Today I learned that Mathematica 13.0 ships with a builtin language server. There are actually two VS Code plugins that provide client-side code for Wolfram LSP: lsp-wl and the official wolfram extension.

I first tried to configure lsp-wl with Neovim builtin lspconfig, using a custom server config. Neither of wolframscript or netcat proved to work in this case. However, I got something close to what we have in VS Code with the official extension using the following setup:

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

configs.lsp_wl = {
  default_config = {
    cmd = {
      "wolfram",
      "kernel",
      "-noinit",
      "-noprompt",
      "-nopaclet",
      "-noicon",
      "-nostartuppaclets",
      "-run",
      'Needs["LSPServer`"];LSPServer`StartServer[]',
    },
    filetypes = { "mma", "wl" },
    root_dir = nvim_lsp.util.path.dirname,
  },
}

nvim_lsp.lsp_wl.setup({ on_attach = lsp_attach({}) })

The lsp_attach function does take care of formatting on save, completion and common key mappings across LSPs.

I mostly use the mma filetype because I rely on mash for batch processing Mathematica code in Org document, as described in a minimal Org setup to write scientific notebooks.¹

I still have to manage how to get omnifunc completion working, but for the moment I have hover information, diagnostics and formatting.