don't crash when cleaning non mix projects

Author: lukaszsamson

apps/language_server/lib/language_server/json_rpc.ex

@@ -262,7 +262,7 @@ defmodule ElixirLS.LanguageServer.JsonRpc do
   defp error_code_and_message(:unknown_error_code), do: {-32001, "Unknown error code"}
 
   # -32899 - -32800 - LSP reserved error codes
-  defp error_code_and_message(:request_failed), do: {-32803, "Request cancelled"}
+  defp error_code_and_message(:request_failed), do: {-32803, "Request failed"}
   defp error_code_and_message(:server_cancelled), do: {-32802, "Server cancelled"}
   defp error_code_and_message(:content_modified), do: {-32801, "Content modified"}
   defp error_code_and_message(:request_cancelled), do: {-32800, "Request cancelled"}

apps/language_server/lib/language_server/providers/execute_command/mix_clean.ex

@@ -2,9 +2,14 @@ defmodule ElixirLS.LanguageServer.Providers.ExecuteCommand.MixClean do
   @behaviour ElixirLS.LanguageServer.Providers.ExecuteCommand
 
   @impl ElixirLS.LanguageServer.Providers.ExecuteCommand
-  def execute([clean_deps?], state) do
-    case ElixirLS.LanguageServer.Build.clean(state.project_dir, clean_deps?) do
+  def execute(_, %{project_dir: nil}) do
+    {:error, :invalid_request, "No mix project", false}
+  end
+
+  def execute([clean_deps?], %{project_dir: project_dir}) do
+    case ElixirLS.LanguageServer.Build.clean(project_dir, clean_deps?) do
       :ok -> {:ok, %{}}
+      :no_mixfile -> {:error, :invalid_request, "No mix.exs in project dir", false}
       {:error, reason} -> {:error, :request_failed, "Mix clean failed: #{inspect(reason)}", true}
     end
   end