Language Server Protocol (LSP) Guide

Turmeric ships a built-in language server that speaks Language Server Protocol over stdio (JSON-RPC 2.0). The server is invoked as:

tur lsp

Editors launch it as a subprocess and communicate via stdin/stdout.

Current capabilities

When you open or edit a .tur file, the server compiles it in check-only mode and publishes any parse or type errors back to the editor as diagnostics (red underlines, error panel entries, etc.).

Behaviours worth knowing about:

• Analysis is debounced. Compiling is not free and runs on the same thread that serves requests, so a changed file is not analyzed until the editor has been quiet for ~200ms. Requests that need symbols (hover, completion, definition, document symbols) force any pending analysis to run first, so this delays diagnostics slightly but never returns a stale answer.
• Positions are byte offsets. The server advertises "positionEncoding": "utf-8" (LSP 3.17), so character in a Position counts UTF-8 bytes rather than the UTF-16 code units the specification defaults to. Clients that honour the negotiated encoding need no special handling; a client that assumes UTF-16 regardless will be off on lines containing non-ASCII.
• Completion degrades in two tiers, never to nothing. Completion, hover, and go-to-definition are driven by the symbols a compile produced. A buffer that does not parse -- one with an unclosed paren, which is the normal state mid-keystroke -- produces none, so the server falls back rather than answering with an empty list. If the document has ever parsed successfully, the last good index is retained and served until a compile yields a new one; a few stale entries are far more useful than nothing, and the index changes much more slowly than the text does. If it has never parsed -- opening a file that already contains a syntax error -- there is no last-good index, so the server serves a process-wide stdlib-only fallback instead. That cache is primed lazily from an empty buffer (the stdlib is auto-loaded, so an empty file alone yields the whole surface), costs roughly 8ms once per process, and its membership is a path-prefix test against TUR_STDLIB_DIR. It deliberately carries no document-local symbols: while the file does not parse, what the document itself declares cannot be known.
• Completion returns a CompletionList, with isIncomplete set when the 200-item cap truncated the result. Items are prefix-filtered against what has been typed before the cursor, and the document's own definitions are emitted ahead of stdlib symbols so they are never the ones the cap drops.
• Cancellation has a real window. The server is single-threaded, so a $/cancelRequest is honoured if it arrives while the request it names is waiting on analysis — the expensive step. A cancel for a request already answered is ignored, as the specification requires. Cancelled requests are answered with error code -32800.
• Hover honours contentFormat. A client that advertises only plaintext in capabilities.textDocument.hover.contentFormat gets unfenced text instead of markdown it would have to strip itself.
• Formatting runs in-process. textDocument/formatting returns a single full-document TextEdit produced by the same code as tur fmt, so there is no need to shell out to the binary. FormattingOptions.tabSize and insertSpaces are ignored: the formatter is not configurable (two-space indent, 80 columns), and honouring the request halfway would produce output that tur fmt --check then rejects. A buffer that does not parse yields null — "no edits" — rather than an error.
• Unsaved buffers work. Analysis routes the buffer through a temp file, so a document with an untitled: URI and no filesystem path still gets diagnostics, symbols, completion, and formatting. A buffer that does have a path also gets its spice resolved from that path rather than from the temp copy, so intra-spice imports resolve in the editor exactly as they do for tur check.

Scope, highlight, rename and references

The symbol index records global bindings. On its own that is enough for hover and an outline and not enough for any question about a name the cursor is standing inside: a parameter named x has no entry at all, so highlighting it matched every x in the file.

A second pass (src/lsp/lsp_scope.c) records the locals -- defn and fn parameters, let and letrec bindings, match binders -- each with the source region it is visible in. It rides the same elaboration hook the symbol harvest does, so it is one walk over the tree the compiler already built, not a second front end.

What that buys:

• documentHighlight is lexical. A local's marks stop at its own scope, and a global's marks skip every region where a local of the same name shadows it. Both halves matter and they fail in opposite directions: without the first, highlighting the inner total of (let [total ...] ...) paints the outer one; without the second, highlighting the outer one paints the inner. With the minimap on, the answer is painted down the whole file, so a wrong one is visible at a glance.
• rename is safe or it refuses. Renaming a local edits exactly the occurrences in its scope. Renaming a top-level name defined in this file edits this file and every workspace file that imports its module -- the file set comes from the manifest (the project's own src/, plus each :path :spices dep's src/), resolved in the compiler rather than in the client, because a second implementation of the module search path would eventually disagree with the first and the disagreement would be an edit applied to the wrong file.

Every other case refuses, with a reason, through prepareRename -- which is why the server advertises "renameProvider": {"prepareProvider": true} rather than the bare boolean: the message reaches the user before they type a new name.

The last two are about the workspace half. Each importing file is compiled for its own binding table before it is edited, because rewriting every textual occurrence in a file that imports the module is the cross-file version of the shadowing bug -- and the destructive one: a sibling module that binds a local total and separately imports the global total would have its local silently renamed too.

tur lsp --rename-exports lifts the :exports refusal. It is off by default because such a name is published surface: a spice that fetched this one by :url may import it, and those files are outside the workspace.

• references is the workspace walk without the edit. includeDeclaration is honoured. A local's references are its scope; a global's are every importing file's real uses. An oversized workspace returns a shorter list rather than an error -- an incomplete list of references is still true about every entry in it, where an incomplete edit is not.

Editor configuration

Neovim (nvim-lspconfig)

Add a custom server entry -- nvim-lspconfig does not bundle Turmeric by default, so you register it manually:

local lspconfig = require("lspconfig")
local configs   = require("lspconfig.configs")

if not configs.turmeric then
  configs.turmeric = {
    default_config = {
      cmd        = { "tur", "lsp" },
      filetypes  = { "tur" },
      root_dir   = lspconfig.util.root_pattern("build.tur", ".git"),
      single_file_support = true,
    },
  }
end

lspconfig.turmeric.setup({})

If you use lazy.nvim and want this to load alongside nvim-lspconfig:

{
  "neovim/nvim-lspconfig",
  config = function()
    -- paste the block above here
  end,
}

Neovim does not auto-detect .tur files as tur filetype. Add this to your config or to ~/.config/nvim/ftdetect/tur.lua:

vim.filetype.add({ extension = { tur = "tur" } })

Neovim (built-in LSP, no plugin)

vim.api.nvim_create_autocmd("FileType", {
  pattern = "tur",
  callback = function(ev)
    vim.lsp.start({
      name    = "turmeric",
      cmd     = { "tur", "lsp" },
      root_dir = vim.fs.dirname(
        vim.fs.find({ "build.tur", ".git" }, { upward = true })[1]
      ),
    })
  end,
})

Vim (vim-lsp)

Install vim-lsp, then add:

if executable('tur')
  au User lsp_setup call lsp#register_server({
    \ 'name': 'turmeric',
    \ 'cmd': {server_info -> ['tur', 'lsp']},
    \ 'allowlist': ['tur'],
    \ })
endif

Add filetype detection if not already present:

augroup TurmericFt
  autocmd!
  autocmd BufRead,BufNewFile *.tur setfiletype tur
augroup END

Vim (ALE)

ALE can drive an LSP binary directly. Add to your ~/.vim/after/ftplugin/tur.vim (or equivalent):

let g:ale_linters = { 'tur': ['turmeric_lsp'] }

Then register the linter in your vimrc or in ~/.vim/ale_linters/tur/turmeric_lsp.vim:

call ale#linter#Define('tur', {
\   'name':            'turmeric_lsp',
\   'lsp':             'stdio',
\   'executable':      'tur',
\   'command':         '%e lsp',
\   'project_root':    function('ale#util#FindProjectRoot'),
\   'language':        'tur',
\ })

VS Code

The bundled VS Code extension (vscode-syntax-ext/) provides syntax highlighting only. To add LSP diagnostics, install a generic LSP client such as vscode-glspc or configure vscode-languageclient in your own extension wrapper.

A minimal settings.json entry using the multi-lsp extension:

{
  "multi-lsp.servers": [
    {
      "language": "tur",
      "command": "tur",
      "args": ["lsp"]
    }
  ]
}

The bundled extension in vscode-syntax-ext/ already speaks LSP natively via vscode-languageclient, spawning tur lsp over stdio; the turmeric.serverPath setting overrides which tur it uses. The multi-lsp recipe above is only needed if you would rather drive the server yourself.

Emacs (eglot)

Eglot is built into Emacs 29+. Add a major mode for Turmeric first (or use lisp-mode as a fallback), then register the server:

;; Simple major mode derived from lisp-mode
(define-derived-mode turmeric-mode lisp-mode "Turmeric"
  "Major mode for Turmeric source files.")
(add-to-list 'auto-mode-alist '("\\.tur\\'" . turmeric-mode))

;; Register the LSP server with eglot
(with-eval-after-load 'eglot
  (add-to-list 'eglot-server-programs
               '(turmeric-mode . ("tur" "lsp"))))

;; Auto-start eglot when opening .tur files
(add-hook 'turmeric-mode-hook #'eglot-ensure)

Emacs (lsp-mode)

(with-eval-after-load 'lsp-mode
  (lsp-register-client
   (make-lsp-client
    :new-connection (lsp-stdio-connection '("tur" "lsp"))
    :activation-fn  (lsp-activate-on "tur")
    :server-id      'turmeric)))

(add-hook 'turmeric-mode-hook #'lsp)

Helix

Add to ~/.config/helix/languages.toml:

[[language]]
name              = "turmeric"
scope             = "source.tur"
file-types        = ["tur"]
comment-token     = ";"
indent            = { tab-width = 2, unit = "  " }
language-servers  = ["turmeric-lsp"]

[language-server.turmeric-lsp]
command = "tur"
args    = ["lsp"]

Zed

In ~/.config/zed/settings.json:

{
  "lsp": {
    "turmeric": {
      "binary": {
        "path": "tur",
        "arguments": ["lsp"]
      }
    }
  }
}

Zed also requires a language extension for filetype detection. Until an official extension is published, use the Zed extension API to register .tur manually or rely on generic highlighting.

How it works

When a .tur file is opened or modified, the server:

1. Writes the current buffer text to a temporary file in the platform temp directory ($TMPDIR on Unix, %TMP%/%TEMP% on Windows).
2. Runs the Turmeric compiler in type-check-only mode (tur_check_only).
3. Collects all diagnostics via the internal diag_lsp_* API.
4. Remaps temp-file paths back to the real document URI.
5. Adopts the collected symbols as the document's index — unless the compile produced none and failed, in which case the previous index is kept (see "the last good symbol index is retained" above).
6. Sends a textDocument/publishDiagnostics notification to the editor.
7. Deletes the temporary file.

Diagnostics whose span is zero-width are widened by one character before they go out. A zero-width range paints nothing, so the diagnostic would be present in the response but invisible in the editor.

The server uses TextDocumentSyncKind.Full (sync kind 1): the entire file content is sent on every change, not just diffs. This keeps the implementation simple at the cost of slightly more data per keystroke for large files.

Troubleshooting

No diagnostics appear. Verify tur is on your $PATH:

which tur
tur --version

Server exits immediately. Run tur lsp in a terminal and type a minimal JSON-RPC initialize request. Any startup error (missing stdlib, bad install) will appear on stderr.

Diagnostics are stale or missing after save. Some editors only sync on save (not on every keystroke). Check your editor's LSP sync setting; the server responds to both textDocument/didOpen and textDocument/didChange.

See also

• src/lsp/lsp.c -- JSON-RPC dispatcher and diagnostic publisher
• src/lsp/lsp_docs.c -- In-memory document store
• src/lsp/lsp_io.c -- Framed stdio read/write
• vscode-guide.md -- VS Code syntax extension
• vim-guide.md -- Vim / Neovim syntax highlighting
• formatter-guide.md -- tur format CLI