Buf Language Server

bufls is a prototype for the beginnings of a Protobuf language server compatible with Buf modules and workspaces. This currently only supports go-to-definition.

This is a proof-of-concept that we wanted to share with the community. We do not actively maintain this, and there are no guarantees in terms of stability, but we want to hear your feedback!

For details on where we could go with this, please refer to future work.

Usage

Regardless of the LSP-compatible editor you use, you'll need to install bufls so that it's available on your $PATH.

go install github.com/bufbuild/buf-language-server/cmd/bufls@latest

Vim

With vim-lsp, the only configuration you need is the following:

Plug 'prabirshrestha/vim-lsp'

augroup LspBuf
  au!
  autocmd User lsp_setup call lsp#register_server({
      \ 'name': 'bufls',
      \ 'cmd': {server_info->['bufls', 'serve']},
      \ 'whitelist': ['proto'],
      \ })
  autocmd FileType proto nmap <buffer> gd <plug>(lsp-definition)
augroup END

Supported features

Buf's language server behaves similarly to the rest of the buf CLI. If the user has a buf.work.yaml defined, the modules defined in the workspace will take precedence over the modules specified in the buf.lock (i.e. the modules found in the module cache). The language server requires that inputs are of the protofile type.

Go to definition

Go to definition resolves the definition location of a symbol at a given text document position (i.e. textDocument/definition).

This feature is currently only implemented on the textDocument/definition endpoint. It may make sense to move this to textDocument/typeDefinition and/or textDocument/typeImplementation. The Protobuf grammar is far more limited than a programming language grammar, so not all of the semantics for each LSP endpoint apply here.

Today, this feature is only supported for messages and enums. The well-known types (WKT), and [custom] options are not yet supported.

Implementation

Protobuf compilation is fast, so the implementation is currently naive. Every editor command will compile the input file (e.g. file://proto/pet/v1/pet.proto) from scratch (there isn't any caching). Simple caching is fairly straightforward, but the cache would need to be cleared whenever a file is edited during the same language server session, which would require a file watcher. For now, performance is fine as-is (even for workspaces and large modules), but we might need to revisit this later as build graphs continue to grow.

Future work

More LSP features

This is just the tip of the iceberg - there's way more that a fully-featured Protobuf language server can do for the Protobuf community. For starters, the following set of endpoints are next in line:

• textDocument/completion
• textDocument/codeLens
• textDocument/foldingRange
• textDocument/formatting
• textDocument/hover

Go to definition

A couple features remain for full go to definition support:

• Add go to definition support for [custom] options.
• Add go to definition support for the well-known types (i.e. synthesize the WKT in the module cache).