config: ensure {mode, ..} expansion does not override existing settings

also: do not export rlx_config:load/2 since it is unused at the moment

see: erlang/rebar3#2853

Author: sg2342

src/rlx_config.erl

@@ -1,7 +1,6 @@
 -module(rlx_config).
 
 -export([to_state/1,
-         load/2,
          format_error/1]).
 
 -include("relx.hrl").
@@ -15,7 +14,11 @@
 to_state(Config) ->
     to_state(Config, rlx_state:new()).
 
-to_state(Config, State) ->
+to_state(Config0, State) ->
+    %% ensure 'mode' elements are at the head of the Config list,
+    %% this makes it possible to override options the modes expand
+    Modes = [V || {mode, _} = V <- Config0],
+    Config =  Modes ++ (Config0 -- Modes),
     %% setup warnings_as_errors before loading the rest so we can error on
     %% any warning during the load
     State1 = rlx_state:warnings_as_errors(State, proplists:get_bool(warnings_as_errors, Config)),