Error when lines not extractable to function

Author: robmckinnon

apps/language_server/lib/language_server/experimental/code_mod/extract_function.ex

@@ -10,27 +10,30 @@ defmodule ElixirLS.LanguageServer.Experimental.CodeMod.ExtractFunction do
   """
   def extract_function(zipper, start_line, end_line, function_name) do
     {quoted_after_extract, acc} = extract_lines(zipper, start_line, end_line, function_name)
-
-    new_function_zipper = new_function(function_name, [], acc.lines) |> Z.zip()
-    declared_vars = vars_declared(new_function_zipper) |> Enum.uniq()
-    used_vars = vars_used(new_function_zipper) |> Enum.uniq()
-
-    args = used_vars -- declared_vars
-    returns = declared_vars |> Enum.filter(&(&1 in acc.vars))
-
-    {zipper, extracted} =
-      add_returned_vars(Z.zip(quoted_after_extract), returns, function_name, args, acc.lines)
-
-    enclosing = acc.def
-
-    zipper
-    |> top_find(fn
-      {:def, _meta, [{^enclosing, _, _}, _]} -> true
-      _ -> false
-    end)
-    |> Z.insert_right(extracted)
-    |> fix_block()
-    |> Z.root()
+    if Enum.empty?(acc.lines) do
+      {:error, :not_extractable}
+    else
+      new_function_zipper = new_function(function_name, [], acc.lines) |> Z.zip()
+      declared_vars = vars_declared(new_function_zipper) |> Enum.uniq()
+      used_vars = vars_used(new_function_zipper) |> Enum.uniq()
+
+      args = used_vars -- declared_vars
+      returns = declared_vars |> Enum.filter(&(&1 in acc.vars))
+
+      {zipper, extracted} =
+        add_returned_vars(Z.zip(quoted_after_extract), returns, function_name, args, acc.lines)
+
+      enclosing = acc.def
+
+      zipper
+      |> top_find(fn
+        {:def, _meta, [{^enclosing, _, _}, _]} -> true
+        _ -> false
+      end)
+      |> Z.insert_right(extracted)
+      |> fix_block()
+      |> Z.root()
+    end
   end
 
   @doc """

apps/language_server/test/experimental/code_mod/extract_function_test.exs

@@ -204,6 +204,11 @@ defmodule ElixirLS.LanguageServer.Experimental.CodeMod.ExtractFunctionTest do
 
       Code.eval_string(source)
     end
+
+    @tag no: 6
+    test "errors when extract on second line of multi-line function call", %{quoted: quoted} do
+      {:error, :not_extractable} = ExtractFunction.extract_function(Z.zip(quoted), 11, 11, :bar)
+    end
   end
 
   describe "extract_lines/3" do
@@ -254,5 +259,21 @@ defmodule ElixirLS.LanguageServer.Experimental.CodeMod.ExtractFunctionTest do
                "{:vars, []}"
              ] = lines |> Enum.map(&Sourceror.to_string(&1))
     end
+
+    @tag no: 23
+    test "noop when second line of multi-line function call", %{quoted: quoted} do
+      {zipper, lines} = ExtractFunction.extract_lines(Z.zip(quoted), 11, 11)
+
+      assert "defmodule Baz23 do\n  def foo(one, two) do\n    three = 3\n    IO.inspect(one)\n    IO.inspect(two)\n    IO.inspect(three)\n    four = 4\n    IO.inspect(three)\n\n    IO.inspect(\n      four: four,\n      force_format_on_new_line_with_really_long_atom: true\n    )\n\n    # comment\n  end\nend" =
+               Sourceror.to_string(zipper)
+
+      assert [
+               "{:def, :foo}",
+               "{:def_end, 15}",
+               "{:lines, []}",
+               "{:replace_with, nil}",
+               "{:vars, []}"
+             ] = lines |> Enum.map(&Sourceror.to_string(&1))
+    end
   end
 end