The code action needs to fix up the line numbers

Code mods deal with snippets of code that need to have their line
numbers fixed up by the code actions.

apps/language_server/lib/language_server/experimental/provider/code_action/replace_with_underscore.ex

@@ -2,11 +2,13 @@ defmodule ElixirLS.LanguageServer.Experimental.Provider.CodeAction.ReplaceWithUn
   @moduledoc """
   A code action that prefixes unused variables with an underscore
   """
+
   alias ElixirLS.LanguageServer.Experimental.CodeMod
   alias ElixirLS.LanguageServer.Experimental.CodeMod.Ast
   alias ElixirLS.LanguageServer.Experimental.Protocol.Requests.CodeAction
   alias ElixirLS.LanguageServer.Experimental.Protocol.Types.CodeAction, as: CodeActionResult
   alias ElixirLS.LanguageServer.Experimental.Protocol.Types.Diagnostic
+  alias ElixirLS.LanguageServer.Experimental.Protocol.Types.TextEdit
   alias ElixirLS.LanguageServer.Experimental.Protocol.Types.WorkspaceEdit
   alias ElixirLS.LanguageServer.Experimental.SourceFile
 
@@ -37,6 +39,8 @@ defmodule ElixirLS.LanguageServer.Experimental.Provider.CodeAction.ReplaceWithUn
           :error
 
         [_ | _] ->
+          text_edits = Enum.map(text_edits, &update_line(&1, one_based_line))
+
           reply =
             CodeActionResult.new(
               title: "Rename to _#{variable_name}",
@@ -49,6 +53,12 @@ defmodule ElixirLS.LanguageServer.Experimental.Provider.CodeAction.ReplaceWithUn
     end
   end
 
+  defp update_line(%TextEdit{} = text_edit, line_number) do
+    text_edit
+    |> put_in([:range, :start, :line], line_number - 1)
+    |> put_in([:range, :end, :line], line_number - 1)
+  end
+
   defp extract_variable_and_line(%Diagnostic{} = diagnostic) do
     with {:ok, variable_name} <- extract_variable_name(diagnostic.message),
          {:ok, line} <- extract_line(diagnostic) do

apps/language_server/test/experimental/provider/code_action/replace_with_underscore_test.exs

@@ -131,4 +131,18 @@ defmodule ElixirLS.LanguageServer.Experimental.Provider.CodeAction.ReplaceWithUn
     assert [%CodeActionReply{edit: %{changes: %{^file_uri => [edit]}}}] = apply(code_action)
     assert edit.new_text == "_"
   end
+
+  test "works with multiple lines" do
+    {file_uri, code_action} = ~S[
+      defmodule MyModule do
+        def my_func(a) do
+        end
+      end
+    ] |> code_action("/project/file.ex", 1, "a")
+
+    assert [%CodeActionReply{edit: %{changes: %{^file_uri => [edit]}}}] = apply(code_action)
+    assert edit.new_text == "_"
+    assert edit.range.start.line == 1
+    assert edit.range.end.line == 1
+  end
 end