Tidy up reflection in advance of attempting to implement DynamicMessage.

There are corner cases where MessageDescriptor.{ClrType,Parser} will return null, and these are now documented. However, normally they *should* be implemented, even for descriptors of for dynamic messages. Ditto FieldDescriptor.Accessor.
We'll still need a fair amount of work to implement dynamic messages, but this change means that the public API will be remain intact.

Additionally, this change starts making use of C# 6 features in the files that it touches. This is far from exhaustive, and later PRs will have more.

Generated code changes coming in the next commit.

1 files changed, 5 insertions, 10 deletions

diff --git a/csharp/src/Google.Protobuf/Reflection/OneofDescriptor.cs b/csharp/src/Google.Protobuf/Reflection/OneofDescriptor.cs
index d51ee526..22020acf 100644
--- a/csharp/src/Google.Protobuf/Reflection/OneofDescriptor.cs
+++ b/csharp/src/Google.Protobuf/Reflection/OneofDescriptor.cs
@@ -86,8 +86,7 @@ namespace Google.Protobuf.Reflection
         /// in a particular message.
         /// </summary>
         /// <value>
-        /// The accessor used for reflective access, or <c>null</c> if reflection is not
-        /// supported by this descriptor.
+        /// The accessor used for reflective access.
         /// </value>
         public OneofAccessor Accessor { get { return accessor; } }
 
@@ -106,19 +105,15 @@ namespace Google.Protobuf.Reflection
 
         private OneofAccessor CreateAccessor(string clrName)
         {
-            if (containingType.GeneratedType == null || clrName == null)
-            {
-                return null;
-            }
-            var caseProperty = containingType.GeneratedType.GetProperty(clrName + "Case");
+            var caseProperty = containingType.ClrType.GetProperty(clrName + "Case");
             if (caseProperty == null)
             {
-                throw new DescriptorValidationException(this, "Property " + clrName + "Case not found in " + containingType.GeneratedType);
+                throw new DescriptorValidationException(this, $"Property {clrName}Case not found in {containingType.ClrType}");
             }
-            var clearMethod = containingType.GeneratedType.GetMethod("Clear" + clrName);
+            var clearMethod = containingType.ClrType.GetMethod("Clear" + clrName);
             if (clearMethod == null)
             {
-                throw new DescriptorValidationException(this, "Method Clear" + clrName + " not found in " + containingType.GeneratedType);
+                throw new DescriptorValidationException(this, $"Method Clear{clrName} not found in {containingType.ClrType}");
             }
 
             return new OneofAccessor(caseProperty, clearMethod, this);