hir_ty/next_solver/infer/relate/
higher_ranked.rs

1//! Helper routines for higher-ranked things. See the `doc` module at
2//! the end of the file for details.
3
4use rustc_type_ir::TypeFoldable;
5use tracing::{debug, instrument};
6
7use crate::next_solver::fold::FnMutDelegate;
8use crate::next_solver::infer::InferCtxt;
9use crate::next_solver::{
10    Binder, BoundConst, BoundRegion, BoundTy, Const, DbInterner, PlaceholderConst,
11    PlaceholderRegion, PlaceholderType, Region, Ty,
12};
13
14impl<'db> InferCtxt<'db> {
15    /// Replaces all bound variables (lifetimes, types, and constants) bound by
16    /// `binder` with placeholder variables in a new universe. This means that the
17    /// new placeholders can only be named by inference variables created after
18    /// this method has been called.
19    ///
20    /// This is the first step of checking subtyping when higher-ranked things are involved.
21    /// For more details visit the relevant sections of the [rustc dev guide].
22    ///
23    /// `fn enter_forall` should be preferred over this method.
24    ///
25    /// [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/traits/hrtb.html
26    #[instrument(level = "debug", skip(self), ret)]
27    pub fn enter_forall_and_leak_universe<T>(&self, binder: Binder<'db, T>) -> T
28    where
29        T: TypeFoldable<DbInterner<'db>> + Clone,
30    {
31        if let Some(inner) = binder.clone().no_bound_vars() {
32            return inner;
33        }
34
35        let next_universe = self.create_next_universe();
36
37        let delegate = FnMutDelegate {
38            regions: &mut |br: BoundRegion<'db>| {
39                Region::new_placeholder(self.interner, PlaceholderRegion::new(next_universe, br))
40            },
41            types: &mut |bound_ty: BoundTy<'db>| {
42                Ty::new_placeholder(self.interner, PlaceholderType::new(next_universe, bound_ty))
43            },
44            consts: &mut |bound: BoundConst<'db>| {
45                Const::new_placeholder(self.interner, PlaceholderConst::new(next_universe, bound))
46            },
47        };
48
49        debug!(?next_universe);
50        self.interner.replace_bound_vars_uncached(binder, delegate)
51    }
52
53    /// Replaces all bound variables (lifetimes, types, and constants) bound by
54    /// `binder` with placeholder variables in a new universe and then calls the
55    /// closure `f` with the instantiated value. The new placeholders can only be
56    /// named by inference variables created inside of the closure `f` or afterwards.
57    ///
58    /// This is the first step of checking subtyping when higher-ranked things are involved.
59    /// For more details visit the relevant sections of the [rustc dev guide].
60    ///
61    /// This method should be preferred over `fn enter_forall_and_leak_universe`.
62    ///
63    /// [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/traits/hrtb.html
64    #[instrument(level = "debug", skip(self, f))]
65    pub fn enter_forall<T, U>(&self, forall: Binder<'db, T>, f: impl FnOnce(T) -> U) -> U
66    where
67        T: TypeFoldable<DbInterner<'db>> + Clone,
68    {
69        // FIXME: currently we do nothing to prevent placeholders with the new universe being
70        // used after exiting `f`. For example region subtyping can result in outlives constraints
71        // that name placeholders created in this function. Nested goals from type relations can
72        // also contain placeholders created by this function.
73        let value = self.enter_forall_and_leak_universe(forall);
74        debug!(?value);
75        f(value)
76    }
77}
hir_ty/next_solver/infer/relate/higher_ranked.rs

hir_ty/next_solver/infer/relate/
higher_ranked.rs
