bjoernager/rust
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clean up ADT sized constraint computation

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This commit is contained in:
Lukas Markeffsky 2024-03-13 23:33:45 +01:00
parent 0e7e1bfdbc
commit 8ad94111ad
8 changed files with 90 additions and 92 deletions
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14
compiler/rustc_trait_selection/src/solve/assembly/structural_traits.rs
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@ -157,10 +157,20 @@ pub(in crate::solve) fn instantiate_constituent_tys_for_sized_trait<'tcx>(
// impl Sized for (T1, T2, .., Tn) where T1: Sized, T2: Sized, .. Tn: Sized
ty::Tuple(tys) => Ok(tys.iter().map(ty::Binder::dummy).collect()),
// impl Sized for Adt where T: Sized forall T in field types
// impl Sized for Adt<Args...> where sized_constraint(Adt)<Args...>: Sized
// `sized_constraint(Adt)` is the deepest struct trail that can be determined
// by the definition of `Adt`, independent of the generic args.
// impl Sized for Adt<Args...> if sized_constraint(Adt) == None
// As a performance optimization, `sized_constraint(Adt)` can return `None`
// if the ADTs definition implies that it is sized by for all possible args.
// In this case, the builtin impl will have no nested subgoals. This is a
// "best effort" optimization and `sized_constraint` may return `Some`, even
// if the ADT is sized for all possible args.
ty::Adt(def, args) => {
let sized_crit = def.sized_constraint(ecx.tcx());
Ok(sized_crit.iter_instantiated(ecx.tcx(), args).map(ty::Binder::dummy).collect())
Ok(sized_crit.map_or_else(Vec::new, |ty| {
vec![ty::Binder::dummy(ty.instantiate(ecx.tcx(), args))]
}))
}
}
}