[nll] overly strict `T: 'static` bound arising from closure

[nikomatsakis]

The recent crater run found an incorrect T: 'static bound compiling cswinter.locustdb.c5942997e6bdbb94fe0920e67bd96b0637399b97 (log). This looks perhaps like a variant of #53119.

Minimized reproduction available here..

[nikomatsakis]

The following errors look similar, but it's hard to tell if it's the same problem:

• proptest-arbitrary-0.2.2: log

[nikomatsakis]

Did a bit of digging. The error here seems to result from us (incorrectly, I think?) promoting a '_#5 bound (which represents 'a in the minimized example) to 'static. I'm not 100% sure why this is happening yet, had to stop digging for now, will return to it.

[nikomatsakis]

OK, I see the problem and have a forthcoming fix.

[nikomatsakis]

Leaving this on the RC milestone — fix is in #53745