rextio-lsp 0.1.1

Language Server for the Rextio native-promotion tooling contract.

rextio-lsp

Language Server for Rextio — native-promotion routes and guidance in your editor.

A Python (pygls) LSP server that consumes Rextio’s tooling-contract JSON and reports per-function execution routes (native-direct, native-plugin:<id>, native-shim, fallback-python, fallback-accelerated:numba, rejected:<RXT>) with actionable promotion guidance.

Status: 0.1.1

This is package version rextio-lsp 0.1.1, the current release. It supersedes the previous cut, rextio-lsp 0.1.0 (2026-07-12).

What 0.1.1 adds (dual-map)

• Tooling-contract majors {1, 2} are fully supported (0.1.0 gated major 1 only).
• Major 2 (core 0.1.2 producer, contract_version 2.0.0): every diagnostic column, including RXT000, is a 0-based UTF-8 byte offset.
• Major 1 (published core through 0.1.1): legacy RXT000 columns remain 1-based Unicode code-point SyntaxError.offset; all other codes stay UTF-8-byte → UTF-16.
• Unsupported majors (e.g. 3+) still degrade to generic diagnostics without guidance enrichment.

rextio is not a package dependency of this server. The server acquires the tooling-contract JSON via in-process import or a discovered subprocess (see Features), choosing order from the configured interpreter and environment match, and no-ops silently when Rextio is absent.

Safe deployment order

Publish / deploy in this strict order — no simultaneous ship:

1. rextio-lsp 0.1.1 (this dual-map consumer) — merge and release first
2. core rextio 0.1.2 (tooling-contract major 2)
3. rextio-numpy 0.1.1 (requires core >= 0.1.2)

Core must not publish alone first: a contract-2.x producer against major-1-only rextio-lsp 0.1.0 is an unsupported pairing and can misplace RXT000.

See the CHANGELOG for the full release notes and the preserved 0.1.0 history.

Designed to coexist

rextio-lsp registers only Rextio-semantic capabilities and stays out of everything else:

• Provides: diagnostics (source: "rextio", RXT/RXTP codes only; Warning for rejection codes, Hint for informational codes, Information otherwise — never Error), hover (route info + rejection and advisory guidance), code lens (per-function route badges), code actions (promotion quick fixes)
• Does not provide: completion, formatting, rename, definition, references, syntax/style linting — those remain with your existing Python LSP (Pylance/pyright, ruff, …)
• Activates only when rextio.toml exists in the workspace; silent no-op when Rextio isn't installed in the project environment

Features

M1

• Whole-project rextio check on open/save (debounced), published as source: "rextio" diagnostics
• Severity is capped: rejection codes → Warning, informational codes (RXT075/080/090/091) → Hint, everything else → Information (never Error)
• Hover on a function definition line shows its route, native status, and rejection guidance (from the capability manifest)
• Acquisition supports both in-process (import rextio) and subprocess (discovered rextio binary). Order is environment-aware: an explicit initializationOptions.interpreter.path whose neighbouring rextio exists prefers that subprocess; a project-venv rextio in a different environment than the server also prefers subprocess; when the server and project share the same environment, in-process is used (equivalent, no spawn). The non-preferred path remains a fallback. A bare PATH hit does not displace in-process.
• Tooling-contract majors {1, 2} fully supported: major 2 maps every column as 0-based UTF-8 bytes; major 1 keeps legacy RXT000 1-based code-point mapping. Other majors → degraded (generic) diagnostics without guidance enrichment

M2

• initializationOptions contract (see below): toggle code lens, pin the interpreter used for binary discovery
• Code lens: one Rextio: <route> lens per analyzed function, carrying the informational rextio.showRouteInfo command with [qualname] (registered only when codeLens.enable is true)
• Code actions (quick fix): on a rejected function that carries an explicit @rextio.native marker, offer "Rextio: keep on Python fallback (@rextio.exempt)" — rewrites the decorator to @rextio.exempt (indentation preserved)
• Hover also surfaces an Advisory section for informational codes present on the function, not just rejections
• Watches **/rextio.toml; on change, drops the project's cached capability manifest and re-analyzes open documents
• Real diagnostic spans when the contract provides end_line/end_column (else a zero-width range)
• Latency instrumentation: each whole-project check is logged via window/logMessage (Info when > 2.0s, else Log)

initializationOptions

The server reads the following shape (all keys optional; defaults shown):

{
  "codeLens": { "enable": true },
  "interpreter": { "path": null }
}

• codeLens.enable — when false, the code lens capability is not advertised at all.
• interpreter.path — path to the project's Python interpreter. When set, the server looks for rextio next to that interpreter first (before project .venv/venv and PATH). If that neighbour binary exists, subprocess acquisition via it takes precedence over in-process; if it does not, discovery continues and in-process may still win.

Install

Install into the project environment so the server stays in version lock-step with the project's rextio and its plugins:

pip install rextio-lsp

Note: pip install rextio-lsp installs 0.1.1 (the current release). To hack on the server itself, install from a source checkout of this branch instead (see Development).

The server speaks LSP over stdio via the rextio-lsp console script (equivalently python -m rextio_lsp).

Editor setup

Neovim (nvim-lspconfig, manual command)

rextio-lsp is not yet a built-in lspconfig server, so register it manually:

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

if not configs.rextio_lsp then
  configs.rextio_lsp = {
    default_config = {
      -- run the server from the project's own environment
      cmd = { ".venv/bin/rextio-lsp" },
      filetypes = { "python" },
      root_dir = lspconfig.util.root_pattern("rextio.toml"),
      init_options = {
        codeLens = { enable = true },
        interpreter = { path = vim.fn.getcwd() .. "/.venv/bin/python" },
      },
    },
  }
end

lspconfig.rextio_lsp.setup({})

Enable code lens rendering with vim.lsp.codelens.refresh() (e.g. on BufEnter/CursorHold) and :lua vim.lsp.codelens.display().

Generic stdio client

Any LSP client that launches a stdio subprocess works. The essentials:

• command: rextio-lsp (or python -m rextio_lsp) from the project environment
• transport: stdio
• languages: python
• root: nearest directory containing rextio.toml
• initializationOptions: the shape documented above

Development

pip install -e '.[dev]'
ruff check src tests
mypy
pytest -q

Integration tests marked needs_rextio are auto-skipped when rextio is not importable.

Contributor and agent guidance lives in the repository (AGENTS.md).

Compatibility floors

Component	Floor
Package version	0.1.1 (see __about__.__version__)
Python	>= 3.11
pygls	>= 2.1, < 3
Tooling-contract majors	{1, 2} fully supported; other majors → degraded
rextio package dep	none (peer contract consumer only)

License

MIT