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`.
219 seg: &hir::PathSegment,
220 generics: &ty::Generics,
222 let explicit = !seg.infer_args;
223 let impl_trait = generics.params.iter().any(|param| match param.kind {
224 ty::GenericParamDefKind::Type {
225 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait), ..
230 if explicit && impl_trait {
231 let mut err = struct_span_err! {
235 "cannot provide explicit generic arguments when `impl Trait` is \
236 used in argument position"
245 /// Checks that the correct number of generic arguments have been provided.
246 /// Used specifically for function calls.
247 pub fn check_generic_arg_count_for_call(
251 seg: &hir::PathSegment,
252 is_method_call: bool,
254 let empty_args = P(hir::GenericArgs {
255 args: HirVec::new(), bindings: HirVec::new(), parenthesized: false,
257 let suppress_mismatch = Self::check_impl_trait(tcx, span, seg, &def);
258 Self::check_generic_arg_count(
262 if let Some(ref args) = seg.args {
268 GenericArgPosition::MethodCall
270 GenericArgPosition::Value
272 def.parent.is_none() && def.has_self, // `has_self`
273 seg.infer_args || suppress_mismatch, // `infer_args`
277 /// Checks that the correct number of generic arguments have been provided.
278 /// This is used both for datatypes and function calls.
279 fn check_generic_arg_count(
283 args: &hir::GenericArgs,
284 position: GenericArgPosition,
287 ) -> (bool, Option<Vec<Span>>) {
288 // At this stage we are guaranteed that the generic arguments are in the correct order, e.g.
289 // that lifetimes will proceed types. So it suffices to check the number of each generic
290 // arguments in order to validate them with respect to the generic parameters.
291 let param_counts = def.own_counts();
292 let arg_counts = args.own_counts();
293 let infer_lifetimes = position != GenericArgPosition::Type && arg_counts.lifetimes == 0;
295 let mut defaults: ty::GenericParamCount = Default::default();
296 for param in &def.params {
298 GenericParamDefKind::Lifetime => {}
299 GenericParamDefKind::Type { has_default, .. } => {
300 defaults.types += has_default as usize
302 GenericParamDefKind::Const => {
303 // FIXME(const_generics:defaults)
308 if position != GenericArgPosition::Type && !args.bindings.is_empty() {
309 AstConv::prohibit_assoc_ty_binding(tcx, args.bindings[0].span);
312 // Prohibit explicit lifetime arguments if late-bound lifetime parameters are present.
313 let mut reported_late_bound_region_err = None;
314 if !infer_lifetimes {
315 if let Some(span_late) = def.has_late_bound_regions {
316 let msg = "cannot specify lifetime arguments explicitly \
317 if late bound lifetime parameters are present";
318 let note = "the late bound lifetime parameter is introduced here";
319 let span = args.args[0].span();
320 if position == GenericArgPosition::Value
321 && arg_counts.lifetimes != param_counts.lifetimes {
322 let mut err = tcx.sess.struct_span_err(span, msg);
323 err.span_note(span_late, note);
325 reported_late_bound_region_err = Some(true);
327 let mut multispan = MultiSpan::from_span(span);
328 multispan.push_span_label(span_late, note.to_string());
329 tcx.lint_hir(lint::builtin::LATE_BOUND_LIFETIME_ARGUMENTS,
330 args.args[0].id(), multispan, msg);
331 reported_late_bound_region_err = Some(false);
336 let check_kind_count = |kind, required, permitted, provided, offset| {
338 "check_kind_count: kind: {} required: {} permitted: {} provided: {} offset: {}",
345 // We enforce the following: `required` <= `provided` <= `permitted`.
346 // For kinds without defaults (e.g.., lifetimes), `required == permitted`.
347 // For other kinds (i.e., types), `permitted` may be greater than `required`.
348 if required <= provided && provided <= permitted {
349 return (reported_late_bound_region_err.unwrap_or(false), None);
352 // Unfortunately lifetime and type parameter mismatches are typically styled
353 // differently in diagnostics, which means we have a few cases to consider here.
354 let (bound, quantifier) = if required != permitted {
355 if provided < required {
356 (required, "at least ")
357 } else { // provided > permitted
358 (permitted, "at most ")
364 let mut potential_assoc_types: Option<Vec<Span>> = None;
365 let (spans, label) = if required == permitted && provided > permitted {
366 // In the case when the user has provided too many arguments,
367 // we want to point to the unexpected arguments.
368 let spans: Vec<Span> = args.args[offset+permitted .. offset+provided]
370 .map(|arg| arg.span())
372 potential_assoc_types = Some(spans.clone());
373 (spans, format!( "unexpected {} argument", kind))
375 (vec![span], format!(
376 "expected {}{} {} argument{}",
384 let mut err = tcx.sess.struct_span_err_with_code(
387 "wrong number of {} arguments: expected {}{}, found {}",
393 DiagnosticId::Error("E0107".into())
396 err.span_label(span, label.as_str());
401 provided > required, // `suppress_error`
402 potential_assoc_types,
406 if reported_late_bound_region_err.is_none()
407 && (!infer_lifetimes || arg_counts.lifetimes > param_counts.lifetimes) {
410 param_counts.lifetimes,
411 param_counts.lifetimes,
412 arg_counts.lifetimes,
416 // FIXME(const_generics:defaults)
417 if !infer_args || arg_counts.consts > param_counts.consts {
423 arg_counts.lifetimes + arg_counts.types,
426 // Note that type errors are currently be emitted *after* const errors.
428 || arg_counts.types > param_counts.types - defaults.types - has_self as usize {
431 param_counts.types - defaults.types - has_self as usize,
432 param_counts.types - has_self as usize,
434 arg_counts.lifetimes,
437 (reported_late_bound_region_err.unwrap_or(false), None)
441 /// Creates the relevant generic argument substitutions
442 /// corresponding to a set of generic parameters. This is a
443 /// rather complex function. Let us try to explain the role
444 /// of each of its parameters:
446 /// To start, we are given the `def_id` of the thing we are
447 /// creating the substitutions for, and a partial set of
448 /// substitutions `parent_substs`. In general, the substitutions
449 /// for an item begin with substitutions for all the "parents" of
450 /// that item -- e.g., for a method it might include the
451 /// parameters from the impl.
453 /// Therefore, the method begins by walking down these parents,
454 /// starting with the outermost parent and proceed inwards until
455 /// it reaches `def_id`. For each parent `P`, it will check `parent_substs`
456 /// first to see if the parent's substitutions are listed in there. If so,
457 /// we can append those and move on. Otherwise, it invokes the
458 /// three callback functions:
460 /// - `args_for_def_id`: given the `DefId` `P`, supplies back the
461 /// generic arguments that were given to that parent from within
462 /// the path; so e.g., if you have `<T as Foo>::Bar`, the `DefId`
463 /// might refer to the trait `Foo`, and the arguments might be
464 /// `[T]`. The boolean value indicates whether to infer values
465 /// for arguments whose values were not explicitly provided.
466 /// - `provided_kind`: given the generic parameter and the value from `args_for_def_id`,
467 /// instantiate a `GenericArg`.
468 /// - `inferred_kind`: if no parameter was provided, and inference is enabled, then
469 /// creates a suitable inference variable.
470 pub fn create_substs_for_generic_args<'b>(
473 parent_substs: &[subst::GenericArg<'tcx>],
475 self_ty: Option<Ty<'tcx>>,
476 args_for_def_id: impl Fn(DefId) -> (Option<&'b GenericArgs>, bool),
477 provided_kind: impl Fn(&GenericParamDef, &GenericArg) -> subst::GenericArg<'tcx>,
478 inferred_kind: impl Fn(Option<&[subst::GenericArg<'tcx>]>, &GenericParamDef, bool)
479 -> subst::GenericArg<'tcx>,
480 ) -> SubstsRef<'tcx> {
481 // Collect the segments of the path; we need to substitute arguments
482 // for parameters throughout the entire path (wherever there are
483 // generic parameters).
484 let mut parent_defs = tcx.generics_of(def_id);
485 let count = parent_defs.count();
486 let mut stack = vec![(def_id, parent_defs)];
487 while let Some(def_id) = parent_defs.parent {
488 parent_defs = tcx.generics_of(def_id);
489 stack.push((def_id, parent_defs));
492 // We manually build up the substitution, rather than using convenience
493 // methods in `subst.rs`, so that we can iterate over the arguments and
494 // parameters in lock-step linearly, instead of trying to match each pair.
495 let mut substs: SmallVec<[subst::GenericArg<'tcx>; 8]> = SmallVec::with_capacity(count);
497 // Iterate over each segment of the path.
498 while let Some((def_id, defs)) = stack.pop() {
499 let mut params = defs.params.iter().peekable();
501 // If we have already computed substitutions for parents, we can use those directly.
502 while let Some(¶m) = params.peek() {
503 if let Some(&kind) = parent_substs.get(param.index as usize) {
511 // `Self` is handled first, unless it's been handled in `parent_substs`.
513 if let Some(¶m) = params.peek() {
514 if param.index == 0 {
515 if let GenericParamDefKind::Type { .. } = param.kind {
516 substs.push(self_ty.map(|ty| ty.into())
517 .unwrap_or_else(|| inferred_kind(None, param, true)));
524 // Check whether this segment takes generic arguments and the user has provided any.
525 let (generic_args, infer_args) = args_for_def_id(def_id);
527 let mut args = generic_args.iter().flat_map(|generic_args| generic_args.args.iter())
531 // We're going to iterate through the generic arguments that the user
532 // provided, matching them with the generic parameters we expect.
533 // Mismatches can occur as a result of elided lifetimes, or for malformed
534 // input. We try to handle both sensibly.
535 match (args.peek(), params.peek()) {
536 (Some(&arg), Some(¶m)) => {
537 match (arg, ¶m.kind) {
538 (GenericArg::Lifetime(_), GenericParamDefKind::Lifetime)
539 | (GenericArg::Type(_), GenericParamDefKind::Type { .. })
540 | (GenericArg::Const(_), GenericParamDefKind::Const) => {
541 substs.push(provided_kind(param, arg));
545 (GenericArg::Type(_), GenericParamDefKind::Lifetime)
546 | (GenericArg::Const(_), GenericParamDefKind::Lifetime) => {
547 // We expected a lifetime argument, but got a type or const
548 // argument. That means we're inferring the lifetimes.
549 substs.push(inferred_kind(None, param, infer_args));
553 // We expected one kind of parameter, but the user provided
554 // another. This is an error, but we need to handle it
555 // gracefully so we can report sensible errors.
556 // In this case, we're simply going to infer this argument.
562 // We should never be able to reach this point with well-formed input.
563 // Getting to this point means the user supplied more arguments than
564 // there are parameters.
567 (None, Some(¶m)) => {
568 // If there are fewer arguments than parameters, it means
569 // we're inferring the remaining arguments.
570 substs.push(inferred_kind(Some(&substs), param, infer_args));
574 (None, None) => break,
579 tcx.intern_substs(&substs)
582 /// Given the type/lifetime/const arguments provided to some path (along with
583 /// an implicit `Self`, if this is a trait reference), returns the complete
584 /// set of substitutions. This may involve applying defaulted type parameters.
585 /// Also returns back constriants on associated types.
590 /// T: std::ops::Index<usize, Output = u32>
591 /// ^1 ^^^^^^^^^^^^^^2 ^^^^3 ^^^^^^^^^^^4
594 /// 1. The `self_ty` here would refer to the type `T`.
595 /// 2. The path in question is the path to the trait `std::ops::Index`,
596 /// which will have been resolved to a `def_id`
597 /// 3. The `generic_args` contains info on the `<...>` contents. The `usize` type
598 /// parameters are returned in the `SubstsRef`, the associated type bindings like
599 /// `Output = u32` are returned in the `Vec<ConvertedBinding...>` result.
601 /// Note that the type listing given here is *exactly* what the user provided.
602 fn create_substs_for_ast_path<'a>(&self,
605 generic_args: &'a hir::GenericArgs,
607 self_ty: Option<Ty<'tcx>>)
608 -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'a, 'tcx>>, Option<Vec<Span>>)
610 // If the type is parameterized by this region, then replace this
611 // region with the current anon region binding (in other words,
612 // whatever & would get replaced with).
613 debug!("create_substs_for_ast_path(def_id={:?}, self_ty={:?}, \
615 def_id, self_ty, generic_args);
617 let tcx = self.tcx();
618 let generic_params = tcx.generics_of(def_id);
620 // If a self-type was declared, one should be provided.
621 assert_eq!(generic_params.has_self, self_ty.is_some());
623 let has_self = generic_params.has_self;
624 let (_, potential_assoc_types) = Self::check_generic_arg_count(
629 GenericArgPosition::Type,
634 let is_object = self_ty.map_or(false, |ty| {
635 ty == self.tcx().types.trait_object_dummy_self
637 let default_needs_object_self = |param: &ty::GenericParamDef| {
638 if let GenericParamDefKind::Type { has_default, .. } = param.kind {
639 if is_object && has_default && has_self {
640 let self_param = tcx.types.self_param;
641 if tcx.at(span).type_of(param.def_id).walk().any(|ty| ty == self_param) {
642 // There is no suitable inference default for a type parameter
643 // that references self, in an object type.
652 let substs = Self::create_substs_for_generic_args(
658 // Provide the generic args, and whether types should be inferred.
659 |_| (Some(generic_args), infer_args),
660 // Provide substitutions for parameters for which (valid) arguments have been provided.
662 match (¶m.kind, arg) {
663 (GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => {
664 self.ast_region_to_region(<, Some(param)).into()
666 (GenericParamDefKind::Type { .. }, GenericArg::Type(ty)) => {
667 self.ast_ty_to_ty(&ty).into()
669 (GenericParamDefKind::Const, GenericArg::Const(ct)) => {
670 self.ast_const_to_const(&ct.value, tcx.type_of(param.def_id)).into()
675 // Provide substitutions for parameters for which arguments are inferred.
676 |substs, param, infer_args| {
678 GenericParamDefKind::Lifetime => tcx.lifetimes.re_static.into(),
679 GenericParamDefKind::Type { has_default, .. } => {
680 if !infer_args && has_default {
681 // No type parameter provided, but a default exists.
683 // If we are converting an object type, then the
684 // `Self` parameter is unknown. However, some of the
685 // other type parameters may reference `Self` in their
686 // defaults. This will lead to an ICE if we are not
688 if default_needs_object_self(param) {
689 struct_span_err!(tcx.sess, span, E0393,
690 "the type parameter `{}` must be explicitly specified",
693 .span_label(span, format!(
694 "missing reference to `{}`", param.name))
696 "because of the default `Self` reference, type parameters \
697 must be specified on object types"))
701 // This is a default type parameter.
704 tcx.at(span).type_of(param.def_id)
705 .subst_spanned(tcx, substs.unwrap(), Some(span))
708 } else if infer_args {
709 // No type parameters were provided, we can infer all.
710 let param = if !default_needs_object_self(param) {
715 self.ty_infer(param, span).into()
717 // We've already errored above about the mismatch.
721 GenericParamDefKind::Const => {
722 // FIXME(const_generics:defaults)
724 // No const parameters were provided, we can infer all.
725 let ty = tcx.at(span).type_of(param.def_id);
726 self.ct_infer(ty, Some(param), span).into()
728 // We've already errored above about the mismatch.
729 tcx.consts.err.into()
736 // Convert associated-type bindings or constraints into a separate vector.
737 // Example: Given this:
739 // T: Iterator<Item = u32>
741 // The `T` is passed in as a self-type; the `Item = u32` is
742 // not a "type parameter" of the `Iterator` trait, but rather
743 // a restriction on `<T as Iterator>::Item`, so it is passed
745 let assoc_bindings = generic_args.bindings.iter()
747 let kind = match binding.kind {
748 hir::TypeBindingKind::Equality { ref ty } =>
749 ConvertedBindingKind::Equality(self.ast_ty_to_ty(ty)),
750 hir::TypeBindingKind::Constraint { ref bounds } =>
751 ConvertedBindingKind::Constraint(bounds),
754 item_name: binding.ident,
761 debug!("create_substs_for_ast_path(generic_params={:?}, self_ty={:?}) -> {:?}",
762 generic_params, self_ty, substs);
764 (substs, assoc_bindings, potential_assoc_types)
767 /// Instantiates the path for the given trait reference, assuming that it's
768 /// bound to a valid trait type. Returns the `DefId` of the defining trait.
769 /// The type _cannot_ be a type other than a trait type.
771 /// If the `projections` argument is `None`, then assoc type bindings like `Foo<T = X>`
772 /// are disallowed. Otherwise, they are pushed onto the vector given.
773 pub fn instantiate_mono_trait_ref(&self,
774 trait_ref: &hir::TraitRef,
776 ) -> ty::TraitRef<'tcx>
778 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
780 self.ast_path_to_mono_trait_ref(trait_ref.path.span,
781 trait_ref.trait_def_id(),
783 trait_ref.path.segments.last().unwrap())
786 /// The given trait-ref must actually be a trait.
787 pub(super) fn instantiate_poly_trait_ref_inner(&self,
788 trait_ref: &hir::TraitRef,
791 bounds: &mut Bounds<'tcx>,
793 ) -> Option<Vec<Span>> {
794 let trait_def_id = trait_ref.trait_def_id();
796 debug!("instantiate_poly_trait_ref({:?}, def_id={:?})", trait_ref, trait_def_id);
798 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
800 let (substs, assoc_bindings, potential_assoc_types) = self.create_substs_for_ast_trait_ref(
804 trait_ref.path.segments.last().unwrap(),
806 let poly_trait_ref = ty::Binder::bind(ty::TraitRef::new(trait_def_id, substs));
808 bounds.trait_bounds.push((poly_trait_ref, span));
810 let mut dup_bindings = FxHashMap::default();
811 for binding in &assoc_bindings {
812 // Specify type to assert that error was already reported in `Err` case.
813 let _: Result<_, ErrorReported> =
814 self.add_predicates_for_ast_type_binding(
815 trait_ref.hir_ref_id,
822 // Okay to ignore `Err` because of `ErrorReported` (see above).
825 debug!("instantiate_poly_trait_ref({:?}, bounds={:?}) -> {:?}",
826 trait_ref, bounds, poly_trait_ref);
827 potential_assoc_types
830 /// Given a trait bound like `Debug`, applies that trait bound the given self-type to construct
831 /// a full trait reference. The resulting trait reference is returned. This may also generate
832 /// auxiliary bounds, which are added to `bounds`.
837 /// poly_trait_ref = Iterator<Item = u32>
841 /// this would return `Foo: Iterator` and add `<Foo as Iterator>::Item = u32` into `bounds`.
843 /// **A note on binders:** against our usual convention, there is an implied bounder around
844 /// the `self_ty` and `poly_trait_ref` parameters here. So they may reference bound regions.
845 /// If for example you had `for<'a> Foo<'a>: Bar<'a>`, then the `self_ty` would be `Foo<'a>`
846 /// where `'a` is a bound region at depth 0. Similarly, the `poly_trait_ref` would be
847 /// `Bar<'a>`. The returned poly-trait-ref will have this binder instantiated explicitly,
849 pub fn instantiate_poly_trait_ref(&self,
850 poly_trait_ref: &hir::PolyTraitRef,
852 bounds: &mut Bounds<'tcx>,
853 ) -> Option<Vec<Span>> {
854 self.instantiate_poly_trait_ref_inner(
855 &poly_trait_ref.trait_ref,
863 fn ast_path_to_mono_trait_ref(&self,
867 trait_segment: &hir::PathSegment
868 ) -> ty::TraitRef<'tcx>
870 let (substs, assoc_bindings, _) =
871 self.create_substs_for_ast_trait_ref(span,
875 assoc_bindings.first().map(|b| AstConv::prohibit_assoc_ty_binding(self.tcx(), b.span));
876 ty::TraitRef::new(trait_def_id, substs)
879 fn create_substs_for_ast_trait_ref<'a>(
884 trait_segment: &'a hir::PathSegment,
885 ) -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'a, 'tcx>>, Option<Vec<Span>>) {
886 debug!("create_substs_for_ast_trait_ref(trait_segment={:?})",
889 let trait_def = self.tcx().trait_def(trait_def_id);
891 if !self.tcx().features().unboxed_closures &&
892 trait_segment.generic_args().parenthesized != trait_def.paren_sugar
894 // For now, require that parenthetical notation be used only with `Fn()` etc.
895 let msg = if trait_def.paren_sugar {
896 "the precise format of `Fn`-family traits' type parameters is subject to change. \
897 Use parenthetical notation (Fn(Foo, Bar) -> Baz) instead"
899 "parenthetical notation is only stable when used with `Fn`-family traits"
901 emit_feature_err(&self.tcx().sess.parse_sess, sym::unboxed_closures,
902 span, GateIssue::Language, msg);
905 self.create_substs_for_ast_path(span,
907 trait_segment.generic_args(),
908 trait_segment.infer_args,
912 fn trait_defines_associated_type_named(&self,
914 assoc_name: ast::Ident)
917 self.tcx().associated_items(trait_def_id).any(|item| {
918 item.kind == ty::AssocKind::Type &&
919 self.tcx().hygienic_eq(assoc_name, item.ident, trait_def_id)
923 // Returns `true` if a bounds list includes `?Sized`.
924 pub fn is_unsized(&self, ast_bounds: &[hir::GenericBound], span: Span) -> bool {
925 let tcx = self.tcx();
927 // Try to find an unbound in bounds.
928 let mut unbound = None;
929 for ab in ast_bounds {
930 if let &hir::GenericBound::Trait(ref ptr, hir::TraitBoundModifier::Maybe) = ab {
931 if unbound.is_none() {
932 unbound = Some(&ptr.trait_ref);
938 "type parameter has more than one relaxed default \
939 bound, only one is supported"
945 let kind_id = tcx.lang_items().require(SizedTraitLangItem);
948 // FIXME(#8559) currently requires the unbound to be built-in.
949 if let Ok(kind_id) = kind_id {
950 if tpb.path.res != Res::Def(DefKind::Trait, kind_id) {
953 "default bound relaxed for a type parameter, but \
954 this does nothing because the given bound is not \
955 a default; only `?Sized` is supported",
960 _ if kind_id.is_ok() => {
963 // No lang item for `Sized`, so we can't add it as a bound.
970 /// This helper takes a *converted* parameter type (`param_ty`)
971 /// and an *unconverted* list of bounds:
975 /// ^ ^^^^^ `ast_bounds` parameter, in HIR form
977 /// `param_ty`, in ty form
980 /// It adds these `ast_bounds` into the `bounds` structure.
982 /// **A note on binders:** there is an implied binder around
983 /// `param_ty` and `ast_bounds`. See `instantiate_poly_trait_ref`
984 /// for more details.
987 ast_bounds: &[hir::GenericBound],
988 bounds: &mut Bounds<'tcx>,
990 let mut trait_bounds = Vec::new();
991 let mut region_bounds = Vec::new();
993 for ast_bound in ast_bounds {
995 hir::GenericBound::Trait(ref b, hir::TraitBoundModifier::None) =>
996 trait_bounds.push(b),
997 hir::GenericBound::Trait(_, hir::TraitBoundModifier::Maybe) => {}
998 hir::GenericBound::Outlives(ref l) =>
999 region_bounds.push(l),
1003 for bound in trait_bounds {
1004 let _ = self.instantiate_poly_trait_ref(
1011 bounds.region_bounds.extend(region_bounds
1013 .map(|r| (self.ast_region_to_region(r, None), r.span))
1017 /// Translates a list of bounds from the HIR into the `Bounds` data structure.
1018 /// The self-type for the bounds is given by `param_ty`.
1023 /// fn foo<T: Bar + Baz>() { }
1024 /// ^ ^^^^^^^^^ ast_bounds
1028 /// The `sized_by_default` parameter indicates if, in this context, the `param_ty` should be
1029 /// considered `Sized` unless there is an explicit `?Sized` bound. This would be true in the
1030 /// example above, but is not true in supertrait listings like `trait Foo: Bar + Baz`.
1032 /// `span` should be the declaration size of the parameter.
1033 pub fn compute_bounds(&self,
1035 ast_bounds: &[hir::GenericBound],
1036 sized_by_default: SizedByDefault,
1039 let mut bounds = Bounds::default();
1041 self.add_bounds(param_ty, ast_bounds, &mut bounds);
1042 bounds.trait_bounds.sort_by_key(|(t, _)| t.def_id());
1044 bounds.implicitly_sized = if let SizedByDefault::Yes = sized_by_default {
1045 if !self.is_unsized(ast_bounds, span) {
1057 /// Given an HIR binding like `Item = Foo` or `Item: Foo`, pushes the corresponding predicates
1060 /// **A note on binders:** given something like `T: for<'a> Iterator<Item = &'a u32>`, the
1061 /// `trait_ref` here will be `for<'a> T: Iterator`. The `binding` data however is from *inside*
1062 /// the binder (e.g., `&'a u32`) and hence may reference bound regions.
1063 fn add_predicates_for_ast_type_binding(
1065 hir_ref_id: hir::HirId,
1066 trait_ref: ty::PolyTraitRef<'tcx>,
1067 binding: &ConvertedBinding<'_, 'tcx>,
1068 bounds: &mut Bounds<'tcx>,
1070 dup_bindings: &mut FxHashMap<DefId, Span>,
1071 ) -> Result<(), ErrorReported> {
1072 let tcx = self.tcx();
1075 // Given something like `U: SomeTrait<T = X>`, we want to produce a
1076 // predicate like `<U as SomeTrait>::T = X`. This is somewhat
1077 // subtle in the event that `T` is defined in a supertrait of
1078 // `SomeTrait`, because in that case we need to upcast.
1080 // That is, consider this case:
1083 // trait SubTrait: SuperTrait<int> { }
1084 // trait SuperTrait<A> { type T; }
1086 // ... B: SubTrait<T = foo> ...
1089 // We want to produce `<B as SuperTrait<int>>::T == foo`.
1091 // Find any late-bound regions declared in `ty` that are not
1092 // declared in the trait-ref. These are not well-formed.
1096 // for<'a> <T as Iterator>::Item = &'a str // <-- 'a is bad
1097 // for<'a> <T as FnMut<(&'a u32,)>>::Output = &'a str // <-- 'a is ok
1098 if let ConvertedBindingKind::Equality(ty) = binding.kind {
1099 let late_bound_in_trait_ref =
1100 tcx.collect_constrained_late_bound_regions(&trait_ref);
1101 let late_bound_in_ty =
1102 tcx.collect_referenced_late_bound_regions(&ty::Binder::bind(ty));
1103 debug!("late_bound_in_trait_ref = {:?}", late_bound_in_trait_ref);
1104 debug!("late_bound_in_ty = {:?}", late_bound_in_ty);
1105 for br in late_bound_in_ty.difference(&late_bound_in_trait_ref) {
1106 let br_name = match *br {
1107 ty::BrNamed(_, name) => name,
1111 "anonymous bound region {:?} in binding but not trait ref",
1115 struct_span_err!(tcx.sess,
1118 "binding for associated type `{}` references lifetime `{}`, \
1119 which does not appear in the trait input types",
1120 binding.item_name, br_name)
1126 let candidate = if self.trait_defines_associated_type_named(trait_ref.def_id(),
1127 binding.item_name) {
1128 // Simple case: X is defined in the current trait.
1131 // Otherwise, we have to walk through the supertraits to find
1133 let candidates = traits::supertraits(tcx, trait_ref).filter(|r| {
1134 self.trait_defines_associated_type_named(r.def_id(), binding.item_name)
1136 self.one_bound_for_assoc_type(candidates, &trait_ref.to_string(),
1137 binding.item_name, binding.span)
1140 let (assoc_ident, def_scope) =
1141 tcx.adjust_ident_and_get_scope(binding.item_name, candidate.def_id(), hir_ref_id);
1142 let assoc_ty = tcx.associated_items(candidate.def_id()).find(|i| {
1143 i.kind == ty::AssocKind::Type && i.ident.modern() == assoc_ident
1144 }).expect("missing associated type");
1146 if !assoc_ty.vis.is_accessible_from(def_scope, tcx) {
1147 let msg = format!("associated type `{}` is private", binding.item_name);
1148 tcx.sess.span_err(binding.span, &msg);
1150 tcx.check_stability(assoc_ty.def_id, Some(hir_ref_id), binding.span);
1153 dup_bindings.entry(assoc_ty.def_id)
1154 .and_modify(|prev_span| {
1155 struct_span_err!(self.tcx().sess, binding.span, E0719,
1156 "the value of the associated type `{}` (from the trait `{}`) \
1157 is already specified",
1159 tcx.def_path_str(assoc_ty.container.id()))
1160 .span_label(binding.span, "re-bound here")
1161 .span_label(*prev_span, format!("`{}` bound here first", binding.item_name))
1164 .or_insert(binding.span);
1167 match binding.kind {
1168 ConvertedBindingKind::Equality(ref ty) => {
1169 // "Desugar" a constraint like `T: Iterator<Item = u32>` this to
1170 // the "projection predicate" for:
1172 // `<T as Iterator>::Item = u32`
1173 bounds.projection_bounds.push((candidate.map_bound(|trait_ref| {
1174 ty::ProjectionPredicate {
1175 projection_ty: ty::ProjectionTy::from_ref_and_name(
1184 ConvertedBindingKind::Constraint(ast_bounds) => {
1185 // "Desugar" a constraint like `T: Iterator<Item: Debug>` to
1187 // `<T as Iterator>::Item: Debug`
1189 // Calling `skip_binder` is okay, because `add_bounds` expects the `param_ty`
1190 // parameter to have a skipped binder.
1191 let param_ty = tcx.mk_projection(assoc_ty.def_id, candidate.skip_binder().substs);
1192 self.add_bounds(param_ty, ast_bounds, bounds);
1198 fn ast_path_to_ty(&self,
1201 item_segment: &hir::PathSegment)
1204 let substs = self.ast_path_substs_for_ty(span, did, item_segment);
1207 self.tcx().at(span).type_of(did).subst(self.tcx(), substs)
1211 /// Transform a `PolyTraitRef` into a `PolyExistentialTraitRef` by
1212 /// removing the dummy `Self` type (`trait_object_dummy_self`).
1213 fn trait_ref_to_existential(&self, trait_ref: ty::TraitRef<'tcx>)
1214 -> ty::ExistentialTraitRef<'tcx> {
1215 if trait_ref.self_ty() != self.tcx().types.trait_object_dummy_self {
1216 bug!("trait_ref_to_existential called on {:?} with non-dummy Self", trait_ref);
1218 ty::ExistentialTraitRef::erase_self_ty(self.tcx(), trait_ref)
1221 fn conv_object_ty_poly_trait_ref(&self,
1223 trait_bounds: &[hir::PolyTraitRef],
1224 lifetime: &hir::Lifetime)
1227 let tcx = self.tcx();
1229 let mut bounds = Bounds::default();
1230 let mut potential_assoc_types = Vec::new();
1231 let dummy_self = self.tcx().types.trait_object_dummy_self;
1232 for trait_bound in trait_bounds.iter().rev() {
1233 let cur_potential_assoc_types = self.instantiate_poly_trait_ref(
1238 potential_assoc_types.extend(cur_potential_assoc_types.into_iter().flatten());
1241 // Expand trait aliases recursively and check that only one regular (non-auto) trait
1242 // is used and no 'maybe' bounds are used.
1243 let expanded_traits =
1244 traits::expand_trait_aliases(tcx, bounds.trait_bounds.iter().cloned());
1245 let (mut auto_traits, regular_traits): (Vec<_>, Vec<_>) =
1246 expanded_traits.partition(|i| tcx.trait_is_auto(i.trait_ref().def_id()));
1247 if regular_traits.len() > 1 {
1248 let first_trait = ®ular_traits[0];
1249 let additional_trait = ®ular_traits[1];
1250 let mut err = struct_span_err!(tcx.sess, additional_trait.bottom().1, E0225,
1251 "only auto traits can be used as additional traits in a trait object"
1253 additional_trait.label_with_exp_info(&mut err,
1254 "additional non-auto trait", "additional use");
1255 first_trait.label_with_exp_info(&mut err,
1256 "first non-auto trait", "first use");
1260 if regular_traits.is_empty() && auto_traits.is_empty() {
1261 span_err!(tcx.sess, span, E0224,
1262 "at least one trait is required for an object type");
1263 return tcx.types.err;
1266 // Check that there are no gross object safety violations;
1267 // most importantly, that the supertraits don't contain `Self`,
1269 for item in ®ular_traits {
1270 let object_safety_violations =
1271 tcx.astconv_object_safety_violations(item.trait_ref().def_id());
1272 if !object_safety_violations.is_empty() {
1273 tcx.report_object_safety_error(
1275 item.trait_ref().def_id(),
1276 object_safety_violations
1278 return tcx.types.err;
1282 // Use a `BTreeSet` to keep output in a more consistent order.
1283 let mut associated_types = BTreeSet::default();
1285 let regular_traits_refs = bounds.trait_bounds
1287 .filter(|(trait_ref, _)| !tcx.trait_is_auto(trait_ref.def_id()))
1288 .map(|(trait_ref, _)| trait_ref);
1289 for trait_ref in traits::elaborate_trait_refs(tcx, regular_traits_refs) {
1290 debug!("conv_object_ty_poly_trait_ref: observing object predicate `{:?}`", trait_ref);
1292 ty::Predicate::Trait(pred) => {
1294 .extend(tcx.associated_items(pred.def_id())
1295 .filter(|item| item.kind == ty::AssocKind::Type)
1296 .map(|item| item.def_id));
1298 ty::Predicate::Projection(pred) => {
1299 // A `Self` within the original bound will be substituted with a
1300 // `trait_object_dummy_self`, so check for that.
1301 let references_self =
1302 pred.skip_binder().ty.walk().any(|t| t == dummy_self);
1304 // If the projection output contains `Self`, force the user to
1305 // elaborate it explicitly to avoid a lot of complexity.
1307 // The "classicaly useful" case is the following:
1309 // trait MyTrait: FnMut() -> <Self as MyTrait>::MyOutput {
1314 // Here, the user could theoretically write `dyn MyTrait<Output = X>`,
1315 // but actually supporting that would "expand" to an infinitely-long type
1316 // `fix $ τ → dyn MyTrait<MyOutput = X, Output = <τ as MyTrait>::MyOutput`.
1318 // Instead, we force the user to write `dyn MyTrait<MyOutput = X, Output = X>`,
1319 // which is uglier but works. See the discussion in #56288 for alternatives.
1320 if !references_self {
1321 // Include projections defined on supertraits.
1322 bounds.projection_bounds.push((pred, DUMMY_SP))
1329 for (projection_bound, _) in &bounds.projection_bounds {
1330 associated_types.remove(&projection_bound.projection_def_id());
1333 if !associated_types.is_empty() {
1334 let names = associated_types.iter().map(|item_def_id| {
1335 let assoc_item = tcx.associated_item(*item_def_id);
1336 let trait_def_id = assoc_item.container.id();
1338 "`{}` (from the trait `{}`)",
1340 tcx.def_path_str(trait_def_id),
1342 }).collect::<Vec<_>>().join(", ");
1343 let mut err = struct_span_err!(
1347 "the value of the associated type{} {} must be specified",
1348 pluralise!(associated_types.len()),
1351 let (suggest, potential_assoc_types_spans) =
1352 if potential_assoc_types.len() == associated_types.len() {
1353 // Only suggest when the amount of missing associated types equals the number of
1354 // extra type arguments present, as that gives us a relatively high confidence
1355 // that the user forgot to give the associtated type's name. The canonical
1356 // example would be trying to use `Iterator<isize>` instead of
1357 // `Iterator<Item = isize>`.
1358 (true, potential_assoc_types)
1362 let mut suggestions = Vec::new();
1363 for (i, item_def_id) in associated_types.iter().enumerate() {
1364 let assoc_item = tcx.associated_item(*item_def_id);
1367 format!("associated type `{}` must be specified", assoc_item.ident),
1369 if let Some(sp) = tcx.hir().span_if_local(*item_def_id) {
1370 err.span_label(sp, format!("`{}` defined here", assoc_item.ident));
1373 if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(
1374 potential_assoc_types_spans[i],
1377 potential_assoc_types_spans[i],
1378 format!("{} = {}", assoc_item.ident, snippet),
1383 if !suggestions.is_empty() {
1384 let msg = format!("if you meant to specify the associated {}, write",
1385 if suggestions.len() == 1 { "type" } else { "types" });
1386 err.multipart_suggestion(
1389 Applicability::MaybeIncorrect,
1395 // De-duplicate auto traits so that, e.g., `dyn Trait + Send + Send` is the same as
1396 // `dyn Trait + Send`.
1397 auto_traits.sort_by_key(|i| i.trait_ref().def_id());
1398 auto_traits.dedup_by_key(|i| i.trait_ref().def_id());
1399 debug!("regular_traits: {:?}", regular_traits);
1400 debug!("auto_traits: {:?}", auto_traits);
1402 // Erase the `dummy_self` (`trait_object_dummy_self`) used above.
1403 let existential_trait_refs = regular_traits.iter().map(|i| {
1404 i.trait_ref().map_bound(|trait_ref| self.trait_ref_to_existential(trait_ref))
1406 let existential_projections = bounds.projection_bounds.iter().map(|(bound, _)| {
1407 bound.map_bound(|b| {
1408 let trait_ref = self.trait_ref_to_existential(b.projection_ty.trait_ref(tcx));
1409 ty::ExistentialProjection {
1411 item_def_id: b.projection_ty.item_def_id,
1412 substs: trait_ref.substs,
1417 // Calling `skip_binder` is okay because the predicates are re-bound.
1418 let regular_trait_predicates = existential_trait_refs.map(
1419 |trait_ref| ty::ExistentialPredicate::Trait(*trait_ref.skip_binder()));
1420 let auto_trait_predicates = auto_traits.into_iter().map(
1421 |trait_ref| ty::ExistentialPredicate::AutoTrait(trait_ref.trait_ref().def_id()));
1423 regular_trait_predicates
1424 .chain(auto_trait_predicates)
1425 .chain(existential_projections
1426 .map(|x| ty::ExistentialPredicate::Projection(*x.skip_binder())))
1427 .collect::<SmallVec<[_; 8]>>();
1428 v.sort_by(|a, b| a.stable_cmp(tcx, b));
1430 let existential_predicates = ty::Binder::bind(tcx.mk_existential_predicates(v.into_iter()));
1432 // Use explicitly-specified region bound.
1433 let region_bound = if !lifetime.is_elided() {
1434 self.ast_region_to_region(lifetime, None)
1436 self.compute_object_lifetime_bound(span, existential_predicates).unwrap_or_else(|| {
1437 if tcx.named_region(lifetime.hir_id).is_some() {
1438 self.ast_region_to_region(lifetime, None)
1440 self.re_infer(None, span).unwrap_or_else(|| {
1441 span_err!(tcx.sess, span, E0228,
1442 "the lifetime bound for this object type cannot be deduced \
1443 from context; please supply an explicit bound");
1444 tcx.lifetimes.re_static
1449 debug!("region_bound: {:?}", region_bound);
1451 let ty = tcx.mk_dynamic(existential_predicates, region_bound);
1452 debug!("trait_object_type: {:?}", ty);
1456 fn report_ambiguous_associated_type(
1463 let mut err = struct_span_err!(self.tcx().sess, span, E0223, "ambiguous associated type");
1464 if let (Some(_), Ok(snippet)) = (
1465 self.tcx().sess.confused_type_with_std_module.borrow().get(&span),
1466 self.tcx().sess.source_map().span_to_snippet(span),
1468 err.span_suggestion(
1470 "you are looking for the module in `std`, not the primitive type",
1471 format!("std::{}", snippet),
1472 Applicability::MachineApplicable,
1475 err.span_suggestion(
1477 "use fully-qualified syntax",
1478 format!("<{} as {}>::{}", type_str, trait_str, name),
1479 Applicability::HasPlaceholders
1485 // Search for a bound on a type parameter which includes the associated item
1486 // given by `assoc_name`. `ty_param_def_id` is the `DefId` of the type parameter
1487 // This function will fail if there are no suitable bounds or there is
1489 fn find_bound_for_assoc_item(&self,
1490 ty_param_def_id: DefId,
1491 assoc_name: ast::Ident,
1493 -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
1495 let tcx = self.tcx();
1498 "find_bound_for_assoc_item(ty_param_def_id={:?}, assoc_name={:?}, span={:?})",
1504 let predicates = &self.get_type_parameter_bounds(span, ty_param_def_id).predicates;
1506 debug!("find_bound_for_assoc_item: predicates={:#?}", predicates);
1508 let bounds = predicates.iter().filter_map(|(p, _)| p.to_opt_poly_trait_ref());
1510 // Check that there is exactly one way to find an associated type with the
1512 let suitable_bounds = traits::transitive_bounds(tcx, bounds)
1513 .filter(|b| self.trait_defines_associated_type_named(b.def_id(), assoc_name));
1515 let param_hir_id = tcx.hir().as_local_hir_id(ty_param_def_id).unwrap();
1516 let param_name = tcx.hir().ty_param_name(param_hir_id);
1517 self.one_bound_for_assoc_type(suitable_bounds,
1518 ¶m_name.as_str(),
1523 // Checks that `bounds` contains exactly one element and reports appropriate
1524 // errors otherwise.
1525 fn one_bound_for_assoc_type<I>(&self,
1527 ty_param_name: &str,
1528 assoc_name: ast::Ident,
1530 -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
1531 where I: Iterator<Item = ty::PolyTraitRef<'tcx>>
1533 let bound = match bounds.next() {
1534 Some(bound) => bound,
1536 struct_span_err!(self.tcx().sess, span, E0220,
1537 "associated type `{}` not found for `{}`",
1540 .span_label(span, format!("associated type `{}` not found", assoc_name))
1542 return Err(ErrorReported);
1546 debug!("one_bound_for_assoc_type: bound = {:?}", bound);
1548 if let Some(bound2) = bounds.next() {
1549 debug!("one_bound_for_assoc_type: bound2 = {:?}", bound2);
1551 let bounds = iter::once(bound).chain(iter::once(bound2)).chain(bounds);
1552 let mut err = struct_span_err!(
1553 self.tcx().sess, span, E0221,
1554 "ambiguous associated type `{}` in bounds of `{}`",
1557 err.span_label(span, format!("ambiguous associated type `{}`", assoc_name));
1559 for bound in bounds {
1560 let bound_span = self.tcx().associated_items(bound.def_id()).find(|item| {
1561 item.kind == ty::AssocKind::Type &&
1562 self.tcx().hygienic_eq(assoc_name, item.ident, bound.def_id())
1564 .and_then(|item| self.tcx().hir().span_if_local(item.def_id));
1566 if let Some(span) = bound_span {
1567 err.span_label(span, format!("ambiguous `{}` from `{}`",
1571 span_note!(&mut err, span,
1572 "associated type `{}` could derive from `{}`",
1583 // Create a type from a path to an associated type.
1584 // For a path `A::B::C::D`, `qself_ty` and `qself_def` are the type and def for `A::B::C`
1585 // and item_segment is the path segment for `D`. We return a type and a def for
1587 // Will fail except for `T::A` and `Self::A`; i.e., if `qself_ty`/`qself_def` are not a type
1588 // parameter or `Self`.
1589 pub fn associated_path_to_ty(
1591 hir_ref_id: hir::HirId,
1595 assoc_segment: &hir::PathSegment,
1596 permit_variants: bool,
1597 ) -> Result<(Ty<'tcx>, DefKind, DefId), ErrorReported> {
1598 let tcx = self.tcx();
1599 let assoc_ident = assoc_segment.ident;
1601 debug!("associated_path_to_ty: {:?}::{}", qself_ty, assoc_ident);
1603 self.prohibit_generics(slice::from_ref(assoc_segment));
1605 // Check if we have an enum variant.
1606 let mut variant_resolution = None;
1607 if let ty::Adt(adt_def, _) = qself_ty.kind {
1608 if adt_def.is_enum() {
1609 let variant_def = adt_def.variants.iter().find(|vd| {
1610 tcx.hygienic_eq(assoc_ident, vd.ident, adt_def.did)
1612 if let Some(variant_def) = variant_def {
1613 if permit_variants {
1614 tcx.check_stability(variant_def.def_id, Some(hir_ref_id), span);
1615 return Ok((qself_ty, DefKind::Variant, variant_def.def_id));
1617 variant_resolution = Some(variant_def.def_id);
1623 // Find the type of the associated item, and the trait where the associated
1624 // item is declared.
1625 let bound = match (&qself_ty.kind, qself_res) {
1626 (_, Res::SelfTy(Some(_), Some(impl_def_id))) => {
1627 // `Self` in an impl of a trait -- we have a concrete self type and a
1629 let trait_ref = match tcx.impl_trait_ref(impl_def_id) {
1630 Some(trait_ref) => trait_ref,
1632 // A cycle error occurred, most likely.
1633 return Err(ErrorReported);
1637 let candidates = traits::supertraits(tcx, ty::Binder::bind(trait_ref))
1638 .filter(|r| self.trait_defines_associated_type_named(r.def_id(), assoc_ident));
1640 self.one_bound_for_assoc_type(candidates, "Self", assoc_ident, span)?
1642 (&ty::Param(_), Res::SelfTy(Some(param_did), None)) |
1643 (&ty::Param(_), Res::Def(DefKind::TyParam, param_did)) => {
1644 self.find_bound_for_assoc_item(param_did, assoc_ident, span)?
1647 if variant_resolution.is_some() {
1648 // Variant in type position
1649 let msg = format!("expected type, found variant `{}`", assoc_ident);
1650 tcx.sess.span_err(span, &msg);
1651 } else if qself_ty.is_enum() {
1652 let mut err = tcx.sess.struct_span_err(
1654 &format!("no variant `{}` in enum `{}`", assoc_ident, qself_ty),
1657 let adt_def = qself_ty.ty_adt_def().expect("enum is not an ADT");
1658 if let Some(suggested_name) = find_best_match_for_name(
1659 adt_def.variants.iter().map(|variant| &variant.ident.name),
1660 &assoc_ident.as_str(),
1663 err.span_suggestion(
1665 "there is a variant with a similar name",
1666 suggested_name.to_string(),
1667 Applicability::MaybeIncorrect,
1672 format!("variant not found in `{}`", qself_ty),
1676 if let Some(sp) = tcx.hir().span_if_local(adt_def.did) {
1677 let sp = tcx.sess.source_map().def_span(sp);
1678 err.span_label(sp, format!("variant `{}` not found here", assoc_ident));
1682 } else if !qself_ty.references_error() {
1683 // Don't print `TyErr` to the user.
1684 self.report_ambiguous_associated_type(
1686 &qself_ty.to_string(),
1691 return Err(ErrorReported);
1695 let trait_did = bound.def_id();
1696 let (assoc_ident, def_scope) =
1697 tcx.adjust_ident_and_get_scope(assoc_ident, trait_did, hir_ref_id);
1698 let item = tcx.associated_items(trait_did).find(|i| {
1699 Namespace::from(i.kind) == Namespace::Type &&
1700 i.ident.modern() == assoc_ident
1701 }).expect("missing associated type");
1703 let ty = self.projected_ty_from_poly_trait_ref(span, item.def_id, bound);
1704 let ty = self.normalize_ty(span, ty);
1706 let kind = DefKind::AssocTy;
1707 if !item.vis.is_accessible_from(def_scope, tcx) {
1708 let msg = format!("{} `{}` is private", kind.descr(item.def_id), assoc_ident);
1709 tcx.sess.span_err(span, &msg);
1711 tcx.check_stability(item.def_id, Some(hir_ref_id), span);
1713 if let Some(variant_def_id) = variant_resolution {
1714 let mut err = tcx.struct_span_lint_hir(
1715 AMBIGUOUS_ASSOCIATED_ITEMS,
1718 "ambiguous associated item",
1721 let mut could_refer_to = |kind: DefKind, def_id, also| {
1722 let note_msg = format!("`{}` could{} refer to {} defined here",
1723 assoc_ident, also, kind.descr(def_id));
1724 err.span_note(tcx.def_span(def_id), ¬e_msg);
1726 could_refer_to(DefKind::Variant, variant_def_id, "");
1727 could_refer_to(kind, item.def_id, " also");
1729 err.span_suggestion(
1731 "use fully-qualified syntax",
1732 format!("<{} as {}>::{}", qself_ty, tcx.item_name(trait_did), assoc_ident),
1733 Applicability::MachineApplicable,
1737 Ok((ty, kind, item.def_id))
1740 fn qpath_to_ty(&self,
1742 opt_self_ty: Option<Ty<'tcx>>,
1744 trait_segment: &hir::PathSegment,
1745 item_segment: &hir::PathSegment)
1748 let tcx = self.tcx();
1749 let trait_def_id = tcx.parent(item_def_id).unwrap();
1751 self.prohibit_generics(slice::from_ref(item_segment));
1753 let self_ty = if let Some(ty) = opt_self_ty {
1756 let path_str = tcx.def_path_str(trait_def_id);
1757 self.report_ambiguous_associated_type(
1761 item_segment.ident.name,
1763 return tcx.types.err;
1766 debug!("qpath_to_ty: self_type={:?}", self_ty);
1768 let trait_ref = self.ast_path_to_mono_trait_ref(span,
1773 debug!("qpath_to_ty: trait_ref={:?}", trait_ref);
1775 self.normalize_ty(span, tcx.mk_projection(item_def_id, trait_ref.substs))
1778 pub fn prohibit_generics<'a, T: IntoIterator<Item = &'a hir::PathSegment>>(
1779 &self, segments: T) -> bool {
1780 let mut has_err = false;
1781 for segment in segments {
1782 let (mut err_for_lt, mut err_for_ty, mut err_for_ct) = (false, false, false);
1783 for arg in &segment.generic_args().args {
1784 let (span, kind) = match arg {
1785 hir::GenericArg::Lifetime(lt) => {
1786 if err_for_lt { continue }
1789 (lt.span, "lifetime")
1791 hir::GenericArg::Type(ty) => {
1792 if err_for_ty { continue }
1797 hir::GenericArg::Const(ct) => {
1798 if err_for_ct { continue }
1803 let mut err = struct_span_err!(
1807 "{} arguments are not allowed for this type",
1810 err.span_label(span, format!("{} argument not allowed", kind));
1812 if err_for_lt && err_for_ty && err_for_ct {
1816 for binding in &segment.generic_args().bindings {
1818 Self::prohibit_assoc_ty_binding(self.tcx(), binding.span);
1825 pub fn prohibit_assoc_ty_binding(tcx: TyCtxt<'_>, span: Span) {
1826 let mut err = struct_span_err!(tcx.sess, span, E0229,
1827 "associated type bindings are not allowed here");
1828 err.span_label(span, "associated type not allowed here").emit();
1831 // FIXME(eddyb, varkor) handle type paths here too, not just value ones.
1832 pub fn def_ids_for_value_path_segments(
1834 segments: &[hir::PathSegment],
1835 self_ty: Option<Ty<'tcx>>,
1839 // We need to extract the type parameters supplied by the user in
1840 // the path `path`. Due to the current setup, this is a bit of a
1841 // tricky-process; the problem is that resolve only tells us the
1842 // end-point of the path resolution, and not the intermediate steps.
1843 // Luckily, we can (at least for now) deduce the intermediate steps
1844 // just from the end-point.
1846 // There are basically five cases to consider:
1848 // 1. Reference to a constructor of a struct:
1850 // struct Foo<T>(...)
1852 // In this case, the parameters are declared in the type space.
1854 // 2. Reference to a constructor of an enum variant:
1856 // enum E<T> { Foo(...) }
1858 // In this case, the parameters are defined in the type space,
1859 // but may be specified either on the type or the variant.
1861 // 3. Reference to a fn item or a free constant:
1865 // In this case, the path will again always have the form
1866 // `a::b::foo::<T>` where only the final segment should have
1867 // type parameters. However, in this case, those parameters are
1868 // declared on a value, and hence are in the `FnSpace`.
1870 // 4. Reference to a method or an associated constant:
1872 // impl<A> SomeStruct<A> {
1876 // Here we can have a path like
1877 // `a::b::SomeStruct::<A>::foo::<B>`, in which case parameters
1878 // may appear in two places. The penultimate segment,
1879 // `SomeStruct::<A>`, contains parameters in TypeSpace, and the
1880 // final segment, `foo::<B>` contains parameters in fn space.
1882 // The first step then is to categorize the segments appropriately.
1884 let tcx = self.tcx();
1886 assert!(!segments.is_empty());
1887 let last = segments.len() - 1;
1889 let mut path_segs = vec![];
1892 // Case 1. Reference to a struct constructor.
1893 DefKind::Ctor(CtorOf::Struct, ..) => {
1894 // Everything but the final segment should have no
1895 // parameters at all.
1896 let generics = tcx.generics_of(def_id);
1897 // Variant and struct constructors use the
1898 // generics of their parent type definition.
1899 let generics_def_id = generics.parent.unwrap_or(def_id);
1900 path_segs.push(PathSeg(generics_def_id, last));
1903 // Case 2. Reference to a variant constructor.
1904 DefKind::Ctor(CtorOf::Variant, ..)
1905 | DefKind::Variant => {
1906 let adt_def = self_ty.map(|t| t.ty_adt_def().unwrap());
1907 let (generics_def_id, index) = if let Some(adt_def) = adt_def {
1908 debug_assert!(adt_def.is_enum());
1910 } else if last >= 1 && segments[last - 1].args.is_some() {
1911 // Everything but the penultimate segment should have no
1912 // parameters at all.
1913 let mut def_id = def_id;
1915 // `DefKind::Ctor` -> `DefKind::Variant`
1916 if let DefKind::Ctor(..) = kind {
1917 def_id = tcx.parent(def_id).unwrap()
1920 // `DefKind::Variant` -> `DefKind::Enum`
1921 let enum_def_id = tcx.parent(def_id).unwrap();
1922 (enum_def_id, last - 1)
1924 // FIXME: lint here recommending `Enum::<...>::Variant` form
1925 // instead of `Enum::Variant::<...>` form.
1927 // Everything but the final segment should have no
1928 // parameters at all.
1929 let generics = tcx.generics_of(def_id);
1930 // Variant and struct constructors use the
1931 // generics of their parent type definition.
1932 (generics.parent.unwrap_or(def_id), last)
1934 path_segs.push(PathSeg(generics_def_id, index));
1937 // Case 3. Reference to a top-level value.
1940 | DefKind::ConstParam
1941 | DefKind::Static => {
1942 path_segs.push(PathSeg(def_id, last));
1945 // Case 4. Reference to a method or associated const.
1947 | DefKind::AssocConst => {
1948 if segments.len() >= 2 {
1949 let generics = tcx.generics_of(def_id);
1950 path_segs.push(PathSeg(generics.parent.unwrap(), last - 1));
1952 path_segs.push(PathSeg(def_id, last));
1955 kind => bug!("unexpected definition kind {:?} for {:?}", kind, def_id),
1958 debug!("path_segs = {:?}", path_segs);
1963 // Check a type `Path` and convert it to a `Ty`.
1964 pub fn res_to_ty(&self,
1965 opt_self_ty: Option<Ty<'tcx>>,
1967 permit_variants: bool)
1969 let tcx = self.tcx();
1971 debug!("res_to_ty(res={:?}, opt_self_ty={:?}, path_segments={:?})",
1972 path.res, opt_self_ty, path.segments);
1974 let span = path.span;
1976 Res::Def(DefKind::OpaqueTy, did) => {
1977 // Check for desugared `impl Trait`.
1978 assert!(ty::is_impl_trait_defn(tcx, did).is_none());
1979 let item_segment = path.segments.split_last().unwrap();
1980 self.prohibit_generics(item_segment.1);
1981 let substs = self.ast_path_substs_for_ty(span, did, item_segment.0);
1984 tcx.mk_opaque(did, substs),
1987 Res::Def(DefKind::Enum, did)
1988 | Res::Def(DefKind::TyAlias, did)
1989 | Res::Def(DefKind::Struct, did)
1990 | Res::Def(DefKind::Union, did)
1991 | Res::Def(DefKind::ForeignTy, did) => {
1992 assert_eq!(opt_self_ty, None);
1993 self.prohibit_generics(path.segments.split_last().unwrap().1);
1994 self.ast_path_to_ty(span, did, path.segments.last().unwrap())
1996 Res::Def(kind @ DefKind::Variant, def_id) if permit_variants => {
1997 // Convert "variant type" as if it were a real type.
1998 // The resulting `Ty` is type of the variant's enum for now.
1999 assert_eq!(opt_self_ty, None);
2002 self.def_ids_for_value_path_segments(&path.segments, None, kind, def_id);
2003 let generic_segs: FxHashSet<_> =
2004 path_segs.iter().map(|PathSeg(_, index)| index).collect();
2005 self.prohibit_generics(path.segments.iter().enumerate().filter_map(|(index, seg)| {
2006 if !generic_segs.contains(&index) {
2013 let PathSeg(def_id, index) = path_segs.last().unwrap();
2014 self.ast_path_to_ty(span, *def_id, &path.segments[*index])
2016 Res::Def(DefKind::TyParam, def_id) => {
2017 assert_eq!(opt_self_ty, None);
2018 self.prohibit_generics(&path.segments);
2020 let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
2021 let item_id = tcx.hir().get_parent_node(hir_id);
2022 let item_def_id = tcx.hir().local_def_id(item_id);
2023 let generics = tcx.generics_of(item_def_id);
2024 let index = generics.param_def_id_to_index[&def_id];
2025 tcx.mk_ty_param(index, tcx.hir().name(hir_id))
2027 Res::SelfTy(Some(_), None) => {
2028 // `Self` in trait or type alias.
2029 assert_eq!(opt_self_ty, None);
2030 self.prohibit_generics(&path.segments);
2031 tcx.types.self_param
2033 Res::SelfTy(_, Some(def_id)) => {
2034 // `Self` in impl (we know the concrete type).
2035 assert_eq!(opt_self_ty, None);
2036 self.prohibit_generics(&path.segments);
2037 // Try to evaluate any array length constants.
2038 self.normalize_ty(span, tcx.at(span).type_of(def_id))
2040 Res::Def(DefKind::AssocTy, def_id) => {
2041 debug_assert!(path.segments.len() >= 2);
2042 self.prohibit_generics(&path.segments[..path.segments.len() - 2]);
2043 self.qpath_to_ty(span,
2046 &path.segments[path.segments.len() - 2],
2047 path.segments.last().unwrap())
2049 Res::PrimTy(prim_ty) => {
2050 assert_eq!(opt_self_ty, None);
2051 self.prohibit_generics(&path.segments);
2053 hir::Bool => tcx.types.bool,
2054 hir::Char => tcx.types.char,
2055 hir::Int(it) => tcx.mk_mach_int(it),
2056 hir::Uint(uit) => tcx.mk_mach_uint(uit),
2057 hir::Float(ft) => tcx.mk_mach_float(ft),
2058 hir::Str => tcx.mk_str()
2062 self.set_tainted_by_errors();
2063 return self.tcx().types.err;
2065 _ => span_bug!(span, "unexpected resolution: {:?}", path.res)
2069 /// Parses the programmer's textual representation of a type into our
2070 /// internal notion of a type.
2071 pub fn ast_ty_to_ty(&self, ast_ty: &hir::Ty) -> Ty<'tcx> {
2072 debug!("ast_ty_to_ty(id={:?}, ast_ty={:?} ty_ty={:?})",
2073 ast_ty.hir_id, ast_ty, ast_ty.kind);
2075 let tcx = self.tcx();
2077 let result_ty = match ast_ty.kind {
2078 hir::TyKind::Slice(ref ty) => {
2079 tcx.mk_slice(self.ast_ty_to_ty(&ty))
2081 hir::TyKind::Ptr(ref mt) => {
2082 tcx.mk_ptr(ty::TypeAndMut {
2083 ty: self.ast_ty_to_ty(&mt.ty),
2087 hir::TyKind::Rptr(ref region, ref mt) => {
2088 let r = self.ast_region_to_region(region, None);
2089 debug!("ast_ty_to_ty: r={:?}", r);
2090 let t = self.ast_ty_to_ty(&mt.ty);
2091 tcx.mk_ref(r, ty::TypeAndMut {ty: t, mutbl: mt.mutbl})
2093 hir::TyKind::Never => {
2096 hir::TyKind::Tup(ref fields) => {
2097 tcx.mk_tup(fields.iter().map(|t| self.ast_ty_to_ty(&t)))
2099 hir::TyKind::BareFn(ref bf) => {
2100 require_c_abi_if_c_variadic(tcx, &bf.decl, bf.abi, ast_ty.span);
2101 tcx.mk_fn_ptr(self.ty_of_fn(bf.unsafety, bf.abi, &bf.decl))
2103 hir::TyKind::TraitObject(ref bounds, ref lifetime) => {
2104 self.conv_object_ty_poly_trait_ref(ast_ty.span, bounds, lifetime)
2106 hir::TyKind::Path(hir::QPath::Resolved(ref maybe_qself, ref path)) => {
2107 debug!("ast_ty_to_ty: maybe_qself={:?} path={:?}", maybe_qself, path);
2108 let opt_self_ty = maybe_qself.as_ref().map(|qself| {
2109 self.ast_ty_to_ty(qself)
2111 self.res_to_ty(opt_self_ty, path, false)
2113 hir::TyKind::Def(item_id, ref lifetimes) => {
2114 let did = tcx.hir().local_def_id(item_id.id);
2115 self.impl_trait_ty_to_ty(did, lifetimes)
2117 hir::TyKind::Path(hir::QPath::TypeRelative(ref qself, ref segment)) => {
2118 debug!("ast_ty_to_ty: qself={:?} segment={:?}", qself, segment);
2119 let ty = self.ast_ty_to_ty(qself);
2121 let res = if let hir::TyKind::Path(hir::QPath::Resolved(_, ref path)) = qself.kind {
2126 self.associated_path_to_ty(ast_ty.hir_id, ast_ty.span, ty, res, segment, false)
2127 .map(|(ty, _, _)| ty).unwrap_or(tcx.types.err)
2129 hir::TyKind::Array(ref ty, ref length) => {
2130 let length = self.ast_const_to_const(length, tcx.types.usize);
2131 let array_ty = tcx.mk_ty(ty::Array(self.ast_ty_to_ty(&ty), length));
2132 self.normalize_ty(ast_ty.span, array_ty)
2134 hir::TyKind::Typeof(ref _e) => {
2135 struct_span_err!(tcx.sess, ast_ty.span, E0516,
2136 "`typeof` is a reserved keyword but unimplemented")
2137 .span_label(ast_ty.span, "reserved keyword")
2142 hir::TyKind::Infer => {
2143 // Infer also appears as the type of arguments or return
2144 // values in a ExprKind::Closure, or as
2145 // the type of local variables. Both of these cases are
2146 // handled specially and will not descend into this routine.
2147 self.ty_infer(None, ast_ty.span)
2149 hir::TyKind::Err => {
2154 debug!("ast_ty_to_ty: result_ty={:?}", result_ty);
2156 self.record_ty(ast_ty.hir_id, result_ty, ast_ty.span);
2160 /// Returns the `DefId` of the constant parameter that the provided expression is a path to.
2161 pub fn const_param_def_id(&self, expr: &hir::Expr) -> Option<DefId> {
2162 // Unwrap a block, so that e.g. `{ P }` is recognised as a parameter. Const arguments
2163 // currently have to be wrapped in curly brackets, so it's necessary to special-case.
2164 let expr = match &expr.kind {
2165 ExprKind::Block(block, _) if block.stmts.is_empty() && block.expr.is_some() =>
2166 block.expr.as_ref().unwrap(),
2171 ExprKind::Path(hir::QPath::Resolved(_, path)) => match path.res {
2172 Res::Def(DefKind::ConstParam, did) => Some(did),
2179 pub fn ast_const_to_const(
2181 ast_const: &hir::AnonConst,
2183 ) -> &'tcx ty::Const<'tcx> {
2184 debug!("ast_const_to_const(id={:?}, ast_const={:?})", ast_const.hir_id, ast_const);
2186 let tcx = self.tcx();
2187 let def_id = tcx.hir().local_def_id(ast_const.hir_id);
2189 let mut const_ = ty::Const {
2190 val: ConstValue::Unevaluated(
2192 InternalSubsts::identity_for_item(tcx, def_id),
2197 let expr = &tcx.hir().body(ast_const.body).value;
2198 if let Some(def_id) = self.const_param_def_id(expr) {
2199 // Find the name and index of the const parameter by indexing the generics of the
2200 // parent item and construct a `ParamConst`.
2201 let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
2202 let item_id = tcx.hir().get_parent_node(hir_id);
2203 let item_def_id = tcx.hir().local_def_id(item_id);
2204 let generics = tcx.generics_of(item_def_id);
2205 let index = generics.param_def_id_to_index[&tcx.hir().local_def_id(hir_id)];
2206 let name = tcx.hir().name(hir_id);
2207 const_.val = ConstValue::Param(ty::ParamConst::new(index, name));
2210 tcx.mk_const(const_)
2213 pub fn impl_trait_ty_to_ty(
2216 lifetimes: &[hir::GenericArg],
2218 debug!("impl_trait_ty_to_ty(def_id={:?}, lifetimes={:?})", def_id, lifetimes);
2219 let tcx = self.tcx();
2221 let generics = tcx.generics_of(def_id);
2223 debug!("impl_trait_ty_to_ty: generics={:?}", generics);
2224 let substs = InternalSubsts::for_item(tcx, def_id, |param, _| {
2225 if let Some(i) = (param.index as usize).checked_sub(generics.parent_count) {
2226 // Our own parameters are the resolved lifetimes.
2228 GenericParamDefKind::Lifetime => {
2229 if let hir::GenericArg::Lifetime(lifetime) = &lifetimes[i] {
2230 self.ast_region_to_region(lifetime, None).into()
2238 // Replace all parent lifetimes with `'static`.
2240 GenericParamDefKind::Lifetime => {
2241 tcx.lifetimes.re_static.into()
2243 _ => tcx.mk_param_from_def(param)
2247 debug!("impl_trait_ty_to_ty: substs={:?}", substs);
2249 let ty = tcx.mk_opaque(def_id, substs);
2250 debug!("impl_trait_ty_to_ty: {}", ty);
2254 pub fn ty_of_arg(&self,
2256 expected_ty: Option<Ty<'tcx>>)
2260 hir::TyKind::Infer if expected_ty.is_some() => {
2261 self.record_ty(ty.hir_id, expected_ty.unwrap(), ty.span);
2262 expected_ty.unwrap()
2264 _ => self.ast_ty_to_ty(ty),
2268 pub fn ty_of_fn(&self,
2269 unsafety: hir::Unsafety,
2272 -> ty::PolyFnSig<'tcx> {
2275 let tcx = self.tcx();
2277 decl.inputs.iter().map(|a| self.ty_of_arg(a, None));
2279 let output_ty = match decl.output {
2280 hir::Return(ref output) => self.ast_ty_to_ty(output),
2281 hir::DefaultReturn(..) => tcx.mk_unit(),
2284 debug!("ty_of_fn: output_ty={:?}", output_ty);
2286 let bare_fn_ty = ty::Binder::bind(tcx.mk_fn_sig(
2294 // Find any late-bound regions declared in return type that do
2295 // not appear in the arguments. These are not well-formed.
2298 // for<'a> fn() -> &'a str <-- 'a is bad
2299 // for<'a> fn(&'a String) -> &'a str <-- 'a is ok
2300 let inputs = bare_fn_ty.inputs();
2301 let late_bound_in_args = tcx.collect_constrained_late_bound_regions(
2302 &inputs.map_bound(|i| i.to_owned()));
2303 let output = bare_fn_ty.output();
2304 let late_bound_in_ret = tcx.collect_referenced_late_bound_regions(&output);
2305 for br in late_bound_in_ret.difference(&late_bound_in_args) {
2306 let lifetime_name = match *br {
2307 ty::BrNamed(_, name) => format!("lifetime `{}`,", name),
2308 ty::BrAnon(_) | ty::BrEnv => "an anonymous lifetime".to_string(),
2310 let mut err = struct_span_err!(tcx.sess,
2313 "return type references {} \
2314 which is not constrained by the fn input types",
2316 if let ty::BrAnon(_) = *br {
2317 // The only way for an anonymous lifetime to wind up
2318 // in the return type but **also** be unconstrained is
2319 // if it only appears in "associated types" in the
2320 // input. See #47511 for an example. In this case,
2321 // though we can easily give a hint that ought to be
2323 err.note("lifetimes appearing in an associated type \
2324 are not considered constrained");
2332 /// Given the bounds on an object, determines what single region bound (if any) we can
2333 /// use to summarize this type. The basic idea is that we will use the bound the user
2334 /// provided, if they provided one, and otherwise search the supertypes of trait bounds
2335 /// for region bounds. It may be that we can derive no bound at all, in which case
2336 /// we return `None`.
2337 fn compute_object_lifetime_bound(&self,
2339 existential_predicates: ty::Binder<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>>)
2340 -> Option<ty::Region<'tcx>> // if None, use the default
2342 let tcx = self.tcx();
2344 debug!("compute_opt_region_bound(existential_predicates={:?})",
2345 existential_predicates);
2347 // No explicit region bound specified. Therefore, examine trait
2348 // bounds and see if we can derive region bounds from those.
2349 let derived_region_bounds =
2350 object_region_bounds(tcx, existential_predicates);
2352 // If there are no derived region bounds, then report back that we
2353 // can find no region bound. The caller will use the default.
2354 if derived_region_bounds.is_empty() {
2358 // If any of the derived region bounds are 'static, that is always
2360 if derived_region_bounds.iter().any(|&r| ty::ReStatic == *r) {
2361 return Some(tcx.lifetimes.re_static);
2364 // Determine whether there is exactly one unique region in the set
2365 // of derived region bounds. If so, use that. Otherwise, report an
2367 let r = derived_region_bounds[0];
2368 if derived_region_bounds[1..].iter().any(|r1| r != *r1) {
2369 span_err!(tcx.sess, span, E0227,
2370 "ambiguous lifetime bound, explicit lifetime bound required");
2376 /// Collects together a list of bounds that are applied to some type,
2377 /// after they've been converted into `ty` form (from the HIR
2378 /// representations). These lists of bounds occur in many places in
2382 /// trait Foo: Bar + Baz { }
2383 /// ^^^^^^^^^ supertrait list bounding the `Self` type parameter
2385 /// fn foo<T: Bar + Baz>() { }
2386 /// ^^^^^^^^^ bounding the type parameter `T`
2388 /// impl dyn Bar + Baz
2389 /// ^^^^^^^^^ bounding the forgotten dynamic type
2392 /// Our representation is a bit mixed here -- in some cases, we
2393 /// include the self type (e.g., `trait_bounds`) but in others we do
2394 #[derive(Default, PartialEq, Eq, Clone, Debug)]
2395 pub struct Bounds<'tcx> {
2396 /// A list of region bounds on the (implicit) self type. So if you
2397 /// had `T: 'a + 'b` this might would be a list `['a, 'b]` (but
2398 /// the `T` is not explicitly included).
2399 pub region_bounds: Vec<(ty::Region<'tcx>, Span)>,
2401 /// A list of trait bounds. So if you had `T: Debug` this would be
2402 /// `T: Debug`. Note that the self-type is explicit here.
2403 pub trait_bounds: Vec<(ty::PolyTraitRef<'tcx>, Span)>,
2405 /// A list of projection equality bounds. So if you had `T:
2406 /// Iterator<Item = u32>` this would include `<T as
2407 /// Iterator>::Item => u32`. Note that the self-type is explicit
2409 pub projection_bounds: Vec<(ty::PolyProjectionPredicate<'tcx>, Span)>,
2411 /// `Some` if there is *no* `?Sized` predicate. The `span`
2412 /// is the location in the source of the `T` declaration which can
2413 /// be cited as the source of the `T: Sized` requirement.
2414 pub implicitly_sized: Option<Span>,
2417 impl<'tcx> Bounds<'tcx> {
2418 /// Converts a bounds list into a flat set of predicates (like
2419 /// where-clauses). Because some of our bounds listings (e.g.,
2420 /// regions) don't include the self-type, you must supply the
2421 /// self-type here (the `param_ty` parameter).
2426 ) -> Vec<(ty::Predicate<'tcx>, Span)> {
2427 // If it could be sized, and is, add the `Sized` predicate.
2428 let sized_predicate = self.implicitly_sized.and_then(|span| {
2429 tcx.lang_items().sized_trait().map(|sized| {
2430 let trait_ref = ty::TraitRef {
2432 substs: tcx.mk_substs_trait(param_ty, &[])
2434 (trait_ref.to_predicate(), span)
2438 sized_predicate.into_iter().chain(
2439 self.region_bounds.iter().map(|&(region_bound, span)| {
2440 // Account for the binder being introduced below; no need to shift `param_ty`
2441 // because, at present at least, it can only refer to early-bound regions.
2442 let region_bound = ty::fold::shift_region(tcx, region_bound, 1);
2443 let outlives = ty::OutlivesPredicate(param_ty, region_bound);
2444 (ty::Binder::dummy(outlives).to_predicate(), span)
2446 self.trait_bounds.iter().map(|&(bound_trait_ref, span)| {
2447 (bound_trait_ref.to_predicate(), span)
2450 self.projection_bounds.iter().map(|&(projection, span)| {
2451 (projection.to_predicate(), span)