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diff --git a/third_party/protobuf/3.6.0/csharp/src/Google.Protobuf/Reflection/ReflectionUtil.cs b/third_party/protobuf/3.6.0/csharp/src/Google.Protobuf/Reflection/ReflectionUtil.cs
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+#region Copyright notice and license
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#endregion
+
+using Google.Protobuf.Compatibility;
+using System;
+using System.Reflection;
+
+namespace Google.Protobuf.Reflection
+{
+    /// <summary>
+    /// The methods in this class are somewhat evil, and should not be tampered with lightly.
+    /// Basically they allow the creation of relatively weakly typed delegates from MethodInfos
+    /// which are more strongly typed. They do this by creating an appropriate strongly typed
+    /// delegate from the MethodInfo, and then calling that within an anonymous method.
+    /// Mind-bending stuff (at least to your humble narrator) but the resulting delegates are
+    /// very fast compared with calling Invoke later on.
+    /// </summary>
+    internal static class ReflectionUtil
+    {
+        static ReflectionUtil()
+        {
+            ForceInitialize<string>(); // Handles all reference types
+            ForceInitialize<int>();
+            ForceInitialize<long>();
+            ForceInitialize<uint>();
+            ForceInitialize<ulong>();
+            ForceInitialize<float>();
+            ForceInitialize<double>();
+            ForceInitialize<bool>();
+            ForceInitialize<int?>();
+            ForceInitialize<long?>();
+            ForceInitialize<uint?>();
+            ForceInitialize<ulong?>();
+            ForceInitialize<float?>();
+            ForceInitialize<double?>();
+            ForceInitialize<bool?>();
+            ForceInitialize<SampleEnum>();
+            SampleEnumMethod();
+        }
+
+        internal static void ForceInitialize<T>() => new ReflectionHelper<IMessage, T>();
+
+        /// <summary>
+        /// Empty Type[] used when calling GetProperty to force property instead of indexer fetching.
+        /// </summary>
+        internal static readonly Type[] EmptyTypes = new Type[0];
+
+        /// <summary>
+        /// Creates a delegate which will cast the argument to the type that declares the method,
+        /// call the method on it, then convert the result to object.
+        /// </summary>
+        /// <param name="method">The method to create a delegate for, which must be declared in an IMessage
+        /// implementation.</param>
+        internal static Func<IMessage, object> CreateFuncIMessageObject(MethodInfo method) =>
+            GetReflectionHelper(method.DeclaringType, method.ReturnType).CreateFuncIMessageObject(method);
+
+        /// <summary>
+        /// Creates a delegate which will cast the argument to the type that declares the method,
+        /// call the method on it, then convert the result to the specified type. The method is expected
+        /// to actually return an enum (because of where we're calling it - for oneof cases). Sometimes that
+        /// means we need some extra work to perform conversions.
+        /// </summary>
+        /// <param name="method">The method to create a delegate for, which must be declared in an IMessage
+        /// implementation.</param>
+        internal static Func<IMessage, int> CreateFuncIMessageInt32(MethodInfo method) =>
+            GetReflectionHelper(method.DeclaringType, method.ReturnType).CreateFuncIMessageInt32(method);
+
+        /// <summary>
+        /// Creates a delegate which will execute the given method after casting the first argument to
+        /// the type that declares the method, and the second argument to the first parameter type of the method.
+        /// </summary>
+        /// <param name="method">The method to create a delegate for, which must be declared in an IMessage
+        /// implementation.</param>
+        internal static Action<IMessage, object> CreateActionIMessageObject(MethodInfo method) =>
+            GetReflectionHelper(method.DeclaringType, method.GetParameters()[0].ParameterType).CreateActionIMessageObject(method);
+
+        /// <summary>
+        /// Creates a delegate which will execute the given method after casting the first argument to
+        /// type that declares the method.
+        /// </summary>
+        /// <param name="method">The method to create a delegate for, which must be declared in an IMessage
+        /// implementation.</param>
+        internal static Action<IMessage> CreateActionIMessage(MethodInfo method) =>
+            GetReflectionHelper(method.DeclaringType, typeof(object)).CreateActionIMessage(method);
+
+        /// <summary>
+        /// Creates a reflection helper for the given type arguments. Currently these are created on demand
+        /// rather than cached; this will be "busy" when initially loading a message's descriptor, but after that
+        /// they can be garbage collected. We could cache them by type if that proves to be important, but creating
+        /// an object is pretty cheap.
+        /// </summary>
+        private static IReflectionHelper GetReflectionHelper(Type t1, Type t2) =>
+            (IReflectionHelper) Activator.CreateInstance(typeof(ReflectionHelper<,>).MakeGenericType(t1, t2));
+
+        // Non-generic interface allowing us to use an instance of ReflectionHelper<T1, T2> without statically
+        // knowing the types involved.
+        private interface IReflectionHelper
+        {
+            Func<IMessage, int> CreateFuncIMessageInt32(MethodInfo method);
+            Action<IMessage> CreateActionIMessage(MethodInfo method);
+            Func<IMessage, object> CreateFuncIMessageObject(MethodInfo method);
+            Action<IMessage, object> CreateActionIMessageObject(MethodInfo method);
+        }
+
+        private class ReflectionHelper<T1, T2> : IReflectionHelper
+        {
+
+            public Func<IMessage, int> CreateFuncIMessageInt32(MethodInfo method)
+            {
+                // On pleasant runtimes, we can create a Func<int> from a method returning
+                // an enum based on an int. That's the fast path.
+                if (CanConvertEnumFuncToInt32Func)
+                {
+                    var del = (Func<T1, int>) method.CreateDelegate(typeof(Func<T1, int>));
+                    return message => del((T1) message);
+                }
+                else
+                {
+                    // On some runtimes (e.g. old Mono) the return type has to be exactly correct,
+                    // so we go via boxing. Reflection is already fairly inefficient, and this is
+                    // only used for one-of case checking, fortunately.
+                    var del = (Func<T1, T2>) method.CreateDelegate(typeof(Func<T1, T2>));
+                    return message => (int) (object) del((T1) message);
+                }
+            }
+
+            public Action<IMessage> CreateActionIMessage(MethodInfo method)
+            {
+                var del = (Action<T1>) method.CreateDelegate(typeof(Action<T1>));
+                return message => del((T1) message);
+            }
+
+            public Func<IMessage, object> CreateFuncIMessageObject(MethodInfo method)
+            {
+                var del = (Func<T1, T2>) method.CreateDelegate(typeof(Func<T1, T2>));
+                return message => del((T1) message);
+            }
+
+            public Action<IMessage, object> CreateActionIMessageObject(MethodInfo method)
+            {
+                var del = (Action<T1, T2>) method.CreateDelegate(typeof(Action<T1, T2>));
+                return (message, arg) => del((T1) message, (T2) arg);
+            }
+        }
+
+        // Runtime compatibility checking code - see ReflectionHelper<T1, T2>.CreateFuncIMessageInt32 for
+        // details about why we're doing this.
+
+        // Deliberately not inside the generic type. We only want to check this once.
+        private static bool CanConvertEnumFuncToInt32Func { get; } = CheckCanConvertEnumFuncToInt32Func();
+
+        private static bool CheckCanConvertEnumFuncToInt32Func()
+        {
+            try
+            {
+                // Try to do the conversion using reflection, so we can see whether it's supported.
+                MethodInfo method = typeof(ReflectionUtil).GetMethod(nameof(SampleEnumMethod));
+                // If this passes, we're in a reasonable runtime.
+                method.CreateDelegate(typeof(Func<int>));
+                return true;
+            }
+            catch (ArgumentException)
+            {
+                return false;
+            }
+        }
+
+        public enum SampleEnum
+        {
+            X
+        }
+
+        // Public to make the reflection simpler.
+        public static SampleEnum SampleEnumMethod() => SampleEnum.X;
+    }
+}