Nightly panics on an unused type parameter when lifetimes are involved?

[cdbfoster]

This causes a panic with the nightly compiler: https://is.gd/OAufPJ
The stable compiler correctly reports an error about the unused type parameter.

[cdbfoster]

Even more succinctly: https://is.gd/jFGYBg

[TimNN]

nightly-2016-09-03 is still good, nightly-2016-09-04 causes the ICE, changes.