Warn if unable to locate elixir and OTP sources

Fixes elixir-lsp/elixir_sense#44

Author: lukaszsamson

apps/language_server/lib/language_server/cli.ex

@@ -39,6 +39,8 @@ defmodule ElixirLS.LanguageServer.CLI do
     )
 
     check_otp_doc_chunks()
+    check_elixir_sources()
+    check_otp_sources()
 
     Launch.limit_num_schedulers()
 
@@ -91,4 +93,21 @@ defmodule ElixirLS.LanguageServer.CLI do
       Logger.warn("OTP compiled without EEP48 documentation chunks. Language features for erlang modules will run in limited mode. Please reinstall or rebuild OTP with approperiate flags.")
     end
   end
+
+  def check_elixir_sources() do
+    enum_ex_path = Enum.module_info[:compile][:source]
+    unless File.exists?(enum_ex_path, [:raw]) do
+      dir = Path.join(enum_ex_path, "../../../..") |> Path.expand
+      Logger.notice("Elixir sources not found (checking in #{dir}). Code navigation to Elixir modules disabled.")
+    end
+  end
+
+  def check_otp_sources() do
+    {_module, _binary, beam_filename} = :code.get_object_code(:erlang)
+    erlang_erl_path = beam_filename |> to_string |> String.replace(Regex.recompile!(~r/(.+)\/ebin\/([^\s]+)\.beam$/), "\\1/src/\\2.erl")
+    unless File.exists?(erlang_erl_path, [:raw]) do
+      dir = Path.join(erlang_erl_path, "../../../..") |> Path.expand
+      Logger.notice("OTP sources not found (checking in #{dir}). Code navigation to OTP modules disabled.")
+    end
+  end
 end