Improve log message when module startup has failed

diff --git a/src/gen_mod.erl b/src/gen_mod.erl
index 4bdca70f9c8843236d9731b2dc3223699603c1c0..5f8283df73d5624309cd2ed92a45acbd444d61a2 100644 (file)
--- a/src/gen_mod.erl
+++ b/src/gen_mod.erl
@@ -218,10 +218,23 @@ start_module(Host, Module, Opts0, NeedValidation) ->
            catch Class:Reason ->
                    ets:delete(ejabberd_modules, {Module, Host}),
                    ErrorText =
-                       io_lib:format("Problem starting the module ~s for host "
-                                     "~s ~n options: ~p~n ~p: ~p~n~p",
-                                     [Module, Host, Opts, Class, Reason,
-                                      erlang:get_stacktrace()]),
+                       case Reason == undef andalso
+                            code:ensure_loaded(Module) /= {module, Module} of
+                           true ->
+                               io_lib:format("Failed to load unknown module "
+                                             "~s for host ~s: make sure "
+                                             "there is no typo and ~s.beam "
+                                             "exists inside either ~s or ~s "
+                                             "directory",
+                                             [Module, Host, Module,
+                                              filename:dirname(code:which(?MODULE)),
+                                              ext_mod:modules_dir()]);
+                           false ->
+                               io_lib:format("Problem starting the module ~s for host "
+                                             "~s ~n options: ~p~n ~p: ~p~n~p",
+                                             [Module, Host, Opts, Class, Reason,
+                                              erlang:get_stacktrace()])
+                       end,
                    ?CRITICAL_MSG(ErrorText, []),
                    maybe_halt_ejabberd(ErrorText),
                    erlang:raise(Class, Reason, erlang:get_stacktrace())