1 //! Conversion from AST representation of types to the `ty.rs` representation.
2 //! The main routine here is `ast_ty_to_ty()`; each use is parameterized by an
3 //! instance of `AstConv`.
5 use errors::{Applicability, DiagnosticId};
6 use crate::hir::{self, GenericArg, GenericArgs, ExprKind};
7 use crate::hir::def::{CtorOf, Res, DefKind};
8 use crate::hir::def_id::DefId;
9 use crate::hir::HirVec;
10 use crate::hir::ptr::P;
12 use crate::middle::lang_items::SizedTraitLangItem;
13 use crate::middle::resolve_lifetime as rl;
14 use crate::namespace::Namespace;
15 use rustc::lint::builtin::AMBIGUOUS_ASSOCIATED_ITEMS;
17 use rustc::ty::{self, DefIdTree, Ty, TyCtxt, Const, ToPredicate, TypeFoldable};
18 use rustc::ty::{GenericParamDef, GenericParamDefKind};
19 use rustc::ty::subst::{self, Subst, InternalSubsts, SubstsRef};
20 use rustc::ty::wf::object_region_bounds;
21 use rustc::mir::interpret::ConstValue;
22 use rustc_target::spec::abi;
23 use crate::require_c_abi_if_c_variadic;
24 use smallvec::SmallVec;
26 use syntax::errors::pluralise;
27 use syntax::feature_gate::{GateIssue, emit_feature_err};
28 use syntax::util::lev_distance::find_best_match_for_name;
29 use syntax::symbol::sym;
30 use syntax_pos::{DUMMY_SP, Span, MultiSpan};
31 use crate::util::common::ErrorReported;
32 use crate::util::nodemap::FxHashMap;
34 use std::collections::BTreeSet;
38 use rustc_data_structures::fx::FxHashSet;
41 pub struct PathSeg(pub DefId, pub usize);
43 pub trait AstConv<'tcx> {
44 fn tcx<'a>(&'a self) -> TyCtxt<'tcx>;
46 /// Returns predicates in scope of the form `X: Foo`, where `X` is
47 /// a type parameter `X` with the given id `def_id`. This is a
48 /// subset of the full set of predicates.
50 /// This is used for one specific purpose: resolving "short-hand"
51 /// associated type references like `T::Item`. In principle, we
52 /// would do that by first getting the full set of predicates in
53 /// scope and then filtering down to find those that apply to `T`,
54 /// but this can lead to cycle errors. The problem is that we have
55 /// to do this resolution *in order to create the predicates in
56 /// the first place*. Hence, we have this "special pass".
57 fn get_type_parameter_bounds(&self, span: Span, def_id: DefId)
58 -> &'tcx ty::GenericPredicates<'tcx>;
60 /// Returns the lifetime to use when a lifetime is omitted (and not elided).
63 param: Option<&ty::GenericParamDef>,
66 -> Option<ty::Region<'tcx>>;
68 /// Returns the type to use when a type is omitted.
69 fn ty_infer(&self, param: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx>;
71 /// Returns the const to use when a const is omitted.
75 param: Option<&ty::GenericParamDef>,
77 ) -> &'tcx Const<'tcx>;
79 /// Projecting an associated type from a (potentially)
80 /// higher-ranked trait reference is more complicated, because of
81 /// the possibility of late-bound regions appearing in the
82 /// associated type binding. This is not legal in function
83 /// signatures for that reason. In a function body, we can always
84 /// handle it because we can use inference variables to remove the
85 /// late-bound regions.
86 fn projected_ty_from_poly_trait_ref(&self,
89 poly_trait_ref: ty::PolyTraitRef<'tcx>)
92 /// Normalize an associated type coming from the user.
93 fn normalize_ty(&self, span: Span, ty: Ty<'tcx>) -> Ty<'tcx>;
95 /// Invoked when we encounter an error from some prior pass
96 /// (e.g., resolve) that is translated into a ty-error. This is
97 /// used to help suppress derived errors typeck might otherwise
99 fn set_tainted_by_errors(&self);
101 fn record_ty(&self, hir_id: hir::HirId, ty: Ty<'tcx>, span: Span);
104 pub enum SizedByDefault {
109 struct ConvertedBinding<'a, 'tcx> {
110 item_name: ast::Ident,
111 kind: ConvertedBindingKind<'a, 'tcx>,
115 enum ConvertedBindingKind<'a, 'tcx> {
117 Constraint(&'a [hir::GenericBound]),
121 enum GenericArgPosition {
123 Value, // e.g., functions
127 impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
128 pub fn ast_region_to_region(&self,
129 lifetime: &hir::Lifetime,
130 def: Option<&ty::GenericParamDef>)
133 let tcx = self.tcx();
134 let lifetime_name = |def_id| {
135 tcx.hir().name(tcx.hir().as_local_hir_id(def_id).unwrap()).as_interned_str()
138 let r = match tcx.named_region(lifetime.hir_id) {
139 Some(rl::Region::Static) => {
140 tcx.lifetimes.re_static
143 Some(rl::Region::LateBound(debruijn, id, _)) => {
144 let name = lifetime_name(id);
145 tcx.mk_region(ty::ReLateBound(debruijn,
146 ty::BrNamed(id, name)))
149 Some(rl::Region::LateBoundAnon(debruijn, index)) => {
150 tcx.mk_region(ty::ReLateBound(debruijn, ty::BrAnon(index)))
153 Some(rl::Region::EarlyBound(index, id, _)) => {
154 let name = lifetime_name(id);
155 tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion {
162 Some(rl::Region::Free(scope, id)) => {
163 let name = lifetime_name(id);
164 tcx.mk_region(ty::ReFree(ty::FreeRegion {
166 bound_region: ty::BrNamed(id, name)
169 // (*) -- not late-bound, won't change
173 self.re_infer(def, lifetime.span)
175 // This indicates an illegal lifetime
176 // elision. `resolve_lifetime` should have
177 // reported an error in this case -- but if
178 // not, let's error out.
179 tcx.sess.delay_span_bug(lifetime.span, "unelided lifetime in signature");
181 // Supply some dummy value. We don't have an
182 // `re_error`, annoyingly, so use `'static`.
183 tcx.lifetimes.re_static
188 debug!("ast_region_to_region(lifetime={:?}) yields {:?}",
195 /// Given a path `path` that refers to an item `I` with the declared generics `decl_generics`,
196 /// returns an appropriate set of substitutions for this particular reference to `I`.
197 pub fn ast_path_substs_for_ty(&self,
200 item_segment: &hir::PathSegment)
203 let (substs, assoc_bindings, _) = self.create_substs_for_ast_path(
206 item_segment.generic_args(),
207 item_segment.infer_args,
211 assoc_bindings.first().map(|b| Self::prohibit_assoc_ty_binding(self.tcx(), b.span));
216 /// Report error if there is an explicit type parameter when using `impl Trait`.
220 seg: &hir::PathSegment,
221 generics: &ty::Generics,
223 let explicit = !seg.infer_args;
224 let impl_trait = generics.params.iter().any(|param| match param.kind {
225 ty::GenericParamDefKind::Type {
226 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait), ..
231 if explicit && impl_trait {
232 let mut err = struct_span_err! {
236 "cannot provide explicit type parameters when `impl Trait` is \
237 used in argument position."
246 /// Checks that the correct number of generic arguments have been provided.
247 /// Used specifically for function calls.
248 pub fn check_generic_arg_count_for_call(
252 seg: &hir::PathSegment,
253 is_method_call: bool,
255 let empty_args = P(hir::GenericArgs {
256 args: HirVec::new(), bindings: HirVec::new(), parenthesized: false,
258 let suppress_mismatch = Self::check_impl_trait(tcx, span, seg, &def);
259 Self::check_generic_arg_count(
263 if let Some(ref args) = seg.args {
269 GenericArgPosition::MethodCall
271 GenericArgPosition::Value
273 def.parent.is_none() && def.has_self, // `has_self`
274 seg.infer_args || suppress_mismatch, // `infer_args`
278 /// Checks that the correct number of generic arguments have been provided.
279 /// This is used both for datatypes and function calls.
280 fn check_generic_arg_count(
284 args: &hir::GenericArgs,
285 position: GenericArgPosition,
288 ) -> (bool, Option<Vec<Span>>) {
289 // At this stage we are guaranteed that the generic arguments are in the correct order, e.g.
290 // that lifetimes will proceed types. So it suffices to check the number of each generic
291 // arguments in order to validate them with respect to the generic parameters.
292 let param_counts = def.own_counts();
293 let arg_counts = args.own_counts();
294 let infer_lifetimes = position != GenericArgPosition::Type && arg_counts.lifetimes == 0;
296 let mut defaults: ty::GenericParamCount = Default::default();
297 for param in &def.params {
299 GenericParamDefKind::Lifetime => {}
300 GenericParamDefKind::Type { has_default, .. } => {
301 defaults.types += has_default as usize
303 GenericParamDefKind::Const => {
304 // FIXME(const_generics:defaults)
309 if position != GenericArgPosition::Type && !args.bindings.is_empty() {
310 AstConv::prohibit_assoc_ty_binding(tcx, args.bindings[0].span);
313 // Prohibit explicit lifetime arguments if late-bound lifetime parameters are present.
314 let mut reported_late_bound_region_err = None;
315 if !infer_lifetimes {
316 if let Some(span_late) = def.has_late_bound_regions {
317 let msg = "cannot specify lifetime arguments explicitly \
318 if late bound lifetime parameters are present";
319 let note = "the late bound lifetime parameter is introduced here";
320 let span = args.args[0].span();
321 if position == GenericArgPosition::Value
322 && arg_counts.lifetimes != param_counts.lifetimes {
323 let mut err = tcx.sess.struct_span_err(span, msg);
324 err.span_note(span_late, note);
326 reported_late_bound_region_err = Some(true);
328 let mut multispan = MultiSpan::from_span(span);
329 multispan.push_span_label(span_late, note.to_string());
330 tcx.lint_hir(lint::builtin::LATE_BOUND_LIFETIME_ARGUMENTS,
331 args.args[0].id(), multispan, msg);
332 reported_late_bound_region_err = Some(false);
337 let check_kind_count = |kind, required, permitted, provided, offset| {
339 "check_kind_count: kind: {} required: {} permitted: {} provided: {} offset: {}",
346 // We enforce the following: `required` <= `provided` <= `permitted`.
347 // For kinds without defaults (e.g.., lifetimes), `required == permitted`.
348 // For other kinds (i.e., types), `permitted` may be greater than `required`.
349 if required <= provided && provided <= permitted {
350 return (reported_late_bound_region_err.unwrap_or(false), None);
353 // Unfortunately lifetime and type parameter mismatches are typically styled
354 // differently in diagnostics, which means we have a few cases to consider here.
355 let (bound, quantifier) = if required != permitted {
356 if provided < required {
357 (required, "at least ")
358 } else { // provided > permitted
359 (permitted, "at most ")
365 let mut potential_assoc_types: Option<Vec<Span>> = None;
366 let (spans, label) = if required == permitted && provided > permitted {
367 // In the case when the user has provided too many arguments,
368 // we want to point to the unexpected arguments.
369 let spans: Vec<Span> = args.args[offset+permitted .. offset+provided]
371 .map(|arg| arg.span())
373 potential_assoc_types = Some(spans.clone());
374 (spans, format!( "unexpected {} argument", kind))
376 (vec![span], format!(
377 "expected {}{} {} argument{}",
385 let mut err = tcx.sess.struct_span_err_with_code(
388 "wrong number of {} arguments: expected {}{}, found {}",
394 DiagnosticId::Error("E0107".into())
397 err.span_label(span, label.as_str());
402 provided > required, // `suppress_error`
403 potential_assoc_types,
407 if reported_late_bound_region_err.is_none()
408 && (!infer_lifetimes || arg_counts.lifetimes > param_counts.lifetimes) {
411 param_counts.lifetimes,
412 param_counts.lifetimes,
413 arg_counts.lifetimes,
417 // FIXME(const_generics:defaults)
418 if !infer_args || arg_counts.consts > param_counts.consts {
424 arg_counts.lifetimes + arg_counts.types,
427 // Note that type errors are currently be emitted *after* const errors.
429 || arg_counts.types > param_counts.types - defaults.types - has_self as usize {
432 param_counts.types - defaults.types - has_self as usize,
433 param_counts.types - has_self as usize,
435 arg_counts.lifetimes,
438 (reported_late_bound_region_err.unwrap_or(false), None)
442 /// Creates the relevant generic argument substitutions
443 /// corresponding to a set of generic parameters. This is a
444 /// rather complex function. Let us try to explain the role
445 /// of each of its parameters:
447 /// To start, we are given the `def_id` of the thing we are
448 /// creating the substitutions for, and a partial set of
449 /// substitutions `parent_substs`. In general, the substitutions
450 /// for an item begin with substitutions for all the "parents" of
451 /// that item -- e.g., for a method it might include the
452 /// parameters from the impl.
454 /// Therefore, the method begins by walking down these parents,
455 /// starting with the outermost parent and proceed inwards until
456 /// it reaches `def_id`. For each parent `P`, it will check `parent_substs`
457 /// first to see if the parent's substitutions are listed in there. If so,
458 /// we can append those and move on. Otherwise, it invokes the
459 /// three callback functions:
461 /// - `args_for_def_id`: given the `DefId` `P`, supplies back the
462 /// generic arguments that were given to that parent from within
463 /// the path; so e.g., if you have `<T as Foo>::Bar`, the `DefId`
464 /// might refer to the trait `Foo`, and the arguments might be
465 /// `[T]`. The boolean value indicates whether to infer values
466 /// for arguments whose values were not explicitly provided.
467 /// - `provided_kind`: given the generic parameter and the value from `args_for_def_id`,
468 /// instantiate a `GenericArg`.
469 /// - `inferred_kind`: if no parameter was provided, and inference is enabled, then
470 /// creates a suitable inference variable.
471 pub fn create_substs_for_generic_args<'b>(
474 parent_substs: &[subst::GenericArg<'tcx>],
476 self_ty: Option<Ty<'tcx>>,
477 args_for_def_id: impl Fn(DefId) -> (Option<&'b GenericArgs>, bool),
478 provided_kind: impl Fn(&GenericParamDef, &GenericArg) -> subst::GenericArg<'tcx>,
479 inferred_kind: impl Fn(Option<&[subst::GenericArg<'tcx>]>, &GenericParamDef, bool)
480 -> subst::GenericArg<'tcx>,
481 ) -> SubstsRef<'tcx> {
482 // Collect the segments of the path; we need to substitute arguments
483 // for parameters throughout the entire path (wherever there are
484 // generic parameters).
485 let mut parent_defs = tcx.generics_of(def_id);
486 let count = parent_defs.count();
487 let mut stack = vec![(def_id, parent_defs)];
488 while let Some(def_id) = parent_defs.parent {
489 parent_defs = tcx.generics_of(def_id);
490 stack.push((def_id, parent_defs));
493 // We manually build up the substitution, rather than using convenience
494 // methods in `subst.rs`, so that we can iterate over the arguments and
495 // parameters in lock-step linearly, instead of trying to match each pair.
496 let mut substs: SmallVec<[subst::GenericArg<'tcx>; 8]> = SmallVec::with_capacity(count);
498 // Iterate over each segment of the path.
499 while let Some((def_id, defs)) = stack.pop() {
500 let mut params = defs.params.iter().peekable();
502 // If we have already computed substitutions for parents, we can use those directly.
503 while let Some(¶m) = params.peek() {
504 if let Some(&kind) = parent_substs.get(param.index as usize) {
512 // `Self` is handled first, unless it's been handled in `parent_substs`.
514 if let Some(¶m) = params.peek() {
515 if param.index == 0 {
516 if let GenericParamDefKind::Type { .. } = param.kind {
517 substs.push(self_ty.map(|ty| ty.into())
518 .unwrap_or_else(|| inferred_kind(None, param, true)));
525 // Check whether this segment takes generic arguments and the user has provided any.
526 let (generic_args, infer_args) = args_for_def_id(def_id);
528 let mut args = generic_args.iter().flat_map(|generic_args| generic_args.args.iter())
532 // We're going to iterate through the generic arguments that the user
533 // provided, matching them with the generic parameters we expect.
534 // Mismatches can occur as a result of elided lifetimes, or for malformed
535 // input. We try to handle both sensibly.
536 match (args.peek(), params.peek()) {
537 (Some(&arg), Some(¶m)) => {
538 match (arg, ¶m.kind) {
539 (GenericArg::Lifetime(_), GenericParamDefKind::Lifetime)
540 | (GenericArg::Type(_), GenericParamDefKind::Type { .. })
541 | (GenericArg::Const(_), GenericParamDefKind::Const) => {
542 substs.push(provided_kind(param, arg));
546 (GenericArg::Type(_), GenericParamDefKind::Lifetime)
547 | (GenericArg::Const(_), GenericParamDefKind::Lifetime) => {
548 // We expected a lifetime argument, but got a type or const
549 // argument. That means we're inferring the lifetimes.
550 substs.push(inferred_kind(None, param, infer_args));
554 // We expected one kind of parameter, but the user provided
555 // another. This is an error, but we need to handle it
556 // gracefully so we can report sensible errors.
557 // In this case, we're simply going to infer this argument.
563 // We should never be able to reach this point with well-formed input.
564 // Getting to this point means the user supplied more arguments than
565 // there are parameters.
568 (None, Some(¶m)) => {
569 // If there are fewer arguments than parameters, it means
570 // we're inferring the remaining arguments.
571 substs.push(inferred_kind(Some(&substs), param, infer_args));
575 (None, None) => break,
580 tcx.intern_substs(&substs)
583 /// Given the type/lifetime/const arguments provided to some path (along with
584 /// an implicit `Self`, if this is a trait reference), returns the complete
585 /// set of substitutions. This may involve applying defaulted type parameters.
586 /// Also returns back constriants on associated types.
591 /// T: std::ops::Index<usize, Output = u32>
592 /// ^1 ^^^^^^^^^^^^^^2 ^^^^3 ^^^^^^^^^^^4
595 /// 1. The `self_ty` here would refer to the type `T`.
596 /// 2. The path in question is the path to the trait `std::ops::Index`,
597 /// which will have been resolved to a `def_id`
598 /// 3. The `generic_args` contains info on the `<...>` contents. The `usize` type
599 /// parameters are returned in the `SubstsRef`, the associated type bindings like
600 /// `Output = u32` are returned in the `Vec<ConvertedBinding...>` result.
602 /// Note that the type listing given here is *exactly* what the user provided.
603 fn create_substs_for_ast_path<'a>(&self,
606 generic_args: &'a hir::GenericArgs,
608 self_ty: Option<Ty<'tcx>>)
609 -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'a, 'tcx>>, Option<Vec<Span>>)
611 // If the type is parameterized by this region, then replace this
612 // region with the current anon region binding (in other words,
613 // whatever & would get replaced with).
614 debug!("create_substs_for_ast_path(def_id={:?}, self_ty={:?}, \
616 def_id, self_ty, generic_args);
618 let tcx = self.tcx();
619 let generic_params = tcx.generics_of(def_id);
621 // If a self-type was declared, one should be provided.
622 assert_eq!(generic_params.has_self, self_ty.is_some());
624 let has_self = generic_params.has_self;
625 let (_, potential_assoc_types) = Self::check_generic_arg_count(
630 GenericArgPosition::Type,
635 let is_object = self_ty.map_or(false, |ty| {
636 ty == self.tcx().types.trait_object_dummy_self
638 let default_needs_object_self = |param: &ty::GenericParamDef| {
639 if let GenericParamDefKind::Type { has_default, .. } = param.kind {
640 if is_object && has_default && has_self {
641 let self_param = tcx.types.self_param;
642 if tcx.at(span).type_of(param.def_id).walk().any(|ty| ty == self_param) {
643 // There is no suitable inference default for a type parameter
644 // that references self, in an object type.
653 let substs = Self::create_substs_for_generic_args(
659 // Provide the generic args, and whether types should be inferred.
660 |_| (Some(generic_args), infer_args),
661 // Provide substitutions for parameters for which (valid) arguments have been provided.
663 match (¶m.kind, arg) {
664 (GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => {
665 self.ast_region_to_region(<, Some(param)).into()
667 (GenericParamDefKind::Type { .. }, GenericArg::Type(ty)) => {
668 self.ast_ty_to_ty(&ty).into()
670 (GenericParamDefKind::Const, GenericArg::Const(ct)) => {
671 self.ast_const_to_const(&ct.value, tcx.type_of(param.def_id)).into()
676 // Provide substitutions for parameters for which arguments are inferred.
677 |substs, param, infer_args| {
679 GenericParamDefKind::Lifetime => tcx.lifetimes.re_static.into(),
680 GenericParamDefKind::Type { has_default, .. } => {
681 if !infer_args && has_default {
682 // No type parameter provided, but a default exists.
684 // If we are converting an object type, then the
685 // `Self` parameter is unknown. However, some of the
686 // other type parameters may reference `Self` in their
687 // defaults. This will lead to an ICE if we are not
689 if default_needs_object_self(param) {
690 struct_span_err!(tcx.sess, span, E0393,
691 "the type parameter `{}` must be explicitly specified",
694 .span_label(span, format!(
695 "missing reference to `{}`", param.name))
697 "because of the default `Self` reference, type parameters \
698 must be specified on object types"))
702 // This is a default type parameter.
705 tcx.at(span).type_of(param.def_id)
706 .subst_spanned(tcx, substs.unwrap(), Some(span))
709 } else if infer_args {
710 // No type parameters were provided, we can infer all.
711 let param = if !default_needs_object_self(param) {
716 self.ty_infer(param, span).into()
718 // We've already errored above about the mismatch.
722 GenericParamDefKind::Const => {
723 // FIXME(const_generics:defaults)
725 // No const parameters were provided, we can infer all.
726 let ty = tcx.at(span).type_of(param.def_id);
727 self.ct_infer(ty, Some(param), span).into()
729 // We've already errored above about the mismatch.
730 tcx.consts.err.into()
737 // Convert associated-type bindings or constraints into a separate vector.
738 // Example: Given this:
740 // T: Iterator<Item = u32>
742 // The `T` is passed in as a self-type; the `Item = u32` is
743 // not a "type parameter" of the `Iterator` trait, but rather
744 // a restriction on `<T as Iterator>::Item`, so it is passed
746 let assoc_bindings = generic_args.bindings.iter()
748 let kind = match binding.kind {
749 hir::TypeBindingKind::Equality { ref ty } =>
750 ConvertedBindingKind::Equality(self.ast_ty_to_ty(ty)),
751 hir::TypeBindingKind::Constraint { ref bounds } =>
752 ConvertedBindingKind::Constraint(bounds),
755 item_name: binding.ident,
762 debug!("create_substs_for_ast_path(generic_params={:?}, self_ty={:?}) -> {:?}",
763 generic_params, self_ty, substs);
765 (substs, assoc_bindings, potential_assoc_types)
768 /// Instantiates the path for the given trait reference, assuming that it's
769 /// bound to a valid trait type. Returns the `DefId` of the defining trait.
770 /// The type _cannot_ be a type other than a trait type.
772 /// If the `projections` argument is `None`, then assoc type bindings like `Foo<T = X>`
773 /// are disallowed. Otherwise, they are pushed onto the vector given.
774 pub fn instantiate_mono_trait_ref(&self,
775 trait_ref: &hir::TraitRef,
777 ) -> ty::TraitRef<'tcx>
779 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
781 self.ast_path_to_mono_trait_ref(trait_ref.path.span,
782 trait_ref.trait_def_id(),
784 trait_ref.path.segments.last().unwrap())
787 /// The given trait-ref must actually be a trait.
788 pub(super) fn instantiate_poly_trait_ref_inner(&self,
789 trait_ref: &hir::TraitRef,
792 bounds: &mut Bounds<'tcx>,
794 ) -> Option<Vec<Span>> {
795 let trait_def_id = trait_ref.trait_def_id();
797 debug!("instantiate_poly_trait_ref({:?}, def_id={:?})", trait_ref, trait_def_id);
799 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
801 let (substs, assoc_bindings, potential_assoc_types) = self.create_substs_for_ast_trait_ref(
805 trait_ref.path.segments.last().unwrap(),
807 let poly_trait_ref = ty::Binder::bind(ty::TraitRef::new(trait_def_id, substs));
809 bounds.trait_bounds.push((poly_trait_ref, span));
811 let mut dup_bindings = FxHashMap::default();
812 for binding in &assoc_bindings {
813 // Specify type to assert that error was already reported in `Err` case.
814 let _: Result<_, ErrorReported> =
815 self.add_predicates_for_ast_type_binding(
816 trait_ref.hir_ref_id,
823 // Okay to ignore `Err` because of `ErrorReported` (see above).
826 debug!("instantiate_poly_trait_ref({:?}, bounds={:?}) -> {:?}",
827 trait_ref, bounds, poly_trait_ref);
828 potential_assoc_types
831 /// Given a trait bound like `Debug`, applies that trait bound the given self-type to construct
832 /// a full trait reference. The resulting trait reference is returned. This may also generate
833 /// auxiliary bounds, which are added to `bounds`.
838 /// poly_trait_ref = Iterator<Item = u32>
842 /// this would return `Foo: Iterator` and add `<Foo as Iterator>::Item = u32` into `bounds`.
844 /// **A note on binders:** against our usual convention, there is an implied bounder around
845 /// the `self_ty` and `poly_trait_ref` parameters here. So they may reference bound regions.
846 /// If for example you had `for<'a> Foo<'a>: Bar<'a>`, then the `self_ty` would be `Foo<'a>`
847 /// where `'a` is a bound region at depth 0. Similarly, the `poly_trait_ref` would be
848 /// `Bar<'a>`. The returned poly-trait-ref will have this binder instantiated explicitly,
850 pub fn instantiate_poly_trait_ref(&self,
851 poly_trait_ref: &hir::PolyTraitRef,
853 bounds: &mut Bounds<'tcx>,
854 ) -> Option<Vec<Span>> {
855 self.instantiate_poly_trait_ref_inner(
856 &poly_trait_ref.trait_ref,
864 fn ast_path_to_mono_trait_ref(&self,
868 trait_segment: &hir::PathSegment
869 ) -> ty::TraitRef<'tcx>
871 let (substs, assoc_bindings, _) =
872 self.create_substs_for_ast_trait_ref(span,
876 assoc_bindings.first().map(|b| AstConv::prohibit_assoc_ty_binding(self.tcx(), b.span));
877 ty::TraitRef::new(trait_def_id, substs)
880 fn create_substs_for_ast_trait_ref<'a>(
885 trait_segment: &'a hir::PathSegment,
886 ) -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'a, 'tcx>>, Option<Vec<Span>>) {
887 debug!("create_substs_for_ast_trait_ref(trait_segment={:?})",
890 let trait_def = self.tcx().trait_def(trait_def_id);
892 if !self.tcx().features().unboxed_closures &&
893 trait_segment.generic_args().parenthesized != trait_def.paren_sugar
895 // For now, require that parenthetical notation be used only with `Fn()` etc.
896 let msg = if trait_def.paren_sugar {
897 "the precise format of `Fn`-family traits' type parameters is subject to change. \
898 Use parenthetical notation (Fn(Foo, Bar) -> Baz) instead"
900 "parenthetical notation is only stable when used with `Fn`-family traits"
902 emit_feature_err(&self.tcx().sess.parse_sess, sym::unboxed_closures,
903 span, GateIssue::Language, msg);
906 self.create_substs_for_ast_path(span,
908 trait_segment.generic_args(),
909 trait_segment.infer_args,
913 fn trait_defines_associated_type_named(&self,
915 assoc_name: ast::Ident)
918 self.tcx().associated_items(trait_def_id).any(|item| {
919 item.kind == ty::AssocKind::Type &&
920 self.tcx().hygienic_eq(assoc_name, item.ident, trait_def_id)
924 // Returns `true` if a bounds list includes `?Sized`.
925 pub fn is_unsized(&self, ast_bounds: &[hir::GenericBound], span: Span) -> bool {
926 let tcx = self.tcx();
928 // Try to find an unbound in bounds.
929 let mut unbound = None;
930 for ab in ast_bounds {
931 if let &hir::GenericBound::Trait(ref ptr, hir::TraitBoundModifier::Maybe) = ab {
932 if unbound.is_none() {
933 unbound = Some(&ptr.trait_ref);
939 "type parameter has more than one relaxed default \
940 bound, only one is supported"
946 let kind_id = tcx.lang_items().require(SizedTraitLangItem);
949 // FIXME(#8559) currently requires the unbound to be built-in.
950 if let Ok(kind_id) = kind_id {
951 if tpb.path.res != Res::Def(DefKind::Trait, kind_id) {
954 "default bound relaxed for a type parameter, but \
955 this does nothing because the given bound is not \
956 a default. Only `?Sized` is supported",
961 _ if kind_id.is_ok() => {
964 // No lang item for `Sized`, so we can't add it as a bound.
971 /// This helper takes a *converted* parameter type (`param_ty`)
972 /// and an *unconverted* list of bounds:
976 /// ^ ^^^^^ `ast_bounds` parameter, in HIR form
978 /// `param_ty`, in ty form
981 /// It adds these `ast_bounds` into the `bounds` structure.
983 /// **A note on binders:** there is an implied binder around
984 /// `param_ty` and `ast_bounds`. See `instantiate_poly_trait_ref`
985 /// for more details.
988 ast_bounds: &[hir::GenericBound],
989 bounds: &mut Bounds<'tcx>,
991 let mut trait_bounds = Vec::new();
992 let mut region_bounds = Vec::new();
994 for ast_bound in ast_bounds {
996 hir::GenericBound::Trait(ref b, hir::TraitBoundModifier::None) =>
997 trait_bounds.push(b),
998 hir::GenericBound::Trait(_, hir::TraitBoundModifier::Maybe) => {}
999 hir::GenericBound::Outlives(ref l) =>
1000 region_bounds.push(l),
1004 for bound in trait_bounds {
1005 let _ = self.instantiate_poly_trait_ref(
1012 bounds.region_bounds.extend(region_bounds
1014 .map(|r| (self.ast_region_to_region(r, None), r.span))
1018 /// Translates a list of bounds from the HIR into the `Bounds` data structure.
1019 /// The self-type for the bounds is given by `param_ty`.
1024 /// fn foo<T: Bar + Baz>() { }
1025 /// ^ ^^^^^^^^^ ast_bounds
1029 /// The `sized_by_default` parameter indicates if, in this context, the `param_ty` should be
1030 /// considered `Sized` unless there is an explicit `?Sized` bound. This would be true in the
1031 /// example above, but is not true in supertrait listings like `trait Foo: Bar + Baz`.
1033 /// `span` should be the declaration size of the parameter.
1034 pub fn compute_bounds(&self,
1036 ast_bounds: &[hir::GenericBound],
1037 sized_by_default: SizedByDefault,
1040 let mut bounds = Bounds::default();
1042 self.add_bounds(param_ty, ast_bounds, &mut bounds);
1043 bounds.trait_bounds.sort_by_key(|(t, _)| t.def_id());
1045 bounds.implicitly_sized = if let SizedByDefault::Yes = sized_by_default {
1046 if !self.is_unsized(ast_bounds, span) {
1058 /// Given an HIR binding like `Item = Foo` or `Item: Foo`, pushes the corresponding predicates
1061 /// **A note on binders:** given something like `T: for<'a> Iterator<Item = &'a u32>`, the
1062 /// `trait_ref` here will be `for<'a> T: Iterator`. The `binding` data however is from *inside*
1063 /// the binder (e.g., `&'a u32`) and hence may reference bound regions.
1064 fn add_predicates_for_ast_type_binding(
1066 hir_ref_id: hir::HirId,
1067 trait_ref: ty::PolyTraitRef<'tcx>,
1068 binding: &ConvertedBinding<'_, 'tcx>,
1069 bounds: &mut Bounds<'tcx>,
1071 dup_bindings: &mut FxHashMap<DefId, Span>,
1072 ) -> Result<(), ErrorReported> {
1073 let tcx = self.tcx();
1076 // Given something like `U: SomeTrait<T = X>`, we want to produce a
1077 // predicate like `<U as SomeTrait>::T = X`. This is somewhat
1078 // subtle in the event that `T` is defined in a supertrait of
1079 // `SomeTrait`, because in that case we need to upcast.
1081 // That is, consider this case:
1084 // trait SubTrait: SuperTrait<int> { }
1085 // trait SuperTrait<A> { type T; }
1087 // ... B: SubTrait<T = foo> ...
1090 // We want to produce `<B as SuperTrait<int>>::T == foo`.
1092 // Find any late-bound regions declared in `ty` that are not
1093 // declared in the trait-ref. These are not well-formed.
1097 // for<'a> <T as Iterator>::Item = &'a str // <-- 'a is bad
1098 // for<'a> <T as FnMut<(&'a u32,)>>::Output = &'a str // <-- 'a is ok
1099 if let ConvertedBindingKind::Equality(ty) = binding.kind {
1100 let late_bound_in_trait_ref =
1101 tcx.collect_constrained_late_bound_regions(&trait_ref);
1102 let late_bound_in_ty =
1103 tcx.collect_referenced_late_bound_regions(&ty::Binder::bind(ty));
1104 debug!("late_bound_in_trait_ref = {:?}", late_bound_in_trait_ref);
1105 debug!("late_bound_in_ty = {:?}", late_bound_in_ty);
1106 for br in late_bound_in_ty.difference(&late_bound_in_trait_ref) {
1107 let br_name = match *br {
1108 ty::BrNamed(_, name) => name,
1112 "anonymous bound region {:?} in binding but not trait ref",
1116 struct_span_err!(tcx.sess,
1119 "binding for associated type `{}` references lifetime `{}`, \
1120 which does not appear in the trait input types",
1121 binding.item_name, br_name)
1127 let candidate = if self.trait_defines_associated_type_named(trait_ref.def_id(),
1128 binding.item_name) {
1129 // Simple case: X is defined in the current trait.
1132 // Otherwise, we have to walk through the supertraits to find
1134 let candidates = traits::supertraits(tcx, trait_ref).filter(|r| {
1135 self.trait_defines_associated_type_named(r.def_id(), binding.item_name)
1137 self.one_bound_for_assoc_type(candidates, &trait_ref.to_string(),
1138 binding.item_name, binding.span)
1141 let (assoc_ident, def_scope) =
1142 tcx.adjust_ident_and_get_scope(binding.item_name, candidate.def_id(), hir_ref_id);
1143 let assoc_ty = tcx.associated_items(candidate.def_id()).find(|i| {
1144 i.kind == ty::AssocKind::Type && i.ident.modern() == assoc_ident
1145 }).expect("missing associated type");
1147 if !assoc_ty.vis.is_accessible_from(def_scope, tcx) {
1148 let msg = format!("associated type `{}` is private", binding.item_name);
1149 tcx.sess.span_err(binding.span, &msg);
1151 tcx.check_stability(assoc_ty.def_id, Some(hir_ref_id), binding.span);
1154 dup_bindings.entry(assoc_ty.def_id)
1155 .and_modify(|prev_span| {
1156 struct_span_err!(self.tcx().sess, binding.span, E0719,
1157 "the value of the associated type `{}` (from the trait `{}`) \
1158 is already specified",
1160 tcx.def_path_str(assoc_ty.container.id()))
1161 .span_label(binding.span, "re-bound here")
1162 .span_label(*prev_span, format!("`{}` bound here first", binding.item_name))
1165 .or_insert(binding.span);
1168 match binding.kind {
1169 ConvertedBindingKind::Equality(ref ty) => {
1170 // "Desugar" a constraint like `T: Iterator<Item = u32>` this to
1171 // the "projection predicate" for:
1173 // `<T as Iterator>::Item = u32`
1174 bounds.projection_bounds.push((candidate.map_bound(|trait_ref| {
1175 ty::ProjectionPredicate {
1176 projection_ty: ty::ProjectionTy::from_ref_and_name(
1185 ConvertedBindingKind::Constraint(ast_bounds) => {
1186 // "Desugar" a constraint like `T: Iterator<Item: Debug>` to
1188 // `<T as Iterator>::Item: Debug`
1190 // Calling `skip_binder` is okay, because `add_bounds` expects the `param_ty`
1191 // parameter to have a skipped binder.
1192 let param_ty = tcx.mk_projection(assoc_ty.def_id, candidate.skip_binder().substs);
1193 self.add_bounds(param_ty, ast_bounds, bounds);
1199 fn ast_path_to_ty(&self,
1202 item_segment: &hir::PathSegment)
1205 let substs = self.ast_path_substs_for_ty(span, did, item_segment);
1208 self.tcx().at(span).type_of(did).subst(self.tcx(), substs)
1212 /// Transform a `PolyTraitRef` into a `PolyExistentialTraitRef` by
1213 /// removing the dummy `Self` type (`trait_object_dummy_self`).
1214 fn trait_ref_to_existential(&self, trait_ref: ty::TraitRef<'tcx>)
1215 -> ty::ExistentialTraitRef<'tcx> {
1216 if trait_ref.self_ty() != self.tcx().types.trait_object_dummy_self {
1217 bug!("trait_ref_to_existential called on {:?} with non-dummy Self", trait_ref);
1219 ty::ExistentialTraitRef::erase_self_ty(self.tcx(), trait_ref)
1222 fn conv_object_ty_poly_trait_ref(&self,
1224 trait_bounds: &[hir::PolyTraitRef],
1225 lifetime: &hir::Lifetime)
1228 let tcx = self.tcx();
1230 let mut bounds = Bounds::default();
1231 let mut potential_assoc_types = Vec::new();
1232 let dummy_self = self.tcx().types.trait_object_dummy_self;
1233 for trait_bound in trait_bounds.iter().rev() {
1234 let cur_potential_assoc_types = self.instantiate_poly_trait_ref(
1239 potential_assoc_types.extend(cur_potential_assoc_types.into_iter().flatten());
1242 // Expand trait aliases recursively and check that only one regular (non-auto) trait
1243 // is used and no 'maybe' bounds are used.
1244 let expanded_traits =
1245 traits::expand_trait_aliases(tcx, bounds.trait_bounds.iter().cloned());
1246 let (mut auto_traits, regular_traits): (Vec<_>, Vec<_>) =
1247 expanded_traits.partition(|i| tcx.trait_is_auto(i.trait_ref().def_id()));
1248 if regular_traits.len() > 1 {
1249 let first_trait = ®ular_traits[0];
1250 let additional_trait = ®ular_traits[1];
1251 let mut err = struct_span_err!(tcx.sess, additional_trait.bottom().1, E0225,
1252 "only auto traits can be used as additional traits in a trait object"
1254 additional_trait.label_with_exp_info(&mut err,
1255 "additional non-auto trait", "additional use");
1256 first_trait.label_with_exp_info(&mut err,
1257 "first non-auto trait", "first use");
1261 if regular_traits.is_empty() && auto_traits.is_empty() {
1262 span_err!(tcx.sess, span, E0224,
1263 "at least one trait is required for an object type");
1264 return tcx.types.err;
1267 // Check that there are no gross object safety violations;
1268 // most importantly, that the supertraits don't contain `Self`,
1270 for item in ®ular_traits {
1271 let object_safety_violations =
1272 tcx.astconv_object_safety_violations(item.trait_ref().def_id());
1273 if !object_safety_violations.is_empty() {
1274 tcx.report_object_safety_error(
1276 item.trait_ref().def_id(),
1277 object_safety_violations
1279 .map(|mut err| err.emit());
1280 return tcx.types.err;
1284 // Use a `BTreeSet` to keep output in a more consistent order.
1285 let mut associated_types = BTreeSet::default();
1287 let regular_traits_refs = bounds.trait_bounds
1289 .filter(|(trait_ref, _)| !tcx.trait_is_auto(trait_ref.def_id()))
1290 .map(|(trait_ref, _)| trait_ref);
1291 for trait_ref in traits::elaborate_trait_refs(tcx, regular_traits_refs) {
1292 debug!("conv_object_ty_poly_trait_ref: observing object predicate `{:?}`", trait_ref);
1294 ty::Predicate::Trait(pred) => {
1296 .extend(tcx.associated_items(pred.def_id())
1297 .filter(|item| item.kind == ty::AssocKind::Type)
1298 .map(|item| item.def_id));
1300 ty::Predicate::Projection(pred) => {
1301 // A `Self` within the original bound will be substituted with a
1302 // `trait_object_dummy_self`, so check for that.
1303 let references_self =
1304 pred.skip_binder().ty.walk().any(|t| t == dummy_self);
1306 // If the projection output contains `Self`, force the user to
1307 // elaborate it explicitly to avoid a lot of complexity.
1309 // The "classicaly useful" case is the following:
1311 // trait MyTrait: FnMut() -> <Self as MyTrait>::MyOutput {
1316 // Here, the user could theoretically write `dyn MyTrait<Output = X>`,
1317 // but actually supporting that would "expand" to an infinitely-long type
1318 // `fix $ τ → dyn MyTrait<MyOutput = X, Output = <τ as MyTrait>::MyOutput`.
1320 // Instead, we force the user to write `dyn MyTrait<MyOutput = X, Output = X>`,
1321 // which is uglier but works. See the discussion in #56288 for alternatives.
1322 if !references_self {
1323 // Include projections defined on supertraits.
1324 bounds.projection_bounds.push((pred, DUMMY_SP))
1331 for (projection_bound, _) in &bounds.projection_bounds {
1332 associated_types.remove(&projection_bound.projection_def_id());
1335 if !associated_types.is_empty() {
1336 let names = associated_types.iter().map(|item_def_id| {
1337 let assoc_item = tcx.associated_item(*item_def_id);
1338 let trait_def_id = assoc_item.container.id();
1340 "`{}` (from the trait `{}`)",
1342 tcx.def_path_str(trait_def_id),
1344 }).collect::<Vec<_>>().join(", ");
1345 let mut err = struct_span_err!(
1349 "the value of the associated type{} {} must be specified",
1350 pluralise!(associated_types.len()),
1353 let (suggest, potential_assoc_types_spans) =
1354 if potential_assoc_types.len() == associated_types.len() {
1355 // Only suggest when the amount of missing associated types equals the number of
1356 // extra type arguments present, as that gives us a relatively high confidence
1357 // that the user forgot to give the associtated type's name. The canonical
1358 // example would be trying to use `Iterator<isize>` instead of
1359 // `Iterator<Item = isize>`.
1360 (true, potential_assoc_types)
1364 let mut suggestions = Vec::new();
1365 for (i, item_def_id) in associated_types.iter().enumerate() {
1366 let assoc_item = tcx.associated_item(*item_def_id);
1369 format!("associated type `{}` must be specified", assoc_item.ident),
1371 if item_def_id.is_local() {
1373 tcx.def_span(*item_def_id),
1374 format!("`{}` defined here", assoc_item.ident),
1378 if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(
1379 potential_assoc_types_spans[i],
1382 potential_assoc_types_spans[i],
1383 format!("{} = {}", assoc_item.ident, snippet),
1388 if !suggestions.is_empty() {
1389 let msg = format!("if you meant to specify the associated {}, write",
1390 if suggestions.len() == 1 { "type" } else { "types" });
1391 err.multipart_suggestion(
1394 Applicability::MaybeIncorrect,
1400 // De-duplicate auto traits so that, e.g., `dyn Trait + Send + Send` is the same as
1401 // `dyn Trait + Send`.
1402 auto_traits.sort_by_key(|i| i.trait_ref().def_id());
1403 auto_traits.dedup_by_key(|i| i.trait_ref().def_id());
1404 debug!("regular_traits: {:?}", regular_traits);
1405 debug!("auto_traits: {:?}", auto_traits);
1407 // Erase the `dummy_self` (`trait_object_dummy_self`) used above.
1408 let existential_trait_refs = regular_traits.iter().map(|i| {
1409 i.trait_ref().map_bound(|trait_ref| self.trait_ref_to_existential(trait_ref))
1411 let existential_projections = bounds.projection_bounds.iter().map(|(bound, _)| {
1412 bound.map_bound(|b| {
1413 let trait_ref = self.trait_ref_to_existential(b.projection_ty.trait_ref(tcx));
1414 ty::ExistentialProjection {
1416 item_def_id: b.projection_ty.item_def_id,
1417 substs: trait_ref.substs,
1422 // Calling `skip_binder` is okay because the predicates are re-bound.
1423 let regular_trait_predicates = existential_trait_refs.map(
1424 |trait_ref| ty::ExistentialPredicate::Trait(*trait_ref.skip_binder()));
1425 let auto_trait_predicates = auto_traits.into_iter().map(
1426 |trait_ref| ty::ExistentialPredicate::AutoTrait(trait_ref.trait_ref().def_id()));
1428 regular_trait_predicates
1429 .chain(auto_trait_predicates)
1430 .chain(existential_projections
1431 .map(|x| ty::ExistentialPredicate::Projection(*x.skip_binder())))
1432 .collect::<SmallVec<[_; 8]>>();
1433 v.sort_by(|a, b| a.stable_cmp(tcx, b));
1435 let existential_predicates = ty::Binder::bind(tcx.mk_existential_predicates(v.into_iter()));
1437 // Use explicitly-specified region bound.
1438 let region_bound = if !lifetime.is_elided() {
1439 self.ast_region_to_region(lifetime, None)
1441 self.compute_object_lifetime_bound(span, existential_predicates).unwrap_or_else(|| {
1442 if tcx.named_region(lifetime.hir_id).is_some() {
1443 self.ast_region_to_region(lifetime, None)
1445 self.re_infer(None, span).unwrap_or_else(|| {
1446 span_err!(tcx.sess, span, E0228,
1447 "the lifetime bound for this object type cannot be deduced \
1448 from context; please supply an explicit bound");
1449 tcx.lifetimes.re_static
1454 debug!("region_bound: {:?}", region_bound);
1456 let ty = tcx.mk_dynamic(existential_predicates, region_bound);
1457 debug!("trait_object_type: {:?}", ty);
1461 fn report_ambiguous_associated_type(
1468 let mut err = struct_span_err!(self.tcx().sess, span, E0223, "ambiguous associated type");
1469 if let (Some(_), Ok(snippet)) = (
1470 self.tcx().sess.confused_type_with_std_module.borrow().get(&span),
1471 self.tcx().sess.source_map().span_to_snippet(span),
1473 err.span_suggestion(
1475 "you are looking for the module in `std`, not the primitive type",
1476 format!("std::{}", snippet),
1477 Applicability::MachineApplicable,
1480 err.span_suggestion(
1482 "use fully-qualified syntax",
1483 format!("<{} as {}>::{}", type_str, trait_str, name),
1484 Applicability::HasPlaceholders
1490 // Search for a bound on a type parameter which includes the associated item
1491 // given by `assoc_name`. `ty_param_def_id` is the `DefId` of the type parameter
1492 // This function will fail if there are no suitable bounds or there is
1494 fn find_bound_for_assoc_item(&self,
1495 ty_param_def_id: DefId,
1496 assoc_name: ast::Ident,
1498 -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
1500 let tcx = self.tcx();
1503 "find_bound_for_assoc_item(ty_param_def_id={:?}, assoc_name={:?}, span={:?})",
1509 let predicates = &self.get_type_parameter_bounds(span, ty_param_def_id).predicates;
1511 debug!("find_bound_for_assoc_item: predicates={:#?}", predicates);
1513 let bounds = predicates.iter().filter_map(|(p, _)| p.to_opt_poly_trait_ref());
1515 // Check that there is exactly one way to find an associated type with the
1517 let suitable_bounds = traits::transitive_bounds(tcx, bounds)
1518 .filter(|b| self.trait_defines_associated_type_named(b.def_id(), assoc_name));
1520 let param_hir_id = tcx.hir().as_local_hir_id(ty_param_def_id).unwrap();
1521 let param_name = tcx.hir().ty_param_name(param_hir_id);
1522 self.one_bound_for_assoc_type(suitable_bounds,
1523 ¶m_name.as_str(),
1528 // Checks that `bounds` contains exactly one element and reports appropriate
1529 // errors otherwise.
1530 fn one_bound_for_assoc_type<I>(&self,
1532 ty_param_name: &str,
1533 assoc_name: ast::Ident,
1535 -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
1536 where I: Iterator<Item = ty::PolyTraitRef<'tcx>>
1538 let bound = match bounds.next() {
1539 Some(bound) => bound,
1541 struct_span_err!(self.tcx().sess, span, E0220,
1542 "associated type `{}` not found for `{}`",
1545 .span_label(span, format!("associated type `{}` not found", assoc_name))
1547 return Err(ErrorReported);
1551 debug!("one_bound_for_assoc_type: bound = {:?}", bound);
1553 if let Some(bound2) = bounds.next() {
1554 debug!("one_bound_for_assoc_type: bound2 = {:?}", bound2);
1556 let bounds = iter::once(bound).chain(iter::once(bound2)).chain(bounds);
1557 let mut err = struct_span_err!(
1558 self.tcx().sess, span, E0221,
1559 "ambiguous associated type `{}` in bounds of `{}`",
1562 err.span_label(span, format!("ambiguous associated type `{}`", assoc_name));
1564 for bound in bounds {
1565 let bound_span = self.tcx().associated_items(bound.def_id()).find(|item| {
1566 item.kind == ty::AssocKind::Type &&
1567 self.tcx().hygienic_eq(assoc_name, item.ident, bound.def_id())
1569 .and_then(|item| self.tcx().hir().span_if_local(item.def_id));
1571 if let Some(span) = bound_span {
1572 err.span_label(span, format!("ambiguous `{}` from `{}`",
1576 span_note!(&mut err, span,
1577 "associated type `{}` could derive from `{}`",
1588 // Create a type from a path to an associated type.
1589 // For a path `A::B::C::D`, `qself_ty` and `qself_def` are the type and def for `A::B::C`
1590 // and item_segment is the path segment for `D`. We return a type and a def for
1592 // Will fail except for `T::A` and `Self::A`; i.e., if `qself_ty`/`qself_def` are not a type
1593 // parameter or `Self`.
1594 pub fn associated_path_to_ty(
1596 hir_ref_id: hir::HirId,
1600 assoc_segment: &hir::PathSegment,
1601 permit_variants: bool,
1602 ) -> Result<(Ty<'tcx>, DefKind, DefId), ErrorReported> {
1603 let tcx = self.tcx();
1604 let assoc_ident = assoc_segment.ident;
1606 debug!("associated_path_to_ty: {:?}::{}", qself_ty, assoc_ident);
1608 self.prohibit_generics(slice::from_ref(assoc_segment));
1610 // Check if we have an enum variant.
1611 let mut variant_resolution = None;
1612 if let ty::Adt(adt_def, _) = qself_ty.kind {
1613 if adt_def.is_enum() {
1614 let variant_def = adt_def.variants.iter().find(|vd| {
1615 tcx.hygienic_eq(assoc_ident, vd.ident, adt_def.did)
1617 if let Some(variant_def) = variant_def {
1618 if permit_variants {
1619 tcx.check_stability(variant_def.def_id, Some(hir_ref_id), span);
1620 return Ok((qself_ty, DefKind::Variant, variant_def.def_id));
1622 variant_resolution = Some(variant_def.def_id);
1628 // Find the type of the associated item, and the trait where the associated
1629 // item is declared.
1630 let bound = match (&qself_ty.kind, qself_res) {
1631 (_, Res::SelfTy(Some(_), Some(impl_def_id))) => {
1632 // `Self` in an impl of a trait -- we have a concrete self type and a
1634 let trait_ref = match tcx.impl_trait_ref(impl_def_id) {
1635 Some(trait_ref) => trait_ref,
1637 // A cycle error occurred, most likely.
1638 return Err(ErrorReported);
1642 let candidates = traits::supertraits(tcx, ty::Binder::bind(trait_ref))
1643 .filter(|r| self.trait_defines_associated_type_named(r.def_id(), assoc_ident));
1645 self.one_bound_for_assoc_type(candidates, "Self", assoc_ident, span)?
1647 (&ty::Param(_), Res::SelfTy(Some(param_did), None)) |
1648 (&ty::Param(_), Res::Def(DefKind::TyParam, param_did)) => {
1649 self.find_bound_for_assoc_item(param_did, assoc_ident, span)?
1652 if variant_resolution.is_some() {
1653 // Variant in type position
1654 let msg = format!("expected type, found variant `{}`", assoc_ident);
1655 tcx.sess.span_err(span, &msg);
1656 } else if qself_ty.is_enum() {
1657 let mut err = tcx.sess.struct_span_err(
1659 &format!("no variant `{}` in enum `{}`", assoc_ident, qself_ty),
1662 let adt_def = qself_ty.ty_adt_def().expect("enum is not an ADT");
1663 if let Some(suggested_name) = find_best_match_for_name(
1664 adt_def.variants.iter().map(|variant| &variant.ident.name),
1665 &assoc_ident.as_str(),
1668 err.span_suggestion(
1670 "there is a variant with a similar name",
1671 suggested_name.to_string(),
1672 Applicability::MaybeIncorrect,
1677 format!("variant not found in `{}`", qself_ty),
1681 if let Some(sp) = tcx.hir().span_if_local(adt_def.did) {
1682 let sp = tcx.sess.source_map().def_span(sp);
1683 err.span_label(sp, format!("variant `{}` not found here", assoc_ident));
1687 } else if !qself_ty.references_error() {
1688 // Don't print `TyErr` to the user.
1689 self.report_ambiguous_associated_type(
1691 &qself_ty.to_string(),
1696 return Err(ErrorReported);
1700 let trait_did = bound.def_id();
1701 let (assoc_ident, def_scope) =
1702 tcx.adjust_ident_and_get_scope(assoc_ident, trait_did, hir_ref_id);
1703 let item = tcx.associated_items(trait_did).find(|i| {
1704 Namespace::from(i.kind) == Namespace::Type &&
1705 i.ident.modern() == assoc_ident
1706 }).expect("missing associated type");
1708 let ty = self.projected_ty_from_poly_trait_ref(span, item.def_id, bound);
1709 let ty = self.normalize_ty(span, ty);
1711 let kind = DefKind::AssocTy;
1712 if !item.vis.is_accessible_from(def_scope, tcx) {
1713 let msg = format!("{} `{}` is private", kind.descr(item.def_id), assoc_ident);
1714 tcx.sess.span_err(span, &msg);
1716 tcx.check_stability(item.def_id, Some(hir_ref_id), span);
1718 if let Some(variant_def_id) = variant_resolution {
1719 let mut err = tcx.struct_span_lint_hir(
1720 AMBIGUOUS_ASSOCIATED_ITEMS,
1723 "ambiguous associated item",
1726 let mut could_refer_to = |kind: DefKind, def_id, also| {
1727 let note_msg = format!("`{}` could{} refer to {} defined here",
1728 assoc_ident, also, kind.descr(def_id));
1729 err.span_note(tcx.def_span(def_id), ¬e_msg);
1731 could_refer_to(DefKind::Variant, variant_def_id, "");
1732 could_refer_to(kind, item.def_id, " also");
1734 err.span_suggestion(
1736 "use fully-qualified syntax",
1737 format!("<{} as {}>::{}", qself_ty, tcx.item_name(trait_did), assoc_ident),
1738 Applicability::MachineApplicable,
1742 Ok((ty, kind, item.def_id))
1745 fn qpath_to_ty(&self,
1747 opt_self_ty: Option<Ty<'tcx>>,
1749 trait_segment: &hir::PathSegment,
1750 item_segment: &hir::PathSegment)
1753 let tcx = self.tcx();
1754 let trait_def_id = tcx.parent(item_def_id).unwrap();
1756 self.prohibit_generics(slice::from_ref(item_segment));
1758 let self_ty = if let Some(ty) = opt_self_ty {
1761 let path_str = tcx.def_path_str(trait_def_id);
1762 self.report_ambiguous_associated_type(
1766 item_segment.ident.name,
1768 return tcx.types.err;
1771 debug!("qpath_to_ty: self_type={:?}", self_ty);
1773 let trait_ref = self.ast_path_to_mono_trait_ref(span,
1778 debug!("qpath_to_ty: trait_ref={:?}", trait_ref);
1780 self.normalize_ty(span, tcx.mk_projection(item_def_id, trait_ref.substs))
1783 pub fn prohibit_generics<'a, T: IntoIterator<Item = &'a hir::PathSegment>>(
1784 &self, segments: T) -> bool {
1785 let mut has_err = false;
1786 for segment in segments {
1787 let (mut err_for_lt, mut err_for_ty, mut err_for_ct) = (false, false, false);
1788 for arg in &segment.generic_args().args {
1789 let (span, kind) = match arg {
1790 hir::GenericArg::Lifetime(lt) => {
1791 if err_for_lt { continue }
1794 (lt.span, "lifetime")
1796 hir::GenericArg::Type(ty) => {
1797 if err_for_ty { continue }
1802 hir::GenericArg::Const(ct) => {
1803 if err_for_ct { continue }
1808 let mut err = struct_span_err!(
1812 "{} arguments are not allowed for this type",
1815 err.span_label(span, format!("{} argument not allowed", kind));
1817 if err_for_lt && err_for_ty && err_for_ct {
1821 for binding in &segment.generic_args().bindings {
1823 Self::prohibit_assoc_ty_binding(self.tcx(), binding.span);
1830 pub fn prohibit_assoc_ty_binding(tcx: TyCtxt<'_>, span: Span) {
1831 let mut err = struct_span_err!(tcx.sess, span, E0229,
1832 "associated type bindings are not allowed here");
1833 err.span_label(span, "associated type not allowed here").emit();
1836 // FIXME(eddyb, varkor) handle type paths here too, not just value ones.
1837 pub fn def_ids_for_value_path_segments(
1839 segments: &[hir::PathSegment],
1840 self_ty: Option<Ty<'tcx>>,
1844 // We need to extract the type parameters supplied by the user in
1845 // the path `path`. Due to the current setup, this is a bit of a
1846 // tricky-process; the problem is that resolve only tells us the
1847 // end-point of the path resolution, and not the intermediate steps.
1848 // Luckily, we can (at least for now) deduce the intermediate steps
1849 // just from the end-point.
1851 // There are basically five cases to consider:
1853 // 1. Reference to a constructor of a struct:
1855 // struct Foo<T>(...)
1857 // In this case, the parameters are declared in the type space.
1859 // 2. Reference to a constructor of an enum variant:
1861 // enum E<T> { Foo(...) }
1863 // In this case, the parameters are defined in the type space,
1864 // but may be specified either on the type or the variant.
1866 // 3. Reference to a fn item or a free constant:
1870 // In this case, the path will again always have the form
1871 // `a::b::foo::<T>` where only the final segment should have
1872 // type parameters. However, in this case, those parameters are
1873 // declared on a value, and hence are in the `FnSpace`.
1875 // 4. Reference to a method or an associated constant:
1877 // impl<A> SomeStruct<A> {
1881 // Here we can have a path like
1882 // `a::b::SomeStruct::<A>::foo::<B>`, in which case parameters
1883 // may appear in two places. The penultimate segment,
1884 // `SomeStruct::<A>`, contains parameters in TypeSpace, and the
1885 // final segment, `foo::<B>` contains parameters in fn space.
1887 // The first step then is to categorize the segments appropriately.
1889 let tcx = self.tcx();
1891 assert!(!segments.is_empty());
1892 let last = segments.len() - 1;
1894 let mut path_segs = vec![];
1897 // Case 1. Reference to a struct constructor.
1898 DefKind::Ctor(CtorOf::Struct, ..) => {
1899 // Everything but the final segment should have no
1900 // parameters at all.
1901 let generics = tcx.generics_of(def_id);
1902 // Variant and struct constructors use the
1903 // generics of their parent type definition.
1904 let generics_def_id = generics.parent.unwrap_or(def_id);
1905 path_segs.push(PathSeg(generics_def_id, last));
1908 // Case 2. Reference to a variant constructor.
1909 DefKind::Ctor(CtorOf::Variant, ..)
1910 | DefKind::Variant => {
1911 let adt_def = self_ty.map(|t| t.ty_adt_def().unwrap());
1912 let (generics_def_id, index) = if let Some(adt_def) = adt_def {
1913 debug_assert!(adt_def.is_enum());
1915 } else if last >= 1 && segments[last - 1].args.is_some() {
1916 // Everything but the penultimate segment should have no
1917 // parameters at all.
1918 let mut def_id = def_id;
1920 // `DefKind::Ctor` -> `DefKind::Variant`
1921 if let DefKind::Ctor(..) = kind {
1922 def_id = tcx.parent(def_id).unwrap()
1925 // `DefKind::Variant` -> `DefKind::Enum`
1926 let enum_def_id = tcx.parent(def_id).unwrap();
1927 (enum_def_id, last - 1)
1929 // FIXME: lint here recommending `Enum::<...>::Variant` form
1930 // instead of `Enum::Variant::<...>` form.
1932 // Everything but the final segment should have no
1933 // parameters at all.
1934 let generics = tcx.generics_of(def_id);
1935 // Variant and struct constructors use the
1936 // generics of their parent type definition.
1937 (generics.parent.unwrap_or(def_id), last)
1939 path_segs.push(PathSeg(generics_def_id, index));
1942 // Case 3. Reference to a top-level value.
1945 | DefKind::ConstParam
1946 | DefKind::Static => {
1947 path_segs.push(PathSeg(def_id, last));
1950 // Case 4. Reference to a method or associated const.
1952 | DefKind::AssocConst => {
1953 if segments.len() >= 2 {
1954 let generics = tcx.generics_of(def_id);
1955 path_segs.push(PathSeg(generics.parent.unwrap(), last - 1));
1957 path_segs.push(PathSeg(def_id, last));
1960 kind => bug!("unexpected definition kind {:?} for {:?}", kind, def_id),
1963 debug!("path_segs = {:?}", path_segs);
1968 // Check a type `Path` and convert it to a `Ty`.
1969 pub fn res_to_ty(&self,
1970 opt_self_ty: Option<Ty<'tcx>>,
1972 permit_variants: bool)
1974 let tcx = self.tcx();
1976 debug!("res_to_ty(res={:?}, opt_self_ty={:?}, path_segments={:?})",
1977 path.res, opt_self_ty, path.segments);
1979 let span = path.span;
1981 Res::Def(DefKind::OpaqueTy, did) => {
1982 // Check for desugared `impl Trait`.
1983 assert!(ty::is_impl_trait_defn(tcx, did).is_none());
1984 let item_segment = path.segments.split_last().unwrap();
1985 self.prohibit_generics(item_segment.1);
1986 let substs = self.ast_path_substs_for_ty(span, did, item_segment.0);
1989 tcx.mk_opaque(did, substs),
1992 Res::Def(DefKind::Enum, did)
1993 | Res::Def(DefKind::TyAlias, did)
1994 | Res::Def(DefKind::Struct, did)
1995 | Res::Def(DefKind::Union, did)
1996 | Res::Def(DefKind::ForeignTy, did) => {
1997 assert_eq!(opt_self_ty, None);
1998 self.prohibit_generics(path.segments.split_last().unwrap().1);
1999 self.ast_path_to_ty(span, did, path.segments.last().unwrap())
2001 Res::Def(kind @ DefKind::Variant, def_id) if permit_variants => {
2002 // Convert "variant type" as if it were a real type.
2003 // The resulting `Ty` is type of the variant's enum for now.
2004 assert_eq!(opt_self_ty, None);
2007 self.def_ids_for_value_path_segments(&path.segments, None, kind, def_id);
2008 let generic_segs: FxHashSet<_> =
2009 path_segs.iter().map(|PathSeg(_, index)| index).collect();
2010 self.prohibit_generics(path.segments.iter().enumerate().filter_map(|(index, seg)| {
2011 if !generic_segs.contains(&index) {
2018 let PathSeg(def_id, index) = path_segs.last().unwrap();
2019 self.ast_path_to_ty(span, *def_id, &path.segments[*index])
2021 Res::Def(DefKind::TyParam, def_id) => {
2022 assert_eq!(opt_self_ty, None);
2023 self.prohibit_generics(&path.segments);
2025 let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
2026 let item_id = tcx.hir().get_parent_node(hir_id);
2027 let item_def_id = tcx.hir().local_def_id(item_id);
2028 let generics = tcx.generics_of(item_def_id);
2029 let index = generics.param_def_id_to_index[&def_id];
2030 tcx.mk_ty_param(index, tcx.hir().name(hir_id).as_interned_str())
2032 Res::SelfTy(Some(_), None) => {
2033 // `Self` in trait or type alias.
2034 assert_eq!(opt_self_ty, None);
2035 self.prohibit_generics(&path.segments);
2036 tcx.types.self_param
2038 Res::SelfTy(_, Some(def_id)) => {
2039 // `Self` in impl (we know the concrete type).
2040 assert_eq!(opt_self_ty, None);
2041 self.prohibit_generics(&path.segments);
2042 // Try to evaluate any array length constants.
2043 self.normalize_ty(span, tcx.at(span).type_of(def_id))
2045 Res::Def(DefKind::AssocTy, def_id) => {
2046 debug_assert!(path.segments.len() >= 2);
2047 self.prohibit_generics(&path.segments[..path.segments.len() - 2]);
2048 self.qpath_to_ty(span,
2051 &path.segments[path.segments.len() - 2],
2052 path.segments.last().unwrap())
2054 Res::PrimTy(prim_ty) => {
2055 assert_eq!(opt_self_ty, None);
2056 self.prohibit_generics(&path.segments);
2058 hir::Bool => tcx.types.bool,
2059 hir::Char => tcx.types.char,
2060 hir::Int(it) => tcx.mk_mach_int(it),
2061 hir::Uint(uit) => tcx.mk_mach_uint(uit),
2062 hir::Float(ft) => tcx.mk_mach_float(ft),
2063 hir::Str => tcx.mk_str()
2067 self.set_tainted_by_errors();
2068 return self.tcx().types.err;
2070 _ => span_bug!(span, "unexpected resolution: {:?}", path.res)
2074 /// Parses the programmer's textual representation of a type into our
2075 /// internal notion of a type.
2076 pub fn ast_ty_to_ty(&self, ast_ty: &hir::Ty) -> Ty<'tcx> {
2077 debug!("ast_ty_to_ty(id={:?}, ast_ty={:?} ty_ty={:?})",
2078 ast_ty.hir_id, ast_ty, ast_ty.kind);
2080 let tcx = self.tcx();
2082 let result_ty = match ast_ty.kind {
2083 hir::TyKind::Slice(ref ty) => {
2084 tcx.mk_slice(self.ast_ty_to_ty(&ty))
2086 hir::TyKind::Ptr(ref mt) => {
2087 tcx.mk_ptr(ty::TypeAndMut {
2088 ty: self.ast_ty_to_ty(&mt.ty),
2092 hir::TyKind::Rptr(ref region, ref mt) => {
2093 let r = self.ast_region_to_region(region, None);
2094 debug!("ast_ty_to_ty: r={:?}", r);
2095 let t = self.ast_ty_to_ty(&mt.ty);
2096 tcx.mk_ref(r, ty::TypeAndMut {ty: t, mutbl: mt.mutbl})
2098 hir::TyKind::Never => {
2101 hir::TyKind::Tup(ref fields) => {
2102 tcx.mk_tup(fields.iter().map(|t| self.ast_ty_to_ty(&t)))
2104 hir::TyKind::BareFn(ref bf) => {
2105 require_c_abi_if_c_variadic(tcx, &bf.decl, bf.abi, ast_ty.span);
2106 tcx.mk_fn_ptr(self.ty_of_fn(bf.unsafety, bf.abi, &bf.decl))
2108 hir::TyKind::TraitObject(ref bounds, ref lifetime) => {
2109 self.conv_object_ty_poly_trait_ref(ast_ty.span, bounds, lifetime)
2111 hir::TyKind::Path(hir::QPath::Resolved(ref maybe_qself, ref path)) => {
2112 debug!("ast_ty_to_ty: maybe_qself={:?} path={:?}", maybe_qself, path);
2113 let opt_self_ty = maybe_qself.as_ref().map(|qself| {
2114 self.ast_ty_to_ty(qself)
2116 self.res_to_ty(opt_self_ty, path, false)
2118 hir::TyKind::Def(item_id, ref lifetimes) => {
2119 let did = tcx.hir().local_def_id(item_id.id);
2120 self.impl_trait_ty_to_ty(did, lifetimes)
2122 hir::TyKind::Path(hir::QPath::TypeRelative(ref qself, ref segment)) => {
2123 debug!("ast_ty_to_ty: qself={:?} segment={:?}", qself, segment);
2124 let ty = self.ast_ty_to_ty(qself);
2126 let res = if let hir::TyKind::Path(hir::QPath::Resolved(_, ref path)) = qself.kind {
2131 self.associated_path_to_ty(ast_ty.hir_id, ast_ty.span, ty, res, segment, false)
2132 .map(|(ty, _, _)| ty).unwrap_or(tcx.types.err)
2134 hir::TyKind::Array(ref ty, ref length) => {
2135 let length = self.ast_const_to_const(length, tcx.types.usize);
2136 let array_ty = tcx.mk_ty(ty::Array(self.ast_ty_to_ty(&ty), length));
2137 self.normalize_ty(ast_ty.span, array_ty)
2139 hir::TyKind::Typeof(ref _e) => {
2140 struct_span_err!(tcx.sess, ast_ty.span, E0516,
2141 "`typeof` is a reserved keyword but unimplemented")
2142 .span_label(ast_ty.span, "reserved keyword")
2147 hir::TyKind::Infer => {
2148 // Infer also appears as the type of arguments or return
2149 // values in a ExprKind::Closure, or as
2150 // the type of local variables. Both of these cases are
2151 // handled specially and will not descend into this routine.
2152 self.ty_infer(None, ast_ty.span)
2154 hir::TyKind::CVarArgs(lt) => {
2155 let va_list_did = match tcx.lang_items().va_list() {
2157 None => span_bug!(ast_ty.span,
2158 "`va_list` lang item required for variadics"),
2160 let region = self.ast_region_to_region(<, None);
2161 tcx.type_of(va_list_did).subst(tcx, &[region.into()])
2163 hir::TyKind::Err => {
2168 debug!("ast_ty_to_ty: result_ty={:?}", result_ty);
2170 self.record_ty(ast_ty.hir_id, result_ty, ast_ty.span);
2174 /// Returns the `DefId` of the constant parameter that the provided expression is a path to.
2175 pub fn const_param_def_id(&self, expr: &hir::Expr) -> Option<DefId> {
2176 // Unwrap a block, so that e.g. `{ P }` is recognised as a parameter. Const arguments
2177 // currently have to be wrapped in curly brackets, so it's necessary to special-case.
2178 let expr = match &expr.kind {
2179 ExprKind::Block(block, _) if block.stmts.is_empty() && block.expr.is_some() =>
2180 block.expr.as_ref().unwrap(),
2185 ExprKind::Path(hir::QPath::Resolved(_, path)) => match path.res {
2186 Res::Def(DefKind::ConstParam, did) => Some(did),
2193 pub fn ast_const_to_const(
2195 ast_const: &hir::AnonConst,
2197 ) -> &'tcx ty::Const<'tcx> {
2198 debug!("ast_const_to_const(id={:?}, ast_const={:?})", ast_const.hir_id, ast_const);
2200 let tcx = self.tcx();
2201 let def_id = tcx.hir().local_def_id(ast_const.hir_id);
2203 let mut const_ = ty::Const {
2204 val: ConstValue::Unevaluated(
2206 InternalSubsts::identity_for_item(tcx, def_id),
2211 let expr = &tcx.hir().body(ast_const.body).value;
2212 if let Some(def_id) = self.const_param_def_id(expr) {
2213 // Find the name and index of the const parameter by indexing the generics of the
2214 // parent item and construct a `ParamConst`.
2215 let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
2216 let item_id = tcx.hir().get_parent_node(hir_id);
2217 let item_def_id = tcx.hir().local_def_id(item_id);
2218 let generics = tcx.generics_of(item_def_id);
2219 let index = generics.param_def_id_to_index[&tcx.hir().local_def_id(hir_id)];
2220 let name = tcx.hir().name(hir_id).as_interned_str();
2221 const_.val = ConstValue::Param(ty::ParamConst::new(index, name));
2224 tcx.mk_const(const_)
2227 pub fn impl_trait_ty_to_ty(
2230 lifetimes: &[hir::GenericArg],
2232 debug!("impl_trait_ty_to_ty(def_id={:?}, lifetimes={:?})", def_id, lifetimes);
2233 let tcx = self.tcx();
2235 let generics = tcx.generics_of(def_id);
2237 debug!("impl_trait_ty_to_ty: generics={:?}", generics);
2238 let substs = InternalSubsts::for_item(tcx, def_id, |param, _| {
2239 if let Some(i) = (param.index as usize).checked_sub(generics.parent_count) {
2240 // Our own parameters are the resolved lifetimes.
2242 GenericParamDefKind::Lifetime => {
2243 if let hir::GenericArg::Lifetime(lifetime) = &lifetimes[i] {
2244 self.ast_region_to_region(lifetime, None).into()
2252 // Replace all parent lifetimes with `'static`.
2254 GenericParamDefKind::Lifetime => {
2255 tcx.lifetimes.re_static.into()
2257 _ => tcx.mk_param_from_def(param)
2261 debug!("impl_trait_ty_to_ty: substs={:?}", substs);
2263 let ty = tcx.mk_opaque(def_id, substs);
2264 debug!("impl_trait_ty_to_ty: {}", ty);
2268 pub fn ty_of_arg(&self,
2270 expected_ty: Option<Ty<'tcx>>)
2274 hir::TyKind::Infer if expected_ty.is_some() => {
2275 self.record_ty(ty.hir_id, expected_ty.unwrap(), ty.span);
2276 expected_ty.unwrap()
2278 _ => self.ast_ty_to_ty(ty),
2282 pub fn ty_of_fn(&self,
2283 unsafety: hir::Unsafety,
2286 -> ty::PolyFnSig<'tcx> {
2289 let tcx = self.tcx();
2291 decl.inputs.iter().map(|a| self.ty_of_arg(a, None));
2293 let output_ty = match decl.output {
2294 hir::Return(ref output) => self.ast_ty_to_ty(output),
2295 hir::DefaultReturn(..) => tcx.mk_unit(),
2298 debug!("ty_of_fn: output_ty={:?}", output_ty);
2300 let bare_fn_ty = ty::Binder::bind(tcx.mk_fn_sig(
2308 // Find any late-bound regions declared in return type that do
2309 // not appear in the arguments. These are not well-formed.
2312 // for<'a> fn() -> &'a str <-- 'a is bad
2313 // for<'a> fn(&'a String) -> &'a str <-- 'a is ok
2314 let inputs = bare_fn_ty.inputs();
2315 let late_bound_in_args = tcx.collect_constrained_late_bound_regions(
2316 &inputs.map_bound(|i| i.to_owned()));
2317 let output = bare_fn_ty.output();
2318 let late_bound_in_ret = tcx.collect_referenced_late_bound_regions(&output);
2319 for br in late_bound_in_ret.difference(&late_bound_in_args) {
2320 let lifetime_name = match *br {
2321 ty::BrNamed(_, name) => format!("lifetime `{}`,", name),
2322 ty::BrAnon(_) | ty::BrEnv => "an anonymous lifetime".to_string(),
2324 let mut err = struct_span_err!(tcx.sess,
2327 "return type references {} \
2328 which is not constrained by the fn input types",
2330 if let ty::BrAnon(_) = *br {
2331 // The only way for an anonymous lifetime to wind up
2332 // in the return type but **also** be unconstrained is
2333 // if it only appears in "associated types" in the
2334 // input. See #47511 for an example. In this case,
2335 // though we can easily give a hint that ought to be
2337 err.note("lifetimes appearing in an associated type \
2338 are not considered constrained");
2346 /// Given the bounds on an object, determines what single region bound (if any) we can
2347 /// use to summarize this type. The basic idea is that we will use the bound the user
2348 /// provided, if they provided one, and otherwise search the supertypes of trait bounds
2349 /// for region bounds. It may be that we can derive no bound at all, in which case
2350 /// we return `None`.
2351 fn compute_object_lifetime_bound(&self,
2353 existential_predicates: ty::Binder<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>>)
2354 -> Option<ty::Region<'tcx>> // if None, use the default
2356 let tcx = self.tcx();
2358 debug!("compute_opt_region_bound(existential_predicates={:?})",
2359 existential_predicates);
2361 // No explicit region bound specified. Therefore, examine trait
2362 // bounds and see if we can derive region bounds from those.
2363 let derived_region_bounds =
2364 object_region_bounds(tcx, existential_predicates);
2366 // If there are no derived region bounds, then report back that we
2367 // can find no region bound. The caller will use the default.
2368 if derived_region_bounds.is_empty() {
2372 // If any of the derived region bounds are 'static, that is always
2374 if derived_region_bounds.iter().any(|&r| ty::ReStatic == *r) {
2375 return Some(tcx.lifetimes.re_static);
2378 // Determine whether there is exactly one unique region in the set
2379 // of derived region bounds. If so, use that. Otherwise, report an
2381 let r = derived_region_bounds[0];
2382 if derived_region_bounds[1..].iter().any(|r1| r != *r1) {
2383 span_err!(tcx.sess, span, E0227,
2384 "ambiguous lifetime bound, explicit lifetime bound required");
2390 /// Collects together a list of bounds that are applied to some type,
2391 /// after they've been converted into `ty` form (from the HIR
2392 /// representations). These lists of bounds occur in many places in
2396 /// trait Foo: Bar + Baz { }
2397 /// ^^^^^^^^^ supertrait list bounding the `Self` type parameter
2399 /// fn foo<T: Bar + Baz>() { }
2400 /// ^^^^^^^^^ bounding the type parameter `T`
2402 /// impl dyn Bar + Baz
2403 /// ^^^^^^^^^ bounding the forgotten dynamic type
2406 /// Our representation is a bit mixed here -- in some cases, we
2407 /// include the self type (e.g., `trait_bounds`) but in others we do
2408 #[derive(Default, PartialEq, Eq, Clone, Debug)]
2409 pub struct Bounds<'tcx> {
2410 /// A list of region bounds on the (implicit) self type. So if you
2411 /// had `T: 'a + 'b` this might would be a list `['a, 'b]` (but
2412 /// the `T` is not explicitly included).
2413 pub region_bounds: Vec<(ty::Region<'tcx>, Span)>,
2415 /// A list of trait bounds. So if you had `T: Debug` this would be
2416 /// `T: Debug`. Note that the self-type is explicit here.
2417 pub trait_bounds: Vec<(ty::PolyTraitRef<'tcx>, Span)>,
2419 /// A list of projection equality bounds. So if you had `T:
2420 /// Iterator<Item = u32>` this would include `<T as
2421 /// Iterator>::Item => u32`. Note that the self-type is explicit
2423 pub projection_bounds: Vec<(ty::PolyProjectionPredicate<'tcx>, Span)>,
2425 /// `Some` if there is *no* `?Sized` predicate. The `span`
2426 /// is the location in the source of the `T` declaration which can
2427 /// be cited as the source of the `T: Sized` requirement.
2428 pub implicitly_sized: Option<Span>,
2431 impl<'tcx> Bounds<'tcx> {
2432 /// Converts a bounds list into a flat set of predicates (like
2433 /// where-clauses). Because some of our bounds listings (e.g.,
2434 /// regions) don't include the self-type, you must supply the
2435 /// self-type here (the `param_ty` parameter).
2440 ) -> Vec<(ty::Predicate<'tcx>, Span)> {
2441 // If it could be sized, and is, add the `Sized` predicate.
2442 let sized_predicate = self.implicitly_sized.and_then(|span| {
2443 tcx.lang_items().sized_trait().map(|sized| {
2444 let trait_ref = ty::TraitRef {
2446 substs: tcx.mk_substs_trait(param_ty, &[])
2448 (trait_ref.to_predicate(), span)
2452 sized_predicate.into_iter().chain(
2453 self.region_bounds.iter().map(|&(region_bound, span)| {
2454 // Account for the binder being introduced below; no need to shift `param_ty`
2455 // because, at present at least, it can only refer to early-bound regions.
2456 let region_bound = ty::fold::shift_region(tcx, region_bound, 1);
2457 let outlives = ty::OutlivesPredicate(param_ty, region_bound);
2458 (ty::Binder::dummy(outlives).to_predicate(), span)
2460 self.trait_bounds.iter().map(|&(bound_trait_ref, span)| {
2461 (bound_trait_ref.to_predicate(), span)
2464 self.projection_bounds.iter().map(|&(projection, span)| {
2465 (projection.to_predicate(), span)