Implement merged overlays

This allows overlay_vars to merge comma delimited var config files

src/rebar_reltool.erl

@@ -166,22 +166,32 @@ process_overlay(Config, ReltoolConfig) ->
 %% providing an additional file on the command-line.
 %%
 overlay_vars(Config, Vars0, ReltoolConfig) ->
-    BaseVars = load_vars_file(proplists:get_value(overlay_vars, ReltoolConfig)),
-    OverrideVars = load_vars_file(rebar_config:get_global(Config,
-                                                          overlay_vars,
-                                                          undefined)),
-    M = fun(_Key, _Base, Override) -> Override end,
+    BaseVars = load_vars_file([proplists:get_value(overlay_vars, ReltoolConfig)]),
+    OverlayVars = rebar_config:get_global(Config, overlay_vars, []),
+    OverrideVars = load_vars_file(string:tokens(OverlayVars, ",")),
+    M = fun merge_overlay_var/3, 
     dict:merge(M, dict:merge(M, Vars0, BaseVars), OverrideVars).
 
+merge_overlay_var(_Key, _Base, Override) -> Override.
+
 %%
 %% If a filename is provided, construct a dict of terms
 %%
-load_vars_file(undefined) ->
+load_vars_file([undefined]) ->
+    dict:new();
+load_vars_file([]) ->
     dict:new();
-load_vars_file(File) ->
+load_vars_file(Files) ->
+    load_vars_file(Files, dict:new()).
+
+load_vars_file([], Dict) ->
+    Dict;
+load_vars_file([File | Files], BaseVars) ->
     case rebar_config:consult_file(File) of
         {ok, Terms} ->
-            dict:from_list(Terms);
+            OverrideVars = dict:from_list(Terms),
+            M = fun merge_overlay_var/3,
+            load_vars_file(Files, dict:merge(M, BaseVars, OverrideVars));
         {error, Reason} ->
             ?ABORT("Unable to load overlay_vars from ~p: ~p\n", [File, Reason])
     end.