Overcome the ref struct limitation for pre-roslyn compilers by introducing GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE for generated code (#7490)

* enable compatibility mode in codegen

* regenerate protos

* improve readability

* more robust way of figuring out path to old C# compiler

* add recent C# changes

Author: jtattermusch

CHANGES.txt

@@ -13,6 +13,17 @@ Unreleased Changes
   * Improved the error message when AttributeError is returned from __getattr__
     in EnumTypeWrapper.
 
+  C#:
+  * Dropped support for netstandard1.0 (replaced by support for netstandard1.1).
+    This was required to modernize the parsing stack to use the `Span<byte>`
+    type internally. (#7351)
+  * Add `ParseFrom(ReadOnlySequence<byte>)` method to enable GC friendly
+    parsing with reduced allocations and buffer copies. (#7351)
+  * Add `GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE` define to make
+    generated code compatible with old C# compilers (pre-roslyn compilers
+    from .NET framework and old versions of mono) that do not support
+    ref structs. (#7490)
+
 2020-05-26 version 3.12.2 (C++/Java/Python/PHP/Objective-C/C#/Ruby/JavaScript)
 
   C++

Makefile.am

@@ -127,6 +127,7 @@ csharp_EXTRA_DIST=                                                           \
   csharp/src/Google.Protobuf.Test/MessageParsingHelpers.cs                   \
   csharp/src/Google.Protobuf.Test/Proto3OptionalTest.cs                      \
   csharp/src/Google.Protobuf.Test/ReadOnlySequenceFactory.cs                 \
+  csharp/src/Google.Protobuf.Test/RefStructCompatibilityTest.cs              \
   csharp/src/Google.Protobuf.Test/Reflection/CustomOptionsTest.cs            \
   csharp/src/Google.Protobuf.Test/Reflection/DescriptorDeclarationTest.cs    \
   csharp/src/Google.Protobuf.Test/Reflection/DescriptorsTest.cs              \

csharp/src/AddressBook/Addressbook.cs

@@ -49,7 +49,11 @@ static AddressbookReflection() {
   /// <summary>
   /// [START messages]
   /// </summary>
-  public sealed partial class Person : pb::IMessage<Person>, pb::IBufferMessage {
+  public sealed partial class Person : pb::IMessage<Person>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<Person> _parser = new pb::MessageParser<Person>(() => new Person());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -256,9 +260,44 @@ public void MergeFrom(Person other) {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            Name = input.ReadString();
+            break;
+          }
+          case 16: {
+            Id = input.ReadInt32();
+            break;
+          }
+          case 26: {
+            Email = input.ReadString();
+            break;
+          }
+          case 34: {
+            phones_.AddEntriesFrom(input, _repeated_phones_codec);
+            break;
+          }
+          case 42: {
+            if (lastUpdated_ == null) {
+              LastUpdated = new global::Google.Protobuf.WellKnownTypes.Timestamp();
+            }
+            input.ReadMessage(LastUpdated);
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -293,6 +332,7 @@ public void MergeFrom(pb::CodedInputStream input) {
         }
       }
     }
+    #endif
 
     #region Nested types
     /// <summary>Container for nested types declared in the Person message type.</summary>
@@ -304,7 +344,11 @@ public enum PhoneType {
         [pbr::OriginalName("WORK")] Work = 2,
       }
 
-      public sealed partial class PhoneNumber : pb::IMessage<PhoneNumber>, pb::IBufferMessage {
+      public sealed partial class PhoneNumber : pb::IMessage<PhoneNumber>
+      #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+          , pb::IBufferMessage
+      #endif
+      {
         private static readonly pb::MessageParser<PhoneNumber> _parser = new pb::MessageParser<PhoneNumber>(() => new PhoneNumber());
         private pb::UnknownFieldSet _unknownFields;
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -441,9 +485,29 @@ public void MergeFrom(PhoneNumber other) {
 
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
         public void MergeFrom(pb::CodedInputStream input) {
+        #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
           input.ReadRawMessage(this);
+        #else
+          uint tag;
+          while ((tag = input.ReadTag()) != 0) {
+            switch(tag) {
+              default:
+                _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+                break;
+              case 10: {
+                Number = input.ReadString();
+                break;
+              }
+              case 16: {
+                Type = (global::Google.Protobuf.Examples.AddressBook.Person.Types.PhoneType) input.ReadEnum();
+                break;
+              }
+            }
+          }
+        #endif
         }
 
+        #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
         [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
         void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
           uint tag;
@@ -463,6 +527,7 @@ public void MergeFrom(pb::CodedInputStream input) {
             }
           }
         }
+        #endif
 
       }
 
@@ -474,7 +539,11 @@ public void MergeFrom(pb::CodedInputStream input) {
   /// <summary>
   /// Our address book file is just one of these.
   /// </summary>
-  public sealed partial class AddressBook : pb::IMessage<AddressBook>, pb::IBufferMessage {
+  public sealed partial class AddressBook : pb::IMessage<AddressBook>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
     private static readonly pb::MessageParser<AddressBook> _parser = new pb::MessageParser<AddressBook>(() => new AddressBook());
     private pb::UnknownFieldSet _unknownFields;
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
@@ -579,9 +648,25 @@ public void MergeFrom(AddressBook other) {
 
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
       input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            people_.AddEntriesFrom(input, _repeated_people_codec);
+            break;
+          }
+        }
+      }
+    #endif
     }
 
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
     [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
     void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
       uint tag;
@@ -597,6 +682,7 @@ public void MergeFrom(pb::CodedInputStream input) {
         }
       }
     }
+    #endif
 
   }