Lua 5.1 incompatibility

[sewbacca]

We found a bug when running LuaRocks 3.12.2 using Lua 5.1 via compat53 (see luarocks/luarocks#1831).

They rely on file:write() behavior from Lua >= 5.2 to return the fd if no error occurs:

local fd, err = io.open(path, 'w')
if not fd then return nil, err end
fd, err = f:write(data)
if not fd then return nil, err end
fd:close()
return true

There is already a patch in this repo, however it's not applied if we use native Lua 5.1 with no LuaJIT:

lua-compat-5.3/compat53/file_mt.lua

Lines 59 to 68 in dfd83b4

	if not is_luajit52 then
	local file_write = file_meta.__index.write
	file_meta.__index.write = function(self, ...)
	local ret, err = file_write(self, ...)
	if ret then
	return self
	end
	return ret, err
	end
	end

A dirty workarround we found is to just call this function on the metatable, if Lua version is 5.1:

diff --git a/src/compat53/module.lua b/src/compat53/module.lua
index 52b1dd63..b6a69af3 100644
--- a/src/compat53/module.lua
+++ b/src/compat53/module.lua
@@ -824,6 +824,7 @@ if lua_version < "5.3" then
             end
             return lines_iterator, st
          end
+         require'compat53.file_mt'.update_file_meta(debug.getmetatable(io.stdin), false)
       end -- not luajit

       if is_luajit then

This only seems to affect module.lua, as init.lua always calls the update function.

[hishamhm]

Could you please test if it work work if here, instead of is_luajit, we checked for not is_luajit52 ? I think that should make io.open return an fd with the updated compat metatable, without affecting the global environment:
https://github.com/lunarmodules/lua-compat-5.3/blob/master/compat53/module.lua#L829

If that does work, a PR is welcome!

[sewbacca]

We tried setting that if unconditionally to true, but then we got a weird error with no stacktrace, no matter if the module was namespaced or not:

$ luarocks install sewbacca/luachild
/usr/bin/lua5.1: bad argument #1 to '?' (FILE* expected, got userdata)
$ luarocks install luachild
/usr/bin/lua5.1: bad argument #1 to '?' (FILE* expected, got userdata)