Initial Implementation of a CUE LSP

Originally, this was forked from https://cue-review.googlesource.com/c/cue/+/5840. However, the current implementation uses its own ast abstraction.

Some changes had to be made for certain structs for them to be accessible within the context of the lsp package. For example, builtin had to be exposed.

Project Layout

cue-vscode-ext/

Contains a Visual Studio Code extension to use the cue LSP with.

To test it out, you can just run code --extensionDevelopmentPath=$PWD/cue-vscode-ext from the root of the repository, after you compiled the command line with go build -o cue-lsp ./cmd/cue.

cmd/cue/cmd/lsp.go

Contains the definitions for a new command available: lsp:

lsp starts the CUE language server.

At the moment, communication is limited to stdio.

Usage:
  cue lsp [flags]

Flags:
      --config-file string   Path to yml config file. (default "cue-lsp.yml")
  -h, --help                 help for lsp

Global Flags:
  -E, --all-errors   print all available errors
  -i, --ignore       proceed in the presence of errors
  -s, --simplify     simplify output
      --strict       report errors for lossy mappings
      --trace        trace computation
  -v, --verbose      print information about progress

cue/lsp/

Package that exposes a simple function to start the lsp at the moment. For now this is needed, as the lsp resides in the internal directory and as such cannot be directly accessed by the command package.

cue/internal/lsp/

This contains the actual implementation of the lsp, as well as any helper packages.

Everything in here was originally taken from promql-server. However, the specific implementations, were reworked for CUE (e.g. completion.go).

cue/internal/lsp/internal/vendored/

To use all the types, interfaces, etc. already created for the gopls language server, we need to clone a part of that here (since those reside in internal of gopls as well). This was copied from the promql-server

cue/internal/lsp/update_internal.sh pulls in the latest changes from the gopls repository. This was copied from the Makefile of promql-server.

cue/internal/lsp/asg/

This package is used to provide the lsp with information about CUE files. The package is fairly documented, so check out the documentation there.

cue/internal/lsp/cache/

This was copied over from promql-server, but has seen heavy rewrites to make it work with CUE. Still needs work to make packages work nicely. See the documentation there, for more information (specifically doc.go).