flix.nvim

• Neovim support for Flix

Requirements

• Neovim 0.11+ — uses the native vim.lsp.config / vim.lsp.enable API introduced in 0.11.
• Java 21+ in your PATH (Flix runs on the JVM).
• flix.jar in your project root (or set an absolute path via jar, see Configuration).

Run :checkhealth flix to verify your setup.

Functionality

Flix leverages LSP for syntax highlighting via semantic tokens, which Neovim enables automatically when the server attaches — no extra configuration needed.

This plugin serves three main purposes:

1. create an LSP configuration for Flix
2. set the flix filetype and language defaults (see ftplugin/flix.lua)
3. Lua functions for interacting with the Flix CLI

Installation

Install with your plugin manager of choice using the repo flix/nvim.

Neovim 0.12 ships a built-in plugin manager, so no third party is required:

-- Neovim 0.12+ (vim.pack)vim.pack.add({ "https://github.com/flix/nvim" })
require("flix").setup()
vim.lsp.enable("flix")

With lazy.nvim:

{
"flix/nvim",
ft="flix",
config=function()
require("flix").setup()
vim.lsp.enable("flix")
end,
}

LSP

Call require("flix").setup() to register the config, then enable the server:

-- create the Flix LSP configrequire("flix").setup()
-- enable the servervim.lsp.enable("flix")

Configuration

setup() accepts an options table (all fields optional):

require("flix").setup({
java="java", -- executable used to launch the jarjar="flix.jar", -- relative paths resolve from the project rootroot_markers= { "flix.toml" },
terminal= { -- how `flix_cmd` opens its terminalwindow="split", -- "split" (default) or "float" (floating window)width=0.60, -- float = fraction of editor, integer = columnsheight=0.5, -- float = fraction of editor, integer = rowspos_x="center", -- number or "center" (float = fraction of width)pos_y="center", -- number or "center" (float = fraction of height)close_binding="q", -- Normal-mode key that closes the floating window
},
features= {
codelens=true, -- refresh code lenses while editingcompletion=false, -- native autocompletion (see below)
},
lsp= { -- merged into vim.lsp.config("flix", ...)-- settings = { ... },
},
})

Floating terminal

By default flix_cmd opens in a belowright split. Set terminal.window = "float" to open it in a floating window instead. The remaining terminal fields only apply to the float: width/height accept a fraction of the editor size (e.g. 0.5) or an integer column/row count, pos_x/pos_y accept a number or "center", and close_binding (default q) closes the window from Normal mode.

Native completion (Neovim 0.11+)

Set features.completion = true to get insert-mode autocompletion straight from the LSP — no nvim-cmp / blink.cmp required. Leave it false (the default) if you already drive completion with one of those plugins to avoid duplicate menus.

In Neovim 0.12 the built-in LSP client also supports inlineCompletion, onTypeFormatting, and linkedEditingRange. They will activate automatically when the Flix server advertises them (:help lsp for details).

Commands

Set local Flix keybindings with an autocommand or by creating ftplugin/flix.lua in your own config. The example below maps run/test for a Flix project:

-- import the `flix_cmd` functionlocalflix_cmd=require("flix.commands").flix_cmd-- setting `buffer` keeps the mappings scoped to Flix bufferslocalbufnr=vim.api.nvim_get_current_buf()
vim.keymap.set("n", "<Space>br", function() flix_cmd("run") end,
{ noremap=true, silent=true, buffer=bufnr, desc="run flix project" })
vim.keymap.set("n", "<Space>bt", function() flix_cmd("test") end,
{ noremap=true, silent=true, buffer=bufnr, desc="test flix project" })

flix_cmd finds the project root from root_markers, so it works even when the LSP is not attached, and reports an error if no flix.toml is found.

Full setup example (for lazy.nvim)

{
"flix/nvim",
ft="flix",
config=function()
-- show lsp diagnostics by highlighting line numbersvim.diagnostic.config({
signs= {
text= {
[vim.diagnostic.severity.ERROR] ="",
[vim.diagnostic.severity.WARN] ="",
},
numhl= {
[vim.diagnostic.severity.ERROR] ="ErrorMsg",
[vim.diagnostic.severity.WARN] ="WarningMsg",
},
},
severity_sort=true,
})
-- buffer-local LSP mappingsvim.api.nvim_create_autocmd("LspAttach", {
group=vim.api.nvim_create_augroup("my.lsp", {}),
callback=function(args)
localfunctionget_opts(desc)
return { desc=desc, buffer=args.buf, noremap=true, silent=true }
endlocalclient=assert(vim.lsp.get_client_by_id(args.data.client_id))
ifclient:supports_method("textDocument/formatting") thenvim.keymap.set("n", "<space>=", vim.lsp.buf.format, get_opts("format buffer"))
endifclient:supports_method("textDocument/rename") thenvim.keymap.set("n", "<space>rn", vim.lsp.buf.rename, get_opts("rename"))
endvim.keymap.set("n", "<space>ee", vim.diagnostic.open_float, get_opts("diagnostic open float"))
end,
})
-- register the flix lsp config and enable itrequire("flix").setup()
vim.lsp.enable("flix")
end,
}