Penlight rockspec read non-permission, why?

[Dirk Laurie <dirk.laurie@...>]

Under Linux, I have to "sudo luarocks install" otherwise the stuff
can't go into /usr/local.

The most recent rock I installed (2014-11-03) is Penlight.
An ordinary user can't show it.

$ luarocks show penlight
Error: Could not load rockspec file
/usr/local/lib/luarocks/rocks/penlight/1.3.1-1/penlight-1.3.1-1.rockspec
(cannot open /usr/local/lib/luarocks/rocks/penlight/1.3.1-1/penlight-1.3.1-1.rockspec:
Permission denied)

I reinstalled it, no difference. I have to `sudo` to show it.

None of my other rocks has this problem.

Theory 1: It only affects rocks installed after a certain date. Test it by
installing another rock. Can show it, theory is wrong.
Theory 2: Something funny about Penlight itself. Test it by downloading
the rock.

$ unzip -l penlight-1.3.1-1.src.rock | grep rockspec
     2169  2013-09-24 19:17   penlight-1.3.1-1.rockspec
     2157  2013-09-24 19:17   Penlight/penlight-1.1.0-3.rockspec

There's an old rockspec lying around in the Penlight directory.
That _is_ funny. But can it cause the error?