Avoid reversing relx overlays.

This mostly moves a lists:reverse/1 which ensures that profile overlays
are run first but keeps the order of overlays otherwise.

src/rebar_relx.erl

@@ -6,6 +6,10 @@
 -export([do/4,
          format_error/1]).
 
+-ifdef(TEST).
+-export([merge_overlays/1]).
+-endif.
+
 -include("rebar.hrl").
 
 %% ===================================================================
@@ -64,5 +68,5 @@ merge_overlays(Config) ->
                            (_) -> false
                         end, Config),
     %% Have profile overlay entries come before others to match how profiles work elsewhere
-    NewOverlay = lists:reverse(lists:flatmap(fun({overlay, Overlay}) -> Overlay end, Overlays)),
+    NewOverlay = lists:flatmap(fun({overlay, Overlay}) -> Overlay end, lists:reverse(Overlays)),
     [{overlay, NewOverlay} | Others].

test/rebar_release_SUITE.erl

@@ -11,6 +11,7 @@ all() -> [release,
           profile_ordering_sys_config_extend_3_tuple_merge,
           extend_release,
           user_output_dir, profile_overlays,
+          profile_overlay_merge,
           overlay_vars].
 
 init_per_testcase(Case, Config0) ->
@@ -217,6 +218,30 @@ profile_overlays(Config) ->
             {dir, filename:join(ReleaseDir, "randomdir")}]}
      ).
 
+profile_overlay_merge (_Config) ->
+    % when profile and relx overlays both exist, the profile overlays should be
+    % first, then the relx overlays, all the rest of the config should come
+    % after, rebar_relx:merge_overlays/1 should do this.
+    RelxOverlay = [{mkdir, "1_from_relx"}, {mkdir, "2_from_relx"}],
+    ProfileOverlay = [{mkdir, "0_from_other_profile"}],
+    OtherConfig = [{other1, config}, {other2, config}],
+
+    % test with no overlays
+    ?assertEqual([{overlay,[]}] ++ OtherConfig,
+                 rebar_relx:merge_overlays(OtherConfig)),
+
+    % test with relx only, just move overlays to the top
+    RelxOnly = OtherConfig ++ [{overlay, RelxOverlay}],
+    ?assertEqual([{overlay, RelxOverlay}]++OtherConfig,
+                 rebar_relx:merge_overlays(RelxOnly)),
+
+    % now test with a profile (profiles end up after relx overlays
+    ProfilesToMerge = OtherConfig ++
+                      [{overlay, RelxOverlay},
+                       {overlay, ProfileOverlay}],
+    ?assertEqual([{overlay, ProfileOverlay ++ RelxOverlay}] ++ OtherConfig,
+                 rebar_relx:merge_overlays(ProfilesToMerge)).
+
 overlay_vars(Config) ->
     AppDir = ?config(apps, Config),
     Name = ?config(name, Config),