3799 lines
154 KiB
Rust
3799 lines
154 KiB
Rust
// ignore-tidy-filelength
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//! 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 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;
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use super::project::{normalize_with_depth, normalize_with_depth_to};
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use super::util;
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use super::util::{closure_trait_ref_and_return_type, predicate_for_trait_def};
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use super::wf;
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use super::DerivedObligationCause;
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use super::Selection;
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use super::SelectionResult;
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use super::TraitNotObjectSafe;
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use super::TraitQueryMode;
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use super::{BuiltinDerivedObligation, ImplDerivedObligation, ObligationCauseCode};
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use super::{Normalized, ProjectionCacheKey};
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use super::{ObjectCastObligation, Obligation};
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use super::{ObligationCause, PredicateObligation, TraitObligation};
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use super::{OutputTypeParameterMismatch, Overflow, SelectionError, Unimplemented};
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use super::{
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VtableAutoImpl, VtableBuiltin, VtableClosure, VtableFnPointer, VtableGenerator, VtableImpl,
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VtableObject, VtableParam, VtableTraitAlias,
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};
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use super::{
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VtableAutoImplData, VtableBuiltinData, VtableClosureData, VtableFnPointerData,
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VtableGeneratorData, VtableImplData, VtableObjectData, VtableTraitAliasData,
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};
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use crate::infer::{CombinedSnapshot, InferCtxt, InferOk, PlaceholderMap, TypeFreshener};
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use crate::traits::error_reporting::InferCtxtExt;
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use crate::traits::project::ProjectionCacheKeyExt;
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use rustc_ast::attr;
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use rustc_data_structures::fx::{FxHashMap, FxHashSet};
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use rustc_hir as hir;
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use rustc_hir::def_id::DefId;
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use rustc_hir::lang_items;
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use rustc_index::bit_set::GrowableBitSet;
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use rustc_middle::dep_graph::{DepKind, DepNodeIndex};
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use rustc_middle::ty::fast_reject;
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use rustc_middle::ty::relate::TypeRelation;
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use rustc_middle::ty::subst::{GenericArg, GenericArgKind, Subst, SubstsRef};
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use rustc_middle::ty::{
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self, ToPolyTraitRef, ToPredicate, Ty, TyCtxt, TypeFoldable, WithConstness,
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};
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use rustc_span::symbol::sym;
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use rustc_target::spec::abi::Abi;
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use std::cell::{Cell, RefCell};
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use std::cmp;
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use std::fmt::{self, Display};
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use std::iter;
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use std::rc::Rc;
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pub use rustc_middle::traits::select::*;
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pub struct SelectionContext<'cx, 'tcx> {
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infcx: &'cx InferCtxt<'cx, '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 `true`, indicates that the evaluation should be conservative
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/// and consider the possibility of types outside this crate.
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/// This comes up primarily when resolving ambiguity. Imagine
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/// there is some trait reference `$0: Bar` where `$0` is an
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/// inference variable. If `intercrate` is true, then we can never
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/// say for sure that this reference is not implemented, even if
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/// there are *no impls at all for `Bar`*, because `$0` could be
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/// bound to some type that in a downstream crate that implements
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/// `Bar`. This is the suitable mode for coherence. Elsewhere,
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/// though, we set this to false, because we are only interested
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/// in types that the user could actually have written --- in
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/// other words, we consider `$0: Bar` to be unimplemented if
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/// there is no type that the user could *actually name* that
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/// would satisfy it. This avoids crippling inference, basically.
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intercrate: bool,
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intercrate_ambiguity_causes: Option<Vec<IntercrateAmbiguityCause>>,
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/// Controls whether or not to filter out negative impls when selecting.
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/// This is used in librustdoc to distinguish between the lack of an impl
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/// and a negative impl
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allow_negative_impls: bool,
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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 TraitObligation<'tcx>,
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/// The trait ref 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_ref: ty::PolyTraitRef<'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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enum BuiltinImplConditions<'tcx> {
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/// The impl is conditional on `T1, T2, ...: Trait`.
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Where(ty::Binder<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<'cx, '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: false,
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intercrate_ambiguity_causes: None,
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allow_negative_impls: false,
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query_mode: TraitQueryMode::Standard,
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}
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}
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pub fn intercrate(infcx: &'cx InferCtxt<'cx, '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: true,
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intercrate_ambiguity_causes: None,
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allow_negative_impls: false,
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query_mode: TraitQueryMode::Standard,
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}
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}
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pub fn with_negative(
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infcx: &'cx InferCtxt<'cx, 'tcx>,
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allow_negative_impls: bool,
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) -> SelectionContext<'cx, 'tcx> {
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debug!("with_negative({:?})", allow_negative_impls);
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SelectionContext {
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infcx,
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freshener: infcx.freshener(),
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intercrate: false,
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intercrate_ambiguity_causes: None,
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allow_negative_impls,
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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<'cx, 'tcx>,
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query_mode: TraitQueryMode,
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) -> SelectionContext<'cx, 'tcx> {
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debug!("with_query_mode({:?})", query_mode);
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SelectionContext {
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infcx,
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freshener: infcx.freshener(),
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intercrate: false,
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intercrate_ambiguity_causes: None,
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allow_negative_impls: false,
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query_mode,
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}
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}
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/// Enables tracking of intercrate ambiguity causes. These are
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/// used in coherence to give improved diagnostics. We don't do
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/// this until we detect a coherence error because it can lead to
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/// false overflow results (#47139) and because it costs
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/// computation time.
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pub fn enable_tracking_intercrate_ambiguity_causes(&mut self) {
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assert!(self.intercrate);
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assert!(self.intercrate_ambiguity_causes.is_none());
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self.intercrate_ambiguity_causes = Some(vec![]);
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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(&mut self) -> Vec<IntercrateAmbiguityCause> {
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assert!(self.intercrate);
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self.intercrate_ambiguity_causes.take().unwrap_or(vec![])
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}
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pub fn infcx(&self) -> &'cx InferCtxt<'cx, 'tcx> {
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self.infcx
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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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pub fn closure_typer(&self) -> &'cx InferCtxt<'cx, 'tcx> {
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self.infcx
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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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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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debug!("select({:?})", obligation);
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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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let candidate = match self.candidate_from_obligation(&stack) {
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Err(SelectionError::Overflow) => {
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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);
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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) => {
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assert!(self.query_mode == TraitQueryMode::Canonical);
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Err(SelectionError::Overflow)
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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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///////////////////////////////////////////////////////////////////////////
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// EVALUATION
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//
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// Tests whether an obligation can be selected or whether an impl
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// can be applied to particular types. It skips the "confirmation"
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// step and hence completely ignores output type parameters.
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//
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// The result is "true" if the obligation *may* hold and "false" if
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// we can be sure it does not.
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/// Evaluates whether the obligation `obligation` can be satisfied (by any means).
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pub fn predicate_may_hold_fatal(&mut self, obligation: &PredicateObligation<'tcx>) -> bool {
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debug!("predicate_may_hold_fatal({:?})", obligation);
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// This fatal query is a stopgap that should only be used in standard mode,
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// where we do not expect overflow to be propagated.
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assert!(self.query_mode == TraitQueryMode::Standard);
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self.evaluate_root_obligation(obligation)
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.expect("Overflow should be caught earlier in standard query mode")
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.may_apply()
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}
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/// Evaluates whether the obligation `obligation` can be satisfied
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/// and returns an `EvaluationResult`. This is meant for the
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/// *initial* call.
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pub fn evaluate_root_obligation(
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&mut self,
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obligation: &PredicateObligation<'tcx>,
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) -> Result<EvaluationResult, OverflowError> {
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self.evaluation_probe(|this| {
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this.evaluate_predicate_recursively(
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TraitObligationStackList::empty(&ProvisionalEvaluationCache::default()),
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obligation.clone(),
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)
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})
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}
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fn evaluation_probe(
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&mut self,
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op: impl FnOnce(&mut Self) -> Result<EvaluationResult, OverflowError>,
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) -> Result<EvaluationResult, OverflowError> {
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self.infcx.probe(|snapshot| -> Result<EvaluationResult, OverflowError> {
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let result = op(self)?;
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match self.infcx.region_constraints_added_in_snapshot(snapshot) {
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None => Ok(result),
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Some(_) => Ok(result.max(EvaluatedToOkModuloRegions)),
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}
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})
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}
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/// Evaluates the predicates in `predicates` recursively. Note that
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/// this applies projections in the predicates, and therefore
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/// is run within an inference probe.
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fn evaluate_predicates_recursively<'o, I>(
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&mut self,
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stack: TraitObligationStackList<'o, 'tcx>,
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predicates: I,
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) -> Result<EvaluationResult, OverflowError>
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where
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I: IntoIterator<Item = PredicateObligation<'tcx>>,
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{
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let mut result = EvaluatedToOk;
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for obligation in predicates {
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let eval = self.evaluate_predicate_recursively(stack, obligation.clone())?;
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debug!("evaluate_predicate_recursively({:?}) = {:?}", obligation, eval);
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if let EvaluatedToErr = eval {
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// fast-path - EvaluatedToErr is the top of the lattice,
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// so we don't need to look on the other predicates.
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return Ok(EvaluatedToErr);
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} else {
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result = cmp::max(result, eval);
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}
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}
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Ok(result)
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}
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fn evaluate_predicate_recursively<'o>(
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&mut self,
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previous_stack: TraitObligationStackList<'o, 'tcx>,
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obligation: PredicateObligation<'tcx>,
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) -> Result<EvaluationResult, OverflowError> {
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debug!(
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"evaluate_predicate_recursively(previous_stack={:?}, obligation={:?})",
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previous_stack.head(),
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obligation
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);
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// `previous_stack` stores a `TraitObligatiom`, while `obligation` is
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// a `PredicateObligation`. These are distinct types, so we can't
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// use any `Option` combinator method that would force them to be
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// the same.
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match previous_stack.head() {
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Some(h) => self.check_recursion_limit(&obligation, h.obligation)?,
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None => self.check_recursion_limit(&obligation, &obligation)?,
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}
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match obligation.predicate {
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ty::Predicate::Trait(ref t, _) => {
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debug_assert!(!t.has_escaping_bound_vars());
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let obligation = obligation.with(t.clone());
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self.evaluate_trait_predicate_recursively(previous_stack, obligation)
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}
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ty::Predicate::Subtype(ref p) => {
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// Does this code ever run?
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match self.infcx.subtype_predicate(&obligation.cause, obligation.param_env, p) {
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Some(Ok(InferOk { mut obligations, .. })) => {
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self.add_depth(obligations.iter_mut(), obligation.recursion_depth);
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self.evaluate_predicates_recursively(
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previous_stack,
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obligations.into_iter(),
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)
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}
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Some(Err(_)) => Ok(EvaluatedToErr),
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None => Ok(EvaluatedToAmbig),
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}
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}
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ty::Predicate::WellFormed(ty) => match wf::obligations(
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self.infcx,
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obligation.param_env,
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obligation.cause.body_id,
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ty,
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obligation.cause.span,
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) {
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Some(mut obligations) => {
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self.add_depth(obligations.iter_mut(), obligation.recursion_depth);
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self.evaluate_predicates_recursively(previous_stack, obligations.into_iter())
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}
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None => Ok(EvaluatedToAmbig),
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},
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ty::Predicate::TypeOutlives(..) | ty::Predicate::RegionOutlives(..) => {
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// We do not consider region relationships when evaluating trait matches.
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Ok(EvaluatedToOkModuloRegions)
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}
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ty::Predicate::ObjectSafe(trait_def_id) => {
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if self.tcx().is_object_safe(trait_def_id) {
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Ok(EvaluatedToOk)
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} else {
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Ok(EvaluatedToErr)
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}
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}
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ty::Predicate::Projection(ref data) => {
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let project_obligation = obligation.with(data.clone());
|
|
match project::poly_project_and_unify_type(self, &project_obligation) {
|
|
Ok(Some(mut subobligations)) => {
|
|
self.add_depth(subobligations.iter_mut(), obligation.recursion_depth);
|
|
let result = self.evaluate_predicates_recursively(
|
|
previous_stack,
|
|
subobligations.into_iter(),
|
|
);
|
|
if let Some(key) =
|
|
ProjectionCacheKey::from_poly_projection_predicate(self, data)
|
|
{
|
|
self.infcx.inner.borrow_mut().projection_cache.complete(key);
|
|
}
|
|
result
|
|
}
|
|
Ok(None) => Ok(EvaluatedToAmbig),
|
|
Err(_) => Ok(EvaluatedToErr),
|
|
}
|
|
}
|
|
|
|
ty::Predicate::ClosureKind(_, closure_substs, kind) => {
|
|
match self.infcx.closure_kind(closure_substs) {
|
|
Some(closure_kind) => {
|
|
if closure_kind.extends(kind) {
|
|
Ok(EvaluatedToOk)
|
|
} else {
|
|
Ok(EvaluatedToErr)
|
|
}
|
|
}
|
|
None => Ok(EvaluatedToAmbig),
|
|
}
|
|
}
|
|
|
|
ty::Predicate::ConstEvaluatable(def_id, substs) => {
|
|
match self.tcx().const_eval_resolve(
|
|
obligation.param_env,
|
|
def_id,
|
|
substs,
|
|
None,
|
|
None,
|
|
) {
|
|
Ok(_) => Ok(EvaluatedToOk),
|
|
Err(_) => Ok(EvaluatedToErr),
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
fn evaluate_trait_predicate_recursively<'o>(
|
|
&mut self,
|
|
previous_stack: TraitObligationStackList<'o, 'tcx>,
|
|
mut obligation: TraitObligation<'tcx>,
|
|
) -> Result<EvaluationResult, OverflowError> {
|
|
debug!("evaluate_trait_predicate_recursively({:?})", obligation);
|
|
|
|
if !self.intercrate
|
|
&& obligation.is_global()
|
|
&& obligation.param_env.caller_bounds.iter().all(|bound| bound.needs_subst())
|
|
{
|
|
// 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!("evaluate_trait_predicate_recursively({:?}) - in global", obligation);
|
|
obligation.param_env = obligation.param_env.without_caller_bounds();
|
|
}
|
|
|
|
let stack = self.push_stack(previous_stack, &obligation);
|
|
let fresh_trait_ref = stack.fresh_trait_ref;
|
|
if let Some(result) = self.check_evaluation_cache(obligation.param_env, fresh_trait_ref) {
|
|
debug!("CACHE HIT: EVAL({:?})={:?}", fresh_trait_ref, result);
|
|
return Ok(result);
|
|
}
|
|
|
|
if let Some(result) = stack.cache().get_provisional(fresh_trait_ref) {
|
|
debug!("PROVISIONAL CACHE HIT: EVAL({:?})={:?}", fresh_trait_ref, result);
|
|
stack.update_reached_depth(stack.cache().current_reached_depth());
|
|
return Ok(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| this.evaluate_stack(&stack));
|
|
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: EVAL({:?})={:?}", fresh_trait_ref, result);
|
|
self.insert_evaluation_cache(obligation.param_env, fresh_trait_ref, dep_node, result);
|
|
|
|
stack.cache().on_completion(stack.depth, |fresh_trait_ref, provisional_result| {
|
|
self.insert_evaluation_cache(
|
|
obligation.param_env,
|
|
fresh_trait_ref,
|
|
dep_node,
|
|
provisional_result.max(result),
|
|
);
|
|
});
|
|
} else {
|
|
debug!("PROVISIONAL: {:?}={:?}", fresh_trait_ref, result);
|
|
debug!(
|
|
"evaluate_trait_predicate_recursively: caching provisionally because {:?} \
|
|
is a cycle participant (at depth {}, reached depth {})",
|
|
fresh_trait_ref, stack.depth, reached_depth,
|
|
);
|
|
|
|
stack.cache().insert_provisional(stack.dfn, reached_depth, fresh_trait_ref, 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_ref == prev.fresh_trait_ref
|
|
})
|
|
.map(|stack| stack.depth)
|
|
{
|
|
debug!(
|
|
"evaluate_stack({:?}) --> recursive at depth {}",
|
|
stack.fresh_trait_ref, 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 cycle = cycle.map(|stack| {
|
|
ty::Predicate::Trait(stack.obligation.predicate, hir::Constness::NotConst)
|
|
});
|
|
if self.coinductive_match(cycle) {
|
|
debug!("evaluate_stack({:?}) --> recursive, coinductive", stack.fresh_trait_ref);
|
|
Some(EvaluatedToOk)
|
|
} else {
|
|
debug!("evaluate_stack({:?}) --> recursive, inductive", stack.fresh_trait_ref);
|
|
Some(EvaluatedToRecur)
|
|
}
|
|
} else {
|
|
None
|
|
}
|
|
}
|
|
|
|
fn evaluate_stack<'o>(
|
|
&mut self,
|
|
stack: &TraitObligationStack<'o, 'tcx>,
|
|
) -> Result<EvaluationResult, OverflowError> {
|
|
// 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_ref.skip_binder().substs.types().any(|ty| ty.is_fresh());
|
|
// This check was an imperfect workaround for a bug in the old
|
|
// intercrate mode; it should be removed when that goes away.
|
|
if unbound_input_types && self.intercrate {
|
|
debug!(
|
|
"evaluate_stack({:?}) --> unbound argument, intercrate --> ambiguous",
|
|
stack.fresh_trait_ref
|
|
);
|
|
// Heuristics: show the diagnostics when there are no candidates in crate.
|
|
if self.intercrate_ambiguity_causes.is_some() {
|
|
debug!("evaluate_stack: intercrate_ambiguity_causes is some");
|
|
if let Ok(candidate_set) = self.assemble_candidates(stack) {
|
|
if !candidate_set.ambiguous && candidate_set.vec.is_empty() {
|
|
let trait_ref = stack.obligation.predicate.skip_binder().trait_ref;
|
|
let self_ty = trait_ref.self_ty();
|
|
let cause = IntercrateAmbiguityCause::DownstreamCrate {
|
|
trait_desc: trait_ref.print_only_trait_path().to_string(),
|
|
self_desc: if self_ty.has_concrete_skeleton() {
|
|
Some(self_ty.to_string())
|
|
} else {
|
|
None
|
|
},
|
|
};
|
|
debug!("evaluate_stack: pushing cause = {:?}", cause);
|
|
self.intercrate_ambiguity_causes.as_mut().unwrap().push(cause);
|
|
}
|
|
}
|
|
}
|
|
return Ok(EvaluatedToAmbig);
|
|
}
|
|
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_ref,
|
|
&prev.fresh_trait_ref,
|
|
prev.obligation.param_env,
|
|
)
|
|
})
|
|
{
|
|
debug!(
|
|
"evaluate_stack({:?}) --> unbound argument, recursive --> giving up",
|
|
stack.fresh_trait_ref
|
|
);
|
|
return Ok(EvaluatedToUnknown);
|
|
}
|
|
|
|
match self.candidate_from_obligation(stack) {
|
|
Ok(Some(c)) => self.evaluate_candidate(stack, &c),
|
|
Ok(None) => Ok(EvaluatedToAmbig),
|
|
Err(Overflow) => Err(OverflowError),
|
|
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 fn coinductive_match<I>(&mut self, cycle: I) -> bool
|
|
where
|
|
I: Iterator<Item = ty::Predicate<'tcx>>,
|
|
{
|
|
let mut cycle = cycle;
|
|
cycle.all(|predicate| self.coinductive_predicate(predicate))
|
|
}
|
|
|
|
fn coinductive_predicate(&self, predicate: ty::Predicate<'tcx>) -> bool {
|
|
let result = match predicate {
|
|
ty::Predicate::Trait(ref data, _) => self.tcx().trait_is_auto(data.def_id()),
|
|
_ => false,
|
|
};
|
|
debug!("coinductive_predicate({:?}) = {:?}", predicate, result);
|
|
result
|
|
}
|
|
|
|
/// 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.
|
|
fn evaluate_candidate<'o>(
|
|
&mut self,
|
|
stack: &TraitObligationStack<'o, 'tcx>,
|
|
candidate: &SelectionCandidate<'tcx>,
|
|
) -> Result<EvaluationResult, OverflowError> {
|
|
debug!(
|
|
"evaluate_candidate: depth={} candidate={:?}",
|
|
stack.obligation.recursion_depth, candidate
|
|
);
|
|
let result = self.evaluation_probe(|this| {
|
|
let candidate = (*candidate).clone();
|
|
match this.confirm_candidate(stack.obligation, candidate) {
|
|
Ok(selection) => this.evaluate_predicates_recursively(
|
|
stack.list(),
|
|
selection.nested_obligations().into_iter(),
|
|
),
|
|
Err(..) => Ok(EvaluatedToErr),
|
|
}
|
|
})?;
|
|
debug!(
|
|
"evaluate_candidate: depth={} result={:?}",
|
|
stack.obligation.recursion_depth, result
|
|
);
|
|
Ok(result)
|
|
}
|
|
|
|
fn check_evaluation_cache(
|
|
&self,
|
|
param_env: ty::ParamEnv<'tcx>,
|
|
trait_ref: ty::PolyTraitRef<'tcx>,
|
|
) -> Option<EvaluationResult> {
|
|
let tcx = self.tcx();
|
|
if self.can_use_global_caches(param_env) {
|
|
let cache = tcx.evaluation_cache.hashmap.borrow();
|
|
if let Some(cached) = cache.get(¶m_env.and(trait_ref)) {
|
|
return Some(cached.get(tcx));
|
|
}
|
|
}
|
|
self.infcx
|
|
.evaluation_cache
|
|
.hashmap
|
|
.borrow()
|
|
.get(¶m_env.and(trait_ref))
|
|
.map(|v| v.get(tcx))
|
|
}
|
|
|
|
fn insert_evaluation_cache(
|
|
&mut self,
|
|
param_env: ty::ParamEnv<'tcx>,
|
|
trait_ref: ty::PolyTraitRef<'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;
|
|
}
|
|
|
|
if self.can_use_global_caches(param_env) {
|
|
if !trait_ref.has_local_value() {
|
|
debug!(
|
|
"insert_evaluation_cache(trait_ref={:?}, candidate={:?}) global",
|
|
trait_ref, result,
|
|
);
|
|
// This may overwrite the cache with the same value
|
|
// FIXME: Due to #50507 this overwrites the different values
|
|
// This should be changed to use HashMapExt::insert_same
|
|
// when that is fixed
|
|
self.tcx()
|
|
.evaluation_cache
|
|
.hashmap
|
|
.borrow_mut()
|
|
.insert(param_env.and(trait_ref), WithDepNode::new(dep_node, result));
|
|
return;
|
|
}
|
|
}
|
|
|
|
debug!("insert_evaluation_cache(trait_ref={:?}, candidate={:?})", trait_ref, result,);
|
|
self.infcx
|
|
.evaluation_cache
|
|
.hashmap
|
|
.borrow_mut()
|
|
.insert(param_env.and(trait_ref), WithDepNode::new(dep_node, result));
|
|
}
|
|
|
|
/// For various reasons, it's possible for a subobligation
|
|
/// to have a *lower* recursion_depth than the obligation used to create it.
|
|
/// Projection sub-obligations may be returned from the projection cache,
|
|
/// which results in obligations with an 'old' `recursion_depth`.
|
|
/// Additionally, methods like `wf::obligations` and
|
|
/// `InferCtxt.subtype_predicate` produce subobligations without
|
|
/// taking in a 'parent' depth, causing the generated subobligations
|
|
/// to have a `recursion_depth` of `0`.
|
|
///
|
|
/// To ensure that obligation_depth never decreasees, we force all subobligations
|
|
/// to have at least the depth of the original obligation.
|
|
fn add_depth<T: 'cx, I: Iterator<Item = &'cx mut Obligation<'tcx, T>>>(
|
|
&self,
|
|
it: I,
|
|
min_depth: usize,
|
|
) {
|
|
it.for_each(|o| o.recursion_depth = cmp::max(min_depth, o.recursion_depth) + 1);
|
|
}
|
|
|
|
/// 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.
|
|
fn check_recursion_limit<T: Display + TypeFoldable<'tcx>, V: Display + TypeFoldable<'tcx>>(
|
|
&self,
|
|
obligation: &Obligation<'tcx, T>,
|
|
error_obligation: &Obligation<'tcx, V>,
|
|
) -> Result<(), OverflowError> {
|
|
let recursion_limit = *self.infcx.tcx.sess.recursion_limit.get();
|
|
if obligation.recursion_depth >= recursion_limit {
|
|
match self.query_mode {
|
|
TraitQueryMode::Standard => {
|
|
self.infcx().report_overflow_error(error_obligation, true);
|
|
}
|
|
TraitQueryMode::Canonical => {
|
|
return Err(OverflowError);
|
|
}
|
|
}
|
|
}
|
|
Ok(())
|
|
}
|
|
|
|
///////////////////////////////////////////////////////////////////////////
|
|
// CANDIDATE ASSEMBLY
|
|
//
|
|
// The selection process begins by examining all in-scope impls,
|
|
// caller obligations, and so forth and assembling a list of
|
|
// candidates. See the [rustc dev guide] for more details.
|
|
//
|
|
// [rustc dev guide]:
|
|
// https://rustc-dev-guide.rust-lang.org/traits/resolution.html#candidate-assembly
|
|
|
|
fn candidate_from_obligation<'o>(
|
|
&mut self,
|
|
stack: &TraitObligationStack<'o, 'tcx>,
|
|
) -> SelectionResult<'tcx, SelectionCandidate<'tcx>> {
|
|
// Watch out for overflow. This intentionally bypasses (and does
|
|
// not update) the cache.
|
|
self.check_recursion_limit(&stack.obligation, &stack.obligation)?;
|
|
|
|
// Check the cache. Note that we freshen the trait-ref
|
|
// separately rather than using `stack.fresh_trait_ref` --
|
|
// this is because we want the unbound variables to be
|
|
// replaced with fresh types starting from index 0.
|
|
let cache_fresh_trait_pred = self.infcx.freshen(stack.obligation.predicate.clone());
|
|
debug!(
|
|
"candidate_from_obligation(cache_fresh_trait_pred={:?}, obligation={:?})",
|
|
cache_fresh_trait_pred, stack
|
|
);
|
|
debug_assert!(!stack.obligation.predicate.has_escaping_bound_vars());
|
|
|
|
if let Some(c) =
|
|
self.check_candidate_cache(stack.obligation.param_env, &cache_fresh_trait_pred)
|
|
{
|
|
debug!("CACHE HIT: SELECT({:?})={:?}", cache_fresh_trait_pred, c);
|
|
return c;
|
|
}
|
|
|
|
// If no match, compute result and insert into cache.
|
|
//
|
|
// FIXME(nikomatsakis) -- this cache is not taking into
|
|
// account cycles that may have occurred in forming the
|
|
// candidate. I don't know of any specific problems that
|
|
// result but it seems awfully suspicious.
|
|
let (candidate, dep_node) =
|
|
self.in_task(|this| this.candidate_from_obligation_no_cache(stack));
|
|
|
|
debug!("CACHE MISS: SELECT({:?})={:?}", cache_fresh_trait_pred, candidate);
|
|
self.insert_candidate_cache(
|
|
stack.obligation.param_env,
|
|
cache_fresh_trait_pred,
|
|
dep_node,
|
|
candidate.clone(),
|
|
);
|
|
candidate
|
|
}
|
|
|
|
fn in_task<OP, R>(&mut self, op: OP) -> (R, DepNodeIndex)
|
|
where
|
|
OP: FnOnce(&mut Self) -> R,
|
|
{
|
|
let (result, dep_node) =
|
|
self.tcx().dep_graph.with_anon_task(DepKind::TraitSelect, || op(self));
|
|
self.tcx().dep_graph.read_index(dep_node);
|
|
(result, dep_node)
|
|
}
|
|
|
|
// Treat negative impls as unimplemented, and reservation impls as ambiguity.
|
|
fn filter_negative_and_reservation_impls(
|
|
&mut self,
|
|
candidate: SelectionCandidate<'tcx>,
|
|
) -> SelectionResult<'tcx, SelectionCandidate<'tcx>> {
|
|
if let ImplCandidate(def_id) = candidate {
|
|
let tcx = self.tcx();
|
|
match tcx.impl_polarity(def_id) {
|
|
ty::ImplPolarity::Negative if !self.allow_negative_impls => {
|
|
return Err(Unimplemented);
|
|
}
|
|
ty::ImplPolarity::Reservation => {
|
|
if let Some(intercrate_ambiguity_clauses) =
|
|
&mut self.intercrate_ambiguity_causes
|
|
{
|
|
let attrs = tcx.get_attrs(def_id);
|
|
let attr = attr::find_by_name(&attrs, sym::rustc_reservation_impl);
|
|
let value = attr.and_then(|a| a.value_str());
|
|
if let Some(value) = value {
|
|
debug!(
|
|
"filter_negative_and_reservation_impls: \
|
|
reservation impl ambiguity on {:?}",
|
|
def_id
|
|
);
|
|
intercrate_ambiguity_clauses.push(
|
|
IntercrateAmbiguityCause::ReservationImpl {
|
|
message: value.to_string(),
|
|
},
|
|
);
|
|
}
|
|
}
|
|
return Ok(None);
|
|
}
|
|
_ => {}
|
|
};
|
|
}
|
|
Ok(Some(candidate))
|
|
}
|
|
|
|
fn candidate_from_obligation_no_cache<'o>(
|
|
&mut self,
|
|
stack: &TraitObligationStack<'o, 'tcx>,
|
|
) -> SelectionResult<'tcx, SelectionCandidate<'tcx>> {
|
|
if stack.obligation.predicate.references_error() {
|
|
// If we encounter a `Error`, we generally prefer the
|
|
// most "optimistic" result in response -- that is, the
|
|
// one least likely to report downstream errors. But
|
|
// because this routine is shared by coherence and by
|
|
// trait selection, there isn't an obvious "right" choice
|
|
// here in that respect, so we opt to just return
|
|
// ambiguity and let the upstream clients sort it out.
|
|
return Ok(None);
|
|
}
|
|
|
|
if let Some(conflict) = self.is_knowable(stack) {
|
|
debug!("coherence stage: not knowable");
|
|
if self.intercrate_ambiguity_causes.is_some() {
|
|
debug!("evaluate_stack: intercrate_ambiguity_causes is some");
|
|
// Heuristics: show the diagnostics when there are no candidates in crate.
|
|
if let Ok(candidate_set) = self.assemble_candidates(stack) {
|
|
let mut no_candidates_apply = true;
|
|
{
|
|
let evaluated_candidates =
|
|
candidate_set.vec.iter().map(|c| self.evaluate_candidate(stack, &c));
|
|
|
|
for ec in evaluated_candidates {
|
|
match ec {
|
|
Ok(c) => {
|
|
if c.may_apply() {
|
|
no_candidates_apply = false;
|
|
break;
|
|
}
|
|
}
|
|
Err(e) => return Err(e.into()),
|
|
}
|
|
}
|
|
}
|
|
|
|
if !candidate_set.ambiguous && no_candidates_apply {
|
|
let trait_ref = stack.obligation.predicate.skip_binder().trait_ref;
|
|
let self_ty = trait_ref.self_ty();
|
|
let trait_desc = trait_ref.print_only_trait_path().to_string();
|
|
let self_desc = if self_ty.has_concrete_skeleton() {
|
|
Some(self_ty.to_string())
|
|
} else {
|
|
None
|
|
};
|
|
let cause = if let Conflict::Upstream = conflict {
|
|
IntercrateAmbiguityCause::UpstreamCrateUpdate { trait_desc, self_desc }
|
|
} else {
|
|
IntercrateAmbiguityCause::DownstreamCrate { trait_desc, self_desc }
|
|
};
|
|
debug!("evaluate_stack: pushing cause = {:?}", cause);
|
|
self.intercrate_ambiguity_causes.as_mut().unwrap().push(cause);
|
|
}
|
|
}
|
|
}
|
|
return Ok(None);
|
|
}
|
|
|
|
let candidate_set = self.assemble_candidates(stack)?;
|
|
|
|
if candidate_set.ambiguous {
|
|
debug!("candidate set contains ambig");
|
|
return Ok(None);
|
|
}
|
|
|
|
let mut candidates = candidate_set.vec;
|
|
|
|
debug!("assembled {} candidates for {:?}: {:?}", candidates.len(), stack, candidates);
|
|
|
|
// At this point, we know that each of the entries in the
|
|
// candidate set is *individually* applicable. Now we have to
|
|
// figure out if they contain mutual incompatibilities. This
|
|
// frequently arises if we have an unconstrained input type --
|
|
// for example, we are looking for `$0: Eq` where `$0` is some
|
|
// unconstrained type variable. In that case, we'll get a
|
|
// candidate which assumes $0 == int, one that assumes `$0 ==
|
|
// usize`, etc. This spells an ambiguity.
|
|
|
|
// If there is more than one candidate, first winnow them down
|
|
// by considering extra conditions (nested obligations and so
|
|
// forth). We don't winnow if there is exactly one
|
|
// candidate. This is a relatively minor distinction but it
|
|
// can lead to better inference and error-reporting. An
|
|
// example would be if there was an impl:
|
|
//
|
|
// impl<T:Clone> Vec<T> { fn push_clone(...) { ... } }
|
|
//
|
|
// and we were to see some code `foo.push_clone()` where `boo`
|
|
// is a `Vec<Bar>` and `Bar` does not implement `Clone`. If
|
|
// we were to winnow, we'd wind up with zero candidates.
|
|
// Instead, we select the right impl now but report "`Bar` does
|
|
// not implement `Clone`".
|
|
if candidates.len() == 1 {
|
|
return self.filter_negative_and_reservation_impls(candidates.pop().unwrap());
|
|
}
|
|
|
|
// Winnow, but record the exact outcome of evaluation, which
|
|
// is needed for specialization. Propagate overflow if it occurs.
|
|
let mut 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) => Err(Overflow),
|
|
})
|
|
.flat_map(Result::transpose)
|
|
.collect::<Result<Vec<_>, _>>()?;
|
|
|
|
debug!("winnowed to {} candidates for {:?}: {:?}", candidates.len(), stack, candidates);
|
|
|
|
let needs_infer = stack.obligation.predicate.needs_infer();
|
|
|
|
// If there are STILL multiple candidates, we can further
|
|
// reduce the list by dropping duplicates -- including
|
|
// resolving specializations.
|
|
if candidates.len() > 1 {
|
|
let mut i = 0;
|
|
while i < candidates.len() {
|
|
let is_dup = (0..candidates.len()).filter(|&j| i != j).any(|j| {
|
|
self.candidate_should_be_dropped_in_favor_of(
|
|
&candidates[i],
|
|
&candidates[j],
|
|
needs_infer,
|
|
)
|
|
});
|
|
if is_dup {
|
|
debug!("Dropping candidate #{}/{}: {:?}", i, candidates.len(), candidates[i]);
|
|
candidates.swap_remove(i);
|
|
} else {
|
|
debug!("Retaining candidate #{}/{}: {:?}", i, candidates.len(), candidates[i]);
|
|
i += 1;
|
|
|
|
// If there are *STILL* multiple candidates, give up
|
|
// and report ambiguity.
|
|
if i > 1 {
|
|
debug!("multiple matches, ambig");
|
|
return Ok(None);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
// 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() {
|
|
return Err(Unimplemented);
|
|
}
|
|
|
|
// Just one candidate left.
|
|
self.filter_negative_and_reservation_impls(candidates.pop().unwrap().candidate)
|
|
}
|
|
|
|
fn is_knowable<'o>(&mut self, stack: &TraitObligationStack<'o, 'tcx>) -> Option<Conflict> {
|
|
debug!("is_knowable(intercrate={:?})", self.intercrate);
|
|
|
|
if !self.intercrate {
|
|
return None;
|
|
}
|
|
|
|
let obligation = &stack.obligation;
|
|
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.tcx(), trait_ref)
|
|
}
|
|
|
|
/// Returns `true` if the global caches can be used.
|
|
/// Do note that if the type itself is not in the
|
|
/// global tcx, the local caches will be used.
|
|
fn can_use_global_caches(&self, param_env: ty::ParamEnv<'tcx>) -> bool {
|
|
// If there are any e.g. 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_local_value() {
|
|
return false;
|
|
}
|
|
|
|
// Avoid using the master cache during coherence and just rely
|
|
// on the local cache. This effectively disables caching
|
|
// during coherence. 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.
|
|
if self.intercrate {
|
|
return false;
|
|
}
|
|
|
|
// Otherwise, we can use the global cache.
|
|
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 tcx = self.tcx();
|
|
let trait_ref = &cache_fresh_trait_pred.skip_binder().trait_ref;
|
|
if self.can_use_global_caches(param_env) {
|
|
let cache = tcx.selection_cache.hashmap.borrow();
|
|
if let Some(cached) = cache.get(¶m_env.and(*trait_ref)) {
|
|
return Some(cached.get(tcx));
|
|
}
|
|
}
|
|
self.infcx
|
|
.selection_cache
|
|
.hashmap
|
|
.borrow()
|
|
.get(¶m_env.and(*trait_ref))
|
|
.map(|v| v.get(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_local_value(),
|
|
_ => true,
|
|
}
|
|
}
|
|
|
|
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 tcx = self.tcx();
|
|
let trait_ref = cache_fresh_trait_pred.skip_binder().trait_ref;
|
|
|
|
if !self.can_cache_candidate(&candidate) {
|
|
debug!(
|
|
"insert_candidate_cache(trait_ref={:?}, candidate={:?} -\
|
|
candidate is not cacheable",
|
|
trait_ref, candidate
|
|
);
|
|
return;
|
|
}
|
|
|
|
if self.can_use_global_caches(param_env) {
|
|
if let Err(Overflow) = candidate {
|
|
// Don't cache overflow globally; we only produce this in certain modes.
|
|
} else if !trait_ref.has_local_value() {
|
|
if !candidate.has_local_value() {
|
|
debug!(
|
|
"insert_candidate_cache(trait_ref={:?}, candidate={:?}) global",
|
|
trait_ref, candidate,
|
|
);
|
|
// This may overwrite the cache with the same value.
|
|
tcx.selection_cache
|
|
.hashmap
|
|
.borrow_mut()
|
|
.insert(param_env.and(trait_ref), WithDepNode::new(dep_node, candidate));
|
|
return;
|
|
}
|
|
}
|
|
}
|
|
|
|
debug!(
|
|
"insert_candidate_cache(trait_ref={:?}, candidate={:?}) local",
|
|
trait_ref, candidate,
|
|
);
|
|
self.infcx
|
|
.selection_cache
|
|
.hashmap
|
|
.borrow_mut()
|
|
.insert(param_env.and(trait_ref), WithDepNode::new(dep_node, candidate));
|
|
}
|
|
|
|
fn assemble_candidates<'o>(
|
|
&mut self,
|
|
stack: &TraitObligationStack<'o, 'tcx>,
|
|
) -> Result<SelectionCandidateSet<'tcx>, SelectionError<'tcx>> {
|
|
let TraitObligationStack { obligation, .. } = *stack;
|
|
let obligation = &Obligation {
|
|
param_env: obligation.param_env,
|
|
cause: obligation.cause.clone(),
|
|
recursion_depth: obligation.recursion_depth,
|
|
predicate: self.infcx().resolve_vars_if_possible(&obligation.predicate),
|
|
};
|
|
|
|
if obligation.predicate.skip_binder().self_ty().is_ty_var() {
|
|
// Self is a type variable (e.g., `_: AsRef<str>`).
|
|
//
|
|
// This is somewhat problematic, as the current scheme can't really
|
|
// handle it turning to be a projection. This does end up as truly
|
|
// ambiguous in most cases anyway.
|
|
//
|
|
// Take the fast path out - this also improves
|
|
// performance by preventing assemble_candidates_from_impls from
|
|
// matching every impl for this trait.
|
|
return Ok(SelectionCandidateSet { vec: vec![], ambiguous: true });
|
|
}
|
|
|
|
let mut candidates = SelectionCandidateSet { vec: Vec::new(), ambiguous: false };
|
|
|
|
self.assemble_candidates_for_trait_alias(obligation, &mut candidates)?;
|
|
|
|
// Other bounds. Consider both in-scope bounds from fn decl
|
|
// and applicable impls. There is a certain set of precedence rules here.
|
|
let def_id = obligation.predicate.def_id();
|
|
let lang_items = self.tcx().lang_items();
|
|
|
|
if lang_items.copy_trait() == Some(def_id) {
|
|
debug!("obligation self ty is {:?}", obligation.predicate.skip_binder().self_ty());
|
|
|
|
// User-defined copy impls are permitted, but only for
|
|
// structs and enums.
|
|
self.assemble_candidates_from_impls(obligation, &mut candidates)?;
|
|
|
|
// For other types, we'll use the builtin rules.
|
|
let copy_conditions = self.copy_clone_conditions(obligation);
|
|
self.assemble_builtin_bound_candidates(copy_conditions, &mut candidates)?;
|
|
} else if lang_items.sized_trait() == Some(def_id) {
|
|
// Sized is never implementable by end-users, it is
|
|
// always automatically computed.
|
|
let sized_conditions = self.sized_conditions(obligation);
|
|
self.assemble_builtin_bound_candidates(sized_conditions, &mut candidates)?;
|
|
} else if lang_items.unsize_trait() == Some(def_id) {
|
|
self.assemble_candidates_for_unsizing(obligation, &mut candidates);
|
|
} else {
|
|
if lang_items.clone_trait() == Some(def_id) {
|
|
// Same builtin conditions as `Copy`, i.e., every type which has builtin support
|
|
// for `Copy` also has builtin support for `Clone`, and tuples/arrays of `Clone`
|
|
// types have builtin support for `Clone`.
|
|
let clone_conditions = self.copy_clone_conditions(obligation);
|
|
self.assemble_builtin_bound_candidates(clone_conditions, &mut candidates)?;
|
|
}
|
|
|
|
self.assemble_generator_candidates(obligation, &mut candidates)?;
|
|
self.assemble_closure_candidates(obligation, &mut candidates)?;
|
|
self.assemble_fn_pointer_candidates(obligation, &mut candidates)?;
|
|
self.assemble_candidates_from_impls(obligation, &mut candidates)?;
|
|
self.assemble_candidates_from_object_ty(obligation, &mut candidates);
|
|
}
|
|
|
|
self.assemble_candidates_from_projected_tys(obligation, &mut candidates);
|
|
self.assemble_candidates_from_caller_bounds(stack, &mut candidates)?;
|
|
// Auto implementations have lower priority, so we only
|
|
// consider triggering a default if there is no other impl that can apply.
|
|
if candidates.vec.is_empty() {
|
|
self.assemble_candidates_from_auto_impls(obligation, &mut candidates)?;
|
|
}
|
|
debug!("candidate list size: {}", candidates.vec.len());
|
|
Ok(candidates)
|
|
}
|
|
|
|
fn assemble_candidates_from_projected_tys(
|
|
&mut self,
|
|
obligation: &TraitObligation<'tcx>,
|
|
candidates: &mut SelectionCandidateSet<'tcx>,
|
|
) {
|
|
debug!("assemble_candidates_for_projected_tys({:?})", obligation);
|
|
|
|
// Before we go into the whole placeholder thing, just
|
|
// quickly check if the self-type is a projection at all.
|
|
match obligation.predicate.skip_binder().trait_ref.self_ty().kind {
|
|
ty::Projection(_) | ty::Opaque(..) => {}
|
|
ty::Infer(ty::TyVar(_)) => {
|
|
span_bug!(
|
|
obligation.cause.span,
|
|
"Self=_ should have been handled by assemble_candidates"
|
|
);
|
|
}
|
|
_ => return,
|
|
}
|
|
|
|
let result = self.infcx.probe(|snapshot| {
|
|
self.match_projection_obligation_against_definition_bounds(obligation, snapshot)
|
|
});
|
|
|
|
if result {
|
|
candidates.vec.push(ProjectionCandidate);
|
|
}
|
|
}
|
|
|
|
fn match_projection_obligation_against_definition_bounds(
|
|
&mut self,
|
|
obligation: &TraitObligation<'tcx>,
|
|
snapshot: &CombinedSnapshot<'_, 'tcx>,
|
|
) -> bool {
|
|
let poly_trait_predicate = self.infcx().resolve_vars_if_possible(&obligation.predicate);
|
|
let (placeholder_trait_predicate, placeholder_map) =
|
|
self.infcx().replace_bound_vars_with_placeholders(&poly_trait_predicate);
|
|
debug!(
|
|
"match_projection_obligation_against_definition_bounds: \
|
|
placeholder_trait_predicate={:?}",
|
|
placeholder_trait_predicate,
|
|
);
|
|
|
|
let (def_id, substs) = match placeholder_trait_predicate.trait_ref.self_ty().kind {
|
|
ty::Projection(ref data) => (data.trait_ref(self.tcx()).def_id, data.substs),
|
|
ty::Opaque(def_id, substs) => (def_id, substs),
|
|
_ => {
|
|
span_bug!(
|
|
obligation.cause.span,
|
|
"match_projection_obligation_against_definition_bounds() called \
|
|
but self-ty is not a projection: {:?}",
|
|
placeholder_trait_predicate.trait_ref.self_ty()
|
|
);
|
|
}
|
|
};
|
|
debug!(
|
|
"match_projection_obligation_against_definition_bounds: \
|
|
def_id={:?}, substs={:?}",
|
|
def_id, substs
|
|
);
|
|
|
|
let predicates_of = self.tcx().predicates_of(def_id);
|
|
let bounds = predicates_of.instantiate(self.tcx(), substs);
|
|
debug!(
|
|
"match_projection_obligation_against_definition_bounds: \
|
|
bounds={:?}",
|
|
bounds
|
|
);
|
|
|
|
let elaborated_predicates = util::elaborate_predicates(self.tcx(), bounds.predicates);
|
|
let matching_bound = elaborated_predicates.filter_to_traits().find(|bound| {
|
|
self.infcx.probe(|_| {
|
|
self.match_projection(
|
|
obligation,
|
|
bound.clone(),
|
|
placeholder_trait_predicate.trait_ref.clone(),
|
|
&placeholder_map,
|
|
snapshot,
|
|
)
|
|
})
|
|
});
|
|
|
|
debug!(
|
|
"match_projection_obligation_against_definition_bounds: \
|
|
matching_bound={:?}",
|
|
matching_bound
|
|
);
|
|
match matching_bound {
|
|
None => false,
|
|
Some(bound) => {
|
|
// Repeat the successful match, if any, this time outside of a probe.
|
|
let result = self.match_projection(
|
|
obligation,
|
|
bound,
|
|
placeholder_trait_predicate.trait_ref.clone(),
|
|
&placeholder_map,
|
|
snapshot,
|
|
);
|
|
|
|
assert!(result);
|
|
true
|
|
}
|
|
}
|
|
}
|
|
|
|
fn match_projection(
|
|
&mut self,
|
|
obligation: &TraitObligation<'tcx>,
|
|
trait_bound: ty::PolyTraitRef<'tcx>,
|
|
placeholder_trait_ref: ty::TraitRef<'tcx>,
|
|
placeholder_map: &PlaceholderMap<'tcx>,
|
|
snapshot: &CombinedSnapshot<'_, 'tcx>,
|
|
) -> bool {
|
|
debug_assert!(!placeholder_trait_ref.has_escaping_bound_vars());
|
|
self.infcx
|
|
.at(&obligation.cause, obligation.param_env)
|
|
.sup(ty::Binder::dummy(placeholder_trait_ref), trait_bound)
|
|
.is_ok()
|
|
&& self.infcx.leak_check(false, placeholder_map, snapshot).is_ok()
|
|
}
|
|
|
|
/// Given an obligation like `<SomeTrait for T>`, searches the obligations that the caller
|
|
/// supplied to find out whether it is listed among them.
|
|
///
|
|
/// Never affects the inference environment.
|
|
fn assemble_candidates_from_caller_bounds<'o>(
|
|
&mut self,
|
|
stack: &TraitObligationStack<'o, 'tcx>,
|
|
candidates: &mut SelectionCandidateSet<'tcx>,
|
|
) -> Result<(), SelectionError<'tcx>> {
|
|
debug!("assemble_candidates_from_caller_bounds({:?})", stack.obligation);
|
|
|
|
let all_bounds = stack
|
|
.obligation
|
|
.param_env
|
|
.caller_bounds
|
|
.iter()
|
|
.filter_map(|o| o.to_opt_poly_trait_ref());
|
|
|
|
// Micro-optimization: filter out predicates relating to different traits.
|
|
let matching_bounds =
|
|
all_bounds.filter(|p| p.def_id() == stack.obligation.predicate.def_id());
|
|
|
|
// Keep only those bounds which may apply, and propagate overflow if it occurs.
|
|
let mut param_candidates = vec![];
|
|
for bound in matching_bounds {
|
|
let wc = self.evaluate_where_clause(stack, bound.clone())?;
|
|
if wc.may_apply() {
|
|
param_candidates.push(ParamCandidate(bound));
|
|
}
|
|
}
|
|
|
|
candidates.vec.extend(param_candidates);
|
|
|
|
Ok(())
|
|
}
|
|
|
|
fn evaluate_where_clause<'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.into_iter())
|
|
}
|
|
Err(()) => Ok(EvaluatedToErr),
|
|
}
|
|
})
|
|
}
|
|
|
|
fn assemble_generator_candidates(
|
|
&mut self,
|
|
obligation: &TraitObligation<'tcx>,
|
|
candidates: &mut SelectionCandidateSet<'tcx>,
|
|
) -> Result<(), SelectionError<'tcx>> {
|
|
if self.tcx().lang_items().gen_trait() != Some(obligation.predicate.def_id()) {
|
|
return Ok(());
|
|
}
|
|
|
|
// Okay to skip binder because the substs on generator types never
|
|
// touch bound regions, they just capture the in-scope
|
|
// type/region parameters.
|
|
let self_ty = *obligation.self_ty().skip_binder();
|
|
match self_ty.kind {
|
|
ty::Generator(..) => {
|
|
debug!(
|
|
"assemble_generator_candidates: self_ty={:?} obligation={:?}",
|
|
self_ty, obligation
|
|
);
|
|
|
|
candidates.vec.push(GeneratorCandidate);
|
|
}
|
|
ty::Infer(ty::TyVar(_)) => {
|
|
debug!("assemble_generator_candidates: ambiguous self-type");
|
|
candidates.ambiguous = true;
|
|
}
|
|
_ => {}
|
|
}
|
|
|
|
Ok(())
|
|
}
|
|
|
|
/// Checks for the artificial impl that the compiler will create for an obligation like `X :
|
|
/// FnMut<..>` where `X` is a closure type.
|
|
///
|
|
/// Note: the type parameters on a closure candidate are modeled as *output* type
|
|
/// parameters and hence do not affect whether this trait is a match or not. They will be
|
|
/// unified during the confirmation step.
|
|
fn assemble_closure_candidates(
|
|
&mut self,
|
|
obligation: &TraitObligation<'tcx>,
|
|
candidates: &mut SelectionCandidateSet<'tcx>,
|
|
) -> Result<(), SelectionError<'tcx>> {
|
|
let kind = match self.tcx().fn_trait_kind_from_lang_item(obligation.predicate.def_id()) {
|
|
Some(k) => k,
|
|
None => {
|
|
return Ok(());
|
|
}
|
|
};
|
|
|
|
// Okay to skip binder because the substs on closure types never
|
|
// touch bound regions, they just capture the in-scope
|
|
// type/region parameters
|
|
match obligation.self_ty().skip_binder().kind {
|
|
ty::Closure(_, closure_substs) => {
|
|
debug!("assemble_unboxed_candidates: kind={:?} obligation={:?}", kind, obligation);
|
|
match self.infcx.closure_kind(closure_substs) {
|
|
Some(closure_kind) => {
|
|
debug!("assemble_unboxed_candidates: closure_kind = {:?}", closure_kind);
|
|
if closure_kind.extends(kind) {
|
|
candidates.vec.push(ClosureCandidate);
|
|
}
|
|
}
|
|
None => {
|
|
debug!("assemble_unboxed_candidates: closure_kind not yet known");
|
|
candidates.vec.push(ClosureCandidate);
|
|
}
|
|
}
|
|
}
|
|
ty::Infer(ty::TyVar(_)) => {
|
|
debug!("assemble_unboxed_closure_candidates: ambiguous self-type");
|
|
candidates.ambiguous = true;
|
|
}
|
|
_ => {}
|
|
}
|
|
|
|
Ok(())
|
|
}
|
|
|
|
/// Implements one of the `Fn()` family for a fn pointer.
|
|
fn assemble_fn_pointer_candidates(
|
|
&mut self,
|
|
obligation: &TraitObligation<'tcx>,
|
|
candidates: &mut SelectionCandidateSet<'tcx>,
|
|
) -> Result<(), SelectionError<'tcx>> {
|
|
// We provide impl of all fn traits for fn pointers.
|
|
if self.tcx().fn_trait_kind_from_lang_item(obligation.predicate.def_id()).is_none() {
|
|
return Ok(());
|
|
}
|
|
|
|
// Okay to skip binder because what we are inspecting doesn't involve bound regions.
|
|
let self_ty = *obligation.self_ty().skip_binder();
|
|
match self_ty.kind {
|
|
ty::Infer(ty::TyVar(_)) => {
|
|
debug!("assemble_fn_pointer_candidates: ambiguous self-type");
|
|
candidates.ambiguous = true; // Could wind up being a fn() type.
|
|
}
|
|
// Provide an impl, but only for suitable `fn` pointers.
|
|
ty::FnDef(..) | ty::FnPtr(_) => {
|
|
if let ty::FnSig {
|
|
unsafety: hir::Unsafety::Normal,
|
|
abi: Abi::Rust,
|
|
c_variadic: false,
|
|
..
|
|
} = self_ty.fn_sig(self.tcx()).skip_binder()
|
|
{
|
|
candidates.vec.push(FnPointerCandidate);
|
|
}
|
|
}
|
|
_ => {}
|
|
}
|
|
|
|
Ok(())
|
|
}
|
|
|
|
/// Searches for impls that might apply to `obligation`.
|
|
fn assemble_candidates_from_impls(
|
|
&mut self,
|
|
obligation: &TraitObligation<'tcx>,
|
|
candidates: &mut SelectionCandidateSet<'tcx>,
|
|
) -> Result<(), SelectionError<'tcx>> {
|
|
debug!("assemble_candidates_from_impls(obligation={:?})", obligation);
|
|
|
|
self.tcx().for_each_relevant_impl(
|
|
obligation.predicate.def_id(),
|
|
obligation.predicate.skip_binder().trait_ref.self_ty(),
|
|
|impl_def_id| {
|
|
self.infcx.probe(|snapshot| {
|
|
if let Ok(_substs) = self.match_impl(impl_def_id, obligation, snapshot) {
|
|
candidates.vec.push(ImplCandidate(impl_def_id));
|
|
}
|
|
});
|
|
},
|
|
);
|
|
|
|
Ok(())
|
|
}
|
|
|
|
fn assemble_candidates_from_auto_impls(
|
|
&mut self,
|
|
obligation: &TraitObligation<'tcx>,
|
|
candidates: &mut SelectionCandidateSet<'tcx>,
|
|
) -> Result<(), SelectionError<'tcx>> {
|
|
// Okay to skip binder here because the tests we do below do not involve bound regions.
|
|
let self_ty = *obligation.self_ty().skip_binder();
|
|
debug!("assemble_candidates_from_auto_impls(self_ty={:?})", self_ty);
|
|
|
|
let def_id = obligation.predicate.def_id();
|
|
|
|
if self.tcx().trait_is_auto(def_id) {
|
|
match self_ty.kind {
|
|
ty::Dynamic(..) => {
|
|
// For object types, we don't know what the closed
|
|
// over types are. This means we conservatively
|
|
// say nothing; a candidate may be added by
|
|
// `assemble_candidates_from_object_ty`.
|
|
}
|
|
ty::Foreign(..) => {
|
|
// Since the contents of foreign types is unknown,
|
|
// we don't add any `..` impl. Default traits could
|
|
// still be provided by a manual implementation for
|
|
// this trait and type.
|
|
}
|
|
ty::Param(..) | ty::Projection(..) => {
|
|
// In these cases, we don't know what the actual
|
|
// type is. Therefore, we cannot break it down
|
|
// into its constituent types. So we don't
|
|
// consider the `..` impl but instead just add no
|
|
// candidates: this means that typeck will only
|
|
// succeed if there is another reason to believe
|
|
// that this obligation holds. That could be a
|
|
// where-clause or, in the case of an object type,
|
|
// it could be that the object type lists the
|
|
// trait (e.g., `Foo+Send : Send`). See
|
|
// `compile-fail/typeck-default-trait-impl-send-param.rs`
|
|
// for an example of a test case that exercises
|
|
// this path.
|
|
}
|
|
ty::Infer(ty::TyVar(_)) => {
|
|
// The auto impl might apply; we don't know.
|
|
candidates.ambiguous = true;
|
|
}
|
|
ty::Generator(_, _, movability)
|
|
if self.tcx().lang_items().unpin_trait() == Some(def_id) =>
|
|
{
|
|
match movability {
|
|
hir::Movability::Static => {
|
|
// Immovable generators are never `Unpin`, so
|
|
// suppress the normal auto-impl candidate for it.
|
|
}
|
|
hir::Movability::Movable => {
|
|
// Movable generators are always `Unpin`, so add an
|
|
// unconditional builtin candidate.
|
|
candidates.vec.push(BuiltinCandidate { has_nested: false });
|
|
}
|
|
}
|
|
}
|
|
|
|
_ => candidates.vec.push(AutoImplCandidate(def_id)),
|
|
}
|
|
}
|
|
|
|
Ok(())
|
|
}
|
|
|
|
/// Searches for impls that might apply to `obligation`.
|
|
fn assemble_candidates_from_object_ty(
|
|
&mut self,
|
|
obligation: &TraitObligation<'tcx>,
|
|
candidates: &mut SelectionCandidateSet<'tcx>,
|
|
) {
|
|
debug!(
|
|
"assemble_candidates_from_object_ty(self_ty={:?})",
|
|
obligation.self_ty().skip_binder()
|
|
);
|
|
|
|
self.infcx.probe(|_snapshot| {
|
|
// The code below doesn't care about regions, and the
|
|
// self-ty here doesn't escape this probe, so just erase
|
|
// any LBR.
|
|
let self_ty = self.tcx().erase_late_bound_regions(&obligation.self_ty());
|
|
let poly_trait_ref = match self_ty.kind {
|
|
ty::Dynamic(ref data, ..) => {
|
|
if data.auto_traits().any(|did| did == obligation.predicate.def_id()) {
|
|
debug!(
|
|
"assemble_candidates_from_object_ty: matched builtin bound, \
|
|
pushing candidate"
|
|
);
|
|
candidates.vec.push(BuiltinObjectCandidate);
|
|
return;
|
|
}
|
|
|
|
if let Some(principal) = data.principal() {
|
|
if !self.infcx.tcx.features().object_safe_for_dispatch {
|
|
principal.with_self_ty(self.tcx(), self_ty)
|
|
} else if self.tcx().is_object_safe(principal.def_id()) {
|
|
principal.with_self_ty(self.tcx(), self_ty)
|
|
} else {
|
|
return;
|
|
}
|
|
} else {
|
|
// Only auto trait bounds exist.
|
|
return;
|
|
}
|
|
}
|
|
ty::Infer(ty::TyVar(_)) => {
|
|
debug!("assemble_candidates_from_object_ty: ambiguous");
|
|
candidates.ambiguous = true; // could wind up being an object type
|
|
return;
|
|
}
|
|
_ => return,
|
|
};
|
|
|
|
debug!("assemble_candidates_from_object_ty: poly_trait_ref={:?}", poly_trait_ref);
|
|
|
|
// Count only those upcast versions that match the trait-ref
|
|
// we are looking for. Specifically, do not only check for the
|
|
// correct trait, but also the correct type parameters.
|
|
// For example, we may be trying to upcast `Foo` to `Bar<i32>`,
|
|
// but `Foo` is declared as `trait Foo: Bar<u32>`.
|
|
let upcast_trait_refs = util::supertraits(self.tcx(), poly_trait_ref)
|
|
.filter(|upcast_trait_ref| {
|
|
self.infcx
|
|
.probe(|_| self.match_poly_trait_ref(obligation, *upcast_trait_ref).is_ok())
|
|
})
|
|
.count();
|
|
|
|
if upcast_trait_refs > 1 {
|
|
// Can be upcast in many ways; need more type information.
|
|
candidates.ambiguous = true;
|
|
} else if upcast_trait_refs == 1 {
|
|
candidates.vec.push(ObjectCandidate);
|
|
}
|
|
})
|
|
}
|
|
|
|
/// Searches for unsizing that might apply to `obligation`.
|
|
fn assemble_candidates_for_unsizing(
|
|
&mut self,
|
|
obligation: &TraitObligation<'tcx>,
|
|
candidates: &mut SelectionCandidateSet<'tcx>,
|
|
) {
|
|
// We currently never consider higher-ranked obligations e.g.
|
|
// `for<'a> &'a T: Unsize<Trait+'a>` to be implemented. This is not
|
|
// because they are a priori invalid, and we could potentially add support
|
|
// for them later, it's just that there isn't really a strong need for it.
|
|
// A `T: Unsize<U>` obligation is always used as part of a `T: CoerceUnsize<U>`
|
|
// impl, and those are generally applied to concrete types.
|
|
//
|
|
// That said, one might try to write a fn with a where clause like
|
|
// for<'a> Foo<'a, T>: Unsize<Foo<'a, Trait>>
|
|
// where the `'a` is kind of orthogonal to the relevant part of the `Unsize`.
|
|
// Still, you'd be more likely to write that where clause as
|
|
// T: Trait
|
|
// so it seems ok if we (conservatively) fail to accept that `Unsize`
|
|
// obligation above. Should be possible to extend this in the future.
|
|
let source = match obligation.self_ty().no_bound_vars() {
|
|
Some(t) => t,
|
|
None => {
|
|
// Don't add any candidates if there are bound regions.
|
|
return;
|
|
}
|
|
};
|
|
let target = obligation.predicate.skip_binder().trait_ref.substs.type_at(1);
|
|
|
|
debug!("assemble_candidates_for_unsizing(source={:?}, target={:?})", source, target);
|
|
|
|
let may_apply = match (&source.kind, &target.kind) {
|
|
// Trait+Kx+'a -> Trait+Ky+'b (upcasts).
|
|
(&ty::Dynamic(ref data_a, ..), &ty::Dynamic(ref data_b, ..)) => {
|
|
// Upcasts permit two things:
|
|
//
|
|
// 1. Dropping auto traits, e.g., `Foo + Send` to `Foo`
|
|
// 2. Tightening the region bound, e.g., `Foo + 'a` to `Foo + 'b` if `'a: 'b`
|
|
//
|
|
// Note that neither of these changes requires any
|
|
// change at runtime. Eventually this will be
|
|
// generalized.
|
|
//
|
|
// We always upcast when we can because of reason
|
|
// #2 (region bounds).
|
|
data_a.principal_def_id() == data_b.principal_def_id()
|
|
&& data_b
|
|
.auto_traits()
|
|
// All of a's auto traits need to be in b's auto traits.
|
|
.all(|b| data_a.auto_traits().any(|a| a == b))
|
|
}
|
|
|
|
// `T` -> `Trait`
|
|
(_, &ty::Dynamic(..)) => true,
|
|
|
|
// Ambiguous handling is below `T` -> `Trait`, because inference
|
|
// variables can still implement `Unsize<Trait>` and nested
|
|
// obligations will have the final say (likely deferred).
|
|
(&ty::Infer(ty::TyVar(_)), _) | (_, &ty::Infer(ty::TyVar(_))) => {
|
|
debug!("assemble_candidates_for_unsizing: ambiguous");
|
|
candidates.ambiguous = true;
|
|
false
|
|
}
|
|
|
|
// `[T; n]` -> `[T]`
|
|
(&ty::Array(..), &ty::Slice(_)) => true,
|
|
|
|
// `Struct<T>` -> `Struct<U>`
|
|
(&ty::Adt(def_id_a, _), &ty::Adt(def_id_b, _)) if def_id_a.is_struct() => {
|
|
def_id_a == def_id_b
|
|
}
|
|
|
|
// `(.., T)` -> `(.., U)`
|
|
(&ty::Tuple(tys_a), &ty::Tuple(tys_b)) => tys_a.len() == tys_b.len(),
|
|
|
|
_ => false,
|
|
};
|
|
|
|
if may_apply {
|
|
candidates.vec.push(BuiltinUnsizeCandidate);
|
|
}
|
|
}
|
|
|
|
fn assemble_candidates_for_trait_alias(
|
|
&mut self,
|
|
obligation: &TraitObligation<'tcx>,
|
|
candidates: &mut SelectionCandidateSet<'tcx>,
|
|
) -> Result<(), SelectionError<'tcx>> {
|
|
// Okay to skip binder here because the tests we do below do not involve bound regions.
|
|
let self_ty = *obligation.self_ty().skip_binder();
|
|
debug!("assemble_candidates_for_trait_alias(self_ty={:?})", self_ty);
|
|
|
|
let def_id = obligation.predicate.def_id();
|
|
|
|
if self.tcx().is_trait_alias(def_id) {
|
|
candidates.vec.push(TraitAliasCandidate(def_id));
|
|
}
|
|
|
|
Ok(())
|
|
}
|
|
|
|
///////////////////////////////////////////////////////////////////////////
|
|
// WINNOW
|
|
//
|
|
// 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.
|
|
|
|
/// Returns `true` if `victim` should be dropped in favor of
|
|
/// `other`. Generally speaking we will drop duplicate
|
|
/// candidates and prefer where-clause candidates.
|
|
///
|
|
/// See the comment for "SelectionCandidate" for more details.
|
|
fn candidate_should_be_dropped_in_favor_of(
|
|
&mut self,
|
|
victim: &EvaluatedCandidate<'tcx>,
|
|
other: &EvaluatedCandidate<'tcx>,
|
|
needs_infer: bool,
|
|
) -> bool {
|
|
if victim.candidate == other.candidate {
|
|
return true;
|
|
}
|
|
|
|
// Check if a bound would previously have been removed when normalizing
|
|
// the param_env so that it can be given the lowest priority. See
|
|
// #50825 for the motivation for this.
|
|
let is_global =
|
|
|cand: &ty::PolyTraitRef<'_>| cand.is_global() && !cand.has_late_bound_regions();
|
|
|
|
match other.candidate {
|
|
// Prefer `BuiltinCandidate { has_nested: false }` to anything else.
|
|
// This is a fix for #53123 and prevents winnowing from accidentally extending the
|
|
// lifetime of a variable.
|
|
BuiltinCandidate { has_nested: false } => true,
|
|
ParamCandidate(ref cand) => match victim.candidate {
|
|
AutoImplCandidate(..) => {
|
|
bug!(
|
|
"default implementations shouldn't be recorded \
|
|
when there are other valid candidates"
|
|
);
|
|
}
|
|
// Prefer `BuiltinCandidate { has_nested: false }` to anything else.
|
|
// This is a fix for #53123 and prevents winnowing from accidentally extending the
|
|
// lifetime of a variable.
|
|
BuiltinCandidate { has_nested: false } => false,
|
|
ImplCandidate(..)
|
|
| ClosureCandidate
|
|
| GeneratorCandidate
|
|
| FnPointerCandidate
|
|
| BuiltinObjectCandidate
|
|
| BuiltinUnsizeCandidate
|
|
| BuiltinCandidate { .. }
|
|
| TraitAliasCandidate(..) => {
|
|
// Global bounds from the where clause should be ignored
|
|
// here (see issue #50825). Otherwise, we have a where
|
|
// clause so don't go around looking for impls.
|
|
!is_global(cand)
|
|
}
|
|
ObjectCandidate | ProjectionCandidate => {
|
|
// Arbitrarily give param candidates priority
|
|
// over projection and object candidates.
|
|
!is_global(cand)
|
|
}
|
|
ParamCandidate(..) => false,
|
|
},
|
|
ObjectCandidate | ProjectionCandidate => match victim.candidate {
|
|
AutoImplCandidate(..) => {
|
|
bug!(
|
|
"default implementations shouldn't be recorded \
|
|
when there are other valid candidates"
|
|
);
|
|
}
|
|
// Prefer `BuiltinCandidate { has_nested: false }` to anything else.
|
|
// This is a fix for #53123 and prevents winnowing from accidentally extending the
|
|
// lifetime of a variable.
|
|
BuiltinCandidate { has_nested: false } => false,
|
|
ImplCandidate(..)
|
|
| ClosureCandidate
|
|
| GeneratorCandidate
|
|
| FnPointerCandidate
|
|
| BuiltinObjectCandidate
|
|
| BuiltinUnsizeCandidate
|
|
| BuiltinCandidate { .. }
|
|
| TraitAliasCandidate(..) => true,
|
|
ObjectCandidate | ProjectionCandidate => {
|
|
// Arbitrarily give param candidates priority
|
|
// over projection and object candidates.
|
|
true
|
|
}
|
|
ParamCandidate(ref cand) => is_global(cand),
|
|
},
|
|
ImplCandidate(other_def) => {
|
|
// See if we can toss out `victim` based on specialization.
|
|
// This requires us to know *for sure* that the `other` impl applies
|
|
// i.e., `EvaluatedToOk`.
|
|
if other.evaluation.must_apply_modulo_regions() {
|
|
match victim.candidate {
|
|
ImplCandidate(victim_def) => {
|
|
let tcx = self.tcx();
|
|
if tcx.specializes((other_def, victim_def)) {
|
|
return true;
|
|
}
|
|
return match tcx.impls_are_allowed_to_overlap(other_def, victim_def) {
|
|
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
|
|
// constrainting 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 constrin)
|
|
// 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.
|
|
!needs_infer
|
|
}
|
|
Some(_) => true,
|
|
None => false,
|
|
};
|
|
}
|
|
ParamCandidate(ref cand) => {
|
|
// Prefer the impl to a global where clause candidate.
|
|
return is_global(cand);
|
|
}
|
|
_ => (),
|
|
}
|
|
}
|
|
|
|
false
|
|
}
|
|
ClosureCandidate
|
|
| GeneratorCandidate
|
|
| FnPointerCandidate
|
|
| BuiltinObjectCandidate
|
|
| BuiltinUnsizeCandidate
|
|
| BuiltinCandidate { has_nested: true } => {
|
|
match victim.candidate {
|
|
ParamCandidate(ref cand) => {
|
|
// Prefer these to a global where-clause bound
|
|
// (see issue #50825).
|
|
is_global(cand) && other.evaluation.must_apply_modulo_regions()
|
|
}
|
|
_ => false,
|
|
}
|
|
}
|
|
_ => false,
|
|
}
|
|
}
|
|
|
|
///////////////////////////////////////////////////////////////////////////
|
|
// BUILTIN BOUNDS
|
|
//
|
|
// These cover the traits that are built-in to the language
|
|
// itself: `Copy`, `Clone` and `Sized`.
|
|
|
|
fn assemble_builtin_bound_candidates(
|
|
&mut self,
|
|
conditions: BuiltinImplConditions<'tcx>,
|
|
candidates: &mut SelectionCandidateSet<'tcx>,
|
|
) -> Result<(), SelectionError<'tcx>> {
|
|
match conditions {
|
|
BuiltinImplConditions::Where(nested) => {
|
|
debug!("builtin_bound: nested={:?}", nested);
|
|
candidates
|
|
.vec
|
|
.push(BuiltinCandidate { has_nested: !nested.skip_binder().is_empty() });
|
|
}
|
|
BuiltinImplConditions::None => {}
|
|
BuiltinImplConditions::Ambiguous => {
|
|
debug!("assemble_builtin_bound_candidates: ambiguous builtin");
|
|
candidates.ambiguous = true;
|
|
}
|
|
}
|
|
|
|
Ok(())
|
|
}
|
|
|
|
fn sized_conditions(
|
|
&mut self,
|
|
obligation: &TraitObligation<'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::Infer(ty::FloatVar(_))
|
|
| ty::Uint(_)
|
|
| ty::Int(_)
|
|
| ty::Bool
|
|
| ty::Float(_)
|
|
| ty::FnDef(..)
|
|
| ty::FnPtr(_)
|
|
| ty::RawPtr(..)
|
|
| ty::Char
|
|
| ty::Ref(..)
|
|
| ty::Generator(..)
|
|
| ty::GeneratorWitness(..)
|
|
| ty::Array(..)
|
|
| ty::Closure(..)
|
|
| ty::Never
|
|
| ty::Error => {
|
|
// safe for everything
|
|
Where(ty::Binder::dummy(Vec::new()))
|
|
}
|
|
|
|
ty::Str | ty::Slice(_) | ty::Dynamic(..) | ty::Foreign(..) => None,
|
|
|
|
ty::Tuple(tys) => {
|
|
Where(ty::Binder::bind(tys.last().into_iter().map(|k| k.expect_ty()).collect()))
|
|
}
|
|
|
|
ty::Adt(def, substs) => {
|
|
let sized_crit = def.sized_constraint(self.tcx());
|
|
// (*) binder moved here
|
|
Where(ty::Binder::bind(
|
|
sized_crit.iter().map(|ty| ty.subst(self.tcx(), substs)).collect(),
|
|
))
|
|
}
|
|
|
|
ty::Projection(_) | ty::Param(_) | ty::Opaque(..) => None,
|
|
ty::Infer(ty::TyVar(_)) => Ambiguous,
|
|
|
|
ty::UnnormalizedProjection(..)
|
|
| ty::Placeholder(..)
|
|
| ty::Bound(..)
|
|
| ty::Infer(ty::FreshTy(_))
|
|
| ty::Infer(ty::FreshIntTy(_))
|
|
| ty::Infer(ty::FreshFloatTy(_)) => {
|
|
bug!("asked to assemble builtin bounds of unexpected type: {:?}", self_ty);
|
|
}
|
|
}
|
|
}
|
|
|
|
fn copy_clone_conditions(
|
|
&mut self,
|
|
obligation: &TraitObligation<'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::Infer(ty::IntVar(_))
|
|
| ty::Infer(ty::FloatVar(_))
|
|
| ty::FnDef(..)
|
|
| ty::FnPtr(_)
|
|
| ty::Error => Where(ty::Binder::dummy(Vec::new())),
|
|
|
|
ty::Uint(_)
|
|
| ty::Int(_)
|
|
| ty::Bool
|
|
| ty::Float(_)
|
|
| ty::Char
|
|
| ty::RawPtr(..)
|
|
| ty::Never
|
|
| ty::Ref(_, _, hir::Mutability::Not) => {
|
|
// Implementations provided in libcore
|
|
None
|
|
}
|
|
|
|
ty::Dynamic(..)
|
|
| ty::Str
|
|
| ty::Slice(..)
|
|
| ty::Generator(..)
|
|
| ty::GeneratorWitness(..)
|
|
| ty::Foreign(..)
|
|
| ty::Ref(_, _, hir::Mutability::Mut) => None,
|
|
|
|
ty::Array(element_ty, _) => {
|
|
// (*) binder moved here
|
|
Where(ty::Binder::bind(vec![element_ty]))
|
|
}
|
|
|
|
ty::Tuple(tys) => {
|
|
// (*) binder moved here
|
|
Where(ty::Binder::bind(tys.iter().map(|k| k.expect_ty()).collect()))
|
|
}
|
|
|
|
ty::Closure(_, substs) => {
|
|
// (*) binder moved here
|
|
Where(ty::Binder::bind(substs.as_closure().upvar_tys().collect()))
|
|
}
|
|
|
|
ty::Adt(..) | ty::Projection(..) | ty::Param(..) | ty::Opaque(..) => {
|
|
// 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
|
|
}
|
|
|
|
ty::UnnormalizedProjection(..)
|
|
| ty::Placeholder(..)
|
|
| ty::Bound(..)
|
|
| ty::Infer(ty::FreshTy(_))
|
|
| ty::Infer(ty::FreshIntTy(_))
|
|
| ty::Infer(ty::FreshFloatTy(_)) => {
|
|
bug!("asked to assemble builtin bounds of unexpected type: {:?}", self_ty);
|
|
}
|
|
}
|
|
}
|
|
|
|
/// 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:
|
|
///
|
|
/// ```
|
|
/// (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]
|
|
/// ```
|
|
fn constituent_types_for_ty(&self, t: Ty<'tcx>) -> Vec<Ty<'tcx>> {
|
|
match t.kind {
|
|
ty::Uint(_)
|
|
| ty::Int(_)
|
|
| ty::Bool
|
|
| ty::Float(_)
|
|
| ty::FnDef(..)
|
|
| ty::FnPtr(_)
|
|
| ty::Str
|
|
| ty::Error
|
|
| ty::Infer(ty::IntVar(_))
|
|
| ty::Infer(ty::FloatVar(_))
|
|
| ty::Never
|
|
| ty::Char => Vec::new(),
|
|
|
|
ty::UnnormalizedProjection(..)
|
|
| ty::Placeholder(..)
|
|
| ty::Dynamic(..)
|
|
| ty::Param(..)
|
|
| ty::Foreign(..)
|
|
| ty::Projection(..)
|
|
| ty::Bound(..)
|
|
| ty::Infer(ty::TyVar(_))
|
|
| ty::Infer(ty::FreshTy(_))
|
|
| ty::Infer(ty::FreshIntTy(_))
|
|
| ty::Infer(ty::FreshFloatTy(_)) => {
|
|
bug!("asked to assemble constituent types of unexpected type: {:?}", t);
|
|
}
|
|
|
|
ty::RawPtr(ty::TypeAndMut { ty: element_ty, .. }) | ty::Ref(_, element_ty, _) => {
|
|
vec![element_ty]
|
|
}
|
|
|
|
ty::Array(element_ty, _) | ty::Slice(element_ty) => vec![element_ty],
|
|
|
|
ty::Tuple(ref tys) => {
|
|
// (T1, ..., Tn) -- meets any bound that all of T1...Tn meet
|
|
tys.iter().map(|k| k.expect_ty()).collect()
|
|
}
|
|
|
|
ty::Closure(_, ref substs) => substs.as_closure().upvar_tys().collect(),
|
|
|
|
ty::Generator(_, ref substs, _) => {
|
|
let witness = substs.as_generator().witness();
|
|
substs.as_generator().upvar_tys().chain(iter::once(witness)).collect()
|
|
}
|
|
|
|
ty::GeneratorWitness(types) => {
|
|
// This is sound because no regions in the witness can refer to
|
|
// the binder outside the witness. So we'll effectivly reuse
|
|
// the implicit binder around the witness.
|
|
types.skip_binder().to_vec()
|
|
}
|
|
|
|
// For `PhantomData<T>`, we pass `T`.
|
|
ty::Adt(def, substs) if def.is_phantom_data() => substs.types().collect(),
|
|
|
|
ty::Adt(def, substs) => def.all_fields().map(|f| f.ty(self.tcx(), substs)).collect(),
|
|
|
|
ty::Opaque(def_id, substs) => {
|
|
// We can resolve the `impl Trait` to its concrete type,
|
|
// which enforces a DAG between the functions requiring
|
|
// the auto trait bounds in question.
|
|
vec![self.tcx().type_of(def_id).subst(self.tcx(), substs)]
|
|
}
|
|
}
|
|
}
|
|
|
|
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<Vec<Ty<'tcx>>>,
|
|
) -> Vec<PredicateObligation<'tcx>> {
|
|
// Because the types were potentially derived from
|
|
// higher-ranked obligations they may reference late-bound
|
|
// regions. For example, `for<'a> Foo<&'a int> : Copy` would
|
|
// yield a type like `for<'a> &'a int`. 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 int` becomes `&0 int`.
|
|
// 2. Produce something like `&'0 int : Copy`
|
|
// 3. Re-bind the regions back to `for<'a> &'a int : Copy`
|
|
|
|
types
|
|
.skip_binder()
|
|
.iter()
|
|
.flat_map(|ty| {
|
|
// binder moved -\
|
|
let ty: ty::Binder<Ty<'tcx>> = ty::Binder::bind(ty); // <----/
|
|
|
|
self.infcx.commit_unconditionally(|_| {
|
|
let (skol_ty, _) = self.infcx.replace_bound_vars_with_placeholders(&ty);
|
|
let Normalized { value: normalized_ty, mut obligations } =
|
|
project::normalize_with_depth(
|
|
self,
|
|
param_env,
|
|
cause.clone(),
|
|
recursion_depth,
|
|
&skol_ty,
|
|
);
|
|
let skol_obligation = predicate_for_trait_def(
|
|
self.tcx(),
|
|
param_env,
|
|
cause.clone(),
|
|
trait_def_id,
|
|
recursion_depth,
|
|
normalized_ty,
|
|
&[],
|
|
);
|
|
obligations.push(skol_obligation);
|
|
obligations
|
|
})
|
|
})
|
|
.collect()
|
|
}
|
|
|
|
///////////////////////////////////////////////////////////////////////////
|
|
// CONFIRMATION
|
|
//
|
|
// Confirmation unifies the output type parameters of the trait
|
|
// with the values found in the obligation, possibly yielding a
|
|
// type error. See the [rustc dev guide] for more details.
|
|
//
|
|
// [rustc dev guide]:
|
|
// https://rustc-dev-guide.rust-lang.org/traits/resolution.html#confirmation
|
|
|
|
fn confirm_candidate(
|
|
&mut self,
|
|
obligation: &TraitObligation<'tcx>,
|
|
candidate: SelectionCandidate<'tcx>,
|
|
) -> Result<Selection<'tcx>, SelectionError<'tcx>> {
|
|
debug!("confirm_candidate({:?}, {:?})", obligation, candidate);
|
|
|
|
match candidate {
|
|
BuiltinCandidate { has_nested } => {
|
|
let data = self.confirm_builtin_candidate(obligation, has_nested);
|
|
Ok(VtableBuiltin(data))
|
|
}
|
|
|
|
ParamCandidate(param) => {
|
|
let obligations = self.confirm_param_candidate(obligation, param);
|
|
Ok(VtableParam(obligations))
|
|
}
|
|
|
|
ImplCandidate(impl_def_id) => {
|
|
Ok(VtableImpl(self.confirm_impl_candidate(obligation, impl_def_id)))
|
|
}
|
|
|
|
AutoImplCandidate(trait_def_id) => {
|
|
let data = self.confirm_auto_impl_candidate(obligation, trait_def_id);
|
|
Ok(VtableAutoImpl(data))
|
|
}
|
|
|
|
ProjectionCandidate => {
|
|
self.confirm_projection_candidate(obligation);
|
|
Ok(VtableParam(Vec::new()))
|
|
}
|
|
|
|
ClosureCandidate => {
|
|
let vtable_closure = self.confirm_closure_candidate(obligation)?;
|
|
Ok(VtableClosure(vtable_closure))
|
|
}
|
|
|
|
GeneratorCandidate => {
|
|
let vtable_generator = self.confirm_generator_candidate(obligation)?;
|
|
Ok(VtableGenerator(vtable_generator))
|
|
}
|
|
|
|
FnPointerCandidate => {
|
|
let data = self.confirm_fn_pointer_candidate(obligation)?;
|
|
Ok(VtableFnPointer(data))
|
|
}
|
|
|
|
TraitAliasCandidate(alias_def_id) => {
|
|
let data = self.confirm_trait_alias_candidate(obligation, alias_def_id);
|
|
Ok(VtableTraitAlias(data))
|
|
}
|
|
|
|
ObjectCandidate => {
|
|
let data = self.confirm_object_candidate(obligation);
|
|
Ok(VtableObject(data))
|
|
}
|
|
|
|
BuiltinObjectCandidate => {
|
|
// This indicates something like `Trait + Send: Send`. In this case, we know that
|
|
// this holds because that's what the object type is telling us, and there's really
|
|
// no additional obligations to prove and no types in particular to unify, etc.
|
|
Ok(VtableParam(Vec::new()))
|
|
}
|
|
|
|
BuiltinUnsizeCandidate => {
|
|
let data = self.confirm_builtin_unsize_candidate(obligation)?;
|
|
Ok(VtableBuiltin(data))
|
|
}
|
|
}
|
|
}
|
|
|
|
fn confirm_projection_candidate(&mut self, obligation: &TraitObligation<'tcx>) {
|
|
self.infcx.commit_unconditionally(|snapshot| {
|
|
let result =
|
|
self.match_projection_obligation_against_definition_bounds(obligation, snapshot);
|
|
assert!(result);
|
|
})
|
|
}
|
|
|
|
fn confirm_param_candidate(
|
|
&mut self,
|
|
obligation: &TraitObligation<'tcx>,
|
|
param: ty::PolyTraitRef<'tcx>,
|
|
) -> Vec<PredicateObligation<'tcx>> {
|
|
debug!("confirm_param_candidate({:?},{:?})", obligation, param);
|
|
|
|
// During evaluation, we already checked that this
|
|
// where-clause trait-ref could be unified with the obligation
|
|
// trait-ref. Repeat that unification now without any
|
|
// transactional boundary; it should not fail.
|
|
match self.match_where_clause_trait_ref(obligation, param.clone()) {
|
|
Ok(obligations) => obligations,
|
|
Err(()) => {
|
|
bug!(
|
|
"Where clause `{:?}` was applicable to `{:?}` but now is not",
|
|
param,
|
|
obligation
|
|
);
|
|
}
|
|
}
|
|
}
|
|
|
|
fn confirm_builtin_candidate(
|
|
&mut self,
|
|
obligation: &TraitObligation<'tcx>,
|
|
has_nested: bool,
|
|
) -> VtableBuiltinData<PredicateObligation<'tcx>> {
|
|
debug!("confirm_builtin_candidate({:?}, {:?})", obligation, has_nested);
|
|
|
|
let lang_items = self.tcx().lang_items();
|
|
let obligations = if has_nested {
|
|
let trait_def = obligation.predicate.def_id();
|
|
let conditions = if Some(trait_def) == lang_items.sized_trait() {
|
|
self.sized_conditions(obligation)
|
|
} else if Some(trait_def) == lang_items.copy_trait() {
|
|
self.copy_clone_conditions(obligation)
|
|
} else if Some(trait_def) == lang_items.clone_trait() {
|
|
self.copy_clone_conditions(obligation)
|
|
} else {
|
|
bug!("unexpected builtin trait {:?}", trait_def)
|
|
};
|
|
let nested = match conditions {
|
|
BuiltinImplConditions::Where(nested) => nested,
|
|
_ => bug!("obligation {:?} had matched a builtin impl but now doesn't", obligation),
|
|
};
|
|
|
|
let cause = obligation.derived_cause(BuiltinDerivedObligation);
|
|
self.collect_predicates_for_types(
|
|
obligation.param_env,
|
|
cause,
|
|
obligation.recursion_depth + 1,
|
|
trait_def,
|
|
nested,
|
|
)
|
|
} else {
|
|
vec![]
|
|
};
|
|
|
|
debug!("confirm_builtin_candidate: obligations={:?}", obligations);
|
|
|
|
VtableBuiltinData { nested: obligations }
|
|
}
|
|
|
|
/// This handles the case where a `auto trait Foo` impl is being used.
|
|
/// The idea is that the impl applies to `X : Foo` if the following conditions are met:
|
|
///
|
|
/// 1. For each constituent type `Y` in `X`, `Y : Foo` holds
|
|
/// 2. For each where-clause `C` declared on `Foo`, `[Self => X] C` holds.
|
|
fn confirm_auto_impl_candidate(
|
|
&mut self,
|
|
obligation: &TraitObligation<'tcx>,
|
|
trait_def_id: DefId,
|
|
) -> VtableAutoImplData<PredicateObligation<'tcx>> {
|
|
debug!("confirm_auto_impl_candidate({:?}, {:?})", obligation, trait_def_id);
|
|
|
|
let types = obligation.predicate.map_bound(|inner| {
|
|
let self_ty = self.infcx.shallow_resolve(inner.self_ty());
|
|
self.constituent_types_for_ty(self_ty)
|
|
});
|
|
self.vtable_auto_impl(obligation, trait_def_id, types)
|
|
}
|
|
|
|
/// See `confirm_auto_impl_candidate`.
|
|
fn vtable_auto_impl(
|
|
&mut self,
|
|
obligation: &TraitObligation<'tcx>,
|
|
trait_def_id: DefId,
|
|
nested: ty::Binder<Vec<Ty<'tcx>>>,
|
|
) -> VtableAutoImplData<PredicateObligation<'tcx>> {
|
|
debug!("vtable_auto_impl: nested={:?}", nested);
|
|
|
|
let cause = obligation.derived_cause(BuiltinDerivedObligation);
|
|
let mut obligations = self.collect_predicates_for_types(
|
|
obligation.param_env,
|
|
cause,
|
|
obligation.recursion_depth + 1,
|
|
trait_def_id,
|
|
nested,
|
|
);
|
|
|
|
let trait_obligations: Vec<PredicateObligation<'_>> =
|
|
self.infcx.commit_unconditionally(|_| {
|
|
let poly_trait_ref = obligation.predicate.to_poly_trait_ref();
|
|
let (trait_ref, _) =
|
|
self.infcx.replace_bound_vars_with_placeholders(&poly_trait_ref);
|
|
let cause = obligation.derived_cause(ImplDerivedObligation);
|
|
self.impl_or_trait_obligations(
|
|
cause,
|
|
obligation.recursion_depth + 1,
|
|
obligation.param_env,
|
|
trait_def_id,
|
|
&trait_ref.substs,
|
|
)
|
|
});
|
|
|
|
// Adds the predicates from the trait. Note that this contains a `Self: Trait`
|
|
// predicate as usual. It won't have any effect since auto traits are coinductive.
|
|
obligations.extend(trait_obligations);
|
|
|
|
debug!("vtable_auto_impl: obligations={:?}", obligations);
|
|
|
|
VtableAutoImplData { trait_def_id, nested: obligations }
|
|
}
|
|
|
|
fn confirm_impl_candidate(
|
|
&mut self,
|
|
obligation: &TraitObligation<'tcx>,
|
|
impl_def_id: DefId,
|
|
) -> VtableImplData<'tcx, PredicateObligation<'tcx>> {
|
|
debug!("confirm_impl_candidate({:?},{:?})", obligation, impl_def_id);
|
|
|
|
// First, create the substitutions by matching the impl again,
|
|
// this time not in a probe.
|
|
self.infcx.commit_unconditionally(|snapshot| {
|
|
let substs = self.rematch_impl(impl_def_id, obligation, snapshot);
|
|
debug!("confirm_impl_candidate: substs={:?}", substs);
|
|
let cause = obligation.derived_cause(ImplDerivedObligation);
|
|
self.vtable_impl(
|
|
impl_def_id,
|
|
substs,
|
|
cause,
|
|
obligation.recursion_depth + 1,
|
|
obligation.param_env,
|
|
)
|
|
})
|
|
}
|
|
|
|
fn vtable_impl(
|
|
&mut self,
|
|
impl_def_id: DefId,
|
|
mut substs: Normalized<'tcx, SubstsRef<'tcx>>,
|
|
cause: ObligationCause<'tcx>,
|
|
recursion_depth: usize,
|
|
param_env: ty::ParamEnv<'tcx>,
|
|
) -> VtableImplData<'tcx, PredicateObligation<'tcx>> {
|
|
debug!(
|
|
"vtable_impl(impl_def_id={:?}, substs={:?}, recursion_depth={})",
|
|
impl_def_id, substs, recursion_depth,
|
|
);
|
|
|
|
let mut impl_obligations = self.impl_or_trait_obligations(
|
|
cause,
|
|
recursion_depth,
|
|
param_env,
|
|
impl_def_id,
|
|
&substs.value,
|
|
);
|
|
|
|
debug!(
|
|
"vtable_impl: impl_def_id={:?} impl_obligations={:?}",
|
|
impl_def_id, impl_obligations
|
|
);
|
|
|
|
// Because of RFC447, the impl-trait-ref and obligations
|
|
// are sufficient to determine the impl substs, without
|
|
// relying on projections in the impl-trait-ref.
|
|
//
|
|
// e.g., `impl<U: Tr, V: Iterator<Item=U>> Foo<<U as Tr>::T> for V`
|
|
impl_obligations.append(&mut substs.obligations);
|
|
|
|
VtableImplData { impl_def_id, substs: substs.value, nested: impl_obligations }
|
|
}
|
|
|
|
fn confirm_object_candidate(
|
|
&mut self,
|
|
obligation: &TraitObligation<'tcx>,
|
|
) -> VtableObjectData<'tcx, PredicateObligation<'tcx>> {
|
|
debug!("confirm_object_candidate({:?})", obligation);
|
|
|
|
// FIXME(nmatsakis) skipping binder here seems wrong -- we should
|
|
// probably flatten the binder from the obligation and the binder
|
|
// from the object. Have to try to make a broken test case that
|
|
// results.
|
|
let self_ty = self.infcx.shallow_resolve(*obligation.self_ty().skip_binder());
|
|
let poly_trait_ref = match self_ty.kind {
|
|
ty::Dynamic(ref data, ..) => data
|
|
.principal()
|
|
.unwrap_or_else(|| {
|
|
span_bug!(obligation.cause.span, "object candidate with no principal")
|
|
})
|
|
.with_self_ty(self.tcx(), self_ty),
|
|
_ => span_bug!(obligation.cause.span, "object candidate with non-object"),
|
|
};
|
|
|
|
let mut upcast_trait_ref = None;
|
|
let mut nested = vec![];
|
|
let vtable_base;
|
|
|
|
{
|
|
let tcx = self.tcx();
|
|
|
|
// We want to find the first supertrait in the list of
|
|
// supertraits that we can unify with, and do that
|
|
// unification. We know that there is exactly one in the list
|
|
// where we can unify, because otherwise select would have
|
|
// reported an ambiguity. (When we do find a match, also
|
|
// record it for later.)
|
|
let nonmatching = util::supertraits(tcx, poly_trait_ref).take_while(|&t| {
|
|
match self.infcx.commit_if_ok(|_| self.match_poly_trait_ref(obligation, t)) {
|
|
Ok(obligations) => {
|
|
upcast_trait_ref = Some(t);
|
|
nested.extend(obligations);
|
|
false
|
|
}
|
|
Err(_) => true,
|
|
}
|
|
});
|
|
|
|
// Additionally, for each of the non-matching predicates that
|
|
// we pass over, we sum up the set of number of vtable
|
|
// entries, so that we can compute the offset for the selected
|
|
// trait.
|
|
vtable_base = nonmatching.map(|t| super::util::count_own_vtable_entries(tcx, t)).sum();
|
|
}
|
|
|
|
VtableObjectData { upcast_trait_ref: upcast_trait_ref.unwrap(), vtable_base, nested }
|
|
}
|
|
|
|
fn confirm_fn_pointer_candidate(
|
|
&mut self,
|
|
obligation: &TraitObligation<'tcx>,
|
|
) -> Result<VtableFnPointerData<'tcx, PredicateObligation<'tcx>>, SelectionError<'tcx>> {
|
|
debug!("confirm_fn_pointer_candidate({:?})", obligation);
|
|
|
|
// Okay to skip binder; it is reintroduced below.
|
|
let self_ty = self.infcx.shallow_resolve(*obligation.self_ty().skip_binder());
|
|
let sig = self_ty.fn_sig(self.tcx());
|
|
let trait_ref = closure_trait_ref_and_return_type(
|
|
self.tcx(),
|
|
obligation.predicate.def_id(),
|
|
self_ty,
|
|
sig,
|
|
util::TupleArgumentsFlag::Yes,
|
|
)
|
|
.map_bound(|(trait_ref, _)| trait_ref);
|
|
|
|
let Normalized { value: trait_ref, obligations } = project::normalize_with_depth(
|
|
self,
|
|
obligation.param_env,
|
|
obligation.cause.clone(),
|
|
obligation.recursion_depth + 1,
|
|
&trait_ref,
|
|
);
|
|
|
|
self.confirm_poly_trait_refs(
|
|
obligation.cause.clone(),
|
|
obligation.param_env,
|
|
obligation.predicate.to_poly_trait_ref(),
|
|
trait_ref,
|
|
)?;
|
|
Ok(VtableFnPointerData { fn_ty: self_ty, nested: obligations })
|
|
}
|
|
|
|
fn confirm_trait_alias_candidate(
|
|
&mut self,
|
|
obligation: &TraitObligation<'tcx>,
|
|
alias_def_id: DefId,
|
|
) -> VtableTraitAliasData<'tcx, PredicateObligation<'tcx>> {
|
|
debug!("confirm_trait_alias_candidate({:?}, {:?})", obligation, alias_def_id);
|
|
|
|
self.infcx.commit_unconditionally(|_| {
|
|
let (predicate, _) =
|
|
self.infcx().replace_bound_vars_with_placeholders(&obligation.predicate);
|
|
let trait_ref = predicate.trait_ref;
|
|
let trait_def_id = trait_ref.def_id;
|
|
let substs = trait_ref.substs;
|
|
|
|
let trait_obligations = self.impl_or_trait_obligations(
|
|
obligation.cause.clone(),
|
|
obligation.recursion_depth,
|
|
obligation.param_env,
|
|
trait_def_id,
|
|
&substs,
|
|
);
|
|
|
|
debug!(
|
|
"confirm_trait_alias_candidate: trait_def_id={:?} trait_obligations={:?}",
|
|
trait_def_id, trait_obligations
|
|
);
|
|
|
|
VtableTraitAliasData { alias_def_id, substs, nested: trait_obligations }
|
|
})
|
|
}
|
|
|
|
fn confirm_generator_candidate(
|
|
&mut self,
|
|
obligation: &TraitObligation<'tcx>,
|
|
) -> Result<VtableGeneratorData<'tcx, PredicateObligation<'tcx>>, SelectionError<'tcx>> {
|
|
// Okay to skip binder because the substs on generator types never
|
|
// touch bound regions, they just capture the in-scope
|
|
// type/region parameters.
|
|
let self_ty = self.infcx.shallow_resolve(*obligation.self_ty().skip_binder());
|
|
let (generator_def_id, substs) = match self_ty.kind {
|
|
ty::Generator(id, substs, _) => (id, substs),
|
|
_ => bug!("closure candidate for non-closure {:?}", obligation),
|
|
};
|
|
|
|
debug!("confirm_generator_candidate({:?},{:?},{:?})", obligation, generator_def_id, substs);
|
|
|
|
let trait_ref = self.generator_trait_ref_unnormalized(obligation, substs);
|
|
let Normalized { value: trait_ref, mut obligations } = normalize_with_depth(
|
|
self,
|
|
obligation.param_env,
|
|
obligation.cause.clone(),
|
|
obligation.recursion_depth + 1,
|
|
&trait_ref,
|
|
);
|
|
|
|
debug!(
|
|
"confirm_generator_candidate(generator_def_id={:?}, \
|
|
trait_ref={:?}, obligations={:?})",
|
|
generator_def_id, trait_ref, obligations
|
|
);
|
|
|
|
obligations.extend(self.confirm_poly_trait_refs(
|
|
obligation.cause.clone(),
|
|
obligation.param_env,
|
|
obligation.predicate.to_poly_trait_ref(),
|
|
trait_ref,
|
|
)?);
|
|
|
|
Ok(VtableGeneratorData { generator_def_id, substs, nested: obligations })
|
|
}
|
|
|
|
fn confirm_closure_candidate(
|
|
&mut self,
|
|
obligation: &TraitObligation<'tcx>,
|
|
) -> Result<VtableClosureData<'tcx, PredicateObligation<'tcx>>, SelectionError<'tcx>> {
|
|
debug!("confirm_closure_candidate({:?})", obligation);
|
|
|
|
let kind = self
|
|
.tcx()
|
|
.fn_trait_kind_from_lang_item(obligation.predicate.def_id())
|
|
.unwrap_or_else(|| bug!("closure candidate for non-fn trait {:?}", obligation));
|
|
|
|
// Okay to skip binder because the substs on closure types never
|
|
// touch bound regions, they just capture the in-scope
|
|
// type/region parameters.
|
|
let self_ty = self.infcx.shallow_resolve(*obligation.self_ty().skip_binder());
|
|
let (closure_def_id, substs) = match self_ty.kind {
|
|
ty::Closure(id, substs) => (id, substs),
|
|
_ => bug!("closure candidate for non-closure {:?}", obligation),
|
|
};
|
|
|
|
let trait_ref = self.closure_trait_ref_unnormalized(obligation, substs);
|
|
let Normalized { value: trait_ref, mut obligations } = normalize_with_depth(
|
|
self,
|
|
obligation.param_env,
|
|
obligation.cause.clone(),
|
|
obligation.recursion_depth + 1,
|
|
&trait_ref,
|
|
);
|
|
|
|
debug!(
|
|
"confirm_closure_candidate(closure_def_id={:?}, trait_ref={:?}, obligations={:?})",
|
|
closure_def_id, trait_ref, obligations
|
|
);
|
|
|
|
obligations.extend(self.confirm_poly_trait_refs(
|
|
obligation.cause.clone(),
|
|
obligation.param_env,
|
|
obligation.predicate.to_poly_trait_ref(),
|
|
trait_ref,
|
|
)?);
|
|
|
|
obligations.push(Obligation::new(
|
|
obligation.cause.clone(),
|
|
obligation.param_env,
|
|
ty::Predicate::ClosureKind(closure_def_id, substs, kind),
|
|
));
|
|
|
|
Ok(VtableClosureData { closure_def_id, substs, nested: obligations })
|
|
}
|
|
|
|
/// In the case of closure types and fn pointers,
|
|
/// we currently treat the input type parameters on the trait as
|
|
/// outputs. This means that when we have a match we have only
|
|
/// considered the self type, so we have to go back and make sure
|
|
/// to relate the argument types too. This is kind of wrong, but
|
|
/// since we control the full set of impls, also not that wrong,
|
|
/// and it DOES yield better error messages (since we don't report
|
|
/// errors as if there is no applicable impl, but rather report
|
|
/// errors are about mismatched argument types.
|
|
///
|
|
/// Here is an example. Imagine we have a closure expression
|
|
/// and we desugared it so that the type of the expression is
|
|
/// `Closure`, and `Closure` expects an int as argument. Then it
|
|
/// is "as if" the compiler generated this impl:
|
|
///
|
|
/// impl Fn(int) for Closure { ... }
|
|
///
|
|
/// Now imagine our obligation is `Fn(usize) for Closure`. So far
|
|
/// we have matched the self type `Closure`. At this point we'll
|
|
/// compare the `int` to `usize` and generate an error.
|
|
///
|
|
/// Note that this checking occurs *after* the impl has selected,
|
|
/// because these output type parameters should not affect the
|
|
/// selection of the impl. Therefore, if there is a mismatch, we
|
|
/// report an error to the user.
|
|
fn confirm_poly_trait_refs(
|
|
&mut self,
|
|
obligation_cause: ObligationCause<'tcx>,
|
|
obligation_param_env: ty::ParamEnv<'tcx>,
|
|
obligation_trait_ref: ty::PolyTraitRef<'tcx>,
|
|
expected_trait_ref: ty::PolyTraitRef<'tcx>,
|
|
) -> Result<Vec<PredicateObligation<'tcx>>, SelectionError<'tcx>> {
|
|
self.infcx
|
|
.at(&obligation_cause, obligation_param_env)
|
|
.sup(obligation_trait_ref, expected_trait_ref)
|
|
.map(|InferOk { obligations, .. }| obligations)
|
|
.map_err(|e| OutputTypeParameterMismatch(expected_trait_ref, obligation_trait_ref, e))
|
|
}
|
|
|
|
fn confirm_builtin_unsize_candidate(
|
|
&mut self,
|
|
obligation: &TraitObligation<'tcx>,
|
|
) -> Result<VtableBuiltinData<PredicateObligation<'tcx>>, SelectionError<'tcx>> {
|
|
let tcx = self.tcx();
|
|
|
|
// `assemble_candidates_for_unsizing` should ensure there are no late-bound
|
|
// regions here. See the comment there for more details.
|
|
let source = self.infcx.shallow_resolve(obligation.self_ty().no_bound_vars().unwrap());
|
|
let target = obligation.predicate.skip_binder().trait_ref.substs.type_at(1);
|
|
let target = self.infcx.shallow_resolve(target);
|
|
|
|
debug!("confirm_builtin_unsize_candidate(source={:?}, target={:?})", source, target);
|
|
|
|
let mut nested = vec![];
|
|
match (&source.kind, &target.kind) {
|
|
// Trait+Kx+'a -> Trait+Ky+'b (upcasts).
|
|
(&ty::Dynamic(ref data_a, r_a), &ty::Dynamic(ref data_b, r_b)) => {
|
|
// See `assemble_candidates_for_unsizing` for more info.
|
|
let existential_predicates = data_a.map_bound(|data_a| {
|
|
let iter = data_a
|
|
.principal()
|
|
.map(ty::ExistentialPredicate::Trait)
|
|
.into_iter()
|
|
.chain(data_a.projection_bounds().map(ty::ExistentialPredicate::Projection))
|
|
.chain(data_b.auto_traits().map(ty::ExistentialPredicate::AutoTrait));
|
|
tcx.mk_existential_predicates(iter)
|
|
});
|
|
let source_trait = tcx.mk_dynamic(existential_predicates, r_b);
|
|
|
|
// Require that the traits involved in this upcast are **equal**;
|
|
// only the **lifetime bound** is changed.
|
|
//
|
|
// FIXME: This condition is arguably too strong -- it would
|
|
// suffice for the source trait to be a *subtype* of the target
|
|
// trait. In particular, changing from something like
|
|
// `for<'a, 'b> Foo<'a, 'b>` to `for<'a> Foo<'a, 'a>` should be
|
|
// permitted. And, indeed, in the in commit
|
|
// 904a0bde93f0348f69914ee90b1f8b6e4e0d7cbc, this
|
|
// condition was loosened. However, when the leak check was
|
|
// added back, using subtype here actually guides the coercion
|
|
// code in such a way that it accepts `old-lub-glb-object.rs`.
|
|
// This is probably a good thing, but I've modified this to `.eq`
|
|
// because I want to continue rejecting that test (as we have
|
|
// done for quite some time) before we are firmly comfortable
|
|
// with what our behavior should be there. -nikomatsakis
|
|
let InferOk { obligations, .. } = self
|
|
.infcx
|
|
.at(&obligation.cause, obligation.param_env)
|
|
.eq(target, source_trait) // FIXME -- see below
|
|
.map_err(|_| Unimplemented)?;
|
|
nested.extend(obligations);
|
|
|
|
// Register one obligation for 'a: 'b.
|
|
let cause = ObligationCause::new(
|
|
obligation.cause.span,
|
|
obligation.cause.body_id,
|
|
ObjectCastObligation(target),
|
|
);
|
|
let outlives = ty::OutlivesPredicate(r_a, r_b);
|
|
nested.push(Obligation::with_depth(
|
|
cause,
|
|
obligation.recursion_depth + 1,
|
|
obligation.param_env,
|
|
ty::Binder::bind(outlives).to_predicate(),
|
|
));
|
|
}
|
|
|
|
// `T` -> `Trait`
|
|
(_, &ty::Dynamic(ref data, r)) => {
|
|
let mut object_dids = data.auto_traits().chain(data.principal_def_id());
|
|
if let Some(did) = object_dids.find(|did| !tcx.is_object_safe(*did)) {
|
|
return Err(TraitNotObjectSafe(did));
|
|
}
|
|
|
|
let cause = ObligationCause::new(
|
|
obligation.cause.span,
|
|
obligation.cause.body_id,
|
|
ObjectCastObligation(target),
|
|
);
|
|
|
|
let predicate_to_obligation = |predicate| {
|
|
Obligation::with_depth(
|
|
cause.clone(),
|
|
obligation.recursion_depth + 1,
|
|
obligation.param_env,
|
|
predicate,
|
|
)
|
|
};
|
|
|
|
// Create obligations:
|
|
// - Casting `T` to `Trait`
|
|
// - For all the various builtin bounds attached to the object cast. (In other
|
|
// words, if the object type is `Foo + Send`, this would create an obligation for
|
|
// the `Send` check.)
|
|
// - Projection predicates
|
|
nested.extend(
|
|
data.iter().map(|predicate| {
|
|
predicate_to_obligation(predicate.with_self_ty(tcx, source))
|
|
}),
|
|
);
|
|
|
|
// We can only make objects from sized types.
|
|
let tr = ty::TraitRef::new(
|
|
tcx.require_lang_item(lang_items::SizedTraitLangItem, None),
|
|
tcx.mk_substs_trait(source, &[]),
|
|
);
|
|
nested.push(predicate_to_obligation(tr.without_const().to_predicate()));
|
|
|
|
// If the type is `Foo + 'a`, ensure that the type
|
|
// being cast to `Foo + 'a` outlives `'a`:
|
|
let outlives = ty::OutlivesPredicate(source, r);
|
|
nested.push(predicate_to_obligation(ty::Binder::dummy(outlives).to_predicate()));
|
|
}
|
|
|
|
// `[T; n]` -> `[T]`
|
|
(&ty::Array(a, _), &ty::Slice(b)) => {
|
|
let InferOk { obligations, .. } = self
|
|
.infcx
|
|
.at(&obligation.cause, obligation.param_env)
|
|
.eq(b, a)
|
|
.map_err(|_| Unimplemented)?;
|
|
nested.extend(obligations);
|
|
}
|
|
|
|
// `Struct<T>` -> `Struct<U>`
|
|
(&ty::Adt(def, substs_a), &ty::Adt(_, substs_b)) => {
|
|
let maybe_unsizing_param_idx = |arg: GenericArg<'tcx>| match arg.unpack() {
|
|
GenericArgKind::Type(ty) => match ty.kind {
|
|
ty::Param(p) => Some(p.index),
|
|
_ => None,
|
|
},
|
|
|
|
// Lifetimes aren't allowed to change during unsizing.
|
|
GenericArgKind::Lifetime(_) => None,
|
|
|
|
GenericArgKind::Const(ct) => match ct.val {
|
|
ty::ConstKind::Param(p) => Some(p.index),
|
|
_ => None,
|
|
},
|
|
};
|
|
|
|
// The last field of the structure has to exist and contain type/const parameters.
|
|
let (tail_field, prefix_fields) =
|
|
def.non_enum_variant().fields.split_last().ok_or(Unimplemented)?;
|
|
let tail_field_ty = tcx.type_of(tail_field.did);
|
|
|
|
let mut unsizing_params = GrowableBitSet::new_empty();
|
|
let mut found = false;
|
|
for arg in tail_field_ty.walk() {
|
|
if let Some(i) = maybe_unsizing_param_idx(arg) {
|
|
unsizing_params.insert(i);
|
|
found = true;
|
|
}
|
|
}
|
|
if !found {
|
|
return Err(Unimplemented);
|
|
}
|
|
|
|
// Ensure none of the other fields mention the parameters used
|
|
// in unsizing.
|
|
// FIXME(eddyb) cache this (including computing `unsizing_params`)
|
|
// by putting it in a query; it would only need the `DefId` as it
|
|
// looks at declared field types, not anything substituted.
|
|
for field in prefix_fields {
|
|
for arg in tcx.type_of(field.did).walk() {
|
|
if let Some(i) = maybe_unsizing_param_idx(arg) {
|
|
if unsizing_params.contains(i) {
|
|
return Err(Unimplemented);
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
// Extract `TailField<T>` and `TailField<U>` from `Struct<T>` and `Struct<U>`.
|
|
let source_tail = tail_field_ty.subst(tcx, substs_a);
|
|
let target_tail = tail_field_ty.subst(tcx, substs_b);
|
|
|
|
// Check that the source struct with the target's
|
|
// unsizing parameters is equal to the target.
|
|
let substs = tcx.mk_substs(substs_a.iter().enumerate().map(|(i, &k)| {
|
|
if unsizing_params.contains(i as u32) { substs_b[i] } else { k }
|
|
}));
|
|
let new_struct = tcx.mk_adt(def, substs);
|
|
let InferOk { obligations, .. } = self
|
|
.infcx
|
|
.at(&obligation.cause, obligation.param_env)
|
|
.eq(target, new_struct)
|
|
.map_err(|_| Unimplemented)?;
|
|
nested.extend(obligations);
|
|
|
|
// Construct the nested `TailField<T>: Unsize<TailField<U>>` predicate.
|
|
nested.push(predicate_for_trait_def(
|
|
tcx,
|
|
obligation.param_env,
|
|
obligation.cause.clone(),
|
|
obligation.predicate.def_id(),
|
|
obligation.recursion_depth + 1,
|
|
source_tail,
|
|
&[target_tail.into()],
|
|
));
|
|
}
|
|
|
|
// `(.., T)` -> `(.., U)`
|
|
(&ty::Tuple(tys_a), &ty::Tuple(tys_b)) => {
|
|
assert_eq!(tys_a.len(), tys_b.len());
|
|
|
|
// The last field of the tuple has to exist.
|
|
let (&a_last, a_mid) = if let Some(x) = tys_a.split_last() {
|
|
x
|
|
} else {
|
|
return Err(Unimplemented);
|
|
};
|
|
let &b_last = tys_b.last().unwrap();
|
|
|
|
// Check that the source tuple with the target's
|
|
// last element is equal to the target.
|
|
let new_tuple = tcx.mk_tup(
|
|
a_mid.iter().map(|k| k.expect_ty()).chain(iter::once(b_last.expect_ty())),
|
|
);
|
|
let InferOk { obligations, .. } = self
|
|
.infcx
|
|
.at(&obligation.cause, obligation.param_env)
|
|
.eq(target, new_tuple)
|
|
.map_err(|_| Unimplemented)?;
|
|
nested.extend(obligations);
|
|
|
|
// Construct the nested `T: Unsize<U>` predicate.
|
|
nested.push(predicate_for_trait_def(
|
|
tcx,
|
|
obligation.param_env,
|
|
obligation.cause.clone(),
|
|
obligation.predicate.def_id(),
|
|
obligation.recursion_depth + 1,
|
|
a_last.expect_ty(),
|
|
&[b_last],
|
|
));
|
|
}
|
|
|
|
_ => bug!(),
|
|
};
|
|
|
|
Ok(VtableBuiltinData { nested })
|
|
}
|
|
|
|
///////////////////////////////////////////////////////////////////////////
|
|
// 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: &TraitObligation<'tcx>,
|
|
snapshot: &CombinedSnapshot<'_, 'tcx>,
|
|
) -> Normalized<'tcx, SubstsRef<'tcx>> {
|
|
match self.match_impl(impl_def_id, obligation, snapshot) {
|
|
Ok(substs) => substs,
|
|
Err(()) => {
|
|
bug!(
|
|
"Impl {:?} was matchable against {:?} but now is not",
|
|
impl_def_id,
|
|
obligation
|
|
);
|
|
}
|
|
}
|
|
}
|
|
|
|
fn match_impl(
|
|
&mut self,
|
|
impl_def_id: DefId,
|
|
obligation: &TraitObligation<'tcx>,
|
|
snapshot: &CombinedSnapshot<'_, 'tcx>,
|
|
) -> Result<Normalized<'tcx, SubstsRef<'tcx>>, ()> {
|
|
let impl_trait_ref = self.tcx().impl_trait_ref(impl_def_id).unwrap();
|
|
|
|
// Before we create the substitutions and everything, first
|
|
// consider a "quick reject". This avoids creating more types
|
|
// and so forth that we need to.
|
|
if self.fast_reject_trait_refs(obligation, &impl_trait_ref) {
|
|
return Err(());
|
|
}
|
|
|
|
let (skol_obligation, placeholder_map) =
|
|
self.infcx().replace_bound_vars_with_placeholders(&obligation.predicate);
|
|
let skol_obligation_trait_ref = skol_obligation.trait_ref;
|
|
|
|
let impl_substs = self.infcx.fresh_substs_for_item(obligation.cause.span, impl_def_id);
|
|
|
|
let impl_trait_ref = impl_trait_ref.subst(self.tcx(), impl_substs);
|
|
|
|
let Normalized { value: impl_trait_ref, obligations: mut nested_obligations } =
|
|
project::normalize_with_depth(
|
|
self,
|
|
obligation.param_env,
|
|
obligation.cause.clone(),
|
|
obligation.recursion_depth + 1,
|
|
&impl_trait_ref,
|
|
);
|
|
|
|
debug!(
|
|
"match_impl(impl_def_id={:?}, obligation={:?}, \
|
|
impl_trait_ref={:?}, skol_obligation_trait_ref={:?})",
|
|
impl_def_id, obligation, impl_trait_ref, skol_obligation_trait_ref
|
|
);
|
|
|
|
let InferOk { obligations, .. } = self
|
|
.infcx
|
|
.at(&obligation.cause, obligation.param_env)
|
|
.eq(skol_obligation_trait_ref, impl_trait_ref)
|
|
.map_err(|e| debug!("match_impl: failed eq_trait_refs due to `{}`", e))?;
|
|
nested_obligations.extend(obligations);
|
|
|
|
if let Err(e) = self.infcx.leak_check(false, &placeholder_map, snapshot) {
|
|
debug!("match_impl: failed leak check due to `{}`", e);
|
|
return Err(());
|
|
}
|
|
|
|
if !self.intercrate
|
|
&& self.tcx().impl_polarity(impl_def_id) == ty::ImplPolarity::Reservation
|
|
{
|
|
debug!("match_impl: reservation impls only apply in intercrate mode");
|
|
return Err(());
|
|
}
|
|
|
|
debug!("match_impl: success impl_substs={:?}", impl_substs);
|
|
Ok(Normalized { value: impl_substs, obligations: nested_obligations })
|
|
}
|
|
|
|
fn fast_reject_trait_refs(
|
|
&mut self,
|
|
obligation: &TraitObligation<'_>,
|
|
impl_trait_ref: &ty::TraitRef<'_>,
|
|
) -> bool {
|
|
// We can avoid creating type variables and doing the full
|
|
// substitution if we find that any of the input types, when
|
|
// simplified, do not match.
|
|
|
|
obligation.predicate.skip_binder().trait_ref.substs.iter().zip(impl_trait_ref.substs).any(
|
|
|(obligation_arg, impl_arg)| {
|
|
match (obligation_arg.unpack(), impl_arg.unpack()) {
|
|
(GenericArgKind::Type(obligation_ty), GenericArgKind::Type(impl_ty)) => {
|
|
let simplified_obligation_ty =
|
|
fast_reject::simplify_type(self.tcx(), obligation_ty, true);
|
|
let simplified_impl_ty =
|
|
fast_reject::simplify_type(self.tcx(), impl_ty, false);
|
|
|
|
simplified_obligation_ty.is_some()
|
|
&& simplified_impl_ty.is_some()
|
|
&& simplified_obligation_ty != simplified_impl_ty
|
|
}
|
|
(GenericArgKind::Lifetime(_), GenericArgKind::Lifetime(_)) => {
|
|
// Lifetimes can never cause a rejection.
|
|
false
|
|
}
|
|
(GenericArgKind::Const(_), GenericArgKind::Const(_)) => {
|
|
// Conservatively ignore consts (i.e. assume they might
|
|
// unify later) until we have `fast_reject` support for
|
|
// them (if we'll ever need it, even).
|
|
false
|
|
}
|
|
_ => unreachable!(),
|
|
}
|
|
},
|
|
)
|
|
}
|
|
|
|
/// Normalize `where_clause_trait_ref` and try to match it against
|
|
/// `obligation`. If successful, return any predicates that
|
|
/// result from the normalization. Normalization is necessary
|
|
/// because where-clauses are stored in the parameter environment
|
|
/// unnormalized.
|
|
fn match_where_clause_trait_ref(
|
|
&mut self,
|
|
obligation: &TraitObligation<'tcx>,
|
|
where_clause_trait_ref: ty::PolyTraitRef<'tcx>,
|
|
) -> Result<Vec<PredicateObligation<'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.
|
|
fn match_poly_trait_ref(
|
|
&mut self,
|
|
obligation: &TraitObligation<'tcx>,
|
|
poly_trait_ref: ty::PolyTraitRef<'tcx>,
|
|
) -> Result<Vec<PredicateObligation<'tcx>>, ()> {
|
|
debug!(
|
|
"match_poly_trait_ref: obligation={:?} poly_trait_ref={:?}",
|
|
obligation, poly_trait_ref
|
|
);
|
|
|
|
self.infcx
|
|
.at(&obligation.cause, obligation.param_env)
|
|
.sup(obligation.predicate.to_poly_trait_ref(), poly_trait_ref)
|
|
.map(|InferOk { obligations, .. }| obligations)
|
|
.map_err(|_| ())
|
|
}
|
|
|
|
///////////////////////////////////////////////////////////////////////////
|
|
// Miscellany
|
|
|
|
fn match_fresh_trait_refs(
|
|
&self,
|
|
previous: &ty::PolyTraitRef<'tcx>,
|
|
current: &ty::PolyTraitRef<'tcx>,
|
|
param_env: ty::ParamEnv<'tcx>,
|
|
) -> bool {
|
|
let mut matcher = ty::_match::Match::new(self.tcx(), param_env);
|
|
matcher.relate(previous, current).is_ok()
|
|
}
|
|
|
|
fn push_stack<'o>(
|
|
&mut self,
|
|
previous_stack: TraitObligationStackList<'o, 'tcx>,
|
|
obligation: &'o TraitObligation<'tcx>,
|
|
) -> TraitObligationStack<'o, 'tcx> {
|
|
let fresh_trait_ref =
|
|
obligation.predicate.to_poly_trait_ref().fold_with(&mut self.freshener);
|
|
|
|
let dfn = previous_stack.cache.next_dfn();
|
|
let depth = previous_stack.depth() + 1;
|
|
TraitObligationStack {
|
|
obligation,
|
|
fresh_trait_ref,
|
|
reached_depth: Cell::new(depth),
|
|
previous: previous_stack,
|
|
dfn,
|
|
depth,
|
|
}
|
|
}
|
|
|
|
fn closure_trait_ref_unnormalized(
|
|
&mut self,
|
|
obligation: &TraitObligation<'tcx>,
|
|
substs: SubstsRef<'tcx>,
|
|
) -> ty::PolyTraitRef<'tcx> {
|
|
debug!("closure_trait_ref_unnormalized(obligation={:?}, substs={:?})", obligation, substs);
|
|
let closure_sig = substs.as_closure().sig();
|
|
|
|
debug!("closure_trait_ref_unnormalized: closure_sig = {:?}", closure_sig);
|
|
|
|
// (1) Feels icky to skip the binder here, but OTOH we know
|
|
// that the self-type is an unboxed closure type and hence is
|
|
// in fact unparameterized (or at least does not reference any
|
|
// regions bound in the obligation). Still probably some
|
|
// refactoring could make this nicer.
|
|
closure_trait_ref_and_return_type(
|
|
self.tcx(),
|
|
obligation.predicate.def_id(),
|
|
obligation.predicate.skip_binder().self_ty(), // (1)
|
|
closure_sig,
|
|
util::TupleArgumentsFlag::No,
|
|
)
|
|
.map_bound(|(trait_ref, _)| trait_ref)
|
|
}
|
|
|
|
fn generator_trait_ref_unnormalized(
|
|
&mut self,
|
|
obligation: &TraitObligation<'tcx>,
|
|
substs: SubstsRef<'tcx>,
|
|
) -> ty::PolyTraitRef<'tcx> {
|
|
let gen_sig = substs.as_generator().poly_sig();
|
|
|
|
// (1) Feels icky to skip the binder here, but OTOH we know
|
|
// that the self-type is an generator type and hence is
|
|
// in fact unparameterized (or at least does not reference any
|
|
// regions bound in the obligation). Still probably some
|
|
// refactoring could make this nicer.
|
|
|
|
super::util::generator_trait_ref_and_outputs(
|
|
self.tcx(),
|
|
obligation.predicate.def_id(),
|
|
obligation.predicate.skip_binder().self_ty(), // (1)
|
|
gen_sig,
|
|
)
|
|
.map_bound(|(trait_ref, ..)| trait_ref)
|
|
}
|
|
|
|
/// Returns the obligations that are implied by instantiating an
|
|
/// impl or trait. The obligations are substituted and fully
|
|
/// normalized. This is used when confirming an impl or default
|
|
/// impl.
|
|
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
|
|
substs: SubstsRef<'tcx>, // for impl or trait
|
|
) -> Vec<PredicateObligation<'tcx>> {
|
|
debug!("impl_or_trait_obligations(def_id={:?})", def_id);
|
|
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 substitute, 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 mut obligations = Vec::with_capacity(predicates.predicates.len());
|
|
for (predicate, _) in predicates.predicates {
|
|
let predicate = normalize_with_depth_to(
|
|
self,
|
|
param_env,
|
|
cause.clone(),
|
|
recursion_depth,
|
|
&predicate.subst(tcx, substs),
|
|
&mut obligations,
|
|
);
|
|
obligations.push(Obligation {
|
|
cause: cause.clone(),
|
|
recursion_depth,
|
|
param_env,
|
|
predicate,
|
|
});
|
|
}
|
|
|
|
// We are performing deduplication here to avoid exponential blowups
|
|
// (#38528) from happening, but the real cause of the duplication is
|
|
// unknown. What we know is that the deduplication avoids exponential
|
|
// amount of predicates being propagated when processing deeply nested
|
|
// types.
|
|
//
|
|
// This code is hot enough that it's worth avoiding the allocation
|
|
// required for the FxHashSet when possible. Special-casing lengths 0,
|
|
// 1 and 2 covers roughly 75-80% of the cases.
|
|
if obligations.len() <= 1 {
|
|
// No possibility of duplicates.
|
|
} else if obligations.len() == 2 {
|
|
// Only two elements. Drop the second if they are equal.
|
|
if obligations[0] == obligations[1] {
|
|
obligations.truncate(1);
|
|
}
|
|
} else {
|
|
// Three or more elements. Use a general deduplication process.
|
|
let mut seen = FxHashSet::default();
|
|
obligations.retain(|i| seen.insert(i.clone()));
|
|
}
|
|
|
|
obligations
|
|
}
|
|
}
|
|
|
|
trait TraitObligationExt<'tcx> {
|
|
fn derived_cause(
|
|
&self,
|
|
variant: fn(DerivedObligationCause<'tcx>) -> ObligationCauseCode<'tcx>,
|
|
) -> ObligationCause<'tcx>;
|
|
}
|
|
|
|
impl<'tcx> TraitObligationExt<'tcx> for TraitObligation<'tcx> {
|
|
#[allow(unused_comparisons)]
|
|
fn derived_cause(
|
|
&self,
|
|
variant: fn(DerivedObligationCause<'tcx>) -> ObligationCauseCode<'tcx>,
|
|
) -> ObligationCause<'tcx> {
|
|
/*!
|
|
* Creates a cause for obligations that are derived from
|
|
* `obligation` by a recursive search (e.g., for a builtin
|
|
* bound, or eventually a `auto trait Foo`). If `obligation`
|
|
* is itself a derived obligation, this is just a clone, but
|
|
* otherwise we create a "derived obligation" cause so as to
|
|
* keep track of the original root obligation for error
|
|
* reporting.
|
|
*/
|
|
|
|
let obligation = self;
|
|
|
|
// NOTE(flaper87): As of now, it keeps track of the whole error
|
|
// chain. Ideally, we should have a way to configure this either
|
|
// by using -Z verbose or just a CLI argument.
|
|
let derived_cause = DerivedObligationCause {
|
|
parent_trait_ref: obligation.predicate.to_poly_trait_ref(),
|
|
parent_code: Rc::new(obligation.cause.code.clone()),
|
|
};
|
|
let derived_code = variant(derived_cause);
|
|
ObligationCause::new(obligation.cause.span, obligation.cause.body_id, derived_code)
|
|
}
|
|
}
|
|
|
|
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!("update_reached_depth(reached_depth={})", reached_depth);
|
|
let mut p = self;
|
|
while reached_depth < p.depth {
|
|
debug!("update_reached_depth: marking {:?} as cycle participant", p.fresh_trait_ref);
|
|
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>,
|
|
|
|
/// Stores the "coldest" depth (bottom of stack) reached by any of
|
|
/// the evaluation entries. The idea here is that all things in the provisional
|
|
/// cache are always dependent on *something* that is colder in the stack:
|
|
/// therefore, if we add a new entry that is dependent on something *colder still*,
|
|
/// we have to modify the depth for all entries at once.
|
|
///
|
|
/// Example:
|
|
///
|
|
/// Imagine we have a stack `A B C D E` (with `E` being the top of
|
|
/// the stack). We cache something with depth 2, which means that
|
|
/// it was dependent on C. Then we pop E but go on and process a
|
|
/// new node F: A B C D F. Now F adds something to the cache with
|
|
/// depth 1, meaning it is dependent on B. Our original cache
|
|
/// entry is also dependent on B, because there is a path from E
|
|
/// to C and then from C to F and from F to B.
|
|
reached_depth: 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 dependices 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<FxHashMap<ty::PolyTraitRef<'tcx>, ProvisionalEvaluation>>,
|
|
}
|
|
|
|
/// A cache value for the provisional cache: contains the depth-first
|
|
/// number (DFN) and result.
|
|
#[derive(Copy, Clone, Debug)]
|
|
struct ProvisionalEvaluation {
|
|
from_dfn: usize,
|
|
result: EvaluationResult,
|
|
}
|
|
|
|
impl<'tcx> Default for ProvisionalEvaluationCache<'tcx> {
|
|
fn default() -> Self {
|
|
Self { dfn: Cell::new(0), reached_depth: Cell::new(usize::MAX), map: 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
|
|
/// `self.current_reached_depth()` and above.
|
|
fn get_provisional(&self, fresh_trait_ref: ty::PolyTraitRef<'tcx>) -> Option<EvaluationResult> {
|
|
debug!(
|
|
"get_provisional(fresh_trait_ref={:?}) = {:#?} with reached-depth {}",
|
|
fresh_trait_ref,
|
|
self.map.borrow().get(&fresh_trait_ref),
|
|
self.reached_depth.get(),
|
|
);
|
|
Some(self.map.borrow().get(&fresh_trait_ref)?.result)
|
|
}
|
|
|
|
/// Current value of the `reached_depth` counter -- all the
|
|
/// provisional cache entries are dependent on the item at this
|
|
/// depth.
|
|
fn current_reached_depth(&self) -> usize {
|
|
self.reached_depth.get()
|
|
}
|
|
|
|
/// 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_ref`
|
|
/// and resulted in `result`.
|
|
fn insert_provisional(
|
|
&self,
|
|
from_dfn: usize,
|
|
reached_depth: usize,
|
|
fresh_trait_ref: ty::PolyTraitRef<'tcx>,
|
|
result: EvaluationResult,
|
|
) {
|
|
debug!(
|
|
"insert_provisional(from_dfn={}, reached_depth={}, fresh_trait_ref={:?}, result={:?})",
|
|
from_dfn, reached_depth, fresh_trait_ref, result,
|
|
);
|
|
let r_d = self.reached_depth.get();
|
|
self.reached_depth.set(r_d.min(reached_depth));
|
|
|
|
debug!("insert_provisional: reached_depth={:?}", self.reached_depth.get());
|
|
|
|
self.map.borrow_mut().insert(fresh_trait_ref, ProvisionalEvaluation { from_dfn, 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!("on_failure(dfn={:?})", dfn,);
|
|
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). The callback `op` will be invoked for each
|
|
/// provisional entry that we can now confirm.
|
|
fn on_completion(
|
|
&self,
|
|
depth: usize,
|
|
mut op: impl FnMut(ty::PolyTraitRef<'tcx>, EvaluationResult),
|
|
) {
|
|
debug!("on_completion(depth={}, reached_depth={})", depth, self.reached_depth.get(),);
|
|
|
|
if self.reached_depth.get() < depth {
|
|
debug!("on_completion: did not yet reach depth to complete");
|
|
return;
|
|
}
|
|
|
|
for (fresh_trait_ref, eval) in self.map.borrow_mut().drain() {
|
|
debug!("on_completion: fresh_trait_ref={:?} eval={:?}", fresh_trait_ref, eval,);
|
|
|
|
op(fresh_trait_ref, eval.result);
|
|
}
|
|
|
|
self.reached_depth.set(usize::MAX);
|
|
}
|
|
}
|
|
|
|
#[derive(Copy, Clone)]
|
|
struct TraitObligationStackList<'o, 'tcx> {
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cache: &'o ProvisionalEvaluationCache<'tcx>,
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head: Option<&'o TraitObligationStack<'o, 'tcx>>,
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}
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|
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impl<'o, 'tcx> TraitObligationStackList<'o, 'tcx> {
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fn empty(cache: &'o ProvisionalEvaluationCache<'tcx>) -> TraitObligationStackList<'o, 'tcx> {
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TraitObligationStackList { cache, head: None }
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}
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fn with(r: &'o TraitObligationStack<'o, 'tcx>) -> TraitObligationStackList<'o, 'tcx> {
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TraitObligationStackList { cache: r.cache(), head: Some(r) }
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}
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|
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fn head(&self) -> Option<&'o TraitObligationStack<'o, 'tcx>> {
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self.head
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}
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|
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fn depth(&self) -> usize {
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if let Some(head) = self.head { head.depth } else { 0 }
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}
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|
}
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|
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impl<'o, 'tcx> Iterator for TraitObligationStackList<'o, 'tcx> {
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type Item = &'o TraitObligationStack<'o, 'tcx>;
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|
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fn next(&mut self) -> Option<&'o TraitObligationStack<'o, 'tcx>> {
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|
match self.head {
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|
Some(o) => {
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|
*self = o.previous;
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|
Some(o)
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|
}
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|
None => None,
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|
}
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|
}
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|
}
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|
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impl<'o, 'tcx> fmt::Debug for TraitObligationStack<'o, 'tcx> {
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fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
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write!(f, "TraitObligationStack({:?})", self.obligation)
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}
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|
}
|