From 460645219de1fea56e2d6885ec1ce355232c63e4 Mon Sep 17 00:00:00 2001
From: Guilherme Andrade <g@gandrade.net>
Date: Sat, 17 Aug 2019 14:49:29 +0100
Subject: Keep expected overlay behaviour - make API overlays the lesser
 authority

---
 src/rlx_prv_overlay.erl    | 12 ++++++++----
 test/rlx_release_SUITE.erl | 32 ++++++++++++++++++++++++++------
 test/rlx_test_utils.erl    |  2 +-
 3 files changed, 35 insertions(+), 11 deletions(-)

diff --git a/src/rlx_prv_overlay.erl b/src/rlx_prv_overlay.erl
index 5ba3f75..ec8a97f 100644
--- a/src/rlx_prv_overlay.erl
+++ b/src/rlx_prv_overlay.erl
@@ -152,10 +152,15 @@ get_overlay_vars_from_file(State, OverlayVars) ->
 -spec read_overlay_vars(rlx_state:t(), proplists:proplist(), [file:name()]) ->
                                proplists:proplist() | relx:error().
 read_overlay_vars(State, OverlayVars, FileNames) ->
+    ApiCallerVars = rlx_state:api_caller_overlays(State),
     Terms = merge_overlay_vars(State, FileNames),
-    case render_overlay_vars(OverlayVars, Terms, []) of
+    case render_overlay_vars(OverlayVars ++ ApiCallerVars, Terms, []) of
         {ok, NewTerms} ->
-            OverlayVars ++ NewTerms;
+            % We place `ApiCallerVars' at the end on purpose; their
+            % definitions should be overwrittenable by both internal
+            % and rendered vars, as not to change behaviour in
+            % setups preceding the support for API caller overlays.
+            OverlayVars ++ NewTerms ++ ApiCallerVars;
         Error ->
             Error
     end.
@@ -273,8 +278,7 @@ generate_state_vars(State) ->
                                erlang:atom_to_list(Name1);
                            {Name1, Vsn1} ->
                                erlang:atom_to_list(Name1) ++ "-" ++ Vsn1
-                       end}
-     | rlx_state:api_caller_overlays(State)].
+                       end}].
 
 -spec do_overlay(rlx_state:t(), list(), proplists:proplist()) ->
                                    {ok, rlx_state:t()} | relx:error().
diff --git a/test/rlx_release_SUITE.erl b/test/rlx_release_SUITE.erl
index b6289d6..a2aab71 100644
--- a/test/rlx_release_SUITE.erl
+++ b/test/rlx_release_SUITE.erl
@@ -818,15 +818,14 @@ overlay_release(Config) ->
                     goal_app_2]}]),
 
     VarsFile1 = filename:join([LibDir1, "vars1.config"]),
-    ProfileString = "prod-v5",
     %% `tpl_var' is defined in vars1, but redifined in vars2 using template.
-    %% `profile_string' is to be injected as an API caller overlay var
+    %% `api_caller_var' is to be injected as an API caller overlay var.
     rlx_test_utils:write_config(VarsFile1, [{yahoo, "yahoo"},
                                             {yahoo2, [{foo, "bar"}]},
                                             {foo_yahoo, "foo_{{yahoo}}"},
                                             {foo_dir, "foodir"},
                                             {tpl_var, "defined in vars1"},
-                                            {profile_string_value, "{{profile_string}}"}]),
+                                            {api_caller_var, "{{api_caller_var}}"}]),
 
     VarsFile2 = filename:join([LibDir1, "vars2.config"]),
     rlx_test_utils:write_config(VarsFile2, [{google, "yahoo"},
@@ -854,7 +853,16 @@ overlay_release(Config) ->
     OutputDir = filename:join([proplists:get_value(priv_dir, Config),
                                rlx_test_utils:create_random_name("relx-output")]),
 
-    ApiCallerOverlays = [{profile_string, ProfileString}],
+    ApiCallerVarValue = "api-caller-var",
+    ApiCallerReleaseNameValue = "release-var-conflict",
+    ApiCallerConfigFileValue = "state-var-conflict",
+    ApiCallerYahooValue = "overlays-file-conflict",
+    ApiCallerOverlays =
+        [{api_caller_var, ApiCallerVarValue},
+         {release_name, ApiCallerReleaseNameValue},
+         {config_file, ApiCallerConfigFileValue},
+         {yahoo, ApiCallerYahooValue}],
+
     {ok, State} = relx:do([{relname, undefined},
                            {relvsn, undefined},
                            {goals, []},
@@ -900,6 +908,8 @@ overlay_release(Config) ->
                  proplists:get_value(release_version, TemplateData)),
     ?assertEqual(foo,
                  proplists:get_value(release_name, TemplateData)),
+    ?assertMatch(ConfigFile,
+                 proplists:get_value(config_file, TemplateData)),
     ?assertEqual("yahoo/foo4",
                  proplists:get_value(yahoo4, TemplateData)),
     ?assertEqual("foo_yahoo",
@@ -914,8 +924,18 @@ overlay_release(Config) ->
     %% of tpl_var defined in VarsFile1 or not.
     ?assertEqual("Redefined in vars2 with a template value",
                  proplists:get_value(tpl_var, TemplateData)),
-    ?assertEqual(ProfileString,
-                 proplists:get_value(profile_string_value, TemplateData)).
+
+    ?assertEqual(ApiCallerVarValue,
+                 proplists:get_value(api_caller_var, TemplateData)),
+    % The following complements a few of the assertions above
+    % by ensuring that the values of the overwritten API caller
+    % overlays were distinct from their internal values.
+    ?assertNotEqual(ApiCallerReleaseNameValue,
+                    proplists:get_value(release_name, TemplateData)),
+    ?assertNotEqual(ApiCallerConfigFileValue,
+                    proplists:get_value(config_file, TemplateData)),
+    ?assertNotEqual(ApiCallerYahooValue,
+                    proplists:get_value(yahoo, TemplateData)).
 
 make_goalless_release(Config) ->
     LibDir1 = proplists:get_value(lib1, Config),
diff --git a/test/rlx_test_utils.erl b/test/rlx_test_utils.erl
index dc1e0b0..2c5f7af 100644
--- a/test/rlx_test_utils.erl
+++ b/test/rlx_test_utils.erl
@@ -187,7 +187,7 @@ test_template_contents() ->
         "{prop1, \"{{prop1}}\"}.\n"
         "{prop2, {{prop2}}}.\n"
         "{tpl_var, \"{{tpl_var}}\"}.\n"
-        "{profile_string_value, \"{{profile_string_value}}\"}.\n".
+        "{api_caller_var, \"{{api_caller_var}}\"}.\n".
 
 escript_contents() ->
     "#!/usr/bin/env escript\n"
-- 
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