use std::rc::Rc; use crate::borrow_check::nll::{ constraints::{ graph::NormalConstraintGraph, ConstraintSccIndex, OutlivesConstraint, OutlivesConstraintSet, }, member_constraints::{MemberConstraintSet, NllMemberConstraintIndex}, region_infer::values::{ PlaceholderIndices, RegionElement, ToElementIndex }, type_check::{free_region_relations::UniversalRegionRelations, Locations}, }; use crate::borrow_check::Upvar; use rustc::hir::def_id::DefId; use rustc::infer::canonical::QueryOutlivesConstraint; use rustc::infer::opaque_types; use rustc::infer::region_constraints::{GenericKind, VarInfos, VerifyBound}; use rustc::infer::{InferCtxt, NLLRegionVariableOrigin, RegionVariableOrigin}; use rustc::mir::{ Body, ClosureOutlivesRequirement, ClosureOutlivesSubject, ClosureRegionRequirements, ConstraintCategory, Local, Location, }; use rustc::ty::{self, subst::SubstsRef, RegionVid, Ty, TyCtxt, TypeFoldable}; use rustc::util::common::ErrorReported; use rustc_data_structures::binary_search_util; use rustc_index::bit_set::BitSet; use rustc_data_structures::fx::{FxHashMap, FxHashSet}; use rustc_data_structures::graph::WithSuccessors; use rustc_data_structures::graph::scc::Sccs; use rustc_data_structures::graph::vec_graph::VecGraph; use rustc_index::vec::IndexVec; use rustc_errors::{Diagnostic, DiagnosticBuilder}; use syntax_pos::Span; crate use self::error_reporting::{RegionName, RegionNameSource, RegionErrorNamingCtx}; use self::values::{LivenessValues, RegionValueElements, RegionValues}; use super::universal_regions::UniversalRegions; use super::ToRegionVid; mod dump_mir; mod error_reporting; mod graphviz; pub mod values; pub struct RegionInferenceContext<'tcx> { /// Contains the definition for every region variable. Region /// variables are identified by their index (`RegionVid`). The /// definition contains information about where the region came /// from as well as its final inferred value. definitions: IndexVec>, /// The liveness constraints added to each region. For most /// regions, these start out empty and steadily grow, though for /// each universally quantified region R they start out containing /// the entire CFG and `end(R)`. liveness_constraints: LivenessValues, /// The outlives constraints computed by the type-check. constraints: Rc, /// The constraint-set, but in graph form, making it easy to traverse /// the constraints adjacent to a particular region. Used to construct /// the SCC (see `constraint_sccs`) and for error reporting. constraint_graph: Rc, /// The SCC computed from `constraints` and the constraint /// graph. We have an edge from SCC A to SCC B if `A: B`. Used to /// compute the values of each region. constraint_sccs: Rc>, /// Reverse of the SCC constraint graph -- i.e., an edge `A -> B` /// exists if `B: A`. Computed lazilly. rev_constraint_graph: Option>>, /// The "R0 member of [R1..Rn]" constraints, indexed by SCC. member_constraints: Rc>, /// Records the member constraints that we applied to each scc. /// This is useful for error reporting. Once constraint /// propagation is done, this vector is sorted according to /// `member_region_scc`. member_constraints_applied: Vec, /// Map closure bounds to a `Span` that should be used for error reporting. closure_bounds_mapping: FxHashMap>, /// 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. scc_universes: IndexVec, /// Contains a "representative" from each SCC. This will be the /// minimal RegionVid belonging to that universe. It is used as a /// kind of hacky way to manage checking outlives relationships, /// since we can 'canonicalize' each region to the representative /// of its SCC and be sure that -- if they have the same repr -- /// they *must* be equal (though not having the same repr does not /// mean they are unequal). scc_representatives: IndexVec, /// The final inferred values of the region variables; we compute /// one value per SCC. To get the value for any given *region*, /// you first find which scc it is a part of. scc_values: RegionValues, /// Type constraints that we check after solving. type_tests: Vec>, /// Information about the universally quantified regions in scope /// on this function. universal_regions: Rc>, /// Information about how the universally quantified regions in /// scope on this function relate to one another. universal_region_relations: Rc>, } /// Each time that `apply_member_constraint` is successful, it appends /// one of these structs to the `member_constraints_applied` field. /// This is used in error reporting to trace out what happened. /// /// The way that `apply_member_constraint` works is that it effectively /// adds a new lower bound to the SCC it is analyzing: so you wind up /// with `'R: 'O` where `'R` is the pick-region and `'O` is the /// minimal viable option. #[derive(Copy, Clone, Debug, Eq, PartialEq, Ord, PartialOrd)] struct AppliedMemberConstraint { /// The SCC that was affected. (The "member region".) /// /// The vector if `AppliedMemberConstraint` elements is kept sorted /// by this field. member_region_scc: ConstraintSccIndex, /// The "best option" that `apply_member_constraint` found -- this was /// added as an "ad-hoc" lower-bound to `member_region_scc`. min_choice: ty::RegionVid, /// The "member constraint index" -- we can find out details about /// the constraint from /// `set.member_constraints[member_constraint_index]`. member_constraint_index: NllMemberConstraintIndex, } struct RegionDefinition<'tcx> { /// What kind of variable is this -- a free region? existential /// variable? etc. (See the `NLLRegionVariableOrigin` for more /// info.) origin: NLLRegionVariableOrigin, /// Which universe is this region variable defined in? This is /// most often `ty::UniverseIndex::ROOT`, but when we encounter /// forall-quantifiers like `for<'a> { 'a = 'b }`, we would create /// the variable for `'a` in a fresh universe that extends ROOT. universe: ty::UniverseIndex, /// If this is 'static or an early-bound region, then this is /// `Some(X)` where `X` is the name of the region. external_name: Option>, } /// N.B., the variants in `Cause` are intentionally ordered. Lower /// values are preferred when it comes to error messages. Do not /// reorder willy nilly. #[derive(Copy, Clone, Debug, PartialOrd, Ord, PartialEq, Eq)] pub(crate) enum Cause { /// point inserted because Local was live at the given Location LiveVar(Local, Location), /// point inserted because Local was dropped at the given Location DropVar(Local, Location), } /// A "type test" corresponds to an outlives constraint between a type /// and a lifetime, like `T: 'x` or `::Bar: 'x`. They are /// translated from the `Verify` region constraints in the ordinary /// inference context. /// /// These sorts of constraints are handled differently than ordinary /// constraints, at least at present. During type checking, the /// `InferCtxt::process_registered_region_obligations` method will /// attempt to convert a type test like `T: 'x` into an ordinary /// outlives constraint when possible (for example, `&'a T: 'b` will /// be converted into `'a: 'b` and registered as a `Constraint`). /// /// In some cases, however, there are outlives relationships that are /// not converted into a region constraint, but rather into one of /// these "type tests". The distinction is that a type test does not /// influence the inference result, but instead just examines the /// values that we ultimately inferred for each region variable and /// checks that they meet certain extra criteria. If not, an error /// can be issued. /// /// One reason for this is that these type tests typically boil down /// to a check like `'a: 'x` where `'a` is a universally quantified /// region -- and therefore not one whose value is really meant to be /// *inferred*, precisely (this is not always the case: one can have a /// type test like `>::Bar: 'x`, where `'?0` is an /// inference variable). Another reason is that these type tests can /// involve *disjunction* -- that is, they can be satisfied in more /// than one way. /// /// For more information about this translation, see /// `InferCtxt::process_registered_region_obligations` and /// `InferCtxt::type_must_outlive` in `rustc::infer::outlives`. #[derive(Clone, Debug)] pub struct TypeTest<'tcx> { /// The type `T` that must outlive the region. pub generic_kind: GenericKind<'tcx>, /// The region `'x` that the type must outlive. pub lower_bound: RegionVid, /// Where did this constraint arise and why? pub locations: Locations, /// A test which, if met by the region `'x`, proves that this type /// constraint is satisfied. pub verify_bound: VerifyBound<'tcx>, } impl<'tcx> RegionInferenceContext<'tcx> { /// Creates a new region inference context with a total of /// `num_region_variables` valid inference variables; the first N /// of those will be constant regions representing the free /// regions defined in `universal_regions`. /// /// The `outlives_constraints` and `type_tests` are an initial set /// of constraints produced by the MIR type check. pub(crate) fn new( var_infos: VarInfos, universal_regions: Rc>, placeholder_indices: Rc, universal_region_relations: Rc>, _body: &Body<'tcx>, outlives_constraints: OutlivesConstraintSet, member_constraints_in: MemberConstraintSet<'tcx, RegionVid>, closure_bounds_mapping: FxHashMap< Location, FxHashMap<(RegionVid, RegionVid), (ConstraintCategory, Span)>, >, type_tests: Vec>, liveness_constraints: LivenessValues, elements: &Rc, ) -> Self { // Create a RegionDefinition for each inference variable. let definitions: IndexVec<_, _> = var_infos .into_iter() .map(|info| RegionDefinition::new(info.universe, info.origin)) .collect(); let constraints = Rc::new(outlives_constraints); // freeze constraints let constraint_graph = Rc::new(constraints.graph(definitions.len())); let fr_static = universal_regions.fr_static; let constraint_sccs = Rc::new(constraints.compute_sccs(&constraint_graph, fr_static)); let mut scc_values = RegionValues::new(elements, universal_regions.len(), &placeholder_indices); for region in liveness_constraints.rows() { let scc = constraint_sccs.scc(region); scc_values.merge_liveness(scc, region, &liveness_constraints); } let scc_universes = Self::compute_scc_universes(&constraint_sccs, &definitions); let scc_representatives = Self::compute_scc_representatives(&constraint_sccs, &definitions); let member_constraints = Rc::new(member_constraints_in.into_mapped(|r| constraint_sccs.scc(r))); let mut result = Self { definitions, liveness_constraints, constraints, constraint_graph, constraint_sccs, rev_constraint_graph: None, member_constraints, member_constraints_applied: Vec::new(), closure_bounds_mapping, scc_universes, scc_representatives, scc_values, type_tests, universal_regions, universal_region_relations, }; result.init_free_and_bound_regions(); result } /// Each SCC is the combination of many region variables which /// have been equated. Therefore, we can associate a universe with /// each SCC which is minimum of all the universes of its /// constituent regions -- this is because whatever value the SCC /// takes on must be a value that each of the regions within the /// SCC could have as well. This implies that the SCC must have /// the minimum, or narrowest, universe. fn compute_scc_universes( constraints_scc: &Sccs, definitions: &IndexVec>, ) -> IndexVec { let num_sccs = constraints_scc.num_sccs(); let mut scc_universes = IndexVec::from_elem_n(ty::UniverseIndex::MAX, num_sccs); for (region_vid, region_definition) in definitions.iter_enumerated() { let scc = constraints_scc.scc(region_vid); let scc_universe = &mut scc_universes[scc]; *scc_universe = ::std::cmp::min(*scc_universe, region_definition.universe); } debug!("compute_scc_universes: scc_universe = {:#?}", scc_universes); scc_universes } /// For each SCC, we compute a unique `RegionVid` (in fact, the /// minimal one that belongs to the SCC). See /// `scc_representatives` field of `RegionInferenceContext` for /// more details. fn compute_scc_representatives( constraints_scc: &Sccs, definitions: &IndexVec>, ) -> IndexVec { let num_sccs = constraints_scc.num_sccs(); let next_region_vid = definitions.next_index(); let mut scc_representatives = IndexVec::from_elem_n(next_region_vid, num_sccs); for region_vid in definitions.indices() { let scc = constraints_scc.scc(region_vid); let prev_min = scc_representatives[scc]; scc_representatives[scc] = region_vid.min(prev_min); } scc_representatives } /// Initializes the region variables for each universally /// quantified region (lifetime parameter). The first N variables /// always correspond to the regions appearing in the function /// signature (both named and anonymous) and where-clauses. This /// function iterates over those regions and initializes them with /// minimum values. /// /// For example: /// /// fn foo<'a, 'b>(..) where 'a: 'b /// /// would initialize two variables like so: /// /// R0 = { CFG, R0 } // 'a /// R1 = { CFG, R0, R1 } // 'b /// /// Here, R0 represents `'a`, and it contains (a) the entire CFG /// and (b) any universally quantified regions that it outlives, /// which in this case is just itself. R1 (`'b`) in contrast also /// outlives `'a` and hence contains R0 and R1. fn init_free_and_bound_regions(&mut self) { // Update the names (if any) for (external_name, variable) in self.universal_regions.named_universal_regions() { debug!( "init_universal_regions: region {:?} has external name {:?}", variable, external_name ); self.definitions[variable].external_name = Some(external_name); } for variable in self.definitions.indices() { let scc = self.constraint_sccs.scc(variable); match self.definitions[variable].origin { NLLRegionVariableOrigin::FreeRegion => { // For each free, universally quantified region X: // Add all nodes in the CFG to liveness constraints self.liveness_constraints.add_all_points(variable); self.scc_values.add_all_points(scc); // Add `end(X)` into the set for X. self.scc_values.add_element(scc, variable); } NLLRegionVariableOrigin::Placeholder(placeholder) => { // Each placeholder region is only visible from // its universe `ui` and its extensions. So we // can't just add it into `scc` unless the // universe of the scc can name this region. let scc_universe = self.scc_universes[scc]; if scc_universe.can_name(placeholder.universe) { self.scc_values.add_element(scc, placeholder); } else { debug!( "init_free_and_bound_regions: placeholder {:?} is \ not compatible with universe {:?} of its SCC {:?}", placeholder, scc_universe, scc, ); self.add_incompatible_universe(scc); } } NLLRegionVariableOrigin::Existential => { // For existential, regions, nothing to do. } } } } /// Returns an iterator over all the region indices. pub fn regions(&self) -> impl Iterator { self.definitions.indices() } /// Given a universal region in scope on the MIR, returns the /// corresponding index. /// /// (Panics if `r` is not a registered universal region.) pub fn to_region_vid(&self, r: ty::Region<'tcx>) -> RegionVid { self.universal_regions.to_region_vid(r) } /// Adds annotations for `#[rustc_regions]`; see `UniversalRegions::annotate`. crate fn annotate(&self, tcx: TyCtxt<'tcx>, err: &mut DiagnosticBuilder<'_>) { self.universal_regions.annotate(tcx, err) } /// Returns `true` if the region `r` contains the point `p`. /// /// Panics if called before `solve()` executes, crate fn region_contains(&self, r: impl ToRegionVid, p: impl ToElementIndex) -> bool { let scc = self.constraint_sccs.scc(r.to_region_vid()); self.scc_values.contains(scc, p) } /// Returns access to the value of `r` for debugging purposes. crate fn region_value_str(&self, r: RegionVid) -> String { let scc = self.constraint_sccs.scc(r.to_region_vid()); self.scc_values.region_value_str(scc) } /// Returns access to the value of `r` for debugging purposes. crate fn region_universe(&self, r: RegionVid) -> ty::UniverseIndex { let scc = self.constraint_sccs.scc(r.to_region_vid()); self.scc_universes[scc] } /// Once region solving has completed, this function will return /// the member constraints that were applied to the value of a given /// region `r`. See `AppliedMemberConstraint`. fn applied_member_constraints(&self, r: impl ToRegionVid) -> &[AppliedMemberConstraint] { let scc = self.constraint_sccs.scc(r.to_region_vid()); binary_search_util::binary_search_slice( &self.member_constraints_applied, |applied| applied.member_region_scc, &scc, ) } /// Performs region inference and report errors if we see any /// unsatisfiable constraints. If this is a closure, returns the /// region requirements to propagate to our creator, if any. pub(super) fn solve( &mut self, infcx: &InferCtxt<'_, 'tcx>, body: &Body<'tcx>, upvars: &[Upvar], mir_def_id: DefId, errors_buffer: &mut Vec, ) -> Option> { self.propagate_constraints(body); // If this is a closure, we can propagate unsatisfied // `outlives_requirements` to our creator, so create a vector // to store those. Otherwise, we'll pass in `None` to the // functions below, which will trigger them to report errors // eagerly. let mut outlives_requirements = if infcx.tcx.is_closure(mir_def_id) { Some(vec![]) } else { None }; self.check_type_tests( infcx, body, mir_def_id, outlives_requirements.as_mut(), errors_buffer, ); // If we produce any errors, we keep track of the names of all regions, so that we can use // the same error names in any suggestions we produce. Note that we need names to be unique // across different errors for the same MIR def so that we can make suggestions that fix // multiple problems. let mut region_naming = RegionErrorNamingCtx::new(); self.check_universal_regions( infcx, body, upvars, mir_def_id, outlives_requirements.as_mut(), errors_buffer, &mut region_naming, ); self.check_member_constraints(infcx, mir_def_id, errors_buffer); let outlives_requirements = outlives_requirements.unwrap_or(vec![]); if outlives_requirements.is_empty() { None } else { let num_external_vids = self.universal_regions.num_global_and_external_regions(); Some(ClosureRegionRequirements { num_external_vids, outlives_requirements }) } } /// Propagate the region constraints: this will grow the values /// for each region variable until all the constraints are /// satisfied. Note that some values may grow **too** large to be /// feasible, but we check this later. fn propagate_constraints(&mut self, _body: &Body<'tcx>) { debug!("propagate_constraints()"); debug!("propagate_constraints: constraints={:#?}", { let mut constraints: Vec<_> = self.constraints.outlives().iter().collect(); constraints.sort(); constraints .into_iter() .map(|c| (c, self.constraint_sccs.scc(c.sup), self.constraint_sccs.scc(c.sub))) .collect::>() }); // To propagate constraints, we walk the DAG induced by the // SCC. For each SCC, we visit its successors and compute // their values, then we union all those values to get our // own. let visited = &mut BitSet::new_empty(self.constraint_sccs.num_sccs()); for scc_index in self.constraint_sccs.all_sccs() { self.propagate_constraint_sccs_if_new(scc_index, visited); } // Sort the applied member constraints so we can binary search // through them later. self.member_constraints_applied.sort_by_key(|applied| applied.member_region_scc); } /// Computes the value of the SCC `scc_a` if it has not already /// been computed. The `visited` parameter is a bitset #[inline] fn propagate_constraint_sccs_if_new( &mut self, scc_a: ConstraintSccIndex, visited: &mut BitSet, ) { if visited.insert(scc_a) { self.propagate_constraint_sccs_new(scc_a, visited); } } /// Computes the value of the SCC `scc_a`, which has not yet been /// computed. This works by first computing all successors of the /// SCC (if they haven't been computed already) and then unioning /// together their elements. fn propagate_constraint_sccs_new( &mut self, scc_a: ConstraintSccIndex, visited: &mut BitSet, ) { let constraint_sccs = self.constraint_sccs.clone(); // Walk each SCC `B` such that `A: B`... for &scc_b in constraint_sccs.successors(scc_a) { debug!("propagate_constraint_sccs: scc_a = {:?} scc_b = {:?}", scc_a, scc_b); // ...compute the value of `B`... self.propagate_constraint_sccs_if_new(scc_b, visited); // ...and add elements from `B` into `A`. One complication // arises because of universes: If `B` contains something // that `A` cannot name, then `A` can only contain `B` if // it outlives static. if self.universe_compatible(scc_b, scc_a) { // `A` can name everything that is in `B`, so just // merge the bits. self.scc_values.add_region(scc_a, scc_b); } else { self.add_incompatible_universe(scc_a); } } // Now take member constraints into account. let member_constraints = self.member_constraints.clone(); for m_c_i in member_constraints.indices(scc_a) { self.apply_member_constraint( scc_a, m_c_i, member_constraints.choice_regions(m_c_i), ); } debug!( "propagate_constraint_sccs: scc_a = {:?} has value {:?}", scc_a, self.scc_values.region_value_str(scc_a), ); } /// Invoked for each `R0 member of [R1..Rn]` constraint. /// /// `scc` is the SCC containing R0, and `choice_regions` are the /// `R1..Rn` regions -- they are always known to be universal /// regions (and if that's not true, we just don't attempt to /// enforce the constraint). /// /// The current value of `scc` at the time the method is invoked /// is considered a *lower bound*. If possible, we will modify /// the constraint to set it equal to one of the option regions. /// If we make any changes, returns true, else false. fn apply_member_constraint( &mut self, scc: ConstraintSccIndex, member_constraint_index: NllMemberConstraintIndex, choice_regions: &[ty::RegionVid], ) -> bool { debug!("apply_member_constraint(scc={:?}, choice_regions={:#?})", scc, choice_regions,); if let Some(uh_oh) = choice_regions.iter().find(|&&r| !self.universal_regions.is_universal_region(r)) { // FIXME(#61773): This case can only occur with // `impl_trait_in_bindings`, I believe, and we are just // opting not to handle it for now. See #61773 for // details. bug!( "member constraint for `{:?}` has an option region `{:?}` \ that is not a universal region", self.member_constraints[member_constraint_index].opaque_type_def_id, uh_oh, ); } // Create a mutable vector of the options. We'll try to winnow // them down. let mut choice_regions: Vec = choice_regions.to_vec(); // The 'member region' in a member constraint is part of the // hidden type, which must be in the root universe. Therefore, // it cannot have any placeholders in its value. assert!(self.scc_universes[scc] == ty::UniverseIndex::ROOT); debug_assert!( self.scc_values.placeholders_contained_in(scc).next().is_none(), "scc {:?} in a member constraint has placeholder value: {:?}", scc, self.scc_values.region_value_str(scc), ); // The existing value for `scc` is a lower-bound. This will // consist of some set `{P} + {LB}` of points `{P}` and // lower-bound free regions `{LB}`. As each choice region `O` // is a free region, it will outlive the points. But we can // only consider the option `O` if `O: LB`. choice_regions.retain(|&o_r| { self.scc_values .universal_regions_outlived_by(scc) .all(|lb| self.universal_region_relations.outlives(o_r, lb)) }); debug!("apply_member_constraint: after lb, choice_regions={:?}", choice_regions); // Now find all the *upper bounds* -- that is, each UB is a // free region that must outlive the member region `R0` (`UB: // R0`). Therefore, we need only keep an option `O` if `UB: O` // for all UB. if choice_regions.len() > 1 { let universal_region_relations = self.universal_region_relations.clone(); let rev_constraint_graph = self.rev_constraint_graph(); for ub in self.upper_bounds(scc, &rev_constraint_graph) { debug!("apply_member_constraint: ub={:?}", ub); choice_regions.retain(|&o_r| universal_region_relations.outlives(ub, o_r)); } debug!("apply_member_constraint: after ub, choice_regions={:?}", choice_regions); } // If we ruled everything out, we're done. if choice_regions.is_empty() { return false; } // Otherwise, we need to find the minimum remaining choice, if // any, and take that. debug!("apply_member_constraint: choice_regions remaining are {:#?}", choice_regions); let min = |r1: ty::RegionVid, r2: ty::RegionVid| -> Option { let r1_outlives_r2 = self.universal_region_relations.outlives(r1, r2); let r2_outlives_r1 = self.universal_region_relations.outlives(r2, r1); if r1_outlives_r2 && r2_outlives_r1 { Some(r1.min(r2)) } else if r1_outlives_r2 { Some(r2) } else if r2_outlives_r1 { Some(r1) } else { None } }; let mut min_choice = choice_regions[0]; for &other_option in &choice_regions[1..] { debug!( "apply_member_constraint: min_choice={:?} other_option={:?}", min_choice, other_option, ); match min(min_choice, other_option) { Some(m) => min_choice = m, None => { debug!( "apply_member_constraint: {:?} and {:?} are incomparable; no min choice", min_choice, other_option, ); return false; } } } let min_choice_scc = self.constraint_sccs.scc(min_choice); debug!( "apply_member_constraint: min_choice={:?} best_choice_scc={:?}", min_choice, min_choice_scc, ); if self.scc_values.add_region(scc, min_choice_scc) { self.member_constraints_applied.push(AppliedMemberConstraint { member_region_scc: scc, min_choice, member_constraint_index, }); true } else { false } } /// Compute and return the reverse SCC-based constraint graph (lazilly). fn upper_bounds( &'a mut self, scc0: ConstraintSccIndex, rev_constraint_graph: &'a VecGraph, ) -> impl Iterator + 'a { let scc_values = &self.scc_values; let mut duplicates = FxHashSet::default(); rev_constraint_graph .depth_first_search(scc0) .skip(1) .flat_map(move |scc1| scc_values.universal_regions_outlived_by(scc1)) .filter(move |&r| duplicates.insert(r)) } /// Compute and return the reverse SCC-based constraint graph (lazilly). fn rev_constraint_graph( &mut self, ) -> Rc> { if let Some(g) = &self.rev_constraint_graph { return g.clone(); } let rev_graph = Rc::new(self.constraint_sccs.reverse()); self.rev_constraint_graph = Some(rev_graph.clone()); rev_graph } /// Returns `true` if all the elements in the value of `scc_b` are nameable /// in `scc_a`. Used during constraint propagation, and only once /// the value of `scc_b` has been computed. fn universe_compatible(&self, scc_b: ConstraintSccIndex, scc_a: ConstraintSccIndex) -> bool { let universe_a = self.scc_universes[scc_a]; // Quick check: if scc_b's declared universe is a subset of // scc_a's declared univese (typically, both are ROOT), then // it cannot contain any problematic universe elements. if universe_a.can_name(self.scc_universes[scc_b]) { return true; } // Otherwise, we have to iterate over the universe elements in // B's value, and check whether all of them are nameable // from universe_a self.scc_values.placeholders_contained_in(scc_b).all(|p| universe_a.can_name(p.universe)) } /// Extend `scc` so that it can outlive some placeholder region /// from a universe it can't name; at present, the only way for /// this to be true is if `scc` outlives `'static`. This is /// actually stricter than necessary: ideally, we'd support bounds /// like `for<'a: 'b`>` that might then allow us to approximate /// `'a` with `'b` and not `'static`. But it will have to do for /// now. fn add_incompatible_universe(&mut self, scc: ConstraintSccIndex) { debug!("add_incompatible_universe(scc={:?})", scc); let fr_static = self.universal_regions.fr_static; self.scc_values.add_all_points(scc); self.scc_values.add_element(scc, fr_static); } /// Once regions have been propagated, this method is used to see /// whether the "type tests" produced by typeck were satisfied; /// type tests encode type-outlives relationships like `T: /// 'a`. See `TypeTest` for more details. fn check_type_tests( &self, infcx: &InferCtxt<'_, 'tcx>, body: &Body<'tcx>, mir_def_id: DefId, mut propagated_outlives_requirements: Option<&mut Vec>>, errors_buffer: &mut Vec, ) { let tcx = infcx.tcx; // Sometimes we register equivalent type-tests that would // result in basically the exact same error being reported to // the user. Avoid that. let mut deduplicate_errors = FxHashSet::default(); for type_test in &self.type_tests { debug!("check_type_test: {:?}", type_test); let generic_ty = type_test.generic_kind.to_ty(tcx); if self.eval_verify_bound( tcx, body, generic_ty, type_test.lower_bound, &type_test.verify_bound, ) { continue; } if let Some(propagated_outlives_requirements) = &mut propagated_outlives_requirements { if self.try_promote_type_test( infcx, body, type_test, propagated_outlives_requirements, ) { continue; } } // Type-test failed. Report the error. // Try to convert the lower-bound region into something named we can print for the user. let lower_bound_region = self.to_error_region(type_test.lower_bound); // Skip duplicate-ish errors. let type_test_span = type_test.locations.span(body); let erased_generic_kind = tcx.erase_regions(&type_test.generic_kind); if !deduplicate_errors.insert(( erased_generic_kind, lower_bound_region, type_test.locations, )) { continue; } else { debug!( "check_type_test: reporting error for erased_generic_kind={:?}, \ lower_bound_region={:?}, \ type_test.locations={:?}", erased_generic_kind, lower_bound_region, type_test.locations, ); } if let Some(lower_bound_region) = lower_bound_region { let region_scope_tree = &tcx.region_scope_tree(mir_def_id); infcx .construct_generic_bound_failure( region_scope_tree, type_test_span, None, type_test.generic_kind, lower_bound_region, ) .buffer(errors_buffer); } else { // FIXME. We should handle this case better. It // indicates that we have e.g., some region variable // whose value is like `'a+'b` where `'a` and `'b` are // distinct unrelated univesal regions that are not // known to outlive one another. It'd be nice to have // some examples where this arises to decide how best // to report it; we could probably handle it by // iterating over the universal regions and reporting // an error that multiple bounds are required. tcx.sess .struct_span_err( type_test_span, &format!("`{}` does not live long enough", type_test.generic_kind,), ) .buffer(errors_buffer); } } } /// Converts a region inference variable into a `ty::Region` that /// we can use for error reporting. If `r` is universally bound, /// then we use the name that we have on record for it. If `r` is /// existentially bound, then we check its inferred value and try /// to find a good name from that. Returns `None` if we can't find /// one (e.g., this is just some random part of the CFG). pub fn to_error_region(&self, r: RegionVid) -> Option> { self.to_error_region_vid(r).and_then(|r| self.definitions[r].external_name) } /// Returns the [RegionVid] corresponding to the region returned by /// `to_error_region`. pub fn to_error_region_vid(&self, r: RegionVid) -> Option { if self.universal_regions.is_universal_region(r) { Some(r) } else { let r_scc = self.constraint_sccs.scc(r); let upper_bound = self.universal_upper_bound(r); if self.scc_values.contains(r_scc, upper_bound) { self.to_error_region_vid(upper_bound) } else { None } } } /// Invoked when we have some type-test (e.g., `T: 'X`) that we cannot /// prove to be satisfied. If this is a closure, we will attempt to /// "promote" this type-test into our `ClosureRegionRequirements` and /// hence pass it up the creator. To do this, we have to phrase the /// type-test in terms of external free regions, as local free /// regions are not nameable by the closure's creator. /// /// Promotion works as follows: we first check that the type `T` /// contains only regions that the creator knows about. If this is /// true, then -- as a consequence -- we know that all regions in /// the type `T` are free regions that outlive the closure body. If /// false, then promotion fails. /// /// Once we've promoted T, we have to "promote" `'X` to some region /// that is "external" to the closure. Generally speaking, a region /// may be the union of some points in the closure body as well as /// various free lifetimes. We can ignore the points in the closure /// body: if the type T can be expressed in terms of external regions, /// we know it outlives the points in the closure body. That /// just leaves the free regions. /// /// The idea then is to lower the `T: 'X` constraint into multiple /// bounds -- e.g., if `'X` is the union of two free lifetimes, /// `'1` and `'2`, then we would create `T: '1` and `T: '2`. fn try_promote_type_test( &self, infcx: &InferCtxt<'_, 'tcx>, body: &Body<'tcx>, type_test: &TypeTest<'tcx>, propagated_outlives_requirements: &mut Vec>, ) -> bool { let tcx = infcx.tcx; let TypeTest { generic_kind, lower_bound, locations, verify_bound: _ } = type_test; let generic_ty = generic_kind.to_ty(tcx); let subject = match self.try_promote_type_test_subject(infcx, generic_ty) { Some(s) => s, None => return false, }; // For each region outlived by lower_bound find a non-local, // universal region (it may be the same region) and add it to // `ClosureOutlivesRequirement`. let r_scc = self.constraint_sccs.scc(*lower_bound); for ur in self.scc_values.universal_regions_outlived_by(r_scc) { // Check whether we can already prove that the "subject" outlives `ur`. // If so, we don't have to propagate this requirement to our caller. // // To continue the example from the function, if we are trying to promote // a requirement that `T: 'X`, and we know that `'X = '1 + '2` (i.e., the union // `'1` and `'2`), then in this loop `ur` will be `'1` (and `'2`). So here // we check whether `T: '1` is something we *can* prove. If so, no need // to propagate that requirement. // // This is needed because -- particularly in the case // where `ur` is a local bound -- we are sometimes in a // position to prove things that our caller cannot. See // #53570 for an example. if self.eval_verify_bound(tcx, body, generic_ty, ur, &type_test.verify_bound) { continue; } debug!("try_promote_type_test: ur={:?}", ur); let non_local_ub = self.universal_region_relations.non_local_upper_bounds(&ur); debug!("try_promote_type_test: non_local_ub={:?}", non_local_ub); // This is slightly too conservative. To show T: '1, given `'2: '1` // and `'3: '1` we only need to prove that T: '2 *or* T: '3, but to // avoid potential non-determinism we approximate this by requiring // T: '1 and T: '2. for &upper_bound in non_local_ub { debug_assert!(self.universal_regions.is_universal_region(upper_bound)); debug_assert!(!self.universal_regions.is_local_free_region(upper_bound)); let requirement = ClosureOutlivesRequirement { subject, outlived_free_region: upper_bound, blame_span: locations.span(body), category: ConstraintCategory::Boring, }; debug!("try_promote_type_test: pushing {:#?}", requirement); propagated_outlives_requirements.push(requirement); } } true } /// When we promote a type test `T: 'r`, we have to convert the /// type `T` into something we can store in a query result (so /// something allocated for `'tcx`). This is problematic if `ty` /// contains regions. During the course of NLL region checking, we /// will have replaced all of those regions with fresh inference /// variables. To create a test subject, we want to replace those /// inference variables with some region from the closure /// signature -- this is not always possible, so this is a /// fallible process. Presuming we do find a suitable region, we /// will represent it with a `ReClosureBound`, which is a /// `RegionKind` variant that can be allocated in the gcx. fn try_promote_type_test_subject( &self, infcx: &InferCtxt<'_, 'tcx>, ty: Ty<'tcx>, ) -> Option> { let tcx = infcx.tcx; debug!("try_promote_type_test_subject(ty = {:?})", ty); let ty = tcx.fold_regions(&ty, &mut false, |r, _depth| { let region_vid = self.to_region_vid(r); // The challenge if this. We have some region variable `r` // whose value is a set of CFG points and universal // regions. We want to find if that set is *equivalent* to // any of the named regions found in the closure. // // To do so, we compute the // `non_local_universal_upper_bound`. This will be a // non-local, universal region that is greater than `r`. // However, it might not be *contained* within `r`, so // then we further check whether this bound is contained // in `r`. If so, we can say that `r` is equivalent to the // bound. // // Let's work through a few examples. For these, imagine // that we have 3 non-local regions (I'll denote them as // `'static`, `'a`, and `'b`, though of course in the code // they would be represented with indices) where: // // - `'static: 'a` // - `'static: 'b` // // First, let's assume that `r` is some existential // variable with an inferred value `{'a, 'static}` (plus // some CFG nodes). In this case, the non-local upper // bound is `'static`, since that outlives `'a`. `'static` // is also a member of `r` and hence we consider `r` // equivalent to `'static` (and replace it with // `'static`). // // Now let's consider the inferred value `{'a, 'b}`. This // means `r` is effectively `'a | 'b`. I'm not sure if // this can come about, actually, but assuming it did, we // would get a non-local upper bound of `'static`. Since // `'static` is not contained in `r`, we would fail to // find an equivalent. let upper_bound = self.non_local_universal_upper_bound(region_vid); if self.region_contains(region_vid, upper_bound) { tcx.mk_region(ty::ReClosureBound(upper_bound)) } else { // In the case of a failure, use a `ReVar` // result. This will cause the `lift` later on to // fail. r } }); debug!("try_promote_type_test_subject: folded ty = {:?}", ty); // `has_local_value` will only be true if we failed to promote some region. if ty.has_local_value() { return None; } Some(ClosureOutlivesSubject::Ty(ty)) } /// Given some universal or existential region `r`, finds a /// non-local, universal region `r+` that outlives `r` at entry to (and /// exit from) the closure. In the worst case, this will be /// `'static`. /// /// This is used for two purposes. First, if we are propagated /// some requirement `T: r`, we can use this method to enlarge `r` /// to something we can encode for our creator (which only knows /// about non-local, universal regions). It is also used when /// encoding `T` as part of `try_promote_type_test_subject` (see /// that fn for details). /// /// This is based on the result `'y` of `universal_upper_bound`, /// except that it converts further takes the non-local upper /// bound of `'y`, so that the final result is non-local. fn non_local_universal_upper_bound(&self, r: RegionVid) -> RegionVid { debug!("non_local_universal_upper_bound(r={:?}={})", r, self.region_value_str(r)); let lub = self.universal_upper_bound(r); // Grow further to get smallest universal region known to // creator. let non_local_lub = self.universal_region_relations.non_local_upper_bound(lub); debug!("non_local_universal_upper_bound: non_local_lub={:?}", non_local_lub); non_local_lub } /// Returns a universally quantified region that outlives the /// value of `r` (`r` may be existentially or universally /// quantified). /// /// Since `r` is (potentially) an existential region, it has some /// value which may include (a) any number of points in the CFG /// and (b) any number of `end('x)` elements of universally /// quantified regions. To convert this into a single universal /// region we do as follows: /// /// - Ignore the CFG points in `'r`. All universally quantified regions /// include the CFG anyhow. /// - For each `end('x)` element in `'r`, compute the mutual LUB, yielding /// a result `'y`. fn universal_upper_bound(&self, r: RegionVid) -> RegionVid { debug!("universal_upper_bound(r={:?}={})", r, self.region_value_str(r)); // Find the smallest universal region that contains all other // universal regions within `region`. let mut lub = self.universal_regions.fr_fn_body; let r_scc = self.constraint_sccs.scc(r); for ur in self.scc_values.universal_regions_outlived_by(r_scc) { lub = self.universal_region_relations.postdom_upper_bound(lub, ur); } debug!("universal_upper_bound: r={:?} lub={:?}", r, lub); lub } /// Tests if `test` is true when applied to `lower_bound` at /// `point`. fn eval_verify_bound( &self, tcx: TyCtxt<'tcx>, body: &Body<'tcx>, generic_ty: Ty<'tcx>, lower_bound: RegionVid, verify_bound: &VerifyBound<'tcx>, ) -> bool { debug!("eval_verify_bound(lower_bound={:?}, verify_bound={:?})", lower_bound, verify_bound); match verify_bound { VerifyBound::IfEq(test_ty, verify_bound1) => { self.eval_if_eq(tcx, body, generic_ty, lower_bound, test_ty, verify_bound1) } VerifyBound::OutlivedBy(r) => { let r_vid = self.to_region_vid(r); self.eval_outlives(r_vid, lower_bound) } VerifyBound::AnyBound(verify_bounds) => verify_bounds.iter().any(|verify_bound| { self.eval_verify_bound(tcx, body, generic_ty, lower_bound, verify_bound) }), VerifyBound::AllBounds(verify_bounds) => verify_bounds.iter().all(|verify_bound| { self.eval_verify_bound(tcx, body, generic_ty, lower_bound, verify_bound) }), } } fn eval_if_eq( &self, tcx: TyCtxt<'tcx>, body: &Body<'tcx>, generic_ty: Ty<'tcx>, lower_bound: RegionVid, test_ty: Ty<'tcx>, verify_bound: &VerifyBound<'tcx>, ) -> bool { let generic_ty_normalized = self.normalize_to_scc_representatives(tcx, generic_ty); let test_ty_normalized = self.normalize_to_scc_representatives(tcx, test_ty); if generic_ty_normalized == test_ty_normalized { self.eval_verify_bound(tcx, body, generic_ty, lower_bound, verify_bound) } else { false } } /// This is a conservative normalization procedure. It takes every /// free region in `value` and replaces it with the /// "representative" of its SCC (see `scc_representatives` field). /// We are guaranteed that if two values normalize to the same /// thing, then they are equal; this is a conservative check in /// that they could still be equal even if they normalize to /// different results. (For example, there might be two regions /// with the same value that are not in the same SCC). /// /// N.B., this is not an ideal approach and I would like to revisit /// it. However, it works pretty well in practice. In particular, /// this is needed to deal with projection outlives bounds like /// /// >::Item: '1 /// /// In particular, this routine winds up being important when /// there are bounds like `where >::Item: 'b` in the /// environment. In this case, if we can show that `'0 == 'a`, /// and that `'b: '1`, then we know that the clause is /// satisfied. In such cases, particularly due to limitations of /// the trait solver =), we usually wind up with a where-clause like /// `T: Foo<'a>` in scope, which thus forces `'0 == 'a` to be added as /// a constraint, and thus ensures that they are in the same SCC. /// /// So why can't we do a more correct routine? Well, we could /// *almost* use the `relate_tys` code, but the way it is /// currently setup it creates inference variables to deal with /// higher-ranked things and so forth, and right now the inference /// context is not permitted to make more inference variables. So /// we use this kind of hacky solution. fn normalize_to_scc_representatives(&self, tcx: TyCtxt<'tcx>, value: T) -> T where T: TypeFoldable<'tcx>, { tcx.fold_regions(&value, &mut false, |r, _db| { let vid = self.to_region_vid(r); let scc = self.constraint_sccs.scc(vid); let repr = self.scc_representatives[scc]; tcx.mk_region(ty::ReVar(repr)) }) } // Evaluate whether `sup_region == sub_region`. fn eval_equal(&self, r1: RegionVid, r2: RegionVid) -> bool { self.eval_outlives(r1, r2) && self.eval_outlives(r2, r1) } // Evaluate whether `sup_region: sub_region`. fn eval_outlives(&self, sup_region: RegionVid, sub_region: RegionVid) -> bool { debug!("eval_outlives({:?}: {:?})", sup_region, sub_region); debug!( "eval_outlives: sup_region's value = {:?} universal={:?}", self.region_value_str(sup_region), self.universal_regions.is_universal_region(sup_region), ); debug!( "eval_outlives: sub_region's value = {:?} universal={:?}", self.region_value_str(sub_region), self.universal_regions.is_universal_region(sub_region), ); let sub_region_scc = self.constraint_sccs.scc(sub_region); let sup_region_scc = self.constraint_sccs.scc(sup_region); // Both the `sub_region` and `sup_region` consist of the union // of some number of universal regions (along with the union // of various points in the CFG; ignore those points for // now). Therefore, the sup-region outlives the sub-region if, // for each universal region R1 in the sub-region, there // exists some region R2 in the sup-region that outlives R1. let universal_outlives = self.scc_values.universal_regions_outlived_by(sub_region_scc).all(|r1| { self.scc_values .universal_regions_outlived_by(sup_region_scc) .any(|r2| self.universal_region_relations.outlives(r2, r1)) }); if !universal_outlives { return false; } // Now we have to compare all the points in the sub region and make // sure they exist in the sup region. if self.universal_regions.is_universal_region(sup_region) { // Micro-opt: universal regions contain all points. return true; } self.scc_values.contains_points(sup_region_scc, sub_region_scc) } /// Once regions have been propagated, this method is used to see /// whether any of the constraints were too strong. In particular, /// we want to check for a case where a universally quantified /// region exceeded its bounds. Consider: /// /// fn foo<'a, 'b>(x: &'a u32) -> &'b u32 { x } /// /// In this case, returning `x` requires `&'a u32 <: &'b u32` /// and hence we establish (transitively) a constraint that /// `'a: 'b`. The `propagate_constraints` code above will /// therefore add `end('a)` into the region for `'b` -- but we /// have no evidence that `'b` outlives `'a`, so we want to report /// an error. /// /// If `propagated_outlives_requirements` is `Some`, then we will /// push unsatisfied obligations into there. Otherwise, we'll /// report them as errors. fn check_universal_regions( &self, infcx: &InferCtxt<'_, 'tcx>, body: &Body<'tcx>, upvars: &[Upvar], mir_def_id: DefId, mut propagated_outlives_requirements: Option<&mut Vec>>, errors_buffer: &mut Vec, region_naming: &mut RegionErrorNamingCtx, ) { for (fr, fr_definition) in self.definitions.iter_enumerated() { match fr_definition.origin { NLLRegionVariableOrigin::FreeRegion => { // Go through each of the universal regions `fr` and check that // they did not grow too large, accumulating any requirements // for our caller into the `outlives_requirements` vector. self.check_universal_region( infcx, body, upvars, mir_def_id, fr, &mut propagated_outlives_requirements, errors_buffer, region_naming, ); } NLLRegionVariableOrigin::Placeholder(placeholder) => { self.check_bound_universal_region(infcx, body, mir_def_id, fr, placeholder); } NLLRegionVariableOrigin::Existential => { // nothing to check here } } } } /// Checks the final value for the free region `fr` to see if it /// grew too large. In particular, examine what `end(X)` points /// wound up in `fr`'s final value; for each `end(X)` where `X != /// fr`, we want to check that `fr: X`. If not, that's either an /// error, or something we have to propagate to our creator. /// /// Things that are to be propagated are accumulated into the /// `outlives_requirements` vector. fn check_universal_region( &self, infcx: &InferCtxt<'_, 'tcx>, body: &Body<'tcx>, upvars: &[Upvar], mir_def_id: DefId, longer_fr: RegionVid, propagated_outlives_requirements: &mut Option<&mut Vec>>, errors_buffer: &mut Vec, region_naming: &mut RegionErrorNamingCtx, ) { debug!("check_universal_region(fr={:?})", longer_fr); let longer_fr_scc = self.constraint_sccs.scc(longer_fr); // Because this free region must be in the ROOT universe, we // know it cannot contain any bound universes. assert!(self.scc_universes[longer_fr_scc] == ty::UniverseIndex::ROOT); debug_assert!(self.scc_values.placeholders_contained_in(longer_fr_scc).next().is_none()); // Only check all of the relations for the main representative of each // SCC, otherwise just check that we outlive said representative. This // reduces the number of redundant relations propagated out of // closures. // Note that the representative will be a universal region if there is // one in this SCC, so we will always check the representative here. let representative = self.scc_representatives[longer_fr_scc]; if representative != longer_fr { self.check_universal_region_relation( longer_fr, representative, infcx, body, upvars, mir_def_id, propagated_outlives_requirements, errors_buffer, region_naming, ); return; } // Find every region `o` such that `fr: o` // (because `fr` includes `end(o)`). for shorter_fr in self.scc_values.universal_regions_outlived_by(longer_fr_scc) { if let Some(ErrorReported) = self.check_universal_region_relation( longer_fr, shorter_fr, infcx, body, upvars, mir_def_id, propagated_outlives_requirements, errors_buffer, region_naming, ) { // continuing to iterate just reports more errors than necessary // // FIXME It would also allow us to report more Outlives Suggestions, though, so // it's not clear that that's a bad thing. Somebody should try commenting out this // line and see it is actually a regression. return; } } } fn check_universal_region_relation( &self, longer_fr: RegionVid, shorter_fr: RegionVid, infcx: &InferCtxt<'_, 'tcx>, body: &Body<'tcx>, upvars: &[Upvar], mir_def_id: DefId, propagated_outlives_requirements: &mut Option<&mut Vec>>, errors_buffer: &mut Vec, region_naming: &mut RegionErrorNamingCtx, ) -> Option { // If it is known that `fr: o`, carry on. if self.universal_region_relations.outlives(longer_fr, shorter_fr) { return None; } debug!( "check_universal_region_relation: fr={:?} does not outlive shorter_fr={:?}", longer_fr, shorter_fr, ); if let Some(propagated_outlives_requirements) = propagated_outlives_requirements { // Shrink `longer_fr` until we find a non-local region (if we do). // We'll call it `fr-` -- it's ever so slightly smaller than // `longer_fr`. if let Some(fr_minus) = self.universal_region_relations.non_local_lower_bound(longer_fr) { debug!("check_universal_region: fr_minus={:?}", fr_minus); let blame_span_category = self.find_outlives_blame_span(body, longer_fr, shorter_fr); // Grow `shorter_fr` until we find some non-local regions. (We // always will.) We'll call them `shorter_fr+` -- they're ever // so slightly larger than `shorter_fr`. let shorter_fr_plus = self.universal_region_relations.non_local_upper_bounds(&shorter_fr); debug!("check_universal_region: shorter_fr_plus={:?}", shorter_fr_plus); for &&fr in &shorter_fr_plus { // Push the constraint `fr-: shorter_fr+` propagated_outlives_requirements.push(ClosureOutlivesRequirement { subject: ClosureOutlivesSubject::Region(fr_minus), outlived_free_region: fr, blame_span: blame_span_category.1, category: blame_span_category.0, }); } return None; } } // If we are not in a context where we can't propagate errors, or we // could not shrink `fr` to something smaller, then just report an // error. // // Note: in this case, we use the unapproximated regions to report the // error. This gives better error messages in some cases. let db = self.report_error( body, upvars, infcx, mir_def_id, longer_fr, shorter_fr, region_naming, ); db.buffer(errors_buffer); Some(ErrorReported) } fn check_bound_universal_region( &self, infcx: &InferCtxt<'_, 'tcx>, body: &Body<'tcx>, _mir_def_id: DefId, longer_fr: RegionVid, placeholder: ty::PlaceholderRegion, ) { debug!("check_bound_universal_region(fr={:?}, placeholder={:?})", longer_fr, placeholder,); let longer_fr_scc = self.constraint_sccs.scc(longer_fr); debug!("check_bound_universal_region: longer_fr_scc={:?}", longer_fr_scc,); // If we have some bound universal region `'a`, then the only // elements it can contain is itself -- we don't know anything // else about it! let error_element = match { self.scc_values.elements_contained_in(longer_fr_scc).find(|element| match element { RegionElement::Location(_) => true, RegionElement::RootUniversalRegion(_) => true, RegionElement::PlaceholderRegion(placeholder1) => placeholder != *placeholder1, }) } { Some(v) => v, None => return, }; debug!("check_bound_universal_region: error_element = {:?}", error_element); // Find the region that introduced this `error_element`. let error_region = match error_element { RegionElement::Location(l) => self.find_sub_region_live_at(longer_fr, l), RegionElement::RootUniversalRegion(r) => r, RegionElement::PlaceholderRegion(error_placeholder) => self .definitions .iter_enumerated() .filter_map(|(r, definition)| match definition.origin { NLLRegionVariableOrigin::Placeholder(p) if p == error_placeholder => Some(r), _ => None, }) .next() .unwrap(), }; // Find the code to blame for the fact that `longer_fr` outlives `error_fr`. let (_, span) = self.find_outlives_blame_span(body, longer_fr, error_region); // Obviously, this error message is far from satisfactory. // At present, though, it only appears in unit tests -- // the AST-based checker uses a more conservative check, // so to even see this error, one must pass in a special // flag. let mut diag = infcx.tcx.sess.struct_span_err(span, "higher-ranked subtype error"); diag.emit(); } fn check_member_constraints( &self, infcx: &InferCtxt<'_, 'tcx>, mir_def_id: DefId, errors_buffer: &mut Vec, ) { let member_constraints = self.member_constraints.clone(); for m_c_i in member_constraints.all_indices() { debug!("check_member_constraint(m_c_i={:?})", m_c_i); let m_c = &member_constraints[m_c_i]; let member_region_vid = m_c.member_region_vid; debug!( "check_member_constraint: member_region_vid={:?} with value {}", member_region_vid, self.region_value_str(member_region_vid), ); let choice_regions = member_constraints.choice_regions(m_c_i); debug!("check_member_constraint: choice_regions={:?}", choice_regions); // Did the member region wind up equal to any of the option regions? if let Some(o) = choice_regions.iter().find(|&&o_r| { self.eval_equal(o_r, m_c.member_region_vid) }) { debug!("check_member_constraint: evaluated as equal to {:?}", o); continue; } // If not, report an error. let region_scope_tree = &infcx.tcx.region_scope_tree(mir_def_id); let member_region = infcx.tcx.mk_region(ty::ReVar(member_region_vid)); opaque_types::unexpected_hidden_region_diagnostic( infcx.tcx, Some(region_scope_tree), m_c.opaque_type_def_id, m_c.hidden_ty, member_region, ) .buffer(errors_buffer); } } } impl<'tcx> RegionDefinition<'tcx> { fn new(universe: ty::UniverseIndex, rv_origin: RegionVariableOrigin) -> Self { // Create a new region definition. Note that, for free // regions, the `external_name` field gets updated later in // `init_universal_regions`. let origin = match rv_origin { RegionVariableOrigin::NLL(origin) => origin, _ => NLLRegionVariableOrigin::Existential, }; Self { origin, universe, external_name: None } } } pub trait ClosureRegionRequirementsExt<'tcx> { fn apply_requirements( &self, tcx: TyCtxt<'tcx>, closure_def_id: DefId, closure_substs: SubstsRef<'tcx>, ) -> Vec>; fn subst_closure_mapping( &self, tcx: TyCtxt<'tcx>, closure_mapping: &IndexVec>, value: &T, ) -> T where T: TypeFoldable<'tcx>; } impl<'tcx> ClosureRegionRequirementsExt<'tcx> for ClosureRegionRequirements<'tcx> { /// Given an instance T of the closure type, this method /// instantiates the "extra" requirements that we computed for the /// closure into the inference context. This has the effect of /// adding new outlives obligations to existing variables. /// /// As described on `ClosureRegionRequirements`, the extra /// requirements are expressed in terms of regionvids that index /// into the free regions that appear on the closure type. So, to /// do this, we first copy those regions out from the type T into /// a vector. Then we can just index into that vector to extract /// out the corresponding region from T and apply the /// requirements. fn apply_requirements( &self, tcx: TyCtxt<'tcx>, closure_def_id: DefId, closure_substs: SubstsRef<'tcx>, ) -> Vec> { debug!( "apply_requirements(closure_def_id={:?}, closure_substs={:?})", closure_def_id, closure_substs ); // Extract the values of the free regions in `closure_substs` // into a vector. These are the regions that we will be // relating to one another. let closure_mapping = &UniversalRegions::closure_mapping( tcx, closure_substs, self.num_external_vids, tcx.closure_base_def_id(closure_def_id), ); debug!("apply_requirements: closure_mapping={:?}", closure_mapping); // Create the predicates. self.outlives_requirements .iter() .map(|outlives_requirement| { let outlived_region = closure_mapping[outlives_requirement.outlived_free_region]; match outlives_requirement.subject { ClosureOutlivesSubject::Region(region) => { let region = closure_mapping[region]; debug!( "apply_requirements: region={:?} \ outlived_region={:?} \ outlives_requirement={:?}", region, outlived_region, outlives_requirement, ); ty::Binder::dummy(ty::OutlivesPredicate(region.into(), outlived_region)) } ClosureOutlivesSubject::Ty(ty) => { let ty = self.subst_closure_mapping(tcx, closure_mapping, &ty); debug!( "apply_requirements: ty={:?} \ outlived_region={:?} \ outlives_requirement={:?}", ty, outlived_region, outlives_requirement, ); ty::Binder::dummy(ty::OutlivesPredicate(ty.into(), outlived_region)) } } }) .collect() } fn subst_closure_mapping( &self, tcx: TyCtxt<'tcx>, closure_mapping: &IndexVec>, value: &T, ) -> T where T: TypeFoldable<'tcx>, { tcx.fold_regions(value, &mut false, |r, _depth| { if let ty::ReClosureBound(vid) = r { closure_mapping[*vid] } else { bug!("subst_closure_mapping: encountered non-closure bound free region {:?}", r) } }) } }