scala/scala — pull request #2291 by retronym (2013-03-23 08:50:13+00:00)
Title: SI-7290 Discard duplicates in switchable alternative patterns.

The pattern matcher must not allow duplicates to hit the
backend when generating switches. It already eliminates then
if they appear on different cases (with an unreachability warning.)

This commit does the same for duplicated literal patterns in an
alternative pattern: discard and warn.

Review by @adriaanm