Add SwitchExpressionException

Fixes: #33284

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

@@ -1842,6 +1842,17 @@ public static class ProfileOptimization
         public static void StartProfile(string profile) { throw null; }
     }
 }
+namespace System.Runtime.CompilerServices
+{
+    [Serializable]
+    public sealed class SwitchExpressionException : System.InvalidOperationException
+    {
+        public SwitchExpressionException() { }
+        public SwitchExpressionException(object unmatchedValue) { }
+        public object UnmatchedValue { get { throw null; } }
+        public override void GetObjectData(System.Runtime.Serialization.SerializationInfo info, System.Runtime.Serialization.StreamingContext context) { }
+    }
+}
 namespace System.Runtime.Versioning
 {
     public sealed partial class FrameworkName : System.IEquatable<System.Runtime.Versioning.FrameworkName>

src/System.Runtime.Extensions/src/Resources/Strings.resx

@@ -166,6 +166,9 @@
   <data name="Arg_AppDomainUnloadedException" xml:space="preserve">
     <value>Attempted to access an unloaded AppDomain.</value>
   </data>
+  <data name="Arg_SwitchExpressionException" xml:space="preserve">
+    <value>Non-exhaustive switch expression failed to match its input.</value>
+  </data>
   <data name="ZeroLengthString" xml:space="preserve">
     <value>String cannot have zero length.</value>
   </data>

src/System.Runtime.Extensions/src/System.Runtime.Extensions.csproj

@@ -44,6 +44,7 @@
     <Compile Include="System\IO\InvalidDataException.cs" />
     <Compile Include="System\Net\WebUtility.cs" />
     <Compile Include="System\Reflection\AssemblyNameProxy.cs" />
+    <Compile Include="System\Runtime\CompilerServices\SwitchExpressionException.cs" />
     <Compile Include="System\Runtime\ProfileOptimization.cs" />
     <Compile Include="System\Runtime\Versioning\FrameworkName.cs" />
     <Compile Include="System\Runtime\Versioning\ComponentGuaranteesAttribute.cs" />

src/System.Runtime.Extensions/src/System/Runtime/CompilerServices/SwitchExpressionException.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.
+// See the LICENSE file in the project root for more information.
+
+using System.Runtime.Serialization;
+
+namespace System.Runtime.CompilerServices
+{
+    /// <summary>
+    /// Indicates that a switch expression that was non-exhaustive failed to match its input
+    /// at runtime, e.g. in the C# 8 expression <code>3 switch { 4 => 5 }</code>.
+    /// The exception optionally contains an object representing the unmatched value.
+    /// </summary>
+    [Serializable]
+    [System.Runtime.CompilerServices.TypeForwardedFrom("mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089")]
+    public sealed class SwitchExpressionException : InvalidOperationException//, ISerializable
+    {
+        public SwitchExpressionException()
+            : base(SR.Arg_SwitchExpressionException) { }
+
+        public SwitchExpressionException(object unmatchedValue)
+            : base()
+        {
+            UnmatchedValue = unmatchedValue;
+        }
+
+        private SwitchExpressionException(SerializationInfo info, StreamingContext context) 
+            : base(info, context)
+        {
+            info.AddValue(nameof(UnmatchedValue), UnmatchedValue, typeof(object));
+        }
+
+        public object UnmatchedValue { get; }
+
+        public override void GetObjectData(SerializationInfo info, StreamingContext context)
+        {
+           base.GetObjectData(info, context);
+            info.AddValue(nameof(UnmatchedValue), UnmatchedValue, typeof(object));
+        }
+    }
+}

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

@@ -50,6 +50,7 @@
     <Compile Include="System\Diagnostics\Stopwatch.cs" />
     <Compile Include="System\Environment.MachineName.cs" />
     <Compile Include="System\IO\PathTests_Combine.cs" />
+    <Compile Include="System\Runtime\CompilerServices\SwitchExpressionExceptionTests.cs" />
     <Compile Include="System\Runtime\Versioning\FrameworkName.cs" />
     <Compile Include="System\IO\PathTestsBase.cs" />
     <Compile Include="System\Net\WebUtility.cs" />

src/System.Runtime.Extensions/tests/System/Runtime/CompilerServices/SwitchExpressionExceptionTests.cs

@@ -0,0 +1,29 @@
+// 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.Runtime.CompilerServices;
+using Xunit;
+
+namespace System.Runtime.CompilerServices.Tests
+{
+    public class SwitchExpressionExceptionTests
+    {
+        [Fact]
+        public void UnmatchedValue()
+        {
+            var ex = new SwitchExpressionException(34);
+            Assert.Equal(34, ex.UnmatchedValue);
+
+            var data = new byte[] { 1, 2, 3 };
+            ex = new SwitchExpressionException(data);
+            Assert.Equal(data, ex.UnmatchedValue);
+
+            ex = new SwitchExpressionException(true);
+            Assert.Equal(true, ex.UnmatchedValue);
+
+            ex = new SwitchExpressionException("34");
+            Assert.Equal("34", ex.UnmatchedValue);
+        }
+    }
+}