Add dotFormatter configuration option

CHANGELOG.md

@@ -1,4 +1,5 @@
 ### Unreleased
+- Added option `elixirLS.dotFormatter` to specify path to custom `.formatter.exs`
 
 ### v0.28.1: 24 May 2025
 

README.md

@@ -486,6 +486,7 @@ Below is a list of configuration options supported by the ElixirLS language serv
 <dt>elixirLS.additionalWatchedExtensions</dt><dd>Additional file types capable of triggering a build on change</dd>
 <dt>elixirLS.languageServerOverridePath</dt><dd>Absolute path to an alternative ElixirLS release that will override the packaged release</dd>
 <dt>elixirLS.stdlibSrcDir</dt><dd>Path to Elixir's std lib source code. See [here](https://github.com/elixir-lsp/elixir_sense/pull/277) for more info</dd>
+<dt>elixirLS.dotFormatter</dt><dd>Path to a custom <code>.formatter.exs</code> file used when formatting documents</dd>
 </dl>
 
 ## Debug Adapter configuration options

apps/language_server/lib/language_server/providers/formatting.ex

@@ -4,18 +4,26 @@ defmodule ElixirLS.LanguageServer.Providers.Formatting do
   import ElixirLS.LanguageServer.RangeUtils
   require Logger
 
-  def format(%SourceFile{} = source_file, uri = "file:" <> _, project_dir, mix_project?)
+  def format(source_file, uri, project_dir, mix_project?, opts \\ [])
+
+  def format(
+        %SourceFile{} = source_file,
+        uri = "file:" <> _,
+        project_dir,
+        mix_project?,
+        opts
+      )
       when is_binary(project_dir) do
     file_path = SourceFile.Path.absolute_from_uri(uri, project_dir)
     # file_path and project_dir are absolute paths with universal separators
     if SourceFile.Path.path_in_dir?(file_path, project_dir) do
       # file in project_dir we find formatter and options for file
-      case SourceFile.formatter_for(uri, project_dir, mix_project?) do
-        {:ok, {formatter, opts}} ->
-          formatter_exs_dir = opts[:root]
+      case SourceFile.formatter_for(uri, project_dir, mix_project?, opts) do
+        {:ok, {formatter, formatter_opts}} ->
+          formatter_exs_dir = formatter_opts[:root]
 
-          if should_format?(uri, formatter_exs_dir, opts[:inputs], project_dir) do
-            do_format(source_file, formatter, opts)
+          if should_format?(uri, formatter_exs_dir, formatter_opts[:inputs], project_dir) do
+            do_format(source_file, formatter, formatter_opts)
           else
             JsonRpc.show_message(
               :info,
@@ -47,8 +55,8 @@ defmodule ElixirLS.LanguageServer.Providers.Formatting do
     end
   end
 
-  # if project_dir is not set or schema is not file we format with default options
-  def format(%SourceFile{} = source_file, _uri, _project_dir, _mix_project?) do
+  # if project_dir is not set or scheme is not file we format with default options
+  def format(%SourceFile{} = source_file, _uri, _project_dir, _mix_project?, _opts) do
     do_format(source_file, nil, [])
   end
 

apps/language_server/lib/language_server/server.ex

@@ -1535,7 +1535,14 @@ defmodule ElixirLS.LanguageServer.Server do
          state = %__MODULE__{}
        ) do
     source_file = get_source_file(state, uri)
-    fun = fn -> Formatting.format(source_file, uri, state.project_dir, state.mix_project?) end
+    dot_formatter = Map.get(state.settings || %{}, "dotFormatter")
+
+    fun = fn ->
+      Formatting.format(source_file, uri, state.project_dir, state.mix_project?,
+        dot_formatter: dot_formatter
+      )
+    end
+
     {:async, fun, state}
   end
 

apps/language_server/lib/language_server/source_file.ex

@@ -235,9 +235,12 @@ defmodule ElixirLS.LanguageServer.SourceFile do
     """
   end
 
-  @spec formatter_for(String.t(), String.t() | nil, boolean) ::
+  @spec formatter_for(String.t(), String.t() | nil, boolean, keyword()) ::
           {:ok, {function | nil, keyword()}} | {:error, any}
-  def formatter_for(uri = "file:" <> _, project_dir, mix_project?) when is_binary(project_dir) do
+  def formatter_for(uri, project_dir, mix_project?, opts \\ [])
+
+  def formatter_for(uri = "file:" <> _, project_dir, mix_project?, opts)
+      when is_binary(project_dir) do
     path = __MODULE__.Path.from_uri(uri)
 
     try do
@@ -250,7 +253,7 @@ defmodule ElixirLS.LanguageServer.SourceFile do
           {:ok, config_mtime} = MixProjectCache.config_mtime()
           {:ok, mix_project} = MixProjectCache.get()
 
-          opts = [
+          formatter_opts = [
             deps_paths: deps_paths,
             manifest_path: manifest_path,
             config_mtime: config_mtime,
@@ -286,16 +289,20 @@ defmodule ElixirLS.LanguageServer.SourceFile do
             end
           ]
 
-          {:ok, Mix.Tasks.ElixirLSFormat.formatter_for_file(path, opts)}
+          formatter_opts =
+            formatter_opts
+            |> maybe_put_dot_formatter(opts)
+
+          {:ok, Mix.Tasks.ElixirLSFormat.formatter_for_file(path, formatter_opts)}
         else
           {:error, :project_not_loaded}
         end
       else
-        opts = [
-          root: project_dir
-        ]
+        formatter_opts =
+          [root: project_dir]
+          |> maybe_put_dot_formatter(opts)
 
-        {:ok, Mix.Tasks.ElixirLSFormat.formatter_for_file(path, opts)}
+        {:ok, Mix.Tasks.ElixirLSFormat.formatter_for_file(path, formatter_opts)}
       end
     catch
       kind, payload ->
@@ -322,7 +329,15 @@ defmodule ElixirLS.LanguageServer.SourceFile do
     end
   end
 
-  def formatter_for(_, _, _), do: {:error, :project_dir_not_set}
+  def formatter_for(_, _, _, _), do: {:error, :project_dir_not_set}
+
+  defp maybe_put_dot_formatter(opts_list, opts) do
+    if dot = Keyword.get(opts, :dot_formatter) do
+      Keyword.put(opts_list, :dot_formatter, dot)
+    else
+      opts_list
+    end
+  end
 
   defp format_code(code, opts) do
     try do

apps/language_server/test/providers/formatting_test.exs

@@ -503,4 +503,24 @@ defmodule ElixirLS.LanguageServer.Providers.FormattingTest do
 
     MixProjectCache.store(state)
   end
+
+  @tag :fixture
+  test "custom dot formatter path is used" do
+    in_fixture(Path.join(__DIR__, ".."), "formatter", fn ->
+      store_mix_cache()
+      project_dir = Path.expand(".")
+      path = Path.join(project_dir, "lib/custom.ex")
+      File.write!(path, "foo 1")
+      source_file = %SourceFile{text: "foo 1", version: 1, dirty?: true}
+      uri = SourceFile.Path.to_uri(path)
+
+      assert {:ok, [%TextEdit{}, %TextEdit{}]} =
+               Formatting.format(source_file, uri, project_dir, true)
+
+      assert {:ok, []} =
+               Formatting.format(source_file, uri, project_dir, true,
+                 dot_formatter: Path.join(project_dir, "lib/.formatter.exs")
+               )
+    end)
+  end
 end