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use std::ops::ControlFlow;
use rustc_data_structures::intern::Interned;
use rustc_query_system::cache::Cache;
use crate::infer::canonical::{CanonicalVarValues, QueryRegionConstraints};
use crate::traits::query::NoSolution;
use crate::traits::Canonical;
use crate::ty::{
self, FallibleTypeFolder, ToPredicate, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeVisitable,
TypeVisitor,
};
pub type EvaluationCache<'tcx> = Cache<CanonicalGoal<'tcx>, QueryResult<'tcx>>;
/// A goal is a statement, i.e. `predicate`, we want to prove
/// given some assumptions, i.e. `param_env`.
///
/// Most of the time the `param_env` contains the `where`-bounds of the function
/// we're currently typechecking while the `predicate` is some trait bound.
#[derive(Debug, PartialEq, Eq, Clone, Copy, Hash, TypeFoldable, TypeVisitable)]
pub struct Goal<'tcx, P> {
pub predicate: P,
pub param_env: ty::ParamEnv<'tcx>,
}
impl<'tcx, P> Goal<'tcx, P> {
pub fn new(
tcx: TyCtxt<'tcx>,
param_env: ty::ParamEnv<'tcx>,
predicate: impl ToPredicate<'tcx, P>,
) -> Goal<'tcx, P> {
Goal { param_env, predicate: predicate.to_predicate(tcx) }
}
/// Updates the goal to one with a different `predicate` but the same `param_env`.
pub fn with<Q>(self, tcx: TyCtxt<'tcx>, predicate: impl ToPredicate<'tcx, Q>) -> Goal<'tcx, Q> {
Goal { param_env: self.param_env, predicate: predicate.to_predicate(tcx) }
}
}
#[derive(Debug, PartialEq, Eq, Clone, Copy, Hash, TypeFoldable, TypeVisitable)]
pub struct Response<'tcx> {
pub certainty: Certainty,
pub var_values: CanonicalVarValues<'tcx>,
/// Additional constraints returned by this query.
pub external_constraints: ExternalConstraints<'tcx>,
}
#[derive(Debug, PartialEq, Eq, Clone, Copy, Hash, TypeFoldable, TypeVisitable)]
pub enum Certainty {
Yes,
Maybe(MaybeCause),
}
impl Certainty {
pub const AMBIGUOUS: Certainty = Certainty::Maybe(MaybeCause::Ambiguity);
/// Use this function to merge the certainty of multiple nested subgoals.
///
/// Given an impl like `impl<T: Foo + Bar> Baz for T {}`, we have 2 nested
/// subgoals whenever we use the impl as a candidate: `T: Foo` and `T: Bar`.
/// If evaluating `T: Foo` results in ambiguity and `T: Bar` results in
/// success, we merge these two responses. This results in ambiguity.
///
/// If we unify ambiguity with overflow, we return overflow. This doesn't matter
/// inside of the solver as we distinguish ambiguity from overflow. It does
/// however matter for diagnostics. If `T: Foo` resulted in overflow and `T: Bar`
/// in ambiguity without changing the inference state, we still want to tell the
/// user that `T: Baz` results in overflow.
pub fn unify_with(self, other: Certainty) -> Certainty {
match (self, other) {
(Certainty::Yes, Certainty::Yes) => Certainty::Yes,
(Certainty::Yes, Certainty::Maybe(_)) => other,
(Certainty::Maybe(_), Certainty::Yes) => self,
(Certainty::Maybe(MaybeCause::Ambiguity), Certainty::Maybe(MaybeCause::Ambiguity)) => {
Certainty::Maybe(MaybeCause::Ambiguity)
}
(Certainty::Maybe(MaybeCause::Ambiguity), Certainty::Maybe(MaybeCause::Overflow))
| (Certainty::Maybe(MaybeCause::Overflow), Certainty::Maybe(MaybeCause::Ambiguity))
| (Certainty::Maybe(MaybeCause::Overflow), Certainty::Maybe(MaybeCause::Overflow)) => {
Certainty::Maybe(MaybeCause::Overflow)
}
}
}
}
/// Why we failed to evaluate a goal.
#[derive(Debug, PartialEq, Eq, Clone, Copy, Hash, TypeFoldable, TypeVisitable)]
pub enum MaybeCause {
/// We failed due to ambiguity. This ambiguity can either
/// be a true ambiguity, i.e. there are multiple different answers,
/// or we hit a case where we just don't bother, e.g. `?x: Trait` goals.
Ambiguity,
/// We gave up due to an overflow, most often by hitting the recursion limit.
Overflow,
}
pub type CanonicalGoal<'tcx, T = ty::Predicate<'tcx>> = Canonical<'tcx, Goal<'tcx, T>>;
pub type CanonicalResponse<'tcx> = Canonical<'tcx, Response<'tcx>>;
/// The result of evaluating a canonical query.
///
/// FIXME: We use a different type than the existing canonical queries. This is because
/// we need to add a `Certainty` for `overflow` and may want to restructure this code without
/// having to worry about changes to currently used code. Once we've made progress on this
/// solver, merge the two responses again.
pub type QueryResult<'tcx> = Result<CanonicalResponse<'tcx>, NoSolution>;
#[derive(Debug, PartialEq, Eq, Copy, Clone, Hash)]
pub struct ExternalConstraints<'tcx>(pub(crate) Interned<'tcx, ExternalConstraintsData<'tcx>>);
impl<'tcx> std::ops::Deref for ExternalConstraints<'tcx> {
type Target = ExternalConstraintsData<'tcx>;
fn deref(&self) -> &Self::Target {
&self.0
}
}
/// Additional constraints returned on success.
#[derive(Debug, PartialEq, Eq, Clone, Hash, Default, TypeFoldable, TypeVisitable)]
pub struct ExternalConstraintsData<'tcx> {
// FIXME: implement this.
pub region_constraints: QueryRegionConstraints<'tcx>,
pub opaque_types: Vec<(Ty<'tcx>, Ty<'tcx>)>,
}
// FIXME: Having to clone `region_constraints` for folding feels bad and
// probably isn't great wrt performance.
//
// Not sure how to fix this, maybe we should also intern `opaque_types` and
// `region_constraints` here or something.
impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for ExternalConstraints<'tcx> {
fn try_fold_with<F: FallibleTypeFolder<TyCtxt<'tcx>>>(
self,
folder: &mut F,
) -> Result<Self, F::Error> {
Ok(FallibleTypeFolder::interner(folder).mk_external_constraints(ExternalConstraintsData {
region_constraints: self.region_constraints.clone().try_fold_with(folder)?,
opaque_types: self
.opaque_types
.iter()
.map(|opaque| opaque.try_fold_with(folder))
.collect::<Result<_, F::Error>>()?,
}))
}
fn fold_with<F: TypeFolder<TyCtxt<'tcx>>>(self, folder: &mut F) -> Self {
TypeFolder::interner(folder).mk_external_constraints(ExternalConstraintsData {
region_constraints: self.region_constraints.clone().fold_with(folder),
opaque_types: self.opaque_types.iter().map(|opaque| opaque.fold_with(folder)).collect(),
})
}
}
impl<'tcx> TypeVisitable<TyCtxt<'tcx>> for ExternalConstraints<'tcx> {
fn visit_with<V: TypeVisitor<TyCtxt<'tcx>>>(
&self,
visitor: &mut V,
) -> std::ops::ControlFlow<V::BreakTy> {
self.region_constraints.visit_with(visitor)?;
self.opaque_types.visit_with(visitor)?;
ControlFlow::Continue(())
}
}
|
