Structs
The
TypeOutlives struct has the job of “lowering” a T: 'a
obligation into a series of 'a: 'b constraints and “verifys”, as
described on the module comment. The final constraints are emitted
via a “delegate” of type D – this is usually the infcx, which
accrues them into the region_obligations code, but for NLL we
use something else.