From 475de3d98acfd620aba4347af1047f1722ae386b Mon Sep 17 00:00:00 2001
From: Jesse Stimpson <jstimpson@relaypro.com>
Date: Wed, 15 Sep 2021 13:46:22 +0000
Subject: [PATCH] Allow apps_vars_file to be specified per application in
 config

---
 src/rebar_otp_app.erl | 29 ++++++++++++++++++++++++++---
 1 file changed, 26 insertions(+), 3 deletions(-)

diff --git a/src/rebar_otp_app.erl b/src/rebar_otp_app.erl
index 9b94e8e16..12971f2e3 100644
--- a/src/rebar_otp_app.erl
+++ b/src/rebar_otp_app.erl
@@ -118,7 +118,7 @@ preprocess(State, AppInfo, AppSrcFile) ->
             %% substitute. Note that we include the list of modules available in
             %% ebin/ and update the app data accordingly.
             OutDir = rebar_app_info:out_dir(AppInfo),
-            AppVars = load_app_vars(State) ++ [{modules, ebin_modules(AppInfo, OutDir)}],
+            AppVars = load_app_vars(AppName, State) ++ [{modules, ebin_modules(AppInfo, OutDir)}],
             A1 = apply_app_vars(AppVars, AppData),
 
             %% AppSrcFile may contain instructions for generating a vsn number
@@ -146,8 +146,8 @@ preprocess(State, AppInfo, AppSrcFile) ->
             throw(?PRV_ERROR({file_read, rebar_app_info:name(AppInfo), ".app.src", Reason}))
     end.
 
-load_app_vars(State) ->
-    case rebar_state:get(State, app_vars_file, undefined) of
+load_app_vars(AppName, State) ->
+    case get_app_vars_file_from_state(AppName, State) of
         undefined ->
             [];
         Filename ->
@@ -156,6 +156,29 @@ load_app_vars(State) ->
             Vars
     end.
 
+get_app_vars_file_from_state(AppName, State) ->
+    case rebar_state:get(State, app_vars_file, undefined) of
+        undefined ->
+            undefined;
+        AppVarsProplist=[T|_] when is_tuple(T) ->
+            %% When `apps_vars_file' is a proplist, assume that each key
+            %% of the proplist corresponds to an app name (atom). This
+            %% allows the developer to provide any number of `app_vars_file's
+            %% and apply the vars in any application's .app file specifically.
+            case proplists:get_value(AppName, AppVarsProplist) of
+                undefined ->
+                    undefined;
+                Filename ->
+                    Filename
+            end;
+        Filename ->
+            %% When app_vars_file is not a proplist, assume that it is
+            %% a filename. When a filename is provided, the env vars
+            %% contained within will be applied to all apps being
+            %% compiled by rebar.
+            Filename
+    end.
+
 apply_app_vars([], AppData) ->
     AppData;
 apply_app_vars([{Key, Value} | Rest], AppData) ->