Fix some compiler errors that can occur with specific project setups

contributing.md

@@ -192,7 +192,7 @@ Example:
 
 #pragma warning disable
 
-#if TASKSEXTENSIONSREFERENCED && (NETFRAMEWORK || NETSTANDARD2_0 || NETCOREAPP2_0)
+#if TASKSEXTENSIONSREFERENCED && MEMORYREFERENCED && (NETFRAMEWORK || NETSTANDARD2_0 || NETCOREAPP2_0)
 
 using System;
 using System.Buffers;

src/Polyfill/Nullability/NullabilityInfo.cs

@@ -6,6 +6,10 @@
 
 using System.Linq;
 using System.Diagnostics.CodeAnalysis;
+
+// Some code bases define their own Debug class, which can cause clashes and compile errors if we aren't explicit here
+using Debug = System.Diagnostics.Debug;
+
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 

src/Polyfill/Nullability/NullabilityInfoContext.cs

@@ -6,6 +6,10 @@
 
 using System.Linq;
 using System.Diagnostics.CodeAnalysis;
+
+// Some code bases define their own Debug class, which can cause clashes and compile errors if we aren't explicit here
+using Debug = System.Diagnostics.Debug;
+
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 

src/Polyfill/PolyfillExtensions_Stream.cs

@@ -13,6 +13,8 @@
 
 static partial class PolyfillExtensions
 {
+#if MEMORYREFERENCED
+
     /// <summary>
     /// Asynchronously reads a sequence of bytes from the current stream, advances the position within the stream by
     /// the number of bytes read, and monitors cancellation requests.
@@ -64,6 +66,8 @@ public static ValueTask WriteAsync(
         return new(target.WriteAsync(segment.Array!, segment.Offset, segment.Count, cancellationToken));
     }
 
+#endif
+
     /// <summary>
     /// Asynchronously reads the bytes from the current stream and writes them to another stream, using a specified
     /// cancellation token. Both streams positions are advanced by the number of bytes copied.

src/Polyfill/PolyfillExtensions_TextReader.cs

@@ -11,7 +11,7 @@
 
 static partial class PolyfillExtensions
 {
-#if TASKSEXTENSIONSREFERENCED && (NETFRAMEWORK || NETSTANDARD2_0 || NETCOREAPP2_0)
+#if TASKSEXTENSIONSREFERENCED && MEMORYREFERENCED && (NETFRAMEWORK || NETSTANDARD2_0 || NETCOREAPP2_0)
     /// <summary>
     /// Asynchronously reads the characters from the current stream into a memory block.
     /// </summary>

src/Polyfill/PolyfillExtensions_TextWriter.cs

@@ -2,7 +2,7 @@
 
 #pragma warning disable
 
-#if TASKSEXTENSIONSREFERENCED && (NETFRAMEWORK || NETSTANDARD2_0 || NETCOREAPP2_0)
+#if TASKSEXTENSIONSREFERENCED && MEMORYREFERENCED && (NETFRAMEWORK || NETSTANDARD2_0 || NETCOREAPP2_0)
 
 using System;
 using System.Buffers;

src/Tests/NullabilitySync.cs

@@ -50,6 +50,10 @@ public async Task Run()
                      using System.Linq;
                      using System.Diagnostics.CodeAnalysis;
 
+                     // Some code bases define their own Debug class, which can cause clashes and compile errors if we aren't explicit here
+                     using Debug = System.Diagnostics.Debug;
+
+
                      """;
 
         var suffix = """