Add emqx.app.src.script file (#2923)

src/emqx.app.src.script

@@ -0,0 +1,34 @@
+%%-*- mode: erlang -*-
+	%% .app.src.script
+	
+Config = case os:getenv("EMQX_DESC") of
+	false -> CONFIG; % env var not defined
+	[]    -> CONFIG; % env var set to empty string
+	Desc ->
+		[begin
+			AppConf0 = lists:keystore(description, 1, AppConf, {description, Desc}),
+			{application, App, AppConf0}
+		end || Conf = {application, App, AppConf} <- CONFIG]
+end,
+
+RemoveLeadingV =
+	fun(Tag) ->
+		case re:run(Tag, "v\[0-9\]+\.\[0-9\]+\.*") of
+			nomatch ->
+				Tag;
+			{match, _} ->
+				%% if it is a version number prefixed by 'v' then remove the 'v'
+				"v" ++ Vsn = Tag,
+				Vsn
+		end
+	end,
+
+case os:getenv("EMQX_DEPS_DEFAULT_VSN") of
+	false -> Config; % env var not defined
+	[]    -> Config; % env var set to empty string
+	Tag ->
+		[begin
+			AppConf0 = lists:keystore(vsn, 1, AppConf, {vsn, RemoveLeadingV(Tag)}),
+			{application, App, AppConf0}
+		end || Conf = {application, App, AppConf} <- Config]
+end.