Fix dotnet/runtime#88244: StreamReader implements IAsyncDisposable

src/libraries/System.Private.CoreLib/src/System/IO/StreamReader.cs

@@ -16,6 +16,13 @@ namespace System.IO
     // whereas the Stream class is designed for byte input and output.
     public class StreamReader : TextReader
     {
+        public override async ValueTask DisposeAsync()
+        {
+            Dispose(true);
+            GC.SuppressFinalize(this);
+            await Task.CompletedTask;
+        }
+
         // StreamReader.Null is threadsafe.
         public static new readonly StreamReader Null = new NullStreamReader();
 

src/libraries/System.Private.CoreLib/src/System/IO/TextReader.cs

@@ -17,7 +17,7 @@ namespace System.IO
     //
     // This class is intended for character input, not bytes.
     // There are methods on the Stream class for reading bytes.
-    public abstract partial class TextReader : MarshalByRefObject, IDisposable
+    public abstract partial class TextReader : MarshalByRefObject, IDisposable, IAsyncDisposable
     {
         // Create our own instance to avoid static field initialization order problems on Mono.
         public static readonly TextReader Null = new StreamReader.NullStreamReader();
@@ -40,6 +40,13 @@ protected virtual void Dispose(bool disposing)
         {
         }
 
+        public virtual ValueTask DisposeAsync()
+        {
+            Dispose();
+            return default;
+        }
+        }
+
         // Returns the next available character without actually reading it from
         // the input stream. The current position of the TextReader is not changed by
         // this operation. The returned value is -1 if no further characters are

src/libraries/System.Runtime/ref/System.Runtime.cs

@@ -10909,6 +10909,8 @@ public virtual void WriteByte(byte value) { }
     }
     public partial class StreamReader : System.IO.TextReader
     {
+        public override System.Threading.Tasks.ValueTask DisposeAsync() { throw null; }
+
         public static readonly new System.IO.StreamReader Null;
         public StreamReader(System.IO.Stream stream) { }
         public StreamReader(System.IO.Stream stream, bool detectEncodingFromByteOrderMarks) { }
@@ -11046,11 +11048,12 @@ public override void WriteLine(System.Text.StringBuilder? value) { }
         public override System.Threading.Tasks.Task WriteLineAsync(string? value) { throw null; }
         public override System.Threading.Tasks.Task WriteLineAsync(System.Text.StringBuilder? value, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) { throw null; }
     }
-    public abstract partial class TextReader : System.MarshalByRefObject, System.IDisposable
+    public abstract partial class TextReader : System.MarshalByRefObject, System.IDisposable, System.IAsyncDisposable
     {
         public static readonly System.IO.TextReader Null;
         protected TextReader() { }
         public virtual void Close() { }
+        public virtual System.Threading.Tasks.ValueTask DisposeAsync() { throw null; }
         public void Dispose() { }
         protected virtual void Dispose(bool disposing) { }
         public virtual int Peek() { throw null; }

src/libraries/System.Runtime/tests/System.IO.Tests/StreamReader/StreamReader.cs

@@ -4,6 +4,23 @@
 using System.Collections.Generic;
 using System.Text;
 using Xunit;
+using System.Threading.Tasks;
+
+namespace System.IO.Tests
+{
+    public partial class StreamReaderTests : FileCleanupTestBase
+    {
+        [Fact]
+        public async Task DisposeAsync_ClosesStreamAsync()
+        {
+            var ms = new MemoryStream(Encoding.UTF8.GetBytes("Hello World"));
+            var reader = new StreamReader(ms);
+            await reader.DisposeAsync();
+            Assert.Throws<ObjectDisposedException>(() => ms.ReadByte());
+        }
+    }
+}
+
 
 namespace System.IO.Tests
 {