Improve upvar analysis for deref of child capture #138517
Merged
+128
−6
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Two fixes to the heuristic I implemented in #123660. As I noted in the code:
This indeed fixes unnecessary borrowck errors.
r? oli-obk
The heuristic is only valid if we deref a
&T
, not a&mut T
orBox<T>
, so make sure to check the type. This fixes:Since the capture from
f
to&f.precise
needs to be treated as a lending borrow from the parent coroutine-closure to the child coroutine.The heuristic is also valid if any deref projection in the child capture's projections is a
&T
, but we were only looking at the last one. This ensures that this function is considered not to be lending:(Specifically, checking that
impl Fn() -> _
is satisfied is exercising that the coroutine is not considered to be lending.)