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 fn item_def_id(&self) -> Option<DefId>;
48 /// Returns predicates in scope of the form `X: Foo`, where `X` is
49 /// a type parameter `X` with the given id `def_id`. This is a
50 /// subset of the full set of predicates.
52 /// This is used for one specific purpose: resolving "short-hand"
53 /// associated type references like `T::Item`. In principle, we
54 /// would do that by first getting the full set of predicates in
55 /// scope and then filtering down to find those that apply to `T`,
56 /// but this can lead to cycle errors. The problem is that we have
57 /// to do this resolution *in order to create the predicates in
58 /// the first place*. Hence, we have this "special pass".
59 fn get_type_parameter_bounds(&self, span: Span, def_id: DefId) -> ty::GenericPredicates<'tcx>;
61 /// Returns the lifetime to use when a lifetime is omitted (and not elided).
64 param: Option<&ty::GenericParamDef>,
67 -> Option<ty::Region<'tcx>>;
69 /// Returns the type to use when a type is omitted.
70 fn ty_infer(&self, param: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx>;
72 /// Returns the const to use when a const is omitted.
76 param: Option<&ty::GenericParamDef>,
78 ) -> &'tcx Const<'tcx>;
80 /// Projecting an associated type from a (potentially)
81 /// higher-ranked trait reference is more complicated, because of
82 /// the possibility of late-bound regions appearing in the
83 /// associated type binding. This is not legal in function
84 /// signatures for that reason. In a function body, we can always
85 /// handle it because we can use inference variables to remove the
86 /// late-bound regions.
87 fn projected_ty_from_poly_trait_ref(&self,
90 poly_trait_ref: ty::PolyTraitRef<'tcx>)
93 /// Normalize an associated type coming from the user.
94 fn normalize_ty(&self, span: Span, ty: Ty<'tcx>) -> Ty<'tcx>;
96 /// Invoked when we encounter an error from some prior pass
97 /// (e.g., resolve) that is translated into a ty-error. This is
98 /// used to help suppress derived errors typeck might otherwise
100 fn set_tainted_by_errors(&self);
102 fn record_ty(&self, hir_id: hir::HirId, ty: Ty<'tcx>, span: Span);
105 pub enum SizedByDefault {
110 struct ConvertedBinding<'a, 'tcx> {
111 item_name: ast::Ident,
112 kind: ConvertedBindingKind<'a, 'tcx>,
116 enum ConvertedBindingKind<'a, 'tcx> {
118 Constraint(&'a [hir::GenericBound]),
122 enum GenericArgPosition {
124 Value, // e.g., functions
128 impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
129 pub fn ast_region_to_region(&self,
130 lifetime: &hir::Lifetime,
131 def: Option<&ty::GenericParamDef>)
134 let tcx = self.tcx();
135 let lifetime_name = |def_id| {
136 tcx.hir().name(tcx.hir().as_local_hir_id(def_id).unwrap())
139 let r = match tcx.named_region(lifetime.hir_id) {
140 Some(rl::Region::Static) => {
141 tcx.lifetimes.re_static
144 Some(rl::Region::LateBound(debruijn, id, _)) => {
145 let name = lifetime_name(id);
146 tcx.mk_region(ty::ReLateBound(debruijn,
147 ty::BrNamed(id, name)))
150 Some(rl::Region::LateBoundAnon(debruijn, index)) => {
151 tcx.mk_region(ty::ReLateBound(debruijn, ty::BrAnon(index)))
154 Some(rl::Region::EarlyBound(index, id, _)) => {
155 let name = lifetime_name(id);
156 tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion {
163 Some(rl::Region::Free(scope, id)) => {
164 let name = lifetime_name(id);
165 tcx.mk_region(ty::ReFree(ty::FreeRegion {
167 bound_region: ty::BrNamed(id, name)
170 // (*) -- not late-bound, won't change
174 self.re_infer(def, lifetime.span)
176 // This indicates an illegal lifetime
177 // elision. `resolve_lifetime` should have
178 // reported an error in this case -- but if
179 // not, let's error out.
180 tcx.sess.delay_span_bug(lifetime.span, "unelided lifetime in signature");
182 // Supply some dummy value. We don't have an
183 // `re_error`, annoyingly, so use `'static`.
184 tcx.lifetimes.re_static
189 debug!("ast_region_to_region(lifetime={:?}) yields {:?}",
196 /// Given a path `path` that refers to an item `I` with the declared generics `decl_generics`,
197 /// returns an appropriate set of substitutions for this particular reference to `I`.
198 pub fn ast_path_substs_for_ty(&self,
201 item_segment: &hir::PathSegment)
204 let (substs, assoc_bindings, _) = self.create_substs_for_ast_path(
207 item_segment.generic_args(),
208 item_segment.infer_args,
212 assoc_bindings.first().map(|b| Self::prohibit_assoc_ty_binding(self.tcx(), b.span));
217 /// 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 {
233 seg.generic_args().args
237 GenericArg::Type(_) => Some(arg.span()),
240 .collect::<Vec<_>>();
242 let mut err = struct_span_err! {
246 "cannot provide explicit generic arguments when `impl Trait` is \
247 used in argument position"
251 err.span_label(span, "explicit generic argument not allowed");
260 /// Checks that the correct number of generic arguments have been provided.
261 /// Used specifically for function calls.
262 pub fn check_generic_arg_count_for_call(
266 seg: &hir::PathSegment,
267 is_method_call: bool,
269 let empty_args = P(hir::GenericArgs {
270 args: HirVec::new(), bindings: HirVec::new(), parenthesized: false,
272 let suppress_mismatch = Self::check_impl_trait(tcx, seg, &def);
273 Self::check_generic_arg_count(
277 if let Some(ref args) = seg.args {
283 GenericArgPosition::MethodCall
285 GenericArgPosition::Value
287 def.parent.is_none() && def.has_self, // `has_self`
288 seg.infer_args || suppress_mismatch, // `infer_args`
292 /// Checks that the correct number of generic arguments have been provided.
293 /// This is used both for datatypes and function calls.
294 fn check_generic_arg_count(
298 args: &hir::GenericArgs,
299 position: GenericArgPosition,
302 ) -> (bool, Option<Vec<Span>>) {
303 // At this stage we are guaranteed that the generic arguments are in the correct order, e.g.
304 // that lifetimes will proceed types. So it suffices to check the number of each generic
305 // arguments in order to validate them with respect to the generic parameters.
306 let param_counts = def.own_counts();
307 let arg_counts = args.own_counts();
308 let infer_lifetimes = position != GenericArgPosition::Type && arg_counts.lifetimes == 0;
310 let mut defaults: ty::GenericParamCount = Default::default();
311 for param in &def.params {
313 GenericParamDefKind::Lifetime => {}
314 GenericParamDefKind::Type { has_default, .. } => {
315 defaults.types += has_default as usize
317 GenericParamDefKind::Const => {
318 // FIXME(const_generics:defaults)
323 if position != GenericArgPosition::Type && !args.bindings.is_empty() {
324 AstConv::prohibit_assoc_ty_binding(tcx, args.bindings[0].span);
327 // Prohibit explicit lifetime arguments if late-bound lifetime parameters are present.
328 let mut reported_late_bound_region_err = None;
329 if !infer_lifetimes {
330 if let Some(span_late) = def.has_late_bound_regions {
331 let msg = "cannot specify lifetime arguments explicitly \
332 if late bound lifetime parameters are present";
333 let note = "the late bound lifetime parameter is introduced here";
334 let span = args.args[0].span();
335 if position == GenericArgPosition::Value
336 && arg_counts.lifetimes != param_counts.lifetimes {
337 let mut err = tcx.sess.struct_span_err(span, msg);
338 err.span_note(span_late, note);
340 reported_late_bound_region_err = Some(true);
342 let mut multispan = MultiSpan::from_span(span);
343 multispan.push_span_label(span_late, note.to_string());
344 tcx.lint_hir(lint::builtin::LATE_BOUND_LIFETIME_ARGUMENTS,
345 args.args[0].id(), multispan, msg);
346 reported_late_bound_region_err = Some(false);
351 let check_kind_count = |kind, required, permitted, provided, offset| {
353 "check_kind_count: kind: {} required: {} permitted: {} provided: {} offset: {}",
360 // We enforce the following: `required` <= `provided` <= `permitted`.
361 // For kinds without defaults (e.g.., lifetimes), `required == permitted`.
362 // For other kinds (i.e., types), `permitted` may be greater than `required`.
363 if required <= provided && provided <= permitted {
364 return (reported_late_bound_region_err.unwrap_or(false), None);
367 // Unfortunately lifetime and type parameter mismatches are typically styled
368 // differently in diagnostics, which means we have a few cases to consider here.
369 let (bound, quantifier) = if required != permitted {
370 if provided < required {
371 (required, "at least ")
372 } else { // provided > permitted
373 (permitted, "at most ")
379 let mut potential_assoc_types: Option<Vec<Span>> = None;
380 let (spans, label) = if required == permitted && provided > permitted {
381 // In the case when the user has provided too many arguments,
382 // we want to point to the unexpected arguments.
383 let spans: Vec<Span> = args.args[offset+permitted .. offset+provided]
385 .map(|arg| arg.span())
387 potential_assoc_types = Some(spans.clone());
388 (spans, format!( "unexpected {} argument", kind))
390 (vec![span], format!(
391 "expected {}{} {} argument{}",
399 let mut err = tcx.sess.struct_span_err_with_code(
402 "wrong number of {} arguments: expected {}{}, found {}",
408 DiagnosticId::Error("E0107".into())
411 err.span_label(span, label.as_str());
416 provided > required, // `suppress_error`
417 potential_assoc_types,
421 if reported_late_bound_region_err.is_none()
422 && (!infer_lifetimes || arg_counts.lifetimes > param_counts.lifetimes) {
425 param_counts.lifetimes,
426 param_counts.lifetimes,
427 arg_counts.lifetimes,
431 // FIXME(const_generics:defaults)
432 if !infer_args || arg_counts.consts > param_counts.consts {
438 arg_counts.lifetimes + arg_counts.types,
441 // Note that type errors are currently be emitted *after* const errors.
443 || arg_counts.types > param_counts.types - defaults.types - has_self as usize {
446 param_counts.types - defaults.types - has_self as usize,
447 param_counts.types - has_self as usize,
449 arg_counts.lifetimes,
452 (reported_late_bound_region_err.unwrap_or(false), None)
456 /// Creates the relevant generic argument substitutions
457 /// corresponding to a set of generic parameters. This is a
458 /// rather complex function. Let us try to explain the role
459 /// of each of its parameters:
461 /// To start, we are given the `def_id` of the thing we are
462 /// creating the substitutions for, and a partial set of
463 /// substitutions `parent_substs`. In general, the substitutions
464 /// for an item begin with substitutions for all the "parents" of
465 /// that item -- e.g., for a method it might include the
466 /// parameters from the impl.
468 /// Therefore, the method begins by walking down these parents,
469 /// starting with the outermost parent and proceed inwards until
470 /// it reaches `def_id`. For each parent `P`, it will check `parent_substs`
471 /// first to see if the parent's substitutions are listed in there. If so,
472 /// we can append those and move on. Otherwise, it invokes the
473 /// three callback functions:
475 /// - `args_for_def_id`: given the `DefId` `P`, supplies back the
476 /// generic arguments that were given to that parent from within
477 /// the path; so e.g., if you have `<T as Foo>::Bar`, the `DefId`
478 /// might refer to the trait `Foo`, and the arguments might be
479 /// `[T]`. The boolean value indicates whether to infer values
480 /// for arguments whose values were not explicitly provided.
481 /// - `provided_kind`: given the generic parameter and the value from `args_for_def_id`,
482 /// instantiate a `GenericArg`.
483 /// - `inferred_kind`: if no parameter was provided, and inference is enabled, then
484 /// creates a suitable inference variable.
485 pub fn create_substs_for_generic_args<'b>(
488 parent_substs: &[subst::GenericArg<'tcx>],
490 self_ty: Option<Ty<'tcx>>,
491 args_for_def_id: impl Fn(DefId) -> (Option<&'b GenericArgs>, bool),
492 provided_kind: impl Fn(&GenericParamDef, &GenericArg) -> subst::GenericArg<'tcx>,
493 inferred_kind: impl Fn(Option<&[subst::GenericArg<'tcx>]>, &GenericParamDef, bool)
494 -> subst::GenericArg<'tcx>,
495 ) -> SubstsRef<'tcx> {
496 // Collect the segments of the path; we need to substitute arguments
497 // for parameters throughout the entire path (wherever there are
498 // generic parameters).
499 let mut parent_defs = tcx.generics_of(def_id);
500 let count = parent_defs.count();
501 let mut stack = vec![(def_id, parent_defs)];
502 while let Some(def_id) = parent_defs.parent {
503 parent_defs = tcx.generics_of(def_id);
504 stack.push((def_id, parent_defs));
507 // We manually build up the substitution, rather than using convenience
508 // methods in `subst.rs`, so that we can iterate over the arguments and
509 // parameters in lock-step linearly, instead of trying to match each pair.
510 let mut substs: SmallVec<[subst::GenericArg<'tcx>; 8]> = SmallVec::with_capacity(count);
512 // Iterate over each segment of the path.
513 while let Some((def_id, defs)) = stack.pop() {
514 let mut params = defs.params.iter().peekable();
516 // If we have already computed substitutions for parents, we can use those directly.
517 while let Some(¶m) = params.peek() {
518 if let Some(&kind) = parent_substs.get(param.index as usize) {
526 // `Self` is handled first, unless it's been handled in `parent_substs`.
528 if let Some(¶m) = params.peek() {
529 if param.index == 0 {
530 if let GenericParamDefKind::Type { .. } = param.kind {
531 substs.push(self_ty.map(|ty| ty.into())
532 .unwrap_or_else(|| inferred_kind(None, param, true)));
539 // Check whether this segment takes generic arguments and the user has provided any.
540 let (generic_args, infer_args) = args_for_def_id(def_id);
542 let mut args = generic_args.iter().flat_map(|generic_args| generic_args.args.iter())
546 // We're going to iterate through the generic arguments that the user
547 // provided, matching them with the generic parameters we expect.
548 // Mismatches can occur as a result of elided lifetimes, or for malformed
549 // input. We try to handle both sensibly.
550 match (args.peek(), params.peek()) {
551 (Some(&arg), Some(¶m)) => {
552 match (arg, ¶m.kind) {
553 (GenericArg::Lifetime(_), GenericParamDefKind::Lifetime)
554 | (GenericArg::Type(_), GenericParamDefKind::Type { .. })
555 | (GenericArg::Const(_), GenericParamDefKind::Const) => {
556 substs.push(provided_kind(param, arg));
560 (GenericArg::Type(_), GenericParamDefKind::Lifetime)
561 | (GenericArg::Const(_), GenericParamDefKind::Lifetime) => {
562 // We expected a lifetime argument, but got a type or const
563 // argument. That means we're inferring the lifetimes.
564 substs.push(inferred_kind(None, param, infer_args));
568 // We expected one kind of parameter, but the user provided
569 // another. This is an error, but we need to handle it
570 // gracefully so we can report sensible errors.
571 // In this case, we're simply going to infer this argument.
577 // We should never be able to reach this point with well-formed input.
578 // Getting to this point means the user supplied more arguments than
579 // there are parameters.
582 (None, Some(¶m)) => {
583 // If there are fewer arguments than parameters, it means
584 // we're inferring the remaining arguments.
585 substs.push(inferred_kind(Some(&substs), param, infer_args));
589 (None, None) => break,
594 tcx.intern_substs(&substs)
597 /// Given the type/lifetime/const arguments provided to some path (along with
598 /// an implicit `Self`, if this is a trait reference), returns the complete
599 /// set of substitutions. This may involve applying defaulted type parameters.
600 /// Also returns back constriants on associated types.
605 /// T: std::ops::Index<usize, Output = u32>
606 /// ^1 ^^^^^^^^^^^^^^2 ^^^^3 ^^^^^^^^^^^4
609 /// 1. The `self_ty` here would refer to the type `T`.
610 /// 2. The path in question is the path to the trait `std::ops::Index`,
611 /// which will have been resolved to a `def_id`
612 /// 3. The `generic_args` contains info on the `<...>` contents. The `usize` type
613 /// parameters are returned in the `SubstsRef`, the associated type bindings like
614 /// `Output = u32` are returned in the `Vec<ConvertedBinding...>` result.
616 /// Note that the type listing given here is *exactly* what the user provided.
617 fn create_substs_for_ast_path<'a>(&self,
620 generic_args: &'a hir::GenericArgs,
622 self_ty: Option<Ty<'tcx>>)
623 -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'a, 'tcx>>, Option<Vec<Span>>)
625 // If the type is parameterized by this region, then replace this
626 // region with the current anon region binding (in other words,
627 // whatever & would get replaced with).
628 debug!("create_substs_for_ast_path(def_id={:?}, self_ty={:?}, \
630 def_id, self_ty, generic_args);
632 let tcx = self.tcx();
633 let generic_params = tcx.generics_of(def_id);
635 // If a self-type was declared, one should be provided.
636 assert_eq!(generic_params.has_self, self_ty.is_some());
638 let has_self = generic_params.has_self;
639 let (_, potential_assoc_types) = Self::check_generic_arg_count(
644 GenericArgPosition::Type,
649 let is_object = self_ty.map_or(false, |ty| {
650 ty == self.tcx().types.trait_object_dummy_self
652 let default_needs_object_self = |param: &ty::GenericParamDef| {
653 if let GenericParamDefKind::Type { has_default, .. } = param.kind {
654 if is_object && has_default && has_self {
655 let self_param = tcx.types.self_param;
656 if tcx.at(span).type_of(param.def_id).walk().any(|ty| ty == self_param) {
657 // There is no suitable inference default for a type parameter
658 // that references self, in an object type.
667 let substs = Self::create_substs_for_generic_args(
673 // Provide the generic args, and whether types should be inferred.
674 |_| (Some(generic_args), infer_args),
675 // Provide substitutions for parameters for which (valid) arguments have been provided.
677 match (¶m.kind, arg) {
678 (GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => {
679 self.ast_region_to_region(<, Some(param)).into()
681 (GenericParamDefKind::Type { .. }, GenericArg::Type(ty)) => {
682 self.ast_ty_to_ty(&ty).into()
684 (GenericParamDefKind::Const, GenericArg::Const(ct)) => {
685 self.ast_const_to_const(&ct.value, tcx.type_of(param.def_id)).into()
690 // Provide substitutions for parameters for which arguments are inferred.
691 |substs, param, infer_args| {
693 GenericParamDefKind::Lifetime => tcx.lifetimes.re_static.into(),
694 GenericParamDefKind::Type { has_default, .. } => {
695 if !infer_args && has_default {
696 // No type parameter provided, but a default exists.
698 // If we are converting an object type, then the
699 // `Self` parameter is unknown. However, some of the
700 // other type parameters may reference `Self` in their
701 // defaults. This will lead to an ICE if we are not
703 if default_needs_object_self(param) {
704 struct_span_err!(tcx.sess, span, E0393,
705 "the type parameter `{}` must be explicitly specified",
708 .span_label(span, format!(
709 "missing reference to `{}`", param.name))
711 "because of the default `Self` reference, type parameters \
712 must be specified on object types"))
716 // This is a default type parameter.
719 tcx.at(span).type_of(param.def_id)
720 .subst_spanned(tcx, substs.unwrap(), Some(span))
723 } else if infer_args {
724 // No type parameters were provided, we can infer all.
725 let param = if !default_needs_object_self(param) {
730 self.ty_infer(param, span).into()
732 // We've already errored above about the mismatch.
736 GenericParamDefKind::Const => {
737 // FIXME(const_generics:defaults)
739 // No const parameters were provided, we can infer all.
740 let ty = tcx.at(span).type_of(param.def_id);
741 self.ct_infer(ty, Some(param), span).into()
743 // We've already errored above about the mismatch.
744 tcx.consts.err.into()
751 // Convert associated-type bindings or constraints into a separate vector.
752 // Example: Given this:
754 // T: Iterator<Item = u32>
756 // The `T` is passed in as a self-type; the `Item = u32` is
757 // not a "type parameter" of the `Iterator` trait, but rather
758 // a restriction on `<T as Iterator>::Item`, so it is passed
760 let assoc_bindings = generic_args.bindings.iter()
762 let kind = match binding.kind {
763 hir::TypeBindingKind::Equality { ref ty } =>
764 ConvertedBindingKind::Equality(self.ast_ty_to_ty(ty)),
765 hir::TypeBindingKind::Constraint { ref bounds } =>
766 ConvertedBindingKind::Constraint(bounds),
769 item_name: binding.ident,
776 debug!("create_substs_for_ast_path(generic_params={:?}, self_ty={:?}) -> {:?}",
777 generic_params, self_ty, substs);
779 (substs, assoc_bindings, potential_assoc_types)
782 /// Instantiates the path for the given trait reference, assuming that it's
783 /// bound to a valid trait type. Returns the `DefId` of the defining trait.
784 /// The type _cannot_ be a type other than a trait type.
786 /// If the `projections` argument is `None`, then assoc type bindings like `Foo<T = X>`
787 /// are disallowed. Otherwise, they are pushed onto the vector given.
788 pub fn instantiate_mono_trait_ref(&self,
789 trait_ref: &hir::TraitRef,
791 ) -> ty::TraitRef<'tcx>
793 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
795 self.ast_path_to_mono_trait_ref(trait_ref.path.span,
796 trait_ref.trait_def_id(),
798 trait_ref.path.segments.last().unwrap())
801 /// The given trait-ref must actually be a trait.
802 pub(super) fn instantiate_poly_trait_ref_inner(&self,
803 trait_ref: &hir::TraitRef,
806 bounds: &mut Bounds<'tcx>,
808 ) -> Option<Vec<Span>> {
809 let trait_def_id = trait_ref.trait_def_id();
811 debug!("instantiate_poly_trait_ref({:?}, def_id={:?})", trait_ref, trait_def_id);
813 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
815 let (substs, assoc_bindings, potential_assoc_types) = self.create_substs_for_ast_trait_ref(
819 trait_ref.path.segments.last().unwrap(),
821 let poly_trait_ref = ty::Binder::bind(ty::TraitRef::new(trait_def_id, substs));
823 bounds.trait_bounds.push((poly_trait_ref, span));
825 let mut dup_bindings = FxHashMap::default();
826 for binding in &assoc_bindings {
827 // Specify type to assert that error was already reported in `Err` case.
828 let _: Result<_, ErrorReported> =
829 self.add_predicates_for_ast_type_binding(
830 trait_ref.hir_ref_id,
837 // Okay to ignore `Err` because of `ErrorReported` (see above).
840 debug!("instantiate_poly_trait_ref({:?}, bounds={:?}) -> {:?}",
841 trait_ref, bounds, poly_trait_ref);
842 potential_assoc_types
845 /// Given a trait bound like `Debug`, applies that trait bound the given self-type to construct
846 /// a full trait reference. The resulting trait reference is returned. This may also generate
847 /// auxiliary bounds, which are added to `bounds`.
852 /// poly_trait_ref = Iterator<Item = u32>
856 /// this would return `Foo: Iterator` and add `<Foo as Iterator>::Item = u32` into `bounds`.
858 /// **A note on binders:** against our usual convention, there is an implied bounder around
859 /// the `self_ty` and `poly_trait_ref` parameters here. So they may reference bound regions.
860 /// If for example you had `for<'a> Foo<'a>: Bar<'a>`, then the `self_ty` would be `Foo<'a>`
861 /// where `'a` is a bound region at depth 0. Similarly, the `poly_trait_ref` would be
862 /// `Bar<'a>`. The returned poly-trait-ref will have this binder instantiated explicitly,
864 pub fn instantiate_poly_trait_ref(&self,
865 poly_trait_ref: &hir::PolyTraitRef,
867 bounds: &mut Bounds<'tcx>,
868 ) -> Option<Vec<Span>> {
869 self.instantiate_poly_trait_ref_inner(
870 &poly_trait_ref.trait_ref,
878 fn ast_path_to_mono_trait_ref(&self,
882 trait_segment: &hir::PathSegment
883 ) -> ty::TraitRef<'tcx>
885 let (substs, assoc_bindings, _) =
886 self.create_substs_for_ast_trait_ref(span,
890 assoc_bindings.first().map(|b| AstConv::prohibit_assoc_ty_binding(self.tcx(), b.span));
891 ty::TraitRef::new(trait_def_id, substs)
894 fn create_substs_for_ast_trait_ref<'a>(
899 trait_segment: &'a hir::PathSegment,
900 ) -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'a, 'tcx>>, Option<Vec<Span>>) {
901 debug!("create_substs_for_ast_trait_ref(trait_segment={:?})",
904 let trait_def = self.tcx().trait_def(trait_def_id);
906 if !self.tcx().features().unboxed_closures &&
907 trait_segment.generic_args().parenthesized != trait_def.paren_sugar
909 // For now, require that parenthetical notation be used only with `Fn()` etc.
910 let msg = if trait_def.paren_sugar {
911 "the precise format of `Fn`-family traits' type parameters is subject to change. \
912 Use parenthetical notation (Fn(Foo, Bar) -> Baz) instead"
914 "parenthetical notation is only stable when used with `Fn`-family traits"
916 emit_feature_err(&self.tcx().sess.parse_sess, sym::unboxed_closures,
917 span, GateIssue::Language, msg);
920 self.create_substs_for_ast_path(span,
922 trait_segment.generic_args(),
923 trait_segment.infer_args,
927 fn trait_defines_associated_type_named(&self,
929 assoc_name: ast::Ident)
932 self.tcx().associated_items(trait_def_id).any(|item| {
933 item.kind == ty::AssocKind::Type &&
934 self.tcx().hygienic_eq(assoc_name, item.ident, trait_def_id)
938 // Returns `true` if a bounds list includes `?Sized`.
939 pub fn is_unsized(&self, ast_bounds: &[hir::GenericBound], span: Span) -> bool {
940 let tcx = self.tcx();
942 // Try to find an unbound in bounds.
943 let mut unbound = None;
944 for ab in ast_bounds {
945 if let &hir::GenericBound::Trait(ref ptr, hir::TraitBoundModifier::Maybe) = ab {
946 if unbound.is_none() {
947 unbound = Some(&ptr.trait_ref);
953 "type parameter has more than one relaxed default \
954 bound, only one is supported"
960 let kind_id = tcx.lang_items().require(SizedTraitLangItem);
963 // FIXME(#8559) currently requires the unbound to be built-in.
964 if let Ok(kind_id) = kind_id {
965 if tpb.path.res != Res::Def(DefKind::Trait, kind_id) {
968 "default bound relaxed for a type parameter, but \
969 this does nothing because the given bound is not \
970 a default; only `?Sized` is supported",
975 _ if kind_id.is_ok() => {
978 // No lang item for `Sized`, so we can't add it as a bound.
985 /// This helper takes a *converted* parameter type (`param_ty`)
986 /// and an *unconverted* list of bounds:
990 /// ^ ^^^^^ `ast_bounds` parameter, in HIR form
992 /// `param_ty`, in ty form
995 /// It adds these `ast_bounds` into the `bounds` structure.
997 /// **A note on binders:** there is an implied binder around
998 /// `param_ty` and `ast_bounds`. See `instantiate_poly_trait_ref`
999 /// for more details.
1000 fn add_bounds(&self,
1002 ast_bounds: &[hir::GenericBound],
1003 bounds: &mut Bounds<'tcx>,
1005 let mut trait_bounds = Vec::new();
1006 let mut region_bounds = Vec::new();
1008 for ast_bound in ast_bounds {
1010 hir::GenericBound::Trait(ref b, hir::TraitBoundModifier::None) =>
1011 trait_bounds.push(b),
1012 hir::GenericBound::Trait(_, hir::TraitBoundModifier::Maybe) => {}
1013 hir::GenericBound::Outlives(ref l) =>
1014 region_bounds.push(l),
1018 for bound in trait_bounds {
1019 let _ = self.instantiate_poly_trait_ref(
1026 bounds.region_bounds.extend(region_bounds
1028 .map(|r| (self.ast_region_to_region(r, None), r.span))
1032 /// Translates a list of bounds from the HIR into the `Bounds` data structure.
1033 /// The self-type for the bounds is given by `param_ty`.
1038 /// fn foo<T: Bar + Baz>() { }
1039 /// ^ ^^^^^^^^^ ast_bounds
1043 /// The `sized_by_default` parameter indicates if, in this context, the `param_ty` should be
1044 /// considered `Sized` unless there is an explicit `?Sized` bound. This would be true in the
1045 /// example above, but is not true in supertrait listings like `trait Foo: Bar + Baz`.
1047 /// `span` should be the declaration size of the parameter.
1048 pub fn compute_bounds(&self,
1050 ast_bounds: &[hir::GenericBound],
1051 sized_by_default: SizedByDefault,
1054 let mut bounds = Bounds::default();
1056 self.add_bounds(param_ty, ast_bounds, &mut bounds);
1057 bounds.trait_bounds.sort_by_key(|(t, _)| t.def_id());
1059 bounds.implicitly_sized = if let SizedByDefault::Yes = sized_by_default {
1060 if !self.is_unsized(ast_bounds, span) {
1072 /// Given an HIR binding like `Item = Foo` or `Item: Foo`, pushes the corresponding predicates
1075 /// **A note on binders:** given something like `T: for<'a> Iterator<Item = &'a u32>`, the
1076 /// `trait_ref` here will be `for<'a> T: Iterator`. The `binding` data however is from *inside*
1077 /// the binder (e.g., `&'a u32`) and hence may reference bound regions.
1078 fn add_predicates_for_ast_type_binding(
1080 hir_ref_id: hir::HirId,
1081 trait_ref: ty::PolyTraitRef<'tcx>,
1082 binding: &ConvertedBinding<'_, 'tcx>,
1083 bounds: &mut Bounds<'tcx>,
1085 dup_bindings: &mut FxHashMap<DefId, Span>,
1086 ) -> Result<(), ErrorReported> {
1087 let tcx = self.tcx();
1090 // Given something like `U: SomeTrait<T = X>`, we want to produce a
1091 // predicate like `<U as SomeTrait>::T = X`. This is somewhat
1092 // subtle in the event that `T` is defined in a supertrait of
1093 // `SomeTrait`, because in that case we need to upcast.
1095 // That is, consider this case:
1098 // trait SubTrait: SuperTrait<int> { }
1099 // trait SuperTrait<A> { type T; }
1101 // ... B: SubTrait<T = foo> ...
1104 // We want to produce `<B as SuperTrait<int>>::T == foo`.
1106 // Find any late-bound regions declared in `ty` that are not
1107 // declared in the trait-ref. These are not well-formed.
1111 // for<'a> <T as Iterator>::Item = &'a str // <-- 'a is bad
1112 // for<'a> <T as FnMut<(&'a u32,)>>::Output = &'a str // <-- 'a is ok
1113 if let ConvertedBindingKind::Equality(ty) = binding.kind {
1114 let late_bound_in_trait_ref =
1115 tcx.collect_constrained_late_bound_regions(&trait_ref);
1116 let late_bound_in_ty =
1117 tcx.collect_referenced_late_bound_regions(&ty::Binder::bind(ty));
1118 debug!("late_bound_in_trait_ref = {:?}", late_bound_in_trait_ref);
1119 debug!("late_bound_in_ty = {:?}", late_bound_in_ty);
1120 for br in late_bound_in_ty.difference(&late_bound_in_trait_ref) {
1121 let br_name = match *br {
1122 ty::BrNamed(_, name) => name,
1126 "anonymous bound region {:?} in binding but not trait ref",
1130 struct_span_err!(tcx.sess,
1133 "binding for associated type `{}` references lifetime `{}`, \
1134 which does not appear in the trait input types",
1135 binding.item_name, br_name)
1141 let candidate = if self.trait_defines_associated_type_named(trait_ref.def_id(),
1142 binding.item_name) {
1143 // Simple case: X is defined in the current trait.
1146 // Otherwise, we have to walk through the supertraits to find
1148 let candidates = traits::supertraits(tcx, trait_ref).filter(|r| {
1149 self.trait_defines_associated_type_named(r.def_id(), binding.item_name)
1151 self.one_bound_for_assoc_type(candidates, &trait_ref.to_string(),
1152 binding.item_name, binding.span)
1155 let (assoc_ident, def_scope) =
1156 tcx.adjust_ident_and_get_scope(binding.item_name, candidate.def_id(), hir_ref_id);
1157 let assoc_ty = tcx.associated_items(candidate.def_id()).find(|i| {
1158 i.kind == ty::AssocKind::Type && i.ident.modern() == assoc_ident
1159 }).expect("missing associated type");
1161 if !assoc_ty.vis.is_accessible_from(def_scope, tcx) {
1162 let msg = format!("associated type `{}` is private", binding.item_name);
1163 tcx.sess.span_err(binding.span, &msg);
1165 tcx.check_stability(assoc_ty.def_id, Some(hir_ref_id), binding.span);
1168 dup_bindings.entry(assoc_ty.def_id)
1169 .and_modify(|prev_span| {
1170 struct_span_err!(self.tcx().sess, binding.span, E0719,
1171 "the value of the associated type `{}` (from the trait `{}`) \
1172 is already specified",
1174 tcx.def_path_str(assoc_ty.container.id()))
1175 .span_label(binding.span, "re-bound here")
1176 .span_label(*prev_span, format!("`{}` bound here first", binding.item_name))
1179 .or_insert(binding.span);
1182 match binding.kind {
1183 ConvertedBindingKind::Equality(ref ty) => {
1184 // "Desugar" a constraint like `T: Iterator<Item = u32>` this to
1185 // the "projection predicate" for:
1187 // `<T as Iterator>::Item = u32`
1188 bounds.projection_bounds.push((candidate.map_bound(|trait_ref| {
1189 ty::ProjectionPredicate {
1190 projection_ty: ty::ProjectionTy::from_ref_and_name(
1199 ConvertedBindingKind::Constraint(ast_bounds) => {
1200 // "Desugar" a constraint like `T: Iterator<Item: Debug>` to
1202 // `<T as Iterator>::Item: Debug`
1204 // Calling `skip_binder` is okay, because `add_bounds` expects the `param_ty`
1205 // parameter to have a skipped binder.
1206 let param_ty = tcx.mk_projection(assoc_ty.def_id, candidate.skip_binder().substs);
1207 self.add_bounds(param_ty, ast_bounds, bounds);
1213 fn ast_path_to_ty(&self,
1216 item_segment: &hir::PathSegment)
1219 let substs = self.ast_path_substs_for_ty(span, did, item_segment);
1222 self.tcx().at(span).type_of(did).subst(self.tcx(), substs)
1226 /// Transform a `PolyTraitRef` into a `PolyExistentialTraitRef` by
1227 /// removing the dummy `Self` type (`trait_object_dummy_self`).
1228 fn trait_ref_to_existential(&self, trait_ref: ty::TraitRef<'tcx>)
1229 -> ty::ExistentialTraitRef<'tcx> {
1230 if trait_ref.self_ty() != self.tcx().types.trait_object_dummy_self {
1231 bug!("trait_ref_to_existential called on {:?} with non-dummy Self", trait_ref);
1233 ty::ExistentialTraitRef::erase_self_ty(self.tcx(), trait_ref)
1236 fn conv_object_ty_poly_trait_ref(&self,
1238 trait_bounds: &[hir::PolyTraitRef],
1239 lifetime: &hir::Lifetime)
1242 let tcx = self.tcx();
1244 let mut bounds = Bounds::default();
1245 let mut potential_assoc_types = Vec::new();
1246 let dummy_self = self.tcx().types.trait_object_dummy_self;
1247 for trait_bound in trait_bounds.iter().rev() {
1248 let cur_potential_assoc_types = self.instantiate_poly_trait_ref(
1253 potential_assoc_types.extend(cur_potential_assoc_types.into_iter().flatten());
1256 // Expand trait aliases recursively and check that only one regular (non-auto) trait
1257 // is used and no 'maybe' bounds are used.
1258 let expanded_traits =
1259 traits::expand_trait_aliases(tcx, bounds.trait_bounds.iter().cloned());
1260 let (mut auto_traits, regular_traits): (Vec<_>, Vec<_>) =
1261 expanded_traits.partition(|i| tcx.trait_is_auto(i.trait_ref().def_id()));
1262 if regular_traits.len() > 1 {
1263 let first_trait = ®ular_traits[0];
1264 let additional_trait = ®ular_traits[1];
1265 let mut err = struct_span_err!(tcx.sess, additional_trait.bottom().1, E0225,
1266 "only auto traits can be used as additional traits in a trait object"
1268 additional_trait.label_with_exp_info(&mut err,
1269 "additional non-auto trait", "additional use");
1270 first_trait.label_with_exp_info(&mut err,
1271 "first non-auto trait", "first use");
1275 if regular_traits.is_empty() && auto_traits.is_empty() {
1276 span_err!(tcx.sess, span, E0224,
1277 "at least one trait is required for an object type");
1278 return tcx.types.err;
1281 // Check that there are no gross object safety violations;
1282 // most importantly, that the supertraits don't contain `Self`,
1284 for item in ®ular_traits {
1285 let object_safety_violations =
1286 tcx.astconv_object_safety_violations(item.trait_ref().def_id());
1287 if !object_safety_violations.is_empty() {
1288 tcx.report_object_safety_error(
1290 item.trait_ref().def_id(),
1291 object_safety_violations
1293 return tcx.types.err;
1297 // Use a `BTreeSet` to keep output in a more consistent order.
1298 let mut associated_types = BTreeSet::default();
1300 let regular_traits_refs = bounds.trait_bounds
1302 .filter(|(trait_ref, _)| !tcx.trait_is_auto(trait_ref.def_id()))
1303 .map(|(trait_ref, _)| trait_ref);
1304 for trait_ref in traits::elaborate_trait_refs(tcx, regular_traits_refs) {
1305 debug!("conv_object_ty_poly_trait_ref: observing object predicate `{:?}`", trait_ref);
1307 ty::Predicate::Trait(pred) => {
1309 .extend(tcx.associated_items(pred.def_id())
1310 .filter(|item| item.kind == ty::AssocKind::Type)
1311 .map(|item| item.def_id));
1313 ty::Predicate::Projection(pred) => {
1314 // A `Self` within the original bound will be substituted with a
1315 // `trait_object_dummy_self`, so check for that.
1316 let references_self =
1317 pred.skip_binder().ty.walk().any(|t| t == dummy_self);
1319 // If the projection output contains `Self`, force the user to
1320 // elaborate it explicitly to avoid a lot of complexity.
1322 // The "classicaly useful" case is the following:
1324 // trait MyTrait: FnMut() -> <Self as MyTrait>::MyOutput {
1329 // Here, the user could theoretically write `dyn MyTrait<Output = X>`,
1330 // but actually supporting that would "expand" to an infinitely-long type
1331 // `fix $ τ → dyn MyTrait<MyOutput = X, Output = <τ as MyTrait>::MyOutput`.
1333 // Instead, we force the user to write `dyn MyTrait<MyOutput = X, Output = X>`,
1334 // which is uglier but works. See the discussion in #56288 for alternatives.
1335 if !references_self {
1336 // Include projections defined on supertraits.
1337 bounds.projection_bounds.push((pred, DUMMY_SP))
1344 for (projection_bound, _) in &bounds.projection_bounds {
1345 associated_types.remove(&projection_bound.projection_def_id());
1348 if !associated_types.is_empty() {
1349 let names = associated_types.iter().map(|item_def_id| {
1350 let assoc_item = tcx.associated_item(*item_def_id);
1351 let trait_def_id = assoc_item.container.id();
1353 "`{}` (from the trait `{}`)",
1355 tcx.def_path_str(trait_def_id),
1357 }).collect::<Vec<_>>().join(", ");
1358 let mut err = struct_span_err!(
1362 "the value of the associated type{} {} must be specified",
1363 pluralise!(associated_types.len()),
1366 let (suggest, potential_assoc_types_spans) =
1367 if potential_assoc_types.len() == associated_types.len() {
1368 // Only suggest when the amount of missing associated types equals the number of
1369 // extra type arguments present, as that gives us a relatively high confidence
1370 // that the user forgot to give the associtated type's name. The canonical
1371 // example would be trying to use `Iterator<isize>` instead of
1372 // `Iterator<Item = isize>`.
1373 (true, potential_assoc_types)
1377 let mut suggestions = Vec::new();
1378 for (i, item_def_id) in associated_types.iter().enumerate() {
1379 let assoc_item = tcx.associated_item(*item_def_id);
1382 format!("associated type `{}` must be specified", assoc_item.ident),
1384 if let Some(sp) = tcx.hir().span_if_local(*item_def_id) {
1385 err.span_label(sp, format!("`{}` defined here", assoc_item.ident));
1388 if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(
1389 potential_assoc_types_spans[i],
1392 potential_assoc_types_spans[i],
1393 format!("{} = {}", assoc_item.ident, snippet),
1398 if !suggestions.is_empty() {
1399 let msg = format!("if you meant to specify the associated {}, write",
1400 if suggestions.len() == 1 { "type" } else { "types" });
1401 err.multipart_suggestion(
1404 Applicability::MaybeIncorrect,
1410 // De-duplicate auto traits so that, e.g., `dyn Trait + Send + Send` is the same as
1411 // `dyn Trait + Send`.
1412 auto_traits.sort_by_key(|i| i.trait_ref().def_id());
1413 auto_traits.dedup_by_key(|i| i.trait_ref().def_id());
1414 debug!("regular_traits: {:?}", regular_traits);
1415 debug!("auto_traits: {:?}", auto_traits);
1417 // Erase the `dummy_self` (`trait_object_dummy_self`) used above.
1418 let existential_trait_refs = regular_traits.iter().map(|i| {
1419 i.trait_ref().map_bound(|trait_ref| self.trait_ref_to_existential(trait_ref))
1421 let existential_projections = bounds.projection_bounds.iter().map(|(bound, _)| {
1422 bound.map_bound(|b| {
1423 let trait_ref = self.trait_ref_to_existential(b.projection_ty.trait_ref(tcx));
1424 ty::ExistentialProjection {
1426 item_def_id: b.projection_ty.item_def_id,
1427 substs: trait_ref.substs,
1432 // Calling `skip_binder` is okay because the predicates are re-bound.
1433 let regular_trait_predicates = existential_trait_refs.map(
1434 |trait_ref| ty::ExistentialPredicate::Trait(*trait_ref.skip_binder()));
1435 let auto_trait_predicates = auto_traits.into_iter().map(
1436 |trait_ref| ty::ExistentialPredicate::AutoTrait(trait_ref.trait_ref().def_id()));
1438 regular_trait_predicates
1439 .chain(auto_trait_predicates)
1440 .chain(existential_projections
1441 .map(|x| ty::ExistentialPredicate::Projection(*x.skip_binder())))
1442 .collect::<SmallVec<[_; 8]>>();
1443 v.sort_by(|a, b| a.stable_cmp(tcx, b));
1445 let existential_predicates = ty::Binder::bind(tcx.mk_existential_predicates(v.into_iter()));
1447 // Use explicitly-specified region bound.
1448 let region_bound = if !lifetime.is_elided() {
1449 self.ast_region_to_region(lifetime, None)
1451 self.compute_object_lifetime_bound(span, existential_predicates).unwrap_or_else(|| {
1452 if tcx.named_region(lifetime.hir_id).is_some() {
1453 self.ast_region_to_region(lifetime, None)
1455 self.re_infer(None, span).unwrap_or_else(|| {
1456 span_err!(tcx.sess, span, E0228,
1457 "the lifetime bound for this object type cannot be deduced \
1458 from context; please supply an explicit bound");
1459 tcx.lifetimes.re_static
1464 debug!("region_bound: {:?}", region_bound);
1466 let ty = tcx.mk_dynamic(existential_predicates, region_bound);
1467 debug!("trait_object_type: {:?}", ty);
1471 fn report_ambiguous_associated_type(
1478 let mut err = struct_span_err!(self.tcx().sess, span, E0223, "ambiguous associated type");
1479 if let (Some(_), Ok(snippet)) = (
1480 self.tcx().sess.confused_type_with_std_module.borrow().get(&span),
1481 self.tcx().sess.source_map().span_to_snippet(span),
1483 err.span_suggestion(
1485 "you are looking for the module in `std`, not the primitive type",
1486 format!("std::{}", snippet),
1487 Applicability::MachineApplicable,
1490 err.span_suggestion(
1492 "use fully-qualified syntax",
1493 format!("<{} as {}>::{}", type_str, trait_str, name),
1494 Applicability::HasPlaceholders
1500 // Search for a bound on a type parameter which includes the associated item
1501 // given by `assoc_name`. `ty_param_def_id` is the `DefId` of the type parameter
1502 // This function will fail if there are no suitable bounds or there is
1504 fn find_bound_for_assoc_item(&self,
1505 ty_param_def_id: DefId,
1506 assoc_name: ast::Ident,
1508 -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
1510 let tcx = self.tcx();
1513 "find_bound_for_assoc_item(ty_param_def_id={:?}, assoc_name={:?}, span={:?})",
1519 let predicates = &self.get_type_parameter_bounds(span, ty_param_def_id).predicates;
1521 debug!("find_bound_for_assoc_item: predicates={:#?}", predicates);
1523 let bounds = predicates.iter().filter_map(|(p, _)| p.to_opt_poly_trait_ref());
1525 // Check that there is exactly one way to find an associated type with the
1527 let suitable_bounds = traits::transitive_bounds(tcx, bounds)
1528 .filter(|b| self.trait_defines_associated_type_named(b.def_id(), assoc_name));
1530 let param_hir_id = tcx.hir().as_local_hir_id(ty_param_def_id).unwrap();
1531 let param_name = tcx.hir().ty_param_name(param_hir_id);
1532 self.one_bound_for_assoc_type(suitable_bounds,
1533 ¶m_name.as_str(),
1538 // Checks that `bounds` contains exactly one element and reports appropriate
1539 // errors otherwise.
1540 fn one_bound_for_assoc_type<I>(&self,
1542 ty_param_name: &str,
1543 assoc_name: ast::Ident,
1545 -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
1546 where I: Iterator<Item = ty::PolyTraitRef<'tcx>>
1548 let bound = match bounds.next() {
1549 Some(bound) => bound,
1551 struct_span_err!(self.tcx().sess, span, E0220,
1552 "associated type `{}` not found for `{}`",
1555 .span_label(span, format!("associated type `{}` not found", assoc_name))
1557 return Err(ErrorReported);
1561 debug!("one_bound_for_assoc_type: bound = {:?}", bound);
1563 if let Some(bound2) = bounds.next() {
1564 debug!("one_bound_for_assoc_type: bound2 = {:?}", bound2);
1566 let bounds = iter::once(bound).chain(iter::once(bound2)).chain(bounds);
1567 let mut err = struct_span_err!(
1568 self.tcx().sess, span, E0221,
1569 "ambiguous associated type `{}` in bounds of `{}`",
1572 err.span_label(span, format!("ambiguous associated type `{}`", assoc_name));
1574 for bound in bounds {
1575 let bound_span = self.tcx().associated_items(bound.def_id()).find(|item| {
1576 item.kind == ty::AssocKind::Type &&
1577 self.tcx().hygienic_eq(assoc_name, item.ident, bound.def_id())
1579 .and_then(|item| self.tcx().hir().span_if_local(item.def_id));
1581 if let Some(span) = bound_span {
1582 err.span_label(span, format!("ambiguous `{}` from `{}`",
1586 span_note!(&mut err, span,
1587 "associated type `{}` could derive from `{}`",
1598 // Create a type from a path to an associated type.
1599 // For a path `A::B::C::D`, `qself_ty` and `qself_def` are the type and def for `A::B::C`
1600 // and item_segment is the path segment for `D`. We return a type and a def for
1602 // Will fail except for `T::A` and `Self::A`; i.e., if `qself_ty`/`qself_def` are not a type
1603 // parameter or `Self`.
1604 pub fn associated_path_to_ty(
1606 hir_ref_id: hir::HirId,
1610 assoc_segment: &hir::PathSegment,
1611 permit_variants: bool,
1612 ) -> Result<(Ty<'tcx>, DefKind, DefId), ErrorReported> {
1613 let tcx = self.tcx();
1614 let assoc_ident = assoc_segment.ident;
1616 debug!("associated_path_to_ty: {:?}::{}", qself_ty, assoc_ident);
1618 self.prohibit_generics(slice::from_ref(assoc_segment));
1620 // Check if we have an enum variant.
1621 let mut variant_resolution = None;
1622 if let ty::Adt(adt_def, _) = qself_ty.kind {
1623 if adt_def.is_enum() {
1624 let variant_def = adt_def.variants.iter().find(|vd| {
1625 tcx.hygienic_eq(assoc_ident, vd.ident, adt_def.did)
1627 if let Some(variant_def) = variant_def {
1628 if permit_variants {
1629 tcx.check_stability(variant_def.def_id, Some(hir_ref_id), span);
1630 return Ok((qself_ty, DefKind::Variant, variant_def.def_id));
1632 variant_resolution = Some(variant_def.def_id);
1638 // Find the type of the associated item, and the trait where the associated
1639 // item is declared.
1640 let bound = match (&qself_ty.kind, qself_res) {
1641 (_, Res::SelfTy(Some(_), Some(impl_def_id))) => {
1642 // `Self` in an impl of a trait -- we have a concrete self type and a
1644 let trait_ref = match tcx.impl_trait_ref(impl_def_id) {
1645 Some(trait_ref) => trait_ref,
1647 // A cycle error occurred, most likely.
1648 return Err(ErrorReported);
1652 let candidates = traits::supertraits(tcx, ty::Binder::bind(trait_ref))
1653 .filter(|r| self.trait_defines_associated_type_named(r.def_id(), assoc_ident));
1655 self.one_bound_for_assoc_type(candidates, "Self", assoc_ident, span)?
1657 (&ty::Param(_), Res::SelfTy(Some(param_did), None)) |
1658 (&ty::Param(_), Res::Def(DefKind::TyParam, param_did)) => {
1659 self.find_bound_for_assoc_item(param_did, assoc_ident, span)?
1662 if variant_resolution.is_some() {
1663 // Variant in type position
1664 let msg = format!("expected type, found variant `{}`", assoc_ident);
1665 tcx.sess.span_err(span, &msg);
1666 } else if qself_ty.is_enum() {
1667 let mut err = tcx.sess.struct_span_err(
1669 &format!("no variant `{}` in enum `{}`", assoc_ident, qself_ty),
1672 let adt_def = qself_ty.ty_adt_def().expect("enum is not an ADT");
1673 if let Some(suggested_name) = find_best_match_for_name(
1674 adt_def.variants.iter().map(|variant| &variant.ident.name),
1675 &assoc_ident.as_str(),
1678 err.span_suggestion(
1680 "there is a variant with a similar name",
1681 suggested_name.to_string(),
1682 Applicability::MaybeIncorrect,
1687 format!("variant not found in `{}`", qself_ty),
1691 if let Some(sp) = tcx.hir().span_if_local(adt_def.did) {
1692 let sp = tcx.sess.source_map().def_span(sp);
1693 err.span_label(sp, format!("variant `{}` not found here", assoc_ident));
1697 } else if !qself_ty.references_error() {
1698 // Don't print `TyErr` to the user.
1699 self.report_ambiguous_associated_type(
1701 &qself_ty.to_string(),
1706 return Err(ErrorReported);
1710 let trait_did = bound.def_id();
1711 let (assoc_ident, def_scope) =
1712 tcx.adjust_ident_and_get_scope(assoc_ident, trait_did, hir_ref_id);
1713 let item = tcx.associated_items(trait_did).find(|i| {
1714 Namespace::from(i.kind) == Namespace::Type &&
1715 i.ident.modern() == assoc_ident
1716 }).expect("missing associated type");
1718 let ty = self.projected_ty_from_poly_trait_ref(span, item.def_id, bound);
1719 let ty = self.normalize_ty(span, ty);
1721 let kind = DefKind::AssocTy;
1722 if !item.vis.is_accessible_from(def_scope, tcx) {
1723 let msg = format!("{} `{}` is private", kind.descr(item.def_id), assoc_ident);
1724 tcx.sess.span_err(span, &msg);
1726 tcx.check_stability(item.def_id, Some(hir_ref_id), span);
1728 if let Some(variant_def_id) = variant_resolution {
1729 let mut err = tcx.struct_span_lint_hir(
1730 AMBIGUOUS_ASSOCIATED_ITEMS,
1733 "ambiguous associated item",
1736 let mut could_refer_to = |kind: DefKind, def_id, also| {
1737 let note_msg = format!("`{}` could{} refer to {} defined here",
1738 assoc_ident, also, kind.descr(def_id));
1739 err.span_note(tcx.def_span(def_id), ¬e_msg);
1741 could_refer_to(DefKind::Variant, variant_def_id, "");
1742 could_refer_to(kind, item.def_id, " also");
1744 err.span_suggestion(
1746 "use fully-qualified syntax",
1747 format!("<{} as {}>::{}", qself_ty, tcx.item_name(trait_did), assoc_ident),
1748 Applicability::MachineApplicable,
1752 Ok((ty, kind, item.def_id))
1755 fn qpath_to_ty(&self,
1757 opt_self_ty: Option<Ty<'tcx>>,
1759 trait_segment: &hir::PathSegment,
1760 item_segment: &hir::PathSegment)
1763 let tcx = self.tcx();
1765 let trait_def_id = tcx.parent(item_def_id).unwrap();
1767 debug!("qpath_to_ty: trait_def_id={:?}", trait_def_id);
1769 self.prohibit_generics(slice::from_ref(item_segment));
1771 let self_ty = if let Some(ty) = opt_self_ty {
1774 let path_str = tcx.def_path_str(trait_def_id);
1776 let def_id = self.item_def_id();
1778 debug!("qpath_to_ty: self.item_def_id()={:?}", def_id);
1780 let parent_def_id = def_id.and_then(|def_id| tcx.hir().as_local_hir_id(def_id))
1781 .map(|hir_id| tcx.hir().get_parent_did(hir_id));
1783 debug!("qpath_to_ty: parent_def_id={:?}", parent_def_id);
1785 // If the trait in segment is the same as the trait defining the item,
1786 // use the `<Self as ..>` syntax in the error.
1787 let is_part_of_self_trait_constraints = def_id == Some(trait_def_id);
1788 let is_part_of_fn_in_self_trait = parent_def_id == Some(trait_def_id);
1790 let type_name = if is_part_of_self_trait_constraints || is_part_of_fn_in_self_trait {
1796 self.report_ambiguous_associated_type(
1800 item_segment.ident.name,
1802 return tcx.types.err;
1805 debug!("qpath_to_ty: self_type={:?}", self_ty);
1807 let trait_ref = self.ast_path_to_mono_trait_ref(span,
1812 debug!("qpath_to_ty: trait_ref={:?}", trait_ref);
1814 self.normalize_ty(span, tcx.mk_projection(item_def_id, trait_ref.substs))
1817 pub fn prohibit_generics<'a, T: IntoIterator<Item = &'a hir::PathSegment>>(
1818 &self, segments: T) -> bool {
1819 let mut has_err = false;
1820 for segment in segments {
1821 let (mut err_for_lt, mut err_for_ty, mut err_for_ct) = (false, false, false);
1822 for arg in &segment.generic_args().args {
1823 let (span, kind) = match arg {
1824 hir::GenericArg::Lifetime(lt) => {
1825 if err_for_lt { continue }
1828 (lt.span, "lifetime")
1830 hir::GenericArg::Type(ty) => {
1831 if err_for_ty { continue }
1836 hir::GenericArg::Const(ct) => {
1837 if err_for_ct { continue }
1842 let mut err = struct_span_err!(
1846 "{} arguments are not allowed for this type",
1849 err.span_label(span, format!("{} argument not allowed", kind));
1851 if err_for_lt && err_for_ty && err_for_ct {
1855 for binding in &segment.generic_args().bindings {
1857 Self::prohibit_assoc_ty_binding(self.tcx(), binding.span);
1864 pub fn prohibit_assoc_ty_binding(tcx: TyCtxt<'_>, span: Span) {
1865 let mut err = struct_span_err!(tcx.sess, span, E0229,
1866 "associated type bindings are not allowed here");
1867 err.span_label(span, "associated type not allowed here").emit();
1870 // FIXME(eddyb, varkor) handle type paths here too, not just value ones.
1871 pub fn def_ids_for_value_path_segments(
1873 segments: &[hir::PathSegment],
1874 self_ty: Option<Ty<'tcx>>,
1878 // We need to extract the type parameters supplied by the user in
1879 // the path `path`. Due to the current setup, this is a bit of a
1880 // tricky-process; the problem is that resolve only tells us the
1881 // end-point of the path resolution, and not the intermediate steps.
1882 // Luckily, we can (at least for now) deduce the intermediate steps
1883 // just from the end-point.
1885 // There are basically five cases to consider:
1887 // 1. Reference to a constructor of a struct:
1889 // struct Foo<T>(...)
1891 // In this case, the parameters are declared in the type space.
1893 // 2. Reference to a constructor of an enum variant:
1895 // enum E<T> { Foo(...) }
1897 // In this case, the parameters are defined in the type space,
1898 // but may be specified either on the type or the variant.
1900 // 3. Reference to a fn item or a free constant:
1904 // In this case, the path will again always have the form
1905 // `a::b::foo::<T>` where only the final segment should have
1906 // type parameters. However, in this case, those parameters are
1907 // declared on a value, and hence are in the `FnSpace`.
1909 // 4. Reference to a method or an associated constant:
1911 // impl<A> SomeStruct<A> {
1915 // Here we can have a path like
1916 // `a::b::SomeStruct::<A>::foo::<B>`, in which case parameters
1917 // may appear in two places. The penultimate segment,
1918 // `SomeStruct::<A>`, contains parameters in TypeSpace, and the
1919 // final segment, `foo::<B>` contains parameters in fn space.
1921 // The first step then is to categorize the segments appropriately.
1923 let tcx = self.tcx();
1925 assert!(!segments.is_empty());
1926 let last = segments.len() - 1;
1928 let mut path_segs = vec![];
1931 // Case 1. Reference to a struct constructor.
1932 DefKind::Ctor(CtorOf::Struct, ..) => {
1933 // Everything but the final segment should have no
1934 // parameters at all.
1935 let generics = tcx.generics_of(def_id);
1936 // Variant and struct constructors use the
1937 // generics of their parent type definition.
1938 let generics_def_id = generics.parent.unwrap_or(def_id);
1939 path_segs.push(PathSeg(generics_def_id, last));
1942 // Case 2. Reference to a variant constructor.
1943 DefKind::Ctor(CtorOf::Variant, ..)
1944 | DefKind::Variant => {
1945 let adt_def = self_ty.map(|t| t.ty_adt_def().unwrap());
1946 let (generics_def_id, index) = if let Some(adt_def) = adt_def {
1947 debug_assert!(adt_def.is_enum());
1949 } else if last >= 1 && segments[last - 1].args.is_some() {
1950 // Everything but the penultimate segment should have no
1951 // parameters at all.
1952 let mut def_id = def_id;
1954 // `DefKind::Ctor` -> `DefKind::Variant`
1955 if let DefKind::Ctor(..) = kind {
1956 def_id = tcx.parent(def_id).unwrap()
1959 // `DefKind::Variant` -> `DefKind::Enum`
1960 let enum_def_id = tcx.parent(def_id).unwrap();
1961 (enum_def_id, last - 1)
1963 // FIXME: lint here recommending `Enum::<...>::Variant` form
1964 // instead of `Enum::Variant::<...>` form.
1966 // Everything but the final segment should have no
1967 // parameters at all.
1968 let generics = tcx.generics_of(def_id);
1969 // Variant and struct constructors use the
1970 // generics of their parent type definition.
1971 (generics.parent.unwrap_or(def_id), last)
1973 path_segs.push(PathSeg(generics_def_id, index));
1976 // Case 3. Reference to a top-level value.
1979 | DefKind::ConstParam
1980 | DefKind::Static => {
1981 path_segs.push(PathSeg(def_id, last));
1984 // Case 4. Reference to a method or associated const.
1986 | DefKind::AssocConst => {
1987 if segments.len() >= 2 {
1988 let generics = tcx.generics_of(def_id);
1989 path_segs.push(PathSeg(generics.parent.unwrap(), last - 1));
1991 path_segs.push(PathSeg(def_id, last));
1994 kind => bug!("unexpected definition kind {:?} for {:?}", kind, def_id),
1997 debug!("path_segs = {:?}", path_segs);
2002 // Check a type `Path` and convert it to a `Ty`.
2003 pub fn res_to_ty(&self,
2004 opt_self_ty: Option<Ty<'tcx>>,
2006 permit_variants: bool)
2008 let tcx = self.tcx();
2010 debug!("res_to_ty(res={:?}, opt_self_ty={:?}, path_segments={:?})",
2011 path.res, opt_self_ty, path.segments);
2013 let span = path.span;
2015 Res::Def(DefKind::OpaqueTy, did) => {
2016 // Check for desugared `impl Trait`.
2017 assert!(ty::is_impl_trait_defn(tcx, did).is_none());
2018 let item_segment = path.segments.split_last().unwrap();
2019 self.prohibit_generics(item_segment.1);
2020 let substs = self.ast_path_substs_for_ty(span, did, item_segment.0);
2023 tcx.mk_opaque(did, substs),
2026 Res::Def(DefKind::Enum, did)
2027 | Res::Def(DefKind::TyAlias, did)
2028 | Res::Def(DefKind::Struct, did)
2029 | Res::Def(DefKind::Union, did)
2030 | Res::Def(DefKind::ForeignTy, did) => {
2031 assert_eq!(opt_self_ty, None);
2032 self.prohibit_generics(path.segments.split_last().unwrap().1);
2033 self.ast_path_to_ty(span, did, path.segments.last().unwrap())
2035 Res::Def(kind @ DefKind::Variant, def_id) if permit_variants => {
2036 // Convert "variant type" as if it were a real type.
2037 // The resulting `Ty` is type of the variant's enum for now.
2038 assert_eq!(opt_self_ty, None);
2041 self.def_ids_for_value_path_segments(&path.segments, None, kind, def_id);
2042 let generic_segs: FxHashSet<_> =
2043 path_segs.iter().map(|PathSeg(_, index)| index).collect();
2044 self.prohibit_generics(path.segments.iter().enumerate().filter_map(|(index, seg)| {
2045 if !generic_segs.contains(&index) {
2052 let PathSeg(def_id, index) = path_segs.last().unwrap();
2053 self.ast_path_to_ty(span, *def_id, &path.segments[*index])
2055 Res::Def(DefKind::TyParam, def_id) => {
2056 assert_eq!(opt_self_ty, None);
2057 self.prohibit_generics(&path.segments);
2059 let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
2060 let item_id = tcx.hir().get_parent_node(hir_id);
2061 let item_def_id = tcx.hir().local_def_id(item_id);
2062 let generics = tcx.generics_of(item_def_id);
2063 let index = generics.param_def_id_to_index[&def_id];
2064 tcx.mk_ty_param(index, tcx.hir().name(hir_id))
2066 Res::SelfTy(Some(_), None) => {
2067 // `Self` in trait or type alias.
2068 assert_eq!(opt_self_ty, None);
2069 self.prohibit_generics(&path.segments);
2070 tcx.types.self_param
2072 Res::SelfTy(_, Some(def_id)) => {
2073 // `Self` in impl (we know the concrete type).
2074 assert_eq!(opt_self_ty, None);
2075 self.prohibit_generics(&path.segments);
2076 // Try to evaluate any array length constants.
2077 self.normalize_ty(span, tcx.at(span).type_of(def_id))
2079 Res::Def(DefKind::AssocTy, def_id) => {
2080 debug_assert!(path.segments.len() >= 2);
2081 self.prohibit_generics(&path.segments[..path.segments.len() - 2]);
2082 self.qpath_to_ty(span,
2085 &path.segments[path.segments.len() - 2],
2086 path.segments.last().unwrap())
2088 Res::PrimTy(prim_ty) => {
2089 assert_eq!(opt_self_ty, None);
2090 self.prohibit_generics(&path.segments);
2092 hir::Bool => tcx.types.bool,
2093 hir::Char => tcx.types.char,
2094 hir::Int(it) => tcx.mk_mach_int(it),
2095 hir::Uint(uit) => tcx.mk_mach_uint(uit),
2096 hir::Float(ft) => tcx.mk_mach_float(ft),
2097 hir::Str => tcx.mk_str()
2101 self.set_tainted_by_errors();
2102 return self.tcx().types.err;
2104 _ => span_bug!(span, "unexpected resolution: {:?}", path.res)
2108 /// Parses the programmer's textual representation of a type into our
2109 /// internal notion of a type.
2110 pub fn ast_ty_to_ty(&self, ast_ty: &hir::Ty) -> Ty<'tcx> {
2111 debug!("ast_ty_to_ty(id={:?}, ast_ty={:?} ty_ty={:?})",
2112 ast_ty.hir_id, ast_ty, ast_ty.kind);
2114 let tcx = self.tcx();
2116 let result_ty = match ast_ty.kind {
2117 hir::TyKind::Slice(ref ty) => {
2118 tcx.mk_slice(self.ast_ty_to_ty(&ty))
2120 hir::TyKind::Ptr(ref mt) => {
2121 tcx.mk_ptr(ty::TypeAndMut {
2122 ty: self.ast_ty_to_ty(&mt.ty),
2126 hir::TyKind::Rptr(ref region, ref mt) => {
2127 let r = self.ast_region_to_region(region, None);
2128 debug!("ast_ty_to_ty: r={:?}", r);
2129 let t = self.ast_ty_to_ty(&mt.ty);
2130 tcx.mk_ref(r, ty::TypeAndMut {ty: t, mutbl: mt.mutbl})
2132 hir::TyKind::Never => {
2135 hir::TyKind::Tup(ref fields) => {
2136 tcx.mk_tup(fields.iter().map(|t| self.ast_ty_to_ty(&t)))
2138 hir::TyKind::BareFn(ref bf) => {
2139 require_c_abi_if_c_variadic(tcx, &bf.decl, bf.abi, ast_ty.span);
2140 tcx.mk_fn_ptr(self.ty_of_fn(bf.unsafety, bf.abi, &bf.decl))
2142 hir::TyKind::TraitObject(ref bounds, ref lifetime) => {
2143 self.conv_object_ty_poly_trait_ref(ast_ty.span, bounds, lifetime)
2145 hir::TyKind::Path(hir::QPath::Resolved(ref maybe_qself, ref path)) => {
2146 debug!("ast_ty_to_ty: maybe_qself={:?} path={:?}", maybe_qself, path);
2147 let opt_self_ty = maybe_qself.as_ref().map(|qself| {
2148 self.ast_ty_to_ty(qself)
2150 self.res_to_ty(opt_self_ty, path, false)
2152 hir::TyKind::Def(item_id, ref lifetimes) => {
2153 let did = tcx.hir().local_def_id(item_id.id);
2154 self.impl_trait_ty_to_ty(did, lifetimes)
2156 hir::TyKind::Path(hir::QPath::TypeRelative(ref qself, ref segment)) => {
2157 debug!("ast_ty_to_ty: qself={:?} segment={:?}", qself, segment);
2158 let ty = self.ast_ty_to_ty(qself);
2160 let res = if let hir::TyKind::Path(hir::QPath::Resolved(_, ref path)) = qself.kind {
2165 self.associated_path_to_ty(ast_ty.hir_id, ast_ty.span, ty, res, segment, false)
2166 .map(|(ty, _, _)| ty).unwrap_or(tcx.types.err)
2168 hir::TyKind::Array(ref ty, ref length) => {
2169 let length = self.ast_const_to_const(length, tcx.types.usize);
2170 let array_ty = tcx.mk_ty(ty::Array(self.ast_ty_to_ty(&ty), length));
2171 self.normalize_ty(ast_ty.span, array_ty)
2173 hir::TyKind::Typeof(ref _e) => {
2174 struct_span_err!(tcx.sess, ast_ty.span, E0516,
2175 "`typeof` is a reserved keyword but unimplemented")
2176 .span_label(ast_ty.span, "reserved keyword")
2181 hir::TyKind::Infer => {
2182 // Infer also appears as the type of arguments or return
2183 // values in a ExprKind::Closure, or as
2184 // the type of local variables. Both of these cases are
2185 // handled specially and will not descend into this routine.
2186 self.ty_infer(None, ast_ty.span)
2188 hir::TyKind::Err => {
2193 debug!("ast_ty_to_ty: result_ty={:?}", result_ty);
2195 self.record_ty(ast_ty.hir_id, result_ty, ast_ty.span);
2199 /// Returns the `DefId` of the constant parameter that the provided expression is a path to.
2200 pub fn const_param_def_id(&self, expr: &hir::Expr) -> Option<DefId> {
2201 // Unwrap a block, so that e.g. `{ P }` is recognised as a parameter. Const arguments
2202 // currently have to be wrapped in curly brackets, so it's necessary to special-case.
2203 let expr = match &expr.kind {
2204 ExprKind::Block(block, _) if block.stmts.is_empty() && block.expr.is_some() =>
2205 block.expr.as_ref().unwrap(),
2210 ExprKind::Path(hir::QPath::Resolved(_, path)) => match path.res {
2211 Res::Def(DefKind::ConstParam, did) => Some(did),
2218 pub fn ast_const_to_const(
2220 ast_const: &hir::AnonConst,
2222 ) -> &'tcx ty::Const<'tcx> {
2223 debug!("ast_const_to_const(id={:?}, ast_const={:?})", ast_const.hir_id, ast_const);
2225 let tcx = self.tcx();
2226 let def_id = tcx.hir().local_def_id(ast_const.hir_id);
2228 let mut const_ = ty::Const {
2229 val: ConstValue::Unevaluated(
2231 InternalSubsts::identity_for_item(tcx, def_id),
2236 let expr = &tcx.hir().body(ast_const.body).value;
2237 if let Some(def_id) = self.const_param_def_id(expr) {
2238 // Find the name and index of the const parameter by indexing the generics of the
2239 // parent item and construct a `ParamConst`.
2240 let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
2241 let item_id = tcx.hir().get_parent_node(hir_id);
2242 let item_def_id = tcx.hir().local_def_id(item_id);
2243 let generics = tcx.generics_of(item_def_id);
2244 let index = generics.param_def_id_to_index[&tcx.hir().local_def_id(hir_id)];
2245 let name = tcx.hir().name(hir_id);
2246 const_.val = ConstValue::Param(ty::ParamConst::new(index, name));
2249 tcx.mk_const(const_)
2252 pub fn impl_trait_ty_to_ty(
2255 lifetimes: &[hir::GenericArg],
2257 debug!("impl_trait_ty_to_ty(def_id={:?}, lifetimes={:?})", def_id, lifetimes);
2258 let tcx = self.tcx();
2260 let generics = tcx.generics_of(def_id);
2262 debug!("impl_trait_ty_to_ty: generics={:?}", generics);
2263 let substs = InternalSubsts::for_item(tcx, def_id, |param, _| {
2264 if let Some(i) = (param.index as usize).checked_sub(generics.parent_count) {
2265 // Our own parameters are the resolved lifetimes.
2267 GenericParamDefKind::Lifetime => {
2268 if let hir::GenericArg::Lifetime(lifetime) = &lifetimes[i] {
2269 self.ast_region_to_region(lifetime, None).into()
2277 // Replace all parent lifetimes with `'static`.
2279 GenericParamDefKind::Lifetime => {
2280 tcx.lifetimes.re_static.into()
2282 _ => tcx.mk_param_from_def(param)
2286 debug!("impl_trait_ty_to_ty: substs={:?}", substs);
2288 let ty = tcx.mk_opaque(def_id, substs);
2289 debug!("impl_trait_ty_to_ty: {}", ty);
2293 pub fn ty_of_arg(&self,
2295 expected_ty: Option<Ty<'tcx>>)
2299 hir::TyKind::Infer if expected_ty.is_some() => {
2300 self.record_ty(ty.hir_id, expected_ty.unwrap(), ty.span);
2301 expected_ty.unwrap()
2303 _ => self.ast_ty_to_ty(ty),
2307 pub fn ty_of_fn(&self,
2308 unsafety: hir::Unsafety,
2311 -> ty::PolyFnSig<'tcx> {
2314 let tcx = self.tcx();
2316 decl.inputs.iter().map(|a| self.ty_of_arg(a, None));
2318 let output_ty = match decl.output {
2319 hir::Return(ref output) => self.ast_ty_to_ty(output),
2320 hir::DefaultReturn(..) => tcx.mk_unit(),
2323 debug!("ty_of_fn: output_ty={:?}", output_ty);
2325 let bare_fn_ty = ty::Binder::bind(tcx.mk_fn_sig(
2333 // Find any late-bound regions declared in return type that do
2334 // not appear in the arguments. These are not well-formed.
2337 // for<'a> fn() -> &'a str <-- 'a is bad
2338 // for<'a> fn(&'a String) -> &'a str <-- 'a is ok
2339 let inputs = bare_fn_ty.inputs();
2340 let late_bound_in_args = tcx.collect_constrained_late_bound_regions(
2341 &inputs.map_bound(|i| i.to_owned()));
2342 let output = bare_fn_ty.output();
2343 let late_bound_in_ret = tcx.collect_referenced_late_bound_regions(&output);
2344 for br in late_bound_in_ret.difference(&late_bound_in_args) {
2345 let lifetime_name = match *br {
2346 ty::BrNamed(_, name) => format!("lifetime `{}`,", name),
2347 ty::BrAnon(_) | ty::BrEnv => "an anonymous lifetime".to_string(),
2349 let mut err = struct_span_err!(tcx.sess,
2352 "return type references {} \
2353 which is not constrained by the fn input types",
2355 if let ty::BrAnon(_) = *br {
2356 // The only way for an anonymous lifetime to wind up
2357 // in the return type but **also** be unconstrained is
2358 // if it only appears in "associated types" in the
2359 // input. See #47511 for an example. In this case,
2360 // though we can easily give a hint that ought to be
2362 err.note("lifetimes appearing in an associated type \
2363 are not considered constrained");
2371 /// Given the bounds on an object, determines what single region bound (if any) we can
2372 /// use to summarize this type. The basic idea is that we will use the bound the user
2373 /// provided, if they provided one, and otherwise search the supertypes of trait bounds
2374 /// for region bounds. It may be that we can derive no bound at all, in which case
2375 /// we return `None`.
2376 fn compute_object_lifetime_bound(&self,
2378 existential_predicates: ty::Binder<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>>)
2379 -> Option<ty::Region<'tcx>> // if None, use the default
2381 let tcx = self.tcx();
2383 debug!("compute_opt_region_bound(existential_predicates={:?})",
2384 existential_predicates);
2386 // No explicit region bound specified. Therefore, examine trait
2387 // bounds and see if we can derive region bounds from those.
2388 let derived_region_bounds =
2389 object_region_bounds(tcx, existential_predicates);
2391 // If there are no derived region bounds, then report back that we
2392 // can find no region bound. The caller will use the default.
2393 if derived_region_bounds.is_empty() {
2397 // If any of the derived region bounds are 'static, that is always
2399 if derived_region_bounds.iter().any(|&r| ty::ReStatic == *r) {
2400 return Some(tcx.lifetimes.re_static);
2403 // Determine whether there is exactly one unique region in the set
2404 // of derived region bounds. If so, use that. Otherwise, report an
2406 let r = derived_region_bounds[0];
2407 if derived_region_bounds[1..].iter().any(|r1| r != *r1) {
2408 span_err!(tcx.sess, span, E0227,
2409 "ambiguous lifetime bound, explicit lifetime bound required");
2415 /// Collects together a list of bounds that are applied to some type,
2416 /// after they've been converted into `ty` form (from the HIR
2417 /// representations). These lists of bounds occur in many places in
2421 /// trait Foo: Bar + Baz { }
2422 /// ^^^^^^^^^ supertrait list bounding the `Self` type parameter
2424 /// fn foo<T: Bar + Baz>() { }
2425 /// ^^^^^^^^^ bounding the type parameter `T`
2427 /// impl dyn Bar + Baz
2428 /// ^^^^^^^^^ bounding the forgotten dynamic type
2431 /// Our representation is a bit mixed here -- in some cases, we
2432 /// include the self type (e.g., `trait_bounds`) but in others we do
2433 #[derive(Default, PartialEq, Eq, Clone, Debug)]
2434 pub struct Bounds<'tcx> {
2435 /// A list of region bounds on the (implicit) self type. So if you
2436 /// had `T: 'a + 'b` this might would be a list `['a, 'b]` (but
2437 /// the `T` is not explicitly included).
2438 pub region_bounds: Vec<(ty::Region<'tcx>, Span)>,
2440 /// A list of trait bounds. So if you had `T: Debug` this would be
2441 /// `T: Debug`. Note that the self-type is explicit here.
2442 pub trait_bounds: Vec<(ty::PolyTraitRef<'tcx>, Span)>,
2444 /// A list of projection equality bounds. So if you had `T:
2445 /// Iterator<Item = u32>` this would include `<T as
2446 /// Iterator>::Item => u32`. Note that the self-type is explicit
2448 pub projection_bounds: Vec<(ty::PolyProjectionPredicate<'tcx>, Span)>,
2450 /// `Some` if there is *no* `?Sized` predicate. The `span`
2451 /// is the location in the source of the `T` declaration which can
2452 /// be cited as the source of the `T: Sized` requirement.
2453 pub implicitly_sized: Option<Span>,
2456 impl<'tcx> Bounds<'tcx> {
2457 /// Converts a bounds list into a flat set of predicates (like
2458 /// where-clauses). Because some of our bounds listings (e.g.,
2459 /// regions) don't include the self-type, you must supply the
2460 /// self-type here (the `param_ty` parameter).
2465 ) -> Vec<(ty::Predicate<'tcx>, Span)> {
2466 // If it could be sized, and is, add the `Sized` predicate.
2467 let sized_predicate = self.implicitly_sized.and_then(|span| {
2468 tcx.lang_items().sized_trait().map(|sized| {
2469 let trait_ref = ty::TraitRef {
2471 substs: tcx.mk_substs_trait(param_ty, &[])
2473 (trait_ref.to_predicate(), span)
2477 sized_predicate.into_iter().chain(
2478 self.region_bounds.iter().map(|&(region_bound, span)| {
2479 // Account for the binder being introduced below; no need to shift `param_ty`
2480 // because, at present at least, it can only refer to early-bound regions.
2481 let region_bound = ty::fold::shift_region(tcx, region_bound, 1);
2482 let outlives = ty::OutlivesPredicate(param_ty, region_bound);
2483 (ty::Binder::dummy(outlives).to_predicate(), span)
2485 self.trait_bounds.iter().map(|&(bound_trait_ref, span)| {
2486 (bound_trait_ref.to_predicate(), span)
2489 self.projection_bounds.iter().map(|&(projection, span)| {
2490 (projection.to_predicate(), span)