3206 lines
137 KiB
Rust
3206 lines
137 KiB
Rust
//! Candidate selection. See the [rustc dev guide] for more information on how this works.
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//!
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//! [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/traits/resolution.html#selection
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use std::assert_matches::assert_matches;
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use std::cell::{Cell, RefCell};
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use std::fmt::{self, Display};
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use std::ops::ControlFlow;
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use std::{cmp, iter};
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use hir::def::DefKind;
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use rustc_data_structures::fx::{FxHashSet, FxIndexMap, FxIndexSet};
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use rustc_data_structures::stack::ensure_sufficient_stack;
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use rustc_errors::{Diag, EmissionGuarantee};
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use rustc_hir as hir;
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use rustc_hir::LangItem;
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use rustc_hir::def_id::DefId;
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use rustc_infer::infer::BoundRegionConversionTime::{self, HigherRankedType};
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use rustc_infer::infer::DefineOpaqueTypes;
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use rustc_infer::infer::at::ToTrace;
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use rustc_infer::infer::relate::TypeRelation;
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use rustc_infer::traits::{PredicateObligations, TraitObligation};
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use rustc_middle::bug;
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use rustc_middle::dep_graph::{DepNodeIndex, dep_kinds};
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pub use rustc_middle::traits::select::*;
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use rustc_middle::ty::abstract_const::NotConstEvaluatable;
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use rustc_middle::ty::error::TypeErrorToStringExt;
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use rustc_middle::ty::fold::fold_regions;
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use rustc_middle::ty::print::{PrintTraitRefExt as _, with_no_trimmed_paths};
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use rustc_middle::ty::{
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self, GenericArgsRef, PolyProjectionPredicate, Ty, TyCtxt, TypeFoldable, TypeVisitableExt,
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TypingMode, Upcast,
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};
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use rustc_span::{Symbol, sym};
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use rustc_type_ir::elaborate;
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use tracing::{debug, instrument, trace};
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use self::EvaluationResult::*;
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use self::SelectionCandidate::*;
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use super::coherence::{self, Conflict};
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use super::project::ProjectionTermObligation;
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use super::util::closure_trait_ref_and_return_type;
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use super::{
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ImplDerivedCause, Normalized, Obligation, ObligationCause, ObligationCauseCode, Overflow,
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PolyTraitObligation, PredicateObligation, Selection, SelectionError, SelectionResult,
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TraitQueryMode, const_evaluatable, project, util, wf,
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};
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use crate::error_reporting::InferCtxtErrorExt;
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use crate::infer::{InferCtxt, InferOk, TypeFreshener};
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use crate::solve::InferCtxtSelectExt as _;
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use crate::traits::normalize::{normalize_with_depth, normalize_with_depth_to};
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use crate::traits::project::{ProjectAndUnifyResult, ProjectionCacheKeyExt};
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use crate::traits::{EvaluateConstErr, ProjectionCacheKey, Unimplemented, effects};
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mod _match;
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mod candidate_assembly;
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mod confirmation;
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#[derive(Clone, Debug, Eq, PartialEq, Hash)]
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pub enum IntercrateAmbiguityCause<'tcx> {
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DownstreamCrate { trait_ref: ty::TraitRef<'tcx>, self_ty: Option<Ty<'tcx>> },
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UpstreamCrateUpdate { trait_ref: ty::TraitRef<'tcx>, self_ty: Option<Ty<'tcx>> },
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ReservationImpl { message: Symbol },
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}
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impl<'tcx> IntercrateAmbiguityCause<'tcx> {
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/// Emits notes when the overlap is caused by complex intercrate ambiguities.
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/// See #23980 for details.
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pub fn add_intercrate_ambiguity_hint<G: EmissionGuarantee>(&self, err: &mut Diag<'_, G>) {
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err.note(self.intercrate_ambiguity_hint());
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}
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pub fn intercrate_ambiguity_hint(&self) -> String {
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with_no_trimmed_paths!(match self {
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IntercrateAmbiguityCause::DownstreamCrate { trait_ref, self_ty } => {
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format!(
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"downstream crates may implement trait `{trait_desc}`{self_desc}",
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trait_desc = trait_ref.print_trait_sugared(),
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self_desc = if let Some(self_ty) = self_ty {
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format!(" for type `{self_ty}`")
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} else {
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String::new()
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}
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)
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}
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IntercrateAmbiguityCause::UpstreamCrateUpdate { trait_ref, self_ty } => {
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format!(
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"upstream crates may add a new impl of trait `{trait_desc}`{self_desc} \
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in future versions",
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trait_desc = trait_ref.print_trait_sugared(),
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self_desc = if let Some(self_ty) = self_ty {
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format!(" for type `{self_ty}`")
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} else {
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String::new()
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}
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)
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}
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IntercrateAmbiguityCause::ReservationImpl { message } => message.to_string(),
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})
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}
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}
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pub struct SelectionContext<'cx, 'tcx> {
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pub infcx: &'cx InferCtxt<'tcx>,
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/// Freshener used specifically for entries on the obligation
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/// stack. This ensures that all entries on the stack at one time
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/// will have the same set of placeholder entries, which is
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/// important for checking for trait bounds that recursively
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/// require themselves.
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freshener: TypeFreshener<'cx, 'tcx>,
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/// If `intercrate` is set, we remember predicates which were
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/// considered ambiguous because of impls potentially added in other crates.
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/// This is used in coherence to give improved diagnostics.
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/// We don't do his until we detect a coherence error because it can
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/// lead to false overflow results (#47139) and because always
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/// computing it may negatively impact performance.
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intercrate_ambiguity_causes: Option<FxIndexSet<IntercrateAmbiguityCause<'tcx>>>,
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/// The mode that trait queries run in, which informs our error handling
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/// policy. In essence, canonicalized queries need their errors propagated
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/// rather than immediately reported because we do not have accurate spans.
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query_mode: TraitQueryMode,
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}
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// A stack that walks back up the stack frame.
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struct TraitObligationStack<'prev, 'tcx> {
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obligation: &'prev PolyTraitObligation<'tcx>,
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/// The trait predicate from `obligation` but "freshened" with the
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/// selection-context's freshener. Used to check for recursion.
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fresh_trait_pred: ty::PolyTraitPredicate<'tcx>,
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/// Starts out equal to `depth` -- if, during evaluation, we
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/// encounter a cycle, then we will set this flag to the minimum
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/// depth of that cycle for all participants in the cycle. These
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/// participants will then forego caching their results. This is
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/// not the most efficient solution, but it addresses #60010. The
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/// problem we are trying to prevent:
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///
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/// - If you have `A: AutoTrait` requires `B: AutoTrait` and `C: NonAutoTrait`
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/// - `B: AutoTrait` requires `A: AutoTrait` (coinductive cycle, ok)
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/// - `C: NonAutoTrait` requires `A: AutoTrait` (non-coinductive cycle, not ok)
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///
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/// you don't want to cache that `B: AutoTrait` or `A: AutoTrait`
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/// is `EvaluatedToOk`; this is because they were only considered
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/// ok on the premise that if `A: AutoTrait` held, but we indeed
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/// encountered a problem (later on) with `A: AutoTrait`. So we
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/// currently set a flag on the stack node for `B: AutoTrait` (as
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/// well as the second instance of `A: AutoTrait`) to suppress
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/// caching.
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///
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/// This is a simple, targeted fix. A more-performant fix requires
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/// deeper changes, but would permit more caching: we could
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/// basically defer caching until we have fully evaluated the
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/// tree, and then cache the entire tree at once. In any case, the
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/// performance impact here shouldn't be so horrible: every time
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/// this is hit, we do cache at least one trait, so we only
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/// evaluate each member of a cycle up to N times, where N is the
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/// length of the cycle. This means the performance impact is
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/// bounded and we shouldn't have any terrible worst-cases.
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reached_depth: Cell<usize>,
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previous: TraitObligationStackList<'prev, 'tcx>,
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/// The number of parent frames plus one (thus, the topmost frame has depth 1).
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depth: usize,
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/// The depth-first number of this node in the search graph -- a
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/// pre-order index. Basically, a freshly incremented counter.
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dfn: usize,
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}
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struct SelectionCandidateSet<'tcx> {
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/// A list of candidates that definitely apply to the current
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/// obligation (meaning: types unify).
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vec: Vec<SelectionCandidate<'tcx>>,
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/// If `true`, then there were candidates that might or might
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/// not have applied, but we couldn't tell. This occurs when some
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/// of the input types are type variables, in which case there are
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/// various "builtin" rules that might or might not trigger.
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ambiguous: bool,
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}
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#[derive(PartialEq, Eq, Debug, Clone)]
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struct EvaluatedCandidate<'tcx> {
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candidate: SelectionCandidate<'tcx>,
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evaluation: EvaluationResult,
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}
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/// When does the builtin impl for `T: Trait` apply?
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#[derive(Debug)]
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enum BuiltinImplConditions<'tcx> {
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/// The impl is conditional on `T1, T2, ...: Trait`.
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Where(ty::Binder<'tcx, Vec<Ty<'tcx>>>),
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/// There is no built-in impl. There may be some other
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/// candidate (a where-clause or user-defined impl).
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None,
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/// It is unknown whether there is an impl.
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Ambiguous,
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}
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impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
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pub fn new(infcx: &'cx InferCtxt<'tcx>) -> SelectionContext<'cx, 'tcx> {
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SelectionContext {
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infcx,
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freshener: infcx.freshener(),
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intercrate_ambiguity_causes: None,
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query_mode: TraitQueryMode::Standard,
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}
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}
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pub fn with_query_mode(
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infcx: &'cx InferCtxt<'tcx>,
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query_mode: TraitQueryMode,
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) -> SelectionContext<'cx, 'tcx> {
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debug!(?query_mode, "with_query_mode");
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SelectionContext { query_mode, ..SelectionContext::new(infcx) }
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}
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/// Enables tracking of intercrate ambiguity causes. See
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/// the documentation of [`Self::intercrate_ambiguity_causes`] for more.
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pub fn enable_tracking_intercrate_ambiguity_causes(&mut self) {
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assert_matches!(self.infcx.typing_mode(), TypingMode::Coherence);
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assert!(self.intercrate_ambiguity_causes.is_none());
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self.intercrate_ambiguity_causes = Some(FxIndexSet::default());
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debug!("selcx: enable_tracking_intercrate_ambiguity_causes");
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}
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/// Gets the intercrate ambiguity causes collected since tracking
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/// was enabled and disables tracking at the same time. If
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/// tracking is not enabled, just returns an empty vector.
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pub fn take_intercrate_ambiguity_causes(
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&mut self,
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) -> FxIndexSet<IntercrateAmbiguityCause<'tcx>> {
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assert_matches!(self.infcx.typing_mode(), TypingMode::Coherence);
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self.intercrate_ambiguity_causes.take().unwrap_or_default()
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}
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pub fn tcx(&self) -> TyCtxt<'tcx> {
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self.infcx.tcx
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}
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///////////////////////////////////////////////////////////////////////////
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// Selection
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//
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// The selection phase tries to identify *how* an obligation will
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// be resolved. For example, it will identify which impl or
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// parameter bound is to be used. The process can be inconclusive
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// if the self type in the obligation is not fully inferred. Selection
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// can result in an error in one of two ways:
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//
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// 1. If no applicable impl or parameter bound can be found.
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// 2. If the output type parameters in the obligation do not match
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// those specified by the impl/bound. For example, if the obligation
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// is `Vec<Foo>: Iterable<Bar>`, but the impl specifies
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// `impl<T> Iterable<T> for Vec<T>`, than an error would result.
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/// Attempts to satisfy the obligation. If successful, this will affect the surrounding
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/// type environment by performing unification.
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#[instrument(level = "debug", skip(self), ret)]
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pub fn poly_select(
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&mut self,
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obligation: &PolyTraitObligation<'tcx>,
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) -> SelectionResult<'tcx, Selection<'tcx>> {
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if self.infcx.next_trait_solver() {
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return self.infcx.select_in_new_trait_solver(obligation);
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}
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let candidate = match self.select_from_obligation(obligation) {
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Err(SelectionError::Overflow(OverflowError::Canonical)) => {
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// In standard mode, overflow must have been caught and reported
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// earlier.
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assert!(self.query_mode == TraitQueryMode::Canonical);
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return Err(SelectionError::Overflow(OverflowError::Canonical));
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}
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Err(e) => {
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return Err(e);
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}
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Ok(None) => {
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return Ok(None);
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}
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Ok(Some(candidate)) => candidate,
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};
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match self.confirm_candidate(obligation, candidate) {
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Err(SelectionError::Overflow(OverflowError::Canonical)) => {
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assert!(self.query_mode == TraitQueryMode::Canonical);
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Err(SelectionError::Overflow(OverflowError::Canonical))
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}
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Err(e) => Err(e),
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Ok(candidate) => Ok(Some(candidate)),
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}
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}
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pub fn select(
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&mut self,
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obligation: &TraitObligation<'tcx>,
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) -> SelectionResult<'tcx, Selection<'tcx>> {
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self.poly_select(&Obligation {
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cause: obligation.cause.clone(),
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param_env: obligation.param_env,
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predicate: ty::Binder::dummy(obligation.predicate),
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recursion_depth: obligation.recursion_depth,
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})
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}
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fn select_from_obligation(
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&mut self,
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obligation: &PolyTraitObligation<'tcx>,
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) -> SelectionResult<'tcx, SelectionCandidate<'tcx>> {
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debug_assert!(!obligation.predicate.has_escaping_bound_vars());
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let pec = &ProvisionalEvaluationCache::default();
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let stack = self.push_stack(TraitObligationStackList::empty(pec), obligation);
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self.candidate_from_obligation(&stack)
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}
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#[instrument(level = "debug", skip(self), ret)]
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fn candidate_from_obligation<'o>(
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&mut self,
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stack: &TraitObligationStack<'o, 'tcx>,
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) -> SelectionResult<'tcx, SelectionCandidate<'tcx>> {
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debug_assert!(!self.infcx.next_trait_solver());
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// Watch out for overflow. This intentionally bypasses (and does
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// not update) the cache.
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self.check_recursion_limit(stack.obligation, stack.obligation)?;
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// Check the cache. Note that we freshen the trait-ref
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// separately rather than using `stack.fresh_trait_ref` --
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// this is because we want the unbound variables to be
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// replaced with fresh types starting from index 0.
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let cache_fresh_trait_pred = self.infcx.freshen(stack.obligation.predicate);
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debug!(?cache_fresh_trait_pred);
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debug_assert!(!stack.obligation.predicate.has_escaping_bound_vars());
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if let Some(c) =
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self.check_candidate_cache(stack.obligation.param_env, cache_fresh_trait_pred)
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{
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debug!("CACHE HIT");
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return c;
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}
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// If no match, compute result and insert into cache.
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//
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// FIXME(nikomatsakis) -- this cache is not taking into
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// account cycles that may have occurred in forming the
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// candidate. I don't know of any specific problems that
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// result but it seems awfully suspicious.
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let (candidate, dep_node) =
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self.in_task(|this| this.candidate_from_obligation_no_cache(stack));
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debug!("CACHE MISS");
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self.insert_candidate_cache(
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stack.obligation.param_env,
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cache_fresh_trait_pred,
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dep_node,
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candidate.clone(),
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);
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candidate
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}
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fn candidate_from_obligation_no_cache<'o>(
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&mut self,
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stack: &TraitObligationStack<'o, 'tcx>,
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) -> SelectionResult<'tcx, SelectionCandidate<'tcx>> {
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if let Err(conflict) = self.is_knowable(stack) {
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debug!("coherence stage: not knowable");
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if self.intercrate_ambiguity_causes.is_some() {
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debug!("evaluate_stack: intercrate_ambiguity_causes is some");
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// Heuristics: show the diagnostics when there are no candidates in crate.
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if let Ok(candidate_set) = self.assemble_candidates(stack) {
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let mut no_candidates_apply = true;
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for c in candidate_set.vec.iter() {
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if self.evaluate_candidate(stack, c)?.may_apply() {
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no_candidates_apply = false;
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break;
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}
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}
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if !candidate_set.ambiguous && no_candidates_apply {
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let trait_ref = self.infcx.resolve_vars_if_possible(
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stack.obligation.predicate.skip_binder().trait_ref,
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);
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if !trait_ref.references_error() {
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let self_ty = trait_ref.self_ty();
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let self_ty = self_ty.has_concrete_skeleton().then(|| self_ty);
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let cause = if let Conflict::Upstream = conflict {
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IntercrateAmbiguityCause::UpstreamCrateUpdate { trait_ref, self_ty }
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} else {
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IntercrateAmbiguityCause::DownstreamCrate { trait_ref, self_ty }
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};
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debug!(?cause, "evaluate_stack: pushing cause");
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self.intercrate_ambiguity_causes.as_mut().unwrap().insert(cause);
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}
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}
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}
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}
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return Ok(None);
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}
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let candidate_set = self.assemble_candidates(stack)?;
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if candidate_set.ambiguous {
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debug!("candidate set contains ambig");
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return Ok(None);
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}
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let candidates = candidate_set.vec;
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debug!(?stack, ?candidates, "assembled {} candidates", candidates.len());
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// At this point, we know that each of the entries in the
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// candidate set is *individually* applicable. Now we have to
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// figure out if they contain mutual incompatibilities. This
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// frequently arises if we have an unconstrained input type --
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// for example, we are looking for `$0: Eq` where `$0` is some
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// unconstrained type variable. In that case, we'll get a
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// candidate which assumes $0 == int, one that assumes `$0 ==
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// usize`, etc. This spells an ambiguity.
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let mut candidates = self.filter_impls(candidates, stack.obligation);
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// If there is more than one candidate, first winnow them down
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// by considering extra conditions (nested obligations and so
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// forth). We don't winnow if there is exactly one
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// candidate. This is a relatively minor distinction but it
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// can lead to better inference and error-reporting. An
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// example would be if there was an impl:
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//
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// impl<T:Clone> Vec<T> { fn push_clone(...) { ... } }
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//
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// and we were to see some code `foo.push_clone()` where `boo`
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// is a `Vec<Bar>` and `Bar` does not implement `Clone`. If
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// we were to winnow, we'd wind up with zero candidates.
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// Instead, we select the right impl now but report "`Bar` does
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// not implement `Clone`".
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if candidates.len() == 1 {
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return self.filter_reservation_impls(candidates.pop().unwrap());
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}
|
|
|
|
// Winnow, but record the exact outcome of evaluation, which
|
|
// is needed for specialization. Propagate overflow if it occurs.
|
|
let candidates = candidates
|
|
.into_iter()
|
|
.map(|c| match self.evaluate_candidate(stack, &c) {
|
|
Ok(eval) if eval.may_apply() => {
|
|
Ok(Some(EvaluatedCandidate { candidate: c, evaluation: eval }))
|
|
}
|
|
Ok(_) => Ok(None),
|
|
Err(OverflowError::Canonical) => Err(Overflow(OverflowError::Canonical)),
|
|
Err(OverflowError::Error(e)) => Err(Overflow(OverflowError::Error(e))),
|
|
})
|
|
.flat_map(Result::transpose)
|
|
.collect::<Result<Vec<_>, _>>()?;
|
|
|
|
debug!(?stack, ?candidates, "{} potentially applicable candidates", candidates.len());
|
|
// If there are *NO* candidates, then there are no impls --
|
|
// that we know of, anyway. Note that in the case where there
|
|
// are unbound type variables within the obligation, it might
|
|
// be the case that you could still satisfy the obligation
|
|
// from another crate by instantiating the type variables with
|
|
// a type from another crate that does have an impl. This case
|
|
// is checked for in `evaluate_stack` (and hence users
|
|
// who might care about this case, like coherence, should use
|
|
// that function).
|
|
if candidates.is_empty() {
|
|
// If there's an error type, 'downgrade' our result from
|
|
// `Err(Unimplemented)` to `Ok(None)`. This helps us avoid
|
|
// emitting additional spurious errors, since we're guaranteed
|
|
// to have emitted at least one.
|
|
if stack.obligation.predicate.references_error() {
|
|
debug!(?stack.obligation.predicate, "found error type in predicate, treating as ambiguous");
|
|
Ok(None)
|
|
} else {
|
|
Err(Unimplemented)
|
|
}
|
|
} else {
|
|
let has_non_region_infer = stack.obligation.predicate.has_non_region_infer();
|
|
if let Some(candidate) = self.winnow_candidates(has_non_region_infer, candidates) {
|
|
self.filter_reservation_impls(candidate)
|
|
} else {
|
|
Ok(None)
|
|
}
|
|
}
|
|
}
|
|
|
|
///////////////////////////////////////////////////////////////////////////
|
|
// EVALUATION
|
|
//
|
|
// Tests whether an obligation can be selected or whether an impl
|
|
// can be applied to particular types. It skips the "confirmation"
|
|
// step and hence completely ignores output type parameters.
|
|
//
|
|
// The result is "true" if the obligation *may* hold and "false" if
|
|
// we can be sure it does not.
|
|
|
|
/// Evaluates whether the obligation `obligation` can be satisfied
|
|
/// and returns an `EvaluationResult`. This is meant for the
|
|
/// *initial* call.
|
|
///
|
|
/// Do not use this directly, use `infcx.evaluate_obligation` instead.
|
|
pub fn evaluate_root_obligation(
|
|
&mut self,
|
|
obligation: &PredicateObligation<'tcx>,
|
|
) -> Result<EvaluationResult, OverflowError> {
|
|
debug_assert!(!self.infcx.next_trait_solver());
|
|
self.evaluation_probe(|this| {
|
|
let goal =
|
|
this.infcx.resolve_vars_if_possible((obligation.predicate, obligation.param_env));
|
|
let mut result = this.evaluate_predicate_recursively(
|
|
TraitObligationStackList::empty(&ProvisionalEvaluationCache::default()),
|
|
obligation.clone(),
|
|
)?;
|
|
// If the predicate has done any inference, then downgrade the
|
|
// result to ambiguous.
|
|
if this.infcx.resolve_vars_if_possible(goal) != goal {
|
|
result = result.max(EvaluatedToAmbig);
|
|
}
|
|
Ok(result)
|
|
})
|
|
}
|
|
|
|
/// Computes the evaluation result of `op`, discarding any constraints.
|
|
///
|
|
/// This also runs for leak check to allow higher ranked region errors to impact
|
|
/// selection. By default it checks for leaks from all universes created inside of
|
|
/// `op`, but this can be overwritten if necessary.
|
|
fn evaluation_probe(
|
|
&mut self,
|
|
op: impl FnOnce(&mut Self) -> Result<EvaluationResult, OverflowError>,
|
|
) -> Result<EvaluationResult, OverflowError> {
|
|
self.infcx.probe(|snapshot| -> Result<EvaluationResult, OverflowError> {
|
|
let outer_universe = self.infcx.universe();
|
|
let result = op(self)?;
|
|
|
|
match self.infcx.leak_check(outer_universe, Some(snapshot)) {
|
|
Ok(()) => {}
|
|
Err(_) => return Ok(EvaluatedToErr),
|
|
}
|
|
|
|
if self.infcx.opaque_types_added_in_snapshot(snapshot) {
|
|
return Ok(result.max(EvaluatedToOkModuloOpaqueTypes));
|
|
}
|
|
|
|
if self.infcx.region_constraints_added_in_snapshot(snapshot) {
|
|
Ok(result.max(EvaluatedToOkModuloRegions))
|
|
} else {
|
|
Ok(result)
|
|
}
|
|
})
|
|
}
|
|
|
|
/// Evaluates the predicates in `predicates` recursively. This may
|
|
/// guide inference. If this is not desired, run it inside of a
|
|
/// is run within an inference probe.
|
|
/// `probe`.
|
|
#[instrument(skip(self, stack), level = "debug")]
|
|
fn evaluate_predicates_recursively<'o, I>(
|
|
&mut self,
|
|
stack: TraitObligationStackList<'o, 'tcx>,
|
|
predicates: I,
|
|
) -> Result<EvaluationResult, OverflowError>
|
|
where
|
|
I: IntoIterator<Item = PredicateObligation<'tcx>> + std::fmt::Debug,
|
|
{
|
|
let mut result = EvaluatedToOk;
|
|
for mut obligation in predicates {
|
|
obligation.set_depth_from_parent(stack.depth());
|
|
let eval = self.evaluate_predicate_recursively(stack, obligation.clone())?;
|
|
if let EvaluatedToErr = eval {
|
|
// fast-path - EvaluatedToErr is the top of the lattice,
|
|
// so we don't need to look on the other predicates.
|
|
return Ok(EvaluatedToErr);
|
|
} else {
|
|
result = cmp::max(result, eval);
|
|
}
|
|
}
|
|
Ok(result)
|
|
}
|
|
|
|
#[instrument(
|
|
level = "debug",
|
|
skip(self, previous_stack),
|
|
fields(previous_stack = ?previous_stack.head())
|
|
ret,
|
|
)]
|
|
fn evaluate_predicate_recursively<'o>(
|
|
&mut self,
|
|
previous_stack: TraitObligationStackList<'o, 'tcx>,
|
|
obligation: PredicateObligation<'tcx>,
|
|
) -> Result<EvaluationResult, OverflowError> {
|
|
debug_assert!(!self.infcx.next_trait_solver());
|
|
// `previous_stack` stores a `PolyTraitObligation`, while `obligation` is
|
|
// a `PredicateObligation`. These are distinct types, so we can't
|
|
// use any `Option` combinator method that would force them to be
|
|
// the same.
|
|
match previous_stack.head() {
|
|
Some(h) => self.check_recursion_limit(&obligation, h.obligation)?,
|
|
None => self.check_recursion_limit(&obligation, &obligation)?,
|
|
}
|
|
|
|
ensure_sufficient_stack(|| {
|
|
let bound_predicate = obligation.predicate.kind();
|
|
match bound_predicate.skip_binder() {
|
|
ty::PredicateKind::Clause(ty::ClauseKind::Trait(t)) => {
|
|
let t = bound_predicate.rebind(t);
|
|
debug_assert!(!t.has_escaping_bound_vars());
|
|
let obligation = obligation.with(self.tcx(), t);
|
|
self.evaluate_trait_predicate_recursively(previous_stack, obligation)
|
|
}
|
|
|
|
ty::PredicateKind::Clause(ty::ClauseKind::HostEffect(data)) => {
|
|
self.infcx.enter_forall(bound_predicate.rebind(data), |data| {
|
|
match effects::evaluate_host_effect_obligation(
|
|
self,
|
|
&obligation.with(self.tcx(), data),
|
|
) {
|
|
Ok(nested) => {
|
|
self.evaluate_predicates_recursively(previous_stack, nested)
|
|
}
|
|
Err(effects::EvaluationFailure::Ambiguous) => Ok(EvaluatedToAmbig),
|
|
Err(effects::EvaluationFailure::NoSolution) => Ok(EvaluatedToErr),
|
|
}
|
|
})
|
|
}
|
|
|
|
ty::PredicateKind::Subtype(p) => {
|
|
let p = bound_predicate.rebind(p);
|
|
// Does this code ever run?
|
|
match self.infcx.subtype_predicate(&obligation.cause, obligation.param_env, p) {
|
|
Ok(Ok(InferOk { obligations, .. })) => {
|
|
self.evaluate_predicates_recursively(previous_stack, obligations)
|
|
}
|
|
Ok(Err(_)) => Ok(EvaluatedToErr),
|
|
Err(..) => Ok(EvaluatedToAmbig),
|
|
}
|
|
}
|
|
|
|
ty::PredicateKind::Coerce(p) => {
|
|
let p = bound_predicate.rebind(p);
|
|
// Does this code ever run?
|
|
match self.infcx.coerce_predicate(&obligation.cause, obligation.param_env, p) {
|
|
Ok(Ok(InferOk { obligations, .. })) => {
|
|
self.evaluate_predicates_recursively(previous_stack, obligations)
|
|
}
|
|
Ok(Err(_)) => Ok(EvaluatedToErr),
|
|
Err(..) => Ok(EvaluatedToAmbig),
|
|
}
|
|
}
|
|
|
|
ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(arg)) => {
|
|
// So, there is a bit going on here. First, `WellFormed` predicates
|
|
// are coinductive, like trait predicates with auto traits.
|
|
// This means that we need to detect if we have recursively
|
|
// evaluated `WellFormed(X)`. Otherwise, we would run into
|
|
// a "natural" overflow error.
|
|
//
|
|
// Now, the next question is whether we need to do anything
|
|
// special with caching. Considering the following tree:
|
|
// - `WF(Foo<T>)`
|
|
// - `Bar<T>: Send`
|
|
// - `WF(Foo<T>)`
|
|
// - `Foo<T>: Trait`
|
|
// In this case, the innermost `WF(Foo<T>)` should return
|
|
// `EvaluatedToOk`, since it's coinductive. Then if
|
|
// `Bar<T>: Send` is resolved to `EvaluatedToOk`, it can be
|
|
// inserted into a cache (because without thinking about `WF`
|
|
// goals, it isn't in a cycle). If `Foo<T>: Trait` later doesn't
|
|
// hold, then `Bar<T>: Send` shouldn't hold. Therefore, we
|
|
// *do* need to keep track of coinductive cycles.
|
|
|
|
let cache = previous_stack.cache;
|
|
let dfn = cache.next_dfn();
|
|
|
|
for stack_arg in previous_stack.cache.wf_args.borrow().iter().rev() {
|
|
if stack_arg.0 != arg {
|
|
continue;
|
|
}
|
|
debug!("WellFormed({:?}) on stack", arg);
|
|
if let Some(stack) = previous_stack.head {
|
|
// Okay, let's imagine we have two different stacks:
|
|
// `T: NonAutoTrait -> WF(T) -> T: NonAutoTrait`
|
|
// `WF(T) -> T: NonAutoTrait -> WF(T)`
|
|
// Because of this, we need to check that all
|
|
// predicates between the WF goals are coinductive.
|
|
// Otherwise, we can say that `T: NonAutoTrait` is
|
|
// true.
|
|
// Let's imagine we have a predicate stack like
|
|
// `Foo: Bar -> WF(T) -> T: NonAutoTrait -> T: Auto`
|
|
// depth ^1 ^2 ^3
|
|
// and the current predicate is `WF(T)`. `wf_args`
|
|
// would contain `(T, 1)`. We want to check all
|
|
// trait predicates greater than `1`. The previous
|
|
// stack would be `T: Auto`.
|
|
let cycle = stack.iter().take_while(|s| s.depth > stack_arg.1);
|
|
let tcx = self.tcx();
|
|
let cycle = cycle.map(|stack| stack.obligation.predicate.upcast(tcx));
|
|
if self.coinductive_match(cycle) {
|
|
stack.update_reached_depth(stack_arg.1);
|
|
return Ok(EvaluatedToOk);
|
|
} else {
|
|
return Ok(EvaluatedToAmbigStackDependent);
|
|
}
|
|
}
|
|
return Ok(EvaluatedToOk);
|
|
}
|
|
|
|
match wf::obligations(
|
|
self.infcx,
|
|
obligation.param_env,
|
|
obligation.cause.body_id,
|
|
obligation.recursion_depth + 1,
|
|
arg,
|
|
obligation.cause.span,
|
|
) {
|
|
Some(obligations) => {
|
|
cache.wf_args.borrow_mut().push((arg, previous_stack.depth()));
|
|
let result =
|
|
self.evaluate_predicates_recursively(previous_stack, obligations);
|
|
cache.wf_args.borrow_mut().pop();
|
|
|
|
let result = result?;
|
|
|
|
if !result.must_apply_modulo_regions() {
|
|
cache.on_failure(dfn);
|
|
}
|
|
|
|
cache.on_completion(dfn);
|
|
|
|
Ok(result)
|
|
}
|
|
None => Ok(EvaluatedToAmbig),
|
|
}
|
|
}
|
|
|
|
ty::PredicateKind::Clause(ty::ClauseKind::TypeOutlives(pred)) => {
|
|
// A global type with no free lifetimes or generic parameters
|
|
// outlives anything.
|
|
if pred.0.has_free_regions()
|
|
|| pred.0.has_bound_regions()
|
|
|| pred.0.has_non_region_infer()
|
|
|| pred.0.has_non_region_infer()
|
|
{
|
|
Ok(EvaluatedToOkModuloRegions)
|
|
} else {
|
|
Ok(EvaluatedToOk)
|
|
}
|
|
}
|
|
|
|
ty::PredicateKind::Clause(ty::ClauseKind::RegionOutlives(..)) => {
|
|
// We do not consider region relationships when evaluating trait matches.
|
|
Ok(EvaluatedToOkModuloRegions)
|
|
}
|
|
|
|
ty::PredicateKind::DynCompatible(trait_def_id) => {
|
|
if self.tcx().is_dyn_compatible(trait_def_id) {
|
|
Ok(EvaluatedToOk)
|
|
} else {
|
|
Ok(EvaluatedToErr)
|
|
}
|
|
}
|
|
|
|
ty::PredicateKind::Clause(ty::ClauseKind::Projection(data)) => {
|
|
let data = bound_predicate.rebind(data);
|
|
let project_obligation = obligation.with(self.tcx(), data);
|
|
match project::poly_project_and_unify_term(self, &project_obligation) {
|
|
ProjectAndUnifyResult::Holds(mut subobligations) => {
|
|
'compute_res: {
|
|
// If we've previously marked this projection as 'complete', then
|
|
// use the final cached result (either `EvaluatedToOk` or
|
|
// `EvaluatedToOkModuloRegions`), and skip re-evaluating the
|
|
// sub-obligations.
|
|
if let Some(key) =
|
|
ProjectionCacheKey::from_poly_projection_obligation(
|
|
self,
|
|
&project_obligation,
|
|
)
|
|
{
|
|
if let Some(cached_res) = self
|
|
.infcx
|
|
.inner
|
|
.borrow_mut()
|
|
.projection_cache()
|
|
.is_complete(key)
|
|
{
|
|
break 'compute_res Ok(cached_res);
|
|
}
|
|
}
|
|
|
|
// Need to explicitly set the depth of nested goals here as
|
|
// projection obligations can cycle by themselves and in
|
|
// `evaluate_predicates_recursively` we only add the depth
|
|
// for parent trait goals because only these get added to the
|
|
// `TraitObligationStackList`.
|
|
for subobligation in subobligations.iter_mut() {
|
|
subobligation.set_depth_from_parent(obligation.recursion_depth);
|
|
}
|
|
let res = self.evaluate_predicates_recursively(
|
|
previous_stack,
|
|
subobligations,
|
|
);
|
|
if let Ok(eval_rslt) = res
|
|
&& (eval_rslt == EvaluatedToOk
|
|
|| eval_rslt == EvaluatedToOkModuloRegions)
|
|
&& let Some(key) =
|
|
ProjectionCacheKey::from_poly_projection_obligation(
|
|
self,
|
|
&project_obligation,
|
|
)
|
|
{
|
|
// If the result is something that we can cache, then mark this
|
|
// entry as 'complete'. This will allow us to skip evaluating the
|
|
// subobligations at all the next time we evaluate the projection
|
|
// predicate.
|
|
self.infcx
|
|
.inner
|
|
.borrow_mut()
|
|
.projection_cache()
|
|
.complete(key, eval_rslt);
|
|
}
|
|
res
|
|
}
|
|
}
|
|
ProjectAndUnifyResult::FailedNormalization => Ok(EvaluatedToAmbig),
|
|
ProjectAndUnifyResult::Recursive => Ok(EvaluatedToAmbigStackDependent),
|
|
ProjectAndUnifyResult::MismatchedProjectionTypes(_) => Ok(EvaluatedToErr),
|
|
}
|
|
}
|
|
|
|
ty::PredicateKind::Clause(ty::ClauseKind::ConstEvaluatable(uv)) => {
|
|
match const_evaluatable::is_const_evaluatable(
|
|
self.infcx,
|
|
uv,
|
|
obligation.param_env,
|
|
obligation.cause.span,
|
|
) {
|
|
Ok(()) => Ok(EvaluatedToOk),
|
|
Err(NotConstEvaluatable::MentionsInfer) => Ok(EvaluatedToAmbig),
|
|
Err(NotConstEvaluatable::MentionsParam) => Ok(EvaluatedToErr),
|
|
Err(_) => Ok(EvaluatedToErr),
|
|
}
|
|
}
|
|
|
|
ty::PredicateKind::ConstEquate(c1, c2) => {
|
|
let tcx = self.tcx();
|
|
assert!(
|
|
tcx.features().generic_const_exprs(),
|
|
"`ConstEquate` without a feature gate: {c1:?} {c2:?}",
|
|
);
|
|
|
|
{
|
|
let c1 = tcx.expand_abstract_consts(c1);
|
|
let c2 = tcx.expand_abstract_consts(c2);
|
|
debug!(
|
|
"evaluate_predicate_recursively: equating consts:\nc1= {:?}\nc2= {:?}",
|
|
c1, c2
|
|
);
|
|
|
|
use rustc_hir::def::DefKind;
|
|
match (c1.kind(), c2.kind()) {
|
|
(ty::ConstKind::Unevaluated(a), ty::ConstKind::Unevaluated(b))
|
|
if a.def == b.def && tcx.def_kind(a.def) == DefKind::AssocConst =>
|
|
{
|
|
if let Ok(InferOk { obligations, value: () }) = self
|
|
.infcx
|
|
.at(&obligation.cause, obligation.param_env)
|
|
// Can define opaque types as this is only reachable with
|
|
// `generic_const_exprs`
|
|
.eq(
|
|
DefineOpaqueTypes::Yes,
|
|
ty::AliasTerm::from(a),
|
|
ty::AliasTerm::from(b),
|
|
)
|
|
{
|
|
return self.evaluate_predicates_recursively(
|
|
previous_stack,
|
|
obligations,
|
|
);
|
|
}
|
|
}
|
|
(_, ty::ConstKind::Unevaluated(_))
|
|
| (ty::ConstKind::Unevaluated(_), _) => (),
|
|
(_, _) => {
|
|
if let Ok(InferOk { obligations, value: () }) = self
|
|
.infcx
|
|
.at(&obligation.cause, obligation.param_env)
|
|
// Can define opaque types as this is only reachable with
|
|
// `generic_const_exprs`
|
|
.eq(DefineOpaqueTypes::Yes, c1, c2)
|
|
{
|
|
return self.evaluate_predicates_recursively(
|
|
previous_stack,
|
|
obligations,
|
|
);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
let evaluate = |c: ty::Const<'tcx>| {
|
|
if let ty::ConstKind::Unevaluated(_) = c.kind() {
|
|
match crate::traits::try_evaluate_const(
|
|
self.infcx,
|
|
c,
|
|
obligation.param_env,
|
|
) {
|
|
Ok(val) => Ok(val),
|
|
Err(e) => Err(e),
|
|
}
|
|
} else {
|
|
Ok(c)
|
|
}
|
|
};
|
|
|
|
match (evaluate(c1), evaluate(c2)) {
|
|
(Ok(c1), Ok(c2)) => {
|
|
match self.infcx.at(&obligation.cause, obligation.param_env).eq(
|
|
// Can define opaque types as this is only reachable with
|
|
// `generic_const_exprs`
|
|
DefineOpaqueTypes::Yes,
|
|
c1,
|
|
c2,
|
|
) {
|
|
Ok(inf_ok) => self.evaluate_predicates_recursively(
|
|
previous_stack,
|
|
inf_ok.into_obligations(),
|
|
),
|
|
Err(_) => Ok(EvaluatedToErr),
|
|
}
|
|
}
|
|
(Err(EvaluateConstErr::InvalidConstParamTy(..)), _)
|
|
| (_, Err(EvaluateConstErr::InvalidConstParamTy(..))) => Ok(EvaluatedToErr),
|
|
(Err(EvaluateConstErr::EvaluationFailure(..)), _)
|
|
| (_, Err(EvaluateConstErr::EvaluationFailure(..))) => Ok(EvaluatedToErr),
|
|
(Err(EvaluateConstErr::HasGenericsOrInfers), _)
|
|
| (_, Err(EvaluateConstErr::HasGenericsOrInfers)) => {
|
|
if c1.has_non_region_infer() || c2.has_non_region_infer() {
|
|
Ok(EvaluatedToAmbig)
|
|
} else {
|
|
// Two different constants using generic parameters ~> error.
|
|
Ok(EvaluatedToErr)
|
|
}
|
|
}
|
|
}
|
|
}
|
|
ty::PredicateKind::NormalizesTo(..) => {
|
|
bug!("NormalizesTo is only used by the new solver")
|
|
}
|
|
ty::PredicateKind::AliasRelate(..) => {
|
|
bug!("AliasRelate is only used by the new solver")
|
|
}
|
|
ty::PredicateKind::Ambiguous => Ok(EvaluatedToAmbig),
|
|
ty::PredicateKind::Clause(ty::ClauseKind::ConstArgHasType(ct, ty)) => {
|
|
let ct = self.infcx.shallow_resolve_const(ct);
|
|
let ct_ty = match ct.kind() {
|
|
ty::ConstKind::Infer(_) => {
|
|
return Ok(EvaluatedToAmbig);
|
|
}
|
|
ty::ConstKind::Error(_) => return Ok(EvaluatedToOk),
|
|
ty::ConstKind::Value(cv) => cv.ty,
|
|
ty::ConstKind::Unevaluated(uv) => {
|
|
self.tcx().type_of(uv.def).instantiate(self.tcx(), uv.args)
|
|
}
|
|
// FIXME(generic_const_exprs): See comment in `fulfill.rs`
|
|
ty::ConstKind::Expr(_) => return Ok(EvaluatedToOk),
|
|
ty::ConstKind::Placeholder(_) => {
|
|
bug!("placeholder const {:?} in old solver", ct)
|
|
}
|
|
ty::ConstKind::Bound(_, _) => bug!("escaping bound vars in {:?}", ct),
|
|
ty::ConstKind::Param(param_ct) => {
|
|
param_ct.find_ty_from_env(obligation.param_env)
|
|
}
|
|
};
|
|
|
|
match self.infcx.at(&obligation.cause, obligation.param_env).eq(
|
|
// Only really exercised by generic_const_exprs
|
|
DefineOpaqueTypes::Yes,
|
|
ct_ty,
|
|
ty,
|
|
) {
|
|
Ok(inf_ok) => self.evaluate_predicates_recursively(
|
|
previous_stack,
|
|
inf_ok.into_obligations(),
|
|
),
|
|
Err(_) => Ok(EvaluatedToErr),
|
|
}
|
|
}
|
|
}
|
|
})
|
|
}
|
|
|
|
#[instrument(skip(self, previous_stack), level = "debug", ret)]
|
|
fn evaluate_trait_predicate_recursively<'o>(
|
|
&mut self,
|
|
previous_stack: TraitObligationStackList<'o, 'tcx>,
|
|
mut obligation: PolyTraitObligation<'tcx>,
|
|
) -> Result<EvaluationResult, OverflowError> {
|
|
if !matches!(self.infcx.typing_mode(), TypingMode::Coherence)
|
|
&& obligation.is_global()
|
|
&& obligation.param_env.caller_bounds().iter().all(|bound| bound.has_param())
|
|
{
|
|
// If a param env has no global bounds, global obligations do not
|
|
// depend on its particular value in order to work, so we can clear
|
|
// out the param env and get better caching.
|
|
debug!("in global");
|
|
obligation.param_env = obligation.param_env.without_caller_bounds();
|
|
}
|
|
|
|
let stack = self.push_stack(previous_stack, &obligation);
|
|
let fresh_trait_pred = stack.fresh_trait_pred;
|
|
let param_env = obligation.param_env;
|
|
|
|
debug!(?fresh_trait_pred);
|
|
|
|
// If a trait predicate is in the (local or global) evaluation cache,
|
|
// then we know it holds without cycles.
|
|
if let Some(result) = self.check_evaluation_cache(param_env, fresh_trait_pred) {
|
|
debug!("CACHE HIT");
|
|
return Ok(result);
|
|
}
|
|
|
|
if let Some(result) = stack.cache().get_provisional(fresh_trait_pred) {
|
|
debug!("PROVISIONAL CACHE HIT");
|
|
stack.update_reached_depth(result.reached_depth);
|
|
return Ok(result.result);
|
|
}
|
|
|
|
// Check if this is a match for something already on the
|
|
// stack. If so, we don't want to insert the result into the
|
|
// main cache (it is cycle dependent) nor the provisional
|
|
// cache (which is meant for things that have completed but
|
|
// for a "backedge" -- this result *is* the backedge).
|
|
if let Some(cycle_result) = self.check_evaluation_cycle(&stack) {
|
|
return Ok(cycle_result);
|
|
}
|
|
|
|
let (result, dep_node) = self.in_task(|this| {
|
|
let mut result = this.evaluate_stack(&stack)?;
|
|
|
|
// fix issue #103563, we don't normalize
|
|
// nested obligations which produced by `TraitDef` candidate
|
|
// (i.e. using bounds on assoc items as assumptions).
|
|
// because we don't have enough information to
|
|
// normalize these obligations before evaluating.
|
|
// so we will try to normalize the obligation and evaluate again.
|
|
// we will replace it with new solver in the future.
|
|
if EvaluationResult::EvaluatedToErr == result
|
|
&& fresh_trait_pred.has_aliases()
|
|
&& fresh_trait_pred.is_global()
|
|
{
|
|
let mut nested_obligations = PredicateObligations::new();
|
|
let predicate = normalize_with_depth_to(
|
|
this,
|
|
param_env,
|
|
obligation.cause.clone(),
|
|
obligation.recursion_depth + 1,
|
|
obligation.predicate,
|
|
&mut nested_obligations,
|
|
);
|
|
if predicate != obligation.predicate {
|
|
let mut nested_result = EvaluationResult::EvaluatedToOk;
|
|
for obligation in nested_obligations {
|
|
nested_result = cmp::max(
|
|
this.evaluate_predicate_recursively(previous_stack, obligation)?,
|
|
nested_result,
|
|
);
|
|
}
|
|
|
|
if nested_result.must_apply_modulo_regions() {
|
|
let obligation = obligation.with(this.tcx(), predicate);
|
|
result = cmp::max(
|
|
nested_result,
|
|
this.evaluate_trait_predicate_recursively(previous_stack, obligation)?,
|
|
);
|
|
}
|
|
}
|
|
}
|
|
|
|
Ok::<_, OverflowError>(result)
|
|
});
|
|
|
|
let result = result?;
|
|
|
|
if !result.must_apply_modulo_regions() {
|
|
stack.cache().on_failure(stack.dfn);
|
|
}
|
|
|
|
let reached_depth = stack.reached_depth.get();
|
|
if reached_depth >= stack.depth {
|
|
debug!("CACHE MISS");
|
|
self.insert_evaluation_cache(param_env, fresh_trait_pred, dep_node, result);
|
|
stack.cache().on_completion(stack.dfn);
|
|
} else {
|
|
debug!("PROVISIONAL");
|
|
debug!(
|
|
"caching provisionally because {:?} \
|
|
is a cycle participant (at depth {}, reached depth {})",
|
|
fresh_trait_pred, stack.depth, reached_depth,
|
|
);
|
|
|
|
stack.cache().insert_provisional(stack.dfn, reached_depth, fresh_trait_pred, result);
|
|
}
|
|
|
|
Ok(result)
|
|
}
|
|
|
|
/// If there is any previous entry on the stack that precisely
|
|
/// matches this obligation, then we can assume that the
|
|
/// obligation is satisfied for now (still all other conditions
|
|
/// must be met of course). One obvious case this comes up is
|
|
/// marker traits like `Send`. Think of a linked list:
|
|
///
|
|
/// struct List<T> { data: T, next: Option<Box<List<T>>> }
|
|
///
|
|
/// `Box<List<T>>` will be `Send` if `T` is `Send` and
|
|
/// `Option<Box<List<T>>>` is `Send`, and in turn
|
|
/// `Option<Box<List<T>>>` is `Send` if `Box<List<T>>` is
|
|
/// `Send`.
|
|
///
|
|
/// Note that we do this comparison using the `fresh_trait_ref`
|
|
/// fields. Because these have all been freshened using
|
|
/// `self.freshener`, we can be sure that (a) this will not
|
|
/// affect the inferencer state and (b) that if we see two
|
|
/// fresh regions with the same index, they refer to the same
|
|
/// unbound type variable.
|
|
fn check_evaluation_cycle(
|
|
&mut self,
|
|
stack: &TraitObligationStack<'_, 'tcx>,
|
|
) -> Option<EvaluationResult> {
|
|
if let Some(cycle_depth) = stack
|
|
.iter()
|
|
.skip(1) // Skip top-most frame.
|
|
.find(|prev| {
|
|
stack.obligation.param_env == prev.obligation.param_env
|
|
&& stack.fresh_trait_pred == prev.fresh_trait_pred
|
|
})
|
|
.map(|stack| stack.depth)
|
|
{
|
|
debug!("evaluate_stack --> recursive at depth {}", cycle_depth);
|
|
|
|
// If we have a stack like `A B C D E A`, where the top of
|
|
// the stack is the final `A`, then this will iterate over
|
|
// `A, E, D, C, B` -- i.e., all the participants apart
|
|
// from the cycle head. We mark them as participating in a
|
|
// cycle. This suppresses caching for those nodes. See
|
|
// `in_cycle` field for more details.
|
|
stack.update_reached_depth(cycle_depth);
|
|
|
|
// Subtle: when checking for a coinductive cycle, we do
|
|
// not compare using the "freshened trait refs" (which
|
|
// have erased regions) but rather the fully explicit
|
|
// trait refs. This is important because it's only a cycle
|
|
// if the regions match exactly.
|
|
let cycle = stack.iter().skip(1).take_while(|s| s.depth >= cycle_depth);
|
|
let tcx = self.tcx();
|
|
let cycle = cycle.map(|stack| stack.obligation.predicate.upcast(tcx));
|
|
if self.coinductive_match(cycle) {
|
|
debug!("evaluate_stack --> recursive, coinductive");
|
|
Some(EvaluatedToOk)
|
|
} else {
|
|
debug!("evaluate_stack --> recursive, inductive");
|
|
Some(EvaluatedToAmbigStackDependent)
|
|
}
|
|
} else {
|
|
None
|
|
}
|
|
}
|
|
|
|
fn evaluate_stack<'o>(
|
|
&mut self,
|
|
stack: &TraitObligationStack<'o, 'tcx>,
|
|
) -> Result<EvaluationResult, OverflowError> {
|
|
debug_assert!(!self.infcx.next_trait_solver());
|
|
// In intercrate mode, whenever any of the generics are unbound,
|
|
// there can always be an impl. Even if there are no impls in
|
|
// this crate, perhaps the type would be unified with
|
|
// something from another crate that does provide an impl.
|
|
//
|
|
// In intra mode, we must still be conservative. The reason is
|
|
// that we want to avoid cycles. Imagine an impl like:
|
|
//
|
|
// impl<T:Eq> Eq for Vec<T>
|
|
//
|
|
// and a trait reference like `$0 : Eq` where `$0` is an
|
|
// unbound variable. When we evaluate this trait-reference, we
|
|
// will unify `$0` with `Vec<$1>` (for some fresh variable
|
|
// `$1`), on the condition that `$1 : Eq`. We will then wind
|
|
// up with many candidates (since that are other `Eq` impls
|
|
// that apply) and try to winnow things down. This results in
|
|
// a recursive evaluation that `$1 : Eq` -- as you can
|
|
// imagine, this is just where we started. To avoid that, we
|
|
// check for unbound variables and return an ambiguous (hence possible)
|
|
// match if we've seen this trait before.
|
|
//
|
|
// This suffices to allow chains like `FnMut` implemented in
|
|
// terms of `Fn` etc, but we could probably make this more
|
|
// precise still.
|
|
let unbound_input_types =
|
|
stack.fresh_trait_pred.skip_binder().trait_ref.args.types().any(|ty| ty.is_fresh());
|
|
|
|
if unbound_input_types
|
|
&& stack.iter().skip(1).any(|prev| {
|
|
stack.obligation.param_env == prev.obligation.param_env
|
|
&& self.match_fresh_trait_refs(stack.fresh_trait_pred, prev.fresh_trait_pred)
|
|
})
|
|
{
|
|
debug!("evaluate_stack --> unbound argument, recursive --> giving up",);
|
|
return Ok(EvaluatedToAmbigStackDependent);
|
|
}
|
|
|
|
match self.candidate_from_obligation(stack) {
|
|
Ok(Some(c)) => self.evaluate_candidate(stack, &c),
|
|
Ok(None) => Ok(EvaluatedToAmbig),
|
|
Err(Overflow(OverflowError::Canonical)) => Err(OverflowError::Canonical),
|
|
Err(..) => Ok(EvaluatedToErr),
|
|
}
|
|
}
|
|
|
|
/// For defaulted traits, we use a co-inductive strategy to solve, so
|
|
/// that recursion is ok. This routine returns `true` if the top of the
|
|
/// stack (`cycle[0]`):
|
|
///
|
|
/// - is a defaulted trait,
|
|
/// - it also appears in the backtrace at some position `X`,
|
|
/// - all the predicates at positions `X..` between `X` and the top are
|
|
/// also defaulted traits.
|
|
pub(crate) fn coinductive_match<I>(&mut self, mut cycle: I) -> bool
|
|
where
|
|
I: Iterator<Item = ty::Predicate<'tcx>>,
|
|
{
|
|
cycle.all(|predicate| predicate.is_coinductive(self.tcx()))
|
|
}
|
|
|
|
/// Further evaluates `candidate` to decide whether all type parameters match and whether nested
|
|
/// obligations are met. Returns whether `candidate` remains viable after this further
|
|
/// scrutiny.
|
|
#[instrument(
|
|
level = "debug",
|
|
skip(self, stack),
|
|
fields(depth = stack.obligation.recursion_depth),
|
|
ret
|
|
)]
|
|
fn evaluate_candidate<'o>(
|
|
&mut self,
|
|
stack: &TraitObligationStack<'o, 'tcx>,
|
|
candidate: &SelectionCandidate<'tcx>,
|
|
) -> Result<EvaluationResult, OverflowError> {
|
|
let mut result = self.evaluation_probe(|this| {
|
|
match this.confirm_candidate(stack.obligation, candidate.clone()) {
|
|
Ok(selection) => {
|
|
debug!(?selection);
|
|
this.evaluate_predicates_recursively(
|
|
stack.list(),
|
|
selection.nested_obligations().into_iter(),
|
|
)
|
|
}
|
|
Err(..) => Ok(EvaluatedToErr),
|
|
}
|
|
})?;
|
|
|
|
// If we erased any lifetimes, then we want to use
|
|
// `EvaluatedToOkModuloRegions` instead of `EvaluatedToOk`
|
|
// as your final result. The result will be cached using
|
|
// the freshened trait predicate as a key, so we need
|
|
// our result to be correct by *any* choice of original lifetimes,
|
|
// not just the lifetime choice for this particular (non-erased)
|
|
// predicate.
|
|
// See issue #80691
|
|
if stack.fresh_trait_pred.has_erased_regions() {
|
|
result = result.max(EvaluatedToOkModuloRegions);
|
|
}
|
|
|
|
Ok(result)
|
|
}
|
|
|
|
fn check_evaluation_cache(
|
|
&self,
|
|
param_env: ty::ParamEnv<'tcx>,
|
|
trait_pred: ty::PolyTraitPredicate<'tcx>,
|
|
) -> Option<EvaluationResult> {
|
|
let infcx = self.infcx;
|
|
let tcx = infcx.tcx;
|
|
if self.can_use_global_caches(param_env, trait_pred) {
|
|
let key = (infcx.typing_env(param_env), trait_pred);
|
|
if let Some(res) = tcx.evaluation_cache.get(&key, tcx) {
|
|
Some(res)
|
|
} else {
|
|
debug_assert_eq!(infcx.evaluation_cache.get(&(param_env, trait_pred), tcx), None);
|
|
None
|
|
}
|
|
} else {
|
|
self.infcx.evaluation_cache.get(&(param_env, trait_pred), tcx)
|
|
}
|
|
}
|
|
|
|
fn insert_evaluation_cache(
|
|
&mut self,
|
|
param_env: ty::ParamEnv<'tcx>,
|
|
trait_pred: ty::PolyTraitPredicate<'tcx>,
|
|
dep_node: DepNodeIndex,
|
|
result: EvaluationResult,
|
|
) {
|
|
// Avoid caching results that depend on more than just the trait-ref
|
|
// - the stack can create recursion.
|
|
if result.is_stack_dependent() {
|
|
return;
|
|
}
|
|
|
|
let infcx = self.infcx;
|
|
let tcx = infcx.tcx;
|
|
if self.can_use_global_caches(param_env, trait_pred) {
|
|
debug!(?trait_pred, ?result, "insert_evaluation_cache global");
|
|
// This may overwrite the cache with the same value
|
|
tcx.evaluation_cache.insert(
|
|
(infcx.typing_env(param_env), trait_pred),
|
|
dep_node,
|
|
result,
|
|
);
|
|
return;
|
|
} else {
|
|
debug!(?trait_pred, ?result, "insert_evaluation_cache local");
|
|
self.infcx.evaluation_cache.insert((param_env, trait_pred), dep_node, result);
|
|
}
|
|
}
|
|
|
|
fn check_recursion_depth<T>(
|
|
&self,
|
|
depth: usize,
|
|
error_obligation: &Obligation<'tcx, T>,
|
|
) -> Result<(), OverflowError>
|
|
where
|
|
T: Upcast<TyCtxt<'tcx>, ty::Predicate<'tcx>> + Clone,
|
|
{
|
|
if !self.infcx.tcx.recursion_limit().value_within_limit(depth) {
|
|
match self.query_mode {
|
|
TraitQueryMode::Standard => {
|
|
if let Some(e) = self.infcx.tainted_by_errors() {
|
|
return Err(OverflowError::Error(e));
|
|
}
|
|
self.infcx.err_ctxt().report_overflow_obligation(error_obligation, true);
|
|
}
|
|
TraitQueryMode::Canonical => {
|
|
return Err(OverflowError::Canonical);
|
|
}
|
|
}
|
|
}
|
|
Ok(())
|
|
}
|
|
|
|
/// Checks that the recursion limit has not been exceeded.
|
|
///
|
|
/// The weird return type of this function allows it to be used with the `try` (`?`)
|
|
/// operator within certain functions.
|
|
#[inline(always)]
|
|
fn check_recursion_limit<T: Display + TypeFoldable<TyCtxt<'tcx>>, V>(
|
|
&self,
|
|
obligation: &Obligation<'tcx, T>,
|
|
error_obligation: &Obligation<'tcx, V>,
|
|
) -> Result<(), OverflowError>
|
|
where
|
|
V: Upcast<TyCtxt<'tcx>, ty::Predicate<'tcx>> + Clone,
|
|
{
|
|
self.check_recursion_depth(obligation.recursion_depth, error_obligation)
|
|
}
|
|
|
|
fn in_task<OP, R>(&mut self, op: OP) -> (R, DepNodeIndex)
|
|
where
|
|
OP: FnOnce(&mut Self) -> R,
|
|
{
|
|
self.tcx().dep_graph.with_anon_task(self.tcx(), dep_kinds::TraitSelect, || op(self))
|
|
}
|
|
|
|
/// filter_impls filters candidates that have a positive impl for a negative
|
|
/// goal and a negative impl for a positive goal
|
|
#[instrument(level = "debug", skip(self, candidates))]
|
|
fn filter_impls(
|
|
&mut self,
|
|
candidates: Vec<SelectionCandidate<'tcx>>,
|
|
obligation: &PolyTraitObligation<'tcx>,
|
|
) -> Vec<SelectionCandidate<'tcx>> {
|
|
trace!("{candidates:#?}");
|
|
let tcx = self.tcx();
|
|
let mut result = Vec::with_capacity(candidates.len());
|
|
|
|
for candidate in candidates {
|
|
if let ImplCandidate(def_id) = candidate {
|
|
match (tcx.impl_polarity(def_id), obligation.polarity()) {
|
|
(ty::ImplPolarity::Reservation, _)
|
|
| (ty::ImplPolarity::Positive, ty::PredicatePolarity::Positive)
|
|
| (ty::ImplPolarity::Negative, ty::PredicatePolarity::Negative) => {
|
|
result.push(candidate);
|
|
}
|
|
_ => {}
|
|
}
|
|
} else {
|
|
result.push(candidate);
|
|
}
|
|
}
|
|
|
|
trace!("{result:#?}");
|
|
result
|
|
}
|
|
|
|
/// filter_reservation_impls filter reservation impl for any goal as ambiguous
|
|
#[instrument(level = "debug", skip(self))]
|
|
fn filter_reservation_impls(
|
|
&mut self,
|
|
candidate: SelectionCandidate<'tcx>,
|
|
) -> SelectionResult<'tcx, SelectionCandidate<'tcx>> {
|
|
let tcx = self.tcx();
|
|
// Treat reservation impls as ambiguity.
|
|
if let ImplCandidate(def_id) = candidate {
|
|
if let ty::ImplPolarity::Reservation = tcx.impl_polarity(def_id) {
|
|
if let Some(intercrate_ambiguity_clauses) = &mut self.intercrate_ambiguity_causes {
|
|
let message = tcx
|
|
.get_attr(def_id, sym::rustc_reservation_impl)
|
|
.and_then(|a| a.value_str());
|
|
if let Some(message) = message {
|
|
debug!(
|
|
"filter_reservation_impls: \
|
|
reservation impl ambiguity on {:?}",
|
|
def_id
|
|
);
|
|
intercrate_ambiguity_clauses
|
|
.insert(IntercrateAmbiguityCause::ReservationImpl { message });
|
|
}
|
|
}
|
|
return Ok(None);
|
|
}
|
|
}
|
|
Ok(Some(candidate))
|
|
}
|
|
|
|
fn is_knowable<'o>(&mut self, stack: &TraitObligationStack<'o, 'tcx>) -> Result<(), Conflict> {
|
|
let obligation = &stack.obligation;
|
|
match self.infcx.typing_mode() {
|
|
TypingMode::Coherence => {}
|
|
TypingMode::Analysis { .. }
|
|
| TypingMode::PostBorrowckAnalysis { .. }
|
|
| TypingMode::PostAnalysis => return Ok(()),
|
|
}
|
|
|
|
debug!("is_knowable()");
|
|
|
|
let predicate = self.infcx.resolve_vars_if_possible(obligation.predicate);
|
|
|
|
// Okay to skip binder because of the nature of the
|
|
// trait-ref-is-knowable check, which does not care about
|
|
// bound regions.
|
|
let trait_ref = predicate.skip_binder().trait_ref;
|
|
|
|
coherence::trait_ref_is_knowable(self.infcx, trait_ref, |ty| Ok::<_, !>(ty)).into_ok()
|
|
}
|
|
|
|
/// Returns `true` if the global caches can be used.
|
|
fn can_use_global_caches(
|
|
&self,
|
|
param_env: ty::ParamEnv<'tcx>,
|
|
pred: ty::PolyTraitPredicate<'tcx>,
|
|
) -> bool {
|
|
// If there are any inference variables in the `ParamEnv`, then we
|
|
// always use a cache local to this particular scope. Otherwise, we
|
|
// switch to a global cache.
|
|
if param_env.has_infer() || pred.has_infer() {
|
|
return false;
|
|
}
|
|
|
|
match self.infcx.typing_mode() {
|
|
// Avoid using the global cache during coherence and just rely
|
|
// on the local cache. It is really just a simplification to
|
|
// avoid us having to fear that coherence results "pollute"
|
|
// the master cache. Since coherence executes pretty quickly,
|
|
// it's not worth going to more trouble to increase the
|
|
// hit-rate, I don't think.
|
|
TypingMode::Coherence => false,
|
|
// Avoid using the global cache when we're defining opaque types
|
|
// as their hidden type may impact the result of candidate selection.
|
|
//
|
|
// HACK: This is still theoretically unsound. Goals can indirectly rely
|
|
// on opaques in the defining scope, and it's easier to do so with TAIT.
|
|
// However, if we disqualify *all* goals from being cached, perf suffers.
|
|
// This is likely fixed by better caching in general in the new solver.
|
|
// See: <https://github.com/rust-lang/rust/issues/132064>.
|
|
TypingMode::Analysis { defining_opaque_types } => {
|
|
defining_opaque_types.is_empty() || !pred.has_opaque_types()
|
|
}
|
|
// The hidden types of `defined_opaque_types` is not local to the current
|
|
// inference context, so we can freely move this to the global cache.
|
|
TypingMode::PostBorrowckAnalysis { .. } => true,
|
|
// The global cache is only used if there are no opaque types in
|
|
// the defining scope or we're outside of analysis.
|
|
//
|
|
// FIXME(#132279): This is still incorrect as we treat opaque types
|
|
// and default associated items differently between these two modes.
|
|
TypingMode::PostAnalysis => true,
|
|
}
|
|
}
|
|
|
|
fn check_candidate_cache(
|
|
&mut self,
|
|
param_env: ty::ParamEnv<'tcx>,
|
|
cache_fresh_trait_pred: ty::PolyTraitPredicate<'tcx>,
|
|
) -> Option<SelectionResult<'tcx, SelectionCandidate<'tcx>>> {
|
|
let infcx = self.infcx;
|
|
let tcx = infcx.tcx;
|
|
let pred = cache_fresh_trait_pred.skip_binder();
|
|
|
|
if self.can_use_global_caches(param_env, cache_fresh_trait_pred) {
|
|
if let Some(res) = tcx.selection_cache.get(&(infcx.typing_env(param_env), pred), tcx) {
|
|
return Some(res);
|
|
} else if cfg!(debug_assertions) {
|
|
match infcx.selection_cache.get(&(param_env, pred), tcx) {
|
|
None | Some(Err(Overflow(OverflowError::Canonical))) => {}
|
|
res => bug!("unexpected local cache result: {res:?}"),
|
|
}
|
|
}
|
|
}
|
|
|
|
// Subtle: we need to check the local cache even if we're able to use the
|
|
// global cache as we don't cache overflow in the global cache but need to
|
|
// cache it as otherwise rustdoc hangs when compiling diesel.
|
|
infcx.selection_cache.get(&(param_env, pred), tcx)
|
|
}
|
|
|
|
/// Determines whether can we safely cache the result
|
|
/// of selecting an obligation. This is almost always `true`,
|
|
/// except when dealing with certain `ParamCandidate`s.
|
|
///
|
|
/// Ordinarily, a `ParamCandidate` will contain no inference variables,
|
|
/// since it was usually produced directly from a `DefId`. However,
|
|
/// certain cases (currently only librustdoc's blanket impl finder),
|
|
/// a `ParamEnv` may be explicitly constructed with inference types.
|
|
/// When this is the case, we do *not* want to cache the resulting selection
|
|
/// candidate. This is due to the fact that it might not always be possible
|
|
/// to equate the obligation's trait ref and the candidate's trait ref,
|
|
/// if more constraints end up getting added to an inference variable.
|
|
///
|
|
/// Because of this, we always want to re-run the full selection
|
|
/// process for our obligation the next time we see it, since
|
|
/// we might end up picking a different `SelectionCandidate` (or none at all).
|
|
fn can_cache_candidate(
|
|
&self,
|
|
result: &SelectionResult<'tcx, SelectionCandidate<'tcx>>,
|
|
) -> bool {
|
|
match result {
|
|
Ok(Some(SelectionCandidate::ParamCandidate(trait_ref))) => !trait_ref.has_infer(),
|
|
_ => true,
|
|
}
|
|
}
|
|
|
|
#[instrument(skip(self, param_env, cache_fresh_trait_pred, dep_node), level = "debug")]
|
|
fn insert_candidate_cache(
|
|
&mut self,
|
|
param_env: ty::ParamEnv<'tcx>,
|
|
cache_fresh_trait_pred: ty::PolyTraitPredicate<'tcx>,
|
|
dep_node: DepNodeIndex,
|
|
candidate: SelectionResult<'tcx, SelectionCandidate<'tcx>>,
|
|
) {
|
|
let infcx = self.infcx;
|
|
let tcx = infcx.tcx;
|
|
let pred = cache_fresh_trait_pred.skip_binder();
|
|
|
|
if !self.can_cache_candidate(&candidate) {
|
|
debug!(?pred, ?candidate, "insert_candidate_cache - candidate is not cacheable");
|
|
return;
|
|
}
|
|
|
|
if self.can_use_global_caches(param_env, cache_fresh_trait_pred) {
|
|
if let Err(Overflow(OverflowError::Canonical)) = candidate {
|
|
// Don't cache overflow globally; we only produce this in certain modes.
|
|
} else {
|
|
debug!(?pred, ?candidate, "insert_candidate_cache global");
|
|
debug_assert!(!candidate.has_infer());
|
|
|
|
// This may overwrite the cache with the same value.
|
|
tcx.selection_cache.insert(
|
|
(infcx.typing_env(param_env), pred),
|
|
dep_node,
|
|
candidate,
|
|
);
|
|
return;
|
|
}
|
|
}
|
|
|
|
debug!(?pred, ?candidate, "insert_candidate_cache local");
|
|
self.infcx.selection_cache.insert((param_env, pred), dep_node, candidate);
|
|
}
|
|
|
|
/// Looks at the item bounds of the projection or opaque type.
|
|
/// If this is a nested rigid projection, such as
|
|
/// `<<T as Tr1>::Assoc as Tr2>::Assoc`, consider the item bounds
|
|
/// on both `Tr1::Assoc` and `Tr2::Assoc`, since we may encounter
|
|
/// relative bounds on both via the `associated_type_bounds` feature.
|
|
pub(super) fn for_each_item_bound<T>(
|
|
&mut self,
|
|
mut self_ty: Ty<'tcx>,
|
|
mut for_each: impl FnMut(&mut Self, ty::Clause<'tcx>, usize) -> ControlFlow<T, ()>,
|
|
on_ambiguity: impl FnOnce(),
|
|
) -> ControlFlow<T, ()> {
|
|
let mut idx = 0;
|
|
let mut in_parent_alias_type = false;
|
|
|
|
loop {
|
|
let (kind, alias_ty) = match *self_ty.kind() {
|
|
ty::Alias(kind @ (ty::Projection | ty::Opaque), alias_ty) => (kind, alias_ty),
|
|
ty::Infer(ty::TyVar(_)) => {
|
|
on_ambiguity();
|
|
return ControlFlow::Continue(());
|
|
}
|
|
_ => return ControlFlow::Continue(()),
|
|
};
|
|
|
|
// HACK: On subsequent recursions, we only care about bounds that don't
|
|
// share the same type as `self_ty`. This is because for truly rigid
|
|
// projections, we will never be able to equate, e.g. `<T as Tr>::A`
|
|
// with `<<T as Tr>::A as Tr>::A`.
|
|
let relevant_bounds = if in_parent_alias_type {
|
|
self.tcx().item_non_self_bounds(alias_ty.def_id)
|
|
} else {
|
|
self.tcx().item_self_bounds(alias_ty.def_id)
|
|
};
|
|
|
|
for bound in relevant_bounds.instantiate(self.tcx(), alias_ty.args) {
|
|
for_each(self, bound, idx)?;
|
|
idx += 1;
|
|
}
|
|
|
|
if kind == ty::Projection {
|
|
self_ty = alias_ty.self_ty();
|
|
} else {
|
|
return ControlFlow::Continue(());
|
|
}
|
|
|
|
in_parent_alias_type = true;
|
|
}
|
|
}
|
|
|
|
/// Equates the trait in `obligation` with trait bound. If the two traits
|
|
/// can be equated and the normalized trait bound doesn't contain inference
|
|
/// variables or placeholders, the normalized bound is returned.
|
|
fn match_normalize_trait_ref(
|
|
&mut self,
|
|
obligation: &PolyTraitObligation<'tcx>,
|
|
placeholder_trait_ref: ty::TraitRef<'tcx>,
|
|
trait_bound: ty::PolyTraitRef<'tcx>,
|
|
) -> Result<Option<ty::TraitRef<'tcx>>, ()> {
|
|
debug_assert!(!placeholder_trait_ref.has_escaping_bound_vars());
|
|
if placeholder_trait_ref.def_id != trait_bound.def_id() {
|
|
// Avoid unnecessary normalization
|
|
return Err(());
|
|
}
|
|
|
|
let trait_bound = self.infcx.instantiate_binder_with_fresh_vars(
|
|
obligation.cause.span,
|
|
HigherRankedType,
|
|
trait_bound,
|
|
);
|
|
let Normalized { value: trait_bound, obligations: _ } = ensure_sufficient_stack(|| {
|
|
normalize_with_depth(
|
|
self,
|
|
obligation.param_env,
|
|
obligation.cause.clone(),
|
|
obligation.recursion_depth + 1,
|
|
trait_bound,
|
|
)
|
|
});
|
|
self.infcx
|
|
.at(&obligation.cause, obligation.param_env)
|
|
.eq(DefineOpaqueTypes::No, placeholder_trait_ref, trait_bound)
|
|
.map(|InferOk { obligations: _, value: () }| {
|
|
// This method is called within a probe, so we can't have
|
|
// inference variables and placeholders escape.
|
|
if !trait_bound.has_infer() && !trait_bound.has_placeholders() {
|
|
Some(trait_bound)
|
|
} else {
|
|
None
|
|
}
|
|
})
|
|
.map_err(|_| ())
|
|
}
|
|
|
|
fn where_clause_may_apply<'o>(
|
|
&mut self,
|
|
stack: &TraitObligationStack<'o, 'tcx>,
|
|
where_clause_trait_ref: ty::PolyTraitRef<'tcx>,
|
|
) -> Result<EvaluationResult, OverflowError> {
|
|
self.evaluation_probe(|this| {
|
|
match this.match_where_clause_trait_ref(stack.obligation, where_clause_trait_ref) {
|
|
Ok(obligations) => this.evaluate_predicates_recursively(stack.list(), obligations),
|
|
Err(()) => Ok(EvaluatedToErr),
|
|
}
|
|
})
|
|
}
|
|
|
|
/// Return `Yes` if the obligation's predicate type applies to the env_predicate, and
|
|
/// `No` if it does not. Return `Ambiguous` in the case that the projection type is a GAT,
|
|
/// and applying this env_predicate constrains any of the obligation's GAT parameters.
|
|
///
|
|
/// This behavior is a somewhat of a hack to prevent over-constraining inference variables
|
|
/// in cases like #91762.
|
|
pub(super) fn match_projection_projections(
|
|
&mut self,
|
|
obligation: &ProjectionTermObligation<'tcx>,
|
|
env_predicate: PolyProjectionPredicate<'tcx>,
|
|
potentially_unnormalized_candidates: bool,
|
|
) -> ProjectionMatchesProjection {
|
|
debug_assert_eq!(obligation.predicate.def_id, env_predicate.item_def_id());
|
|
|
|
let mut nested_obligations = PredicateObligations::new();
|
|
let infer_predicate = self.infcx.instantiate_binder_with_fresh_vars(
|
|
obligation.cause.span,
|
|
BoundRegionConversionTime::HigherRankedType,
|
|
env_predicate,
|
|
);
|
|
let infer_projection = if potentially_unnormalized_candidates {
|
|
ensure_sufficient_stack(|| {
|
|
normalize_with_depth_to(
|
|
self,
|
|
obligation.param_env,
|
|
obligation.cause.clone(),
|
|
obligation.recursion_depth + 1,
|
|
infer_predicate.projection_term,
|
|
&mut nested_obligations,
|
|
)
|
|
})
|
|
} else {
|
|
infer_predicate.projection_term
|
|
};
|
|
|
|
let is_match = self
|
|
.infcx
|
|
.at(&obligation.cause, obligation.param_env)
|
|
.eq(DefineOpaqueTypes::No, obligation.predicate, infer_projection)
|
|
.is_ok_and(|InferOk { obligations, value: () }| {
|
|
self.evaluate_predicates_recursively(
|
|
TraitObligationStackList::empty(&ProvisionalEvaluationCache::default()),
|
|
nested_obligations.into_iter().chain(obligations),
|
|
)
|
|
.is_ok_and(|res| res.may_apply())
|
|
});
|
|
|
|
if is_match {
|
|
let generics = self.tcx().generics_of(obligation.predicate.def_id);
|
|
// FIXME(generic-associated-types): Addresses aggressive inference in #92917.
|
|
// If this type is a GAT, and of the GAT args resolve to something new,
|
|
// that means that we must have newly inferred something about the GAT.
|
|
// We should give up in that case.
|
|
// FIXME(generic-associated-types): This only detects one layer of inference,
|
|
// which is probably not what we actually want, but fixing it causes some ambiguity:
|
|
// <https://github.com/rust-lang/rust/issues/125196>.
|
|
if !generics.is_own_empty()
|
|
&& obligation.predicate.args[generics.parent_count..].iter().any(|&p| {
|
|
p.has_non_region_infer()
|
|
&& match p.unpack() {
|
|
ty::GenericArgKind::Const(ct) => {
|
|
self.infcx.shallow_resolve_const(ct) != ct
|
|
}
|
|
ty::GenericArgKind::Type(ty) => self.infcx.shallow_resolve(ty) != ty,
|
|
ty::GenericArgKind::Lifetime(_) => false,
|
|
}
|
|
})
|
|
{
|
|
ProjectionMatchesProjection::Ambiguous
|
|
} else {
|
|
ProjectionMatchesProjection::Yes
|
|
}
|
|
} else {
|
|
ProjectionMatchesProjection::No
|
|
}
|
|
}
|
|
}
|
|
|
|
/// ## Winnowing
|
|
///
|
|
/// Winnowing is the process of attempting to resolve ambiguity by
|
|
/// probing further. During the winnowing process, we unify all
|
|
/// type variables and then we also attempt to evaluate recursive
|
|
/// bounds to see if they are satisfied.
|
|
impl<'tcx> SelectionContext<'_, 'tcx> {
|
|
/// If there are multiple ways to prove a trait goal, we make some
|
|
/// *fairly arbitrary* choices about which candidate is actually used.
|
|
///
|
|
/// For more details, look at the implementation of this method :)
|
|
#[instrument(level = "debug", skip(self), ret)]
|
|
fn winnow_candidates(
|
|
&mut self,
|
|
has_non_region_infer: bool,
|
|
mut candidates: Vec<EvaluatedCandidate<'tcx>>,
|
|
) -> Option<SelectionCandidate<'tcx>> {
|
|
if candidates.len() == 1 {
|
|
return Some(candidates.pop().unwrap().candidate);
|
|
}
|
|
|
|
// We prefer trivial builtin candidates, i.e. builtin impls without any nested
|
|
// requirements, over all others. This is a fix for #53123 and prevents winnowing
|
|
// from accidentally extending the lifetime of a variable.
|
|
let mut trivial_builtin = candidates
|
|
.iter()
|
|
.filter(|c| matches!(c.candidate, BuiltinCandidate { has_nested: false }));
|
|
if let Some(_trivial) = trivial_builtin.next() {
|
|
// There should only ever be a single trivial builtin candidate
|
|
// as they would otherwise overlap.
|
|
debug_assert_eq!(trivial_builtin.next(), None);
|
|
return Some(BuiltinCandidate { has_nested: false });
|
|
}
|
|
|
|
// Before we consider where-bounds, we have to deduplicate them here and also
|
|
// drop where-bounds in case the same where-bound exists without bound vars.
|
|
// This is necessary as elaborating super-trait bounds may result in duplicates.
|
|
'search_victim: loop {
|
|
for (i, this) in candidates.iter().enumerate() {
|
|
let ParamCandidate(this) = this.candidate else { continue };
|
|
for (j, other) in candidates.iter().enumerate() {
|
|
if i == j {
|
|
continue;
|
|
}
|
|
|
|
let ParamCandidate(other) = other.candidate else { continue };
|
|
if this == other {
|
|
candidates.remove(j);
|
|
continue 'search_victim;
|
|
}
|
|
|
|
if this.skip_binder().trait_ref == other.skip_binder().trait_ref
|
|
&& this.skip_binder().polarity == other.skip_binder().polarity
|
|
&& !this.skip_binder().trait_ref.has_escaping_bound_vars()
|
|
{
|
|
candidates.remove(j);
|
|
continue 'search_victim;
|
|
}
|
|
}
|
|
}
|
|
|
|
break;
|
|
}
|
|
|
|
// The next highest priority is for non-global where-bounds. However, while we don't
|
|
// prefer global where-clauses here, we do bail with ambiguity when encountering both
|
|
// a global and a non-global where-clause.
|
|
//
|
|
// Our handling of where-bounds is generally fairly messy but necessary for backwards
|
|
// compatibility, see #50825 for why we need to handle global where-bounds like this.
|
|
let is_global = |c: ty::PolyTraitPredicate<'tcx>| c.is_global() && !c.has_bound_vars();
|
|
let param_candidates = candidates
|
|
.iter()
|
|
.filter_map(|c| if let ParamCandidate(p) = c.candidate { Some(p) } else { None });
|
|
let mut has_global_bounds = false;
|
|
let mut param_candidate = None;
|
|
for c in param_candidates {
|
|
if is_global(c) {
|
|
has_global_bounds = true;
|
|
} else if param_candidate.replace(c).is_some() {
|
|
// Ambiguity, two potentially different where-clauses
|
|
return None;
|
|
}
|
|
}
|
|
if let Some(predicate) = param_candidate {
|
|
// Ambiguity, a global and a non-global where-bound.
|
|
if has_global_bounds {
|
|
return None;
|
|
} else {
|
|
return Some(ParamCandidate(predicate));
|
|
}
|
|
}
|
|
|
|
// Prefer alias-bounds over blanket impls for rigid associated types. This is
|
|
// fairly arbitrary but once again necessary for backwards compatibility.
|
|
// If there are multiple applicable candidates which don't affect type inference,
|
|
// choose the one with the lowest index.
|
|
let alias_bound = candidates
|
|
.iter()
|
|
.filter_map(|c| if let ProjectionCandidate(i) = c.candidate { Some(i) } else { None })
|
|
.try_reduce(|c1, c2| if has_non_region_infer { None } else { Some(c1.min(c2)) });
|
|
match alias_bound {
|
|
Some(Some(index)) => return Some(ProjectionCandidate(index)),
|
|
Some(None) => {}
|
|
None => return None,
|
|
}
|
|
|
|
// Need to prioritize builtin trait object impls as `<dyn Any as Any>::type_id`
|
|
// should use the vtable method and not the method provided by the user-defined
|
|
// impl `impl<T: ?Sized> Any for T { .. }`. This really shouldn't exist but is
|
|
// necessary due to #57893. We again arbitrarily prefer the applicable candidate
|
|
// with the lowest index.
|
|
let object_bound = candidates
|
|
.iter()
|
|
.filter_map(|c| if let ObjectCandidate(i) = c.candidate { Some(i) } else { None })
|
|
.try_reduce(|c1, c2| if has_non_region_infer { None } else { Some(c1.min(c2)) });
|
|
match object_bound {
|
|
Some(Some(index)) => return Some(ObjectCandidate(index)),
|
|
Some(None) => {}
|
|
None => return None,
|
|
}
|
|
// Same for upcasting.
|
|
let upcast_bound = candidates
|
|
.iter()
|
|
.filter_map(|c| {
|
|
if let TraitUpcastingUnsizeCandidate(i) = c.candidate { Some(i) } else { None }
|
|
})
|
|
.try_reduce(|c1, c2| if has_non_region_infer { None } else { Some(c1.min(c2)) });
|
|
match upcast_bound {
|
|
Some(Some(index)) => return Some(TraitUpcastingUnsizeCandidate(index)),
|
|
Some(None) => {}
|
|
None => return None,
|
|
}
|
|
|
|
// Finally, handle overlapping user-written impls.
|
|
let impls = candidates.iter().filter_map(|c| {
|
|
if let ImplCandidate(def_id) = c.candidate {
|
|
Some((def_id, c.evaluation))
|
|
} else {
|
|
None
|
|
}
|
|
});
|
|
let mut impl_candidate = None;
|
|
for c in impls {
|
|
if let Some(prev) = impl_candidate.replace(c) {
|
|
if self.prefer_lhs_over_victim(has_non_region_infer, c, prev) {
|
|
// Ok, prefer `c` over the previous entry
|
|
} else if self.prefer_lhs_over_victim(has_non_region_infer, prev, c) {
|
|
// Ok, keep `prev` instead of the new entry
|
|
impl_candidate = Some(prev);
|
|
} else {
|
|
// Ambiguity, two potentially different where-clauses
|
|
return None;
|
|
}
|
|
}
|
|
}
|
|
if let Some((def_id, _evaluation)) = impl_candidate {
|
|
// Don't use impl candidates which overlap with other candidates.
|
|
// This should pretty much only ever happen with malformed impls.
|
|
if candidates.iter().all(|c| match c.candidate {
|
|
BuiltinCandidate { has_nested: _ }
|
|
| TransmutabilityCandidate
|
|
| AutoImplCandidate
|
|
| ClosureCandidate { .. }
|
|
| AsyncClosureCandidate
|
|
| AsyncFnKindHelperCandidate
|
|
| CoroutineCandidate
|
|
| FutureCandidate
|
|
| IteratorCandidate
|
|
| AsyncIteratorCandidate
|
|
| FnPointerCandidate
|
|
| TraitAliasCandidate
|
|
| TraitUpcastingUnsizeCandidate(_)
|
|
| BuiltinObjectCandidate
|
|
| BuiltinUnsizeCandidate
|
|
| BikeshedGuaranteedNoDropCandidate => false,
|
|
// Non-global param candidates have already been handled, global
|
|
// where-bounds get ignored.
|
|
ParamCandidate(_) | ImplCandidate(_) => true,
|
|
ProjectionCandidate(_) | ObjectCandidate(_) => unreachable!(),
|
|
}) {
|
|
return Some(ImplCandidate(def_id));
|
|
} else {
|
|
return None;
|
|
}
|
|
}
|
|
|
|
if candidates.len() == 1 {
|
|
Some(candidates.pop().unwrap().candidate)
|
|
} else {
|
|
// Also try ignoring all global where-bounds and check whether we end
|
|
// with a unique candidate in this case.
|
|
let mut not_a_global_where_bound = candidates
|
|
.into_iter()
|
|
.filter(|c| !matches!(c.candidate, ParamCandidate(p) if is_global(p)));
|
|
not_a_global_where_bound
|
|
.next()
|
|
.map(|c| c.candidate)
|
|
.filter(|_| not_a_global_where_bound.next().is_none())
|
|
}
|
|
}
|
|
|
|
fn prefer_lhs_over_victim(
|
|
&self,
|
|
has_non_region_infer: bool,
|
|
(lhs, lhs_evaluation): (DefId, EvaluationResult),
|
|
(victim, victim_evaluation): (DefId, EvaluationResult),
|
|
) -> bool {
|
|
let tcx = self.tcx();
|
|
// See if we can toss out `victim` based on specialization.
|
|
//
|
|
// While this requires us to know *for sure* that the `lhs` impl applies
|
|
// we still use modulo regions here. This is fine as specialization currently
|
|
// assumes that specializing impls have to be always applicable, meaning that
|
|
// the only allowed region constraints may be constraints also present on the default impl.
|
|
if lhs_evaluation.must_apply_modulo_regions() {
|
|
if tcx.specializes((lhs, victim)) {
|
|
return true;
|
|
}
|
|
}
|
|
|
|
match tcx.impls_are_allowed_to_overlap(lhs, victim) {
|
|
// For #33140 the impl headers must be exactly equal, the trait must not have
|
|
// any associated items and there are no where-clauses.
|
|
//
|
|
// We can just arbitrarily drop one of the impls.
|
|
Some(ty::ImplOverlapKind::FutureCompatOrderDepTraitObjects) => {
|
|
assert_eq!(lhs_evaluation, victim_evaluation);
|
|
true
|
|
}
|
|
// For candidates which already reference errors it doesn't really
|
|
// matter what we do 🤷
|
|
Some(ty::ImplOverlapKind::Permitted { marker: false }) => {
|
|
lhs_evaluation.must_apply_considering_regions()
|
|
}
|
|
Some(ty::ImplOverlapKind::Permitted { marker: true }) => {
|
|
// Subtle: If the predicate we are evaluating has inference
|
|
// variables, do *not* allow discarding candidates due to
|
|
// marker trait impls.
|
|
//
|
|
// Without this restriction, we could end up accidentally
|
|
// constraining inference variables based on an arbitrarily
|
|
// chosen trait impl.
|
|
//
|
|
// Imagine we have the following code:
|
|
//
|
|
// ```rust
|
|
// #[marker] trait MyTrait {}
|
|
// impl MyTrait for u8 {}
|
|
// impl MyTrait for bool {}
|
|
// ```
|
|
//
|
|
// And we are evaluating the predicate `<_#0t as MyTrait>`.
|
|
//
|
|
// During selection, we will end up with one candidate for each
|
|
// impl of `MyTrait`. If we were to discard one impl in favor
|
|
// of the other, we would be left with one candidate, causing
|
|
// us to "successfully" select the predicate, unifying
|
|
// _#0t with (for example) `u8`.
|
|
//
|
|
// However, we have no reason to believe that this unification
|
|
// is correct - we've essentially just picked an arbitrary
|
|
// *possibility* for _#0t, and required that this be the *only*
|
|
// possibility.
|
|
//
|
|
// Eventually, we will either:
|
|
// 1) Unify all inference variables in the predicate through
|
|
// some other means (e.g. type-checking of a function). We will
|
|
// then be in a position to drop marker trait candidates
|
|
// without constraining inference variables (since there are
|
|
// none left to constrain)
|
|
// 2) Be left with some unconstrained inference variables. We
|
|
// will then correctly report an inference error, since the
|
|
// existence of multiple marker trait impls tells us nothing
|
|
// about which one should actually apply.
|
|
!has_non_region_infer && lhs_evaluation.must_apply_considering_regions()
|
|
}
|
|
None => false,
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<'tcx> SelectionContext<'_, 'tcx> {
|
|
fn sized_conditions(
|
|
&mut self,
|
|
obligation: &PolyTraitObligation<'tcx>,
|
|
) -> BuiltinImplConditions<'tcx> {
|
|
use self::BuiltinImplConditions::{Ambiguous, None, Where};
|
|
|
|
// NOTE: binder moved to (*)
|
|
let self_ty = self.infcx.shallow_resolve(obligation.predicate.skip_binder().self_ty());
|
|
|
|
match self_ty.kind() {
|
|
ty::Infer(ty::IntVar(_) | ty::FloatVar(_))
|
|
| ty::Uint(_)
|
|
| ty::Int(_)
|
|
| ty::Bool
|
|
| ty::Float(_)
|
|
| ty::FnDef(..)
|
|
| ty::FnPtr(..)
|
|
| ty::RawPtr(..)
|
|
| ty::Char
|
|
| ty::Ref(..)
|
|
| ty::Coroutine(..)
|
|
| ty::CoroutineWitness(..)
|
|
| ty::Array(..)
|
|
| ty::Closure(..)
|
|
| ty::CoroutineClosure(..)
|
|
| ty::Never
|
|
| ty::Dynamic(_, _, ty::DynStar)
|
|
| ty::Error(_) => {
|
|
// safe for everything
|
|
Where(ty::Binder::dummy(Vec::new()))
|
|
}
|
|
|
|
ty::Str | ty::Slice(_) | ty::Dynamic(..) | ty::Foreign(..) => None,
|
|
|
|
ty::Tuple(tys) => Where(
|
|
obligation.predicate.rebind(tys.last().map_or_else(Vec::new, |&last| vec![last])),
|
|
),
|
|
|
|
ty::Pat(ty, _) => Where(obligation.predicate.rebind(vec![*ty])),
|
|
|
|
ty::Adt(def, args) => {
|
|
if let Some(sized_crit) = def.sized_constraint(self.tcx()) {
|
|
// (*) binder moved here
|
|
Where(
|
|
obligation.predicate.rebind(vec![sized_crit.instantiate(self.tcx(), args)]),
|
|
)
|
|
} else {
|
|
Where(ty::Binder::dummy(Vec::new()))
|
|
}
|
|
}
|
|
|
|
// FIXME(unsafe_binders): This binder needs to be squashed
|
|
ty::UnsafeBinder(binder_ty) => Where(binder_ty.map_bound(|ty| vec![ty])),
|
|
|
|
ty::Alias(..) | ty::Param(_) | ty::Placeholder(..) => None,
|
|
ty::Infer(ty::TyVar(_)) => Ambiguous,
|
|
|
|
// We can make this an ICE if/once we actually instantiate the trait obligation eagerly.
|
|
ty::Bound(..) => None,
|
|
|
|
ty::Infer(ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)) => {
|
|
bug!("asked to assemble builtin bounds of unexpected type: {:?}", self_ty);
|
|
}
|
|
}
|
|
}
|
|
|
|
fn copy_clone_conditions(
|
|
&mut self,
|
|
obligation: &PolyTraitObligation<'tcx>,
|
|
) -> BuiltinImplConditions<'tcx> {
|
|
// NOTE: binder moved to (*)
|
|
let self_ty = self.infcx.shallow_resolve(obligation.predicate.skip_binder().self_ty());
|
|
|
|
use self::BuiltinImplConditions::{Ambiguous, None, Where};
|
|
|
|
match *self_ty.kind() {
|
|
ty::FnDef(..) | ty::FnPtr(..) | ty::Error(_) => Where(ty::Binder::dummy(Vec::new())),
|
|
|
|
ty::Uint(_)
|
|
| ty::Int(_)
|
|
| ty::Infer(ty::IntVar(_) | ty::FloatVar(_))
|
|
| ty::Bool
|
|
| ty::Float(_)
|
|
| ty::Char
|
|
| ty::RawPtr(..)
|
|
| ty::Never
|
|
| ty::Ref(_, _, hir::Mutability::Not)
|
|
| ty::Array(..) => {
|
|
// Implementations provided in libcore
|
|
None
|
|
}
|
|
|
|
// FIXME(unsafe_binder): Should we conditionally
|
|
// (i.e. universally) implement copy/clone?
|
|
ty::UnsafeBinder(_) => None,
|
|
|
|
ty::Dynamic(..)
|
|
| ty::Str
|
|
| ty::Slice(..)
|
|
| ty::Foreign(..)
|
|
| ty::Ref(_, _, hir::Mutability::Mut) => None,
|
|
|
|
ty::Tuple(tys) => {
|
|
// (*) binder moved here
|
|
Where(obligation.predicate.rebind(tys.iter().collect()))
|
|
}
|
|
|
|
ty::Pat(ty, _) => {
|
|
// (*) binder moved here
|
|
Where(obligation.predicate.rebind(vec![ty]))
|
|
}
|
|
|
|
ty::Coroutine(coroutine_def_id, args) => {
|
|
match self.tcx().coroutine_movability(coroutine_def_id) {
|
|
hir::Movability::Static => None,
|
|
hir::Movability::Movable => {
|
|
if self.tcx().features().coroutine_clone() {
|
|
let resolved_upvars =
|
|
self.infcx.shallow_resolve(args.as_coroutine().tupled_upvars_ty());
|
|
let resolved_witness =
|
|
self.infcx.shallow_resolve(args.as_coroutine().witness());
|
|
if resolved_upvars.is_ty_var() || resolved_witness.is_ty_var() {
|
|
// Not yet resolved.
|
|
Ambiguous
|
|
} else {
|
|
let all = args
|
|
.as_coroutine()
|
|
.upvar_tys()
|
|
.iter()
|
|
.chain([args.as_coroutine().witness()])
|
|
.collect::<Vec<_>>();
|
|
Where(obligation.predicate.rebind(all))
|
|
}
|
|
} else {
|
|
None
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
ty::CoroutineWitness(def_id, args) => {
|
|
let hidden_types = bind_coroutine_hidden_types_above(
|
|
self.infcx,
|
|
def_id,
|
|
args,
|
|
obligation.predicate.bound_vars(),
|
|
);
|
|
Where(hidden_types)
|
|
}
|
|
|
|
ty::Closure(_, args) => {
|
|
// (*) binder moved here
|
|
let ty = self.infcx.shallow_resolve(args.as_closure().tupled_upvars_ty());
|
|
if let ty::Infer(ty::TyVar(_)) = ty.kind() {
|
|
// Not yet resolved.
|
|
Ambiguous
|
|
} else {
|
|
Where(obligation.predicate.rebind(args.as_closure().upvar_tys().to_vec()))
|
|
}
|
|
}
|
|
|
|
ty::CoroutineClosure(_, args) => {
|
|
// (*) binder moved here
|
|
let ty = self.infcx.shallow_resolve(args.as_coroutine_closure().tupled_upvars_ty());
|
|
if let ty::Infer(ty::TyVar(_)) = ty.kind() {
|
|
// Not yet resolved.
|
|
Ambiguous
|
|
} else {
|
|
Where(
|
|
obligation
|
|
.predicate
|
|
.rebind(args.as_coroutine_closure().upvar_tys().to_vec()),
|
|
)
|
|
}
|
|
}
|
|
|
|
// `Copy` and `Clone` are automatically implemented for an anonymous adt
|
|
// if all of its fields are `Copy` and `Clone`
|
|
ty::Adt(adt, args) if adt.is_anonymous() => {
|
|
// (*) binder moved here
|
|
Where(obligation.predicate.rebind(
|
|
adt.non_enum_variant().fields.iter().map(|f| f.ty(self.tcx(), args)).collect(),
|
|
))
|
|
}
|
|
|
|
ty::Adt(..) | ty::Alias(..) | ty::Param(..) | ty::Placeholder(..) => {
|
|
// Fallback to whatever user-defined impls exist in this case.
|
|
None
|
|
}
|
|
|
|
ty::Infer(ty::TyVar(_)) => {
|
|
// Unbound type variable. Might or might not have
|
|
// applicable impls and so forth, depending on what
|
|
// those type variables wind up being bound to.
|
|
Ambiguous
|
|
}
|
|
|
|
// We can make this an ICE if/once we actually instantiate the trait obligation eagerly.
|
|
ty::Bound(..) => None,
|
|
|
|
ty::Infer(ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)) => {
|
|
bug!("asked to assemble builtin bounds of unexpected type: {:?}", self_ty);
|
|
}
|
|
}
|
|
}
|
|
|
|
fn fused_iterator_conditions(
|
|
&mut self,
|
|
obligation: &PolyTraitObligation<'tcx>,
|
|
) -> BuiltinImplConditions<'tcx> {
|
|
let self_ty = self.infcx.shallow_resolve(obligation.self_ty().skip_binder());
|
|
if let ty::Coroutine(did, ..) = *self_ty.kind()
|
|
&& self.tcx().coroutine_is_gen(did)
|
|
{
|
|
BuiltinImplConditions::Where(ty::Binder::dummy(Vec::new()))
|
|
} else {
|
|
BuiltinImplConditions::None
|
|
}
|
|
}
|
|
|
|
/// For default impls, we need to break apart a type into its
|
|
/// "constituent types" -- meaning, the types that it contains.
|
|
///
|
|
/// Here are some (simple) examples:
|
|
///
|
|
/// ```ignore (illustrative)
|
|
/// (i32, u32) -> [i32, u32]
|
|
/// Foo where struct Foo { x: i32, y: u32 } -> [i32, u32]
|
|
/// Bar<i32> where struct Bar<T> { x: T, y: u32 } -> [i32, u32]
|
|
/// Zed<i32> where enum Zed { A(T), B(u32) } -> [i32, u32]
|
|
/// ```
|
|
#[instrument(level = "debug", skip(self), ret)]
|
|
fn constituent_types_for_ty(
|
|
&self,
|
|
t: ty::Binder<'tcx, Ty<'tcx>>,
|
|
) -> Result<ty::Binder<'tcx, Vec<Ty<'tcx>>>, SelectionError<'tcx>> {
|
|
Ok(match *t.skip_binder().kind() {
|
|
ty::Uint(_)
|
|
| ty::Int(_)
|
|
| ty::Bool
|
|
| ty::Float(_)
|
|
| ty::FnDef(..)
|
|
| ty::FnPtr(..)
|
|
| ty::Error(_)
|
|
| ty::Infer(ty::IntVar(_) | ty::FloatVar(_))
|
|
| ty::Never
|
|
| ty::Char => ty::Binder::dummy(Vec::new()),
|
|
|
|
// FIXME(unsafe_binders): Squash the double binder for now, I guess.
|
|
ty::UnsafeBinder(_) => return Err(SelectionError::Unimplemented),
|
|
|
|
// Treat this like `struct str([u8]);`
|
|
ty::Str => ty::Binder::dummy(vec![Ty::new_slice(self.tcx(), self.tcx().types.u8)]),
|
|
|
|
ty::Placeholder(..)
|
|
| ty::Dynamic(..)
|
|
| ty::Param(..)
|
|
| ty::Foreign(..)
|
|
| ty::Alias(ty::Projection | ty::Inherent | ty::Weak, ..)
|
|
| ty::Bound(..)
|
|
| ty::Infer(ty::TyVar(_) | ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)) => {
|
|
bug!("asked to assemble constituent types of unexpected type: {:?}", t);
|
|
}
|
|
|
|
ty::RawPtr(element_ty, _) | ty::Ref(_, element_ty, _) => t.rebind(vec![element_ty]),
|
|
|
|
ty::Pat(ty, _) | ty::Array(ty, _) | ty::Slice(ty) => t.rebind(vec![ty]),
|
|
|
|
ty::Tuple(tys) => {
|
|
// (T1, ..., Tn) -- meets any bound that all of T1...Tn meet
|
|
t.rebind(tys.iter().collect())
|
|
}
|
|
|
|
ty::Closure(_, args) => {
|
|
let ty = self.infcx.shallow_resolve(args.as_closure().tupled_upvars_ty());
|
|
t.rebind(vec![ty])
|
|
}
|
|
|
|
ty::CoroutineClosure(_, args) => {
|
|
let ty = self.infcx.shallow_resolve(args.as_coroutine_closure().tupled_upvars_ty());
|
|
t.rebind(vec![ty])
|
|
}
|
|
|
|
ty::Coroutine(_, args) => {
|
|
let ty = self.infcx.shallow_resolve(args.as_coroutine().tupled_upvars_ty());
|
|
let witness = args.as_coroutine().witness();
|
|
t.rebind([ty].into_iter().chain(iter::once(witness)).collect())
|
|
}
|
|
|
|
ty::CoroutineWitness(def_id, args) => {
|
|
bind_coroutine_hidden_types_above(self.infcx, def_id, args, t.bound_vars())
|
|
}
|
|
|
|
// For `PhantomData<T>`, we pass `T`.
|
|
ty::Adt(def, args) if def.is_phantom_data() => t.rebind(args.types().collect()),
|
|
|
|
ty::Adt(def, args) => {
|
|
t.rebind(def.all_fields().map(|f| f.ty(self.tcx(), args)).collect())
|
|
}
|
|
|
|
ty::Alias(ty::Opaque, ty::AliasTy { def_id, args, .. }) => {
|
|
if self.infcx.can_define_opaque_ty(def_id) {
|
|
unreachable!()
|
|
} else {
|
|
// We can resolve the `impl Trait` to its concrete type,
|
|
// which enforces a DAG between the functions requiring
|
|
// the auto trait bounds in question.
|
|
match self.tcx().type_of_opaque(def_id) {
|
|
Ok(ty) => t.rebind(vec![ty.instantiate(self.tcx(), args)]),
|
|
Err(_) => {
|
|
return Err(SelectionError::OpaqueTypeAutoTraitLeakageUnknown(def_id));
|
|
}
|
|
}
|
|
}
|
|
}
|
|
})
|
|
}
|
|
|
|
fn collect_predicates_for_types(
|
|
&mut self,
|
|
param_env: ty::ParamEnv<'tcx>,
|
|
cause: ObligationCause<'tcx>,
|
|
recursion_depth: usize,
|
|
trait_def_id: DefId,
|
|
types: ty::Binder<'tcx, Vec<Ty<'tcx>>>,
|
|
) -> PredicateObligations<'tcx> {
|
|
// Because the types were potentially derived from
|
|
// higher-ranked obligations they may reference late-bound
|
|
// regions. For example, `for<'a> Foo<&'a i32> : Copy` would
|
|
// yield a type like `for<'a> &'a i32`. In general, we
|
|
// maintain the invariant that we never manipulate bound
|
|
// regions, so we have to process these bound regions somehow.
|
|
//
|
|
// The strategy is to:
|
|
//
|
|
// 1. Instantiate those regions to placeholder regions (e.g.,
|
|
// `for<'a> &'a i32` becomes `&0 i32`.
|
|
// 2. Produce something like `&'0 i32 : Copy`
|
|
// 3. Re-bind the regions back to `for<'a> &'a i32 : Copy`
|
|
|
|
types
|
|
.as_ref()
|
|
.skip_binder() // binder moved -\
|
|
.iter()
|
|
.flat_map(|ty| {
|
|
let ty: ty::Binder<'tcx, Ty<'tcx>> = types.rebind(*ty); // <----/
|
|
|
|
let placeholder_ty = self.infcx.enter_forall_and_leak_universe(ty);
|
|
let Normalized { value: normalized_ty, mut obligations } =
|
|
ensure_sufficient_stack(|| {
|
|
normalize_with_depth(
|
|
self,
|
|
param_env,
|
|
cause.clone(),
|
|
recursion_depth,
|
|
placeholder_ty,
|
|
)
|
|
});
|
|
|
|
let tcx = self.tcx();
|
|
let trait_ref = if tcx.generics_of(trait_def_id).own_params.len() == 1 {
|
|
ty::TraitRef::new(tcx, trait_def_id, [normalized_ty])
|
|
} else {
|
|
// If this is an ill-formed auto/built-in trait, then synthesize
|
|
// new error args for the missing generics.
|
|
let err_args = ty::GenericArgs::extend_with_error(
|
|
tcx,
|
|
trait_def_id,
|
|
&[normalized_ty.into()],
|
|
);
|
|
ty::TraitRef::new_from_args(tcx, trait_def_id, err_args)
|
|
};
|
|
|
|
let obligation = Obligation::new(self.tcx(), cause.clone(), param_env, trait_ref);
|
|
obligations.push(obligation);
|
|
obligations
|
|
})
|
|
.collect()
|
|
}
|
|
|
|
///////////////////////////////////////////////////////////////////////////
|
|
// Matching
|
|
//
|
|
// Matching is a common path used for both evaluation and
|
|
// confirmation. It basically unifies types that appear in impls
|
|
// and traits. This does affect the surrounding environment;
|
|
// therefore, when used during evaluation, match routines must be
|
|
// run inside of a `probe()` so that their side-effects are
|
|
// contained.
|
|
|
|
fn rematch_impl(
|
|
&mut self,
|
|
impl_def_id: DefId,
|
|
obligation: &PolyTraitObligation<'tcx>,
|
|
) -> Normalized<'tcx, GenericArgsRef<'tcx>> {
|
|
let impl_trait_header = self.tcx().impl_trait_header(impl_def_id).unwrap();
|
|
match self.match_impl(impl_def_id, impl_trait_header, obligation) {
|
|
Ok(args) => args,
|
|
Err(()) => {
|
|
let predicate = self.infcx.resolve_vars_if_possible(obligation.predicate);
|
|
bug!("impl {impl_def_id:?} was matchable against {predicate:?} but now is not")
|
|
}
|
|
}
|
|
}
|
|
|
|
#[instrument(level = "debug", skip(self), ret)]
|
|
fn match_impl(
|
|
&mut self,
|
|
impl_def_id: DefId,
|
|
impl_trait_header: ty::ImplTraitHeader<'tcx>,
|
|
obligation: &PolyTraitObligation<'tcx>,
|
|
) -> Result<Normalized<'tcx, GenericArgsRef<'tcx>>, ()> {
|
|
let placeholder_obligation =
|
|
self.infcx.enter_forall_and_leak_universe(obligation.predicate);
|
|
let placeholder_obligation_trait_ref = placeholder_obligation.trait_ref;
|
|
|
|
let impl_args = self.infcx.fresh_args_for_item(obligation.cause.span, impl_def_id);
|
|
|
|
let trait_ref = impl_trait_header.trait_ref.instantiate(self.tcx(), impl_args);
|
|
debug!(?impl_trait_header);
|
|
|
|
let Normalized { value: impl_trait_ref, obligations: mut nested_obligations } =
|
|
ensure_sufficient_stack(|| {
|
|
normalize_with_depth(
|
|
self,
|
|
obligation.param_env,
|
|
obligation.cause.clone(),
|
|
obligation.recursion_depth + 1,
|
|
trait_ref,
|
|
)
|
|
});
|
|
|
|
debug!(?impl_trait_ref, ?placeholder_obligation_trait_ref);
|
|
|
|
let cause = ObligationCause::new(
|
|
obligation.cause.span,
|
|
obligation.cause.body_id,
|
|
ObligationCauseCode::MatchImpl(obligation.cause.clone(), impl_def_id),
|
|
);
|
|
|
|
let InferOk { obligations, .. } = self
|
|
.infcx
|
|
.at(&cause, obligation.param_env)
|
|
.eq(DefineOpaqueTypes::No, placeholder_obligation_trait_ref, impl_trait_ref)
|
|
.map_err(|e| {
|
|
debug!("match_impl: failed eq_trait_refs due to `{}`", e.to_string(self.tcx()))
|
|
})?;
|
|
nested_obligations.extend(obligations);
|
|
|
|
if impl_trait_header.polarity == ty::ImplPolarity::Reservation
|
|
&& !matches!(self.infcx.typing_mode(), TypingMode::Coherence)
|
|
{
|
|
debug!("reservation impls only apply in intercrate mode");
|
|
return Err(());
|
|
}
|
|
|
|
Ok(Normalized { value: impl_args, obligations: nested_obligations })
|
|
}
|
|
|
|
fn match_upcast_principal(
|
|
&mut self,
|
|
obligation: &PolyTraitObligation<'tcx>,
|
|
unnormalized_upcast_principal: ty::PolyTraitRef<'tcx>,
|
|
a_data: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>,
|
|
b_data: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>,
|
|
a_region: ty::Region<'tcx>,
|
|
b_region: ty::Region<'tcx>,
|
|
) -> SelectionResult<'tcx, PredicateObligations<'tcx>> {
|
|
let tcx = self.tcx();
|
|
let mut nested = PredicateObligations::new();
|
|
|
|
// We may upcast to auto traits that are either explicitly listed in
|
|
// the object type's bounds, or implied by the principal trait ref's
|
|
// supertraits.
|
|
let a_auto_traits: FxIndexSet<DefId> = a_data
|
|
.auto_traits()
|
|
.chain(a_data.principal_def_id().into_iter().flat_map(|principal_def_id| {
|
|
elaborate::supertrait_def_ids(tcx, principal_def_id)
|
|
.filter(|def_id| tcx.trait_is_auto(*def_id))
|
|
}))
|
|
.collect();
|
|
|
|
let upcast_principal = normalize_with_depth_to(
|
|
self,
|
|
obligation.param_env,
|
|
obligation.cause.clone(),
|
|
obligation.recursion_depth + 1,
|
|
unnormalized_upcast_principal,
|
|
&mut nested,
|
|
);
|
|
|
|
for bound in b_data {
|
|
match bound.skip_binder() {
|
|
// Check that a_ty's supertrait (upcast_principal) is compatible
|
|
// with the target (b_ty).
|
|
ty::ExistentialPredicate::Trait(target_principal) => {
|
|
let hr_source_principal = upcast_principal.map_bound(|trait_ref| {
|
|
ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref)
|
|
});
|
|
let hr_target_principal = bound.rebind(target_principal);
|
|
|
|
nested.extend(
|
|
self.infcx
|
|
.enter_forall(hr_target_principal, |target_principal| {
|
|
let source_principal =
|
|
self.infcx.instantiate_binder_with_fresh_vars(
|
|
obligation.cause.span,
|
|
HigherRankedType,
|
|
hr_source_principal,
|
|
);
|
|
self.infcx.at(&obligation.cause, obligation.param_env).eq_trace(
|
|
DefineOpaqueTypes::Yes,
|
|
ToTrace::to_trace(
|
|
&obligation.cause,
|
|
hr_target_principal,
|
|
hr_source_principal,
|
|
),
|
|
target_principal,
|
|
source_principal,
|
|
)
|
|
})
|
|
.map_err(|_| SelectionError::Unimplemented)?
|
|
.into_obligations(),
|
|
);
|
|
}
|
|
// Check that b_ty's projection is satisfied by exactly one of
|
|
// a_ty's projections. First, we look through the list to see if
|
|
// any match. If not, error. Then, if *more* than one matches, we
|
|
// return ambiguity. Otherwise, if exactly one matches, equate
|
|
// it with b_ty's projection.
|
|
ty::ExistentialPredicate::Projection(target_projection) => {
|
|
let hr_target_projection = bound.rebind(target_projection);
|
|
|
|
let mut matching_projections =
|
|
a_data.projection_bounds().filter(|&hr_source_projection| {
|
|
// Eager normalization means that we can just use can_eq
|
|
// here instead of equating and processing obligations.
|
|
hr_source_projection.item_def_id() == hr_target_projection.item_def_id()
|
|
&& self.infcx.probe(|_| {
|
|
self.infcx
|
|
.enter_forall(hr_target_projection, |target_projection| {
|
|
let source_projection =
|
|
self.infcx.instantiate_binder_with_fresh_vars(
|
|
obligation.cause.span,
|
|
HigherRankedType,
|
|
hr_source_projection,
|
|
);
|
|
self.infcx
|
|
.at(&obligation.cause, obligation.param_env)
|
|
.eq_trace(
|
|
DefineOpaqueTypes::Yes,
|
|
ToTrace::to_trace(
|
|
&obligation.cause,
|
|
hr_target_projection,
|
|
hr_source_projection,
|
|
),
|
|
target_projection,
|
|
source_projection,
|
|
)
|
|
})
|
|
.is_ok()
|
|
})
|
|
});
|
|
|
|
let Some(hr_source_projection) = matching_projections.next() else {
|
|
return Err(SelectionError::Unimplemented);
|
|
};
|
|
if matching_projections.next().is_some() {
|
|
return Ok(None);
|
|
}
|
|
nested.extend(
|
|
self.infcx
|
|
.enter_forall(hr_target_projection, |target_projection| {
|
|
let source_projection =
|
|
self.infcx.instantiate_binder_with_fresh_vars(
|
|
obligation.cause.span,
|
|
HigherRankedType,
|
|
hr_source_projection,
|
|
);
|
|
self.infcx.at(&obligation.cause, obligation.param_env).eq_trace(
|
|
DefineOpaqueTypes::Yes,
|
|
ToTrace::to_trace(
|
|
&obligation.cause,
|
|
hr_target_projection,
|
|
hr_source_projection,
|
|
),
|
|
target_projection,
|
|
source_projection,
|
|
)
|
|
})
|
|
.map_err(|_| SelectionError::Unimplemented)?
|
|
.into_obligations(),
|
|
);
|
|
}
|
|
// Check that b_ty's auto traits are present in a_ty's bounds.
|
|
ty::ExistentialPredicate::AutoTrait(def_id) => {
|
|
if !a_auto_traits.contains(&def_id) {
|
|
return Err(SelectionError::Unimplemented);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
nested.push(Obligation::with_depth(
|
|
tcx,
|
|
obligation.cause.clone(),
|
|
obligation.recursion_depth + 1,
|
|
obligation.param_env,
|
|
ty::Binder::dummy(ty::OutlivesPredicate(a_region, b_region)),
|
|
));
|
|
|
|
Ok(Some(nested))
|
|
}
|
|
|
|
/// Normalize `where_clause_trait_ref` and try to match it against
|
|
/// `obligation`. If successful, return any predicates that
|
|
/// result from the normalization.
|
|
fn match_where_clause_trait_ref(
|
|
&mut self,
|
|
obligation: &PolyTraitObligation<'tcx>,
|
|
where_clause_trait_ref: ty::PolyTraitRef<'tcx>,
|
|
) -> Result<PredicateObligations<'tcx>, ()> {
|
|
self.match_poly_trait_ref(obligation, where_clause_trait_ref)
|
|
}
|
|
|
|
/// Returns `Ok` if `poly_trait_ref` being true implies that the
|
|
/// obligation is satisfied.
|
|
#[instrument(skip(self), level = "debug")]
|
|
fn match_poly_trait_ref(
|
|
&mut self,
|
|
obligation: &PolyTraitObligation<'tcx>,
|
|
poly_trait_ref: ty::PolyTraitRef<'tcx>,
|
|
) -> Result<PredicateObligations<'tcx>, ()> {
|
|
let predicate = self.infcx.enter_forall_and_leak_universe(obligation.predicate);
|
|
let trait_ref = self.infcx.instantiate_binder_with_fresh_vars(
|
|
obligation.cause.span,
|
|
HigherRankedType,
|
|
poly_trait_ref,
|
|
);
|
|
self.infcx
|
|
.at(&obligation.cause, obligation.param_env)
|
|
.eq(DefineOpaqueTypes::No, predicate.trait_ref, trait_ref)
|
|
.map(|InferOk { obligations, .. }| obligations)
|
|
.map_err(|_| ())
|
|
}
|
|
|
|
///////////////////////////////////////////////////////////////////////////
|
|
// Miscellany
|
|
|
|
fn match_fresh_trait_refs(
|
|
&self,
|
|
previous: ty::PolyTraitPredicate<'tcx>,
|
|
current: ty::PolyTraitPredicate<'tcx>,
|
|
) -> bool {
|
|
let mut matcher = _match::MatchAgainstFreshVars::new(self.tcx());
|
|
matcher.relate(previous, current).is_ok()
|
|
}
|
|
|
|
fn push_stack<'o>(
|
|
&mut self,
|
|
previous_stack: TraitObligationStackList<'o, 'tcx>,
|
|
obligation: &'o PolyTraitObligation<'tcx>,
|
|
) -> TraitObligationStack<'o, 'tcx> {
|
|
let fresh_trait_pred = obligation.predicate.fold_with(&mut self.freshener);
|
|
|
|
let dfn = previous_stack.cache.next_dfn();
|
|
let depth = previous_stack.depth() + 1;
|
|
TraitObligationStack {
|
|
obligation,
|
|
fresh_trait_pred,
|
|
reached_depth: Cell::new(depth),
|
|
previous: previous_stack,
|
|
dfn,
|
|
depth,
|
|
}
|
|
}
|
|
|
|
#[instrument(skip(self), level = "debug")]
|
|
fn closure_trait_ref_unnormalized(
|
|
&mut self,
|
|
self_ty: Ty<'tcx>,
|
|
fn_trait_def_id: DefId,
|
|
) -> ty::PolyTraitRef<'tcx> {
|
|
let ty::Closure(_, args) = *self_ty.kind() else {
|
|
bug!("expected closure, found {self_ty}");
|
|
};
|
|
let closure_sig = args.as_closure().sig();
|
|
|
|
closure_trait_ref_and_return_type(
|
|
self.tcx(),
|
|
fn_trait_def_id,
|
|
self_ty,
|
|
closure_sig,
|
|
util::TupleArgumentsFlag::No,
|
|
)
|
|
.map_bound(|(trait_ref, _)| trait_ref)
|
|
}
|
|
|
|
/// Returns the obligations that are implied by instantiating an
|
|
/// impl or trait. The obligations are instantiated and fully
|
|
/// normalized. This is used when confirming an impl or default
|
|
/// impl.
|
|
#[instrument(level = "debug", skip(self, cause, param_env))]
|
|
fn impl_or_trait_obligations(
|
|
&mut self,
|
|
cause: &ObligationCause<'tcx>,
|
|
recursion_depth: usize,
|
|
param_env: ty::ParamEnv<'tcx>,
|
|
def_id: DefId, // of impl or trait
|
|
args: GenericArgsRef<'tcx>, // for impl or trait
|
|
parent_trait_pred: ty::Binder<'tcx, ty::TraitPredicate<'tcx>>,
|
|
) -> PredicateObligations<'tcx> {
|
|
let tcx = self.tcx();
|
|
|
|
// To allow for one-pass evaluation of the nested obligation,
|
|
// each predicate must be preceded by the obligations required
|
|
// to normalize it.
|
|
// for example, if we have:
|
|
// impl<U: Iterator<Item: Copy>, V: Iterator<Item = U>> Foo for V
|
|
// the impl will have the following predicates:
|
|
// <V as Iterator>::Item = U,
|
|
// U: Iterator, U: Sized,
|
|
// V: Iterator, V: Sized,
|
|
// <U as Iterator>::Item: Copy
|
|
// When we instantiate, say, `V => IntoIter<u32>, U => $0`, the last
|
|
// obligation will normalize to `<$0 as Iterator>::Item = $1` and
|
|
// `$1: Copy`, so we must ensure the obligations are emitted in
|
|
// that order.
|
|
let predicates = tcx.predicates_of(def_id);
|
|
assert_eq!(predicates.parent, None);
|
|
let predicates = predicates.instantiate_own(tcx, args);
|
|
let mut obligations = PredicateObligations::with_capacity(predicates.len());
|
|
for (index, (predicate, span)) in predicates.into_iter().enumerate() {
|
|
let cause = if tcx.is_lang_item(parent_trait_pred.def_id(), LangItem::CoerceUnsized) {
|
|
cause.clone()
|
|
} else {
|
|
cause.clone().derived_cause(parent_trait_pred, |derived| {
|
|
ObligationCauseCode::ImplDerived(Box::new(ImplDerivedCause {
|
|
derived,
|
|
impl_or_alias_def_id: def_id,
|
|
impl_def_predicate_index: Some(index),
|
|
span,
|
|
}))
|
|
})
|
|
};
|
|
let clause = normalize_with_depth_to(
|
|
self,
|
|
param_env,
|
|
cause.clone(),
|
|
recursion_depth,
|
|
predicate,
|
|
&mut obligations,
|
|
);
|
|
obligations.push(Obligation {
|
|
cause,
|
|
recursion_depth,
|
|
param_env,
|
|
predicate: clause.as_predicate(),
|
|
});
|
|
}
|
|
|
|
// Register any outlives obligations from the trait here, cc #124336.
|
|
if matches!(tcx.def_kind(def_id), DefKind::Impl { of_trait: true }) {
|
|
for clause in tcx.impl_super_outlives(def_id).iter_instantiated(tcx, args) {
|
|
let clause = normalize_with_depth_to(
|
|
self,
|
|
param_env,
|
|
cause.clone(),
|
|
recursion_depth,
|
|
clause,
|
|
&mut obligations,
|
|
);
|
|
obligations.push(Obligation {
|
|
cause: cause.clone(),
|
|
recursion_depth,
|
|
param_env,
|
|
predicate: clause.as_predicate(),
|
|
});
|
|
}
|
|
}
|
|
|
|
obligations
|
|
}
|
|
}
|
|
|
|
impl<'o, 'tcx> TraitObligationStack<'o, 'tcx> {
|
|
fn list(&'o self) -> TraitObligationStackList<'o, 'tcx> {
|
|
TraitObligationStackList::with(self)
|
|
}
|
|
|
|
fn cache(&self) -> &'o ProvisionalEvaluationCache<'tcx> {
|
|
self.previous.cache
|
|
}
|
|
|
|
fn iter(&'o self) -> TraitObligationStackList<'o, 'tcx> {
|
|
self.list()
|
|
}
|
|
|
|
/// Indicates that attempting to evaluate this stack entry
|
|
/// required accessing something from the stack at depth `reached_depth`.
|
|
fn update_reached_depth(&self, reached_depth: usize) {
|
|
assert!(
|
|
self.depth >= reached_depth,
|
|
"invoked `update_reached_depth` with something under this stack: \
|
|
self.depth={} reached_depth={}",
|
|
self.depth,
|
|
reached_depth,
|
|
);
|
|
debug!(reached_depth, "update_reached_depth");
|
|
let mut p = self;
|
|
while reached_depth < p.depth {
|
|
debug!(?p.fresh_trait_pred, "update_reached_depth: marking as cycle participant");
|
|
p.reached_depth.set(p.reached_depth.get().min(reached_depth));
|
|
p = p.previous.head.unwrap();
|
|
}
|
|
}
|
|
}
|
|
|
|
/// The "provisional evaluation cache" is used to store intermediate cache results
|
|
/// when solving auto traits. Auto traits are unusual in that they can support
|
|
/// cycles. So, for example, a "proof tree" like this would be ok:
|
|
///
|
|
/// - `Foo<T>: Send` :-
|
|
/// - `Bar<T>: Send` :-
|
|
/// - `Foo<T>: Send` -- cycle, but ok
|
|
/// - `Baz<T>: Send`
|
|
///
|
|
/// Here, to prove `Foo<T>: Send`, we have to prove `Bar<T>: Send` and
|
|
/// `Baz<T>: Send`. Proving `Bar<T>: Send` in turn required `Foo<T>: Send`.
|
|
/// For non-auto traits, this cycle would be an error, but for auto traits (because
|
|
/// they are coinductive) it is considered ok.
|
|
///
|
|
/// However, there is a complication: at the point where we have
|
|
/// "proven" `Bar<T>: Send`, we have in fact only proven it
|
|
/// *provisionally*. In particular, we proved that `Bar<T>: Send`
|
|
/// *under the assumption* that `Foo<T>: Send`. But what if we later
|
|
/// find out this assumption is wrong? Specifically, we could
|
|
/// encounter some kind of error proving `Baz<T>: Send`. In that case,
|
|
/// `Bar<T>: Send` didn't turn out to be true.
|
|
///
|
|
/// In Issue #60010, we found a bug in rustc where it would cache
|
|
/// these intermediate results. This was fixed in #60444 by disabling
|
|
/// *all* caching for things involved in a cycle -- in our example,
|
|
/// that would mean we don't cache that `Bar<T>: Send`. But this led
|
|
/// to large slowdowns.
|
|
///
|
|
/// Specifically, imagine this scenario, where proving `Baz<T>: Send`
|
|
/// first requires proving `Bar<T>: Send` (which is true:
|
|
///
|
|
/// - `Foo<T>: Send` :-
|
|
/// - `Bar<T>: Send` :-
|
|
/// - `Foo<T>: Send` -- cycle, but ok
|
|
/// - `Baz<T>: Send`
|
|
/// - `Bar<T>: Send` -- would be nice for this to be a cache hit!
|
|
/// - `*const T: Send` -- but what if we later encounter an error?
|
|
///
|
|
/// The *provisional evaluation cache* resolves this issue. It stores
|
|
/// cache results that we've proven but which were involved in a cycle
|
|
/// in some way. We track the minimal stack depth (i.e., the
|
|
/// farthest from the top of the stack) that we are dependent on.
|
|
/// The idea is that the cache results within are all valid -- so long as
|
|
/// none of the nodes in between the current node and the node at that minimum
|
|
/// depth result in an error (in which case the cached results are just thrown away).
|
|
///
|
|
/// During evaluation, we consult this provisional cache and rely on
|
|
/// it. Accessing a cached value is considered equivalent to accessing
|
|
/// a result at `reached_depth`, so it marks the *current* solution as
|
|
/// provisional as well. If an error is encountered, we toss out any
|
|
/// provisional results added from the subtree that encountered the
|
|
/// error. When we pop the node at `reached_depth` from the stack, we
|
|
/// can commit all the things that remain in the provisional cache.
|
|
struct ProvisionalEvaluationCache<'tcx> {
|
|
/// next "depth first number" to issue -- just a counter
|
|
dfn: Cell<usize>,
|
|
|
|
/// Map from cache key to the provisionally evaluated thing.
|
|
/// The cache entries contain the result but also the DFN in which they
|
|
/// were added. The DFN is used to clear out values on failure.
|
|
///
|
|
/// Imagine we have a stack like:
|
|
///
|
|
/// - `A B C` and we add a cache for the result of C (DFN 2)
|
|
/// - Then we have a stack `A B D` where `D` has DFN 3
|
|
/// - We try to solve D by evaluating E: `A B D E` (DFN 4)
|
|
/// - `E` generates various cache entries which have cyclic dependencies on `B`
|
|
/// - `A B D E F` and so forth
|
|
/// - the DFN of `F` for example would be 5
|
|
/// - then we determine that `E` is in error -- we will then clear
|
|
/// all cache values whose DFN is >= 4 -- in this case, that
|
|
/// means the cached value for `F`.
|
|
map: RefCell<FxIndexMap<ty::PolyTraitPredicate<'tcx>, ProvisionalEvaluation>>,
|
|
|
|
/// The stack of args that we assume to be true because a `WF(arg)` predicate
|
|
/// is on the stack above (and because of wellformedness is coinductive).
|
|
/// In an "ideal" world, this would share a stack with trait predicates in
|
|
/// `TraitObligationStack`. However, trait predicates are *much* hotter than
|
|
/// `WellFormed` predicates, and it's very likely that the additional matches
|
|
/// will have a perf effect. The value here is the well-formed `GenericArg`
|
|
/// and the depth of the trait predicate *above* that well-formed predicate.
|
|
wf_args: RefCell<Vec<(ty::GenericArg<'tcx>, usize)>>,
|
|
}
|
|
|
|
/// A cache value for the provisional cache: contains the depth-first
|
|
/// number (DFN) and result.
|
|
#[derive(Copy, Clone, Debug)]
|
|
struct ProvisionalEvaluation {
|
|
from_dfn: usize,
|
|
reached_depth: usize,
|
|
result: EvaluationResult,
|
|
}
|
|
|
|
impl<'tcx> Default for ProvisionalEvaluationCache<'tcx> {
|
|
fn default() -> Self {
|
|
Self { dfn: Cell::new(0), map: Default::default(), wf_args: Default::default() }
|
|
}
|
|
}
|
|
|
|
impl<'tcx> ProvisionalEvaluationCache<'tcx> {
|
|
/// Get the next DFN in sequence (basically a counter).
|
|
fn next_dfn(&self) -> usize {
|
|
let result = self.dfn.get();
|
|
self.dfn.set(result + 1);
|
|
result
|
|
}
|
|
|
|
/// Check the provisional cache for any result for
|
|
/// `fresh_trait_ref`. If there is a hit, then you must consider
|
|
/// it an access to the stack slots at depth
|
|
/// `reached_depth` (from the returned value).
|
|
fn get_provisional(
|
|
&self,
|
|
fresh_trait_pred: ty::PolyTraitPredicate<'tcx>,
|
|
) -> Option<ProvisionalEvaluation> {
|
|
debug!(
|
|
?fresh_trait_pred,
|
|
"get_provisional = {:#?}",
|
|
self.map.borrow().get(&fresh_trait_pred),
|
|
);
|
|
Some(*self.map.borrow().get(&fresh_trait_pred)?)
|
|
}
|
|
|
|
/// Insert a provisional result into the cache. The result came
|
|
/// from the node with the given DFN. It accessed a minimum depth
|
|
/// of `reached_depth` to compute. It evaluated `fresh_trait_pred`
|
|
/// and resulted in `result`.
|
|
fn insert_provisional(
|
|
&self,
|
|
from_dfn: usize,
|
|
reached_depth: usize,
|
|
fresh_trait_pred: ty::PolyTraitPredicate<'tcx>,
|
|
result: EvaluationResult,
|
|
) {
|
|
debug!(?from_dfn, ?fresh_trait_pred, ?result, "insert_provisional");
|
|
|
|
let mut map = self.map.borrow_mut();
|
|
|
|
// Subtle: when we complete working on the DFN `from_dfn`, anything
|
|
// that remains in the provisional cache must be dependent on some older
|
|
// stack entry than `from_dfn`. We have to update their depth with our transitive
|
|
// depth in that case or else it would be referring to some popped note.
|
|
//
|
|
// Example:
|
|
// A (reached depth 0)
|
|
// ...
|
|
// B // depth 1 -- reached depth = 0
|
|
// C // depth 2 -- reached depth = 1 (should be 0)
|
|
// B
|
|
// A // depth 0
|
|
// D (reached depth 1)
|
|
// C (cache -- reached depth = 2)
|
|
for (_k, v) in &mut *map {
|
|
if v.from_dfn >= from_dfn {
|
|
v.reached_depth = reached_depth.min(v.reached_depth);
|
|
}
|
|
}
|
|
|
|
map.insert(fresh_trait_pred, ProvisionalEvaluation { from_dfn, reached_depth, result });
|
|
}
|
|
|
|
/// Invoked when the node with dfn `dfn` does not get a successful
|
|
/// result. This will clear out any provisional cache entries
|
|
/// that were added since `dfn` was created. This is because the
|
|
/// provisional entries are things which must assume that the
|
|
/// things on the stack at the time of their creation succeeded --
|
|
/// since the failing node is presently at the top of the stack,
|
|
/// these provisional entries must either depend on it or some
|
|
/// ancestor of it.
|
|
fn on_failure(&self, dfn: usize) {
|
|
debug!(?dfn, "on_failure");
|
|
self.map.borrow_mut().retain(|key, eval| {
|
|
if !eval.from_dfn >= dfn {
|
|
debug!("on_failure: removing {:?}", key);
|
|
false
|
|
} else {
|
|
true
|
|
}
|
|
});
|
|
}
|
|
|
|
/// Invoked when the node at depth `depth` completed without
|
|
/// depending on anything higher in the stack (if that completion
|
|
/// was a failure, then `on_failure` should have been invoked
|
|
/// already).
|
|
///
|
|
/// Note that we may still have provisional cache items remaining
|
|
/// in the cache when this is done. For example, if there is a
|
|
/// cycle:
|
|
///
|
|
/// * A depends on...
|
|
/// * B depends on A
|
|
/// * C depends on...
|
|
/// * D depends on C
|
|
/// * ...
|
|
///
|
|
/// Then as we complete the C node we will have a provisional cache
|
|
/// with results for A, B, C, and D. This method would clear out
|
|
/// the C and D results, but leave A and B provisional.
|
|
///
|
|
/// This is determined based on the DFN: we remove any provisional
|
|
/// results created since `dfn` started (e.g., in our example, dfn
|
|
/// would be 2, representing the C node, and hence we would
|
|
/// remove the result for D, which has DFN 3, but not the results for
|
|
/// A and B, which have DFNs 0 and 1 respectively).
|
|
///
|
|
/// Note that we *do not* attempt to cache these cycle participants
|
|
/// in the evaluation cache. Doing so would require carefully computing
|
|
/// the correct `DepNode` to store in the cache entry:
|
|
/// cycle participants may implicitly depend on query results
|
|
/// related to other participants in the cycle, due to our logic
|
|
/// which examines the evaluation stack.
|
|
///
|
|
/// We used to try to perform this caching,
|
|
/// but it lead to multiple incremental compilation ICEs
|
|
/// (see #92987 and #96319), and was very hard to understand.
|
|
/// Fortunately, removing the caching didn't seem to
|
|
/// have a performance impact in practice.
|
|
fn on_completion(&self, dfn: usize) {
|
|
debug!(?dfn, "on_completion");
|
|
self.map.borrow_mut().retain(|fresh_trait_pred, eval| {
|
|
if eval.from_dfn >= dfn {
|
|
debug!(?fresh_trait_pred, ?eval, "on_completion");
|
|
return false;
|
|
}
|
|
true
|
|
});
|
|
}
|
|
}
|
|
|
|
#[derive(Copy, Clone)]
|
|
struct TraitObligationStackList<'o, 'tcx> {
|
|
cache: &'o ProvisionalEvaluationCache<'tcx>,
|
|
head: Option<&'o TraitObligationStack<'o, 'tcx>>,
|
|
}
|
|
|
|
impl<'o, 'tcx> TraitObligationStackList<'o, 'tcx> {
|
|
fn empty(cache: &'o ProvisionalEvaluationCache<'tcx>) -> TraitObligationStackList<'o, 'tcx> {
|
|
TraitObligationStackList { cache, head: None }
|
|
}
|
|
|
|
fn with(r: &'o TraitObligationStack<'o, 'tcx>) -> TraitObligationStackList<'o, 'tcx> {
|
|
TraitObligationStackList { cache: r.cache(), head: Some(r) }
|
|
}
|
|
|
|
fn head(&self) -> Option<&'o TraitObligationStack<'o, 'tcx>> {
|
|
self.head
|
|
}
|
|
|
|
fn depth(&self) -> usize {
|
|
if let Some(head) = self.head { head.depth } else { 0 }
|
|
}
|
|
}
|
|
|
|
impl<'o, 'tcx> Iterator for TraitObligationStackList<'o, 'tcx> {
|
|
type Item = &'o TraitObligationStack<'o, 'tcx>;
|
|
|
|
fn next(&mut self) -> Option<&'o TraitObligationStack<'o, 'tcx>> {
|
|
let o = self.head?;
|
|
*self = o.previous;
|
|
Some(o)
|
|
}
|
|
}
|
|
|
|
impl<'o, 'tcx> fmt::Debug for TraitObligationStack<'o, 'tcx> {
|
|
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
|
|
write!(f, "TraitObligationStack({:?})", self.obligation)
|
|
}
|
|
}
|
|
|
|
pub(crate) enum ProjectionMatchesProjection {
|
|
Yes,
|
|
Ambiguous,
|
|
No,
|
|
}
|
|
|
|
/// Replace all regions inside the coroutine interior with late bound regions.
|
|
/// Note that each region slot in the types gets a new fresh late bound region, which means that
|
|
/// none of the regions inside relate to any other, even if typeck had previously found constraints
|
|
/// that would cause them to be related.
|
|
#[instrument(level = "trace", skip(infcx), ret)]
|
|
fn bind_coroutine_hidden_types_above<'tcx>(
|
|
infcx: &InferCtxt<'tcx>,
|
|
def_id: DefId,
|
|
args: ty::GenericArgsRef<'tcx>,
|
|
bound_vars: &ty::List<ty::BoundVariableKind>,
|
|
) -> ty::Binder<'tcx, Vec<Ty<'tcx>>> {
|
|
let tcx = infcx.tcx;
|
|
let mut seen_tys = FxHashSet::default();
|
|
|
|
let considering_regions = infcx.considering_regions;
|
|
|
|
let num_bound_variables = bound_vars.len() as u32;
|
|
let mut counter = num_bound_variables;
|
|
|
|
let hidden_types: Vec<_> = tcx
|
|
.coroutine_hidden_types(def_id)
|
|
// Deduplicate tys to avoid repeated work.
|
|
.filter(|bty| seen_tys.insert(*bty))
|
|
.map(|mut bty| {
|
|
// Only remap erased regions if we use them.
|
|
if considering_regions {
|
|
bty = bty.map_bound(|ty| {
|
|
fold_regions(tcx, ty, |r, current_depth| match r.kind() {
|
|
ty::ReErased => {
|
|
let br = ty::BoundRegion {
|
|
var: ty::BoundVar::from_u32(counter),
|
|
kind: ty::BoundRegionKind::Anon,
|
|
};
|
|
counter += 1;
|
|
ty::Region::new_bound(tcx, current_depth, br)
|
|
}
|
|
r => bug!("unexpected region: {r:?}"),
|
|
})
|
|
})
|
|
}
|
|
|
|
bty.instantiate(tcx, args)
|
|
})
|
|
.collect();
|
|
let bound_vars = tcx.mk_bound_variable_kinds_from_iter(
|
|
bound_vars.iter().chain(
|
|
(num_bound_variables..counter)
|
|
.map(|_| ty::BoundVariableKind::Region(ty::BoundRegionKind::Anon)),
|
|
),
|
|
);
|
|
ty::Binder::bind_with_vars(hidden_types, bound_vars)
|
|
}
|