Style guide: Thoughts on Enums about buf

[bufdev]

This is unique to C++; it works fine in every other language.

This isn't a C++ problem - as we talk about in the Buf docs, the issue will lead to protoc not compiling definitions (regardless of whether it was meant to only protect against C++ issues). Your example above won't compile:

$ protoc -o /dev/null foo.proto
foo.proto:9:3: "UNSPECIFIED" is already defined in "foo".
foo.proto:9:3: Note that enum values use C++ scoping rules, meaning that enum values are siblings of their type, not children of it.  Therefore, "UNSPECIFIED" must be unique within "foo", not just within "Bar".

We also find that nesting enums leads to issues with forwards compatibility that while not actually breaking compatibility, breaks the spirit, namely that developers typically think an enum only truly applies to their specific message, only later realizing it is a more global concept. This leads to references in other messages for nested enums, which is worse than standardizing on a prefix.

The Google Style Guide also uses it for their example https://developers.google.com/protocol-buffers/docs/style

We'll stick with this recommendation - we find that many people have opinions on Protobuf style, but the one that leads to the least amount of issues down the road, even if more verbose, is usually preferred, especially to help developers of all levels of familiarity with Protobuf.

[lukesneeringer]

That sounds reasonable. :-)

[noahseger]

@bufdev your comment about nesting is valuable and worth referencing, because the prefix lint rule is the most hated on our team :D Would it make sense to add to https://buf.build/docs/best-practices/style-guide#enums?