feat: add format-dune-file (#602)

Author: ymn64

README.md

@@ -238,6 +238,7 @@ You can view this list in vim with `:help conform-formatters`
 - [fixjson](https://github.com/rhysd/fixjson) - JSON Fixer for Humans using (relaxed) JSON5.
 - [fnlfmt](https://git.sr.ht/~technomancy/fnlfmt) - A formatter for Fennel code.
 - [forge_fmt](https://github.com/foundry-rs/foundry) - Forge is a command-line tool that ships with Foundry. Forge tests, builds, and deploys your smart contracts.
+- [format-dune-file](https://github.com/ocaml/dune) - Auto-formatter for Dune files.
 - [format-queries](https://github.com/nvim-treesitter/nvim-treesitter/blob/main/CONTRIBUTING.md#formatting) - Tree-sitter query formatter.
 - [fourmolu](https://hackage.haskell.org/package/fourmolu) - A fork of ormolu that uses four space indentation and allows arbitrary configuration.
 - [fprettify](https://github.com/fortran-lang/fprettify) - Auto-formatter for modern fortran source code.

doc/conform.txt

@@ -331,6 +331,7 @@ FORMATTERS                                                    *conform-formatter
 `fnlfmt` - A formatter for Fennel code.
 `forge_fmt` - Forge is a command-line tool that ships with Foundry. Forge tests,
             builds, and deploys your smart contracts.
+`format-dune-file` - Auto-formatter for Dune files.
 `format-queries` - Tree-sitter query formatter.
 `fourmolu` - A fork of ormolu that uses four space indentation and allows
            arbitrary configuration.

lua/conform/formatters/format-dune-file.lua

@@ -0,0 +1,10 @@
+---@type conform.FileFormatterConfig
+return {
+  meta = {
+    url = "https://github.com/ocaml/dune",
+    description = "Auto-formatter for Dune files.",
+  },
+  command = "dune",
+  args = { "format-dune-file" },
+  stdin = true,
+}