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) -> ty::GenericPredicates<'tcx>;
59 /// Returns the lifetime to use when a lifetime is omitted (and not elided).
62 param: Option<&ty::GenericParamDef>,
65 -> Option<ty::Region<'tcx>>;
67 /// Returns the type to use when a type is omitted.
68 fn ty_infer(&self, param: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx>;
70 /// Returns the const to use when a const is omitted.
74 param: Option<&ty::GenericParamDef>,
76 ) -> &'tcx Const<'tcx>;
78 /// Projecting an associated type from a (potentially)
79 /// higher-ranked trait reference is more complicated, because of
80 /// the possibility of late-bound regions appearing in the
81 /// associated type binding. This is not legal in function
82 /// signatures for that reason. In a function body, we can always
83 /// handle it because we can use inference variables to remove the
84 /// late-bound regions.
85 fn projected_ty_from_poly_trait_ref(&self,
88 poly_trait_ref: ty::PolyTraitRef<'tcx>)
91 /// Normalize an associated type coming from the user.
92 fn normalize_ty(&self, span: Span, ty: Ty<'tcx>) -> Ty<'tcx>;
94 /// Invoked when we encounter an error from some prior pass
95 /// (e.g., resolve) that is translated into a ty-error. This is
96 /// used to help suppress derived errors typeck might otherwise
98 fn set_tainted_by_errors(&self);
100 fn record_ty(&self, hir_id: hir::HirId, ty: Ty<'tcx>, span: Span);
103 pub enum SizedByDefault {
108 struct ConvertedBinding<'a, 'tcx> {
109 item_name: ast::Ident,
110 kind: ConvertedBindingKind<'a, 'tcx>,
114 enum ConvertedBindingKind<'a, 'tcx> {
116 Constraint(&'a [hir::GenericBound]),
120 enum GenericArgPosition {
122 Value, // e.g., functions
126 impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
127 pub fn ast_region_to_region(&self,
128 lifetime: &hir::Lifetime,
129 def: Option<&ty::GenericParamDef>)
132 let tcx = self.tcx();
133 let lifetime_name = |def_id| {
134 tcx.hir().name(tcx.hir().as_local_hir_id(def_id).unwrap())
137 let r = match tcx.named_region(lifetime.hir_id) {
138 Some(rl::Region::Static) => {
139 tcx.lifetimes.re_static
142 Some(rl::Region::LateBound(debruijn, id, _)) => {
143 let name = lifetime_name(id);
144 tcx.mk_region(ty::ReLateBound(debruijn,
145 ty::BrNamed(id, name)))
148 Some(rl::Region::LateBoundAnon(debruijn, index)) => {
149 tcx.mk_region(ty::ReLateBound(debruijn, ty::BrAnon(index)))
152 Some(rl::Region::EarlyBound(index, id, _)) => {
153 let name = lifetime_name(id);
154 tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion {
161 Some(rl::Region::Free(scope, id)) => {
162 let name = lifetime_name(id);
163 tcx.mk_region(ty::ReFree(ty::FreeRegion {
165 bound_region: ty::BrNamed(id, name)
168 // (*) -- not late-bound, won't change
172 self.re_infer(def, lifetime.span)
174 // This indicates an illegal lifetime
175 // elision. `resolve_lifetime` should have
176 // reported an error in this case -- but if
177 // not, let's error out.
178 tcx.sess.delay_span_bug(lifetime.span, "unelided lifetime in signature");
180 // Supply some dummy value. We don't have an
181 // `re_error`, annoyingly, so use `'static`.
182 tcx.lifetimes.re_static
187 debug!("ast_region_to_region(lifetime={:?}) yields {:?}",
194 /// Given a path `path` that refers to an item `I` with the declared generics `decl_generics`,
195 /// returns an appropriate set of substitutions for this particular reference to `I`.
196 pub fn ast_path_substs_for_ty(&self,
199 item_segment: &hir::PathSegment)
202 let (substs, assoc_bindings, _) = self.create_substs_for_ast_path(
205 item_segment.generic_args(),
206 item_segment.infer_args,
210 assoc_bindings.first().map(|b| Self::prohibit_assoc_ty_binding(self.tcx(), b.span));
215 /// Report error if there is an explicit type parameter when using `impl Trait`.
218 seg: &hir::PathSegment,
219 generics: &ty::Generics,
221 let explicit = !seg.infer_args;
222 let impl_trait = generics.params.iter().any(|param| match param.kind {
223 ty::GenericParamDefKind::Type {
224 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait), ..
229 if explicit && impl_trait {
231 seg.generic_args().args
235 GenericArg::Type(_) => Some(arg.span()),
238 .collect::<Vec<_>>();
240 let mut err = struct_span_err! {
244 "cannot provide explicit generic arguments when `impl Trait` is \
245 used in argument position"
249 err.span_label(span, "explicit generic argument not allowed");
258 /// Checks that the correct number of generic arguments have been provided.
259 /// Used specifically for function calls.
260 pub fn check_generic_arg_count_for_call(
264 seg: &hir::PathSegment,
265 is_method_call: bool,
267 let empty_args = P(hir::GenericArgs {
268 args: HirVec::new(), bindings: HirVec::new(), parenthesized: false,
270 let suppress_mismatch = Self::check_impl_trait(tcx, seg, &def);
271 Self::check_generic_arg_count(
275 if let Some(ref args) = seg.args {
281 GenericArgPosition::MethodCall
283 GenericArgPosition::Value
285 def.parent.is_none() && def.has_self, // `has_self`
286 seg.infer_args || suppress_mismatch, // `infer_args`
290 /// Checks that the correct number of generic arguments have been provided.
291 /// This is used both for datatypes and function calls.
292 fn check_generic_arg_count(
296 args: &hir::GenericArgs,
297 position: GenericArgPosition,
300 ) -> (bool, Option<Vec<Span>>) {
301 // At this stage we are guaranteed that the generic arguments are in the correct order, e.g.
302 // that lifetimes will proceed types. So it suffices to check the number of each generic
303 // arguments in order to validate them with respect to the generic parameters.
304 let param_counts = def.own_counts();
305 let arg_counts = args.own_counts();
306 let infer_lifetimes = position != GenericArgPosition::Type && arg_counts.lifetimes == 0;
308 let mut defaults: ty::GenericParamCount = Default::default();
309 for param in &def.params {
311 GenericParamDefKind::Lifetime => {}
312 GenericParamDefKind::Type { has_default, .. } => {
313 defaults.types += has_default as usize
315 GenericParamDefKind::Const => {
316 // FIXME(const_generics:defaults)
321 if position != GenericArgPosition::Type && !args.bindings.is_empty() {
322 AstConv::prohibit_assoc_ty_binding(tcx, args.bindings[0].span);
325 // Prohibit explicit lifetime arguments if late-bound lifetime parameters are present.
326 let mut reported_late_bound_region_err = None;
327 if !infer_lifetimes {
328 if let Some(span_late) = def.has_late_bound_regions {
329 let msg = "cannot specify lifetime arguments explicitly \
330 if late bound lifetime parameters are present";
331 let note = "the late bound lifetime parameter is introduced here";
332 let span = args.args[0].span();
333 if position == GenericArgPosition::Value
334 && arg_counts.lifetimes != param_counts.lifetimes {
335 let mut err = tcx.sess.struct_span_err(span, msg);
336 err.span_note(span_late, note);
338 reported_late_bound_region_err = Some(true);
340 let mut multispan = MultiSpan::from_span(span);
341 multispan.push_span_label(span_late, note.to_string());
342 tcx.lint_hir(lint::builtin::LATE_BOUND_LIFETIME_ARGUMENTS,
343 args.args[0].id(), multispan, msg);
344 reported_late_bound_region_err = Some(false);
349 let check_kind_count = |kind, required, permitted, provided, offset| {
351 "check_kind_count: kind: {} required: {} permitted: {} provided: {} offset: {}",
358 // We enforce the following: `required` <= `provided` <= `permitted`.
359 // For kinds without defaults (e.g.., lifetimes), `required == permitted`.
360 // For other kinds (i.e., types), `permitted` may be greater than `required`.
361 if required <= provided && provided <= permitted {
362 return (reported_late_bound_region_err.unwrap_or(false), None);
365 // Unfortunately lifetime and type parameter mismatches are typically styled
366 // differently in diagnostics, which means we have a few cases to consider here.
367 let (bound, quantifier) = if required != permitted {
368 if provided < required {
369 (required, "at least ")
370 } else { // provided > permitted
371 (permitted, "at most ")
377 let mut potential_assoc_types: Option<Vec<Span>> = None;
378 let (spans, label) = if required == permitted && provided > permitted {
379 // In the case when the user has provided too many arguments,
380 // we want to point to the unexpected arguments.
381 let spans: Vec<Span> = args.args[offset+permitted .. offset+provided]
383 .map(|arg| arg.span())
385 potential_assoc_types = Some(spans.clone());
386 (spans, format!( "unexpected {} argument", kind))
388 (vec![span], format!(
389 "expected {}{} {} argument{}",
397 let mut err = tcx.sess.struct_span_err_with_code(
400 "wrong number of {} arguments: expected {}{}, found {}",
406 DiagnosticId::Error("E0107".into())
409 err.span_label(span, label.as_str());
414 provided > required, // `suppress_error`
415 potential_assoc_types,
419 if reported_late_bound_region_err.is_none()
420 && (!infer_lifetimes || arg_counts.lifetimes > param_counts.lifetimes) {
423 param_counts.lifetimes,
424 param_counts.lifetimes,
425 arg_counts.lifetimes,
429 // FIXME(const_generics:defaults)
430 if !infer_args || arg_counts.consts > param_counts.consts {
436 arg_counts.lifetimes + arg_counts.types,
439 // Note that type errors are currently be emitted *after* const errors.
441 || arg_counts.types > param_counts.types - defaults.types - has_self as usize {
444 param_counts.types - defaults.types - has_self as usize,
445 param_counts.types - has_self as usize,
447 arg_counts.lifetimes,
450 (reported_late_bound_region_err.unwrap_or(false), None)
454 /// Creates the relevant generic argument substitutions
455 /// corresponding to a set of generic parameters. This is a
456 /// rather complex function. Let us try to explain the role
457 /// of each of its parameters:
459 /// To start, we are given the `def_id` of the thing we are
460 /// creating the substitutions for, and a partial set of
461 /// substitutions `parent_substs`. In general, the substitutions
462 /// for an item begin with substitutions for all the "parents" of
463 /// that item -- e.g., for a method it might include the
464 /// parameters from the impl.
466 /// Therefore, the method begins by walking down these parents,
467 /// starting with the outermost parent and proceed inwards until
468 /// it reaches `def_id`. For each parent `P`, it will check `parent_substs`
469 /// first to see if the parent's substitutions are listed in there. If so,
470 /// we can append those and move on. Otherwise, it invokes the
471 /// three callback functions:
473 /// - `args_for_def_id`: given the `DefId` `P`, supplies back the
474 /// generic arguments that were given to that parent from within
475 /// the path; so e.g., if you have `<T as Foo>::Bar`, the `DefId`
476 /// might refer to the trait `Foo`, and the arguments might be
477 /// `[T]`. The boolean value indicates whether to infer values
478 /// for arguments whose values were not explicitly provided.
479 /// - `provided_kind`: given the generic parameter and the value from `args_for_def_id`,
480 /// instantiate a `GenericArg`.
481 /// - `inferred_kind`: if no parameter was provided, and inference is enabled, then
482 /// creates a suitable inference variable.
483 pub fn create_substs_for_generic_args<'b>(
486 parent_substs: &[subst::GenericArg<'tcx>],
488 self_ty: Option<Ty<'tcx>>,
489 args_for_def_id: impl Fn(DefId) -> (Option<&'b GenericArgs>, bool),
490 provided_kind: impl Fn(&GenericParamDef, &GenericArg) -> subst::GenericArg<'tcx>,
491 inferred_kind: impl Fn(Option<&[subst::GenericArg<'tcx>]>, &GenericParamDef, bool)
492 -> subst::GenericArg<'tcx>,
493 ) -> SubstsRef<'tcx> {
494 // Collect the segments of the path; we need to substitute arguments
495 // for parameters throughout the entire path (wherever there are
496 // generic parameters).
497 let mut parent_defs = tcx.generics_of(def_id);
498 let count = parent_defs.count();
499 let mut stack = vec![(def_id, parent_defs)];
500 while let Some(def_id) = parent_defs.parent {
501 parent_defs = tcx.generics_of(def_id);
502 stack.push((def_id, parent_defs));
505 // We manually build up the substitution, rather than using convenience
506 // methods in `subst.rs`, so that we can iterate over the arguments and
507 // parameters in lock-step linearly, instead of trying to match each pair.
508 let mut substs: SmallVec<[subst::GenericArg<'tcx>; 8]> = SmallVec::with_capacity(count);
510 // Iterate over each segment of the path.
511 while let Some((def_id, defs)) = stack.pop() {
512 let mut params = defs.params.iter().peekable();
514 // If we have already computed substitutions for parents, we can use those directly.
515 while let Some(¶m) = params.peek() {
516 if let Some(&kind) = parent_substs.get(param.index as usize) {
524 // `Self` is handled first, unless it's been handled in `parent_substs`.
526 if let Some(¶m) = params.peek() {
527 if param.index == 0 {
528 if let GenericParamDefKind::Type { .. } = param.kind {
529 substs.push(self_ty.map(|ty| ty.into())
530 .unwrap_or_else(|| inferred_kind(None, param, true)));
537 // Check whether this segment takes generic arguments and the user has provided any.
538 let (generic_args, infer_args) = args_for_def_id(def_id);
540 let mut args = generic_args.iter().flat_map(|generic_args| generic_args.args.iter())
544 // We're going to iterate through the generic arguments that the user
545 // provided, matching them with the generic parameters we expect.
546 // Mismatches can occur as a result of elided lifetimes, or for malformed
547 // input. We try to handle both sensibly.
548 match (args.peek(), params.peek()) {
549 (Some(&arg), Some(¶m)) => {
550 match (arg, ¶m.kind) {
551 (GenericArg::Lifetime(_), GenericParamDefKind::Lifetime)
552 | (GenericArg::Type(_), GenericParamDefKind::Type { .. })
553 | (GenericArg::Const(_), GenericParamDefKind::Const) => {
554 substs.push(provided_kind(param, arg));
558 (GenericArg::Type(_), GenericParamDefKind::Lifetime)
559 | (GenericArg::Const(_), GenericParamDefKind::Lifetime) => {
560 // We expected a lifetime argument, but got a type or const
561 // argument. That means we're inferring the lifetimes.
562 substs.push(inferred_kind(None, param, infer_args));
566 // We expected one kind of parameter, but the user provided
567 // another. This is an error, but we need to handle it
568 // gracefully so we can report sensible errors.
569 // In this case, we're simply going to infer this argument.
575 // We should never be able to reach this point with well-formed input.
576 // Getting to this point means the user supplied more arguments than
577 // there are parameters.
580 (None, Some(¶m)) => {
581 // If there are fewer arguments than parameters, it means
582 // we're inferring the remaining arguments.
583 substs.push(inferred_kind(Some(&substs), param, infer_args));
587 (None, None) => break,
592 tcx.intern_substs(&substs)
595 /// Given the type/lifetime/const arguments provided to some path (along with
596 /// an implicit `Self`, if this is a trait reference), returns the complete
597 /// set of substitutions. This may involve applying defaulted type parameters.
598 /// Also returns back constriants on associated types.
603 /// T: std::ops::Index<usize, Output = u32>
604 /// ^1 ^^^^^^^^^^^^^^2 ^^^^3 ^^^^^^^^^^^4
607 /// 1. The `self_ty` here would refer to the type `T`.
608 /// 2. The path in question is the path to the trait `std::ops::Index`,
609 /// which will have been resolved to a `def_id`
610 /// 3. The `generic_args` contains info on the `<...>` contents. The `usize` type
611 /// parameters are returned in the `SubstsRef`, the associated type bindings like
612 /// `Output = u32` are returned in the `Vec<ConvertedBinding...>` result.
614 /// Note that the type listing given here is *exactly* what the user provided.
615 fn create_substs_for_ast_path<'a>(&self,
618 generic_args: &'a hir::GenericArgs,
620 self_ty: Option<Ty<'tcx>>)
621 -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'a, 'tcx>>, Option<Vec<Span>>)
623 // If the type is parameterized by this region, then replace this
624 // region with the current anon region binding (in other words,
625 // whatever & would get replaced with).
626 debug!("create_substs_for_ast_path(def_id={:?}, self_ty={:?}, \
628 def_id, self_ty, generic_args);
630 let tcx = self.tcx();
631 let generic_params = tcx.generics_of(def_id);
633 // If a self-type was declared, one should be provided.
634 assert_eq!(generic_params.has_self, self_ty.is_some());
636 let has_self = generic_params.has_self;
637 let (_, potential_assoc_types) = Self::check_generic_arg_count(
642 GenericArgPosition::Type,
647 let is_object = self_ty.map_or(false, |ty| {
648 ty == self.tcx().types.trait_object_dummy_self
650 let default_needs_object_self = |param: &ty::GenericParamDef| {
651 if let GenericParamDefKind::Type { has_default, .. } = param.kind {
652 if is_object && has_default && has_self {
653 let self_param = tcx.types.self_param;
654 if tcx.at(span).type_of(param.def_id).walk().any(|ty| ty == self_param) {
655 // There is no suitable inference default for a type parameter
656 // that references self, in an object type.
665 let substs = Self::create_substs_for_generic_args(
671 // Provide the generic args, and whether types should be inferred.
672 |_| (Some(generic_args), infer_args),
673 // Provide substitutions for parameters for which (valid) arguments have been provided.
675 match (¶m.kind, arg) {
676 (GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => {
677 self.ast_region_to_region(<, Some(param)).into()
679 (GenericParamDefKind::Type { .. }, GenericArg::Type(ty)) => {
680 self.ast_ty_to_ty(&ty).into()
682 (GenericParamDefKind::Const, GenericArg::Const(ct)) => {
683 self.ast_const_to_const(&ct.value, tcx.type_of(param.def_id)).into()
688 // Provide substitutions for parameters for which arguments are inferred.
689 |substs, param, infer_args| {
691 GenericParamDefKind::Lifetime => tcx.lifetimes.re_static.into(),
692 GenericParamDefKind::Type { has_default, .. } => {
693 if !infer_args && has_default {
694 // No type parameter provided, but a default exists.
696 // If we are converting an object type, then the
697 // `Self` parameter is unknown. However, some of the
698 // other type parameters may reference `Self` in their
699 // defaults. This will lead to an ICE if we are not
701 if default_needs_object_self(param) {
702 struct_span_err!(tcx.sess, span, E0393,
703 "the type parameter `{}` must be explicitly specified",
706 .span_label(span, format!(
707 "missing reference to `{}`", param.name))
709 "because of the default `Self` reference, type parameters \
710 must be specified on object types"))
714 // This is a default type parameter.
717 tcx.at(span).type_of(param.def_id)
718 .subst_spanned(tcx, substs.unwrap(), Some(span))
721 } else if infer_args {
722 // No type parameters were provided, we can infer all.
723 let param = if !default_needs_object_self(param) {
728 self.ty_infer(param, span).into()
730 // We've already errored above about the mismatch.
734 GenericParamDefKind::Const => {
735 // FIXME(const_generics:defaults)
737 // No const parameters were provided, we can infer all.
738 let ty = tcx.at(span).type_of(param.def_id);
739 self.ct_infer(ty, Some(param), span).into()
741 // We've already errored above about the mismatch.
742 tcx.consts.err.into()
749 // Convert associated-type bindings or constraints into a separate vector.
750 // Example: Given this:
752 // T: Iterator<Item = u32>
754 // The `T` is passed in as a self-type; the `Item = u32` is
755 // not a "type parameter" of the `Iterator` trait, but rather
756 // a restriction on `<T as Iterator>::Item`, so it is passed
758 let assoc_bindings = generic_args.bindings.iter()
760 let kind = match binding.kind {
761 hir::TypeBindingKind::Equality { ref ty } =>
762 ConvertedBindingKind::Equality(self.ast_ty_to_ty(ty)),
763 hir::TypeBindingKind::Constraint { ref bounds } =>
764 ConvertedBindingKind::Constraint(bounds),
767 item_name: binding.ident,
774 debug!("create_substs_for_ast_path(generic_params={:?}, self_ty={:?}) -> {:?}",
775 generic_params, self_ty, substs);
777 (substs, assoc_bindings, potential_assoc_types)
780 /// Instantiates the path for the given trait reference, assuming that it's
781 /// bound to a valid trait type. Returns the `DefId` of the defining trait.
782 /// The type _cannot_ be a type other than a trait type.
784 /// If the `projections` argument is `None`, then assoc type bindings like `Foo<T = X>`
785 /// are disallowed. Otherwise, they are pushed onto the vector given.
786 pub fn instantiate_mono_trait_ref(&self,
787 trait_ref: &hir::TraitRef,
789 ) -> ty::TraitRef<'tcx>
791 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
793 self.ast_path_to_mono_trait_ref(trait_ref.path.span,
794 trait_ref.trait_def_id(),
796 trait_ref.path.segments.last().unwrap())
799 /// The given trait-ref must actually be a trait.
800 pub(super) fn instantiate_poly_trait_ref_inner(&self,
801 trait_ref: &hir::TraitRef,
804 bounds: &mut Bounds<'tcx>,
806 ) -> Option<Vec<Span>> {
807 let trait_def_id = trait_ref.trait_def_id();
809 debug!("instantiate_poly_trait_ref({:?}, def_id={:?})", trait_ref, trait_def_id);
811 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
813 let (substs, assoc_bindings, potential_assoc_types) = self.create_substs_for_ast_trait_ref(
817 trait_ref.path.segments.last().unwrap(),
819 let poly_trait_ref = ty::Binder::bind(ty::TraitRef::new(trait_def_id, substs));
821 bounds.trait_bounds.push((poly_trait_ref, span));
823 let mut dup_bindings = FxHashMap::default();
824 for binding in &assoc_bindings {
825 // Specify type to assert that error was already reported in `Err` case.
826 let _: Result<_, ErrorReported> =
827 self.add_predicates_for_ast_type_binding(
828 trait_ref.hir_ref_id,
835 // Okay to ignore `Err` because of `ErrorReported` (see above).
838 debug!("instantiate_poly_trait_ref({:?}, bounds={:?}) -> {:?}",
839 trait_ref, bounds, poly_trait_ref);
840 potential_assoc_types
843 /// Given a trait bound like `Debug`, applies that trait bound the given self-type to construct
844 /// a full trait reference. The resulting trait reference is returned. This may also generate
845 /// auxiliary bounds, which are added to `bounds`.
850 /// poly_trait_ref = Iterator<Item = u32>
854 /// this would return `Foo: Iterator` and add `<Foo as Iterator>::Item = u32` into `bounds`.
856 /// **A note on binders:** against our usual convention, there is an implied bounder around
857 /// the `self_ty` and `poly_trait_ref` parameters here. So they may reference bound regions.
858 /// If for example you had `for<'a> Foo<'a>: Bar<'a>`, then the `self_ty` would be `Foo<'a>`
859 /// where `'a` is a bound region at depth 0. Similarly, the `poly_trait_ref` would be
860 /// `Bar<'a>`. The returned poly-trait-ref will have this binder instantiated explicitly,
862 pub fn instantiate_poly_trait_ref(&self,
863 poly_trait_ref: &hir::PolyTraitRef,
865 bounds: &mut Bounds<'tcx>,
866 ) -> Option<Vec<Span>> {
867 self.instantiate_poly_trait_ref_inner(
868 &poly_trait_ref.trait_ref,
876 fn ast_path_to_mono_trait_ref(&self,
880 trait_segment: &hir::PathSegment
881 ) -> ty::TraitRef<'tcx>
883 let (substs, assoc_bindings, _) =
884 self.create_substs_for_ast_trait_ref(span,
888 assoc_bindings.first().map(|b| AstConv::prohibit_assoc_ty_binding(self.tcx(), b.span));
889 ty::TraitRef::new(trait_def_id, substs)
892 fn create_substs_for_ast_trait_ref<'a>(
897 trait_segment: &'a hir::PathSegment,
898 ) -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'a, 'tcx>>, Option<Vec<Span>>) {
899 debug!("create_substs_for_ast_trait_ref(trait_segment={:?})",
902 let trait_def = self.tcx().trait_def(trait_def_id);
904 if !self.tcx().features().unboxed_closures &&
905 trait_segment.generic_args().parenthesized != trait_def.paren_sugar
907 // For now, require that parenthetical notation be used only with `Fn()` etc.
908 let msg = if trait_def.paren_sugar {
909 "the precise format of `Fn`-family traits' type parameters is subject to change. \
910 Use parenthetical notation (Fn(Foo, Bar) -> Baz) instead"
912 "parenthetical notation is only stable when used with `Fn`-family traits"
914 emit_feature_err(&self.tcx().sess.parse_sess, sym::unboxed_closures,
915 span, GateIssue::Language, msg);
918 self.create_substs_for_ast_path(span,
920 trait_segment.generic_args(),
921 trait_segment.infer_args,
925 fn trait_defines_associated_type_named(&self,
927 assoc_name: ast::Ident)
930 self.tcx().associated_items(trait_def_id).any(|item| {
931 item.kind == ty::AssocKind::Type &&
932 self.tcx().hygienic_eq(assoc_name, item.ident, trait_def_id)
936 // Returns `true` if a bounds list includes `?Sized`.
937 pub fn is_unsized(&self, ast_bounds: &[hir::GenericBound], span: Span) -> bool {
938 let tcx = self.tcx();
940 // Try to find an unbound in bounds.
941 let mut unbound = None;
942 for ab in ast_bounds {
943 if let &hir::GenericBound::Trait(ref ptr, hir::TraitBoundModifier::Maybe) = ab {
944 if unbound.is_none() {
945 unbound = Some(&ptr.trait_ref);
951 "type parameter has more than one relaxed default \
952 bound, only one is supported"
958 let kind_id = tcx.lang_items().require(SizedTraitLangItem);
961 // FIXME(#8559) currently requires the unbound to be built-in.
962 if let Ok(kind_id) = kind_id {
963 if tpb.path.res != Res::Def(DefKind::Trait, kind_id) {
966 "default bound relaxed for a type parameter, but \
967 this does nothing because the given bound is not \
968 a default; only `?Sized` is supported",
973 _ if kind_id.is_ok() => {
976 // No lang item for `Sized`, so we can't add it as a bound.
983 /// This helper takes a *converted* parameter type (`param_ty`)
984 /// and an *unconverted* list of bounds:
988 /// ^ ^^^^^ `ast_bounds` parameter, in HIR form
990 /// `param_ty`, in ty form
993 /// It adds these `ast_bounds` into the `bounds` structure.
995 /// **A note on binders:** there is an implied binder around
996 /// `param_ty` and `ast_bounds`. See `instantiate_poly_trait_ref`
997 /// for more details.
1000 ast_bounds: &[hir::GenericBound],
1001 bounds: &mut Bounds<'tcx>,
1003 let mut trait_bounds = Vec::new();
1004 let mut region_bounds = Vec::new();
1006 for ast_bound in ast_bounds {
1008 hir::GenericBound::Trait(ref b, hir::TraitBoundModifier::None) =>
1009 trait_bounds.push(b),
1010 hir::GenericBound::Trait(_, hir::TraitBoundModifier::Maybe) => {}
1011 hir::GenericBound::Outlives(ref l) =>
1012 region_bounds.push(l),
1016 for bound in trait_bounds {
1017 let _ = self.instantiate_poly_trait_ref(
1024 bounds.region_bounds.extend(region_bounds
1026 .map(|r| (self.ast_region_to_region(r, None), r.span))
1030 /// Translates a list of bounds from the HIR into the `Bounds` data structure.
1031 /// The self-type for the bounds is given by `param_ty`.
1036 /// fn foo<T: Bar + Baz>() { }
1037 /// ^ ^^^^^^^^^ ast_bounds
1041 /// The `sized_by_default` parameter indicates if, in this context, the `param_ty` should be
1042 /// considered `Sized` unless there is an explicit `?Sized` bound. This would be true in the
1043 /// example above, but is not true in supertrait listings like `trait Foo: Bar + Baz`.
1045 /// `span` should be the declaration size of the parameter.
1046 pub fn compute_bounds(&self,
1048 ast_bounds: &[hir::GenericBound],
1049 sized_by_default: SizedByDefault,
1052 let mut bounds = Bounds::default();
1054 self.add_bounds(param_ty, ast_bounds, &mut bounds);
1055 bounds.trait_bounds.sort_by_key(|(t, _)| t.def_id());
1057 bounds.implicitly_sized = if let SizedByDefault::Yes = sized_by_default {
1058 if !self.is_unsized(ast_bounds, span) {
1070 /// Given an HIR binding like `Item = Foo` or `Item: Foo`, pushes the corresponding predicates
1073 /// **A note on binders:** given something like `T: for<'a> Iterator<Item = &'a u32>`, the
1074 /// `trait_ref` here will be `for<'a> T: Iterator`. The `binding` data however is from *inside*
1075 /// the binder (e.g., `&'a u32`) and hence may reference bound regions.
1076 fn add_predicates_for_ast_type_binding(
1078 hir_ref_id: hir::HirId,
1079 trait_ref: ty::PolyTraitRef<'tcx>,
1080 binding: &ConvertedBinding<'_, 'tcx>,
1081 bounds: &mut Bounds<'tcx>,
1083 dup_bindings: &mut FxHashMap<DefId, Span>,
1084 ) -> Result<(), ErrorReported> {
1085 let tcx = self.tcx();
1088 // Given something like `U: SomeTrait<T = X>`, we want to produce a
1089 // predicate like `<U as SomeTrait>::T = X`. This is somewhat
1090 // subtle in the event that `T` is defined in a supertrait of
1091 // `SomeTrait`, because in that case we need to upcast.
1093 // That is, consider this case:
1096 // trait SubTrait: SuperTrait<int> { }
1097 // trait SuperTrait<A> { type T; }
1099 // ... B: SubTrait<T = foo> ...
1102 // We want to produce `<B as SuperTrait<int>>::T == foo`.
1104 // Find any late-bound regions declared in `ty` that are not
1105 // declared in the trait-ref. These are not well-formed.
1109 // for<'a> <T as Iterator>::Item = &'a str // <-- 'a is bad
1110 // for<'a> <T as FnMut<(&'a u32,)>>::Output = &'a str // <-- 'a is ok
1111 if let ConvertedBindingKind::Equality(ty) = binding.kind {
1112 let late_bound_in_trait_ref =
1113 tcx.collect_constrained_late_bound_regions(&trait_ref);
1114 let late_bound_in_ty =
1115 tcx.collect_referenced_late_bound_regions(&ty::Binder::bind(ty));
1116 debug!("late_bound_in_trait_ref = {:?}", late_bound_in_trait_ref);
1117 debug!("late_bound_in_ty = {:?}", late_bound_in_ty);
1118 for br in late_bound_in_ty.difference(&late_bound_in_trait_ref) {
1119 let br_name = match *br {
1120 ty::BrNamed(_, name) => name,
1124 "anonymous bound region {:?} in binding but not trait ref",
1128 struct_span_err!(tcx.sess,
1131 "binding for associated type `{}` references lifetime `{}`, \
1132 which does not appear in the trait input types",
1133 binding.item_name, br_name)
1139 let candidate = if self.trait_defines_associated_type_named(trait_ref.def_id(),
1140 binding.item_name) {
1141 // Simple case: X is defined in the current trait.
1144 // Otherwise, we have to walk through the supertraits to find
1146 let candidates = traits::supertraits(tcx, trait_ref).filter(|r| {
1147 self.trait_defines_associated_type_named(r.def_id(), binding.item_name)
1149 self.one_bound_for_assoc_type(candidates, &trait_ref.to_string(),
1150 binding.item_name, binding.span)
1153 let (assoc_ident, def_scope) =
1154 tcx.adjust_ident_and_get_scope(binding.item_name, candidate.def_id(), hir_ref_id);
1155 let assoc_ty = tcx.associated_items(candidate.def_id()).find(|i| {
1156 i.kind == ty::AssocKind::Type && i.ident.modern() == assoc_ident
1157 }).expect("missing associated type");
1159 if !assoc_ty.vis.is_accessible_from(def_scope, tcx) {
1160 let msg = format!("associated type `{}` is private", binding.item_name);
1161 tcx.sess.span_err(binding.span, &msg);
1163 tcx.check_stability(assoc_ty.def_id, Some(hir_ref_id), binding.span);
1166 dup_bindings.entry(assoc_ty.def_id)
1167 .and_modify(|prev_span| {
1168 struct_span_err!(self.tcx().sess, binding.span, E0719,
1169 "the value of the associated type `{}` (from the trait `{}`) \
1170 is already specified",
1172 tcx.def_path_str(assoc_ty.container.id()))
1173 .span_label(binding.span, "re-bound here")
1174 .span_label(*prev_span, format!("`{}` bound here first", binding.item_name))
1177 .or_insert(binding.span);
1180 match binding.kind {
1181 ConvertedBindingKind::Equality(ref ty) => {
1182 // "Desugar" a constraint like `T: Iterator<Item = u32>` this to
1183 // the "projection predicate" for:
1185 // `<T as Iterator>::Item = u32`
1186 bounds.projection_bounds.push((candidate.map_bound(|trait_ref| {
1187 ty::ProjectionPredicate {
1188 projection_ty: ty::ProjectionTy::from_ref_and_name(
1197 ConvertedBindingKind::Constraint(ast_bounds) => {
1198 // "Desugar" a constraint like `T: Iterator<Item: Debug>` to
1200 // `<T as Iterator>::Item: Debug`
1202 // Calling `skip_binder` is okay, because `add_bounds` expects the `param_ty`
1203 // parameter to have a skipped binder.
1204 let param_ty = tcx.mk_projection(assoc_ty.def_id, candidate.skip_binder().substs);
1205 self.add_bounds(param_ty, ast_bounds, bounds);
1211 fn ast_path_to_ty(&self,
1214 item_segment: &hir::PathSegment)
1217 let substs = self.ast_path_substs_for_ty(span, did, item_segment);
1220 self.tcx().at(span).type_of(did).subst(self.tcx(), substs)
1224 /// Transform a `PolyTraitRef` into a `PolyExistentialTraitRef` by
1225 /// removing the dummy `Self` type (`trait_object_dummy_self`).
1226 fn trait_ref_to_existential(&self, trait_ref: ty::TraitRef<'tcx>)
1227 -> ty::ExistentialTraitRef<'tcx> {
1228 if trait_ref.self_ty() != self.tcx().types.trait_object_dummy_self {
1229 bug!("trait_ref_to_existential called on {:?} with non-dummy Self", trait_ref);
1231 ty::ExistentialTraitRef::erase_self_ty(self.tcx(), trait_ref)
1234 fn conv_object_ty_poly_trait_ref(&self,
1236 trait_bounds: &[hir::PolyTraitRef],
1237 lifetime: &hir::Lifetime)
1240 let tcx = self.tcx();
1242 let mut bounds = Bounds::default();
1243 let mut potential_assoc_types = Vec::new();
1244 let dummy_self = self.tcx().types.trait_object_dummy_self;
1245 for trait_bound in trait_bounds.iter().rev() {
1246 let cur_potential_assoc_types = self.instantiate_poly_trait_ref(
1251 potential_assoc_types.extend(cur_potential_assoc_types.into_iter().flatten());
1254 // Expand trait aliases recursively and check that only one regular (non-auto) trait
1255 // is used and no 'maybe' bounds are used.
1256 let expanded_traits =
1257 traits::expand_trait_aliases(tcx, bounds.trait_bounds.iter().cloned());
1258 let (mut auto_traits, regular_traits): (Vec<_>, Vec<_>) =
1259 expanded_traits.partition(|i| tcx.trait_is_auto(i.trait_ref().def_id()));
1260 if regular_traits.len() > 1 {
1261 let first_trait = ®ular_traits[0];
1262 let additional_trait = ®ular_traits[1];
1263 let mut err = struct_span_err!(tcx.sess, additional_trait.bottom().1, E0225,
1264 "only auto traits can be used as additional traits in a trait object"
1266 additional_trait.label_with_exp_info(&mut err,
1267 "additional non-auto trait", "additional use");
1268 first_trait.label_with_exp_info(&mut err,
1269 "first non-auto trait", "first use");
1273 if regular_traits.is_empty() && auto_traits.is_empty() {
1274 span_err!(tcx.sess, span, E0224,
1275 "at least one trait is required for an object type");
1276 return tcx.types.err;
1279 // Check that there are no gross object safety violations;
1280 // most importantly, that the supertraits don't contain `Self`,
1282 for item in ®ular_traits {
1283 let object_safety_violations =
1284 tcx.astconv_object_safety_violations(item.trait_ref().def_id());
1285 if !object_safety_violations.is_empty() {
1286 tcx.report_object_safety_error(
1288 item.trait_ref().def_id(),
1289 object_safety_violations
1291 return tcx.types.err;
1295 // Use a `BTreeSet` to keep output in a more consistent order.
1296 let mut associated_types = BTreeSet::default();
1298 let regular_traits_refs = bounds.trait_bounds
1300 .filter(|(trait_ref, _)| !tcx.trait_is_auto(trait_ref.def_id()))
1301 .map(|(trait_ref, _)| trait_ref);
1302 for trait_ref in traits::elaborate_trait_refs(tcx, regular_traits_refs) {
1303 debug!("conv_object_ty_poly_trait_ref: observing object predicate `{:?}`", trait_ref);
1305 ty::Predicate::Trait(pred) => {
1307 .extend(tcx.associated_items(pred.def_id())
1308 .filter(|item| item.kind == ty::AssocKind::Type)
1309 .map(|item| item.def_id));
1311 ty::Predicate::Projection(pred) => {
1312 // A `Self` within the original bound will be substituted with a
1313 // `trait_object_dummy_self`, so check for that.
1314 let references_self =
1315 pred.skip_binder().ty.walk().any(|t| t == dummy_self);
1317 // If the projection output contains `Self`, force the user to
1318 // elaborate it explicitly to avoid a lot of complexity.
1320 // The "classicaly useful" case is the following:
1322 // trait MyTrait: FnMut() -> <Self as MyTrait>::MyOutput {
1327 // Here, the user could theoretically write `dyn MyTrait<Output = X>`,
1328 // but actually supporting that would "expand" to an infinitely-long type
1329 // `fix $ τ → dyn MyTrait<MyOutput = X, Output = <τ as MyTrait>::MyOutput`.
1331 // Instead, we force the user to write `dyn MyTrait<MyOutput = X, Output = X>`,
1332 // which is uglier but works. See the discussion in #56288 for alternatives.
1333 if !references_self {
1334 // Include projections defined on supertraits.
1335 bounds.projection_bounds.push((pred, DUMMY_SP))
1342 for (projection_bound, _) in &bounds.projection_bounds {
1343 associated_types.remove(&projection_bound.projection_def_id());
1346 if !associated_types.is_empty() {
1347 let names = associated_types.iter().map(|item_def_id| {
1348 let assoc_item = tcx.associated_item(*item_def_id);
1349 let trait_def_id = assoc_item.container.id();
1351 "`{}` (from the trait `{}`)",
1353 tcx.def_path_str(trait_def_id),
1355 }).collect::<Vec<_>>().join(", ");
1356 let mut err = struct_span_err!(
1360 "the value of the associated type{} {} must be specified",
1361 pluralise!(associated_types.len()),
1364 let (suggest, potential_assoc_types_spans) =
1365 if potential_assoc_types.len() == associated_types.len() {
1366 // Only suggest when the amount of missing associated types equals the number of
1367 // extra type arguments present, as that gives us a relatively high confidence
1368 // that the user forgot to give the associtated type's name. The canonical
1369 // example would be trying to use `Iterator<isize>` instead of
1370 // `Iterator<Item = isize>`.
1371 (true, potential_assoc_types)
1375 let mut suggestions = Vec::new();
1376 for (i, item_def_id) in associated_types.iter().enumerate() {
1377 let assoc_item = tcx.associated_item(*item_def_id);
1380 format!("associated type `{}` must be specified", assoc_item.ident),
1382 if let Some(sp) = tcx.hir().span_if_local(*item_def_id) {
1383 err.span_label(sp, format!("`{}` defined here", assoc_item.ident));
1386 if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(
1387 potential_assoc_types_spans[i],
1390 potential_assoc_types_spans[i],
1391 format!("{} = {}", assoc_item.ident, snippet),
1396 if !suggestions.is_empty() {
1397 let msg = format!("if you meant to specify the associated {}, write",
1398 if suggestions.len() == 1 { "type" } else { "types" });
1399 err.multipart_suggestion(
1402 Applicability::MaybeIncorrect,
1408 // De-duplicate auto traits so that, e.g., `dyn Trait + Send + Send` is the same as
1409 // `dyn Trait + Send`.
1410 auto_traits.sort_by_key(|i| i.trait_ref().def_id());
1411 auto_traits.dedup_by_key(|i| i.trait_ref().def_id());
1412 debug!("regular_traits: {:?}", regular_traits);
1413 debug!("auto_traits: {:?}", auto_traits);
1415 // Erase the `dummy_self` (`trait_object_dummy_self`) used above.
1416 let existential_trait_refs = regular_traits.iter().map(|i| {
1417 i.trait_ref().map_bound(|trait_ref| self.trait_ref_to_existential(trait_ref))
1419 let existential_projections = bounds.projection_bounds.iter().map(|(bound, _)| {
1420 bound.map_bound(|b| {
1421 let trait_ref = self.trait_ref_to_existential(b.projection_ty.trait_ref(tcx));
1422 ty::ExistentialProjection {
1424 item_def_id: b.projection_ty.item_def_id,
1425 substs: trait_ref.substs,
1430 // Calling `skip_binder` is okay because the predicates are re-bound.
1431 let regular_trait_predicates = existential_trait_refs.map(
1432 |trait_ref| ty::ExistentialPredicate::Trait(*trait_ref.skip_binder()));
1433 let auto_trait_predicates = auto_traits.into_iter().map(
1434 |trait_ref| ty::ExistentialPredicate::AutoTrait(trait_ref.trait_ref().def_id()));
1436 regular_trait_predicates
1437 .chain(auto_trait_predicates)
1438 .chain(existential_projections
1439 .map(|x| ty::ExistentialPredicate::Projection(*x.skip_binder())))
1440 .collect::<SmallVec<[_; 8]>>();
1441 v.sort_by(|a, b| a.stable_cmp(tcx, b));
1443 let existential_predicates = ty::Binder::bind(tcx.mk_existential_predicates(v.into_iter()));
1445 // Use explicitly-specified region bound.
1446 let region_bound = if !lifetime.is_elided() {
1447 self.ast_region_to_region(lifetime, None)
1449 self.compute_object_lifetime_bound(span, existential_predicates).unwrap_or_else(|| {
1450 if tcx.named_region(lifetime.hir_id).is_some() {
1451 self.ast_region_to_region(lifetime, None)
1453 self.re_infer(None, span).unwrap_or_else(|| {
1454 span_err!(tcx.sess, span, E0228,
1455 "the lifetime bound for this object type cannot be deduced \
1456 from context; please supply an explicit bound");
1457 tcx.lifetimes.re_static
1462 debug!("region_bound: {:?}", region_bound);
1464 let ty = tcx.mk_dynamic(existential_predicates, region_bound);
1465 debug!("trait_object_type: {:?}", ty);
1469 fn report_ambiguous_associated_type(
1476 let mut err = struct_span_err!(self.tcx().sess, span, E0223, "ambiguous associated type");
1477 if let (Some(_), Ok(snippet)) = (
1478 self.tcx().sess.confused_type_with_std_module.borrow().get(&span),
1479 self.tcx().sess.source_map().span_to_snippet(span),
1481 err.span_suggestion(
1483 "you are looking for the module in `std`, not the primitive type",
1484 format!("std::{}", snippet),
1485 Applicability::MachineApplicable,
1488 err.span_suggestion(
1490 "use fully-qualified syntax",
1491 format!("<{} as {}>::{}", type_str, trait_str, name),
1492 Applicability::HasPlaceholders
1498 // Search for a bound on a type parameter which includes the associated item
1499 // given by `assoc_name`. `ty_param_def_id` is the `DefId` of the type parameter
1500 // This function will fail if there are no suitable bounds or there is
1502 fn find_bound_for_assoc_item(&self,
1503 ty_param_def_id: DefId,
1504 assoc_name: ast::Ident,
1506 -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
1508 let tcx = self.tcx();
1511 "find_bound_for_assoc_item(ty_param_def_id={:?}, assoc_name={:?}, span={:?})",
1517 let predicates = &self.get_type_parameter_bounds(span, ty_param_def_id).predicates;
1519 debug!("find_bound_for_assoc_item: predicates={:#?}", predicates);
1521 let bounds = predicates.iter().filter_map(|(p, _)| p.to_opt_poly_trait_ref());
1523 // Check that there is exactly one way to find an associated type with the
1525 let suitable_bounds = traits::transitive_bounds(tcx, bounds)
1526 .filter(|b| self.trait_defines_associated_type_named(b.def_id(), assoc_name));
1528 let param_hir_id = tcx.hir().as_local_hir_id(ty_param_def_id).unwrap();
1529 let param_name = tcx.hir().ty_param_name(param_hir_id);
1530 self.one_bound_for_assoc_type(suitable_bounds,
1531 ¶m_name.as_str(),
1536 // Checks that `bounds` contains exactly one element and reports appropriate
1537 // errors otherwise.
1538 fn one_bound_for_assoc_type<I>(&self,
1540 ty_param_name: &str,
1541 assoc_name: ast::Ident,
1543 -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
1544 where I: Iterator<Item = ty::PolyTraitRef<'tcx>>
1546 let bound = match bounds.next() {
1547 Some(bound) => bound,
1549 struct_span_err!(self.tcx().sess, span, E0220,
1550 "associated type `{}` not found for `{}`",
1553 .span_label(span, format!("associated type `{}` not found", assoc_name))
1555 return Err(ErrorReported);
1559 debug!("one_bound_for_assoc_type: bound = {:?}", bound);
1561 if let Some(bound2) = bounds.next() {
1562 debug!("one_bound_for_assoc_type: bound2 = {:?}", bound2);
1564 let bounds = iter::once(bound).chain(iter::once(bound2)).chain(bounds);
1565 let mut err = struct_span_err!(
1566 self.tcx().sess, span, E0221,
1567 "ambiguous associated type `{}` in bounds of `{}`",
1570 err.span_label(span, format!("ambiguous associated type `{}`", assoc_name));
1572 for bound in bounds {
1573 let bound_span = self.tcx().associated_items(bound.def_id()).find(|item| {
1574 item.kind == ty::AssocKind::Type &&
1575 self.tcx().hygienic_eq(assoc_name, item.ident, bound.def_id())
1577 .and_then(|item| self.tcx().hir().span_if_local(item.def_id));
1579 if let Some(span) = bound_span {
1580 err.span_label(span, format!("ambiguous `{}` from `{}`",
1584 span_note!(&mut err, span,
1585 "associated type `{}` could derive from `{}`",
1596 // Create a type from a path to an associated type.
1597 // For a path `A::B::C::D`, `qself_ty` and `qself_def` are the type and def for `A::B::C`
1598 // and item_segment is the path segment for `D`. We return a type and a def for
1600 // Will fail except for `T::A` and `Self::A`; i.e., if `qself_ty`/`qself_def` are not a type
1601 // parameter or `Self`.
1602 pub fn associated_path_to_ty(
1604 hir_ref_id: hir::HirId,
1608 assoc_segment: &hir::PathSegment,
1609 permit_variants: bool,
1610 ) -> Result<(Ty<'tcx>, DefKind, DefId), ErrorReported> {
1611 let tcx = self.tcx();
1612 let assoc_ident = assoc_segment.ident;
1614 debug!("associated_path_to_ty: {:?}::{}", qself_ty, assoc_ident);
1616 self.prohibit_generics(slice::from_ref(assoc_segment));
1618 // Check if we have an enum variant.
1619 let mut variant_resolution = None;
1620 if let ty::Adt(adt_def, _) = qself_ty.kind {
1621 if adt_def.is_enum() {
1622 let variant_def = adt_def.variants.iter().find(|vd| {
1623 tcx.hygienic_eq(assoc_ident, vd.ident, adt_def.did)
1625 if let Some(variant_def) = variant_def {
1626 if permit_variants {
1627 tcx.check_stability(variant_def.def_id, Some(hir_ref_id), span);
1628 return Ok((qself_ty, DefKind::Variant, variant_def.def_id));
1630 variant_resolution = Some(variant_def.def_id);
1636 // Find the type of the associated item, and the trait where the associated
1637 // item is declared.
1638 let bound = match (&qself_ty.kind, qself_res) {
1639 (_, Res::SelfTy(Some(_), Some(impl_def_id))) => {
1640 // `Self` in an impl of a trait -- we have a concrete self type and a
1642 let trait_ref = match tcx.impl_trait_ref(impl_def_id) {
1643 Some(trait_ref) => trait_ref,
1645 // A cycle error occurred, most likely.
1646 return Err(ErrorReported);
1650 let candidates = traits::supertraits(tcx, ty::Binder::bind(trait_ref))
1651 .filter(|r| self.trait_defines_associated_type_named(r.def_id(), assoc_ident));
1653 self.one_bound_for_assoc_type(candidates, "Self", assoc_ident, span)?
1655 (&ty::Param(_), Res::SelfTy(Some(param_did), None)) |
1656 (&ty::Param(_), Res::Def(DefKind::TyParam, param_did)) => {
1657 self.find_bound_for_assoc_item(param_did, assoc_ident, span)?
1660 if variant_resolution.is_some() {
1661 // Variant in type position
1662 let msg = format!("expected type, found variant `{}`", assoc_ident);
1663 tcx.sess.span_err(span, &msg);
1664 } else if qself_ty.is_enum() {
1665 let mut err = tcx.sess.struct_span_err(
1667 &format!("no variant `{}` in enum `{}`", assoc_ident, qself_ty),
1670 let adt_def = qself_ty.ty_adt_def().expect("enum is not an ADT");
1671 if let Some(suggested_name) = find_best_match_for_name(
1672 adt_def.variants.iter().map(|variant| &variant.ident.name),
1673 &assoc_ident.as_str(),
1676 err.span_suggestion(
1678 "there is a variant with a similar name",
1679 suggested_name.to_string(),
1680 Applicability::MaybeIncorrect,
1685 format!("variant not found in `{}`", qself_ty),
1689 if let Some(sp) = tcx.hir().span_if_local(adt_def.did) {
1690 let sp = tcx.sess.source_map().def_span(sp);
1691 err.span_label(sp, format!("variant `{}` not found here", assoc_ident));
1695 } else if !qself_ty.references_error() {
1696 // Don't print `TyErr` to the user.
1697 self.report_ambiguous_associated_type(
1699 &qself_ty.to_string(),
1704 return Err(ErrorReported);
1708 let trait_did = bound.def_id();
1709 let (assoc_ident, def_scope) =
1710 tcx.adjust_ident_and_get_scope(assoc_ident, trait_did, hir_ref_id);
1711 let item = tcx.associated_items(trait_did).find(|i| {
1712 Namespace::from(i.kind) == Namespace::Type &&
1713 i.ident.modern() == assoc_ident
1714 }).expect("missing associated type");
1716 let ty = self.projected_ty_from_poly_trait_ref(span, item.def_id, bound);
1717 let ty = self.normalize_ty(span, ty);
1719 let kind = DefKind::AssocTy;
1720 if !item.vis.is_accessible_from(def_scope, tcx) {
1721 let msg = format!("{} `{}` is private", kind.descr(item.def_id), assoc_ident);
1722 tcx.sess.span_err(span, &msg);
1724 tcx.check_stability(item.def_id, Some(hir_ref_id), span);
1726 if let Some(variant_def_id) = variant_resolution {
1727 let mut err = tcx.struct_span_lint_hir(
1728 AMBIGUOUS_ASSOCIATED_ITEMS,
1731 "ambiguous associated item",
1734 let mut could_refer_to = |kind: DefKind, def_id, also| {
1735 let note_msg = format!("`{}` could{} refer to {} defined here",
1736 assoc_ident, also, kind.descr(def_id));
1737 err.span_note(tcx.def_span(def_id), ¬e_msg);
1739 could_refer_to(DefKind::Variant, variant_def_id, "");
1740 could_refer_to(kind, item.def_id, " also");
1742 err.span_suggestion(
1744 "use fully-qualified syntax",
1745 format!("<{} as {}>::{}", qself_ty, tcx.item_name(trait_did), assoc_ident),
1746 Applicability::MachineApplicable,
1750 Ok((ty, kind, item.def_id))
1753 fn qpath_to_ty(&self,
1755 opt_self_ty: Option<Ty<'tcx>>,
1757 trait_segment: &hir::PathSegment,
1758 item_segment: &hir::PathSegment)
1761 let tcx = self.tcx();
1762 let trait_def_id = tcx.parent(item_def_id).unwrap();
1764 self.prohibit_generics(slice::from_ref(item_segment));
1766 let self_ty = if let Some(ty) = opt_self_ty {
1769 let path_str = tcx.def_path_str(trait_def_id);
1770 self.report_ambiguous_associated_type(
1774 item_segment.ident.name,
1776 return tcx.types.err;
1779 debug!("qpath_to_ty: self_type={:?}", self_ty);
1781 let trait_ref = self.ast_path_to_mono_trait_ref(span,
1786 debug!("qpath_to_ty: trait_ref={:?}", trait_ref);
1788 self.normalize_ty(span, tcx.mk_projection(item_def_id, trait_ref.substs))
1791 pub fn prohibit_generics<'a, T: IntoIterator<Item = &'a hir::PathSegment>>(
1792 &self, segments: T) -> bool {
1793 let mut has_err = false;
1794 for segment in segments {
1795 let (mut err_for_lt, mut err_for_ty, mut err_for_ct) = (false, false, false);
1796 for arg in &segment.generic_args().args {
1797 let (span, kind) = match arg {
1798 hir::GenericArg::Lifetime(lt) => {
1799 if err_for_lt { continue }
1802 (lt.span, "lifetime")
1804 hir::GenericArg::Type(ty) => {
1805 if err_for_ty { continue }
1810 hir::GenericArg::Const(ct) => {
1811 if err_for_ct { continue }
1816 let mut err = struct_span_err!(
1820 "{} arguments are not allowed for this type",
1823 err.span_label(span, format!("{} argument not allowed", kind));
1825 if err_for_lt && err_for_ty && err_for_ct {
1829 for binding in &segment.generic_args().bindings {
1831 Self::prohibit_assoc_ty_binding(self.tcx(), binding.span);
1838 pub fn prohibit_assoc_ty_binding(tcx: TyCtxt<'_>, span: Span) {
1839 let mut err = struct_span_err!(tcx.sess, span, E0229,
1840 "associated type bindings are not allowed here");
1841 err.span_label(span, "associated type not allowed here").emit();
1844 // FIXME(eddyb, varkor) handle type paths here too, not just value ones.
1845 pub fn def_ids_for_value_path_segments(
1847 segments: &[hir::PathSegment],
1848 self_ty: Option<Ty<'tcx>>,
1852 // We need to extract the type parameters supplied by the user in
1853 // the path `path`. Due to the current setup, this is a bit of a
1854 // tricky-process; the problem is that resolve only tells us the
1855 // end-point of the path resolution, and not the intermediate steps.
1856 // Luckily, we can (at least for now) deduce the intermediate steps
1857 // just from the end-point.
1859 // There are basically five cases to consider:
1861 // 1. Reference to a constructor of a struct:
1863 // struct Foo<T>(...)
1865 // In this case, the parameters are declared in the type space.
1867 // 2. Reference to a constructor of an enum variant:
1869 // enum E<T> { Foo(...) }
1871 // In this case, the parameters are defined in the type space,
1872 // but may be specified either on the type or the variant.
1874 // 3. Reference to a fn item or a free constant:
1878 // In this case, the path will again always have the form
1879 // `a::b::foo::<T>` where only the final segment should have
1880 // type parameters. However, in this case, those parameters are
1881 // declared on a value, and hence are in the `FnSpace`.
1883 // 4. Reference to a method or an associated constant:
1885 // impl<A> SomeStruct<A> {
1889 // Here we can have a path like
1890 // `a::b::SomeStruct::<A>::foo::<B>`, in which case parameters
1891 // may appear in two places. The penultimate segment,
1892 // `SomeStruct::<A>`, contains parameters in TypeSpace, and the
1893 // final segment, `foo::<B>` contains parameters in fn space.
1895 // The first step then is to categorize the segments appropriately.
1897 let tcx = self.tcx();
1899 assert!(!segments.is_empty());
1900 let last = segments.len() - 1;
1902 let mut path_segs = vec![];
1905 // Case 1. Reference to a struct constructor.
1906 DefKind::Ctor(CtorOf::Struct, ..) => {
1907 // Everything but the final segment should have no
1908 // parameters at all.
1909 let generics = tcx.generics_of(def_id);
1910 // Variant and struct constructors use the
1911 // generics of their parent type definition.
1912 let generics_def_id = generics.parent.unwrap_or(def_id);
1913 path_segs.push(PathSeg(generics_def_id, last));
1916 // Case 2. Reference to a variant constructor.
1917 DefKind::Ctor(CtorOf::Variant, ..)
1918 | DefKind::Variant => {
1919 let adt_def = self_ty.map(|t| t.ty_adt_def().unwrap());
1920 let (generics_def_id, index) = if let Some(adt_def) = adt_def {
1921 debug_assert!(adt_def.is_enum());
1923 } else if last >= 1 && segments[last - 1].args.is_some() {
1924 // Everything but the penultimate segment should have no
1925 // parameters at all.
1926 let mut def_id = def_id;
1928 // `DefKind::Ctor` -> `DefKind::Variant`
1929 if let DefKind::Ctor(..) = kind {
1930 def_id = tcx.parent(def_id).unwrap()
1933 // `DefKind::Variant` -> `DefKind::Enum`
1934 let enum_def_id = tcx.parent(def_id).unwrap();
1935 (enum_def_id, last - 1)
1937 // FIXME: lint here recommending `Enum::<...>::Variant` form
1938 // instead of `Enum::Variant::<...>` form.
1940 // Everything but the final segment should have no
1941 // parameters at all.
1942 let generics = tcx.generics_of(def_id);
1943 // Variant and struct constructors use the
1944 // generics of their parent type definition.
1945 (generics.parent.unwrap_or(def_id), last)
1947 path_segs.push(PathSeg(generics_def_id, index));
1950 // Case 3. Reference to a top-level value.
1953 | DefKind::ConstParam
1954 | DefKind::Static => {
1955 path_segs.push(PathSeg(def_id, last));
1958 // Case 4. Reference to a method or associated const.
1960 | DefKind::AssocConst => {
1961 if segments.len() >= 2 {
1962 let generics = tcx.generics_of(def_id);
1963 path_segs.push(PathSeg(generics.parent.unwrap(), last - 1));
1965 path_segs.push(PathSeg(def_id, last));
1968 kind => bug!("unexpected definition kind {:?} for {:?}", kind, def_id),
1971 debug!("path_segs = {:?}", path_segs);
1976 // Check a type `Path` and convert it to a `Ty`.
1977 pub fn res_to_ty(&self,
1978 opt_self_ty: Option<Ty<'tcx>>,
1980 permit_variants: bool)
1982 let tcx = self.tcx();
1984 debug!("res_to_ty(res={:?}, opt_self_ty={:?}, path_segments={:?})",
1985 path.res, opt_self_ty, path.segments);
1987 let span = path.span;
1989 Res::Def(DefKind::OpaqueTy, did) => {
1990 // Check for desugared `impl Trait`.
1991 assert!(ty::is_impl_trait_defn(tcx, did).is_none());
1992 let item_segment = path.segments.split_last().unwrap();
1993 self.prohibit_generics(item_segment.1);
1994 let substs = self.ast_path_substs_for_ty(span, did, item_segment.0);
1997 tcx.mk_opaque(did, substs),
2000 Res::Def(DefKind::Enum, did)
2001 | Res::Def(DefKind::TyAlias, did)
2002 | Res::Def(DefKind::Struct, did)
2003 | Res::Def(DefKind::Union, did)
2004 | Res::Def(DefKind::ForeignTy, did) => {
2005 assert_eq!(opt_self_ty, None);
2006 self.prohibit_generics(path.segments.split_last().unwrap().1);
2007 self.ast_path_to_ty(span, did, path.segments.last().unwrap())
2009 Res::Def(kind @ DefKind::Variant, def_id) if permit_variants => {
2010 // Convert "variant type" as if it were a real type.
2011 // The resulting `Ty` is type of the variant's enum for now.
2012 assert_eq!(opt_self_ty, None);
2015 self.def_ids_for_value_path_segments(&path.segments, None, kind, def_id);
2016 let generic_segs: FxHashSet<_> =
2017 path_segs.iter().map(|PathSeg(_, index)| index).collect();
2018 self.prohibit_generics(path.segments.iter().enumerate().filter_map(|(index, seg)| {
2019 if !generic_segs.contains(&index) {
2026 let PathSeg(def_id, index) = path_segs.last().unwrap();
2027 self.ast_path_to_ty(span, *def_id, &path.segments[*index])
2029 Res::Def(DefKind::TyParam, def_id) => {
2030 assert_eq!(opt_self_ty, None);
2031 self.prohibit_generics(&path.segments);
2033 let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
2034 let item_id = tcx.hir().get_parent_node(hir_id);
2035 let item_def_id = tcx.hir().local_def_id(item_id);
2036 let generics = tcx.generics_of(item_def_id);
2037 let index = generics.param_def_id_to_index[&def_id];
2038 tcx.mk_ty_param(index, tcx.hir().name(hir_id))
2040 Res::SelfTy(Some(_), None) => {
2041 // `Self` in trait or type alias.
2042 assert_eq!(opt_self_ty, None);
2043 self.prohibit_generics(&path.segments);
2044 tcx.types.self_param
2046 Res::SelfTy(_, Some(def_id)) => {
2047 // `Self` in impl (we know the concrete type).
2048 assert_eq!(opt_self_ty, None);
2049 self.prohibit_generics(&path.segments);
2050 // Try to evaluate any array length constants.
2051 self.normalize_ty(span, tcx.at(span).type_of(def_id))
2053 Res::Def(DefKind::AssocTy, def_id) => {
2054 debug_assert!(path.segments.len() >= 2);
2055 self.prohibit_generics(&path.segments[..path.segments.len() - 2]);
2056 self.qpath_to_ty(span,
2059 &path.segments[path.segments.len() - 2],
2060 path.segments.last().unwrap())
2062 Res::PrimTy(prim_ty) => {
2063 assert_eq!(opt_self_ty, None);
2064 self.prohibit_generics(&path.segments);
2066 hir::Bool => tcx.types.bool,
2067 hir::Char => tcx.types.char,
2068 hir::Int(it) => tcx.mk_mach_int(it),
2069 hir::Uint(uit) => tcx.mk_mach_uint(uit),
2070 hir::Float(ft) => tcx.mk_mach_float(ft),
2071 hir::Str => tcx.mk_str()
2075 self.set_tainted_by_errors();
2076 return self.tcx().types.err;
2078 _ => span_bug!(span, "unexpected resolution: {:?}", path.res)
2082 /// Parses the programmer's textual representation of a type into our
2083 /// internal notion of a type.
2084 pub fn ast_ty_to_ty(&self, ast_ty: &hir::Ty) -> Ty<'tcx> {
2085 debug!("ast_ty_to_ty(id={:?}, ast_ty={:?} ty_ty={:?})",
2086 ast_ty.hir_id, ast_ty, ast_ty.kind);
2088 let tcx = self.tcx();
2090 let result_ty = match ast_ty.kind {
2091 hir::TyKind::Slice(ref ty) => {
2092 tcx.mk_slice(self.ast_ty_to_ty(&ty))
2094 hir::TyKind::Ptr(ref mt) => {
2095 tcx.mk_ptr(ty::TypeAndMut {
2096 ty: self.ast_ty_to_ty(&mt.ty),
2100 hir::TyKind::Rptr(ref region, ref mt) => {
2101 let r = self.ast_region_to_region(region, None);
2102 debug!("ast_ty_to_ty: r={:?}", r);
2103 let t = self.ast_ty_to_ty(&mt.ty);
2104 tcx.mk_ref(r, ty::TypeAndMut {ty: t, mutbl: mt.mutbl})
2106 hir::TyKind::Never => {
2109 hir::TyKind::Tup(ref fields) => {
2110 tcx.mk_tup(fields.iter().map(|t| self.ast_ty_to_ty(&t)))
2112 hir::TyKind::BareFn(ref bf) => {
2113 require_c_abi_if_c_variadic(tcx, &bf.decl, bf.abi, ast_ty.span);
2114 tcx.mk_fn_ptr(self.ty_of_fn(bf.unsafety, bf.abi, &bf.decl))
2116 hir::TyKind::TraitObject(ref bounds, ref lifetime) => {
2117 self.conv_object_ty_poly_trait_ref(ast_ty.span, bounds, lifetime)
2119 hir::TyKind::Path(hir::QPath::Resolved(ref maybe_qself, ref path)) => {
2120 debug!("ast_ty_to_ty: maybe_qself={:?} path={:?}", maybe_qself, path);
2121 let opt_self_ty = maybe_qself.as_ref().map(|qself| {
2122 self.ast_ty_to_ty(qself)
2124 self.res_to_ty(opt_self_ty, path, false)
2126 hir::TyKind::Def(item_id, ref lifetimes) => {
2127 let did = tcx.hir().local_def_id(item_id.id);
2128 self.impl_trait_ty_to_ty(did, lifetimes)
2130 hir::TyKind::Path(hir::QPath::TypeRelative(ref qself, ref segment)) => {
2131 debug!("ast_ty_to_ty: qself={:?} segment={:?}", qself, segment);
2132 let ty = self.ast_ty_to_ty(qself);
2134 let res = if let hir::TyKind::Path(hir::QPath::Resolved(_, ref path)) = qself.kind {
2139 self.associated_path_to_ty(ast_ty.hir_id, ast_ty.span, ty, res, segment, false)
2140 .map(|(ty, _, _)| ty).unwrap_or(tcx.types.err)
2142 hir::TyKind::Array(ref ty, ref length) => {
2143 let length = self.ast_const_to_const(length, tcx.types.usize);
2144 let array_ty = tcx.mk_ty(ty::Array(self.ast_ty_to_ty(&ty), length));
2145 self.normalize_ty(ast_ty.span, array_ty)
2147 hir::TyKind::Typeof(ref _e) => {
2148 struct_span_err!(tcx.sess, ast_ty.span, E0516,
2149 "`typeof` is a reserved keyword but unimplemented")
2150 .span_label(ast_ty.span, "reserved keyword")
2155 hir::TyKind::Infer => {
2156 // Infer also appears as the type of arguments or return
2157 // values in a ExprKind::Closure, or as
2158 // the type of local variables. Both of these cases are
2159 // handled specially and will not descend into this routine.
2160 self.ty_infer(None, ast_ty.span)
2162 hir::TyKind::Err => {
2167 debug!("ast_ty_to_ty: result_ty={:?}", result_ty);
2169 self.record_ty(ast_ty.hir_id, result_ty, ast_ty.span);
2173 /// Returns the `DefId` of the constant parameter that the provided expression is a path to.
2174 pub fn const_param_def_id(&self, expr: &hir::Expr) -> Option<DefId> {
2175 // Unwrap a block, so that e.g. `{ P }` is recognised as a parameter. Const arguments
2176 // currently have to be wrapped in curly brackets, so it's necessary to special-case.
2177 let expr = match &expr.kind {
2178 ExprKind::Block(block, _) if block.stmts.is_empty() && block.expr.is_some() =>
2179 block.expr.as_ref().unwrap(),
2184 ExprKind::Path(hir::QPath::Resolved(_, path)) => match path.res {
2185 Res::Def(DefKind::ConstParam, did) => Some(did),
2192 pub fn ast_const_to_const(
2194 ast_const: &hir::AnonConst,
2196 ) -> &'tcx ty::Const<'tcx> {
2197 debug!("ast_const_to_const(id={:?}, ast_const={:?})", ast_const.hir_id, ast_const);
2199 let tcx = self.tcx();
2200 let def_id = tcx.hir().local_def_id(ast_const.hir_id);
2202 let mut const_ = ty::Const {
2203 val: ConstValue::Unevaluated(
2205 InternalSubsts::identity_for_item(tcx, def_id),
2210 let expr = &tcx.hir().body(ast_const.body).value;
2211 if let Some(def_id) = self.const_param_def_id(expr) {
2212 // Find the name and index of the const parameter by indexing the generics of the
2213 // parent item and construct a `ParamConst`.
2214 let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
2215 let item_id = tcx.hir().get_parent_node(hir_id);
2216 let item_def_id = tcx.hir().local_def_id(item_id);
2217 let generics = tcx.generics_of(item_def_id);
2218 let index = generics.param_def_id_to_index[&tcx.hir().local_def_id(hir_id)];
2219 let name = tcx.hir().name(hir_id);
2220 const_.val = ConstValue::Param(ty::ParamConst::new(index, name));
2223 tcx.mk_const(const_)
2226 pub fn impl_trait_ty_to_ty(
2229 lifetimes: &[hir::GenericArg],
2231 debug!("impl_trait_ty_to_ty(def_id={:?}, lifetimes={:?})", def_id, lifetimes);
2232 let tcx = self.tcx();
2234 let generics = tcx.generics_of(def_id);
2236 debug!("impl_trait_ty_to_ty: generics={:?}", generics);
2237 let substs = InternalSubsts::for_item(tcx, def_id, |param, _| {
2238 if let Some(i) = (param.index as usize).checked_sub(generics.parent_count) {
2239 // Our own parameters are the resolved lifetimes.
2241 GenericParamDefKind::Lifetime => {
2242 if let hir::GenericArg::Lifetime(lifetime) = &lifetimes[i] {
2243 self.ast_region_to_region(lifetime, None).into()
2251 // Replace all parent lifetimes with `'static`.
2253 GenericParamDefKind::Lifetime => {
2254 tcx.lifetimes.re_static.into()
2256 _ => tcx.mk_param_from_def(param)
2260 debug!("impl_trait_ty_to_ty: substs={:?}", substs);
2262 let ty = tcx.mk_opaque(def_id, substs);
2263 debug!("impl_trait_ty_to_ty: {}", ty);
2267 pub fn ty_of_arg(&self,
2269 expected_ty: Option<Ty<'tcx>>)
2273 hir::TyKind::Infer if expected_ty.is_some() => {
2274 self.record_ty(ty.hir_id, expected_ty.unwrap(), ty.span);
2275 expected_ty.unwrap()
2277 _ => self.ast_ty_to_ty(ty),
2281 pub fn ty_of_fn(&self,
2282 unsafety: hir::Unsafety,
2285 -> ty::PolyFnSig<'tcx> {
2288 let tcx = self.tcx();
2290 decl.inputs.iter().map(|a| self.ty_of_arg(a, None));
2292 let output_ty = match decl.output {
2293 hir::Return(ref output) => self.ast_ty_to_ty(output),
2294 hir::DefaultReturn(..) => tcx.mk_unit(),
2297 debug!("ty_of_fn: output_ty={:?}", output_ty);
2299 let bare_fn_ty = ty::Binder::bind(tcx.mk_fn_sig(
2307 // Find any late-bound regions declared in return type that do
2308 // not appear in the arguments. These are not well-formed.
2311 // for<'a> fn() -> &'a str <-- 'a is bad
2312 // for<'a> fn(&'a String) -> &'a str <-- 'a is ok
2313 let inputs = bare_fn_ty.inputs();
2314 let late_bound_in_args = tcx.collect_constrained_late_bound_regions(
2315 &inputs.map_bound(|i| i.to_owned()));
2316 let output = bare_fn_ty.output();
2317 let late_bound_in_ret = tcx.collect_referenced_late_bound_regions(&output);
2318 for br in late_bound_in_ret.difference(&late_bound_in_args) {
2319 let lifetime_name = match *br {
2320 ty::BrNamed(_, name) => format!("lifetime `{}`,", name),
2321 ty::BrAnon(_) | ty::BrEnv => "an anonymous lifetime".to_string(),
2323 let mut err = struct_span_err!(tcx.sess,
2326 "return type references {} \
2327 which is not constrained by the fn input types",
2329 if let ty::BrAnon(_) = *br {
2330 // The only way for an anonymous lifetime to wind up
2331 // in the return type but **also** be unconstrained is
2332 // if it only appears in "associated types" in the
2333 // input. See #47511 for an example. In this case,
2334 // though we can easily give a hint that ought to be
2336 err.note("lifetimes appearing in an associated type \
2337 are not considered constrained");
2345 /// Given the bounds on an object, determines what single region bound (if any) we can
2346 /// use to summarize this type. The basic idea is that we will use the bound the user
2347 /// provided, if they provided one, and otherwise search the supertypes of trait bounds
2348 /// for region bounds. It may be that we can derive no bound at all, in which case
2349 /// we return `None`.
2350 fn compute_object_lifetime_bound(&self,
2352 existential_predicates: ty::Binder<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>>)
2353 -> Option<ty::Region<'tcx>> // if None, use the default
2355 let tcx = self.tcx();
2357 debug!("compute_opt_region_bound(existential_predicates={:?})",
2358 existential_predicates);
2360 // No explicit region bound specified. Therefore, examine trait
2361 // bounds and see if we can derive region bounds from those.
2362 let derived_region_bounds =
2363 object_region_bounds(tcx, existential_predicates);
2365 // If there are no derived region bounds, then report back that we
2366 // can find no region bound. The caller will use the default.
2367 if derived_region_bounds.is_empty() {
2371 // If any of the derived region bounds are 'static, that is always
2373 if derived_region_bounds.iter().any(|&r| ty::ReStatic == *r) {
2374 return Some(tcx.lifetimes.re_static);
2377 // Determine whether there is exactly one unique region in the set
2378 // of derived region bounds. If so, use that. Otherwise, report an
2380 let r = derived_region_bounds[0];
2381 if derived_region_bounds[1..].iter().any(|r1| r != *r1) {
2382 span_err!(tcx.sess, span, E0227,
2383 "ambiguous lifetime bound, explicit lifetime bound required");
2389 /// Collects together a list of bounds that are applied to some type,
2390 /// after they've been converted into `ty` form (from the HIR
2391 /// representations). These lists of bounds occur in many places in
2395 /// trait Foo: Bar + Baz { }
2396 /// ^^^^^^^^^ supertrait list bounding the `Self` type parameter
2398 /// fn foo<T: Bar + Baz>() { }
2399 /// ^^^^^^^^^ bounding the type parameter `T`
2401 /// impl dyn Bar + Baz
2402 /// ^^^^^^^^^ bounding the forgotten dynamic type
2405 /// Our representation is a bit mixed here -- in some cases, we
2406 /// include the self type (e.g., `trait_bounds`) but in others we do
2407 #[derive(Default, PartialEq, Eq, Clone, Debug)]
2408 pub struct Bounds<'tcx> {
2409 /// A list of region bounds on the (implicit) self type. So if you
2410 /// had `T: 'a + 'b` this might would be a list `['a, 'b]` (but
2411 /// the `T` is not explicitly included).
2412 pub region_bounds: Vec<(ty::Region<'tcx>, Span)>,
2414 /// A list of trait bounds. So if you had `T: Debug` this would be
2415 /// `T: Debug`. Note that the self-type is explicit here.
2416 pub trait_bounds: Vec<(ty::PolyTraitRef<'tcx>, Span)>,
2418 /// A list of projection equality bounds. So if you had `T:
2419 /// Iterator<Item = u32>` this would include `<T as
2420 /// Iterator>::Item => u32`. Note that the self-type is explicit
2422 pub projection_bounds: Vec<(ty::PolyProjectionPredicate<'tcx>, Span)>,
2424 /// `Some` if there is *no* `?Sized` predicate. The `span`
2425 /// is the location in the source of the `T` declaration which can
2426 /// be cited as the source of the `T: Sized` requirement.
2427 pub implicitly_sized: Option<Span>,
2430 impl<'tcx> Bounds<'tcx> {
2431 /// Converts a bounds list into a flat set of predicates (like
2432 /// where-clauses). Because some of our bounds listings (e.g.,
2433 /// regions) don't include the self-type, you must supply the
2434 /// self-type here (the `param_ty` parameter).
2439 ) -> Vec<(ty::Predicate<'tcx>, Span)> {
2440 // If it could be sized, and is, add the `Sized` predicate.
2441 let sized_predicate = self.implicitly_sized.and_then(|span| {
2442 tcx.lang_items().sized_trait().map(|sized| {
2443 let trait_ref = ty::TraitRef {
2445 substs: tcx.mk_substs_trait(param_ty, &[])
2447 (trait_ref.to_predicate(), span)
2451 sized_predicate.into_iter().chain(
2452 self.region_bounds.iter().map(|&(region_bound, span)| {
2453 // Account for the binder being introduced below; no need to shift `param_ty`
2454 // because, at present at least, it can only refer to early-bound regions.
2455 let region_bound = ty::fold::shift_region(tcx, region_bound, 1);
2456 let outlives = ty::OutlivesPredicate(param_ty, region_bound);
2457 (ty::Binder::dummy(outlives).to_predicate(), span)
2459 self.trait_bounds.iter().map(|&(bound_trait_ref, span)| {
2460 (bound_trait_ref.to_predicate(), span)
2463 self.projection_bounds.iter().map(|&(projection, span)| {
2464 (projection.to_predicate(), span)