diff options
Diffstat (limited to 'compiler/rustc_typeck/src/check/method/probe.rs')
| -rw-r--r-- | compiler/rustc_typeck/src/check/method/probe.rs | 1932 |
1 files changed, 1932 insertions, 0 deletions
diff --git a/compiler/rustc_typeck/src/check/method/probe.rs b/compiler/rustc_typeck/src/check/method/probe.rs new file mode 100644 index 000000000..efe15fec7 --- /dev/null +++ b/compiler/rustc_typeck/src/check/method/probe.rs @@ -0,0 +1,1932 @@ +use super::suggest; +use super::CandidateSource; +use super::MethodError; +use super::NoMatchData; + +use crate::check::FnCtxt; +use crate::errors::MethodCallOnUnknownType; +use crate::hir::def::DefKind; +use crate::hir::def_id::DefId; + +use rustc_data_structures::fx::FxHashSet; +use rustc_errors::Applicability; +use rustc_hir as hir; +use rustc_hir::def::Namespace; +use rustc_infer::infer::canonical::OriginalQueryValues; +use rustc_infer::infer::canonical::{Canonical, QueryResponse}; +use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind}; +use rustc_infer::infer::{self, InferOk, TyCtxtInferExt}; +use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind}; +use rustc_middle::middle::stability; +use rustc_middle::ty::fast_reject::{simplify_type, TreatParams}; +use rustc_middle::ty::subst::{InternalSubsts, Subst, SubstsRef}; +use rustc_middle::ty::GenericParamDefKind; +use rustc_middle::ty::{self, ParamEnvAnd, ToPredicate, Ty, TyCtxt, TypeFoldable, TypeVisitable}; +use rustc_session::lint; +use rustc_span::def_id::LocalDefId; +use rustc_span::lev_distance::{ + find_best_match_for_name_with_substrings, lev_distance_with_substrings, +}; +use rustc_span::symbol::sym; +use rustc_span::{symbol::Ident, Span, Symbol, DUMMY_SP}; +use rustc_trait_selection::autoderef::{self, Autoderef}; +use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt; +use rustc_trait_selection::traits::query::method_autoderef::MethodAutoderefBadTy; +use rustc_trait_selection::traits::query::method_autoderef::{ + CandidateStep, MethodAutoderefStepsResult, +}; +use rustc_trait_selection::traits::query::CanonicalTyGoal; +use rustc_trait_selection::traits::{self, ObligationCause}; +use std::cmp::max; +use std::iter; +use std::mem; +use std::ops::Deref; + +use smallvec::{smallvec, SmallVec}; + +use self::CandidateKind::*; +pub use self::PickKind::*; + +/// Boolean flag used to indicate if this search is for a suggestion +/// or not. If true, we can allow ambiguity and so forth. +#[derive(Clone, Copy, Debug)] +pub struct IsSuggestion(pub bool); + +struct ProbeContext<'a, 'tcx> { + fcx: &'a FnCtxt<'a, 'tcx>, + span: Span, + mode: Mode, + method_name: Option<Ident>, + return_type: Option<Ty<'tcx>>, + + /// This is the OriginalQueryValues for the steps queries + /// that are answered in steps. + orig_steps_var_values: OriginalQueryValues<'tcx>, + steps: &'tcx [CandidateStep<'tcx>], + + inherent_candidates: Vec<Candidate<'tcx>>, + extension_candidates: Vec<Candidate<'tcx>>, + impl_dups: FxHashSet<DefId>, + + /// Collects near misses when the candidate functions are missing a `self` keyword and is only + /// used for error reporting + static_candidates: Vec<CandidateSource>, + + /// When probing for names, include names that are close to the + /// requested name (by Levensthein distance) + allow_similar_names: bool, + + /// Some(candidate) if there is a private candidate + private_candidate: Option<(DefKind, DefId)>, + + /// Collects near misses when trait bounds for type parameters are unsatisfied and is only used + /// for error reporting + unsatisfied_predicates: + Vec<(ty::Predicate<'tcx>, Option<ty::Predicate<'tcx>>, Option<ObligationCause<'tcx>>)>, + + is_suggestion: IsSuggestion, + + scope_expr_id: hir::HirId, +} + +impl<'a, 'tcx> Deref for ProbeContext<'a, 'tcx> { + type Target = FnCtxt<'a, 'tcx>; + fn deref(&self) -> &Self::Target { + self.fcx + } +} + +#[derive(Debug, Clone)] +struct Candidate<'tcx> { + // Candidates are (I'm not quite sure, but they are mostly) basically + // some metadata on top of a `ty::AssocItem` (without substs). + // + // However, method probing wants to be able to evaluate the predicates + // for a function with the substs applied - for example, if a function + // has `where Self: Sized`, we don't want to consider it unless `Self` + // is actually `Sized`, and similarly, return-type suggestions want + // to consider the "actual" return type. + // + // The way this is handled is through `xform_self_ty`. It contains + // the receiver type of this candidate, but `xform_self_ty`, + // `xform_ret_ty` and `kind` (which contains the predicates) have the + // generic parameters of this candidate substituted with the *same set* + // of inference variables, which acts as some weird sort of "query". + // + // When we check out a candidate, we require `xform_self_ty` to be + // a subtype of the passed-in self-type, and this equates the type + // variables in the rest of the fields. + // + // For example, if we have this candidate: + // ``` + // trait Foo { + // fn foo(&self) where Self: Sized; + // } + // ``` + // + // Then `xform_self_ty` will be `&'erased ?X` and `kind` will contain + // the predicate `?X: Sized`, so if we are evaluating `Foo` for a + // the receiver `&T`, we'll do the subtyping which will make `?X` + // get the right value, then when we evaluate the predicate we'll check + // if `T: Sized`. + xform_self_ty: Ty<'tcx>, + xform_ret_ty: Option<Ty<'tcx>>, + item: ty::AssocItem, + kind: CandidateKind<'tcx>, + import_ids: SmallVec<[LocalDefId; 1]>, +} + +#[derive(Debug, Clone)] +enum CandidateKind<'tcx> { + InherentImplCandidate( + SubstsRef<'tcx>, + // Normalize obligations + Vec<traits::PredicateObligation<'tcx>>, + ), + ObjectCandidate, + TraitCandidate(ty::TraitRef<'tcx>), + WhereClauseCandidate( + // Trait + ty::PolyTraitRef<'tcx>, + ), +} + +#[derive(Debug, PartialEq, Eq, Copy, Clone)] +enum ProbeResult { + NoMatch, + BadReturnType, + Match, +} + +/// When adjusting a receiver we often want to do one of +/// +/// - Add a `&` (or `&mut`), converting the receiver from `T` to `&T` (or `&mut T`) +/// - If the receiver has type `*mut T`, convert it to `*const T` +/// +/// This type tells us which one to do. +/// +/// Note that in principle we could do both at the same time. For example, when the receiver has +/// type `T`, we could autoref it to `&T`, then convert to `*const T`. Or, when it has type `*mut +/// T`, we could convert it to `*const T`, then autoref to `&*const T`. However, currently we do +/// (at most) one of these. Either the receiver has type `T` and we convert it to `&T` (or with +/// `mut`), or it has type `*mut T` and we convert it to `*const T`. +#[derive(Debug, PartialEq, Copy, Clone)] +pub enum AutorefOrPtrAdjustment { + /// Receiver has type `T`, add `&` or `&mut` (it `T` is `mut`), and maybe also "unsize" it. + /// Unsizing is used to convert a `[T; N]` to `[T]`, which only makes sense when autorefing. + Autoref { + mutbl: hir::Mutability, + + /// Indicates that the source expression should be "unsized" to a target type. + /// This is special-cased for just arrays unsizing to slices. + unsize: bool, + }, + /// Receiver has type `*mut T`, convert to `*const T` + ToConstPtr, +} + +impl AutorefOrPtrAdjustment { + fn get_unsize(&self) -> bool { + match self { + AutorefOrPtrAdjustment::Autoref { mutbl: _, unsize } => *unsize, + AutorefOrPtrAdjustment::ToConstPtr => false, + } + } +} + +#[derive(Debug, PartialEq, Clone)] +pub struct Pick<'tcx> { + pub item: ty::AssocItem, + pub kind: PickKind<'tcx>, + pub import_ids: SmallVec<[LocalDefId; 1]>, + + /// Indicates that the source expression should be autoderef'd N times + /// ```ignore (not-rust) + /// A = expr | *expr | **expr | ... + /// ``` + pub autoderefs: usize, + + /// Indicates that we want to add an autoref (and maybe also unsize it), or if the receiver is + /// `*mut T`, convert it to `*const T`. + pub autoref_or_ptr_adjustment: Option<AutorefOrPtrAdjustment>, + pub self_ty: Ty<'tcx>, +} + +#[derive(Clone, Debug, PartialEq, Eq)] +pub enum PickKind<'tcx> { + InherentImplPick, + ObjectPick, + TraitPick, + WhereClausePick( + // Trait + ty::PolyTraitRef<'tcx>, + ), +} + +pub type PickResult<'tcx> = Result<Pick<'tcx>, MethodError<'tcx>>; + +#[derive(PartialEq, Eq, Copy, Clone, Debug)] +pub enum Mode { + // An expression of the form `receiver.method_name(...)`. + // Autoderefs are performed on `receiver`, lookup is done based on the + // `self` argument of the method, and static methods aren't considered. + MethodCall, + // An expression of the form `Type::item` or `<T>::item`. + // No autoderefs are performed, lookup is done based on the type each + // implementation is for, and static methods are included. + Path, +} + +#[derive(PartialEq, Eq, Copy, Clone, Debug)] +pub enum ProbeScope { + // Assemble candidates coming only from traits in scope. + TraitsInScope, + + // Assemble candidates coming from all traits. + AllTraits, +} + +impl<'a, 'tcx> FnCtxt<'a, 'tcx> { + /// This is used to offer suggestions to users. It returns methods + /// that could have been called which have the desired return + /// type. Some effort is made to rule out methods that, if called, + /// would result in an error (basically, the same criteria we + /// would use to decide if a method is a plausible fit for + /// ambiguity purposes). + #[instrument(level = "debug", skip(self, scope_expr_id))] + pub fn probe_for_return_type( + &self, + span: Span, + mode: Mode, + return_type: Ty<'tcx>, + self_ty: Ty<'tcx>, + scope_expr_id: hir::HirId, + ) -> Vec<ty::AssocItem> { + debug!( + "probe(self_ty={:?}, return_type={}, scope_expr_id={})", + self_ty, return_type, scope_expr_id + ); + let method_names = self + .probe_op( + span, + mode, + None, + Some(return_type), + IsSuggestion(true), + self_ty, + scope_expr_id, + ProbeScope::AllTraits, + |probe_cx| Ok(probe_cx.candidate_method_names()), + ) + .unwrap_or_default(); + method_names + .iter() + .flat_map(|&method_name| { + self.probe_op( + span, + mode, + Some(method_name), + Some(return_type), + IsSuggestion(true), + self_ty, + scope_expr_id, + ProbeScope::AllTraits, + |probe_cx| probe_cx.pick(), + ) + .ok() + .map(|pick| pick.item) + }) + .collect() + } + + #[instrument(level = "debug", skip(self, scope_expr_id))] + pub fn probe_for_name( + &self, + span: Span, + mode: Mode, + item_name: Ident, + is_suggestion: IsSuggestion, + self_ty: Ty<'tcx>, + scope_expr_id: hir::HirId, + scope: ProbeScope, + ) -> PickResult<'tcx> { + debug!( + "probe(self_ty={:?}, item_name={}, scope_expr_id={})", + self_ty, item_name, scope_expr_id + ); + self.probe_op( + span, + mode, + Some(item_name), + None, + is_suggestion, + self_ty, + scope_expr_id, + scope, + |probe_cx| probe_cx.pick(), + ) + } + + fn probe_op<OP, R>( + &'a self, + span: Span, + mode: Mode, + method_name: Option<Ident>, + return_type: Option<Ty<'tcx>>, + is_suggestion: IsSuggestion, + self_ty: Ty<'tcx>, + scope_expr_id: hir::HirId, + scope: ProbeScope, + op: OP, + ) -> Result<R, MethodError<'tcx>> + where + OP: FnOnce(ProbeContext<'a, 'tcx>) -> Result<R, MethodError<'tcx>>, + { + let mut orig_values = OriginalQueryValues::default(); + let param_env_and_self_ty = self.canonicalize_query( + ParamEnvAnd { param_env: self.param_env, value: self_ty }, + &mut orig_values, + ); + + let steps = if mode == Mode::MethodCall { + self.tcx.method_autoderef_steps(param_env_and_self_ty) + } else { + self.probe(|_| { + // Mode::Path - the deref steps is "trivial". This turns + // our CanonicalQuery into a "trivial" QueryResponse. This + // is a bit inefficient, but I don't think that writing + // special handling for this "trivial case" is a good idea. + + let infcx = &self.infcx; + let (ParamEnvAnd { param_env: _, value: self_ty }, canonical_inference_vars) = + infcx.instantiate_canonical_with_fresh_inference_vars( + span, + ¶m_env_and_self_ty, + ); + debug!( + "probe_op: Mode::Path, param_env_and_self_ty={:?} self_ty={:?}", + param_env_and_self_ty, self_ty + ); + MethodAutoderefStepsResult { + steps: infcx.tcx.arena.alloc_from_iter([CandidateStep { + self_ty: self.make_query_response_ignoring_pending_obligations( + canonical_inference_vars, + self_ty, + ), + autoderefs: 0, + from_unsafe_deref: false, + unsize: false, + }]), + opt_bad_ty: None, + reached_recursion_limit: false, + } + }) + }; + + // If our autoderef loop had reached the recursion limit, + // report an overflow error, but continue going on with + // the truncated autoderef list. + if steps.reached_recursion_limit { + self.probe(|_| { + let ty = &steps + .steps + .last() + .unwrap_or_else(|| span_bug!(span, "reached the recursion limit in 0 steps?")) + .self_ty; + let ty = self + .probe_instantiate_query_response(span, &orig_values, ty) + .unwrap_or_else(|_| span_bug!(span, "instantiating {:?} failed?", ty)); + autoderef::report_autoderef_recursion_limit_error(self.tcx, span, ty.value); + }); + } + + // If we encountered an `_` type or an error type during autoderef, this is + // ambiguous. + if let Some(bad_ty) = &steps.opt_bad_ty { + if is_suggestion.0 { + // Ambiguity was encountered during a suggestion. Just keep going. + debug!("ProbeContext: encountered ambiguity in suggestion"); + } else if bad_ty.reached_raw_pointer && !self.tcx.features().arbitrary_self_types { + // this case used to be allowed by the compiler, + // so we do a future-compat lint here for the 2015 edition + // (see https://github.com/rust-lang/rust/issues/46906) + if self.tcx.sess.rust_2018() { + self.tcx.sess.emit_err(MethodCallOnUnknownType { span }); + } else { + self.tcx.struct_span_lint_hir( + lint::builtin::TYVAR_BEHIND_RAW_POINTER, + scope_expr_id, + span, + |lint| { + lint.build("type annotations needed").emit(); + }, + ); + } + } else { + // Encountered a real ambiguity, so abort the lookup. If `ty` is not + // an `Err`, report the right "type annotations needed" error pointing + // to it. + let ty = &bad_ty.ty; + let ty = self + .probe_instantiate_query_response(span, &orig_values, ty) + .unwrap_or_else(|_| span_bug!(span, "instantiating {:?} failed?", ty)); + let ty = self.structurally_resolved_type(span, ty.value); + assert!(matches!(ty.kind(), ty::Error(_))); + return Err(MethodError::NoMatch(NoMatchData { + static_candidates: Vec::new(), + unsatisfied_predicates: Vec::new(), + out_of_scope_traits: Vec::new(), + lev_candidate: None, + mode, + })); + } + } + + debug!("ProbeContext: steps for self_ty={:?} are {:?}", self_ty, steps); + + // this creates one big transaction so that all type variables etc + // that we create during the probe process are removed later + self.probe(|_| { + let mut probe_cx = ProbeContext::new( + self, + span, + mode, + method_name, + return_type, + orig_values, + steps.steps, + is_suggestion, + scope_expr_id, + ); + + probe_cx.assemble_inherent_candidates(); + match scope { + ProbeScope::TraitsInScope => { + probe_cx.assemble_extension_candidates_for_traits_in_scope(scope_expr_id) + } + ProbeScope::AllTraits => probe_cx.assemble_extension_candidates_for_all_traits(), + }; + op(probe_cx) + }) + } +} + +pub fn provide(providers: &mut ty::query::Providers) { + providers.method_autoderef_steps = method_autoderef_steps; +} + +fn method_autoderef_steps<'tcx>( + tcx: TyCtxt<'tcx>, + goal: CanonicalTyGoal<'tcx>, +) -> MethodAutoderefStepsResult<'tcx> { + debug!("method_autoderef_steps({:?})", goal); + + tcx.infer_ctxt().enter_with_canonical(DUMMY_SP, &goal, |ref infcx, goal, inference_vars| { + let ParamEnvAnd { param_env, value: self_ty } = goal; + + let mut autoderef = + Autoderef::new(infcx, param_env, hir::CRATE_HIR_ID, DUMMY_SP, self_ty, DUMMY_SP) + .include_raw_pointers() + .silence_errors(); + let mut reached_raw_pointer = false; + let mut steps: Vec<_> = autoderef + .by_ref() + .map(|(ty, d)| { + let step = CandidateStep { + self_ty: infcx.make_query_response_ignoring_pending_obligations( + inference_vars.clone(), + ty, + ), + autoderefs: d, + from_unsafe_deref: reached_raw_pointer, + unsize: false, + }; + if let ty::RawPtr(_) = ty.kind() { + // all the subsequent steps will be from_unsafe_deref + reached_raw_pointer = true; + } + step + }) + .collect(); + + let final_ty = autoderef.final_ty(true); + let opt_bad_ty = match final_ty.kind() { + ty::Infer(ty::TyVar(_)) | ty::Error(_) => Some(MethodAutoderefBadTy { + reached_raw_pointer, + ty: infcx + .make_query_response_ignoring_pending_obligations(inference_vars, final_ty), + }), + ty::Array(elem_ty, _) => { + let dereferences = steps.len() - 1; + + steps.push(CandidateStep { + self_ty: infcx.make_query_response_ignoring_pending_obligations( + inference_vars, + infcx.tcx.mk_slice(*elem_ty), + ), + autoderefs: dereferences, + // this could be from an unsafe deref if we had + // a *mut/const [T; N] + from_unsafe_deref: reached_raw_pointer, + unsize: true, + }); + + None + } + _ => None, + }; + + debug!("method_autoderef_steps: steps={:?} opt_bad_ty={:?}", steps, opt_bad_ty); + + MethodAutoderefStepsResult { + steps: tcx.arena.alloc_from_iter(steps), + opt_bad_ty: opt_bad_ty.map(|ty| &*tcx.arena.alloc(ty)), + reached_recursion_limit: autoderef.reached_recursion_limit(), + } + }) +} + +impl<'a, 'tcx> ProbeContext<'a, 'tcx> { + fn new( + fcx: &'a FnCtxt<'a, 'tcx>, + span: Span, + mode: Mode, + method_name: Option<Ident>, + return_type: Option<Ty<'tcx>>, + orig_steps_var_values: OriginalQueryValues<'tcx>, + steps: &'tcx [CandidateStep<'tcx>], + is_suggestion: IsSuggestion, + scope_expr_id: hir::HirId, + ) -> ProbeContext<'a, 'tcx> { + ProbeContext { + fcx, + span, + mode, + method_name, + return_type, + inherent_candidates: Vec::new(), + extension_candidates: Vec::new(), + impl_dups: FxHashSet::default(), + orig_steps_var_values, + steps, + static_candidates: Vec::new(), + allow_similar_names: false, + private_candidate: None, + unsatisfied_predicates: Vec::new(), + is_suggestion, + scope_expr_id, + } + } + + fn reset(&mut self) { + self.inherent_candidates.clear(); + self.extension_candidates.clear(); + self.impl_dups.clear(); + self.static_candidates.clear(); + self.private_candidate = None; + } + + /////////////////////////////////////////////////////////////////////////// + // CANDIDATE ASSEMBLY + + fn push_candidate(&mut self, candidate: Candidate<'tcx>, is_inherent: bool) { + let is_accessible = if let Some(name) = self.method_name { + let item = candidate.item; + let def_scope = self + .tcx + .adjust_ident_and_get_scope(name, item.container_id(self.tcx), self.body_id) + .1; + item.visibility(self.tcx).is_accessible_from(def_scope, self.tcx) + } else { + true + }; + if is_accessible { + if is_inherent { + self.inherent_candidates.push(candidate); + } else { + self.extension_candidates.push(candidate); + } + } else if self.private_candidate.is_none() { + self.private_candidate = + Some((candidate.item.kind.as_def_kind(), candidate.item.def_id)); + } + } + + fn assemble_inherent_candidates(&mut self) { + for step in self.steps.iter() { + self.assemble_probe(&step.self_ty); + } + } + + fn assemble_probe(&mut self, self_ty: &Canonical<'tcx, QueryResponse<'tcx, Ty<'tcx>>>) { + debug!("assemble_probe: self_ty={:?}", self_ty); + let raw_self_ty = self_ty.value.value; + match *raw_self_ty.kind() { + ty::Dynamic(data, ..) if let Some(p) = data.principal() => { + // Subtle: we can't use `instantiate_query_response` here: using it will + // commit to all of the type equalities assumed by inference going through + // autoderef (see the `method-probe-no-guessing` test). + // + // However, in this code, it is OK if we end up with an object type that is + // "more general" than the object type that we are evaluating. For *every* + // object type `MY_OBJECT`, a function call that goes through a trait-ref + // of the form `<MY_OBJECT as SuperTraitOf(MY_OBJECT)>::func` is a valid + // `ObjectCandidate`, and it should be discoverable "exactly" through one + // of the iterations in the autoderef loop, so there is no problem with it + // being discoverable in another one of these iterations. + // + // Using `instantiate_canonical_with_fresh_inference_vars` on our + // `Canonical<QueryResponse<Ty<'tcx>>>` and then *throwing away* the + // `CanonicalVarValues` will exactly give us such a generalization - it + // will still match the original object type, but it won't pollute our + // type variables in any form, so just do that! + let (QueryResponse { value: generalized_self_ty, .. }, _ignored_var_values) = + self.fcx + .instantiate_canonical_with_fresh_inference_vars(self.span, self_ty); + + self.assemble_inherent_candidates_from_object(generalized_self_ty); + self.assemble_inherent_impl_candidates_for_type(p.def_id()); + if self.tcx.has_attr(p.def_id(), sym::rustc_has_incoherent_inherent_impls) { + self.assemble_inherent_candidates_for_incoherent_ty(raw_self_ty); + } + } + ty::Adt(def, _) => { + let def_id = def.did(); + self.assemble_inherent_impl_candidates_for_type(def_id); + if self.tcx.has_attr(def_id, sym::rustc_has_incoherent_inherent_impls) { + self.assemble_inherent_candidates_for_incoherent_ty(raw_self_ty); + } + } + ty::Foreign(did) => { + self.assemble_inherent_impl_candidates_for_type(did); + if self.tcx.has_attr(did, sym::rustc_has_incoherent_inherent_impls) { + self.assemble_inherent_candidates_for_incoherent_ty(raw_self_ty); + } + } + ty::Param(p) => { + self.assemble_inherent_candidates_from_param(p); + } + ty::Bool + | ty::Char + | ty::Int(_) + | ty::Uint(_) + | ty::Float(_) + | ty::Str + | ty::Array(..) + | ty::Slice(_) + | ty::RawPtr(_) + | ty::Ref(..) + | ty::Never + | ty::Tuple(..) => self.assemble_inherent_candidates_for_incoherent_ty(raw_self_ty), + _ => {} + } + } + + fn assemble_inherent_candidates_for_incoherent_ty(&mut self, self_ty: Ty<'tcx>) { + let Some(simp) = simplify_type(self.tcx, self_ty, TreatParams::AsInfer) else { + bug!("unexpected incoherent type: {:?}", self_ty) + }; + for &impl_def_id in self.tcx.incoherent_impls(simp) { + self.assemble_inherent_impl_probe(impl_def_id); + } + } + + fn assemble_inherent_impl_candidates_for_type(&mut self, def_id: DefId) { + let impl_def_ids = self.tcx.at(self.span).inherent_impls(def_id); + for &impl_def_id in impl_def_ids.iter() { + self.assemble_inherent_impl_probe(impl_def_id); + } + } + + fn assemble_inherent_impl_probe(&mut self, impl_def_id: DefId) { + if !self.impl_dups.insert(impl_def_id) { + return; // already visited + } + + debug!("assemble_inherent_impl_probe {:?}", impl_def_id); + + for item in self.impl_or_trait_item(impl_def_id) { + if !self.has_applicable_self(&item) { + // No receiver declared. Not a candidate. + self.record_static_candidate(CandidateSource::Impl(impl_def_id)); + continue; + } + + let (impl_ty, impl_substs) = self.impl_ty_and_substs(impl_def_id); + let impl_ty = impl_ty.subst(self.tcx, impl_substs); + + debug!("impl_ty: {:?}", impl_ty); + + // Determine the receiver type that the method itself expects. + let (xform_self_ty, xform_ret_ty) = self.xform_self_ty(&item, impl_ty, impl_substs); + debug!("xform_self_ty: {:?}, xform_ret_ty: {:?}", xform_self_ty, xform_ret_ty); + + // We can't use normalize_associated_types_in as it will pollute the + // fcx's fulfillment context after this probe is over. + // Note: we only normalize `xform_self_ty` here since the normalization + // of the return type can lead to inference results that prohibit + // valid candidates from being found, see issue #85671 + // FIXME Postponing the normalization of the return type likely only hides a deeper bug, + // which might be caused by the `param_env` itself. The clauses of the `param_env` + // maybe shouldn't include `Param`s, but rather fresh variables or be canonicalized, + // see issue #89650 + let cause = traits::ObligationCause::misc(self.span, self.body_id); + let selcx = &mut traits::SelectionContext::new(self.fcx); + let traits::Normalized { value: xform_self_ty, obligations } = + traits::normalize(selcx, self.param_env, cause, xform_self_ty); + debug!( + "assemble_inherent_impl_probe after normalization: xform_self_ty = {:?}/{:?}", + xform_self_ty, xform_ret_ty + ); + + self.push_candidate( + Candidate { + xform_self_ty, + xform_ret_ty, + item, + kind: InherentImplCandidate(impl_substs, obligations), + import_ids: smallvec![], + }, + true, + ); + } + } + + fn assemble_inherent_candidates_from_object(&mut self, self_ty: Ty<'tcx>) { + debug!("assemble_inherent_candidates_from_object(self_ty={:?})", self_ty); + + let principal = match self_ty.kind() { + ty::Dynamic(ref data, ..) => Some(data), + _ => None, + } + .and_then(|data| data.principal()) + .unwrap_or_else(|| { + span_bug!( + self.span, + "non-object {:?} in assemble_inherent_candidates_from_object", + self_ty + ) + }); + + // It is illegal to invoke a method on a trait instance that refers to + // the `Self` type. An [`ObjectSafetyViolation::SupertraitSelf`] error + // will be reported by `object_safety.rs` if the method refers to the + // `Self` type anywhere other than the receiver. Here, we use a + // substitution that replaces `Self` with the object type itself. Hence, + // a `&self` method will wind up with an argument type like `&dyn Trait`. + let trait_ref = principal.with_self_ty(self.tcx, self_ty); + self.elaborate_bounds(iter::once(trait_ref), |this, new_trait_ref, item| { + let new_trait_ref = this.erase_late_bound_regions(new_trait_ref); + + let (xform_self_ty, xform_ret_ty) = + this.xform_self_ty(&item, new_trait_ref.self_ty(), new_trait_ref.substs); + this.push_candidate( + Candidate { + xform_self_ty, + xform_ret_ty, + item, + kind: ObjectCandidate, + import_ids: smallvec![], + }, + true, + ); + }); + } + + fn assemble_inherent_candidates_from_param(&mut self, param_ty: ty::ParamTy) { + // FIXME: do we want to commit to this behavior for param bounds? + debug!("assemble_inherent_candidates_from_param(param_ty={:?})", param_ty); + + let bounds = self.param_env.caller_bounds().iter().filter_map(|predicate| { + let bound_predicate = predicate.kind(); + match bound_predicate.skip_binder() { + ty::PredicateKind::Trait(trait_predicate) => { + match *trait_predicate.trait_ref.self_ty().kind() { + ty::Param(p) if p == param_ty => { + Some(bound_predicate.rebind(trait_predicate.trait_ref)) + } + _ => None, + } + } + ty::PredicateKind::Subtype(..) + | ty::PredicateKind::Coerce(..) + | ty::PredicateKind::Projection(..) + | ty::PredicateKind::RegionOutlives(..) + | ty::PredicateKind::WellFormed(..) + | ty::PredicateKind::ObjectSafe(..) + | ty::PredicateKind::ClosureKind(..) + | ty::PredicateKind::TypeOutlives(..) + | ty::PredicateKind::ConstEvaluatable(..) + | ty::PredicateKind::ConstEquate(..) + | ty::PredicateKind::TypeWellFormedFromEnv(..) => None, + } + }); + + self.elaborate_bounds(bounds, |this, poly_trait_ref, item| { + let trait_ref = this.erase_late_bound_regions(poly_trait_ref); + + let (xform_self_ty, xform_ret_ty) = + this.xform_self_ty(&item, trait_ref.self_ty(), trait_ref.substs); + + // Because this trait derives from a where-clause, it + // should not contain any inference variables or other + // artifacts. This means it is safe to put into the + // `WhereClauseCandidate` and (eventually) into the + // `WhereClausePick`. + assert!(!trait_ref.substs.needs_infer()); + + this.push_candidate( + Candidate { + xform_self_ty, + xform_ret_ty, + item, + kind: WhereClauseCandidate(poly_trait_ref), + import_ids: smallvec![], + }, + true, + ); + }); + } + + // Do a search through a list of bounds, using a callback to actually + // create the candidates. + fn elaborate_bounds<F>( + &mut self, + bounds: impl Iterator<Item = ty::PolyTraitRef<'tcx>>, + mut mk_cand: F, + ) where + F: for<'b> FnMut(&mut ProbeContext<'b, 'tcx>, ty::PolyTraitRef<'tcx>, ty::AssocItem), + { + let tcx = self.tcx; + for bound_trait_ref in traits::transitive_bounds(tcx, bounds) { + debug!("elaborate_bounds(bound_trait_ref={:?})", bound_trait_ref); + for item in self.impl_or_trait_item(bound_trait_ref.def_id()) { + if !self.has_applicable_self(&item) { + self.record_static_candidate(CandidateSource::Trait(bound_trait_ref.def_id())); + } else { + mk_cand(self, bound_trait_ref, item); + } + } + } + } + + fn assemble_extension_candidates_for_traits_in_scope(&mut self, expr_hir_id: hir::HirId) { + let mut duplicates = FxHashSet::default(); + let opt_applicable_traits = self.tcx.in_scope_traits(expr_hir_id); + if let Some(applicable_traits) = opt_applicable_traits { + for trait_candidate in applicable_traits.iter() { + let trait_did = trait_candidate.def_id; + if duplicates.insert(trait_did) { + self.assemble_extension_candidates_for_trait( + &trait_candidate.import_ids, + trait_did, + ); + } + } + } + } + + fn assemble_extension_candidates_for_all_traits(&mut self) { + let mut duplicates = FxHashSet::default(); + for trait_info in suggest::all_traits(self.tcx) { + if duplicates.insert(trait_info.def_id) { + self.assemble_extension_candidates_for_trait(&smallvec![], trait_info.def_id); + } + } + } + + pub fn matches_return_type( + &self, + method: &ty::AssocItem, + self_ty: Option<Ty<'tcx>>, + expected: Ty<'tcx>, + ) -> bool { + match method.kind { + ty::AssocKind::Fn => { + let fty = self.tcx.bound_fn_sig(method.def_id); + self.probe(|_| { + let substs = self.fresh_substs_for_item(self.span, method.def_id); + let fty = fty.subst(self.tcx, substs); + let fty = + self.replace_bound_vars_with_fresh_vars(self.span, infer::FnCall, fty); + + if let Some(self_ty) = self_ty { + if self + .at(&ObligationCause::dummy(), self.param_env) + .sup(fty.inputs()[0], self_ty) + .is_err() + { + return false; + } + } + self.can_sub(self.param_env, fty.output(), expected).is_ok() + }) + } + _ => false, + } + } + + fn assemble_extension_candidates_for_trait( + &mut self, + import_ids: &SmallVec<[LocalDefId; 1]>, + trait_def_id: DefId, + ) { + debug!("assemble_extension_candidates_for_trait(trait_def_id={:?})", trait_def_id); + let trait_substs = self.fresh_item_substs(trait_def_id); + let trait_ref = ty::TraitRef::new(trait_def_id, trait_substs); + + if self.tcx.is_trait_alias(trait_def_id) { + // For trait aliases, assume all supertraits are relevant. + let bounds = iter::once(ty::Binder::dummy(trait_ref)); + self.elaborate_bounds(bounds, |this, new_trait_ref, item| { + let new_trait_ref = this.erase_late_bound_regions(new_trait_ref); + + let (xform_self_ty, xform_ret_ty) = + this.xform_self_ty(&item, new_trait_ref.self_ty(), new_trait_ref.substs); + this.push_candidate( + Candidate { + xform_self_ty, + xform_ret_ty, + item, + import_ids: import_ids.clone(), + kind: TraitCandidate(new_trait_ref), + }, + false, + ); + }); + } else { + debug_assert!(self.tcx.is_trait(trait_def_id)); + for item in self.impl_or_trait_item(trait_def_id) { + // Check whether `trait_def_id` defines a method with suitable name. + if !self.has_applicable_self(&item) { + debug!("method has inapplicable self"); + self.record_static_candidate(CandidateSource::Trait(trait_def_id)); + continue; + } + + let (xform_self_ty, xform_ret_ty) = + self.xform_self_ty(&item, trait_ref.self_ty(), trait_substs); + self.push_candidate( + Candidate { + xform_self_ty, + xform_ret_ty, + item, + import_ids: import_ids.clone(), + kind: TraitCandidate(trait_ref), + }, + false, + ); + } + } + } + + fn candidate_method_names(&self) -> Vec<Ident> { + let mut set = FxHashSet::default(); + let mut names: Vec<_> = self + .inherent_candidates + .iter() + .chain(&self.extension_candidates) + .filter(|candidate| { + if let Some(return_ty) = self.return_type { + self.matches_return_type(&candidate.item, None, return_ty) + } else { + true + } + }) + .map(|candidate| candidate.item.ident(self.tcx)) + .filter(|&name| set.insert(name)) + .collect(); + + // Sort them by the name so we have a stable result. + names.sort_by(|a, b| a.as_str().partial_cmp(b.as_str()).unwrap()); + names + } + + /////////////////////////////////////////////////////////////////////////// + // THE ACTUAL SEARCH + + fn pick(mut self) -> PickResult<'tcx> { + assert!(self.method_name.is_some()); + + if let Some(r) = self.pick_core() { + return r; + } + + debug!("pick: actual search failed, assemble diagnostics"); + + let static_candidates = mem::take(&mut self.static_candidates); + let private_candidate = self.private_candidate.take(); + let unsatisfied_predicates = mem::take(&mut self.unsatisfied_predicates); + + // things failed, so lets look at all traits, for diagnostic purposes now: + self.reset(); + + let span = self.span; + let tcx = self.tcx; + + self.assemble_extension_candidates_for_all_traits(); + + let out_of_scope_traits = match self.pick_core() { + Some(Ok(p)) => vec![p.item.container_id(self.tcx)], + //Some(Ok(p)) => p.iter().map(|p| p.item.container().id()).collect(), + Some(Err(MethodError::Ambiguity(v))) => v + .into_iter() + .map(|source| match source { + CandidateSource::Trait(id) => id, + CandidateSource::Impl(impl_id) => match tcx.trait_id_of_impl(impl_id) { + Some(id) => id, + None => span_bug!(span, "found inherent method when looking at traits"), + }, + }) + .collect(), + Some(Err(MethodError::NoMatch(NoMatchData { + out_of_scope_traits: others, .. + }))) => { + assert!(others.is_empty()); + vec![] + } + _ => vec![], + }; + + if let Some((kind, def_id)) = private_candidate { + return Err(MethodError::PrivateMatch(kind, def_id, out_of_scope_traits)); + } + let lev_candidate = self.probe_for_lev_candidate()?; + + Err(MethodError::NoMatch(NoMatchData { + static_candidates, + unsatisfied_predicates, + out_of_scope_traits, + lev_candidate, + mode: self.mode, + })) + } + + fn pick_core(&mut self) -> Option<PickResult<'tcx>> { + let mut unstable_candidates = Vec::new(); + let pick = self.pick_all_method(Some(&mut unstable_candidates)); + + // In this case unstable picking is done by `pick_method`. + if !self.tcx.sess.opts.unstable_opts.pick_stable_methods_before_any_unstable { + return pick; + } + + match pick { + // Emit a lint if there are unstable candidates alongside the stable ones. + // + // We suppress warning if we're picking the method only because it is a + // suggestion. + Some(Ok(ref p)) if !self.is_suggestion.0 && !unstable_candidates.is_empty() => { + self.emit_unstable_name_collision_hint(p, &unstable_candidates); + pick + } + Some(_) => pick, + None => self.pick_all_method(None), + } + } + + fn pick_all_method( + &mut self, + mut unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>, + ) -> Option<PickResult<'tcx>> { + let steps = self.steps.clone(); + steps + .iter() + .filter(|step| { + debug!("pick_all_method: step={:?}", step); + // skip types that are from a type error or that would require dereferencing + // a raw pointer + !step.self_ty.references_error() && !step.from_unsafe_deref + }) + .flat_map(|step| { + let InferOk { value: self_ty, obligations: _ } = self + .fcx + .probe_instantiate_query_response( + self.span, + &self.orig_steps_var_values, + &step.self_ty, + ) + .unwrap_or_else(|_| { + span_bug!(self.span, "{:?} was applicable but now isn't?", step.self_ty) + }); + self.pick_by_value_method(step, self_ty, unstable_candidates.as_deref_mut()) + .or_else(|| { + self.pick_autorefd_method( + step, + self_ty, + hir::Mutability::Not, + unstable_candidates.as_deref_mut(), + ) + .or_else(|| { + self.pick_autorefd_method( + step, + self_ty, + hir::Mutability::Mut, + unstable_candidates.as_deref_mut(), + ) + }) + .or_else(|| { + self.pick_const_ptr_method( + step, + self_ty, + unstable_candidates.as_deref_mut(), + ) + }) + }) + }) + .next() + } + + /// For each type `T` in the step list, this attempts to find a method where + /// the (transformed) self type is exactly `T`. We do however do one + /// transformation on the adjustment: if we are passing a region pointer in, + /// we will potentially *reborrow* it to a shorter lifetime. This allows us + /// to transparently pass `&mut` pointers, in particular, without consuming + /// them for their entire lifetime. + fn pick_by_value_method( + &mut self, + step: &CandidateStep<'tcx>, + self_ty: Ty<'tcx>, + unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>, + ) -> Option<PickResult<'tcx>> { + if step.unsize { + return None; + } + + self.pick_method(self_ty, unstable_candidates).map(|r| { + r.map(|mut pick| { + pick.autoderefs = step.autoderefs; + + // Insert a `&*` or `&mut *` if this is a reference type: + if let ty::Ref(_, _, mutbl) = *step.self_ty.value.value.kind() { + pick.autoderefs += 1; + pick.autoref_or_ptr_adjustment = Some(AutorefOrPtrAdjustment::Autoref { + mutbl, + unsize: pick.autoref_or_ptr_adjustment.map_or(false, |a| a.get_unsize()), + }) + } + + pick + }) + }) + } + + fn pick_autorefd_method( + &mut self, + step: &CandidateStep<'tcx>, + self_ty: Ty<'tcx>, + mutbl: hir::Mutability, + unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>, + ) -> Option<PickResult<'tcx>> { + let tcx = self.tcx; + + // In general, during probing we erase regions. + let region = tcx.lifetimes.re_erased; + + let autoref_ty = tcx.mk_ref(region, ty::TypeAndMut { ty: self_ty, mutbl }); + self.pick_method(autoref_ty, unstable_candidates).map(|r| { + r.map(|mut pick| { + pick.autoderefs = step.autoderefs; + pick.autoref_or_ptr_adjustment = + Some(AutorefOrPtrAdjustment::Autoref { mutbl, unsize: step.unsize }); + pick + }) + }) + } + + /// If `self_ty` is `*mut T` then this picks `*const T` methods. The reason why we have a + /// special case for this is because going from `*mut T` to `*const T` with autoderefs and + /// autorefs would require dereferencing the pointer, which is not safe. + fn pick_const_ptr_method( + &mut self, + step: &CandidateStep<'tcx>, + self_ty: Ty<'tcx>, + unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>, + ) -> Option<PickResult<'tcx>> { + // Don't convert an unsized reference to ptr + if step.unsize { + return None; + } + + let &ty::RawPtr(ty::TypeAndMut { ty, mutbl: hir::Mutability::Mut }) = self_ty.kind() else { + return None; + }; + + let const_self_ty = ty::TypeAndMut { ty, mutbl: hir::Mutability::Not }; + let const_ptr_ty = self.tcx.mk_ptr(const_self_ty); + self.pick_method(const_ptr_ty, unstable_candidates).map(|r| { + r.map(|mut pick| { + pick.autoderefs = step.autoderefs; + pick.autoref_or_ptr_adjustment = Some(AutorefOrPtrAdjustment::ToConstPtr); + pick + }) + }) + } + + fn pick_method_with_unstable(&mut self, self_ty: Ty<'tcx>) -> Option<PickResult<'tcx>> { + debug!("pick_method_with_unstable(self_ty={})", self.ty_to_string(self_ty)); + + let mut possibly_unsatisfied_predicates = Vec::new(); + let mut unstable_candidates = Vec::new(); + + for (kind, candidates) in + &[("inherent", &self.inherent_candidates), ("extension", &self.extension_candidates)] + { + debug!("searching {} candidates", kind); + let res = self.consider_candidates( + self_ty, + candidates.iter(), + &mut possibly_unsatisfied_predicates, + Some(&mut unstable_candidates), + ); + if let Some(pick) = res { + if !self.is_suggestion.0 && !unstable_candidates.is_empty() { + if let Ok(p) = &pick { + // Emit a lint if there are unstable candidates alongside the stable ones. + // + // We suppress warning if we're picking the method only because it is a + // suggestion. + self.emit_unstable_name_collision_hint(p, &unstable_candidates); + } + } + return Some(pick); + } + } + + debug!("searching unstable candidates"); + let res = self.consider_candidates( + self_ty, + unstable_candidates.iter().map(|(c, _)| c), + &mut possibly_unsatisfied_predicates, + None, + ); + if res.is_none() { + self.unsatisfied_predicates.extend(possibly_unsatisfied_predicates); + } + res + } + + fn pick_method( + &mut self, + self_ty: Ty<'tcx>, + mut unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>, + ) -> Option<PickResult<'tcx>> { + if !self.tcx.sess.opts.unstable_opts.pick_stable_methods_before_any_unstable { + return self.pick_method_with_unstable(self_ty); + } + + debug!("pick_method(self_ty={})", self.ty_to_string(self_ty)); + + let mut possibly_unsatisfied_predicates = Vec::new(); + + for (kind, candidates) in + &[("inherent", &self.inherent_candidates), ("extension", &self.extension_candidates)] + { + debug!("searching {} candidates", kind); + let res = self.consider_candidates( + self_ty, + candidates.iter(), + &mut possibly_unsatisfied_predicates, + unstable_candidates.as_deref_mut(), + ); + if let Some(pick) = res { + return Some(pick); + } + } + + // `pick_method` may be called twice for the same self_ty if no stable methods + // match. Only extend once. + if unstable_candidates.is_some() { + self.unsatisfied_predicates.extend(possibly_unsatisfied_predicates); + } + None + } + + fn consider_candidates<'b, ProbesIter>( + &self, + self_ty: Ty<'tcx>, + probes: ProbesIter, + possibly_unsatisfied_predicates: &mut Vec<( + ty::Predicate<'tcx>, + Option<ty::Predicate<'tcx>>, + Option<ObligationCause<'tcx>>, + )>, + unstable_candidates: Option<&mut Vec<(Candidate<'tcx>, Symbol)>>, + ) -> Option<PickResult<'tcx>> + where + ProbesIter: Iterator<Item = &'b Candidate<'tcx>> + Clone, + 'tcx: 'b, + { + let mut applicable_candidates: Vec<_> = probes + .clone() + .map(|probe| { + (probe, self.consider_probe(self_ty, probe, possibly_unsatisfied_predicates)) + }) + .filter(|&(_, status)| status != ProbeResult::NoMatch) + .collect(); + + debug!("applicable_candidates: {:?}", applicable_candidates); + + if applicable_candidates.len() > 1 { + if let Some(pick) = + self.collapse_candidates_to_trait_pick(self_ty, &applicable_candidates) + { + return Some(Ok(pick)); + } + } + + if let Some(uc) = unstable_candidates { + applicable_candidates.retain(|&(p, _)| { + if let stability::EvalResult::Deny { feature, .. } = + self.tcx.eval_stability(p.item.def_id, None, self.span, None) + { + uc.push((p.clone(), feature)); + return false; + } + true + }); + } + + if applicable_candidates.len() > 1 { + let sources = probes.map(|p| self.candidate_source(p, self_ty)).collect(); + return Some(Err(MethodError::Ambiguity(sources))); + } + + applicable_candidates.pop().map(|(probe, status)| { + if status == ProbeResult::Match { + Ok(probe.to_unadjusted_pick(self_ty)) + } else { + Err(MethodError::BadReturnType) + } + }) + } + + fn emit_unstable_name_collision_hint( + &self, + stable_pick: &Pick<'_>, + unstable_candidates: &[(Candidate<'tcx>, Symbol)], + ) { + self.tcx.struct_span_lint_hir( + lint::builtin::UNSTABLE_NAME_COLLISIONS, + self.scope_expr_id, + self.span, + |lint| { + let def_kind = stable_pick.item.kind.as_def_kind(); + let mut diag = lint.build(&format!( + "{} {} with this name may be added to the standard library in the future", + def_kind.article(), + def_kind.descr(stable_pick.item.def_id), + )); + match (stable_pick.item.kind, stable_pick.item.container) { + (ty::AssocKind::Fn, _) => { + // FIXME: This should be a `span_suggestion` instead of `help` + // However `self.span` only + // highlights the method name, so we can't use it. Also consider reusing + // the code from `report_method_error()`. + diag.help(&format!( + "call with fully qualified syntax `{}(...)` to keep using the current \ + method", + self.tcx.def_path_str(stable_pick.item.def_id), + )); + } + (ty::AssocKind::Const, ty::AssocItemContainer::TraitContainer) => { + let def_id = stable_pick.item.container_id(self.tcx); + diag.span_suggestion( + self.span, + "use the fully qualified path to the associated const", + format!( + "<{} as {}>::{}", + stable_pick.self_ty, + self.tcx.def_path_str(def_id), + stable_pick.item.name + ), + Applicability::MachineApplicable, + ); + } + _ => {} + } + if self.tcx.sess.is_nightly_build() { + for (candidate, feature) in unstable_candidates { + diag.help(&format!( + "add `#![feature({})]` to the crate attributes to enable `{}`", + feature, + self.tcx.def_path_str(candidate.item.def_id), + )); + } + } + + diag.emit(); + }, + ); + } + + fn select_trait_candidate( + &self, + trait_ref: ty::TraitRef<'tcx>, + ) -> traits::SelectionResult<'tcx, traits::Selection<'tcx>> { + let cause = traits::ObligationCause::misc(self.span, self.body_id); + let predicate = ty::Binder::dummy(trait_ref).to_poly_trait_predicate(); + let obligation = traits::Obligation::new(cause, self.param_env, predicate); + traits::SelectionContext::new(self).select(&obligation) + } + + fn candidate_source(&self, candidate: &Candidate<'tcx>, self_ty: Ty<'tcx>) -> CandidateSource { + match candidate.kind { + InherentImplCandidate(..) => { + CandidateSource::Impl(candidate.item.container_id(self.tcx)) + } + ObjectCandidate | WhereClauseCandidate(_) => { + CandidateSource::Trait(candidate.item.container_id(self.tcx)) + } + TraitCandidate(trait_ref) => self.probe(|_| { + let _ = self + .at(&ObligationCause::dummy(), self.param_env) + .define_opaque_types(false) + .sup(candidate.xform_self_ty, self_ty); + match self.select_trait_candidate(trait_ref) { + Ok(Some(traits::ImplSource::UserDefined(ref impl_data))) => { + // If only a single impl matches, make the error message point + // to that impl. + CandidateSource::Impl(impl_data.impl_def_id) + } + _ => CandidateSource::Trait(candidate.item.container_id(self.tcx)), + } + }), + } + } + + fn consider_probe( + &self, + self_ty: Ty<'tcx>, + probe: &Candidate<'tcx>, + possibly_unsatisfied_predicates: &mut Vec<( + ty::Predicate<'tcx>, + Option<ty::Predicate<'tcx>>, + Option<ObligationCause<'tcx>>, + )>, + ) -> ProbeResult { + debug!("consider_probe: self_ty={:?} probe={:?}", self_ty, probe); + + self.probe(|_| { + // First check that the self type can be related. + let sub_obligations = match self + .at(&ObligationCause::dummy(), self.param_env) + .define_opaque_types(false) + .sup(probe.xform_self_ty, self_ty) + { + Ok(InferOk { obligations, value: () }) => obligations, + Err(err) => { + debug!("--> cannot relate self-types {:?}", err); + return ProbeResult::NoMatch; + } + }; + + let mut result = ProbeResult::Match; + let mut xform_ret_ty = probe.xform_ret_ty; + debug!(?xform_ret_ty); + + let selcx = &mut traits::SelectionContext::new(self); + let cause = traits::ObligationCause::misc(self.span, self.body_id); + + let mut parent_pred = None; + + // If so, impls may carry other conditions (e.g., where + // clauses) that must be considered. Make sure that those + // match as well (or at least may match, sometimes we + // don't have enough information to fully evaluate). + match probe.kind { + InherentImplCandidate(ref substs, ref ref_obligations) => { + // `xform_ret_ty` hasn't been normalized yet, only `xform_self_ty`, + // see the reasons mentioned in the comments in `assemble_inherent_impl_probe` + // for why this is necessary + let traits::Normalized { + value: normalized_xform_ret_ty, + obligations: normalization_obligations, + } = traits::normalize(selcx, self.param_env, cause.clone(), probe.xform_ret_ty); + xform_ret_ty = normalized_xform_ret_ty; + debug!("xform_ret_ty after normalization: {:?}", xform_ret_ty); + + // Check whether the impl imposes obligations we have to worry about. + let impl_def_id = probe.item.container_id(self.tcx); + let impl_bounds = self.tcx.predicates_of(impl_def_id); + let impl_bounds = impl_bounds.instantiate(self.tcx, substs); + let traits::Normalized { value: impl_bounds, obligations: norm_obligations } = + traits::normalize(selcx, self.param_env, cause.clone(), impl_bounds); + + // Convert the bounds into obligations. + let impl_obligations = + traits::predicates_for_generics(cause, self.param_env, impl_bounds); + + let candidate_obligations = impl_obligations + .chain(norm_obligations.into_iter()) + .chain(ref_obligations.iter().cloned()) + .chain(normalization_obligations.into_iter()); + + // Evaluate those obligations to see if they might possibly hold. + for o in candidate_obligations { + let o = self.resolve_vars_if_possible(o); + if !self.predicate_may_hold(&o) { + result = ProbeResult::NoMatch; + possibly_unsatisfied_predicates.push(( + o.predicate, + None, + Some(o.cause), + )); + } + } + } + + ObjectCandidate | WhereClauseCandidate(..) => { + // These have no additional conditions to check. + } + + TraitCandidate(trait_ref) => { + if let Some(method_name) = self.method_name { + // Some trait methods are excluded for arrays before 2021. + // (`array.into_iter()` wants a slice iterator for compatibility.) + if self_ty.is_array() && !method_name.span.rust_2021() { + let trait_def = self.tcx.trait_def(trait_ref.def_id); + if trait_def.skip_array_during_method_dispatch { + return ProbeResult::NoMatch; + } + } + } + let predicate = + ty::Binder::dummy(trait_ref).without_const().to_predicate(self.tcx); + parent_pred = Some(predicate); + let obligation = traits::Obligation::new(cause, self.param_env, predicate); + if !self.predicate_may_hold(&obligation) { + result = ProbeResult::NoMatch; + if self.probe(|_| { + match self.select_trait_candidate(trait_ref) { + Err(_) => return true, + Ok(Some(impl_source)) + if !impl_source.borrow_nested_obligations().is_empty() => + { + for obligation in impl_source.borrow_nested_obligations() { + // Determine exactly which obligation wasn't met, so + // that we can give more context in the error. + if !self.predicate_may_hold(obligation) { + let nested_predicate = + self.resolve_vars_if_possible(obligation.predicate); + let predicate = + self.resolve_vars_if_possible(predicate); + let p = if predicate == nested_predicate { + // Avoid "`MyStruct: Foo` which is required by + // `MyStruct: Foo`" in E0599. + None + } else { + Some(predicate) + }; + possibly_unsatisfied_predicates.push(( + nested_predicate, + p, + Some(obligation.cause.clone()), + )); + } + } + } + _ => { + // Some nested subobligation of this predicate + // failed. + let predicate = self.resolve_vars_if_possible(predicate); + possibly_unsatisfied_predicates.push((predicate, None, None)); + } + } + false + }) { + // This candidate's primary obligation doesn't even + // select - don't bother registering anything in + // `potentially_unsatisfied_predicates`. + return ProbeResult::NoMatch; + } + } + } + } + + // Evaluate those obligations to see if they might possibly hold. + for o in sub_obligations { + let o = self.resolve_vars_if_possible(o); + if !self.predicate_may_hold(&o) { + result = ProbeResult::NoMatch; + possibly_unsatisfied_predicates.push((o.predicate, parent_pred, Some(o.cause))); + } + } + + if let ProbeResult::Match = result { + if let (Some(return_ty), Some(xform_ret_ty)) = (self.return_type, xform_ret_ty) { + let xform_ret_ty = self.resolve_vars_if_possible(xform_ret_ty); + debug!( + "comparing return_ty {:?} with xform ret ty {:?}", + return_ty, probe.xform_ret_ty + ); + if self + .at(&ObligationCause::dummy(), self.param_env) + .define_opaque_types(false) + .sup(return_ty, xform_ret_ty) + .is_err() + { + return ProbeResult::BadReturnType; + } + } + } + + result + }) + } + + /// Sometimes we get in a situation where we have multiple probes that are all impls of the + /// same trait, but we don't know which impl to use. In this case, since in all cases the + /// external interface of the method can be determined from the trait, it's ok not to decide. + /// We can basically just collapse all of the probes for various impls into one where-clause + /// probe. This will result in a pending obligation so when more type-info is available we can + /// make the final decision. + /// + /// Example (`src/test/ui/method-two-trait-defer-resolution-1.rs`): + /// + /// ```ignore (illustrative) + /// trait Foo { ... } + /// impl Foo for Vec<i32> { ... } + /// impl Foo for Vec<usize> { ... } + /// ``` + /// + /// Now imagine the receiver is `Vec<_>`. It doesn't really matter at this time which impl we + /// use, so it's ok to just commit to "using the method from the trait Foo". + fn collapse_candidates_to_trait_pick( + &self, + self_ty: Ty<'tcx>, + probes: &[(&Candidate<'tcx>, ProbeResult)], + ) -> Option<Pick<'tcx>> { + // Do all probes correspond to the same trait? + let container = probes[0].0.item.trait_container(self.tcx)?; + for (p, _) in &probes[1..] { + let p_container = p.item.trait_container(self.tcx)?; + if p_container != container { + return None; + } + } + + // FIXME: check the return type here somehow. + // If so, just use this trait and call it a day. + Some(Pick { + item: probes[0].0.item, + kind: TraitPick, + import_ids: probes[0].0.import_ids.clone(), + autoderefs: 0, + autoref_or_ptr_adjustment: None, + self_ty, + }) + } + + /// Similarly to `probe_for_return_type`, this method attempts to find the best matching + /// candidate method where the method name may have been misspelled. Similarly to other + /// Levenshtein based suggestions, we provide at most one such suggestion. + fn probe_for_lev_candidate(&mut self) -> Result<Option<ty::AssocItem>, MethodError<'tcx>> { + debug!("probing for method names similar to {:?}", self.method_name); + + let steps = self.steps.clone(); + self.probe(|_| { + let mut pcx = ProbeContext::new( + self.fcx, + self.span, + self.mode, + self.method_name, + self.return_type, + self.orig_steps_var_values.clone(), + steps, + IsSuggestion(true), + self.scope_expr_id, + ); + pcx.allow_similar_names = true; + pcx.assemble_inherent_candidates(); + + let method_names = pcx.candidate_method_names(); + pcx.allow_similar_names = false; + let applicable_close_candidates: Vec<ty::AssocItem> = method_names + .iter() + .filter_map(|&method_name| { + pcx.reset(); + pcx.method_name = Some(method_name); + pcx.assemble_inherent_candidates(); + pcx.pick_core().and_then(|pick| pick.ok()).map(|pick| pick.item) + }) + .collect(); + + if applicable_close_candidates.is_empty() { + Ok(None) + } else { + let best_name = { + let names = applicable_close_candidates + .iter() + .map(|cand| cand.name) + .collect::<Vec<Symbol>>(); + find_best_match_for_name_with_substrings( + &names, + self.method_name.unwrap().name, + None, + ) + } + .unwrap(); + Ok(applicable_close_candidates.into_iter().find(|method| method.name == best_name)) + } + }) + } + + /////////////////////////////////////////////////////////////////////////// + // MISCELLANY + fn has_applicable_self(&self, item: &ty::AssocItem) -> bool { + // "Fast track" -- check for usage of sugar when in method call + // mode. + // + // In Path mode (i.e., resolving a value like `T::next`), consider any + // associated value (i.e., methods, constants) but not types. + match self.mode { + Mode::MethodCall => item.fn_has_self_parameter, + Mode::Path => match item.kind { + ty::AssocKind::Type => false, + ty::AssocKind::Fn | ty::AssocKind::Const => true, + }, + } + // FIXME -- check for types that deref to `Self`, + // like `Rc<Self>` and so on. + // + // Note also that the current code will break if this type + // includes any of the type parameters defined on the method + // -- but this could be overcome. + } + + fn record_static_candidate(&mut self, source: CandidateSource) { + self.static_candidates.push(source); + } + + #[instrument(level = "debug", skip(self))] + fn xform_self_ty( + &self, + item: &ty::AssocItem, + impl_ty: Ty<'tcx>, + substs: SubstsRef<'tcx>, + ) -> (Ty<'tcx>, Option<Ty<'tcx>>) { + if item.kind == ty::AssocKind::Fn && self.mode == Mode::MethodCall { + let sig = self.xform_method_sig(item.def_id, substs); + (sig.inputs()[0], Some(sig.output())) + } else { + (impl_ty, None) + } + } + + #[instrument(level = "debug", skip(self))] + fn xform_method_sig(&self, method: DefId, substs: SubstsRef<'tcx>) -> ty::FnSig<'tcx> { + let fn_sig = self.tcx.bound_fn_sig(method); + debug!(?fn_sig); + + assert!(!substs.has_escaping_bound_vars()); + + // It is possible for type parameters or early-bound lifetimes + // to appear in the signature of `self`. The substitutions we + // are given do not include type/lifetime parameters for the + // method yet. So create fresh variables here for those too, + // if there are any. + let generics = self.tcx.generics_of(method); + assert_eq!(substs.len(), generics.parent_count as usize); + + let xform_fn_sig = if generics.params.is_empty() { + fn_sig.subst(self.tcx, substs) + } else { + let substs = InternalSubsts::for_item(self.tcx, method, |param, _| { + let i = param.index as usize; + if i < substs.len() { + substs[i] + } else { + match param.kind { + GenericParamDefKind::Lifetime => { + // In general, during probe we erase regions. + self.tcx.lifetimes.re_erased.into() + } + GenericParamDefKind::Type { .. } | GenericParamDefKind::Const { .. } => { + self.var_for_def(self.span, param) + } + } + } + }); + fn_sig.subst(self.tcx, substs) + }; + + self.erase_late_bound_regions(xform_fn_sig) + } + + /// Gets the type of an impl and generate substitutions with inference vars. + fn impl_ty_and_substs( + &self, + impl_def_id: DefId, + ) -> (ty::EarlyBinder<Ty<'tcx>>, SubstsRef<'tcx>) { + (self.tcx.bound_type_of(impl_def_id), self.fresh_item_substs(impl_def_id)) + } + + fn fresh_item_substs(&self, def_id: DefId) -> SubstsRef<'tcx> { + InternalSubsts::for_item(self.tcx, def_id, |param, _| match param.kind { + GenericParamDefKind::Lifetime => self.tcx.lifetimes.re_erased.into(), + GenericParamDefKind::Type { .. } => self + .next_ty_var(TypeVariableOrigin { + kind: TypeVariableOriginKind::SubstitutionPlaceholder, + span: self.tcx.def_span(def_id), + }) + .into(), + GenericParamDefKind::Const { .. } => { + let span = self.tcx.def_span(def_id); + let origin = ConstVariableOrigin { + kind: ConstVariableOriginKind::SubstitutionPlaceholder, + span, + }; + self.next_const_var(self.tcx.type_of(param.def_id), origin).into() + } + }) + } + + /// Replaces late-bound-regions bound by `value` with `'static` using + /// `ty::erase_late_bound_regions`. + /// + /// This is only a reasonable thing to do during the *probe* phase, not the *confirm* phase, of + /// method matching. It is reasonable during the probe phase because we don't consider region + /// relationships at all. Therefore, we can just replace all the region variables with 'static + /// rather than creating fresh region variables. This is nice for two reasons: + /// + /// 1. Because the numbers of the region variables would otherwise be fairly unique to this + /// particular method call, it winds up creating fewer types overall, which helps for memory + /// usage. (Admittedly, this is a rather small effect, though measurable.) + /// + /// 2. It makes it easier to deal with higher-ranked trait bounds, because we can replace any + /// late-bound regions with 'static. Otherwise, if we were going to replace late-bound + /// regions with actual region variables as is proper, we'd have to ensure that the same + /// region got replaced with the same variable, which requires a bit more coordination + /// and/or tracking the substitution and + /// so forth. + fn erase_late_bound_regions<T>(&self, value: ty::Binder<'tcx, T>) -> T + where + T: TypeFoldable<'tcx>, + { + self.tcx.erase_late_bound_regions(value) + } + + /// Finds the method with the appropriate name (or return type, as the case may be). If + /// `allow_similar_names` is set, find methods with close-matching names. + // The length of the returned iterator is nearly always 0 or 1 and this + // method is fairly hot. + fn impl_or_trait_item(&self, def_id: DefId) -> SmallVec<[ty::AssocItem; 1]> { + if let Some(name) = self.method_name { + if self.allow_similar_names { + let max_dist = max(name.as_str().len(), 3) / 3; + self.tcx + .associated_items(def_id) + .in_definition_order() + .filter(|x| { + if x.kind.namespace() != Namespace::ValueNS { + return false; + } + match lev_distance_with_substrings(name.as_str(), x.name.as_str(), max_dist) + { + Some(d) => d > 0, + None => false, + } + }) + .copied() + .collect() + } else { + self.fcx + .associated_value(def_id, name) + .map_or_else(SmallVec::new, |x| SmallVec::from_buf([x])) + } + } else { + self.tcx.associated_items(def_id).in_definition_order().copied().collect() + } + } +} + +impl<'tcx> Candidate<'tcx> { + fn to_unadjusted_pick(&self, self_ty: Ty<'tcx>) -> Pick<'tcx> { + Pick { + item: self.item, + kind: match self.kind { + InherentImplCandidate(..) => InherentImplPick, + ObjectCandidate => ObjectPick, + TraitCandidate(_) => TraitPick, + WhereClauseCandidate(ref trait_ref) => { + // Only trait derived from where-clauses should + // appear here, so they should not contain any + // inference variables or other artifacts. This + // means they are safe to put into the + // `WhereClausePick`. + assert!( + !trait_ref.skip_binder().substs.needs_infer() + && !trait_ref.skip_binder().substs.has_placeholders() + ); + + WhereClausePick(*trait_ref) + } + }, + import_ids: self.import_ids.clone(), + autoderefs: 0, + autoref_or_ptr_adjustment: None, + self_ty, + } + } +} |