commit 90fe996bd1b402070b832725468dcee847e91843
author Joe Tsai <joetsai@digital-static.net> Thu Oct 18 11:06:29 2018 -0700
committer Joe Tsai <thebrokentoaster@gmail.com> Mon Oct 22 17:18:39 2018 +0000
tree 53b27884c45930472ad605614cfb9276ef054aaf
parent bda671fa93a50287670feea131146e6ed2827340

internal/impl: derive descriptors for legacy enums and messages

In order for the v2 rollout to be as seamless as possible, we need to support
the situation where a v2 message depends on some other generated v1 message that
may be stale and does not support the v2 API. In such a situation, there needs
to be some way to wrap a legacy message or enum in such a way that it satisfies
the v2 API.

This wrapping is comprised of two parts:
1) Deriving an enum or message descriptor
2) Providing an reflection implementation for messages

This CL addresses part 1 (while part 2 has already been partially implemented,
since the implementation applies to both v1 and v2).

To derive the enum and message descriptor we rely on a mixture of parsing the
raw descriptor proto and also introspection on the fields in the message.
Methods for obtaining the raw descriptor protos were added in February, 2016,
and so has not always been available. For that reason, we attempt to derive
as much information from the Go type as possible.

As part of this change, we modify prototype to be able to create multiple
standalone messages as a set. This is needed since cyclic dependencies is allowed
between messages within a single proto file.

Change-Id: I71aaf5f977faf9fba03c370b1ee17b3758ce60a6
Reviewed-on: https://go-review.googlesource.com/c/143539
Reviewed-by: Damien Neil <dneil@google.com>