commit 424139789aef7d0b893a01412618f7a749160be9
author Joe Tsai <joetsai@digital-static.net> Fri Jun 21 14:25:16 2019 -0700
committer Joe Tsai <thebrokentoaster@gmail.com> Mon Jun 24 22:35:47 2019 +0000
tree 048322da30eac6c1cc0dc6d37a195f99dfb96cc2
parent a3456c946bcf040c0d8e97cde71650cbb3d7f3f1

reflect/protoreflect: register all desciptors in Files

This change makes it such that Files now functionally registers all
descriptors in a file (not just enums, messages, extensions, and services),
but also including enum values, messages fields/oneofs, and service methods.

The ability to look up any descriptor by full name is needed to:
1) properly detect namespace conflicts on enum values
2) properly implement the relative name lookup logic in reflect/protodesc

The approach taken:
1) Assumes that a FileDescriptor has no internal name conflicts.
This will (in a future CL) be guaranteed by reflect/protodesc and
is guaranteed today by protoc for generated descriptors.
2) Observes that the only declarations that can possibly conflict
with another file are top-level declarations (i.e., enums, enum values,
messages, extensions, and services). Enum values are annoying
since they live in the same scope as the parent enum, rather than
being under the enum.

For the internal data structure of Files, we only register the top-level
declarations. This is the bare minimum needed to detect whether the file
being registered has any namespace conflicts with previously registered files.

We shift the effort to lookups, where we now need to peel off the end fragments
of a full name until we find a match in the internal registry. If a match
is found, we may need to descend into that declaration to find a nested
declaration by name.

For initialization, we modify internal/filedesc to initialize the
enum values for all top-level enums. This performance cost is offsetted
by the fact that Files.Register now avoids internally registering
nested enums, messages, and extensions.

For lookup, the cost has shifted from O(1) to O(N),
where N is the number of segments in the full name.
Top-level descriptors still have O(1) lookup times.
Nested descriptors have O(M) lookup times,
where M is the level of nesting within a single file.

Change-Id: I950163423431f04a503b6201ddcc20a62ccba017
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/183697
Reviewed-by: Damien Neil <dneil@google.com>