Adding ValueTuple and ITuple to corlib in CoreCLR (dotnet/coreclr#8695)

* Adding ValueTuple
* Adding ITuple
* Porting equality comparer optimization from corefx PR dotnet/coreclr#14187

Commit migrated from dotnet/coreclr@2d49c2c

src/coreclr/src/mscorlib/System.Private.CoreLib.csproj

@@ -170,6 +170,10 @@
     <!-- We want the sources to show up nicely in VS-->
     <Compile Include="@(MscorlibSources)">
     </Compile>
+    <Compile Include="src\System\Runtime\CompilerServices\ITuple.cs" />
+    <Compile Include="src\System\Runtime\CompilerServices\TupleElementNamesAttribute.cs" />
+    <Compile Include="src\System\TupleExtensions.cs" />
+    <Compile Include="src\System\ValueTuple.cs" />
   </ItemGroup>
 
   <!-- Resources -->

src/coreclr/src/mscorlib/corefx/SR.cs

@@ -585,4 +585,14 @@ public static string Format(string formatString, params object[] args)
     {
         return string.Format(CultureInfo.CurrentCulture, formatString, args);
     }
+
+    internal static string ArgumentException_ValueTupleIncorrectType
+    {
+        get { return Environment.GetResourceString("ArgumentException_ValueTupleIncorrectType"); }
+    }
+
+    internal static string ArgumentException_ValueTupleLastArgumentNotATuple
+    {
+        get { return Environment.GetResourceString("ArgumentException_ValueTupleLastArgumentNotATuple"); }
+    }
 }

src/coreclr/src/mscorlib/src/System.Private.CoreLib.txt

@@ -2282,3 +2282,6 @@ Globalization.cp_57011 = ISCII Punjabi
 
 ;------------------
 
+; ValueTuple
+ArgumentException_ValueTupleIncorrectType=Argument must be of type {0}.
+ArgumentException_ValueTupleLastArgumentNotAValueTuple=The last element of an eight element ValueTuple must be a ValueTuple.

src/coreclr/src/mscorlib/src/System/Numerics/Hashing/HashHelpers.cs

@@ -8,12 +8,14 @@ namespace System.Numerics.Hashing
 
     internal static class HashHelpers
     {
+        public static readonly int RandomSeed = new Random().Next(Int32.MinValue, Int32.MaxValue);
+
         public static int Combine(int h1, int h2)
         {
-            // The jit optimizes this to use the ROL instruction on x86
+            // RyuJIT optimizes this to use the ROL instruction
             // Related GitHub pull request: dotnet/coreclr#1830
-            uint shift5 = ((uint)h1 << 5) | ((uint)h1 >> 27);
-            return ((int)shift5 + h1) ^ h2;
+            uint rol5 = ((uint)h1 << 5) | ((uint)h1 >> 27);
+            return ((int)rol5 + h1) ^ h2;
         }
     }
 }

src/coreclr/src/mscorlib/src/System/Runtime/CompilerServices/ITuple.cs

@@ -0,0 +1,22 @@
+// 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.
+
+namespace System.Runtime.CompilerServices
+{
+    /// <summary>
+    /// This interface is required for types that want to be indexed into by dynamic patterns.
+    /// </summary>
+    public interface ITuple
+    {
+        /// <summary>
+        /// The number of positions in this data structure.
+        /// </summary>
+        int Length { get; }
+
+        /// <summary>
+        /// Get the element at position <param name="index"/>.
+        /// </summary>
+        object this[int index] { get; }
+    }
+}

src/coreclr/src/mscorlib/src/System/Runtime/CompilerServices/TupleElementNamesAttribute.cs

@@ -0,0 +1,57 @@
+// 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.Collections.Generic;
+
+namespace System.Runtime.CompilerServices
+{
+    /// <summary>
+    /// Indicates that the use of <see cref="System.ValueTuple"/> on a member is meant to be treated as a tuple with element names.
+    /// </summary>
+    [CLSCompliant(false)]
+    [AttributeUsage(AttributeTargets.Field | AttributeTargets.Parameter | AttributeTargets.Property | AttributeTargets.ReturnValue | AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Event)]
+    public sealed class TupleElementNamesAttribute : Attribute
+    {
+        private readonly string[] _transformNames;
+
+        /// <summary>
+        /// Initializes a new instance of the <see
+        /// cref="TupleElementNamesAttribute"/> class.
+        /// </summary>
+        /// <param name="transformNames">
+        /// Specifies, in a pre-order depth-first traversal of a type's
+        /// construction, which <see cref="System.ValueType"/> occurrences are
+        /// meant to carry element names.
+        /// </param>
+        /// <remarks>
+        /// This constructor is meant to be used on types that contain an
+        /// instantiation of <see cref="System.ValueType"/> that contains
+        /// element names.  For instance, if <c>C</c> is a generic type with
+        /// two type parameters, then a use of the constructed type <c>C{<see
+        /// cref="System.ValueTuple{T1, T2}"/>, <see
+        /// cref="System.ValueTuple{T1, T2, T3}"/></c> might be intended to
+        /// treat the first type argument as a tuple with element names and the
+        /// second as a tuple without element names. In which case, the
+        /// appropriate attribute specification should use a
+        /// <c>transformNames</c> value of <c>{ "name1", "name2", null, null,
+        /// null }</c>.
+        /// </remarks>
+        public TupleElementNamesAttribute(string[] transformNames)
+        {
+            if (transformNames == null)
+            {
+                throw new ArgumentNullException(nameof(transformNames));
+            }
+
+            _transformNames = transformNames;
+        }
+
+        /// <summary>
+        /// Specifies, in a pre-order depth-first traversal of a type's
+        /// construction, which <see cref="System.ValueTuple"/> elements are
+        /// meant to carry element names.
+        /// </summary>
+        public IList<string> TransformNames => _transformNames;
+    }
+}