From 91269c56c5c81778234e69240e424b9bdc069b07 Mon Sep 17 00:00:00 2001
From: NotAShelf <raf@notashelf.dev>
Date: Tue, 27 Jan 2026 12:13:25 +0300
Subject: [PATCH] neovim/init: add module option for registering custom
 filetypes

Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: I5f5f576642884c09a8e4afc18499ed606a6a6964
---
 modules/neovim/init/default.nix  |   1 +
 modules/neovim/init/filetype.nix | 121 +++++++++++++++++++++++++++++++
 2 files changed, 122 insertions(+)
 create mode 100644 modules/neovim/init/filetype.nix

diff --git a/modules/neovim/init/default.nix b/modules/neovim/init/default.nix
index 3f195085..641cc0e1 100644
--- a/modules/neovim/init/default.nix
+++ b/modules/neovim/init/default.nix
@@ -5,6 +5,7 @@
     ./clipboard.nix
     ./debug.nix
     ./diagnostics.nix
+    ./filetype.nix
     ./highlight.nix
     ./lsp.nix
     ./spellcheck.nix
diff --git a/modules/neovim/init/filetype.nix b/modules/neovim/init/filetype.nix
new file mode 100644
index 00000000..6f098c54
--- /dev/null
+++ b/modules/neovim/init/filetype.nix
@@ -0,0 +1,121 @@
+{
+  config,
+  lib,
+  ...
+}: let
+  inherit (lib.options) mkOption;
+  inherit (lib.types) nullOr either oneOf attrsOf str listOf submodule ints;
+  inherit (lib.nvim.types) luaInline;
+  inherit (lib.nvim.dag) entryBefore;
+  inherit (lib.nvim.lua) toLuaObject;
+
+  cfg = config.vim;
+
+  # vim.filetype.add() is quite robust, but this makes for a very
+  # complex type that we have to handle. It takes a string, a Lua function
+  # or a dictionary with the priority of the extension.
+  ftOptionType = attrsOf (oneOf [
+    str # "filetype"
+    luaInline # `function(path, bufnr) ... end`
+
+    # { 'dosini', { priority = 10 } },
+    (listOf (either str (submodule {
+      options = {
+        priority = mkOption {
+          type = ints.unsigned;
+          description = ''
+            `vim.filetype.add()` can take an optional priority value to resolve
+            conflicts where a filetype is registered by multiple patterns. When
+            priority is specified, file with the higher priority value will be
+            matched first on conflict.
+          '';
+        };
+      };
+    })))
+  ]);
+in {
+  options.vim.filetype = mkOption {
+    type = submodule {
+      options = {
+        extension = mkOption {
+          type = nullOr ftOptionType;
+          default = null;
+          description = "register a new filetype by extension";
+        };
+
+        filename = mkOption {
+          type = nullOr ftOptionType;
+          default = null;
+          description = "register a new filetype by file name";
+        };
+
+        pattern = mkOption {
+          type = nullOr ftOptionType;
+          default = null;
+          description = "register a new filetype by pattern";
+        };
+      };
+    };
+
+    default = {};
+    example = {
+      filename = {
+        ".foorc" = "toml";
+        "/etc/foo/config" = "toml";
+        "todo.txt" = "todotxt";
+      };
+
+      pattern = {
+        ".*%.scm" = "query";
+        ".*README.(%a+)" = ''
+          function(path, bufnr, ext)
+            if ext == 'md' then
+              return 'markdown'
+            elseif ext == 'rst' then
+              return 'rst'
+            end
+          end,
+        '';
+      };
+
+      extension = {
+        mdx = "markdown";
+        bar = lib.mkLuaInline ''
+          bar = function(path, bufnr)
+            if some_condition() then
+              return 'barscript', function(bufnr)
+                -- Set a buffer variable
+                vim.b[bufnr].barscript_version = 2
+              end
+            end
+            return 'bar'
+          end,
+        '';
+      };
+    };
+
+    description = ''
+      Additional filetypes to be registered through `vim.filetype.add()`
+
+      Filetype mappings can be added either by extension or by filename. The
+      key can be either the "tail" or the full file path. The full file path
+      is checked first, followed by the file name. If a match is not found
+      using the filename, then the filename is matched against the list of
+      Lua patterns (sorted by priority) until a match is found.
+
+      If a pattern matching does not find a filetype, then the file extension
+      is used.
+
+      See `:h vim.filetype.add()` for more details.
+    '';
+  };
+
+  config = {
+    # XXX: some plugins can be loaded on filetype, and unless the filetypes
+    # are registered first, chances are custom filetypes will not be usable
+    # for lazy-loading on ft.
+    vim.luaConfigRC.filetype = entryBefore ["lazyConfigs"] ''
+      vim.filetype.add(${toLuaObject cfg.filetype})
+    '';
+  };
+}