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//! Bounds are restrictions applied to some types after they've been converted into the
//! `ty` form from the HIR.
use rustc_middle::ty::{self, ToPredicate, Ty, TyCtxt};
use rustc_span::Span;
/// Collects together a list of type bounds. These lists of bounds occur in many places
/// in Rust's syntax:
///
/// ```text
/// trait Foo: Bar + Baz { }
/// ^^^^^^^^^ supertrait list bounding the `Self` type parameter
///
/// fn foo<T: Bar + Baz>() { }
/// ^^^^^^^^^ bounding the type parameter `T`
///
/// impl dyn Bar + Baz
/// ^^^^^^^^^ bounding the forgotten dynamic type
/// ```
///
/// Our representation is a bit mixed here -- in some cases, we
/// include the self type (e.g., `trait_bounds`) but in others we do not
#[derive(Default, PartialEq, Eq, Clone, Debug)]
pub struct Bounds<'tcx> {
/// A list of region bounds on the (implicit) self type. So if you
/// had `T: 'a + 'b` this might would be a list `['a, 'b]` (but
/// the `T` is not explicitly included).
pub region_bounds: Vec<(ty::Binder<'tcx, ty::Region<'tcx>>, Span)>,
/// A list of trait bounds. So if you had `T: Debug` this would be
/// `T: Debug`. Note that the self-type is explicit here.
pub trait_bounds: Vec<(ty::PolyTraitRef<'tcx>, Span, ty::BoundConstness)>,
/// A list of projection equality bounds. So if you had `T:
/// Iterator<Item = u32>` this would include `<T as
/// Iterator>::Item => u32`. Note that the self-type is explicit
/// here.
pub projection_bounds: Vec<(ty::PolyProjectionPredicate<'tcx>, Span)>,
/// `Some` if there is *no* `?Sized` predicate. The `span`
/// is the location in the source of the `T` declaration which can
/// be cited as the source of the `T: Sized` requirement.
pub implicitly_sized: Option<Span>,
}
impl<'tcx> Bounds<'tcx> {
/// Converts a bounds list into a flat set of predicates (like
/// where-clauses). Because some of our bounds listings (e.g.,
/// regions) don't include the self-type, you must supply the
/// self-type here (the `param_ty` parameter).
pub fn predicates<'out, 's>(
&'s self,
tcx: TyCtxt<'tcx>,
param_ty: Ty<'tcx>,
// the output must live shorter than the duration of the borrow of self and 'tcx.
) -> impl Iterator<Item = (ty::Predicate<'tcx>, Span)> + 'out
where
'tcx: 'out,
's: 'out,
{
// If it could be sized, and is, add the `Sized` predicate.
let sized_predicate = self.implicitly_sized.and_then(|span| {
// FIXME: use tcx.at(span).mk_trait_ref(LangItem::Sized) here? This may make no-core code harder to write.
let sized = tcx.lang_items().sized_trait()?;
let trait_ref = ty::Binder::dummy(tcx.mk_trait_ref(sized, [param_ty]));
Some((trait_ref.without_const().to_predicate(tcx), span))
});
let region_preds = self.region_bounds.iter().map(move |&(region_bound, span)| {
let pred = region_bound
.map_bound(|region_bound| ty::OutlivesPredicate(param_ty, region_bound))
.to_predicate(tcx);
(pred, span)
});
let trait_bounds =
self.trait_bounds.iter().map(move |&(bound_trait_ref, span, constness)| {
let predicate = bound_trait_ref.with_constness(constness).to_predicate(tcx);
(predicate, span)
});
let projection_bounds = self
.projection_bounds
.iter()
.map(move |&(projection, span)| (projection.to_predicate(tcx), span));
sized_predicate.into_iter().chain(region_preds).chain(trait_bounds).chain(projection_bounds)
}
}
|
