"Loop or previous error loading module" - how to get the error?

[HyperHacker <hyperhacker@...>]

If I do something like:
pcall(require, 'foo')
require('foo')
where foo is a module that just throws an error, the pcall catches the
error as expected, but the second attempt just throws: "loop or
previous error loading module 'foo'". How can I see what the previous
error was? I see package.loaded.foo now holds a userdata, but I don't
know what I can do with it.

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