Added the type registry in advance of implementing Any support.

Biting off just this bit first as I don't need the changes from a previous PR for this part.

csharp/src/Google.Protobuf.Test/Google.Protobuf.Test.csproj

@@ -99,6 +99,7 @@
     <Compile Include="JsonTokenizerTest.cs" />
     <Compile Include="Reflection\DescriptorsTest.cs" />
     <Compile Include="Reflection\FieldAccessTest.cs" />
+    <Compile Include="Reflection\TypeRegistryTest.cs" />
     <Compile Include="SampleEnum.cs" />
     <Compile Include="SampleMessages.cs" />
     <Compile Include="TestProtos\MapUnittestProto3.cs" />

csharp/src/Google.Protobuf.Test/Reflection/TypeRegistryTest.cs

+#region Copyright notice and license
+// Protocol Buffers - Google's data interchange format
+// Copyright 2015 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.TestProtos;
+using Google.Protobuf.WellKnownTypes;
+using NUnit.Framework;
+
+namespace Google.Protobuf.Reflection
+{
+    public class TypeRegistryTest
+    {
+        // Most of our tests use messages. Simple test that we really can use files...
+        [Test]
+        public void CreateWithFileDescriptor()
+        {
+            var registry = TypeRegistry.FromFiles(DurationReflection.Descriptor, StructReflection.Descriptor);
+            AssertDescriptorPresent(registry, Duration.Descriptor);
+            AssertDescriptorPresent(registry, ListValue.Descriptor);
+            AssertDescriptorAbsent(registry, Timestamp.Descriptor);
+        }
+
+        [Test]
+        public void TypesFromSameFile()
+        {
+            // Just for kicks, let's start with a nested type
+            var registry = TypeRegistry.FromMessages(TestAllTypes.Types.NestedMessage.Descriptor);
+            // Top-level...
+            AssertDescriptorPresent(registry, TestFieldOrderings.Descriptor);
+            // ... and nested (not the same as the original NestedMessage!)
+            AssertDescriptorPresent(registry, TestFieldOrderings.Types.NestedMessage.Descriptor);
+        }
+
+        [Test]
+        public void DependenciesAreIncluded()
+        {
+            var registry = TypeRegistry.FromMessages(TestAllTypes.Descriptor);
+            // Direct dependencies
+            AssertDescriptorPresent(registry, ImportMessage.Descriptor);
+            // Public dependencies
+            AssertDescriptorPresent(registry, PublicImportMessage.Descriptor);
+        }
+
+        [Test]
+        public void DuplicateFiles()
+        {
+            // Duplicates via dependencies and simply via repetition
+            var registry = TypeRegistry.FromFiles(
+                UnittestProto3Reflection.Descriptor, UnittestImportProto3Reflection.Descriptor,
+                TimestampReflection.Descriptor, TimestampReflection.Descriptor);
+            AssertDescriptorPresent(registry, TestAllTypes.Descriptor);
+            AssertDescriptorPresent(registry, ImportMessage.Descriptor);
+            AssertDescriptorPresent(registry, Timestamp.Descriptor);
+        }
+
+        private static void AssertDescriptorPresent(TypeRegistry registry, MessageDescriptor descriptor)
+        {
+            Assert.AreSame(descriptor, registry.Find(descriptor.FullName));
+        }
+
+        private static void AssertDescriptorAbsent(TypeRegistry registry, MessageDescriptor descriptor)
+        {
+            Assert.IsNull(registry.Find(descriptor.FullName));
+        }
+    }
+}

csharp/src/Google.Protobuf/Google.Protobuf.csproj

@@ -121,6 +121,7 @@
     <Compile Include="Reflection\ServiceDescriptor.cs" />
     <Compile Include="Reflection\SingleFieldAccessor.cs" />
     <Compile Include="Preconditions.cs" />
+    <Compile Include="Reflection\TypeRegistry.cs" />
     <Compile Include="WellKnownTypes\Any.cs" />
     <Compile Include="WellKnownTypes\AnyPartial.cs" />
     <Compile Include="WellKnownTypes\Api.cs" />

csharp/src/Google.Protobuf/Reflection/TypeRegistry.cs

+#region Copyright notice and license
+// Protocol Buffers - Google's data interchange format
+// Copyright 2015 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 System.Collections.Generic;
+using System.Linq;
+
+namespace Google.Protobuf.Reflection
+{
+    /// <summary>
+    /// An immutable registry of types which can be looked up by their full name.
+    /// </summary>
+    public sealed class TypeRegistry
+    {
+        /// <summary>
+        /// An empty type registry, containing no types.
+        /// </summary>
+        public static TypeRegistry Empty { get; } = new TypeRegistry(new Dictionary<string, MessageDescriptor>());
+
+        private readonly Dictionary<string, MessageDescriptor> fullNameToMessageMap;
+
+        private TypeRegistry(Dictionary<string, MessageDescriptor> fullNameToMessageMap)
+        {
+            this.fullNameToMessageMap = fullNameToMessageMap;
+        }
+
+        /// <summary>
+        /// Attempts to find a message descriptor by its full name.
+        /// </summary>
+        /// <param name="fullName">The full name of the message, which is the dot-separated
+        /// combination of package, containing messages and message name</param>
+        /// <returns>The message descriptor corresponding to <paramref name="fullName"/> or null
+        /// if there is no such message descriptor.</returns>
+        public MessageDescriptor Find(string fullName)
+        {
+            MessageDescriptor ret;
+            // Ignore the return value as ret will end up with the right value either way.
+            fullNameToMessageMap.TryGetValue(fullName, out ret);
+            return ret;
+        }
+
+        /// <summary>
+        /// Creates a type registry from the specified set of file descriptors.
+        /// </summary>
+        /// <remarks>
+        /// This is a convenience overload for <see cref="FromFiles(IEnumerable{FileDescriptor})"/>
+        /// to allow calls such as <c>TypeRegistry.FromFiles(descriptor1, descriptor2)</c>.
+        /// </remarks>
+        /// <param name="fileDescriptors">The set of files to include in the registry. Must not contain null values.</param>
+        /// <returns>A type registry for the given files.</returns>
+        public static TypeRegistry FromFiles(params FileDescriptor[] fileDescriptors)
+        {
+            return FromFiles((IEnumerable<FileDescriptor>) fileDescriptors);
+        }
+
+        /// <summary>
+        /// Creates a type registry from the specified set of file descriptors.
+        /// </summary>
+        /// <remarks>
+        /// All message types within all the specified files are added to the registry, and
+        /// the dependencies of the specified files are also added, recursively.
+        /// </remarks>
+        /// <param name="fileDescriptors">The set of files to include in the registry. Must not contain null values.</param>
+        /// <returns>A type registry for the given files.</returns>
+        public static TypeRegistry FromFiles(IEnumerable<FileDescriptor> fileDescriptors)
+        {
+            Preconditions.CheckNotNull(fileDescriptors, nameof(fileDescriptors));
+            var builder = new Builder();
+            foreach (var file in fileDescriptors)
+            {
+                builder.AddFile(file);
+            }
+            return builder.Build();
+        }
+
+        /// <summary>
+        /// Creates a type registry from the file descriptor parents of the specified set of message descriptors.
+        /// </summary>
+        /// <remarks>
+        /// This is a convenience overload for <see cref="FromMessages(IEnumerable{MessageDescriptor})"/>
+        /// to allow calls such as <c>TypeRegistry.FromFiles(descriptor1, descriptor2)</c>.
+        /// </remarks>
+        /// <param name="messageDescriptors">The set of message descriptors to use to identify file descriptors to include in the registry.
+        /// Must not contain null values.</param>
+        /// <returns>A type registry for the given files.</returns>
+        public static TypeRegistry FromMessages(params MessageDescriptor[] messageDescriptors)
+        {
+            return FromMessages((IEnumerable<MessageDescriptor>) messageDescriptors);
+        }
+
+        /// <summary>
+        /// Creates a type registry from the file descriptor parents of the specified set of message descriptors.
+        /// </summary>
+        /// <remarks>
+        /// The specified message descriptors are only used to identify their file descriptors; the returned registry
+        /// contains all the types within the file descriptors which contain the specified message descriptors (and
+        /// the dependencies of those files), not just the specified messages.
+        /// </remarks>
+        /// <param name="messageDescriptors">The set of message descriptors to use to identify file descriptors to include in the registry.
+        /// Must not contain null values.</param>
+        /// <returns>A type registry for the given files.</returns>
+        public static TypeRegistry FromMessages(IEnumerable<MessageDescriptor> messageDescriptors)
+        {
+            Preconditions.CheckNotNull(messageDescriptors, nameof(messageDescriptors));
+            return FromFiles(messageDescriptors.Select(md => md.File));
+        }
+
+        /// <summary>
+        /// Builder class which isn't exposed, but acts as a convenient alternative to passing round two dictionaries in recursive calls.
+        /// </summary>
+        private class Builder
+        {
+            private readonly Dictionary<string, MessageDescriptor> types;
+            private readonly HashSet<string> fileDescriptorNames;
+
+            internal Builder()
+            {
+                types = new Dictionary<string, MessageDescriptor>();
+                fileDescriptorNames = new HashSet<string>();
+            }
+
+            internal void AddFile(FileDescriptor fileDescriptor)
+            {
+                if (!fileDescriptorNames.Add(fileDescriptor.Name))
+                {
+                    return;
+                }
+                foreach (var dependency in fileDescriptor.Dependencies)
+                {
+                    AddFile(dependency);
+                }
+                foreach (var message in fileDescriptor.MessageTypes)
+                {
+                    AddMessage(message);
+                }
+            }
+
+            private void AddMessage(MessageDescriptor messageDescriptor)
+            {
+                foreach (var nestedType in messageDescriptor.NestedTypes)
+                {
+                    AddMessage(nestedType);
+                }
+                // This will overwrite any previous entry. Given that each file should
+                // only be added once, this could be a problem such as package A.B with type C,
+                // and package A with type B.C... it's unclear what we should do in that case.
+                types[messageDescriptor.FullName] = messageDescriptor;
+            }
+
+            internal TypeRegistry Build()
+            {
+                return new TypeRegistry(types);
+            }
+        }
+    }
+}