This directory contains test files that are not expected to compile. It is useful for writing tests that things which ought not to type-check do not, in fact, type-check.

To write a test, just write a .rs file using Rayon. Then, for each compilation error, write a //~ ERROR E123 annotation on the line where the error occurs. E123 should be the error code that is issued by rustc. This should be reasonably robust against future compiler changes, though in some cases the errors may start showing up on different lines etc as compiler heuristics change.