Deprecate luabins library

Keep the library available in Lua for now, but show a warning when
scripts try to import it.

Luabins is a vendored dependency in Aegisub and is no longer maintained
upstream. It is not directly used anywhere by Aegisub itself; it was
only added as a convenience library for automation scripts, especially
for serializing tables to save as line extradata. However, I am not
aware of any automation script that actually uses it. (Scripts that do
need to serialize data to extradata use the json library for this.)

So, at the moment luabins causes some headaches in the build process for
what seems to be no gain at all, which is why it is now being
deprecated. If no users complain about desperately needing luabins for
their script for the next release cycle, luabins will be removed
entirely afterwards.

Fixes #382.

Author: arch1t3cht

libaegisub/lua/modules.cpp

@@ -28,6 +28,17 @@ extern "C" int luaopen_lpeg(lua_State *L);
 namespace agi::lua {
 int regex_init(lua_State *L);
 
+int wrap_luaopen_luabins(lua_State *L) {
+	lua_getfield(L, LUA_GLOBALSINDEX, "aegisub");
+	lua_getfield(L, -1, "__raise_warning");
+	lua_remove(L, -2);
+
+	push_value(L, "This automation script uses the library luabins. This library is deprecated and will be removed in a future version of Aegisub. If your script critically depends on luabins and cannot be adapted to work without it, please let us know at https://github.com/TypesettingTools/Aegisub/issues/382 .");
+	lua_call(L, 1, 0);
+
+	return luaopen_luabins(L);
+}
+
 void preload_modules(lua_State *L) {
 	luaL_openlibs(L);
 
@@ -38,7 +49,7 @@ void preload_modules(lua_State *L) {
 	set_field(L, "aegisub.__unicode_impl", luaopen_unicode_impl);
 	set_field(L, "aegisub.__lfs_impl", luaopen_lfs_impl);
 	set_field(L, "lpeg", luaopen_lpeg);
-	set_field(L, "luabins", luaopen_luabins);
+	set_field(L, "luabins", wrap_luaopen_luabins);
 
 	lua_pop(L, 2);