New upstream version 1.66.0+dfsg1

[rustc.git] / compiler / rustc_hir_analysis / src / bounds.rs

diff --git a/compiler/rustc_hir_analysis/src/bounds.rs b/compiler/rustc_hir_analysis/src/bounds.rs
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+++ b/compiler/rustc_hir_analysis/src/bounds.rs
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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| {
+            tcx.lang_items().sized_trait().map(move |sized| {
+                let trait_ref = ty::Binder::dummy(ty::TraitRef {
+                    def_id: sized,
+                    substs: tcx.mk_substs_trait(param_ty, &[]),
+                });
+                (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)
+    }
+}