muddles

A language server for the Manufacturer Usage Description (MUD) format.

Details

The Language Server Protocol (LSP) defines common interactions between an Editor (or IDE) as a client and a "Language Server", which conventionally is a tool that parses and analyzes source code and can infer type information, provide completions, warn of errors or likely mistakes, etc. Language server examples are LLVM's clangd or Rust's rust-analyzer.

The editor (client) can synchronize document states with the server, ask it for contextual information (e.g. documentation or type hints), completion, etc. The server can in turn register diagnostic messages such as "this bit of source is syntactically incorrect" or "this thing is not used".

LSP can certainly be applied to non-programming languages and this PoC explores how it might be applied to support the editing of MUD files.

To handle the complexities of parsing to a syntax tree and then understanding that syntax tree, Tree-sitter is used. A (not necessarily complete) Tree-sitter grammar for MUD can be found in parser/tree-sitter-mud/grammar.js. This grammar is intentionally permissive to make parsing more reliable and allow the language server to provide more detailed errors and warnings beyond "unable to parse".

Tree-sitter's parsing can even be done incrementally, and LSP also supports incremental synchronization (as opposed to no synchronization or sending the complete contents on every change), but currently the language server always updates the complete tree for simplicity's sake. Tree-sitter also allows querying tree via Scheme queries. This, e.g., allows easily finding syntax nodes of a certain type but much more complex queries are possible.

Try it!

You can build (and install) this project with cargo. For example, to install the release version (likely to $HOME/.cargo; see cargo help install), run:

$ cargo install --path .

You will need a C compiler on your system for this to work because Cargo needs to compile the Tree-sitter-generated parser sources.

To use it, of course you'll need to configure your (LSP-capable) text editor. While we can't go over complete configuration in this document, here's some snippets to hopefully get you most of the way.

Ultimately this boils down to telling the client to use the muddles binary as a server, communicating via stdin and stdout (as opposed to ports).

Emacs

You can use muddles in Emacs with lsp-mode, declaring a new major mud-mode derived from json-mode. You can install both lsp-mode and json-mode from MELPA (M-x package-install lsp-mode, M-x package-install json-mode)

Here is an example configuration:

(require 'lsp-mode)
(require 'json-mode)
(define-derived-mode mud-mode json-mode "MUD")
(add-to-list 'lsp-language-id-configuration '(mud-mode . "mud"))
(lsp-register-client
  (make-lsp-client :new-connection (lsp-stdio-connection "/path/to/muddles")
                   :major-modes '(mud-mode)
                   :server-id 'muddles))
(add-hook 'mud-mode-hook #'lsp)

For the best experience, I recommend installing flycheck (M-x package-install flycheck) for in-line linting and lsp-ui (M-x package-install lsp-ui) for documentation-on-hover. Both need no additional configuration.

Neovim

Assuming you are already using the lspconfig plugin, here's what the configuration contents could look like:

local lspconfig = require'lspconfig'
local configs = require'lspconfig.configs'

-- ...

if not configs.muddles then
  configs.muddles = {
    default_config = {
      cmd = {'/path/to/my/binary/called/muddles'};
      filetypes = {'mud'}; -- requires ':set ft=mud' in document
      root_dir = function(fname)
        return lspconfig.util.path.dirname(fname)
      end;
    };
  }
end
lspconfig.muddles.setup{}

Vim

As Vim has no native LSP-support, you will need to select and configure the LSP-plugin of your choice, e.g. CoC or vim-lsp.

VSCode

As far as I am aware we will need to create a simple Extension that hooks up the language server. We plan on doing that, but for now consider this marked TODO.

License

Both the Tree-sitter grammar and the language server implementation are licensed under either of

• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

The grammar takes some inspiration from tree-sitter-json which is licensed under the MIT license (c) 2014 Max Brunsfeld.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.

Maintainers

This project is currently maintained by the following developers:

Name	Email Address	GitHub Username
Jan Hensel	mailto:ja_he@uni-bremen.de	ja-he