefs, it may be a "U[]" where U derives from T.)
     //----------------------------------------------------------------------------------------
     internal sealed class SZArrayHelper

src/coreclr/vm/array.cpp

@@ -1235,29 +1235,14 @@ MethodDesc* GetActualImplementationForArrayGenericIListOrIReadOnlyListMethod(Met
     }
     CONTRACTL_END
 
-    int slot = pItfcMeth->GetSlot();
-
-    // We need to pick the right starting method depending on the depth of the inheritance chain
-    static const BinderMethodID startingMethod[] = {
-        METHOD__SZARRAYHELPER__GETENUMERATOR,   // First method of IEnumerable`1
-        METHOD__SZARRAYHELPER__GET_COUNT,       // First method of ICollection`1/IReadOnlyCollection`1
-        METHOD__SZARRAYHELPER__GET_ITEM         // First method of IList`1/IReadOnlyList`1
-    };
-
     // Subtract one for the non-generic IEnumerable that the generic enumerable inherits from
     unsigned int inheritanceDepth = pItfcMeth->GetMethodTable()->GetNumInterfaces() - 1;
-    PREFIX_ASSUME(0 <= inheritanceDepth && inheritanceDepth < ARRAY_SIZE(startingMethod));
-
-    MethodDesc *pGenericImplementor = CoreLibBinder::GetMethod((BinderMethodID)(startingMethod[inheritanceDepth] + slot));
 
-    // The most common reason for this assert is that the order of the SZArrayHelper methods in
-    // corelib.h does not match the order they are implemented on the generic interfaces.
-    _ASSERTE(pGenericImplementor == MemberLoader::FindMethodByName(g_pSZArrayHelperClass, pItfcMeth->GetName()));
+    MethodDesc *pGenericImplementor = MemberLoader::FindMethodByName(g_pSZArrayHelperClass, pItfcMeth->GetName());
 
     // OPTIMIZATION: For any method other than GetEnumerator(), we can safely substitute
     // "Object" for reference-type theT's. This causes fewer methods to be instantiated.
-    if (startingMethod[inheritanceDepth] != METHOD__SZARRAYHELPER__GETENUMERATOR &&
-        !theT.IsValueType())
+    if (inheritanceDepth != 1 && !theT.IsValueType())
     {
         theT = TypeHandle(g_pObjectClass);
     }

src/libraries/Common/tests/System/Collections/CollectionAsserts.cs

@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using Xunit;
@@ -9,6 +10,151 @@ namespace System.Collections.Tests
 {
     internal static class CollectionAsserts
     {
+        public static void HasCount<T>(ICollection<T> collection, int count)
+        {
+            Assert.Equal(count, collection.Count);
+#if !NETFRAMEWORK
+            IReadOnlyCollection<T> readOnlyCollection = collection;
+            Assert.Equal(count, readOnlyCollection.Count);
+#endif
+        }
+
+        public static void EqualAt<T>(IList<T> list, int index, T expected)
+        {
+            Assert.Equal(expected, list[index]);
+#if !NETFRAMEWORK
+            IReadOnlyList<T> readOnlyList = list;
+            Assert.Equal(expected, readOnlyList[index]);
+#endif
+        }
+
+        public static void NotEqualAt<T>(IList<T> list, int index, T expected)
+        {
+            Assert.NotEqual(expected, list[index]);
+#if !NETFRAMEWORK
+            IReadOnlyList<T> readOnlyList = list;
+            Assert.NotEqual(expected, readOnlyList[index]);
+#endif
+        }
+
+        public static void ThrowsElementAt<T>(IList<T> list, int index, Type exceptionType)
+        {
+            Assert.Throws(exceptionType, () => list[index]);
+#if !NETFRAMEWORK
+            IReadOnlyList<T> readOnlyList = list;
+            Assert.Throws(exceptionType, () => readOnlyList[index]);
+#endif
+        }
+
+        public static void ElementAtSucceeds<T>(IList<T> list, int index)
+        {
+            T result = list[index];
+#if !NETFRAMEWORK
+            IReadOnlyList<T> readOnlyList = list;
+            Assert.Equal(result, readOnlyList[index]);
+#endif
+        }
+
+        public static void EqualAt<TKey, TValue>(IDictionary<TKey, TValue> dictionary, TKey key, TValue expected)
+        {
+            Assert.Equal(expected, dictionary[key]);
+#if !NETFRAMEWORK
+            IReadOnlyDictionary<TKey, TValue> readOnlyDictionary = dictionary;
+            Assert.Equal(expected, readOnlyDictionary[key]);
+#endif
+        }
+
+        public static void ContainsKey<TKey, TValue>(IDictionary<TKey, TValue> dictionary, TKey key, bool expected)
+        {
+            Assert.Equal(expected, dictionary.ContainsKey(key));
+#if !NETFRAMEWORK
+            IReadOnlyDictionary<TKey, TValue> readOnlyDictionary = dictionary;
+            Assert.Equal(expected, readOnlyDictionary.ContainsKey(key));
+#endif
+        }
+
+        public static void TryGetValue<TKey, TValue>(IDictionary<TKey, TValue> dictionary, TKey key, bool expected, TValue expectedValue = default)
+        {
+            Assert.Equal(expected, dictionary.TryGetValue(key, out TValue value));
+            if (expected)
+            {
+                Assert.Equal(expectedValue, value);
+            }
+#if !NETFRAMEWORK
+            IReadOnlyDictionary<TKey, TValue> readOnlyDictionary = dictionary;
+            Assert.Equal(expected, readOnlyDictionary.TryGetValue(key, out value));
+            if (expected)
+            {
+                Assert.Equal(expectedValue, value);
+            }
+#endif
+        }
+
+        public static void Contains<T>(ISet<T> set, T expected)
+        {
+            Assert.True(set.Contains(expected));
+#if !NETFRAMEWORK
+            ICollection<T> collection = set;
+            Assert.True(collection.Contains(expected));
+            IReadOnlySet<T> readOnlySet = set;
+            Assert.True(readOnlySet.Contains(expected));
+#endif
+        }
+
+        public static void IsProperSubsetOf<T>(ISet<T> set, IEnumerable<T> enumerable, bool expected)
+        {
+            Assert.Equal(expected, set.IsProperSubsetOf(enumerable));
+#if !NETFRAMEWORK
+            IReadOnlySet<T> readOnlySet = set;
+            Assert.Equal(expected, readOnlySet.IsProperSubsetOf(enumerable));
+#endif
+        }
+
+        public static void IsProperSupersetOf<T>(ISet<T> set, IEnumerable<T> enumerable, bool expected)
+        {
+            Assert.Equal(expected, set.IsProperSupersetOf(enumerable));
+#if !NETFRAMEWORK
+            IReadOnlySet<T> readOnlySet = set;
+            Assert.Equal(expected, readOnlySet.IsProperSupersetOf(enumerable));
+#endif
+        }
+
+        public static void IsSubsetOf<T>(ISet<T> set, IEnumerable<T> enumerable, bool expected)
+        {
+            Assert.Equal(expected, set.IsSubsetOf(enumerable));
+#if !NETFRAMEWORK
+            IReadOnlySet<T> readOnlySet = set;
+            Assert.Equal(expected, readOnlySet.IsSubsetOf(enumerable));
+#endif
+        }
+
+        public static void IsSupersetOf<T>(ISet<T> set, IEnumerable<T> enumerable, bool expected)
+        {
+            Assert.Equal(expected, set.IsSupersetOf(enumerable));
+#if !NETFRAMEWORK
+            IReadOnlySet<T> readOnlySet = set;
+            Assert.Equal(expected, readOnlySet.IsSupersetOf(enumerable));
+#endif
+        }
+
+        public static void Overlaps<T>(ISet<T> set, IEnumerable<T> enumerable, bool expected)
+        {
+            Assert.Equal(expected, set.Overlaps(enumerable));
+#if !NETFRAMEWORK
+            IReadOnlySet<T> readOnlySet = set;
+            Assert.Equal(expected, readOnlySet.Overlaps(enumerable));
+#endif
+        }
+
+        public static void SetEquals<T>(ISet<T> set, IEnumerable<T> enumerable, bool expected)
+        {
+            Assert.Equal(expected, set.SetEquals(enumerable));
+#if !NETFRAMEWORK
+            IReadOnlySet<T> readOnlySet = set;
+            Assert.Equal(expected, readOnlySet.SetEquals(enumerable));
+#endif
+        }
+
         public static void Equal(ICollection expected, ICollection actual)
         {
             Assert.Equal(expected == null, actual == null);
@@ -43,6 +189,12 @@ public static void Equal<T>(ICollection<T> expected, ICollection<T> actual)
                 return;
             }
             Assert.Equal(expected.Count, actual.Count);
+#if !NETFRAMEWORK
+            IReadOnlyCollection<T> readOnlyExpected = expected;
+            Assert.Equal(expected.Count, readOnlyExpected.Count);
+            IReadOnlyCollection<T> readOnlyActual = actual;
+            Assert.Equal(actual.Count, readOnlyActual.Count);
+#endif
             IEnumerator<T> e = expected.GetEnumerator();
             IEnumerator<T> a = actual.GetEnumerator();
             while (e.MoveNext())