Function rustc_mir_transform::coroutine::transform_async_context
source ยท fn transform_async_context<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>)
Expand description
Transforms the body
of the coroutine applying the following transforms:
- Eliminates all the
get_context
calls that async lowering created. - Replace all
Local
ResumeTy
types with&mut Context<'_>
(context_mut_ref
).
The Local
s that have their types replaced are:
- The
resume
argument itself. - The argument to
get_context
. - The yielded value of a
yield
.
The ResumeTy
hides a &mut Context<'_>
behind an unsafe raw pointer, and the
get_context
function is being used to convert that back to a &mut Context<'_>
.
Ideally the async lowering would not use the ResumeTy
/get_context
indirection,
but rather directly use &mut Context<'_>
, however that would currently
lead to higher-kinded lifetime errors.
See https://github.com/rust-lang/rust/issues/105501.
The async lowering step and the type / lifetime inference / checking are
still using the ResumeTy
indirection for the time being, and that indirection
is removed here. After this transform, the coroutine body only knows about &mut Context<'_>
.