tree 662eb878aee5eddc4f0ef2dfc1aea7cca432abf4
parent 14ac241a9605054dd8338e08fa5a8c7d9ad20f73
author Joe Tsai <joetsai@digital-static.net> 1578109948 -0800
committer Joe Tsai <joetsai@google.com> 1578339458 +0000

proto: distinguish between invalid and empty messages in Equal

The v1 proto.Equal function treats (*Message)(nil) and new(Message)
as being different, while v2 proto.Equal treated them as equal since
a typed nil pointer is functionally an empty message since the
protobuf data model has no concept of presence as a first-class
property of messages.

Unfortunately, a significant amount of code depends on this distinction
that it would be difficult to migrate users from v1 to v2 unless we
preserved similar semantics in the v2 proto.Equal.

Also, double down on these semantics for protocmp.Transform.

Fixes #965

Change-Id: I21e78ba6251401a0ac0ccf495188093973cd7f3f
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/213238
Reviewed-by: Damien Neil <dneil@google.com>