How to guard against bugs like this one?

[Ethan Furman]

kj wrote:
...

The right answer to this is to make module search return an
error if two modules satisfy the search criteria. "First find"
isn't a good solution.

John Nagle

Then what happens when you *want* to shadow a module? As MRAB suggests,
if you are really concerned about it use a script that checks for
duplicate modules (not a bad idea for debugging), but don't start
throwing errors... next thing you know we won't be able to shadow
classes, functions, or built-ins! !-)

~Ethan~