tree a840c5e8d7ee9865eadbd5a97c8130678cbb55d2
parent 1605775be0bfd4084c40cac4262ada8900791de1
author Damien Neil <dneil@google.com> 1573590792 -0800
committer Damien Neil <dneil@google.com> 1573592343 +0000

proto, internal/impl: make wire output more consistent with v1

The v1 wire marshaler sorts fields as follows:
  - All extensions, sorted by field number.
  - All non-oneof fields, sorted by field number.
  - All oneof fields, in indeterminate order.

We already make some steps toward supporting this ordering: The
fast path encoder places extensions in sorted order at the start
of the message.

This commit moves oneof fields to the end of the message, makes the
reflection-based encoder use this ordering when deterministic marshaling
is enabled, and adds a test to catch unintentional changes to the
ordering.

Users SHOULD NOT depend on stability of the marshal output. It is
subject to change over time. Without deterministic marshaling enabled,
it is subject to change over calls to Marshal.

Change-Id: I6cfd89090d790a3bb50785f32b94d2781d7d08db
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/206800
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>