Add option to enable csharp nullable reference types

csharp/generate_protos.sh

@@ -75,6 +75,16 @@ $PROTOC -Isrc -I. \
     src/google/protobuf/test_messages_proto2.proto \
     src/google/protobuf/unittest_proto3_optional.proto \
     src/google/protobuf/unittest_retention.proto
+# Test proto for nullable reference types tests
+$PROTOC -Isrc -I. \
+    --experimental_allow_proto3_optional \
+    --csharp_out=csharp/src/Google.Protobuf.Test.TestProtos \
+    --csharp_opt=file_extension=.pb.cs \
+    --csharp_opt=enable_nullable_reference_types \
+    --descriptor_set_out=csharp/src/Google.Protobuf.Test/testprotos.pb \
+    --include_source_info \
+    --include_imports \
+    csharp/protos/unittest_nrt_proto3.proto
 
 # AddressBook sample protos
 $PROTOC -Iexamples -Isrc --csharp_out=csharp/src/AddressBook \

csharp/protos/unittest_nrt_proto3.proto

@@ -0,0 +1,46 @@
+// 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.
+
+// A proto file we will use for unit testing nullable warning context.
+
+syntax = "proto3";
+
+option csharp_namespace = "Google.Protobuf.TestProtos";
+
+package protobuf_unittest3;
+
+message TestNrtMessage {
+  message TestNrtNestedMessage {
+  }
+
+  TestNrtNestedMessage message_field = 1;
+  string string_field = 2;
+  int32 int32_field = 3;
+}