Poly fill Index and Range types

src/libraries/Common/tests/System/Runtime/CompilerServices/RuntimeHelpers.cs

@@ -0,0 +1,45 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+#if (NETSTANDARD2_0 || NETFRAMEWORK)
+namespace System.Runtime.CompilerServices
+{
+    internal static class RuntimeHelpers
+    {
+        /// <summary>
+        /// Slices the specified array using the specified range.
+        /// </summary>
+        internal static T[] GetSubArray<T>(T[] array, Range range)
+        {
+            if (array == null)
+            {
+                throw new ArgumentNullException(nameof(array));
+            }
+
+            (int offset, int length) = range.GetOffsetAndLength(array.Length);
+
+            if (default(T) != null || typeof(T[]) == array.GetType())
+            {
+                // We know the type of the array to be exactly T[].
+
+                if (length == 0)
+                {
+                    return Array.Empty<T>();
+                }
+
+                var dest = new T[length];
+                Array.Copy(array, offset, dest, 0, length);
+                return dest;
+            }
+            else
+            {
+                // The array is actually a U[] where U:T.
+                var dest = (T[])Array.CreateInstance(array.GetType().GetElementType(), length);
+                Array.Copy(array, offset, dest, 0, length);
+                return dest;
+            }
+        }
+    }
+}
+#endif
+

src/libraries/Microsoft.Bcl.Memory/ref/Microsoft.Bcl.Memory.Forwards.ns21.cs

@@ -0,0 +1,5 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+[assembly: System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Index))]
+[assembly: System.Runtime.CompilerServices.TypeForwardedTo(typeof(System.Range))]

src/libraries/Microsoft.Bcl.Memory/ref/Microsoft.Bcl.Memory.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;$(NetFrameworkMinimum);$(NetCoreAppCurrent)</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;netstandard2.1;$(NetFrameworkMinimum);$(NetCoreAppCurrent)</TargetFrameworks>
   </PropertyGroup>
 
   <ItemGroup Condition="'$(TargetFrameworkIdentifier)' != '.NETCoreApp'">
@@ -12,6 +12,18 @@
     <Compile Include="Microsoft.Bcl.Memory.Forwards.cs" />
   </ItemGroup>
 
+  <ItemGroup Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp' Or '$(TargetFramework)' == 'netstandard2.1'">
+    <Compile Include="Microsoft.Bcl.Memory.Forwards.ns21.cs" />
+  </ItemGroup>
+
+  <ItemGroup Condition="'$(TargetFrameworkIdentifier)' == '.NETFramework' Or '$(TargetFramework)' == 'netstandard2.0'">
+    <Compile Include="Microsoft.Bcl.Memory.ns20.cs" />
+  </ItemGroup>
+
+  <ItemGroup Condition="'$(TargetFrameworkIdentifier)' == '.NETFramework'">
+    <PackageReference Include="System.ValueTuple" Version="$(SystemValueTupleVersion)" />
+  </ItemGroup>
+
   <ItemGroup Condition="'$(TargetFrameworkIdentifier)' != '.NETCoreApp'">
     <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
   </ItemGroup>

src/libraries/Microsoft.Bcl.Memory/ref/Microsoft.Bcl.Memory.ns20.cs

@@ -0,0 +1,41 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// ------------------------------------------------------------------------------
+// Changes to this file must follow the https://aka.ms/api-review process.
+// ------------------------------------------------------------------------------
+
+namespace System
+{
+    public readonly partial struct Index : System.IEquatable<System.Index>
+    {
+        private readonly int _dummyPrimitive;
+        public Index(int value, bool fromEnd = false) { throw null; }
+        public static System.Index End { get { throw null; } }
+        public bool IsFromEnd { get { throw null; } }
+        public static System.Index Start { get { throw null; } }
+        public int Value { get { throw null; } }
+        public bool Equals(System.Index other) { throw null; }
+        public override bool Equals([System.Diagnostics.CodeAnalysis.NotNullWhenAttribute(true)] object? value) { throw null; }
+        public static System.Index FromEnd(int value) { throw null; }
+        public static System.Index FromStart(int value) { throw null; }
+        public override int GetHashCode() { throw null; }
+        public int GetOffset(int length) { throw null; }
+        public static implicit operator System.Index (int value) { throw null; }
+        public override string ToString() { throw null; }
+    }
+    public readonly partial struct Range : System.IEquatable<System.Range>
+    {
+        private readonly int _dummyPrimitive;
+        public Range(System.Index start, System.Index end) { throw null; }
+        public static System.Range All { get { throw null; } }
+        public System.Index End { get { throw null; } }
+        public System.Index Start { get { throw null; } }
+        public static System.Range EndAt(System.Index end) { throw null; }
+        public override bool Equals([System.Diagnostics.CodeAnalysis.NotNullWhenAttribute(true)] object? value) { throw null; }
+        public bool Equals(System.Range other) { throw null; }
+        public override int GetHashCode() { throw null; }
+        public (int Offset, int Length) GetOffsetAndLength(int length) { throw null; }
+        public static System.Range StartAt(System.Index start) { throw null; }
+        public override string ToString() { throw null; }
+    }
+}

src/libraries/Microsoft.Bcl.Memory/src/Microsoft.Bcl.Memory.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;$(NetFrameworkMinimum);$(NetCoreAppCurrent)</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;netstandard2.1;$(NetFrameworkMinimum);$(NetCoreAppCurrent)</TargetFrameworks>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <IsPackable>true</IsPackable>
     <!-- Disabling baseline validation since this is a brand new package.
@@ -14,6 +14,7 @@
       Commonly Used Types:
       System.Buffers.Text.Base64Url
     </PackageDescription>
+    <DefineConstants>$(DefineConstants);MICROSOFT_BCL_MEMORY</DefineConstants>
   </PropertyGroup>
 
   <!-- DesignTimeBuild requires all the TargetFramework Derived Properties to not be present in the first property group. -->
@@ -25,6 +26,10 @@
     <Compile Include="..\ref\Microsoft.Bcl.Memory.Forwards.cs" />
   </ItemGroup>
 
+  <ItemGroup Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp' Or '$(TargetFramework)' == 'netstandard2.1'">
+    <Compile Include="..\ref\Microsoft.Bcl.Memory.Forwards.ns21.cs" />
+  </ItemGroup>
+
   <ItemGroup Condition="'$(TargetFrameworkIdentifier)' != '.NETCoreApp'">
     <Compile Include="..\..\System.Private.CoreLib\src\System\Buffers\Text\Base64Helper\Base64Helper.cs">
       <Link>System\Buffers\Text\Base64Helper\Base64Helper.cs</Link>
@@ -49,8 +54,17 @@
     </Compile>
   </ItemGroup>
 
+  <ItemGroup Condition="'$(TargetFrameworkIdentifier)' == '.NETFramework' Or '$(TargetFramework)' == 'netstandard2.0'">
+    <Compile Include="..\..\System.Private.CoreLib\src\System\Index.cs" />
+    <Compile Include="..\..\System.Private.CoreLib\src\System\Range.cs" />
+    <Compile Include="..\..\System.Private.CoreLib\src\System\Numerics\Hashing\HashHelpers.cs" />
+  </ItemGroup>
+
   <ItemGroup Condition="'$(TargetFrameworkIdentifier)' != '.NETCoreApp'">
     <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
   </ItemGroup>
-
+
+  <ItemGroup Condition="'$(TargetFrameworkIdentifier)' == '.NETFramework'">
+    <PackageReference Include="System.ValueTuple" Version="$(SystemValueTupleVersion)" />
+  </ItemGroup>
 </Project>

src/libraries/Microsoft.Bcl.Memory/tests/Microsoft.Bcl.Memory.Tests.csproj

@@ -24,10 +24,19 @@
     <Compile Include="..\..\System.Memory\tests\Base64Url\Base64UrlValidationUnitTests.cs">
       <Link>System\Memory\Base64Url\Base64UrlValidationUnitTests.cs</Link>
     </Compile>
+    <Compile Include="..\..\System.Runtime\tests\System.Runtime.Tests\System\RangeTests.cs">
+      <Link>System\RangeTests.cs</Link>
+    </Compile>
+    <Compile Include="..\..\System.Runtime\tests\System.Runtime.Tests\System\IndexTests.cs">
+      <Link>System\IndexTests.cs</Link>
+    </Compile>
+    <Compile Include="..\..\Common\tests\System\Runtime\CompilerServices\RuntimeHelpers.cs">
+      <Link>System\Runtime\CompilerServices\RuntimeHelpers.cs</Link>
+    </Compile>
   </ItemGroup>
-  
+
   <ItemGroup Condition="'$(TargetFrameworkIdentifier)' != '.NETCoreApp'">
     <ProjectReference Include="..\src\Microsoft.Bcl.Memory.csproj" />
   </ItemGroup>
-  
+
 </Project>

src/libraries/System.Private.CoreLib/src/System/Index.cs

@@ -15,7 +15,7 @@ namespace System
     /// int lastElement = someArray[^1]; // lastElement = 5
     /// </code>
     /// </remarks>
-#if SYSTEM_PRIVATE_CORELIB
+#if SYSTEM_PRIVATE_CORELIB || MICROSOFT_BCL_MEMORY
     public
 #else
     internal

src/libraries/System.Private.CoreLib/src/System/Range.cs

@@ -20,7 +20,7 @@ namespace System
     /// int[] subArray2 = someArray[1..^0]; // { 2, 3, 4, 5 }
     /// </code>
     /// </remarks>
-#if SYSTEM_PRIVATE_CORELIB
+#if SYSTEM_PRIVATE_CORELIB || MICROSOFT_BCL_MEMORY
     public
 #else
     internal