A language server for Fennel. Supports Go-to-definition, and a little bit of completion suggestions. Fennel-LS uses static analysis, and does not execute your code.

You can ask fennel-ls to treat your file as a macro file if the first line exactly matches ;; fennel-ls: macro-file. Expect this to change at some point in the future when I come up with a better way to specify which files are meant to be macro files.

• Installation
• Usage

I recommend building from source. I promise it's really easy! You need to have make and lua (5.1+). Every other dependency is included. See the License section at the bottom of this file for more info on the bundled dependencies.

make && sudo make install

make install PREFIX=$HOME

make

If you are using NixOS, you can use the included /flake.nix or /default.nix.

I recommend just using make if possible, but if not, fennel-ls can be built with LuaRocks.

luarocks install fennel-ls --tree /path/to/your/new/luarocks/tree

Once you've installed the binary somewhere on your computer, the next step is to set up your text editor! Each editor has a different way of doing it.

If you are using vim+lspconfig, it is pretty simple:

require('lspconfig').fennel_ls.setup()

For Emacs, (eglot, built-in to 29+):

(with-eval-after-load 'eglot
  (add-to-list 'eglot-server-programs '(fennel-mode . ("fennel-ls"))))

It should be possible to set up for other text editors, but the instructions depend on which editor you use. Generally you need to give this information to your editor:

• "fennel-ls" is a language server program on the $PATH
• it should be run for .fnl files.

You can gather diagnostics without connecting your editor:

fennel-ls --check my-file.fnl f2.fnl # prints diagnostics for the files given

This will analyze the given files, and print out all compiler errors and lints.

fennel-ls can be configured over LSP. Any setting that's not provided will be filled in with the defaults, which means that {} will be a valid configuration with default settings. You can provide different settings in the same shape as the default settings in order to override the defaults.

fennel-ls default settings:

{
  "fennel-ls": {
    "fennel-path": "./?.fnl;./?/init.fnl;src/?.fnl;src/?/init.fnl",
    "macro-path": "./?.fnl;./?/init-macros.fnl;./?/init.fnl;src/?.fnl;src/?/init-macros.fnl;src/?/init.fnl",
    "checks": {
      "unused-definition": true,
      "unknown-module-field": true,
      "unnecessary-method": true,
      "bad-unpack": true,
      "var-never-set": true,
      "op-with-no-arguments": true,
      "multival-in-middle-of-call": true
    },
    "extra-globals": ""
  }
}

extra-globals : Space separated list of allowed global identifiers; in addition to a set of predefined lua globals.

Your editor can send these settings using one of these two methods:

• The client sends an initialize request with the structure {initializationOptions: {"fennel-ls": {...}}, ...}
• The client sends a workspace/didChangeConfiguration notfication containing the field {settings: {"fennel-ls": {YOUR_SETTINGS}}}

You can't load external lint rules with fennel-ls, but I would love to receive patches that add new lint rules! Instructions to add a lint.

fennel-ls is licensed under the MIT license. See LICENSE for more info. This project also contains files from other projects:

• test/pl/* comes from Penlight [MIT license]
  • LICENSE
• src/fennel-ls/json/* is modified, but is originally from json.lua [MIT license]
  • LICENSE
• src/fennel-ls/docs/* contains information from the lua reference [MIT license]
• test/faith/faith.lua is from faith [MIT license]
• fennel and src/fennel.lua are compiled from fennel [MIT license]