Track causes for universes created during borrowck

compiler/rustc_infer/src/infer/mod.rs

@@ -1506,7 +1506,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         self.inner.borrow_mut().projection_cache().clear();
     }
 
-    fn universe(&self) -> ty::UniverseIndex {
+    pub fn universe(&self) -> ty::UniverseIndex {
         self.universe.get()
     }
 

compiler/rustc_mir/src/borrow_check/diagnostics/bound_region_errors.rs

@@ -0,0 +1,110 @@
+use rustc_infer::infer::canonical::Canonical;
+use rustc_middle::ty::{self, Ty, TypeFoldable};
+use rustc_span::Span;
+use rustc_trait_selection::traits::query::type_op;
+
+use std::fmt;
+use std::rc::Rc;
+
+use crate::borrow_check::region_infer::values::RegionElement;
+use crate::borrow_check::MirBorrowckCtxt;
+
+#[derive(Clone)]
+crate struct UniverseInfo<'tcx>(UniverseInfoInner<'tcx>);
+
+/// What operation a universe was created for.
+#[derive(Clone)]
+enum UniverseInfoInner<'tcx> {
+    /// Relating two types which have binders.
+    RelateTys { expected: Ty<'tcx>, found: Ty<'tcx> },
+    /// Created from performing a `TypeOp`.
+    TypeOp(Rc<dyn TypeOpInfo<'tcx> + 'tcx>),
+    /// Any other reason.
+    Other,
+}
+
+impl UniverseInfo<'tcx> {
+    crate fn other() -> UniverseInfo<'tcx> {
+        UniverseInfo(UniverseInfoInner::Other)
+    }
+
+    crate fn relate(expected: Ty<'tcx>, found: Ty<'tcx>) -> UniverseInfo<'tcx> {
+        UniverseInfo(UniverseInfoInner::RelateTys { expected, found })
+    }
+
+    crate fn _report_error(
+        &self,
+        _mbcx: &mut MirBorrowckCtxt<'_, 'tcx>,
+        _placeholder: ty::PlaceholderRegion,
+        _error_element: RegionElement,
+        _span: Span,
+    ) {
+        todo!();
+    }
+}
+
+crate trait ToUniverseInfo<'tcx> {
+    fn to_universe_info(self, base_universe: ty::UniverseIndex) -> UniverseInfo<'tcx>;
+}
+
+impl<'tcx> ToUniverseInfo<'tcx>
+    for Canonical<'tcx, ty::ParamEnvAnd<'tcx, type_op::prove_predicate::ProvePredicate<'tcx>>>
+{
+    fn to_universe_info(self, base_universe: ty::UniverseIndex) -> UniverseInfo<'tcx> {
+        UniverseInfo(UniverseInfoInner::TypeOp(Rc::new(PredicateQuery {
+            _canonical_query: self,
+            _base_universe: base_universe,
+        })))
+    }
+}
+
+impl<'tcx, T: Copy + fmt::Display + TypeFoldable<'tcx> + 'tcx> ToUniverseInfo<'tcx>
+    for Canonical<'tcx, ty::ParamEnvAnd<'tcx, type_op::Normalize<T>>>
+{
+    fn to_universe_info(self, base_universe: ty::UniverseIndex) -> UniverseInfo<'tcx> {
+        UniverseInfo(UniverseInfoInner::TypeOp(Rc::new(NormalizeQuery {
+            _canonical_query: self,
+            _base_universe: base_universe,
+        })))
+    }
+}
+
+impl<'tcx> ToUniverseInfo<'tcx>
+    for Canonical<'tcx, ty::ParamEnvAnd<'tcx, type_op::AscribeUserType<'tcx>>>
+{
+    fn to_universe_info(self, _base_universe: ty::UniverseIndex) -> UniverseInfo<'tcx> {
+        // Ascribe user type isn't usually called on types that have different
+        // bound regions.
+        UniverseInfo::other()
+    }
+}
+
+impl<'tcx, F, G> ToUniverseInfo<'tcx> for Canonical<'tcx, type_op::custom::CustomTypeOp<F, G>> {
+    fn to_universe_info(self, _base_universe: ty::UniverseIndex) -> UniverseInfo<'tcx> {
+        // We can't rerun custom type ops.
+        UniverseInfo::other()
+    }
+}
+
+#[allow(unused_lifetimes)]
+trait TypeOpInfo<'tcx> {
+    // TODO: Methods for rerunning type op and reporting an error
+}
+
+struct PredicateQuery<'tcx> {
+    _canonical_query:
+        Canonical<'tcx, ty::ParamEnvAnd<'tcx, type_op::prove_predicate::ProvePredicate<'tcx>>>,
+    _base_universe: ty::UniverseIndex,
+}
+
+impl TypeOpInfo<'tcx> for PredicateQuery<'tcx> {}
+
+struct NormalizeQuery<'tcx, T> {
+    _canonical_query: Canonical<'tcx, ty::ParamEnvAnd<'tcx, type_op::Normalize<T>>>,
+    _base_universe: ty::UniverseIndex,
+}
+
+impl<T> TypeOpInfo<'tcx> for NormalizeQuery<'tcx, T> where
+    T: Copy + fmt::Display + TypeFoldable<'tcx> + 'tcx
+{
+}

compiler/rustc_mir/src/borrow_check/diagnostics/mod.rs

@@ -28,12 +28,14 @@ mod outlives_suggestion;
 mod region_name;
 mod var_name;
 
+mod bound_region_errors;
 mod conflict_errors;
 mod explain_borrow;
 mod move_errors;
 mod mutability_errors;
 mod region_errors;
 
+crate use bound_region_errors::{ToUniverseInfo, UniverseInfo};
 crate use mutability_errors::AccessKind;
 crate use outlives_suggestion::OutlivesSuggestionBuilder;
 crate use region_errors::{ErrorConstraintInfo, RegionErrorKind, RegionErrors};

compiler/rustc_mir/src/borrow_check/nll.rs

@@ -239,6 +239,7 @@ pub(in crate::borrow_check) fn compute_regions<'cx, 'tcx>(
         outlives_constraints,
         member_constraints,
         closure_bounds_mapping,
+        universe_causes,
         type_tests,
     } = constraints;
     let placeholder_indices = Rc::new(placeholder_indices);
@@ -260,6 +261,7 @@ pub(in crate::borrow_check) fn compute_regions<'cx, 'tcx>(
         outlives_constraints,
         member_constraints,
         closure_bounds_mapping,
+        universe_causes,
         type_tests,
         liveness_constraints,
         elements,

compiler/rustc_mir/src/borrow_check/region_infer/mod.rs

@@ -21,7 +21,7 @@ use crate::borrow_check::{
     constraints::{
         graph::NormalConstraintGraph, ConstraintSccIndex, OutlivesConstraint, OutlivesConstraintSet,
     },
-    diagnostics::{RegionErrorKind, RegionErrors},
+    diagnostics::{RegionErrorKind, RegionErrors, UniverseInfo},
     member_constraints::{MemberConstraintSet, NllMemberConstraintIndex},
     nll::{PoloniusOutput, ToRegionVid},
     region_infer::reverse_sccs::ReverseSccGraph,
@@ -84,6 +84,9 @@ pub struct RegionInferenceContext<'tcx> {
     closure_bounds_mapping:
         FxHashMap<Location, FxHashMap<(RegionVid, RegionVid), (ConstraintCategory, Span)>>,
 
+    /// Map universe indexes to information on why we created it.
+    _universe_causes: IndexVec<ty::UniverseIndex, UniverseInfo<'tcx>>,
+
     /// Contains the minimum universe of any variable within the same
     /// SCC. We will ensure that no SCC contains values that are not
     /// visible from this index.
@@ -253,6 +256,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             Location,
             FxHashMap<(RegionVid, RegionVid), (ConstraintCategory, Span)>,
         >,
+        universe_causes: IndexVec<ty::UniverseIndex, UniverseInfo<'tcx>>,
         type_tests: Vec<TypeTest<'tcx>>,
         liveness_constraints: LivenessValues<RegionVid>,
         elements: &Rc<RegionValueElements>,
@@ -293,6 +297,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             member_constraints,
             member_constraints_applied: Vec::new(),
             closure_bounds_mapping,
+            _universe_causes: universe_causes,
             scc_universes,
             scc_representatives,
             scc_values,

compiler/rustc_mir/src/borrow_check/type_check/canonical.rs

@@ -0,0 +1,158 @@
+use std::fmt;
+
+use rustc_hir as hir;
+use rustc_infer::infer::canonical::Canonical;
+use rustc_infer::traits::query::NoSolution;
+use rustc_middle::mir::ConstraintCategory;
+use rustc_middle::ty::{self, ToPredicate, TypeFoldable};
+use rustc_span::Span;
+use rustc_trait_selection::traits::query::type_op::{self, TypeOpOutput};
+use rustc_trait_selection::traits::query::Fallible;
+
+use crate::borrow_check::diagnostics::{ToUniverseInfo, UniverseInfo};
+
+use super::{Locations, NormalizeLocation, TypeChecker};
+
+impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
+    /// Given some operation `op` that manipulates types, proves
+    /// predicates, or otherwise uses the inference context, executes
+    /// `op` and then executes all the further obligations that `op`
+    /// returns. This will yield a set of outlives constraints amongst
+    /// regions which are extracted and stored as having occurred at
+    /// `locations`.
+    ///
+    /// **Any `rustc_infer::infer` operations that might generate region
+    /// constraints should occur within this method so that those
+    /// constraints can be properly localized!**
+    pub(super) fn fully_perform_op<R, Op>(
+        &mut self,
+        locations: Locations,
+        category: ConstraintCategory,
+        op: Op,
+    ) -> Fallible<R>
+    where
+        Op: type_op::TypeOp<'tcx, Output = R>,
+        Canonical<'tcx, Op>: ToUniverseInfo<'tcx>,
+    {
+        let old_universe = self.infcx.universe();
+
+        let TypeOpOutput { output, constraints, canonicalized_query } =
+            op.fully_perform(self.infcx)?;
+
+        if let Some(data) = &constraints {
+            self.push_region_constraints(locations, category, data);
+        }
+
+        let universe = self.infcx.universe();
+
+        if old_universe != universe {
+            let universe_info = match canonicalized_query {
+                Some(canonicalized_query) => canonicalized_query.to_universe_info(old_universe),
+                None => UniverseInfo::other(),
+            };
+            for u in old_universe..universe {
+                let info_universe =
+                    self.borrowck_context.constraints.universe_causes.push(universe_info.clone());
+                assert_eq!(u.as_u32() + 1, info_universe.as_u32());
+            }
+        }
+
+        Ok(output)
+    }
+
+    pub(super) fn instantiate_canonical_with_fresh_inference_vars<T>(
+        &mut self,
+        span: Span,
+        canonical: &Canonical<'tcx, T>,
+    ) -> T
+    where
+        T: TypeFoldable<'tcx>,
+    {
+        let (instantiated, _) =
+            self.infcx.instantiate_canonical_with_fresh_inference_vars(span, canonical);
+
+        for _ in 0..canonical.max_universe.as_u32() {
+            let info = UniverseInfo::other();
+            self.borrowck_context.constraints.universe_causes.push(info);
+        }
+
+        instantiated
+    }
+
+    pub(super) fn prove_trait_ref(
+        &mut self,
+        trait_ref: ty::TraitRef<'tcx>,
+        locations: Locations,
+        category: ConstraintCategory,
+    ) {
+        self.prove_predicates(
+            Some(ty::PredicateKind::Trait(ty::TraitPredicate {
+                trait_ref,
+                constness: hir::Constness::NotConst,
+            })),
+            locations,
+            category,
+        );
+    }
+
+    pub(super) fn normalize_and_prove_instantiated_predicates(
+        &mut self,
+        instantiated_predicates: ty::InstantiatedPredicates<'tcx>,
+        locations: Locations,
+    ) {
+        for predicate in instantiated_predicates.predicates {
+            let predicate = self.normalize(predicate, locations);
+            self.prove_predicate(predicate, locations, ConstraintCategory::Boring);
+        }
+    }
+
+    pub(super) fn prove_predicates(
+        &mut self,
+        predicates: impl IntoIterator<Item = impl ToPredicate<'tcx>>,
+        locations: Locations,
+        category: ConstraintCategory,
+    ) {
+        for predicate in predicates {
+            let predicate = predicate.to_predicate(self.tcx());
+            debug!("prove_predicates(predicate={:?}, locations={:?})", predicate, locations,);
+
+            self.prove_predicate(predicate, locations, category);
+        }
+    }
+
+    pub(super) fn prove_predicate(
+        &mut self,
+        predicate: ty::Predicate<'tcx>,
+        locations: Locations,
+        category: ConstraintCategory,
+    ) {
+        debug!("prove_predicate(predicate={:?}, location={:?})", predicate, locations,);
+
+        let param_env = self.param_env;
+        self.fully_perform_op(
+            locations,
+            category,
+            param_env.and(type_op::prove_predicate::ProvePredicate::new(predicate)),
+        )
+        .unwrap_or_else(|NoSolution| {
+            span_mirbug!(self, NoSolution, "could not prove {:?}", predicate);
+        })
+    }
+
+    pub(super) fn normalize<T>(&mut self, value: T, location: impl NormalizeLocation) -> T
+    where
+        T: type_op::normalize::Normalizable<'tcx> + fmt::Display + Copy + 'tcx,
+    {
+        debug!("normalize(value={:?}, location={:?})", value, location);
+        let param_env = self.param_env;
+        self.fully_perform_op(
+            location.to_locations(),
+            ConstraintCategory::Boring,
+            param_env.and(type_op::normalize::Normalize::new(value)),
+        )
+        .unwrap_or_else(|NoSolution| {
+            span_mirbug!(self, NoSolution, "failed to normalize `{:?}`", value);
+            value
+        })
+    }
+}

compiler/rustc_mir/src/borrow_check/type_check/input_output.rs

@@ -44,7 +44,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                     // Instantiate the canonicalized variables from
                     // user-provided signature (e.g., the `_` in the code
                     // above) with fresh variables.
-                    let (poly_sig, _) = self.infcx.instantiate_canonical_with_fresh_inference_vars(
+                    let poly_sig = self.instantiate_canonical_with_fresh_inference_vars(
                         body.span,
                         &user_provided_poly_sig,
                     );