Implement the new proto3 field presence feature #34

[NiematojakTomasz]

Fix #34

[garyp]

Thanks again for taking this on! The changes mostly look good to me. I have one question in FileBuilder.kt about something I'm confused about. The other comments are minor code style fixes.

The only other suggestion I have is to add some unit tests to runtime/commonTest to check that a few invariants are maintained when an instance of Proto3PresenceMain is encoded to a byte array and then that byte array is decoded back into a Proto3PresenceMain instance. Something along these lines (where msg is the result of calling encodeToByteArray() and then decodeFromByteArray()):

• Proto3PresenceMain(optionalInt = 0, requiredInt = 0) => assert that msg.optionalInt == 0 and proto.requiredInt == 0
• Proto3PresenceMain() => assert that msg.optionalInt == null and msg.requiredInt == 0
• Maybe similar tests on some of the other data types like messages, enums, and oneof fields?

[NiematojakTomasz]

Thanks again for taking this on! The changes mostly look good to me. I have one question in FileBuilder.kt about something I'm confused about. The other comments are minor code style fixes.

The only other suggestion I have is to add some unit tests to runtime/commonTest to check that a few invariants are maintained when an instance of Proto3PresenceMain is encoded to a byte array and then that byte array is decoded back into a Proto3PresenceMain instance. Something along these lines (where msg is the result of calling encodeToByteArray() and then decodeFromByteArray()):

• Proto3PresenceMain(optionalInt = 0, requiredInt = 0) => assert that msg.optionalInt == 0 and proto.requiredInt == 0
• Proto3PresenceMain() => assert that msg.optionalInt == null and msg.requiredInt == 0
• Maybe similar tests on some of the other data types like messages, enums, and oneof fields?

Doesn't tests based on kotlinJavaRoundtripTest implicitly cover it? Or is it a matter of testing it explicitly?

[garyp]

@NiematojakTomasz I got a chance to come back to this PR finally and add the unit tests I was suggesting. Sorry for the long delay and thank you again for contributing support for this feature!