Update ICollection<T> usage to IReadOnlyCollection<T> where applicable

src/libraries/Common/src/System/Diagnostics/DiagnosticsHelper.cs

@@ -35,14 +35,22 @@ internal static bool CompareTags(List<KeyValuePair<string, object?>>? sortedTags
             int size = count / (sizeof(ulong) * 8) + 1;
             BitMapper bitMapper = new BitMapper(size <= 100 ? stackalloc ulong[size] : new ulong[size]);
 
+#if NET9_0_OR_GREATER // ICollection<T> : IReadOnlyCollection<T> on .NET 9+
+            if (tags2 is IReadOnlyCollection<KeyValuePair<string, object?>> tagsCol)
+#else
             if (tags2 is ICollection<KeyValuePair<string, object?>> tagsCol)
+#endif
             {
                 if (tagsCol.Count != count)
                 {
                     return false;
                 }
 
+#if NET9_0_OR_GREATER // IList<T> : IReadOnlyList<T> on .NET 9+
+                if (tagsCol is IReadOnlyList<KeyValuePair<string, object?>> secondList)
+#else
                 if (tagsCol is IList<KeyValuePair<string, object?>> secondList)
+#endif
                 {
                     for (int i = 0; i < count; i++)
                     {

src/libraries/System.Collections.Immutable/src/System/Collections/Frozen/FrozenSetInternalBase.cs

@@ -32,7 +32,11 @@ private protected override bool IsProperSubsetOfCore(IEnumerable<T> other)
         {
             Debug.Assert(_thisSet.Count != 0, "EmptyFrozenSet should have been used.");
 
+#if NET9_0_OR_GREATER // ICollection<T> : IReadOnlyCollection<T> on .NET 9+
+            if (other is IReadOnlyCollection<T> otherAsCollection)
+#else
             if (other is ICollection<T> otherAsCollection)
+#endif
             {
                 int otherCount = otherAsCollection.Count;
 
@@ -59,7 +63,11 @@ private protected override bool IsProperSupersetOfCore(IEnumerable<T> other)
         {
             Debug.Assert(_thisSet.Count != 0, "EmptyFrozenSet should have been used.");
 
+#if NET9_0_OR_GREATER // ICollection<T> : IReadOnlyCollection<T> on .NET 9+
+            if (other is IReadOnlyCollection<T> otherAsCollection)
+#else
             if (other is ICollection<T> otherAsCollection)
+#endif
             {
                 int otherCount = otherAsCollection.Count;
 
@@ -103,7 +111,11 @@ private protected override bool IsSupersetOfCore(IEnumerable<T> other)
             Debug.Assert(_thisSet.Count != 0, "EmptyFrozenSet should have been used.");
 
             // Try to compute the answer based purely on counts.
+#if NET9_0_OR_GREATER // ICollection<T> : IReadOnlyCollection<T> on .NET 9+
+            if (other is IReadOnlyCollection<T> otherAsCollection)
+#else
             if (other is ICollection<T> otherAsCollection)
+#endif
             {
                 int otherCount = otherAsCollection.Count;
 

src/libraries/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableExtensions.Minimal.cs

@@ -38,11 +38,13 @@ internal static bool TryGetCount<T>(this IEnumerable sequence, out int count)
                 return true;
             }
 
+#if !NET9_0_OR_GREATER // ICollection<T> : IReadOnlyCollection<T> on .NET 9+
             if (sequence is ICollection<T> collectionOfT)
             {
                 count = collectionOfT.Count;
                 return true;
             }
+#endif
 
             if (sequence is IReadOnlyCollection<T> readOnlyCollection)
             {

src/libraries/System.Collections/src/System/Collections/Generic/PriorityQueue.cs

@@ -462,7 +462,7 @@ public void EnqueueRange(IEnumerable<TElement> elements, TPriority priority)
             ArgumentNullException.ThrowIfNull(elements);
 
             int count;
-            if (elements is ICollection<TElement> collection &&
+            if (elements is IReadOnlyCollection<TElement> collection &&
                 (count = collection.Count) > _nodes.Length - _size)
             {
                 Grow(checked(_size + count));

src/libraries/System.Collections/src/System/Collections/Generic/SortedSet.cs

@@ -1323,7 +1323,7 @@ public bool Overlaps(IEnumerable<T> other)
             if (Count == 0)
                 return false;
 
-            if (other is ICollection<T> c && c.Count == 0)
+            if (other is IReadOnlyCollection<T> c && c.Count == 0)
                 return false;
 
             SortedSet<T>? asSorted = other as SortedSet<T>;

src/libraries/System.Linq.Expressions/src/System/Dynamic/ExpandoObject.cs

@@ -17,7 +17,7 @@ namespace System.Dynamic
     /// <summary>
     /// Represents an object with members that can be dynamically added and removed at runtime.
     /// </summary>
-    public sealed class ExpandoObject : IDynamicMetaObjectProvider, IDictionary<string, object?>, INotifyPropertyChanged
+    public sealed class ExpandoObject : IDynamicMetaObjectProvider, IDictionary<string, object?>, IReadOnlyDictionary<string, object?>, INotifyPropertyChanged
     {
         private static readonly MethodInfo s_expandoTryGetValue =
             typeof(RuntimeOps).GetMethod(nameof(RuntimeOps.ExpandoTryGetValue))!;
@@ -618,6 +618,10 @@ System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
 
         ICollection<object?> IDictionary<string, object?>.Values => new ValueCollection(this);
 
+        IEnumerable<string> IReadOnlyDictionary<string, object?>.Keys => new KeyCollection(this);
+
+        IEnumerable<object?> IReadOnlyDictionary<string, object?>.Values => new ValueCollection(this);
+
         object? IDictionary<string, object?>.this[string key]
         {
             get
@@ -636,6 +640,18 @@ System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
             }
         }
 
+        object? IReadOnlyDictionary<string, object?>.this[string key]
+        {
+            get
+            {
+                if (!TryGetValueForKey(key, out object? value))
+                {
+                    throw System.Linq.Expressions.Error.KeyDoesNotExistInExpando(key);
+                }
+                return value;
+            }
+        }
+
         void IDictionary<string, object?>.Add(string key, object? value)
         {
             this.TryAddMember(key, value);
@@ -650,6 +666,15 @@ System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
             return index >= 0 && data[index] != Uninitialized;
         }
 
+        bool IReadOnlyDictionary<string, object?>.ContainsKey(string key)
+        {
+            ArgumentNullException.ThrowIfNull(key);
+
+            ExpandoData data = _data;
+            int index = data.Class.GetValueIndexCaseSensitive(key);
+            return index >= 0 && data[index] != Uninitialized;
+        }
+
         bool IDictionary<string, object?>.Remove(string key)
         {
             ArgumentNullException.ThrowIfNull(key);
@@ -662,6 +687,11 @@ System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
             return TryGetValueForKey(key, out value);
         }
 
+        bool IReadOnlyDictionary<string, object?>.TryGetValue(string key, out object? value)
+        {
+            return TryGetValueForKey(key, out value);
+        }
+
         #endregion
 
         #region ICollection<KeyValuePair<string, object>> Members

src/libraries/System.Linq.Parallel/src/System/Linq/ParallelEnumerable.cs

@@ -1852,7 +1852,7 @@ public static int Count<TSource>(this ParallelQuery<TSource> source)
             // If the data source is a collection, we can just return the count right away.
             if (source is ParallelEnumerableWrapper<TSource> sourceAsWrapper)
             {
-                if (sourceAsWrapper.WrappedEnumerable is ICollection<TSource> sourceAsCollection)
+                if (sourceAsWrapper.WrappedEnumerable is IReadOnlyCollection<TSource> sourceAsCollection)
                 {
                     return sourceAsCollection.Count;
                 }
@@ -1923,7 +1923,7 @@ public static long LongCount<TSource>(this ParallelQuery<TSource> source)
             // If the data source is a collection, we can just return the count right away.
             if (source is ParallelEnumerableWrapper<TSource> sourceAsWrapper)
             {
-                if (sourceAsWrapper.WrappedEnumerable is ICollection<TSource> sourceAsCollection)
+                if (sourceAsWrapper.WrappedEnumerable is IReadOnlyCollection<TSource> sourceAsCollection)
                 {
                     return sourceAsCollection.Count;
                 }

src/libraries/System.Linq/src/System/Linq/AnyAll.cs

@@ -15,7 +15,7 @@ public static bool Any<TSource>(this IEnumerable<TSource> source)
                 ThrowHelper.ThrowArgumentNullException(ExceptionArgument.source);
             }
 
-            if (source is ICollection<TSource> gc)
+            if (source is IReadOnlyCollection<TSource> gc)
             {
                 return gc.Count != 0;
             }

src/libraries/System.Linq/src/System/Linq/AppendPrepend.SpeedOpt.cs

@@ -127,7 +127,7 @@ public override int GetCount(bool onlyIfCheap)
                     return count == -1 ? -1 : count + 1;
                 }
 
-                return !onlyIfCheap || _source is ICollection<TSource> ? _source.Count() + 1 : -1;
+                return !onlyIfCheap || _source is IReadOnlyCollection<TSource> ? _source.Count() + 1 : -1;
             }
 
             public override TSource? TryGetFirst(out bool found)
@@ -276,7 +276,7 @@ public override int GetCount(bool onlyIfCheap)
                     return count == -1 ? -1 : count + _appendCount + _prependCount;
                 }
 
-                return !onlyIfCheap || _source is ICollection<TSource> ? _source.Count() + _appendCount + _prependCount : -1;
+                return !onlyIfCheap || _source is IReadOnlyCollection<TSource> ? _source.Count() + _appendCount + _prependCount : -1;
             }
         }
     }

src/libraries/System.Linq/src/System/Linq/Count.cs

@@ -15,7 +15,7 @@ public static int Count<TSource>(this IEnumerable<TSource> source)
                 ThrowHelper.ThrowArgumentNullException(ExceptionArgument.source);
             }
 
-            if (source is ICollection<TSource> collectionoft)
+            if (source is IReadOnlyCollection<TSource> collectionoft)
             {
                 return collectionoft.Count;
             }
@@ -101,7 +101,7 @@ public static bool TryGetNonEnumeratedCount<TSource>(this IEnumerable<TSource> s
                 ThrowHelper.ThrowArgumentNullException(ExceptionArgument.source);
             }
 
-            if (source is ICollection<TSource> collectionoft)
+            if (source is IReadOnlyCollection<TSource> collectionoft)
             {
                 count = collectionoft.Count;
                 return true;

src/libraries/System.Linq/src/System/Linq/DefaultIfEmpty.SpeedOpt.cs

@@ -30,7 +30,7 @@ public override List<TSource> ToList()
             public override int GetCount(bool onlyIfCheap)
             {
                 int count;
-                if (!onlyIfCheap || _source is ICollection<TSource> || _source is ICollection)
+                if (!onlyIfCheap || _source is IReadOnlyCollection<TSource> || _source is ICollection)
                 {
                     count = _source.Count();
                 }

src/libraries/System.Linq/src/System/Linq/ElementAt.cs

@@ -16,7 +16,7 @@ public static TSource ElementAt<TSource>(this IEnumerable<TSource> source, int i
                 ThrowHelper.ThrowArgumentNullException(ExceptionArgument.source);
             }
 
-            if (source is IList<TSource> list)
+            if (source is IReadOnlyList<TSource> list)
             {
                 return list[index];
             }
@@ -115,7 +115,7 @@ public static TSource ElementAt<TSource>(this IEnumerable<TSource> source, Index
 
         private static TSource? TryGetElementAt<TSource>(this IEnumerable<TSource> source, int index, out bool found)
         {
-            if (source is IList<TSource> list)
+            if (source is IReadOnlyList<TSource> list)
             {
                 return (found = (uint)index < (uint)list.Count) ?
                     list[index] :

src/libraries/System.Linq/src/System/Linq/First.cs

@@ -78,7 +78,7 @@ public static TSource FirstOrDefault<TSource>(this IEnumerable<TSource> source,
 
         private static TSource? TryGetFirstNonIterator<TSource>(IEnumerable<TSource> source, out bool found)
         {
-            if (source is IList<TSource> list)
+            if (source is IReadOnlyList<TSource> list)
             {
                 if (list.Count > 0)
                 {

src/libraries/System.Linq/src/System/Linq/Grouping.cs

@@ -351,7 +351,7 @@ public interface IGrouping<out TKey, out TElement> : IEnumerable<TElement>
 
     [DebuggerDisplay("Key = {Key}")]
     [DebuggerTypeProxy(typeof(SystemLinq_GroupingDebugView<,>))]
-    internal sealed class Grouping<TKey, TElement> : IGrouping<TKey, TElement>, IList<TElement>
+    internal sealed class Grouping<TKey, TElement> : IGrouping<TKey, TElement>, IList<TElement>, IReadOnlyList<TElement>
     {
         internal readonly TKey _key;
         internal readonly int _hashCode;
@@ -398,6 +398,8 @@ public IEnumerator<TElement> GetEnumerator()
 
         int ICollection<TElement>.Count => _count;
 
+        int IReadOnlyCollection<TElement>.Count => _count;
+
         bool ICollection<TElement>.IsReadOnly => true;
 
         void ICollection<TElement>.Add(TElement item) => ThrowHelper.ThrowNotSupportedException();
@@ -431,5 +433,18 @@ TElement IList<TElement>.this[int index]
 
             set => ThrowHelper.ThrowNotSupportedException();
         }
+
+        TElement IReadOnlyList<TElement>.this[int index]
+        {
+            get
+            {
+                if ((uint)index >= (uint)_count)
+                {
+                    ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument.index);
+                }
+
+                return _elements[index];
+            }
+        }
     }
 }

src/libraries/System.Linq/src/System/Linq/Last.cs

@@ -77,7 +77,7 @@ public static TSource LastOrDefault<TSource>(this IEnumerable<TSource> source, F
 
         private static TSource? TryGetLastNonIterator<TSource>(IEnumerable<TSource> source, out bool found)
         {
-            if (source is IList<TSource> list)
+            if (source is IReadOnlyList<TSource> list)
             {
                 int count = list.Count;
                 if (count > 0)
@@ -126,7 +126,7 @@ public static TSource LastOrDefault<TSource>(this IEnumerable<TSource> source, F
                 return ordered.TryGetLast(predicate, out found);
             }
 
-            if (source is IList<TSource> list)
+            if (source is IReadOnlyList<TSource> list)
             {
                 for (int i = list.Count - 1; i >= 0; --i)
                 {

src/libraries/System.Linq/src/System/Linq/OrderedEnumerable.SpeedOpt.cs

@@ -58,7 +58,7 @@ public override int GetCount(bool onlyIfCheap)
                     return iterator.GetCount(onlyIfCheap);
                 }
 
-                return !onlyIfCheap || _source is ICollection<TElement> || _source is ICollection ? _source.Count() : -1;
+                return !onlyIfCheap || _source is IReadOnlyCollection<TElement> || _source is ICollection ? _source.Count() : -1;
             }
 
             internal TElement[] ToArray(int minIdx, int maxIdx)

src/libraries/System.Linq/src/System/Linq/Reverse.SpeedOpt.cs

@@ -30,7 +30,7 @@ public override int GetCount(bool onlyIfCheap) =>
 
             public override TSource? TryGetElementAt(int index, out bool found)
             {
-                if (_source is IList<TSource> list)
+                if (_source is IReadOnlyList<TSource> list)
                 {
                     int count = list.Count;
                     if ((uint)index < (uint)count)
@@ -59,7 +59,7 @@ public override int GetCount(bool onlyIfCheap) =>
                 {
                     return iterator.TryGetLast(out found);
                 }
-                else if (_source is IList<TSource> list)
+                else if (_source is IReadOnlyList<TSource> list)
                 {
                     int count = list.Count;
                     if (count > 0)
@@ -95,7 +95,7 @@ public override int GetCount(bool onlyIfCheap) =>
                 {
                     return iterator.TryGetFirst(out found);
                 }
-                else if (_source is IList<TSource> list)
+                else if (_source is IReadOnlyList<TSource> list)
                 {
                     if (list.Count > 0)
                     {

src/libraries/System.Linq/src/System/Linq/SequenceEqual.cs

@@ -22,7 +22,7 @@ public static bool SequenceEqual<TSource>(this IEnumerable<TSource> first, IEnum
                 ThrowHelper.ThrowArgumentNullException(ExceptionArgument.second);
             }
 
-            if (first is ICollection<TSource> firstCol && second is ICollection<TSource> secondCol)
+            if (first is IReadOnlyCollection<TSource> firstCol && second is IReadOnlyCollection<TSource> secondCol)
             {
                 if (first.TryGetSpan(out ReadOnlySpan<TSource> firstSpan) && second.TryGetSpan(out ReadOnlySpan<TSource> secondSpan))
                 {
@@ -34,7 +34,7 @@ public static bool SequenceEqual<TSource>(this IEnumerable<TSource> first, IEnum
                     return false;
                 }
 
-                if (firstCol is IList<TSource> firstList && secondCol is IList<TSource> secondList)
+                if (firstCol is IReadOnlyList<TSource> firstList && secondCol is IReadOnlyList<TSource> secondList)
                 {
                     comparer ??= EqualityComparer<TSource>.Default;
 

src/libraries/System.Linq/src/System/Linq/Single.cs

@@ -69,7 +69,7 @@ public static TSource SingleOrDefault<TSource>(this IEnumerable<TSource> source,
                 ThrowHelper.ThrowArgumentNullException(ExceptionArgument.source);
             }
 
-            if (source is IList<TSource> list)
+            if (source is IReadOnlyList<TSource> list)
             {
                 switch (list.Count)
                 {

src/libraries/System.Net.Security/src/System/Security/Authentication/ExtendedProtection/ServiceNameCollection.cs

@@ -147,7 +147,7 @@ private void AddIfNew(string serviceName)
         /// </summary>
         private static int GetCountOrOne(IEnumerable collection)
         {
-            ICollection<string>? c = collection as ICollection<string>;
+            IReadOnlyCollection<string>? c = collection as IReadOnlyCollection<string>;
             return c != null ? c.Count : 1;
         }
 

src/libraries/System.Private.CoreLib/src/System/Collections/Concurrent/ConcurrentQueue.cs

@@ -89,7 +89,7 @@ public ConcurrentQueue(IEnumerable<T> collection)
             // case we round its length up to a power of 2, as all segments must
             // be a power of 2 in length.
             int length = InitialSegmentLength;
-            if (collection is ICollection<T> c)
+            if (collection is IReadOnlyCollection<T> c)
             {
                 int count = c.Count;
                 if (count > length)