From b38da6ffd988737bb26f66472274055274678efd Mon Sep 17 00:00:00 2001
From: gmvar <gmvar@users.noreply.github.com>
Date: Thu, 21 Aug 2025 16:20:58 -0700
Subject: [PATCH] languages/beancount: init

Create the `vim.languages.beancount` module using `bean-format` and
`beancount-language-server`.
---
 configuration.nix                       |   1 +
 docs/release-notes/rl-0.8.md            |   3 +
 modules/plugins/languages/beancount.nix | 122 ++++++++++++++++++++++++
 modules/plugins/languages/default.nix   |   1 +
 4 files changed, 127 insertions(+)
 create mode 100644 modules/plugins/languages/beancount.nix

diff --git a/configuration.nix b/configuration.nix
index 750862af..74995b61 100644
--- a/configuration.nix
+++ b/configuration.nix
@@ -75,6 +75,7 @@ isMaximal: {
       # Language modules that are not as common.
       assembly.enable = false;
       astro.enable = false;
+      beancount.enable = false;
       nu.enable = false;
       csharp.enable = false;
       julia.enable = false;
diff --git a/docs/release-notes/rl-0.8.md b/docs/release-notes/rl-0.8.md
index 83839245..63745adb 100644
--- a/docs/release-notes/rl-0.8.md
+++ b/docs/release-notes/rl-0.8.md
@@ -538,8 +538,11 @@
 [gmvar](https://github.com/gmvar):
 
 [harper-ls]: https://github.com/Automattic/harper
+[beancount-language-server]: https://github.com/polarmutex/beancount-language-server
+[bean-format]: https://github.com/beancount/beancount
 
 - Add [harper-ls] to the `vim.lsp` module.
+- Add beancount support under `vim.languages.beancount` using [beancount-language-server] and [bean-format].
 
 [derethil](https://github.com/derethil):
 
diff --git a/modules/plugins/languages/beancount.nix b/modules/plugins/languages/beancount.nix
new file mode 100644
index 00000000..e1265357
--- /dev/null
+++ b/modules/plugins/languages/beancount.nix
@@ -0,0 +1,122 @@
+{
+  config,
+  pkgs,
+  lib,
+  ...
+}: let
+  inherit (builtins) attrNames;
+  inherit (lib.options) mkOption mkEnableOption literalExpression;
+  inherit (lib.meta) getExe';
+  inherit (lib.modules) mkIf mkMerge;
+  inherit (lib.lists) isList;
+  inherit (lib.types) anything attrsOf either enum listOf package str;
+  inherit (lib.nvim.types) mkGrammarOption;
+
+  cfg = config.vim.languages.beancount;
+
+  defaultServer = "beancount-language-server";
+  servers = {
+    beancount-language-server = {
+      rootmarkers = [".git"];
+      filetypes = ["beancount" "bean"];
+      init_options = cfg.lsp.initOptions;
+      cmd =
+        if (isList cfg.lsp.package)
+        then cfg.lsp.package
+        else [(getExe' cfg.lsp.package cfg.lsp.server)];
+    };
+  };
+
+  defaultFormat = "bean-format";
+  formats = {
+    bean-format = {
+      package = pkgs.beancount;
+    };
+  };
+in {
+  options.vim.languages.beancount = {
+    enable = mkEnableOption "Beancount language support";
+
+    treesitter = {
+      enable = mkEnableOption "Beancount treesitter support" // {default = config.vim.languages.enableTreesitter;};
+      package = mkGrammarOption pkgs "beancount";
+    };
+
+    lsp = {
+      enable = mkEnableOption "Beancount LSP support" // {default = config.vim.lsp.enable;};
+
+      server = mkOption {
+        type = enum (attrNames servers);
+        default = defaultServer;
+        description = ''
+          Beancount LSP server to use.
+
+          ::: {.note}
+          'beancount-language-server' requires 'bean-check' and 'bean-format'.
+          Both are provided by 'pkgs.beancount'. These binaries must be in
+          your PATH or in 'vim.extraPackages'. There are no additional checks
+          to verify if this requirement is met.
+          :::
+        '';
+      };
+
+      package = mkOption {
+        type = either package (listOf str);
+        default = pkgs.beancount-language-server;
+        example = literalExpression ''[lib.getExe pkgs.beancount-language-server]'';
+        description = "Beancount LSP package, or the command to run as a list of strings";
+      };
+
+      initOptions = mkOption {
+        type = attrsOf anything;
+        default = {};
+        example = {
+          journal_file = "/path/to/main.beancount";
+          formatting = {
+            prefix_width = 30;
+            currency_column = 60;
+            number_currency_spacing = 1;
+          };
+        };
+        description = "Init options to pass to beancount-language-server";
+      };
+    };
+
+    format = {
+      enable = mkEnableOption "Beancount formatting" // {default = config.vim.languages.enableFormat;};
+
+      type = mkOption {
+        type = enum (attrNames formats);
+        default = defaultFormat;
+        description = "Beancount formatter to use";
+      };
+
+      package = mkOption {
+        type = package;
+        default = formats.${cfg.format.type}.package;
+        description = "Beancount formatter package";
+      };
+    };
+  };
+
+  config = mkIf cfg.enable (mkMerge [
+    (mkIf cfg.treesitter.enable {
+      vim.treesitter.enable = true;
+      vim.treesitter.grammars = [cfg.treesitter.package];
+    })
+
+    (mkIf cfg.lsp.enable {
+      vim.lsp.servers.${cfg.lsp.server} = servers.${cfg.lsp.server};
+    })
+
+    (mkIf cfg.format.enable {
+      vim.formatter.conform-nvim = {
+        enable = true;
+        setupOpts.formatters_by_ft.beancount = [cfg.format.type];
+        setupOpts.formatters.${cfg.format.type} = {
+          command = getExe' cfg.format.package cfg.format.type;
+        };
+      };
+    })
+  ]);
+}
diff --git a/modules/plugins/languages/default.nix b/modules/plugins/languages/default.nix
index fd45758f..cb2af59e 100644
--- a/modules/plugins/languages/default.nix
+++ b/modules/plugins/languages/default.nix
@@ -6,6 +6,7 @@ in {
     ./asm.nix
     ./astro.nix
     ./bash.nix
+    ./beancount.nix
     ./cue.nix
     ./dart.nix
     ./clang.nix