Add Mix.Tasks.Format.formatter_opts_for_file/2 (#7457)

Returns options to be used for a given file - useful for editor
integrations formatting unsaved files.

Signed-off-by: José Valim <[email protected]>

Author: JakeBecker

lib/mix/lib/mix/tasks/format.ex

@@ -142,6 +142,19 @@ defmodule Mix.Tasks.Format do
     |> check!()
   end
 
+  @doc """
+  Returns formatter options to be used for the given file.
+  """
+  def formatter_opts_for_file(file, opts \\ []) do
+    {dot_formatter, formatter_opts} = eval_dot_formatter(opts)
+
+    {formatter_opts_and_subs, _sources} =
+      eval_deps_and_subdirectories(dot_formatter, [], formatter_opts, [dot_formatter])
+
+    split = file |> Path.relative_to_cwd() |> Path.split()
+    find_formatter_opts_for_file(split, formatter_opts_and_subs)
+  end
+
   defp eval_dot_formatter(opts) do
     cond do
       dot_formatter = opts[:dot_formatter] ->

lib/mix/test/mix/tasks/format_test.exs

@@ -213,6 +213,9 @@ defmodule Mix.Tasks.FormatTest do
       [inputs: "a.ex", locals_without_parens: [my_fun: 2]]
       """)
 
+      formatter_opts = Mix.Tasks.Format.formatter_opts_for_file("lib/extra/a.ex")
+      assert [my_fun: 2] = Keyword.get(formatter_opts, :locals_without_parens)
+
       File.write!("lib/a.ex", """
       my_fun :foo, :bar
       other_fun :baz
@@ -280,6 +283,9 @@ defmodule Mix.Tasks.FormatTest do
       # Let's check that the manifest gets updated if it's stale.
       File.touch!(manifest_path, {{1970, 1, 1}, {0, 0, 0}})
 
+      formatter_opts = Mix.Tasks.Format.formatter_opts_for_file("a.ex")
+      assert [my_fun: 2] = Keyword.get(formatter_opts, :locals_without_parens)
+
       Mix.Tasks.Format.run(["a.ex"])
       assert File.stat!(manifest_path).mtime > {{1970, 1, 1}, {0, 0, 0}}
     end)
@@ -357,6 +363,9 @@ defmodule Mix.Tasks.FormatTest do
       File.touch!("lib/extra/.formatter.exs", {{2030, 1, 1}, {0, 0, 0}})
       Mix.Tasks.Format.run([])
 
+      formatter_opts = Mix.Tasks.Format.formatter_opts_for_file("lib/extra/a.ex")
+      assert [other_fun: 1] = Keyword.get(formatter_opts, :locals_without_parens)
+
       assert File.read!("lib/extra/a.ex") == """
              my_fun(:foo, :bar)
              other_fun :baz