Expose Index and Range with adding tests

src/System.Memory/src/ApiCompatBaseline.netcoreappaot.txt

@@ -0,0 +1,5 @@
+Compat issues with assembly System.Memory:
+MembersMustExist : Member 'System.ReadOnlySpan<T>.Item.get(System.Index)' does not exist in the implementation but it does exist in the contract. 
+MembersMustExist : Member 'System.ReadOnlySpan<T>.Item.get(System.Range)' does not exist in the implementation but it does exist in the contract.
+MembersMustExist : Member 'System.Span<T>.Item.get(System.Index)' does not exist in the implementation but it does exist in the contract.
+MembersMustExist : Member 'System.Span<T>.Item.get(System.Range)' does not exist in the implementation but it does exist in the contract.

src/System.Memory/tests/Span/Indexer.cs

@@ -0,0 +1,49 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Numerics;
+using Xunit;
+
+namespace System.SpanTests
+{
+    public static partial class IndexerTests
+    {
+        [Fact]
+        public static void IndexerWithIndexTest()
+        {
+            ReadOnlySpan<char> span = "Hello".AsSpan();
+            Assert.Equal('H', span[new Index(0, fromEnd: false)]);
+            Assert.Equal('o', span[new Index(1, fromEnd: true)]);
+            Assert.Equal(span[new Index(2, fromEnd: false)], span[new Index(span.Length - 2, fromEnd: true)]);
+
+            Assert.Throws<IndexOutOfRangeException>(() => "Hello".AsSpan()[new Index(0, fromEnd: true)]);
+
+            Span<char> span1 = new Span<char>(new char [] { 'H', 'e', 'l', 'l', 'o'});
+            Assert.Equal('e', span1[new Index(1, fromEnd: false)]);
+            Assert.Equal('l', span1[new Index(2, fromEnd: true)]);
+            Assert.Equal(span1[new Index(2, fromEnd: false)], span1[new Index(span.Length - 2, fromEnd: true)]);
+
+            Assert.Throws<IndexOutOfRangeException>(() =>
+                new Span<char>(new char [] { 'H', 'e', 'l', 'l', 'o'})[new Index(0, fromEnd: true)]);
+        }
+
+        [Fact]
+        public static void IndexerWithRangeTest()
+        {
+            ReadOnlySpan<char> span = "Hello".AsSpan();
+            ReadOnlySpan<char> sliced = span[Range.Create(new Index(1, fromEnd: false), new Index(1, fromEnd: true))];
+            Assert.True(span.Slice(1, 3) == sliced);
+
+            Assert.Throws<ArgumentOutOfRangeException>(() =>
+                { ReadOnlySpan<char> s = "Hello".AsSpan()[Range.Create(new Index(1, fromEnd: true), new Index(1, fromEnd: false))]; });
+
+            Span<char> span1 = new Span<char>(new char [] { 'H', 'e', 'l', 'l', 'o'});
+            Span<char> sliced1 = span1[Range.Create(new Index(2, fromEnd: false), new Index(1, fromEnd: true))];
+            Assert.True(span1.Slice(2, 2) == sliced1);
+
+            Assert.Throws<ArgumentOutOfRangeException>(() =>
+                { Span<char> s = new Span<char>(new char [] { 'H', 'i' })[Range.Create(new Index(0, fromEnd: true), new Index(1, fromEnd: false))]; });
+        }
+    }
+}

src/System.Memory/tests/System.Memory.Tests.csproj

@@ -239,6 +239,10 @@
     <Compile Include="ParsersAndFormatters\TestData.cs" />
     <Compile Include="ParsersAndFormatters\TestUtils.cs" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetGroup)' == 'netcoreapp'">
+    <Compile Include="Span\Indexer.cs" />
+  </ItemGroup>
+
   <ItemGroup>
     <Compile Include="Base64\Base64DecoderUnitTests.cs" />
     <Compile Include="Base64\Base64EncoderUnitTests.cs" />

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

@@ -985,6 +985,33 @@ void System.Runtime.Serialization.IDeserializationCallback.OnDeserialization(obj
         public static bool TryParse(string s, out System.Decimal result) { throw null; }
         public static bool TryParse(string s, System.Globalization.NumberStyles style, System.IFormatProvider provider, out System.Decimal result) { throw null; }
     }
+    public readonly partial struct Index : System.IEquatable<System.Index>
+    {
+        private readonly int _dummyPrimitive;
+        public Index(int value, bool fromEnd) { throw null; }
+        public int Value { get { throw null; } }
+        public bool FromEnd { get { throw null; } }
+        public override bool Equals(object value) { throw null; }
+        public bool Equals(Index other) { throw null; }
+        public override int GetHashCode() { throw null; }
+        public override string ToString() { throw null; }
+        public static implicit operator Index(int value) { throw null; }
+    }
+    public readonly partial struct Range : System.IEquatable<System.Range>
+    {
+        private readonly int _dummyPrimitive;
+        public Index Start { get { throw null; } }
+        public Index End { get { throw null; } }
+        public override bool Equals(object value) { throw null; }
+        public bool Equals(Range other) { throw null; }
+        public override int GetHashCode() { throw null; }
+        public override string ToString() { throw null; }
+        public static Range Create(Index start, Index end) { throw null; }
+        public static Range FromStart(Index start) { throw null; }
+        public static Range ToEnd(Index end) { throw null; }
+        public static Range All() { throw null; }
+    }
+
     public abstract partial class Delegate : System.ICloneable, System.Runtime.Serialization.ISerializable
     {
         protected Delegate(object target, string method) { }
@@ -1983,6 +2010,8 @@ public readonly ref partial struct ReadOnlySpan<T>
         public static System.ReadOnlySpan<T> Empty { get { throw null; } }
         public bool IsEmpty { get { throw null; } }
         public ref readonly T this[int index] { get { throw null; } }
+        public ref readonly T this[Index index] { get { throw null; } }
+        public ReadOnlySpan<T> this[Range range] { get { throw null; } }
         public int Length { get { throw null; } }
         public void CopyTo(System.Span<T> destination) { }
         [System.ComponentModel.EditorBrowsableAttribute((System.ComponentModel.EditorBrowsableState)(1))]
@@ -2185,6 +2214,8 @@ public readonly ref partial struct Span<T>
         public static System.Span<T> Empty { get { throw null; } }
         public bool IsEmpty { get { throw null; } }
         public ref T this[int index] { get { throw null; } }
+        public ref T this[Index index] { get { throw null; } }
+        public Span<T> this[Range range] { get { throw null; } }
         public int Length { get { throw null; } }
         public void Clear() { }
         public void CopyTo(System.Span<T> destination) { }
@@ -7003,7 +7034,7 @@ public StructLayoutAttribute(System.Runtime.InteropServices.LayoutKind layoutKin
 namespace System.Runtime.Remoting
 {
     public class ObjectHandle : MarshalByRefObject
-    {        
+    {
         private ObjectHandle() { }
         public ObjectHandle(Object o) { }
         public Object Unwrap() { throw null; }

src/System.Runtime/src/ApiCompatBaseline.netcoreappaot.txt

@@ -3,3 +3,9 @@ MembersMustExist : Member 'System.String System.Runtime.CompilerServices.Runtime
 TypeCannotChangeClassification : Type 'System.DateTimeOffset' is marked as readonly in the contract so it must also be marked readonly in the implementation.
 TypeCannotChangeClassification : Type 'System.TimeSpan' is marked as readonly in the contract so it must also be marked readonly in the implementation.
 TypeCannotChangeClassification : Type 'System.Runtime.Serialization.SerializationEntry' is marked as readonly in the contract so it must also be marked readonly in the implementation.
+TypesMustExist : Type 'System.Index' does not exist in the implementation but it does exist in the contract. 
+TypesMustExist : Type 'System.Range' does not exist in the implementation but it does exist in the contract.
+MembersMustExist : Member 'System.ReadOnlySpan<T>.Item.get(System.Index)' does not exist in the implementation but it does exist in the contract. 
+MembersMustExist : Member 'System.ReadOnlySpan<T>.Item.get(System.Range)' does not exist in the implementation but it does exist in the contract.
+MembersMustExist : Member 'System.Span<T>.Item.get(System.Index)' does not exist in the implementation but it does exist in the contract.
+MembersMustExist : Member 'System.Span<T>.Item.get(System.Range)' does not exist in the implementation but it does exist in the contract.

src/System.Runtime/src/ApiCompatBaseline.uapaot.txt

@@ -0,0 +1,6 @@
+TypesMustExist : Type 'System.Index' does not exist in the implementation but it does exist in the contract. 
+TypesMustExist : Type 'System.Range' does not exist in the implementation but it does exist in the contract.
+MembersMustExist : Member 'System.ReadOnlySpan<T>.Item.get(System.Index)' does not exist in the implementation but it does exist in the contract. 
+MembersMustExist : Member 'System.ReadOnlySpan<T>.Item.get(System.Range)' does not exist in the implementation but it does exist in the contract.
+MembersMustExist : Member 'System.Span<T>.Item.get(System.Index)' does not exist in the implementation but it does exist in the contract.
+MembersMustExist : Member 'System.Span<T>.Item.get(System.Range)' does not exist in the implementation but it does exist in the contract.

src/System.Runtime/tests/System.Runtime.Tests.csproj

@@ -221,12 +221,14 @@
     <Compile Include="System\FormattableStringTests.netcoreapp.cs" />
     <Compile Include="System\GCTests.netcoreapp.cs" />
     <Compile Include="System\GuidTests.netcoreapp.cs" />
+    <Compile Include="System\IndexTests.cs" />
     <Compile Include="System\Int16Tests.netcoreapp.cs" />
     <Compile Include="System\Int32Tests.netcoreapp.cs" />
     <Compile Include="System\Int64Tests.netcoreapp.cs" />
     <Compile Include="System\IntPtrTests.netcoreapp.cs" />
     <Compile Include="System\Collections\Generic\KeyValuePairTests.netcoreapp.cs" />
     <Compile Include="System\LazyTests.netcoreapp.cs" />
+    <Compile Include="System\RangeTests.cs" />
     <Compile Include="System\SByteTests.netcoreapp.cs" />
     <Compile Include="System\StringComparerTests.netcoreapp.cs" />
     <Compile Include="System\StringGetHashCodeTests.netcoreapp.cs" />

src/System.Runtime/tests/System/IndexTests.cs

@@ -0,0 +1,75 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using Xunit;
+
+namespace System.Tests
+{
+    public static class IndexTests
+    {
+        [Fact]
+        public static void CreationTest()
+        {
+            Index index = new Index(1, fromEnd: false);
+            Assert.Equal(1, index.Value);
+            Assert.False(index.FromEnd);
+
+            index = new Index(11, fromEnd: true);
+            Assert.Equal(11, index.Value);
+            Assert.True(index.FromEnd);
+
+            AssertExtensions.Throws<ArgumentOutOfRangeException>("value", () => new Index(-1, fromEnd: false));
+        }
+
+        [Fact]
+        public static void ImplicitCastTest()
+        {
+            Index index = 10;
+            Assert.Equal(10, index.Value);
+            Assert.False(index.FromEnd);
+        }
+
+        [Fact]
+        public static void EqualityTest()
+        {
+            Index index1 = 10;
+            Index index2 = 10;
+            Assert.True(index1.Equals(index2));
+            Assert.True(index1.Equals((object)index2));
+
+            index2 = new Index(10, fromEnd: true);
+            Assert.False(index1.Equals(index2));
+            Assert.False(index1.Equals((object)index2));
+
+            index2 = new Index(9, fromEnd: false);
+            Assert.False(index1.Equals(index2));
+            Assert.False(index1.Equals((object)index2));
+        }
+
+        [Fact]
+        public static void HashCodeTest()
+        {
+            Index index1 = 10;
+            Index index2 = 10;
+            Assert.Equal(index1.GetHashCode(), index2.GetHashCode());
+
+            index2 = new Index(10, fromEnd: true);
+            Assert.NotEqual(index1.GetHashCode(), index2.GetHashCode());
+
+            index2 = new Index(99999, fromEnd: false);
+            Assert.NotEqual(index1.GetHashCode(), index2.GetHashCode());
+        }
+
+        [Fact]
+        public static void ToStringTest()
+        {
+            Index index1 = 100;
+            Assert.Equal(100.ToString(), index1.ToString());
+
+            index1 = new Index(50, fromEnd: true);
+            Assert.Equal("^" + 50.ToString(), index1.ToString());
+        }
+    }
+}

src/System.Runtime/tests/System/RangeTests.cs

@@ -0,0 +1,81 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using Xunit;
+
+namespace System.Tests
+{
+    public static class RangeTests
+    {
+        [Fact]
+        public static void CreationTest()
+        {
+            Range range = Range.Create(new Index(10, fromEnd: false), new Index(2, fromEnd: true));
+            Assert.Equal(10, range.Start.Value);
+            Assert.False(range.Start.FromEnd);
+            Assert.Equal(2, range.End.Value);
+            Assert.True(range.End.FromEnd);
+
+            range = Range.FromStart(new Index(7, fromEnd: false));
+            Assert.Equal(7, range.Start.Value);
+            Assert.False(range.Start.FromEnd);
+            Assert.Equal(0, range.End.Value);
+            Assert.True(range.End.FromEnd);
+
+            range = Range.ToEnd(new Index(3, fromEnd: true));
+            Assert.Equal(0, range.Start.Value);
+            Assert.False(range.Start.FromEnd);
+            Assert.Equal(3, range.End.Value);
+            Assert.True(range.End.FromEnd);
+
+            range = Range.All();
+            Assert.Equal(0, range.Start.Value);
+            Assert.False(range.Start.FromEnd);
+            Assert.Equal(0, range.End.Value);
+            Assert.True(range.End.FromEnd);
+        }
+
+        [Fact]
+        public static void EqualityTest()
+        {
+            Range range1 = Range.Create(new Index(10, fromEnd: false), new Index(20, fromEnd: false));
+            Range range2 = Range.Create(new Index(10, fromEnd: false), new Index(20, fromEnd: false));
+            Assert.True(range1.Equals(range2));
+            Assert.True(range1.Equals((object)range2));
+
+            range2 = Range.Create(new Index(10, fromEnd: false), new Index(20, fromEnd: true));
+            Assert.False(range1.Equals(range2));
+            Assert.False(range1.Equals((object)range2));
+
+            range2 = Range.Create(new Index(10, fromEnd: false), new Index(21, fromEnd: false));
+            Assert.False(range1.Equals(range2));
+            Assert.False(range1.Equals((object)range2));
+        }
+
+        [Fact]
+        public static void HashCodeTest()
+        {
+            Range range1 = Range.Create(new Index(10, fromEnd: false), new Index(20, fromEnd: false));
+            Range range2 = Range.Create(new Index(10, fromEnd: false), new Index(20, fromEnd: false));
+            Assert.Equal(range1.GetHashCode(), range2.GetHashCode());
+
+            range2 = Range.Create(new Index(10, fromEnd: false), new Index(20, fromEnd: true));
+            Assert.NotEqual(range1.GetHashCode(), range2.GetHashCode());
+
+            range2 = Range.Create(new Index(10, fromEnd: false), new Index(21, fromEnd: false));
+            Assert.NotEqual(range1.GetHashCode(), range2.GetHashCode());
+        }
+
+        [Fact]
+        public static void ToStringTest()
+        {
+            Range range1 = Range.Create(new Index(10, fromEnd: false), new Index(20, fromEnd: false));
+            Assert.Equal(10.ToString() + ".." + 20.ToString(), range1.ToString());
+
+            range1 = Range.Create(new Index(10, fromEnd: false), new Index(20, fromEnd: true));
+            Assert.Equal(10.ToString() + "..^" + 20.ToString(), range1.ToString());
+        }
+    }
+}