Use erlang:nif_error to make dialyzer happy

And mark some of the NIF functions

src/geef.erl

@@ -15,21 +15,26 @@
 hex_to_raw(_Val) ->
     nif_error(?LINE).
 
+-spec repository_open(iolist()) -> {ok, term()} | {error, term()}.
 repository_open(_Val) ->
     nif_error(?LINE).
 
+-spec repository_is_bare(term()) -> boolean().
 repository_is_bare(_Handle) ->
     nif_error(?LINE).
 
+-spec repository_get_path(term()) -> binary().
 repository_get_path(_Val) ->
     nif_error(?LINE).
 
+-spec repository_get_workdir(term()) -> binary().
 repository_get_workdir(_Handle) ->
     nif_error(?LINE).
 
 repository_get_odb(_Val) ->
     nif_error(?LINE).
 
+-spec repository_init(iolist(), boolean()) -> term().
 repository_init(_Path, _Bare) ->
     nif_error(?LINE).
 
@@ -64,7 +69,7 @@ oid_parse(_Sha) ->
     nif_error(?LINE).
 
 nif_error(Line) ->
-    exit({nif_not_loaded,module,?MODULE,line,Line}).
+    erlang:nif_error({nif_not_loaded,module,?MODULE,line,Line}).
 
 load_enif() ->
     case code:priv_dir(geef) of

src/geef_records.hlr

@@ -1,3 +1,5 @@
--record(ref, {handle, type}).
+-record(ref, {handle, type :: atom()}).
 -record(repo, {handle}).
 -record(odb, {handle}).
+
+-type repo() :: repo.

src/geef_repo.erl

@@ -25,7 +25,7 @@ open(Path) ->
 	    Other
     end.
 
--spec init(iolist(), boolean()) -> {ok, term()} | {error, term()}.
+-spec init(iolist(), boolean()) -> {ok, repo()} | {error, term()}.
 init(Path, Bare) ->
     case geef:repository_init(Path, Bare) of
 	{ok, Handle} ->