Better report errors of module startup

diff --git a/src/gen_mod.erl b/src/gen_mod.erl
index ed04767ca621b9da4b9ea701ab123220f731d243..456afca07a830f973c646f7f67a953b4eb0bedcf 100644 (file)
--- a/src/gen_mod.erl
+++ b/src/gen_mod.erl
@@ -217,28 +217,13 @@ start_module(Host, Module, Opts0, Order, NeedValidation) ->
            try case Module:start(Host, Opts) of
                    ok -> ok;
                    {ok, Pid} when is_pid(Pid) -> {ok, Pid};
-                   Err -> erlang:error(Err)
+                   Err -> erlang:error({bad_return, Module, Err})
                end
            catch Class:Reason ->
                    ets:delete(ejabberd_modules, {Module, Host}),
-                   ErrorText =
-                       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,
+                   ErrorText = format_start_error(
+                                 Module, Opts, Class, Reason,
+                                 erlang:get_stacktrace()),
                    ?CRITICAL_MSG(ErrorText, []),
                    maybe_halt_ejabberd(),
                    erlang:raise(Class, Reason, erlang:get_stacktrace())
@@ -722,6 +707,40 @@ get_submodules(Host, Module, Opts) ->
            []
     end.
 
+-spec format_start_error(atom(), opts(),
+                        error | exit | throw, any(),
+                        [erlang:stack_item()]) -> iolist().
+format_start_error(Module, Opts, Class, Reason, St) ->
+    IsLoaded = code:ensure_loaded(Module) == {module, Module},
+    IsStartExported = erlang:function_exported(Module, start, 2),
+    case {Class, Reason} of
+       {error, undef} when not IsLoaded ->
+           io_lib:format("Failed to load unknown module ~s: "
+                         "make sure there is no typo and ~s.beam "
+                         "exists inside either ~s or ~s "
+                         "directory",
+                         [Module, Module,
+                          filename:dirname(code:which(?MODULE)),
+                          ext_mod:modules_dir()]);
+       {error, undef} when not IsStartExported ->
+           io_lib:format("Failed to load module ~s because "
+                         "it doesn't export start/2 callback: "
+                         "is it really an ejabberd module?", [Module]);
+       {error, {bad_return, Module, Ret}} ->
+           io_lib:format("Module ~s returned unexpected value during "
+                         "startup: ~p; this is either not an ejabberd "
+                         "module or it implements ejabbed API incorrectly",
+                         [Module, Ret]);
+       _ ->
+           io_lib:format("Internal error of module ~s has "
+                         "occured during startup:~n"
+                         "** Options: ~p~n"
+                         "** Class: ~p~n"
+                         "** Reason: ~p~n"
+                         "** Stacktrace: ~p",
+                         [Module, Opts, Class, Reason, St])
+    end.
+
 -spec db_type(binary() | global, module()) -> db_type();
             (opts(), module()) -> db_type().