Respect the --config switch when given

Currently the --config switch does not work because when loading
a new rebar config the global setting is ignored for all paths.
This patch provides a check when loading new rebar config to see
whether or not the current config path matches the `base_dir` set in
global conf, which produces the expected behaviour.

inttest/t_custom_config/custom.config

@@ -0,0 +1 @@
+{erl_opts, [warnings_as_errors]}.

inttest/t_custom_config/custom_config.erl

@@ -0,0 +1,6 @@
+-module(custom_config).
+
+-compile(export_all).
+
+test() ->
+    ok.

inttest/t_custom_config/t_custom_config_rt.erl

@@ -0,0 +1,31 @@
+-module(t_custom_config_rt).
+
+-compile(export_all).
+
+-include_lib("eunit/include/eunit.hrl").
+
+files() ->
+    [{copy, "custom.config", "custom.config"},
+     {create, "ebin/custom_config.app", app(custom_config, [custom_config])}].
+
+run(Dir) ->
+    retest_log:log(debug, "Running in Dir: ~s~n", [Dir]),
+    Ref = retest:sh("rebar -C custom.config check-deps -v", [{async, true}]),
+    {ok, Captured} =
+        retest:sh_expect(Ref,
+                         "DEBUG: Consult config file .*/custom.config.*",
+                         [{capture, all, list}]),
+    retest_log:log(debug, "[CAPTURED]: ~s~n", [Captured]),
+    ok.
+
+%%
+%% Generate the contents of a simple .app file
+%%
+app(Name, Modules) ->
+    App = {application, Name,
+           [{description, atom_to_list(Name)},
+            {vsn, "1"},
+            {modules, Modules},
+            {registered, []},
+            {applications, [kernel, stdlib]}]},
+    io_lib:format("~p.\n", [App]).

src/rebar.erl

@@ -108,9 +108,10 @@ run_aux(Commands) ->
                        false ->
                            rebar_config:new()
                    end,
+    BaseConfig = rebar_config:base_config(GlobalConfig),
 
     %% Process each command, resetting any state between each one
-    rebar_core:process_commands(CommandAtoms, GlobalConfig).
+    rebar_core:process_commands(CommandAtoms, BaseConfig).
 
 %%
 %% print help/usage string

src/rebar_config.erl

@@ -26,7 +26,7 @@
 %% -------------------------------------------------------------------
 -module(rebar_config).
 
--export([new/0, new/1,
+-export([new/0, new/1, base_config/1,
          get/3, get_local/3, get_list/3,
          get_all/2,
          set/3,
@@ -48,6 +48,10 @@
 %% Public API
 %% ===================================================================
 
+base_config(#config{opts=Opts0}) ->
+    ConfName = rebar_config:get_global(config, "rebar.config"),
+    new(Opts0, ConfName).
+
 new() ->
     #config { dir = rebar_utils:get_cwd(),
               opts = [] }.
@@ -60,17 +64,10 @@ new(ConfigFile) when is_list(ConfigFile) ->
         Other ->
             ?ABORT("Failed to load ~s: ~p~n", [ConfigFile, Other])
     end;
-new(#config{opts=Opts0}=ParentConfig)->
-    %% If we are at the top level we might want to load another rebar.config
-    %% We can be certain that we are at the top level if we don't have any
-    %% configs yet since if we are at another level we must have some config.
-    ConfName = case ParentConfig of
-                   {config, _, []} ->
-                       rebar_config:get_global(config, "rebar.config");
-                   _ ->
-                       "rebar.config"
-               end,
+new(_ParentConfig=#config{opts=Opts0})->
+    new(Opts0, "rebar.config").
 
+new(Opts0, ConfName) ->
     %% Load terms from rebar.config, if it exists
     Dir = rebar_utils:get_cwd(),
     ConfigFile = filename:join([Dir, ConfName]),