internal: pin_data: use HRTB to work around trivial_bounds for Unpin - #176
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`#[pin_data]` generates a `Unpin` implementation for the user, which requires reasoning using field types. This is rejected by rustc as "trivial bounds", which can only be specified using the `#![feature(trivial_bounds)]`. Currently we use an extra lifetime in `__Unpin` to work around this; use HRTB to introduce a dummy lifetime can achieve the same, which the `Zeroable` implementation already uses. Unify the `Unpin` impl to also use the same HRTB trick that `Zeroable` uses. This produces slightly better error message and slightly shorter expansion. Signed-off-by: Gary Guo <gary@garyguo.net>
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#[pin_data]generates aUnpinimplementation for the user, which requires reasoning using field types. This is rejected by rustc as "trivial bounds", which can only be specified using the#![feature(trivial_bounds)].Currently we use an extra lifetime in
__Unpinto work around this; use HRTB to introduce a dummy lifetime can achieve the same, which theZeroableimplementation already uses.Unify the
Unpinimpl to also use the same HRTB trick thatZeroableuses. This produces slightly better error message and slightly shorter expansion.