Make it configurable (:grimacing:)

README.md

@@ -29,10 +29,33 @@ And that's it! Now when you run `mix format` you'll also get the benefits of Sty
 
 ### Configuration
 
-There isn't any! This is intentional.
+There isn't much! This is intentional.
 
 Styler is @adobe's internal Style Guide Enforcer - allowing exceptions to the styles goes against that ethos. Happily, it's open source and thus yours to do with as you will =)
 
+However, it's possible to gradually implement Styler via minimal config in `.formatter.exs` file:
+
+```
+[
+  plugins: [Styler],
+  styler: [
+    # List of rules to enable
+
+    # Can have a keyword list of options
+    {Styler.Style.ModuleDirectives, []},
+
+    # Or just a module name
+    Styler.Style.Pipes
+  ]
+]
+```
+
+By default, if the `styler` key is not present, all rules are enabled.
+
+#### Supported options
+
+* `ignore_prefixes` - a list of file prefixes to skip when applying the rule. Example: `ignore_prefixes: ["test/"]`
+
 ## Features (or as we call them, "Styles")
 
 At this point, Styler does a lot. We've catalogued a list of Credo rules that it automatically fixes, but it does some things -

lib/styler.ex

@@ -29,11 +29,28 @@ defmodule Styler do
   @doc false
   def style({ast, comments}, file, opts) do
     on_error = opts[:on_error] || :log
+    enabled_styles = opts[:config] || @styles
     zipper = Zipper.zip(ast)
     context = %{comments: comments, file: file}
 
     {{ast, _}, %{comments: comments}} =
-      Enum.reduce(@styles, {zipper, context}, fn style, {zipper, context} ->
+      enabled_styles
+      |> Enum.filter(fn
+        {_style, opts} ->
+          if Keyword.has_key?(opts, :ignore_prefixes) do
+            !Enum.any?(opts[:ignore_prefixes], &String.starts_with?(file, Path.join(File.cwd!(), &1)))
+          else
+            true
+          end
+
+        _style ->
+          true
+      end)
+      |> Enum.map(fn
+        {style, _opts} -> style
+        style -> style
+      end)
+      |> Enum.reduce({zipper, context}, fn style, {zipper, context} ->
         try do
           Zipper.traverse_while(zipper, context, &style.run/2)
         rescue
@@ -56,9 +73,26 @@ defmodule Styler do
   @impl Mix.Tasks.Format
   def features(_opts), do: [sigils: [], extensions: [".ex", ".exs"]]
 
+  @doc """
+  Options is a list of styles, that can have options, à la credo:
+
+  Example `.formatter.exs`:
+
+  [
+    plugins: [Styler],
+    styler: [
+      {Styler.Style.ModuleDirectives, ignore_prefixes: ["lib/"]},
+      {Styler.Style.Pipes, ignore_prefixes: ["test/"]},
+    ]
+  ]
+
+  For now, the only config is `ignore_prefixes`, which is a list of file
+  prefixes to ignore when styling.
+  """
   @impl Mix.Tasks.Format
   def format(input, formatter_opts, opts \\ []) do
     file = formatter_opts[:file]
+    opts = Keyword.put(opts, :config, formatter_opts[:styler])
 
     {ast, comments} =
       input

test/style/pipes_test.exs

@@ -672,4 +672,34 @@ defmodule Styler.Style.PipesTest do
       end
     end
   end
+
+  describe "configurable" do
+    test "filename prefix is ignored" do
+      assert_style("f(g(h(x))) |> j()", "f(g(h(x))) |> j()", "lib/test.exs",
+        config: [
+          {Styler.Style.Pipes, ignore_prefixes: ["lib/"]}
+        ]
+      )
+    end
+
+    test "filename not in prefix is styled" do
+      assert_style("f(g(h(x))) |> j()", "x |> h() |> g() |> f() |> j()", "test/test.exs",
+        config: [
+          {Styler.Style.Pipes, ignore_prefixes: ["lib/"]}
+        ]
+      )
+    end
+
+    test "filename prefix is ignored with multiple prefixes" do
+      assert_style("f(g(h(x))) |> j()", "f(g(h(x))) |> j()", "lib/test.exs",
+        config: [
+          {Styler.Style.Pipes, ignore_prefixes: ["lib/", "test/"]}
+        ]
+      )
+    end
+
+    test "if style is not present, no changes are made" do
+      assert_style("f(g(h(x))) |> j()", "f(g(h(x))) |> j()", "lib/test.exs", config: [])
+    end
+  end
 end

test/support/style_case.ex

@@ -16,18 +16,18 @@ defmodule Styler.StyleCase do
 
   using do
     quote do
-      import unquote(__MODULE__), only: [assert_style: 1, assert_style: 2, style: 1]
+      import unquote(__MODULE__), only: [assert_style: 1, assert_style: 2, assert_style: 3, assert_style: 4, style: 3]
     end
   end
 
-  defmacro assert_style(before, expected \\ nil) do
+  defmacro assert_style(before, expected \\ nil, filename \\ "testfile", opts \\ []) do
     expected = expected || before
 
-    quote bind_quoted: [before: before, expected: expected] do
+    quote bind_quoted: [before: before, expected: expected, filename: filename, opts: opts] do
       alias Styler.Zipper
 
       expected = String.trim(expected)
-      {styled_ast, styled, styled_comments} = style(before)
+      {styled_ast, styled, styled_comments} = style(before, filename, opts)
 
       if styled != expected and ExUnit.configuration()[:trace] do
         IO.puts("\n======Given=============\n")
@@ -89,7 +89,7 @@ defmodule Styler.StyleCase do
       end)
 
       assert expected == styled
-      {_, restyled, _} = style(styled)
+      {_, restyled, _} = style(styled, filename, opts)
 
       assert restyled == styled, """
       expected styling to be idempotent, but a second pass resulted in more changes.
@@ -107,9 +107,12 @@ defmodule Styler.StyleCase do
     end
   end
 
-  def style(code) do
+  def style(code, filename, opts) do
     {ast, comments} = Styler.string_to_quoted_with_comments(code)
-    {styled_ast, comments} = Styler.style({ast, comments}, "testfile", on_error: :raise)
+
+    opts = Keyword.put(opts, :on_error, :raise)
+
+    {styled_ast, comments} = Styler.style({ast, comments}, Path.join(File.cwd!(), filename), opts)
 
     try do
       styled_code = styled_ast |> Styler.quoted_to_string(comments) |> String.trim_trailing("\n")