souther.nvim

Neovim support for the Souther language: filetype detection, buffer settings, a fallback syntax file, and a wired-up souther-lsp for highlighting, diagnostics, go-to-definition, hover, completion, rename, code actions and formatting.

Highlighting comes from the language server's semantic tokens, which know context-aware identifier roles (type vs. value, parameter vs. local) that no regex can. A small syntax/souther.vim covers the cases the server cannot: the seconds before a JVM process attaches, buffers it never attaches to (diff views, fuzzy-finder previews), and machines where souther is not installed. Semantic tokens are applied at a higher priority, so they win wherever they land.

Requirements

• Neovim 0.11 or later (uses vim.lsp.config / vim.lsp.enable)

• The souther command line on your PATH — it bundles the language server:

  brew install souther-lang/souther/souther     # macOS / Linux
  scoop bucket add souther https://github.com/souther-lang/scoop-souther
  scoop install souther                          # Windows

  Alternatively, download souther-lsp.jar from a release and point cmd at it (see Configuration). The jar needs a JDK 25.

Compatibility

souther.nvim	souther / souther-lsp	Neovim
0.1.x	0.2.x	0.11+

Installation

With lazy.nvim:

{ "dskst/souther.nvim", ft = "souther" }

That is enough: the plugin registers the filetype and enables the server on load. Open any .sou file and :checkhealth vim.lsp should show souther attached.

Configuration

There is no setup(). Everything about the client is configured through vim.lsp.config, the same as for any other language server, before the first .sou buffer is opened:

vim.lsp.config("souther", {
  -- How much of what `example` rows cover the server measures.
  -- "witness" | "all"; anything else, "off" included, disables it.
  init_options = { souther = { adequacy = "witness" } },

  on_attach = function(client, bufnr) end,
})

To run the server from a jar instead of the souther launcher, jar_cmd builds the command — including -Xss4m, which the compiler requires:

vim.lsp.config("souther", {
  cmd = require("souther").jar_cmd("~/tools/souther-lsp.jar", {
    java = "/opt/jdk25/bin/java",   -- optional; defaults to `java` on PATH
    jvm_args = { "-Xmx2g" },        -- optional; appended after -Xss4m
  }),
})

cmd is an ordinary list, so cmd_env, cmd_cwd and everything else Neovim does with a command keep working.

Workspace root

souther-lsp does not read build files. It walks its root recursively, collects every *.sou under it, and compiles them as one flat module set — so an import only resolves when both files sit under the same root, and a root that is too narrow is reported as an unknown module rather than degrading quietly. The root is captured once at initialize; the server does not handle workspace/didChangeWorkspaceFolders.

The plugin therefore resolves the widest sane boundary, not the nearest one:

1. The nearest ancestor holding a build file (settings.gradle(.kts), pom.xml, build.gradle(.kts)), then upward while each parent also holds one — in a Maven or Gradle multi-module tree that is the aggregator, so sibling modules resolve against each other.
2. Never above the .git directory.
3. With no build file anywhere, the .git directory.
4. Otherwise nothing, and the client runs without a workspace, which is the right answer for a lone .sou file.

:checkhealth souther reports the root the current buffer would get. To use your own rule, override root_dir — it takes precedence over root_markers, so setting markers alone would have no effect here:

vim.lsp.config("souther", {
  root_dir = function(bufnr, on_dir)
    on_dir(vim.fs.root(bufnr, { "souther.toml", ".git" }))
  end,
})

Highlight groups

Semantic tokens land on Neovim's standard @lsp.type.* groups, which link to @keyword, @string, @type, @function and so on. Any colorscheme that handles those works unchanged. To tweak one:

vim.api.nvim_set_hl(0, "@lsp.type.typeParameter.souther", { link = "@type" })

The fallback syntax file uses souther* groups linked to the standard Keyword, String, Type, Comment and friends. Use :Inspect to see which group a given token actually received.

Development

make test              # unit tests, no souther needed
make test-integration  # needs `souther` on PATH or SOUTHER_LSP_JAR=...
make lint              # stylua --check + luacheck

Tests use plenary.nvim, cloned into .tests/ on first run.

Roadmap

• Tree-sitter queries once a tree-sitter-souther grammar exists upstream. Nothing else in this plugin changes when it does; the grammar layers between the fallback syntax and the semantic tokens.
• Upstreaming lsp/souther.lua to nvim-lspconfig. It is deliberately plain data so that it merges predictably if both end up on the runtimepath; what stays here afterwards is the filetype, buffer settings, syntax fallback and health check.
• Reporting fake / example / examples for as keywords in souther-lsp itself, so every editor benefits rather than each one carrying the rule.

License

MIT