| //! 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 |
| |
| use std::ops::ControlFlow; |
| |
| use hir::LangItem; |
| use hir::def_id::DefId; |
| use rustc_data_structures::fx::{FxHashSet, FxIndexSet}; |
| use rustc_hir::{self as hir, CoroutineDesugaring, CoroutineKind}; |
| use rustc_infer::traits::{Obligation, PolyTraitObligation, SelectionError}; |
| use rustc_middle::ty::fast_reject::DeepRejectCtxt; |
| use rustc_middle::ty::{self, SizedTraitKind, Ty, TypeVisitableExt, TypingMode, elaborate}; |
| use rustc_middle::{bug, span_bug}; |
| use tracing::{debug, instrument, trace}; |
| |
| use super::SelectionCandidate::*; |
| use super::{SelectionCandidateSet, SelectionContext, TraitObligationStack}; |
| use crate::traits::util; |
| |
| impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> { |
| #[instrument(skip(self, stack), level = "debug")] |
| pub(super) 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() { |
| debug!(ty = ?obligation.predicate.skip_binder().self_ty(), "ambiguous inference var or opaque type"); |
| // 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 }; |
| |
| // Negative trait predicates have different rules than positive trait predicates. |
| if obligation.polarity() == ty::PredicatePolarity::Negative { |
| self.assemble_candidates_for_trait_alias(obligation, &mut candidates); |
| self.assemble_candidates_from_impls(obligation, &mut candidates); |
| self.assemble_candidates_from_caller_bounds(stack, &mut candidates)?; |
| } else { |
| 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 tcx = self.tcx(); |
| |
| let lang_item = tcx.as_lang_item(def_id); |
| match lang_item { |
| Some(LangItem::Copy | LangItem::Clone) => { |
| debug!(obligation_self_ty = ?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. |
| self.assemble_builtin_copy_clone_candidate( |
| obligation.predicate.self_ty().skip_binder(), |
| &mut candidates, |
| ); |
| } |
| Some(LangItem::DiscriminantKind) => { |
| // `DiscriminantKind` is automatically implemented for every type. |
| candidates.vec.push(BuiltinCandidate); |
| } |
| Some(LangItem::PointeeTrait) => { |
| // `Pointee` is automatically implemented for every type. |
| candidates.vec.push(BuiltinCandidate); |
| } |
| Some(LangItem::Sized) => { |
| self.assemble_builtin_sized_candidate( |
| obligation.predicate.self_ty().skip_binder(), |
| &mut candidates, |
| SizedTraitKind::Sized, |
| ); |
| } |
| Some(LangItem::MetaSized) => { |
| self.assemble_builtin_sized_candidate( |
| obligation.predicate.self_ty().skip_binder(), |
| &mut candidates, |
| SizedTraitKind::MetaSized, |
| ); |
| } |
| Some(LangItem::PointeeSized) => { |
| bug!("`PointeeSized` is removed during lowering"); |
| } |
| Some(LangItem::Unsize) => { |
| self.assemble_candidates_for_unsizing(obligation, &mut candidates); |
| } |
| Some(LangItem::Destruct) => { |
| self.assemble_const_destruct_candidates(obligation, &mut candidates); |
| } |
| Some(LangItem::TransmuteTrait) => { |
| // User-defined transmutability impls are permitted. |
| self.assemble_candidates_from_impls(obligation, &mut candidates); |
| self.assemble_candidates_for_transmutability(obligation, &mut candidates); |
| } |
| Some(LangItem::Tuple) => { |
| self.assemble_candidate_for_tuple(obligation, &mut candidates); |
| } |
| Some(LangItem::FnPtrTrait) => { |
| self.assemble_candidates_for_fn_ptr_trait(obligation, &mut candidates); |
| } |
| Some(LangItem::BikeshedGuaranteedNoDrop) => { |
| self.assemble_candidates_for_bikeshed_guaranteed_no_drop_trait( |
| obligation, |
| &mut candidates, |
| ); |
| } |
| _ => { |
| // We re-match here for traits that can have both builtin impls and user written impls. |
| // After the builtin impls we need to also add user written impls, which we do not want to |
| // do in general because just checking if there are any is expensive. |
| match lang_item { |
| Some(LangItem::Coroutine) => { |
| self.assemble_coroutine_candidates(obligation, &mut candidates); |
| } |
| Some(LangItem::Future) => { |
| self.assemble_future_candidates(obligation, &mut candidates); |
| } |
| Some(LangItem::Iterator) => { |
| self.assemble_iterator_candidates(obligation, &mut candidates); |
| } |
| Some(LangItem::FusedIterator) => { |
| self.assemble_fused_iterator_candidates(obligation, &mut candidates); |
| } |
| Some(LangItem::AsyncIterator) => { |
| self.assemble_async_iterator_candidates(obligation, &mut candidates); |
| } |
| Some(LangItem::AsyncFnKindHelper) => { |
| self.assemble_async_fn_kind_helper_candidates( |
| obligation, |
| &mut candidates, |
| ); |
| } |
| Some(LangItem::AsyncFn | LangItem::AsyncFnMut | LangItem::AsyncFnOnce) => { |
| self.assemble_async_closure_candidates(obligation, &mut candidates); |
| } |
| Some(LangItem::Fn | LangItem::FnMut | LangItem::FnOnce) => { |
| 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)?; |
| self.assemble_candidates_from_auto_impls(obligation, &mut candidates); |
| } |
| debug!("candidate list size: {}", candidates.vec.len()); |
| Ok(candidates) |
| } |
| |
| #[instrument(level = "debug", skip(self, candidates))] |
| fn assemble_candidates_from_projected_tys( |
| &mut self, |
| obligation: &PolyTraitObligation<'tcx>, |
| candidates: &mut SelectionCandidateSet<'tcx>, |
| ) { |
| // 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() { |
| // Excluding IATs and type aliases here as they don't have meaningful item bounds. |
| ty::Alias(ty::Projection | ty::Opaque, _) => {} |
| ty::Infer(ty::TyVar(_)) => { |
| span_bug!( |
| obligation.cause.span, |
| "Self=_ should have been handled by assemble_candidates" |
| ); |
| } |
| _ => return, |
| } |
| |
| self.infcx.probe(|_| { |
| let poly_trait_predicate = self.infcx.resolve_vars_if_possible(obligation.predicate); |
| let placeholder_trait_predicate = |
| self.infcx.enter_forall_and_leak_universe(poly_trait_predicate); |
| |
| // The bounds returned by `item_bounds` may contain duplicates after |
| // normalization, so try to deduplicate when possible to avoid |
| // unnecessary ambiguity. |
| let mut distinct_normalized_bounds = FxHashSet::default(); |
| let _ = self.for_each_item_bound::<!>( |
| placeholder_trait_predicate.self_ty(), |
| |selcx, bound, idx| { |
| let Some(bound) = bound.as_trait_clause() else { |
| return ControlFlow::Continue(()); |
| }; |
| if bound.polarity() != placeholder_trait_predicate.polarity { |
| return ControlFlow::Continue(()); |
| } |
| |
| selcx.infcx.probe(|_| { |
| let bound = util::lazily_elaborate_sizedness_candidate( |
| selcx.infcx, |
| obligation, |
| bound, |
| ); |
| |
| // We checked the polarity already |
| match selcx.match_normalize_trait_ref( |
| obligation, |
| placeholder_trait_predicate.trait_ref, |
| bound.map_bound(|pred| pred.trait_ref), |
| ) { |
| Ok(None) => { |
| candidates.vec.push(ProjectionCandidate(idx)); |
| } |
| Ok(Some(normalized_trait)) |
| if distinct_normalized_bounds.insert(normalized_trait) => |
| { |
| candidates.vec.push(ProjectionCandidate(idx)); |
| } |
| _ => {} |
| } |
| }); |
| |
| ControlFlow::Continue(()) |
| }, |
| // On ambiguity. |
| || candidates.ambiguous = true, |
| ); |
| }); |
| } |
| |
| /// 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. |
| #[instrument(level = "debug", skip(self, stack, candidates))] |
| fn assemble_candidates_from_caller_bounds<'o>( |
| &mut self, |
| stack: &TraitObligationStack<'o, 'tcx>, |
| candidates: &mut SelectionCandidateSet<'tcx>, |
| ) -> Result<(), SelectionError<'tcx>> { |
| debug!(?stack.obligation); |
| |
| let bounds = stack |
| .obligation |
| .param_env |
| .caller_bounds() |
| .iter() |
| .filter_map(|p| p.as_trait_clause()) |
| // Micro-optimization: filter out predicates with different polarities. |
| .filter(|p| p.polarity() == stack.obligation.predicate.polarity()); |
| |
| let drcx = DeepRejectCtxt::relate_rigid_rigid(self.tcx()); |
| let obligation_args = stack.obligation.predicate.skip_binder().trait_ref.args; |
| // Keep only those bounds which may apply, and propagate overflow if it occurs. |
| for bound in bounds { |
| let bound = |
| util::lazily_elaborate_sizedness_candidate(self.infcx, stack.obligation, bound); |
| |
| // Micro-optimization: filter out predicates relating to different traits. |
| if bound.def_id() != stack.obligation.predicate.def_id() { |
| continue; |
| } |
| |
| let bound_trait_ref = bound.map_bound(|t| t.trait_ref); |
| if !drcx.args_may_unify(obligation_args, bound_trait_ref.skip_binder().args) { |
| continue; |
| } |
| let wc = self.where_clause_may_apply(stack, bound_trait_ref)?; |
| if wc.may_apply() { |
| candidates.vec.push(ParamCandidate(bound)); |
| } |
| } |
| |
| Ok(()) |
| } |
| |
| fn assemble_coroutine_candidates( |
| &mut self, |
| obligation: &PolyTraitObligation<'tcx>, |
| candidates: &mut SelectionCandidateSet<'tcx>, |
| ) { |
| // Okay to skip binder because the args on coroutine 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() { |
| // `async`/`gen` constructs get lowered to a special kind of coroutine that |
| // should *not* `impl Coroutine`. |
| ty::Coroutine(did, ..) if self.tcx().is_general_coroutine(*did) => { |
| debug!(?self_ty, ?obligation, "assemble_coroutine_candidates",); |
| |
| candidates.vec.push(CoroutineCandidate); |
| } |
| ty::Infer(ty::TyVar(_)) => { |
| debug!("assemble_coroutine_candidates: ambiguous self-type"); |
| candidates.ambiguous = true; |
| } |
| _ => {} |
| } |
| } |
| |
| fn assemble_future_candidates( |
| &mut self, |
| obligation: &PolyTraitObligation<'tcx>, |
| candidates: &mut SelectionCandidateSet<'tcx>, |
| ) { |
| let self_ty = obligation.self_ty().skip_binder(); |
| if let ty::Coroutine(did, ..) = self_ty.kind() { |
| // async constructs get lowered to a special kind of coroutine that |
| // should directly `impl Future`. |
| if self.tcx().coroutine_is_async(*did) { |
| debug!(?self_ty, ?obligation, "assemble_future_candidates",); |
| |
| candidates.vec.push(FutureCandidate); |
| } |
| } |
| } |
| |
| fn assemble_iterator_candidates( |
| &mut self, |
| obligation: &PolyTraitObligation<'tcx>, |
| candidates: &mut SelectionCandidateSet<'tcx>, |
| ) { |
| let self_ty = obligation.self_ty().skip_binder(); |
| // gen constructs get lowered to a special kind of coroutine that |
| // should directly `impl Iterator`. |
| if let ty::Coroutine(did, ..) = self_ty.kind() |
| && self.tcx().coroutine_is_gen(*did) |
| { |
| debug!(?self_ty, ?obligation, "assemble_iterator_candidates",); |
| |
| candidates.vec.push(IteratorCandidate); |
| } |
| } |
| |
| fn assemble_fused_iterator_candidates( |
| &mut self, |
| obligation: &PolyTraitObligation<'tcx>, |
| candidates: &mut SelectionCandidateSet<'tcx>, |
| ) { |
| if self.coroutine_is_gen(obligation.self_ty().skip_binder()) { |
| candidates.vec.push(BuiltinCandidate); |
| } |
| } |
| |
| fn assemble_async_iterator_candidates( |
| &mut self, |
| obligation: &PolyTraitObligation<'tcx>, |
| candidates: &mut SelectionCandidateSet<'tcx>, |
| ) { |
| let self_ty = obligation.self_ty().skip_binder(); |
| if let ty::Coroutine(did, args) = *self_ty.kind() { |
| // gen constructs get lowered to a special kind of coroutine that |
| // should directly `impl AsyncIterator`. |
| if self.tcx().coroutine_is_async_gen(did) { |
| debug!(?self_ty, ?obligation, "assemble_iterator_candidates",); |
| |
| // Can only confirm this candidate if we have constrained |
| // the `Yield` type to at least `Poll<Option<?0>>`.. |
| let ty::Adt(_poll_def, args) = *args.as_coroutine().yield_ty().kind() else { |
| candidates.ambiguous = true; |
| return; |
| }; |
| let ty::Adt(_option_def, _) = *args.type_at(0).kind() else { |
| candidates.ambiguous = true; |
| return; |
| }; |
| |
| candidates.vec.push(AsyncIteratorCandidate); |
| } |
| } |
| } |
| |
| /// 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: &PolyTraitObligation<'tcx>, |
| candidates: &mut SelectionCandidateSet<'tcx>, |
| ) { |
| let kind = self.tcx().fn_trait_kind_from_def_id(obligation.predicate.def_id()).unwrap(); |
| |
| // Okay to skip binder because the args on closure 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::Closure(def_id, _) => { |
| let is_const = self.tcx().is_const_fn(def_id); |
| debug!(?kind, ?obligation, "assemble_unboxed_candidates"); |
| match self.infcx.closure_kind(self_ty) { |
| Some(closure_kind) => { |
| debug!(?closure_kind, "assemble_unboxed_candidates"); |
| if closure_kind.extends(kind) { |
| candidates.vec.push(ClosureCandidate { is_const }); |
| } |
| } |
| None => { |
| if kind == ty::ClosureKind::FnOnce { |
| candidates.vec.push(ClosureCandidate { is_const }); |
| } else { |
| candidates.ambiguous = true; |
| } |
| } |
| } |
| } |
| ty::CoroutineClosure(def_id, args) => { |
| let args = args.as_coroutine_closure(); |
| let is_const = self.tcx().is_const_fn(def_id); |
| if let Some(closure_kind) = self.infcx.closure_kind(self_ty) |
| // Ambiguity if upvars haven't been constrained yet |
| && !args.tupled_upvars_ty().is_ty_var() |
| { |
| // A coroutine-closure implements `FnOnce` *always*, since it may |
| // always be called once. It additionally implements `Fn`/`FnMut` |
| // only if it has no upvars referencing the closure-env lifetime, |
| // and if the closure kind permits it. |
| if closure_kind.extends(kind) && !args.has_self_borrows() { |
| candidates.vec.push(ClosureCandidate { is_const }); |
| } else if kind == ty::ClosureKind::FnOnce { |
| candidates.vec.push(ClosureCandidate { is_const }); |
| } |
| } else if kind == ty::ClosureKind::FnOnce { |
| candidates.vec.push(ClosureCandidate { is_const }); |
| } else { |
| // This stays ambiguous until kind+upvars are determined. |
| candidates.ambiguous = true; |
| } |
| } |
| ty::Infer(ty::TyVar(_)) => { |
| debug!("assemble_unboxed_closure_candidates: ambiguous self-type"); |
| candidates.ambiguous = true; |
| } |
| _ => {} |
| } |
| } |
| |
| #[instrument(level = "debug", skip(self, candidates))] |
| fn assemble_async_closure_candidates( |
| &mut self, |
| obligation: &PolyTraitObligation<'tcx>, |
| candidates: &mut SelectionCandidateSet<'tcx>, |
| ) { |
| let goal_kind = |
| self.tcx().async_fn_trait_kind_from_def_id(obligation.predicate.def_id()).unwrap(); |
| |
| debug!("self_ty = {:?}", obligation.self_ty().skip_binder().kind()); |
| match *obligation.self_ty().skip_binder().kind() { |
| ty::CoroutineClosure(def_id, args) => { |
| if let Some(closure_kind) = |
| args.as_coroutine_closure().kind_ty().to_opt_closure_kind() |
| && !closure_kind.extends(goal_kind) |
| { |
| return; |
| } |
| |
| // Make sure this is actually an async closure. |
| let Some(coroutine_kind) = |
| self.tcx().coroutine_kind(self.tcx().coroutine_for_closure(def_id)) |
| else { |
| bug!("coroutine with no kind"); |
| }; |
| |
| debug!(?coroutine_kind); |
| match coroutine_kind { |
| CoroutineKind::Desugared(CoroutineDesugaring::Async, _) => { |
| candidates.vec.push(AsyncClosureCandidate); |
| } |
| _ => (), |
| } |
| } |
| // Closures and fn pointers implement `AsyncFn*` if their return types |
| // implement `Future`, which is checked later. |
| ty::Closure(_, args) => { |
| if let Some(closure_kind) = args.as_closure().kind_ty().to_opt_closure_kind() |
| && !closure_kind.extends(goal_kind) |
| { |
| return; |
| } |
| candidates.vec.push(AsyncClosureCandidate); |
| } |
| // Provide an impl, but only for suitable `fn` pointers. |
| ty::FnPtr(sig_tys, hdr) => { |
| if sig_tys.with(hdr).is_fn_trait_compatible() { |
| candidates.vec.push(AsyncClosureCandidate); |
| } |
| } |
| // Provide an impl for suitable functions, rejecting `#[target_feature]` functions (RFC 2396). |
| ty::FnDef(def_id, _) => { |
| let tcx = self.tcx(); |
| if tcx.fn_sig(def_id).skip_binder().is_fn_trait_compatible() |
| && tcx.codegen_fn_attrs(def_id).target_features.is_empty() |
| { |
| candidates.vec.push(AsyncClosureCandidate); |
| } |
| } |
| _ => {} |
| } |
| } |
| |
| fn assemble_async_fn_kind_helper_candidates( |
| &mut self, |
| obligation: &PolyTraitObligation<'tcx>, |
| candidates: &mut SelectionCandidateSet<'tcx>, |
| ) { |
| let self_ty = obligation.self_ty().skip_binder(); |
| let target_kind_ty = obligation.predicate.skip_binder().trait_ref.args.type_at(1); |
| |
| // `to_opt_closure_kind` is kind of ICEy when it sees non-int types. |
| if !(self_ty.is_integral() || self_ty.is_ty_var()) { |
| return; |
| } |
| if !(target_kind_ty.is_integral() || self_ty.is_ty_var()) { |
| return; |
| } |
| |
| // Check that the self kind extends the goal kind. If it does, |
| // then there's nothing else to check. |
| if let Some(closure_kind) = self_ty.to_opt_closure_kind() |
| && let Some(goal_kind) = target_kind_ty.to_opt_closure_kind() |
| && closure_kind.extends(goal_kind) |
| { |
| candidates.vec.push(AsyncFnKindHelperCandidate); |
| } |
| } |
| |
| /// Implements one of the `Fn()` family for a fn pointer. |
| fn assemble_fn_pointer_candidates( |
| &mut self, |
| obligation: &PolyTraitObligation<'tcx>, |
| candidates: &mut SelectionCandidateSet<'tcx>, |
| ) { |
| // Keep this function in sync with extract_tupled_inputs_and_output_from_callable |
| // until the old solver (and thus this function) is removed. |
| |
| // 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::FnPtr(sig_tys, hdr) => { |
| if sig_tys.with(hdr).is_fn_trait_compatible() { |
| candidates.vec.push(FnPointerCandidate); |
| } |
| } |
| // Provide an impl for suitable functions, rejecting `#[target_feature]` functions (RFC 2396). |
| ty::FnDef(def_id, _) => { |
| let tcx = self.tcx(); |
| if tcx.fn_sig(def_id).skip_binder().is_fn_trait_compatible() |
| && tcx.codegen_fn_attrs(def_id).target_features.is_empty() |
| { |
| candidates.vec.push(FnPointerCandidate); |
| } |
| } |
| _ => {} |
| } |
| } |
| |
| /// Searches for impls that might apply to `obligation`. |
| #[instrument(level = "debug", skip(self, candidates))] |
| fn assemble_candidates_from_impls( |
| &mut self, |
| obligation: &PolyTraitObligation<'tcx>, |
| candidates: &mut SelectionCandidateSet<'tcx>, |
| ) { |
| let drcx = DeepRejectCtxt::relate_rigid_infer(self.tcx()); |
| let obligation_args = obligation.predicate.skip_binder().trait_ref.args; |
| self.tcx().for_each_relevant_impl( |
| obligation.predicate.def_id(), |
| obligation.predicate.skip_binder().trait_ref.self_ty(), |
| |impl_def_id| { |
| // Before we create the generic parameters and everything, first |
| // consider a "quick reject". This avoids creating more types |
| // and so forth that we need to. |
| let impl_trait_header = self.tcx().impl_trait_header(impl_def_id).unwrap(); |
| if !drcx |
| .args_may_unify(obligation_args, impl_trait_header.trait_ref.skip_binder().args) |
| { |
| return; |
| } |
| |
| // For every `default impl`, there's always a non-default `impl` |
| // that will *also* apply. There's no reason to register a candidate |
| // for this impl, since it is *not* proof that the trait goal holds. |
| if self.tcx().defaultness(impl_def_id).is_default() { |
| return; |
| } |
| |
| if self.reject_fn_ptr_impls( |
| impl_def_id, |
| obligation, |
| impl_trait_header.trait_ref.skip_binder().self_ty(), |
| ) { |
| return; |
| } |
| |
| self.infcx.probe(|_| { |
| if let Ok(_args) = self.match_impl(impl_def_id, impl_trait_header, obligation) { |
| candidates.vec.push(ImplCandidate(impl_def_id)); |
| } |
| }); |
| }, |
| ); |
| } |
| |
| /// The various `impl<T: FnPtr> Trait for T` in libcore are more like builtin impls for all function items |
| /// and function pointers and less like blanket impls. Rejecting them when they can't possibly apply (because |
| /// the obligation's self-type does not implement `FnPtr`) avoids reporting that the self type does not implement |
| /// `FnPtr`, when we wanted to report that it doesn't implement `Trait`. |
| #[instrument(level = "trace", skip(self), ret)] |
| fn reject_fn_ptr_impls( |
| &mut self, |
| impl_def_id: DefId, |
| obligation: &PolyTraitObligation<'tcx>, |
| impl_self_ty: Ty<'tcx>, |
| ) -> bool { |
| // Let `impl<T: FnPtr> Trait for Vec<T>` go through the normal rejection path. |
| if !matches!(impl_self_ty.kind(), ty::Param(..)) { |
| return false; |
| } |
| let Some(fn_ptr_trait) = self.tcx().lang_items().fn_ptr_trait() else { |
| return false; |
| }; |
| |
| for &(predicate, _) in self.tcx().predicates_of(impl_def_id).predicates { |
| let ty::ClauseKind::Trait(pred) = predicate.kind().skip_binder() else { continue }; |
| if fn_ptr_trait != pred.trait_ref.def_id { |
| continue; |
| } |
| trace!(?pred); |
| // Not the bound we're looking for |
| if pred.self_ty() != impl_self_ty { |
| continue; |
| } |
| |
| let self_ty = obligation.self_ty().skip_binder(); |
| match self_ty.kind() { |
| // Fast path to avoid evaluating an obligation that trivially holds. |
| // There may be more bounds, but these are checked by the regular path. |
| ty::FnPtr(..) => return false, |
| |
| // These may potentially implement `FnPtr` |
| ty::Placeholder(..) |
| | ty::Dynamic(_, _, _) |
| | ty::Alias(_, _) |
| | ty::Infer(_) |
| | ty::Param(..) |
| | ty::Bound(_, _) => {} |
| |
| // These can't possibly implement `FnPtr` as they are concrete types |
| // and not `FnPtr` |
| ty::Bool |
| | ty::Char |
| | ty::Int(_) |
| | ty::Uint(_) |
| | ty::Float(_) |
| | ty::Adt(_, _) |
| | ty::Foreign(_) |
| | ty::Str |
| | ty::Array(_, _) |
| | ty::Pat(_, _) |
| | ty::Slice(_) |
| | ty::RawPtr(_, _) |
| | ty::Ref(_, _, _) |
| | ty::Closure(..) |
| | ty::CoroutineClosure(..) |
| | ty::Coroutine(_, _) |
| | ty::CoroutineWitness(..) |
| | ty::UnsafeBinder(_) |
| | ty::Never |
| | ty::Tuple(_) |
| | ty::Error(_) => return true, |
| // FIXME: Function definitions could actually implement `FnPtr` by |
| // casting the ZST function def to a function pointer. |
| ty::FnDef(_, _) => return true, |
| } |
| |
| // Generic params can implement `FnPtr` if the predicate |
| // holds within its own environment. |
| let obligation = Obligation::new( |
| self.tcx(), |
| obligation.cause.clone(), |
| obligation.param_env, |
| self.tcx().mk_predicate(obligation.predicate.map_bound(|mut pred| { |
| pred.trait_ref = |
| ty::TraitRef::new(self.tcx(), fn_ptr_trait, [pred.trait_ref.self_ty()]); |
| ty::PredicateKind::Clause(ty::ClauseKind::Trait(pred)) |
| })), |
| ); |
| if let Ok(r) = self.evaluate_root_obligation(&obligation) { |
| if !r.may_apply() { |
| return true; |
| } |
| } |
| } |
| false |
| } |
| |
| fn assemble_candidates_from_auto_impls( |
| &mut self, |
| obligation: &PolyTraitObligation<'tcx>, |
| candidates: &mut SelectionCandidateSet<'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!(?self_ty, "assemble_candidates_from_auto_impls"); |
| |
| let def_id = obligation.predicate.def_id(); |
| |
| let mut check_impls = || { |
| // Only consider auto impls if there are no manual impls for the root of `self_ty`. |
| // |
| // For example, we only consider auto candidates for `&i32: Auto` if no explicit impl |
| // for `&SomeType: Auto` exists. Due to E0321 the only crate where impls |
| // for `&SomeType: Auto` can be defined is the crate where `Auto` has been defined. |
| // |
| // Generally, we have to guarantee that for all `SimplifiedType`s the only crate |
| // which may define impls for that type is either the crate defining the type |
| // or the trait. This should be guaranteed by the orphan check. |
| let mut has_impl = false; |
| self.tcx().for_each_relevant_impl(def_id, self_ty, |_| has_impl = true); |
| if !has_impl { |
| candidates.vec.push(AutoImplCandidate) |
| } |
| }; |
| |
| 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. |
| |
| // Backward compatibility for default auto traits. |
| // Test: ui/traits/default_auto_traits/extern-types.rs |
| if self.tcx().is_default_trait(def_id) { |
| check_impls() |
| } |
| } |
| ty::Param(..) |
| | ty::Alias(ty::Projection | ty::Inherent | ty::Free, ..) |
| | ty::Placeholder(..) |
| | ty::Bound(..) => { |
| // 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 |
| // `ui/typeck/typeck-default-trait-impl-send-param.rs` |
| // for an example of a test case that exercises |
| // this path. |
| } |
| ty::Infer(ty::TyVar(_) | ty::IntVar(_) | ty::FloatVar(_)) => { |
| // The auto impl might apply; we don't know. |
| candidates.ambiguous = true; |
| } |
| ty::Coroutine(coroutine_def_id, _) => { |
| if self.tcx().is_lang_item(def_id, LangItem::Unpin) { |
| match self.tcx().coroutine_movability(coroutine_def_id) { |
| hir::Movability::Static => { |
| // Immovable coroutines are never `Unpin`, so |
| // suppress the normal auto-impl candidate for it. |
| } |
| hir::Movability::Movable => { |
| // Movable coroutines are always `Unpin`, so add an |
| // unconditional builtin candidate with no sub-obligations. |
| candidates.vec.push(BuiltinCandidate); |
| } |
| } |
| } else { |
| if self.should_stall_coroutine(coroutine_def_id) { |
| candidates.ambiguous = true; |
| } else { |
| // Coroutines implement all other auto traits normally. |
| candidates.vec.push(AutoImplCandidate); |
| } |
| } |
| } |
| |
| ty::Infer(ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)) => { |
| bug!( |
| "asked to assemble auto trait candidates of unexpected type: {:?}", |
| self_ty |
| ); |
| } |
| |
| ty::Alias(ty::Opaque, alias) => { |
| if candidates.vec.iter().any(|c| matches!(c, ProjectionCandidate(_))) { |
| // We do not generate an auto impl candidate for `impl Trait`s which already |
| // reference our auto trait. |
| // |
| // For example during candidate assembly for `impl Send: Send`, we don't have |
| // to look at the constituent types for this opaque types to figure out that this |
| // trivially holds. |
| // |
| // Note that this is only sound as projection candidates of opaque types |
| // are always applicable for auto traits. |
| } else if let TypingMode::Coherence = self.infcx.typing_mode() { |
| // We do not emit auto trait candidates for opaque types in coherence. |
| // Doing so can result in weird dependency cycles. |
| candidates.ambiguous = true; |
| } else if self.infcx.can_define_opaque_ty(alias.def_id) { |
| // We do not emit auto trait candidates for opaque types in their defining scope, as |
| // we need to know the hidden type first, which we can't reliably know within the defining |
| // scope. |
| candidates.ambiguous = true; |
| } else { |
| candidates.vec.push(AutoImplCandidate) |
| } |
| } |
| |
| ty::CoroutineWitness(..) => { |
| candidates.vec.push(AutoImplCandidate); |
| } |
| |
| ty::Bool |
| | ty::Char |
| | ty::Int(_) |
| | ty::Uint(_) |
| | ty::Float(_) |
| | ty::Str |
| | ty::Array(_, _) |
| | ty::Pat(_, _) |
| | ty::Slice(_) |
| | ty::Adt(..) |
| | ty::RawPtr(_, _) |
| | ty::Ref(..) |
| | ty::FnDef(..) |
| | ty::FnPtr(..) |
| | ty::Closure(..) |
| | ty::CoroutineClosure(..) |
| | ty::Never |
| | ty::Tuple(_) |
| | ty::UnsafeBinder(_) => { |
| // Only consider auto impls of unsafe traits when there are |
| // no unsafe fields. |
| if self.tcx().trait_def(def_id).safety.is_unsafe() |
| && self_ty.has_unsafe_fields() |
| { |
| return; |
| } |
| |
| check_impls(); |
| } |
| ty::Error(_) => { |
| candidates.vec.push(AutoImplCandidate); |
| } |
| } |
| } |
| } |
| |
| /// Searches for impls that might apply to `obligation`. |
| fn assemble_candidates_from_object_ty( |
| &mut self, |
| obligation: &PolyTraitObligation<'tcx>, |
| candidates: &mut SelectionCandidateSet<'tcx>, |
| ) { |
| debug!( |
| self_ty = ?obligation.self_ty().skip_binder(), |
| "assemble_candidates_from_object_ty", |
| ); |
| |
| if !self.tcx().trait_def(obligation.predicate.def_id()).implement_via_object { |
| return; |
| } |
| |
| self.infcx.probe(|_snapshot| { |
| let poly_trait_predicate = self.infcx.resolve_vars_if_possible(obligation.predicate); |
| self.infcx.enter_forall(poly_trait_predicate, |placeholder_trait_predicate| { |
| let self_ty = placeholder_trait_predicate.self_ty(); |
| let principal_trait_ref = match self_ty.kind() { |
| ty::Dynamic(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() { |
| principal.with_self_ty(self.tcx(), self_ty) |
| } 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!(?principal_trait_ref, "assemble_candidates_from_object_ty"); |
| |
| // 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 candidate_supertraits = util::supertraits(self.tcx(), principal_trait_ref) |
| .enumerate() |
| .filter(|&(_, upcast_trait_ref)| { |
| self.infcx.probe(|_| { |
| self.match_normalize_trait_ref( |
| obligation, |
| placeholder_trait_predicate.trait_ref, |
| upcast_trait_ref, |
| ) |
| .is_ok() |
| }) |
| }) |
| .map(|(idx, _)| ObjectCandidate(idx)); |
| |
| candidates.vec.extend(candidate_supertraits); |
| }) |
| }) |
| } |
| |
| /// Searches for unsizing that might apply to `obligation`. |
| fn assemble_candidates_for_unsizing( |
| &mut self, |
| obligation: &PolyTraitObligation<'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 Some(trait_pred) = obligation.predicate.no_bound_vars() else { |
| // Don't add any candidates if there are bound regions. |
| return; |
| }; |
| let source = trait_pred.self_ty(); |
| let target = trait_pred.trait_ref.args.type_at(1); |
| |
| debug!(?source, ?target, "assemble_candidates_for_unsizing"); |
| |
| match (source.kind(), target.kind()) { |
| // Trait+Kx+'a -> Trait+Ky+'b (upcasts). |
| (&ty::Dynamic(a_data, a_region, ty::Dyn), &ty::Dynamic(b_data, b_region, ty::Dyn)) => { |
| // Upcast coercions permit several 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` |
| // 3. Tightening trait to its super traits, eg. `Foo` to `Bar` if `Foo: Bar` |
| // |
| // Note that neither of the first two of these changes requires any |
| // change at runtime. The third needs to change pointer metadata at runtime. |
| // |
| // We always perform upcasting coercions when we can because of reason |
| // #2 (region bounds). |
| let principal_def_id_a = a_data.principal_def_id(); |
| let principal_def_id_b = b_data.principal_def_id(); |
| if principal_def_id_a == principal_def_id_b || principal_def_id_b.is_none() { |
| // We may upcast to auto traits that are either explicitly listed in |
| // the object type's bounds, or implied by the principal trait ref's |
| // supertraits. |
| let a_auto_traits: FxIndexSet<DefId> = a_data |
| .auto_traits() |
| .chain(principal_def_id_a.into_iter().flat_map(|principal_def_id| { |
| elaborate::supertrait_def_ids(self.tcx(), principal_def_id) |
| .filter(|def_id| self.tcx().trait_is_auto(*def_id)) |
| })) |
| .collect(); |
| let auto_traits_compatible = b_data |
| .auto_traits() |
| // All of a's auto traits need to be in b's auto traits. |
| .all(|b| a_auto_traits.contains(&b)); |
| if auto_traits_compatible { |
| candidates.vec.push(BuiltinUnsizeCandidate); |
| } |
| } else if principal_def_id_a.is_some() && principal_def_id_b.is_some() { |
| // not casual unsizing, now check whether this is trait upcasting coercion. |
| let principal_a = a_data.principal().unwrap(); |
| let target_trait_did = principal_def_id_b.unwrap(); |
| let source_trait_ref = principal_a.with_self_ty(self.tcx(), source); |
| |
| for (idx, upcast_trait_ref) in |
| util::supertraits(self.tcx(), source_trait_ref).enumerate() |
| { |
| self.infcx.probe(|_| { |
| if upcast_trait_ref.def_id() == target_trait_did |
| && let Ok(nested) = self.match_upcast_principal( |
| obligation, |
| upcast_trait_ref, |
| a_data, |
| b_data, |
| a_region, |
| b_region, |
| ) |
| { |
| if nested.is_none() { |
| candidates.ambiguous = true; |
| } |
| candidates.vec.push(TraitUpcastingUnsizeCandidate(idx)); |
| } |
| }) |
| } |
| } |
| } |
| |
| // `T` -> `Trait` |
| (_, &ty::Dynamic(_, _, ty::Dyn)) => { |
| candidates.vec.push(BuiltinUnsizeCandidate); |
| } |
| |
| // 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; |
| } |
| |
| // `[T; n]` -> `[T]` |
| (&ty::Array(..), &ty::Slice(_)) => { |
| candidates.vec.push(BuiltinUnsizeCandidate); |
| } |
| |
| // `Struct<T>` -> `Struct<U>` |
| (&ty::Adt(def_id_a, _), &ty::Adt(def_id_b, _)) if def_id_a.is_struct() => { |
| if def_id_a == def_id_b { |
| candidates.vec.push(BuiltinUnsizeCandidate); |
| } |
| } |
| |
| _ => {} |
| }; |
| } |
| |
| #[instrument(level = "debug", skip(self, obligation, candidates))] |
| fn assemble_candidates_for_transmutability( |
| &mut self, |
| obligation: &PolyTraitObligation<'tcx>, |
| candidates: &mut SelectionCandidateSet<'tcx>, |
| ) { |
| if obligation.predicate.has_non_region_param() { |
| return; |
| } |
| |
| if obligation.has_non_region_infer() { |
| candidates.ambiguous = true; |
| return; |
| } |
| |
| candidates.vec.push(TransmutabilityCandidate); |
| } |
| |
| #[instrument(level = "debug", skip(self, obligation, candidates))] |
| fn assemble_candidates_for_trait_alias( |
| &mut self, |
| obligation: &PolyTraitObligation<'tcx>, |
| candidates: &mut SelectionCandidateSet<'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!(?self_ty); |
| |
| let def_id = obligation.predicate.def_id(); |
| |
| if self.tcx().is_trait_alias(def_id) { |
| candidates.vec.push(TraitAliasCandidate); |
| } |
| } |
| |
| /// Assembles `Copy` and `Clone` candidates for built-in types with no libcore-defined |
| /// `Copy` or `Clone` impls. |
| #[instrument(level = "debug", skip(self, candidates))] |
| fn assemble_builtin_copy_clone_candidate( |
| &mut self, |
| self_ty: Ty<'tcx>, |
| candidates: &mut SelectionCandidateSet<'tcx>, |
| ) { |
| match *self_ty.kind() { |
| // These impls are built-in because we cannot express sufficiently |
| // generic impls in libcore. |
| ty::FnDef(..) | ty::FnPtr(..) | ty::Error(_) | ty::Tuple(..) | ty::Pat(..) => { |
| candidates.vec.push(BuiltinCandidate); |
| } |
| |
| // Implementations provided in libcore. |
| ty::Uint(_) |
| | ty::Int(_) |
| | ty::Infer(ty::IntVar(_) | ty::FloatVar(_)) |
| | ty::Bool |
| | ty::Float(_) |
| | ty::Char |
| | ty::RawPtr(..) |
| | ty::Never |
| | ty::Ref(_, _, hir::Mutability::Not) |
| | ty::Array(..) => {} |
| |
| // FIXME(unsafe_binder): Should we conditionally |
| // (i.e. universally) implement copy/clone? |
| ty::UnsafeBinder(_) => {} |
| |
| // Not `Sized`, which is a supertrait of `Copy`/`Clone`. |
| ty::Dynamic(..) | ty::Str | ty::Slice(..) | ty::Foreign(..) => {} |
| |
| // Not `Copy` or `Clone` by design. |
| ty::Ref(_, _, hir::Mutability::Mut) => {} |
| |
| ty::Coroutine(coroutine_def_id, args) => { |
| if self.should_stall_coroutine(coroutine_def_id) { |
| candidates.ambiguous = true; |
| return; |
| } |
| |
| match self.tcx().coroutine_movability(coroutine_def_id) { |
| hir::Movability::Static => {} |
| hir::Movability::Movable => { |
| if self.tcx().features().coroutine_clone() { |
| let resolved_upvars = |
| self.infcx.shallow_resolve(args.as_coroutine().tupled_upvars_ty()); |
| if resolved_upvars.is_ty_var() { |
| // Not yet resolved. |
| candidates.ambiguous = true; |
| } else { |
| candidates.vec.push(BuiltinCandidate); |
| } |
| } |
| } |
| } |
| } |
| |
| ty::Closure(_, args) => { |
| let resolved_upvars = |
| self.infcx.shallow_resolve(args.as_closure().tupled_upvars_ty()); |
| if resolved_upvars.is_ty_var() { |
| // Not yet resolved. |
| candidates.ambiguous = true; |
| } else { |
| candidates.vec.push(BuiltinCandidate); |
| } |
| } |
| |
| ty::CoroutineClosure(_, args) => { |
| let resolved_upvars = |
| self.infcx.shallow_resolve(args.as_coroutine_closure().tupled_upvars_ty()); |
| if resolved_upvars.is_ty_var() { |
| // Not yet resolved. |
| candidates.ambiguous = true; |
| } else { |
| candidates.vec.push(BuiltinCandidate); |
| } |
| } |
| |
| ty::CoroutineWitness(..) => { |
| candidates.vec.push(SizedCandidate); |
| } |
| |
| // Fallback to whatever user-defined impls or param-env clauses exist in this case. |
| ty::Adt(..) | ty::Alias(..) | ty::Param(..) | ty::Placeholder(..) => {} |
| |
| ty::Infer(ty::TyVar(_)) => { |
| candidates.ambiguous = true; |
| } |
| |
| // Only appears when assembling higher-ranked `for<T> T: Clone`. |
| ty::Bound(..) => {} |
| |
| ty::Infer(ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)) => { |
| bug!("asked to assemble builtin bounds of unexpected type: {:?}", self_ty); |
| } |
| } |
| } |
| |
| /// Assembles the `Sized` and `MetaSized` traits which are built-in to the language itself. |
| #[instrument(level = "debug", skip(self, candidates))] |
| fn assemble_builtin_sized_candidate( |
| &mut self, |
| self_ty: Ty<'tcx>, |
| candidates: &mut SelectionCandidateSet<'tcx>, |
| sizedness: SizedTraitKind, |
| ) { |
| match *self_ty.kind() { |
| // Always sized. |
| ty::Infer(ty::IntVar(_) | ty::FloatVar(_)) |
| | ty::Uint(_) |
| | ty::Int(_) |
| | ty::Bool |
| | ty::Float(_) |
| | ty::FnDef(..) |
| | ty::FnPtr(..) |
| | ty::RawPtr(..) |
| | ty::Char |
| | ty::Ref(..) |
| | ty::Array(..) |
| | ty::Closure(..) |
| | ty::CoroutineClosure(..) |
| | ty::Never |
| | ty::Error(_) => { |
| candidates.vec.push(SizedCandidate); |
| } |
| |
| ty::Coroutine(coroutine_def_id, _) => { |
| if self.should_stall_coroutine(coroutine_def_id) { |
| candidates.ambiguous = true; |
| } else { |
| candidates.vec.push(SizedCandidate); |
| } |
| } |
| |
| ty::CoroutineWitness(..) => { |
| candidates.vec.push(SizedCandidate); |
| } |
| |
| // Conditionally `Sized`. |
| ty::Tuple(..) | ty::Pat(..) | ty::Adt(..) | ty::UnsafeBinder(_) => { |
| candidates.vec.push(SizedCandidate); |
| } |
| |
| // `MetaSized` but not `Sized`. |
| ty::Str | ty::Slice(_) | ty::Dynamic(..) => match sizedness { |
| SizedTraitKind::Sized => {} |
| SizedTraitKind::MetaSized => { |
| candidates.vec.push(SizedCandidate); |
| } |
| }, |
| |
| // Not `MetaSized` or `Sized`. |
| ty::Foreign(..) => {} |
| |
| ty::Alias(..) | ty::Param(_) | ty::Placeholder(..) => {} |
| |
| ty::Infer(ty::TyVar(_)) => { |
| candidates.ambiguous = true; |
| } |
| |
| // Only appears when assembling higher-ranked `for<T> T: Sized`. |
| ty::Bound(..) => {} |
| |
| ty::Infer(ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)) => { |
| bug!("asked to assemble builtin bounds of unexpected type: {:?}", self_ty); |
| } |
| } |
| } |
| |
| fn assemble_const_destruct_candidates( |
| &mut self, |
| _obligation: &PolyTraitObligation<'tcx>, |
| candidates: &mut SelectionCandidateSet<'tcx>, |
| ) { |
| candidates.vec.push(BuiltinCandidate); |
| } |
| |
| fn assemble_candidate_for_tuple( |
| &mut self, |
| obligation: &PolyTraitObligation<'tcx>, |
| candidates: &mut SelectionCandidateSet<'tcx>, |
| ) { |
| let self_ty = self.infcx.shallow_resolve(obligation.self_ty().skip_binder()); |
| match self_ty.kind() { |
| ty::Tuple(_) => { |
| candidates.vec.push(BuiltinCandidate); |
| } |
| ty::Infer(ty::TyVar(_)) => { |
| candidates.ambiguous = true; |
| } |
| ty::Bool |
| | ty::Char |
| | ty::Int(_) |
| | ty::Uint(_) |
| | ty::Float(_) |
| | ty::Adt(_, _) |
| | ty::Foreign(_) |
| | ty::Str |
| | ty::Array(_, _) |
| | ty::Slice(_) |
| | ty::RawPtr(_, _) |
| | ty::Ref(_, _, _) |
| | ty::FnDef(_, _) |
| | ty::Pat(_, _) |
| | ty::FnPtr(..) |
| | ty::UnsafeBinder(_) |
| | ty::Dynamic(_, _, _) |
| | ty::Closure(..) |
| | ty::CoroutineClosure(..) |
| | ty::Coroutine(_, _) |
| | ty::CoroutineWitness(..) |
| | ty::Never |
| | ty::Alias(..) |
| | ty::Param(_) |
| | ty::Bound(_, _) |
| | ty::Error(_) |
| | ty::Infer(_) |
| | ty::Placeholder(_) => {} |
| } |
| } |
| |
| fn assemble_candidates_for_fn_ptr_trait( |
| &mut self, |
| obligation: &PolyTraitObligation<'tcx>, |
| candidates: &mut SelectionCandidateSet<'tcx>, |
| ) { |
| let self_ty = self.infcx.resolve_vars_if_possible(obligation.self_ty()); |
| |
| match self_ty.skip_binder().kind() { |
| ty::FnPtr(..) => candidates.vec.push(BuiltinCandidate), |
| ty::Bool |
| | ty::Char |
| | ty::Int(_) |
| | ty::Uint(_) |
| | ty::Float(_) |
| | ty::Adt(..) |
| | ty::Foreign(..) |
| | ty::Str |
| | ty::Array(..) |
| | ty::Pat(..) |
| | ty::Slice(_) |
| | ty::RawPtr(_, _) |
| | ty::Ref(..) |
| | ty::FnDef(..) |
| | ty::Placeholder(..) |
| | ty::Dynamic(..) |
| | ty::Closure(..) |
| | ty::CoroutineClosure(..) |
| | ty::Coroutine(..) |
| | ty::CoroutineWitness(..) |
| | ty::UnsafeBinder(_) |
| | ty::Never |
| | ty::Tuple(..) |
| | ty::Alias(..) |
| | ty::Param(..) |
| | ty::Bound(..) |
| | ty::Error(_) |
| | ty::Infer( |
| ty::InferTy::IntVar(_) |
| | ty::InferTy::FloatVar(_) |
| | ty::InferTy::FreshIntTy(_) |
| | ty::InferTy::FreshFloatTy(_), |
| ) => {} |
| ty::Infer(ty::InferTy::TyVar(_) | ty::InferTy::FreshTy(_)) => { |
| candidates.ambiguous = true; |
| } |
| } |
| } |
| |
| fn assemble_candidates_for_bikeshed_guaranteed_no_drop_trait( |
| &mut self, |
| obligation: &PolyTraitObligation<'tcx>, |
| candidates: &mut SelectionCandidateSet<'tcx>, |
| ) { |
| match obligation.predicate.self_ty().skip_binder().kind() { |
| ty::Ref(..) |
| | ty::Adt(..) |
| | ty::Tuple(_) |
| | ty::Array(..) |
| | ty::FnDef(..) |
| | ty::FnPtr(..) |
| | ty::Error(_) |
| | ty::Uint(_) |
| | ty::Int(_) |
| | ty::Infer(ty::IntVar(_) | ty::FloatVar(_)) |
| | ty::Bool |
| | ty::Float(_) |
| | ty::Char |
| | ty::RawPtr(..) |
| | ty::Never |
| | ty::Pat(..) |
| | ty::Dynamic(..) |
| | ty::Str |
| | ty::Slice(_) |
| | ty::Foreign(..) |
| | ty::Alias(..) |
| | ty::Param(_) |
| | ty::Placeholder(..) |
| | ty::Closure(..) |
| | ty::CoroutineClosure(..) |
| | ty::Coroutine(..) |
| | ty::UnsafeBinder(_) |
| | ty::CoroutineWitness(..) |
| | ty::Bound(..) => { |
| candidates.vec.push(BikeshedGuaranteedNoDropCandidate); |
| } |
| |
| ty::Infer(ty::TyVar(_) | ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)) => { |
| candidates.ambiguous = true; |
| } |
| } |
| } |
| } |
