Language server

bun lsp is a language server for editors and a command line for agents and scripts. It speaks the Language Server Protocol and passes each request to the server of the document's language. It starts that server the first time a file of that language needs it.

bun lsp finds servers in node_modules/.bin, in the .venv of the project, and on PATH.

Editors

Configure bun lsp as the language server of every language it handles. It reads requests on stdin and writes answers on stdout.

{
  "lsp": {
    "bun": { "binary": { "path": "bun", "arguments": ["lsp"] } }
  }
}

vim.lsp.config("bun", {
  cmd = { "bun", "lsp" },
  filetypes = { "typescript", "javascript", "typescriptreact", "python", "rust", "c", "cpp" },
  root_markers = { ".git" },
})
vim.lsp.enable("bun")

The editor gets the diagnostics of all of a document's servers in one list. Completions, code actions, inlay hints, code lenses and document links are resolved by the server that returned them. workspace/symbol asks every running server.

Queries from the command line

bun lsp query asks one question and prints the answer. The first query of a workspace starts a daemon for it, which keeps the servers running between queries. Later queries take milliseconds instead of the seconds a server needs to load a project.

bun lsp query diagnostics src/index.ts
bun lsp query definition src/index.ts:12:8
bun lsp query references src/index.ts:12:8
bun lsp query hover src/index.ts:12:8
bun lsp query symbols src/index.ts
bun lsp query workspace-symbols . Router
bun lsp query rename src/index.ts:12:8 newName --apply

src/index.ts:3:7: error TS2322: Type 'string' is not assignable to type 'number'.

Lines and columns start at 1, and columns count characters. bun lsp query diagnostics exits with code 1 if there is an error.

The other commands manage the daemon of the workspace in the current directory, or in the given directory:

bun lsp warm            # start the daemon and the servers of each language in the workspace
bun lsp warm --lang typescript,rust
bun lsp status          # the running servers
bun lsp stop
bun lsp servers         # the server that each language would start, or what to install

The daemon of a workspace exits after 30 minutes without a query. A server stops after 15 minutes without a request. When more than 6 servers would run, the least recently used one stops.

C and C++

clangd needs a compile_commands.json. bun lsp looks for it in the project root, then in build/, out/ and cmake-build-debug/ and their subdirectories, with build/debug first. If there is none, it writes one with ninja -t compdb from the build.ninja it finds there, keeping only the compile commands. In a Linux kernel tree, it runs scripts/clang-tools/gen_compile_commands.py after a build.

bun lsp compdb          # write compile_commands.json now

clangd keeps its background index next to compile_commands.json, in .cache/clangd, so it survives restarts. bun lsp starts it with --background-index, --limit-results=100, -j set to half the CPU cores (at most 4), and --pch-storage=disk. On Windows, when INCLUDE is not set, it gives clangd the MSVC and Windows SDK environment from bun msvc env so that clang-cl command lines find their headers.

Configuration

rust-analyzer starts with checkOnSave off, so it does not run cargo check after each save.