all: fix reflection behavior for empty lists and maps

The protoreflect documentation states that Get on an empty repeated or
map field returns an invalid (empty, read-only) List or Map. We weren't
doing this; fix it.

The documentation also states that an invalid List or Map may not be
assigned via Set. We were permitting Set with an invalid map; fix this.

Add tests for this behavior in prototest.

Change-Id: I4678af532e192210af0bde7c96a1439a4cd26efa
Reviewed-by: Joe Tsai <>
5 files changed
tree: 2542582455b9da5edba985567619ea729eb01c72
  1. .gitignore
  2. .travis.yml
  9. benchmarks/
  10. cmd/
  11. compiler/
  12. encoding/
  13. go.mod
  14. go.sum
  15. integration_test.go
  16. internal/
  17. proto/
  18. reflect/
  19. regenerate.bash
  20. release.bash
  21. runtime/
  22. test.bash
  23. testing/
  24. types/

Next Generation Go Protocol Buffers

WARNING: This repository is in active development. There are no guarantees about API stability. Breaking changes will occur until a stable release is made and announced.

This repository is for the development of the next major Go implementation of protocol buffers. This library makes breaking API changes relative to the existing Go protobuf library. Of particular note, this API aims to make protobuf reflection a first-class feature of the API and implements the protobuf ecosystem in terms of reflection.

Design Documents

List of relevant design documents:


We appreciate community contributions. See

Reporting Issues

Issues regarding the new API can be filed at Please use a APIv2: prefix in the title to make it clear that the issue is regarding the new API work.