tree 34308cd9b57036c90477ccc071877c82ae0ac0b8
parent f98dd98c15bbc3e8accc353f5bff6fca06657a4a
author Joe Tsai <joetsai@digital-static.net> 1565036414 -0700
committer Joe Tsai <joetsai@digital-static.net> 1565041126 +0000

internal/impl: defer evaluation of weak reference until actual use

Suppose some init logic performs protobuf reflection.
If so, it will cause the table-driven logic for protobuf reflection
to be initialized. This is problematic for weak fields since we
can not be certain that all weak references have been registered
at this point in time. This is a fundamental issue with with weak
dependencies, since it means that we cannot enforce any ordering
constraints on the weak dependency unless we directly import the weakly
referenced package (which would defeat the point of weak imports).

Alleviate the problem by pushing evaluation of weak reference to
actual usage. This does not completely fix the problem,
but signifcantly reduces the probability of it being problematic.
In general, people should avoid interacting with weak fields at init time.

Change-Id: Iebaefddde8cf07b5cd7dee49b7015b05b5428618
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/188980
Reviewed-by: Damien Neil <dneil@google.com>