1 // ignore-tidy-filelength FIXME(#67418) Split up this file.
2 //! Conversion from AST representation of types to the `ty.rs` representation.
3 //! The main routine here is `ast_ty_to_ty()`; each use is parameterized by an
4 //! instance of `AstConv`.
6 // ignore-tidy-filelength
8 use crate::collect::PlaceholderHirTyCollector;
10 use crate::middle::lang_items::SizedTraitLangItem;
11 use crate::middle::resolve_lifetime as rl;
12 use crate::require_c_abi_if_c_variadic;
13 use crate::util::common::ErrorReported;
14 use rustc::lint::builtin::AMBIGUOUS_ASSOCIATED_ITEMS;
15 use rustc::session::{parse::feature_err, Session};
16 use rustc::ty::subst::{self, InternalSubsts, Subst, SubstsRef};
17 use rustc::ty::{self, Const, DefIdTree, ToPredicate, Ty, TyCtxt, TypeFoldable, WithConstness};
18 use rustc::ty::{GenericParamDef, GenericParamDefKind};
19 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
20 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticId};
22 use rustc_hir::def::{CtorOf, DefKind, Namespace, Res};
23 use rustc_hir::def_id::DefId;
24 use rustc_hir::intravisit::Visitor;
26 use rustc_hir::{Constness, ExprKind, GenericArg, GenericArgs};
27 use rustc_infer::traits;
28 use rustc_infer::traits::astconv_object_safety_violations;
29 use rustc_infer::traits::error_reporting::report_object_safety_error;
30 use rustc_infer::traits::wf::object_region_bounds;
31 use rustc_span::symbol::sym;
32 use rustc_span::{MultiSpan, Span, DUMMY_SP};
33 use rustc_target::spec::abi;
34 use smallvec::SmallVec;
36 use syntax::util::lev_distance::find_best_match_for_name;
38 use std::collections::BTreeSet;
42 use rustc::mir::interpret::LitToConstInput;
45 pub struct PathSeg(pub DefId, pub usize);
47 pub trait AstConv<'tcx> {
48 fn tcx<'a>(&'a self) -> TyCtxt<'tcx>;
50 fn item_def_id(&self) -> Option<DefId>;
52 fn default_constness_for_trait_bounds(&self) -> Constness;
54 /// Returns predicates in scope of the form `X: Foo`, where `X` is
55 /// a type parameter `X` with the given id `def_id`. This is a
56 /// subset of the full set of predicates.
58 /// This is used for one specific purpose: resolving "short-hand"
59 /// associated type references like `T::Item`. In principle, we
60 /// would do that by first getting the full set of predicates in
61 /// scope and then filtering down to find those that apply to `T`,
62 /// but this can lead to cycle errors. The problem is that we have
63 /// to do this resolution *in order to create the predicates in
64 /// the first place*. Hence, we have this "special pass".
65 fn get_type_parameter_bounds(&self, span: Span, def_id: DefId) -> ty::GenericPredicates<'tcx>;
67 /// Returns the lifetime to use when a lifetime is omitted (and not elided).
68 fn re_infer(&self, param: Option<&ty::GenericParamDef>, span: Span)
69 -> Option<ty::Region<'tcx>>;
71 /// Returns the type to use when a type is omitted.
72 fn ty_infer(&self, param: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx>;
74 /// Returns `true` if `_` is allowed in type signatures in the current context.
75 fn allow_ty_infer(&self) -> bool;
77 /// Returns the const to use when a const is omitted.
81 param: Option<&ty::GenericParamDef>,
83 ) -> &'tcx Const<'tcx>;
85 /// Projecting an associated type from a (potentially)
86 /// higher-ranked trait reference is more complicated, because of
87 /// the possibility of late-bound regions appearing in the
88 /// associated type binding. This is not legal in function
89 /// signatures for that reason. In a function body, we can always
90 /// handle it because we can use inference variables to remove the
91 /// late-bound regions.
92 fn projected_ty_from_poly_trait_ref(
96 item_segment: &hir::PathSegment<'_>,
97 poly_trait_ref: ty::PolyTraitRef<'tcx>,
100 /// Normalize an associated type coming from the user.
101 fn normalize_ty(&self, span: Span, ty: Ty<'tcx>) -> Ty<'tcx>;
103 /// Invoked when we encounter an error from some prior pass
104 /// (e.g., resolve) that is translated into a ty-error. This is
105 /// used to help suppress derived errors typeck might otherwise
107 fn set_tainted_by_errors(&self);
109 fn record_ty(&self, hir_id: hir::HirId, ty: Ty<'tcx>, span: Span);
112 pub enum SizedByDefault {
117 struct ConvertedBinding<'a, 'tcx> {
118 item_name: ast::Ident,
119 kind: ConvertedBindingKind<'a, 'tcx>,
123 enum ConvertedBindingKind<'a, 'tcx> {
125 Constraint(&'a [hir::GenericBound<'a>]),
129 enum GenericArgPosition {
131 Value, // e.g., functions
135 /// A marker denoting that the generic arguments that were
136 /// provided did not match the respective generic parameters.
137 pub struct GenericArgCountMismatch {
138 /// Indicates whether a fatal error was reported (`Some`), or just a lint (`None`).
139 pub reported: Option<ErrorReported>,
140 /// A list of spans of arguments provided that were not valid.
141 pub invalid_args: Vec<Span>,
144 impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
145 pub fn ast_region_to_region(
147 lifetime: &hir::Lifetime,
148 def: Option<&ty::GenericParamDef>,
149 ) -> ty::Region<'tcx> {
150 let tcx = self.tcx();
151 let lifetime_name = |def_id| tcx.hir().name(tcx.hir().as_local_hir_id(def_id).unwrap());
153 let r = match tcx.named_region(lifetime.hir_id) {
154 Some(rl::Region::Static) => tcx.lifetimes.re_static,
156 Some(rl::Region::LateBound(debruijn, id, _)) => {
157 let name = lifetime_name(id);
158 tcx.mk_region(ty::ReLateBound(debruijn, ty::BrNamed(id, name)))
161 Some(rl::Region::LateBoundAnon(debruijn, index)) => {
162 tcx.mk_region(ty::ReLateBound(debruijn, ty::BrAnon(index)))
165 Some(rl::Region::EarlyBound(index, id, _)) => {
166 let name = lifetime_name(id);
167 tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion { def_id: id, index, name }))
170 Some(rl::Region::Free(scope, id)) => {
171 let name = lifetime_name(id);
172 tcx.mk_region(ty::ReFree(ty::FreeRegion {
174 bound_region: ty::BrNamed(id, name),
177 // (*) -- not late-bound, won't change
181 self.re_infer(def, lifetime.span).unwrap_or_else(|| {
182 // This indicates an illegal lifetime
183 // elision. `resolve_lifetime` should have
184 // reported an error in this case -- but if
185 // not, let's error out.
186 tcx.sess.delay_span_bug(lifetime.span, "unelided lifetime in signature");
188 // Supply some dummy value. We don't have an
189 // `re_error`, annoyingly, so use `'static`.
190 tcx.lifetimes.re_static
195 debug!("ast_region_to_region(lifetime={:?}) yields {:?}", lifetime, r);
200 /// Given a path `path` that refers to an item `I` with the declared generics `decl_generics`,
201 /// returns an appropriate set of substitutions for this particular reference to `I`.
202 pub fn ast_path_substs_for_ty(
206 item_segment: &hir::PathSegment<'_>,
207 ) -> SubstsRef<'tcx> {
208 let (substs, assoc_bindings, _) = self.create_substs_for_ast_path(
212 item_segment.generic_args(),
213 item_segment.infer_args,
217 assoc_bindings.first().map(|b| Self::prohibit_assoc_ty_binding(self.tcx(), b.span));
222 /// Report error if there is an explicit type parameter when using `impl Trait`.
225 seg: &hir::PathSegment<'_>,
226 generics: &ty::Generics,
228 let explicit = !seg.infer_args;
229 let impl_trait = generics.params.iter().any(|param| match param.kind {
230 ty::GenericParamDefKind::Type {
231 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
237 if explicit && impl_trait {
242 .filter_map(|arg| match arg {
243 GenericArg::Type(_) => Some(arg.span()),
246 .collect::<Vec<_>>();
248 let mut err = struct_span_err! {
252 "cannot provide explicit generic arguments when `impl Trait` is \
253 used in argument position"
257 err.span_label(span, "explicit generic argument not allowed");
266 /// Checks that the correct number of generic arguments have been provided.
267 /// Used specifically for function calls.
268 pub fn check_generic_arg_count_for_call(
272 seg: &hir::PathSegment<'_>,
273 is_method_call: bool,
274 ) -> Result<(), GenericArgCountMismatch> {
275 let empty_args = hir::GenericArgs::none();
276 let suppress_mismatch = Self::check_impl_trait(tcx, seg, &def);
277 Self::check_generic_arg_count(
281 if let Some(ref args) = seg.args { args } else { &empty_args },
282 if is_method_call { GenericArgPosition::MethodCall } else { GenericArgPosition::Value },
283 def.parent.is_none() && def.has_self, // `has_self`
284 seg.infer_args || suppress_mismatch, // `infer_args`
288 /// Checks that the correct number of generic arguments have been provided.
289 /// This is used both for datatypes and function calls.
290 fn check_generic_arg_count(
294 args: &hir::GenericArgs<'_>,
295 position: GenericArgPosition,
298 ) -> Result<(), GenericArgCountMismatch> {
299 // At this stage we are guaranteed that the generic arguments are in the correct order, e.g.
300 // that lifetimes will proceed types. So it suffices to check the number of each generic
301 // arguments in order to validate them with respect to the generic parameters.
302 let param_counts = def.own_counts();
303 let arg_counts = args.own_counts();
304 let infer_lifetimes = position != GenericArgPosition::Type && arg_counts.lifetimes == 0;
306 let mut defaults: ty::GenericParamCount = Default::default();
307 for param in &def.params {
309 GenericParamDefKind::Lifetime => {}
310 GenericParamDefKind::Type { has_default, .. } => {
311 defaults.types += has_default as usize
313 GenericParamDefKind::Const => {
314 // FIXME(const_generics:defaults)
319 if position != GenericArgPosition::Type && !args.bindings.is_empty() {
320 AstConv::prohibit_assoc_ty_binding(tcx, args.bindings[0].span);
323 // Prohibit explicit lifetime arguments if late-bound lifetime parameters are present.
324 let mut explicit_lifetimes = Ok(());
325 if !infer_lifetimes {
326 if let Some(span_late) = def.has_late_bound_regions {
327 let msg = "cannot specify lifetime arguments explicitly \
328 if late bound lifetime parameters are present";
329 let note = "the late bound lifetime parameter is introduced here";
330 let span = args.args[0].span();
331 if position == GenericArgPosition::Value
332 && arg_counts.lifetimes != param_counts.lifetimes
334 explicit_lifetimes = Err(true);
335 let mut err = tcx.sess.struct_span_err(span, msg);
336 err.span_note(span_late, note);
339 explicit_lifetimes = Err(false);
340 let mut multispan = MultiSpan::from_span(span);
341 multispan.push_span_label(span_late, note.to_string());
342 tcx.struct_span_lint_hir(
343 lint::builtin::LATE_BOUND_LIFETIME_ARGUMENTS,
346 |lint| lint.build(msg).emit(),
352 let check_kind_count =
353 |kind, required, permitted, provided, offset, unexpected_spans: &mut Vec<Span>| {
355 "check_kind_count: kind: {} required: {} permitted: {} provided: {} offset: {}",
356 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 {
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 ")
371 // provided > permitted
372 (permitted, "at most ")
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 unexpected_spans.extend(spans.clone());
386 (spans, format!("unexpected {} argument", kind))
391 "expected {}{} {} argument{}",
400 let mut err = tcx.sess.struct_span_err_with_code(
403 "wrong number of {} arguments: expected {}{}, found {}",
404 kind, quantifier, bound, provided,
406 DiagnosticId::Error("E0107".into()),
409 err.span_label(span, label.as_str());
416 let mut arg_count_correct = explicit_lifetimes;
417 let mut unexpected_spans = vec![];
419 if arg_count_correct.is_ok()
420 && (!infer_lifetimes || arg_counts.lifetimes > param_counts.lifetimes)
422 arg_count_correct = check_kind_count(
424 param_counts.lifetimes,
425 param_counts.lifetimes,
426 arg_counts.lifetimes,
428 &mut unexpected_spans,
430 .and(arg_count_correct);
432 // FIXME(const_generics:defaults)
433 if !infer_args || arg_counts.consts > param_counts.consts {
434 arg_count_correct = check_kind_count(
439 arg_counts.lifetimes + arg_counts.types,
440 &mut unexpected_spans,
442 .and(arg_count_correct);
444 // Note that type errors are currently be emitted *after* const errors.
445 if !infer_args || arg_counts.types > param_counts.types - defaults.types - has_self as usize
447 arg_count_correct = check_kind_count(
449 param_counts.types - defaults.types - has_self as usize,
450 param_counts.types - has_self as usize,
452 arg_counts.lifetimes,
453 &mut unexpected_spans,
455 .and(arg_count_correct);
458 arg_count_correct.map_err(|reported_err| GenericArgCountMismatch {
459 reported: if reported_err { Some(ErrorReported) } else { None },
460 invalid_args: unexpected_spans,
464 /// Report an error that a generic argument did not match the generic parameter that was
466 fn generic_arg_mismatch_err(sess: &Session, arg: &GenericArg<'_>, kind: &'static str) {
467 let mut err = struct_span_err!(
471 "{} provided when a {} was expected",
475 // This note will be true as long as generic parameters are strictly ordered by their kind.
476 err.note(&format!("{} arguments must be provided before {} arguments", kind, arg.descr()));
480 /// Creates the relevant generic argument substitutions
481 /// corresponding to a set of generic parameters. This is a
482 /// rather complex function. Let us try to explain the role
483 /// of each of its parameters:
485 /// To start, we are given the `def_id` of the thing we are
486 /// creating the substitutions for, and a partial set of
487 /// substitutions `parent_substs`. In general, the substitutions
488 /// for an item begin with substitutions for all the "parents" of
489 /// that item -- e.g., for a method it might include the
490 /// parameters from the impl.
492 /// Therefore, the method begins by walking down these parents,
493 /// starting with the outermost parent and proceed inwards until
494 /// it reaches `def_id`. For each parent `P`, it will check `parent_substs`
495 /// first to see if the parent's substitutions are listed in there. If so,
496 /// we can append those and move on. Otherwise, it invokes the
497 /// three callback functions:
499 /// - `args_for_def_id`: given the `DefId` `P`, supplies back the
500 /// generic arguments that were given to that parent from within
501 /// the path; so e.g., if you have `<T as Foo>::Bar`, the `DefId`
502 /// might refer to the trait `Foo`, and the arguments might be
503 /// `[T]`. The boolean value indicates whether to infer values
504 /// for arguments whose values were not explicitly provided.
505 /// - `provided_kind`: given the generic parameter and the value from `args_for_def_id`,
506 /// instantiate a `GenericArg`.
507 /// - `inferred_kind`: if no parameter was provided, and inference is enabled, then
508 /// creates a suitable inference variable.
509 pub fn create_substs_for_generic_args<'b>(
512 parent_substs: &[subst::GenericArg<'tcx>],
514 self_ty: Option<Ty<'tcx>>,
515 arg_count_correct: bool,
516 args_for_def_id: impl Fn(DefId) -> (Option<&'b GenericArgs<'b>>, bool),
517 provided_kind: impl Fn(&GenericParamDef, &GenericArg<'_>) -> subst::GenericArg<'tcx>,
518 mut inferred_kind: impl FnMut(
519 Option<&[subst::GenericArg<'tcx>]>,
522 ) -> subst::GenericArg<'tcx>,
523 ) -> SubstsRef<'tcx> {
524 // Collect the segments of the path; we need to substitute arguments
525 // for parameters throughout the entire path (wherever there are
526 // generic parameters).
527 let mut parent_defs = tcx.generics_of(def_id);
528 let count = parent_defs.count();
529 let mut stack = vec![(def_id, parent_defs)];
530 while let Some(def_id) = parent_defs.parent {
531 parent_defs = tcx.generics_of(def_id);
532 stack.push((def_id, parent_defs));
535 // We manually build up the substitution, rather than using convenience
536 // methods in `subst.rs`, so that we can iterate over the arguments and
537 // parameters in lock-step linearly, instead of trying to match each pair.
538 let mut substs: SmallVec<[subst::GenericArg<'tcx>; 8]> = SmallVec::with_capacity(count);
539 // Iterate over each segment of the path.
540 while let Some((def_id, defs)) = stack.pop() {
541 let mut params = defs.params.iter().peekable();
543 // If we have already computed substitutions for parents, we can use those directly.
544 while let Some(¶m) = params.peek() {
545 if let Some(&kind) = parent_substs.get(param.index as usize) {
553 // `Self` is handled first, unless it's been handled in `parent_substs`.
555 if let Some(¶m) = params.peek() {
556 if param.index == 0 {
557 if let GenericParamDefKind::Type { .. } = param.kind {
561 .unwrap_or_else(|| inferred_kind(None, param, true)),
569 // Check whether this segment takes generic arguments and the user has provided any.
570 let (generic_args, infer_args) = args_for_def_id(def_id);
573 generic_args.iter().flat_map(|generic_args| generic_args.args.iter()).peekable();
575 // If we encounter a type or const when we expect a lifetime, we infer the lifetimes.
576 // If we later encounter a lifetime, we know that the arguments were provided in the
577 // wrong order. `force_infer_lt` records the type or const that forced lifetimes to be
578 // inferred, so we can use it for diagnostics later.
579 let mut force_infer_lt = None;
582 // We're going to iterate through the generic arguments that the user
583 // provided, matching them with the generic parameters we expect.
584 // Mismatches can occur as a result of elided lifetimes, or for malformed
585 // input. We try to handle both sensibly.
586 match (args.peek(), params.peek()) {
587 (Some(&arg), Some(¶m)) => {
588 match (arg, ¶m.kind) {
589 (GenericArg::Lifetime(_), GenericParamDefKind::Lifetime)
590 | (GenericArg::Type(_), GenericParamDefKind::Type { .. })
591 | (GenericArg::Const(_), GenericParamDefKind::Const) => {
592 substs.push(provided_kind(param, arg));
596 (GenericArg::Type(_), GenericParamDefKind::Lifetime)
597 | (GenericArg::Const(_), GenericParamDefKind::Lifetime) => {
598 // We expected a lifetime argument, but got a type or const
599 // argument. That means we're inferring the lifetimes.
600 substs.push(inferred_kind(None, param, infer_args));
601 force_infer_lt = Some(arg);
605 // We expected one kind of parameter, but the user provided
606 // another. This is an error. However, if we already know that
607 // the arguments don't match up with the parameters, we won't issue
608 // an additional error, as the user already knows what's wrong.
609 if arg_count_correct {
610 Self::generic_arg_mismatch_err(tcx.sess, arg, kind.descr());
613 // We've reported the error, but we want to make sure that this
614 // problem doesn't bubble down and create additional, irrelevant
615 // errors. In this case, we're simply going to ignore the argument
616 // and any following arguments. The rest of the parameters will be
618 while args.next().is_some() {}
623 (Some(&arg), None) => {
624 // We should never be able to reach this point with well-formed input.
625 // There are two situations in which we can encounter this issue.
627 // 1. The number of arguments is incorrect. In this case, an error
628 // will already have been emitted, and we can ignore it. This case
629 // also occurs when late-bound lifetime parameters are present, yet
630 // the lifetime arguments have also been explicitly specified by the
632 // 2. We've inferred some lifetimes, which have been provided later (i.e.
633 // after a type or const). We want to throw an error in this case.
635 if arg_count_correct {
636 let kind = arg.descr();
637 assert_eq!(kind, "lifetime");
639 force_infer_lt.expect("lifetimes ought to have been inferred");
640 Self::generic_arg_mismatch_err(tcx.sess, provided, kind);
646 (None, Some(¶m)) => {
647 // If there are fewer arguments than parameters, it means
648 // we're inferring the remaining arguments.
649 substs.push(inferred_kind(Some(&substs), param, infer_args));
653 (None, None) => break,
658 tcx.intern_substs(&substs)
661 /// Given the type/lifetime/const arguments provided to some path (along with
662 /// an implicit `Self`, if this is a trait reference), returns the complete
663 /// set of substitutions. This may involve applying defaulted type parameters.
664 /// Also returns back constriants on associated types.
669 /// T: std::ops::Index<usize, Output = u32>
670 /// ^1 ^^^^^^^^^^^^^^2 ^^^^3 ^^^^^^^^^^^4
673 /// 1. The `self_ty` here would refer to the type `T`.
674 /// 2. The path in question is the path to the trait `std::ops::Index`,
675 /// which will have been resolved to a `def_id`
676 /// 3. The `generic_args` contains info on the `<...>` contents. The `usize` type
677 /// parameters are returned in the `SubstsRef`, the associated type bindings like
678 /// `Output = u32` are returned in the `Vec<ConvertedBinding...>` result.
680 /// Note that the type listing given here is *exactly* what the user provided.
682 /// For (generic) associated types
685 /// <Vec<u8> as Iterable<u8>>::Iter::<'a>
688 /// We have the parent substs are the substs for the parent trait:
689 /// `[Vec<u8>, u8]` and `generic_args` are the arguments for the associated
690 /// type itself: `['a]`. The returned `SubstsRef` concatenates these two
691 /// lists: `[Vec<u8>, u8, 'a]`.
692 fn create_substs_for_ast_path<'a>(
696 parent_substs: &[subst::GenericArg<'tcx>],
697 generic_args: &'a hir::GenericArgs<'_>,
699 self_ty: Option<Ty<'tcx>>,
700 ) -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'a, 'tcx>>, Result<(), GenericArgCountMismatch>)
702 // If the type is parameterized by this region, then replace this
703 // region with the current anon region binding (in other words,
704 // whatever & would get replaced with).
706 "create_substs_for_ast_path(def_id={:?}, self_ty={:?}, \
708 def_id, self_ty, generic_args
711 let tcx = self.tcx();
712 let generic_params = tcx.generics_of(def_id);
714 if generic_params.has_self {
715 if generic_params.parent.is_some() {
716 // The parent is a trait so it should have at least one subst
717 // for the `Self` type.
718 assert!(!parent_substs.is_empty())
720 // This item (presumably a trait) needs a self-type.
721 assert!(self_ty.is_some());
724 assert!(self_ty.is_none() && parent_substs.is_empty());
727 let arg_count_correct = Self::check_generic_arg_count(
732 GenericArgPosition::Type,
737 let is_object = self_ty.map_or(false, |ty| ty == self.tcx().types.trait_object_dummy_self);
738 let default_needs_object_self = |param: &ty::GenericParamDef| {
739 if let GenericParamDefKind::Type { has_default, .. } = param.kind {
740 if is_object && has_default {
741 let self_param = tcx.types.self_param;
742 if tcx.at(span).type_of(param.def_id).walk().any(|ty| ty == self_param) {
743 // There is no suitable inference default for a type parameter
744 // that references self, in an object type.
753 let mut missing_type_params = vec![];
754 let substs = Self::create_substs_for_generic_args(
760 arg_count_correct.is_ok(),
761 // Provide the generic args, and whether types should be inferred.
764 (Some(generic_args), infer_args)
766 // The last component of this tuple is unimportant.
770 // Provide substitutions for parameters for which (valid) arguments have been provided.
771 |param, arg| match (¶m.kind, arg) {
772 (GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => {
773 self.ast_region_to_region(<, Some(param)).into()
775 (GenericParamDefKind::Type { .. }, GenericArg::Type(ty)) => {
776 self.ast_ty_to_ty(&ty).into()
778 (GenericParamDefKind::Const, GenericArg::Const(ct)) => {
779 self.ast_const_to_const(&ct.value, tcx.type_of(param.def_id)).into()
783 // Provide substitutions for parameters for which arguments are inferred.
784 |substs, param, infer_args| {
786 GenericParamDefKind::Lifetime => tcx.lifetimes.re_static.into(),
787 GenericParamDefKind::Type { has_default, .. } => {
788 if !infer_args && has_default {
789 // No type parameter provided, but a default exists.
791 // If we are converting an object type, then the
792 // `Self` parameter is unknown. However, some of the
793 // other type parameters may reference `Self` in their
794 // defaults. This will lead to an ICE if we are not
796 if default_needs_object_self(param) {
797 missing_type_params.push(param.name.to_string());
800 // This is a default type parameter.
803 tcx.at(span).type_of(param.def_id).subst_spanned(
811 } else if infer_args {
812 // No type parameters were provided, we can infer all.
814 if !default_needs_object_self(param) { Some(param) } else { None };
815 self.ty_infer(param, span).into()
817 // We've already errored above about the mismatch.
821 GenericParamDefKind::Const => {
822 // FIXME(const_generics:defaults)
824 // No const parameters were provided, we can infer all.
825 let ty = tcx.at(span).type_of(param.def_id);
826 self.ct_infer(ty, Some(param), span).into()
828 // We've already errored above about the mismatch.
829 tcx.consts.err.into()
836 self.complain_about_missing_type_params(
840 generic_args.args.is_empty(),
843 // Convert associated-type bindings or constraints into a separate vector.
844 // Example: Given this:
846 // T: Iterator<Item = u32>
848 // The `T` is passed in as a self-type; the `Item = u32` is
849 // not a "type parameter" of the `Iterator` trait, but rather
850 // a restriction on `<T as Iterator>::Item`, so it is passed
852 let assoc_bindings = generic_args
856 let kind = match binding.kind {
857 hir::TypeBindingKind::Equality { ref ty } => {
858 ConvertedBindingKind::Equality(self.ast_ty_to_ty(ty))
860 hir::TypeBindingKind::Constraint { ref bounds } => {
861 ConvertedBindingKind::Constraint(bounds)
864 ConvertedBinding { item_name: binding.ident, kind, span: binding.span }
869 "create_substs_for_ast_path(generic_params={:?}, self_ty={:?}) -> {:?}",
870 generic_params, self_ty, substs
873 (substs, assoc_bindings, arg_count_correct)
876 crate fn create_substs_for_associated_item(
881 item_segment: &hir::PathSegment<'_>,
882 parent_substs: SubstsRef<'tcx>,
883 ) -> SubstsRef<'tcx> {
884 if tcx.generics_of(item_def_id).params.is_empty() {
885 self.prohibit_generics(slice::from_ref(item_segment));
889 self.create_substs_for_ast_path(
893 item_segment.generic_args(),
894 item_segment.infer_args,
901 /// On missing type parameters, emit an E0393 error and provide a structured suggestion using
902 /// the type parameter's name as a placeholder.
903 fn complain_about_missing_type_params(
905 missing_type_params: Vec<String>,
908 empty_generic_args: bool,
910 if missing_type_params.is_empty() {
914 missing_type_params.iter().map(|n| format!("`{}`", n)).collect::<Vec<_>>().join(", ");
915 let mut err = struct_span_err!(
919 "the type parameter{} {} must be explicitly specified",
920 pluralize!(missing_type_params.len()),
924 self.tcx().def_span(def_id),
926 "type parameter{} {} must be specified for this",
927 pluralize!(missing_type_params.len()),
931 let mut suggested = false;
932 if let (Ok(snippet), true) = (
933 self.tcx().sess.source_map().span_to_snippet(span),
934 // Don't suggest setting the type params if there are some already: the order is
935 // tricky to get right and the user will already know what the syntax is.
938 if snippet.ends_with('>') {
939 // The user wrote `Trait<'a, T>` or similar. To provide an accurate suggestion
940 // we would have to preserve the right order. For now, as clearly the user is
941 // aware of the syntax, we do nothing.
943 // The user wrote `Iterator`, so we don't have a type we can suggest, but at
944 // least we can clue them to the correct syntax `Iterator<Type>`.
948 "set the type parameter{plural} to the desired type{plural}",
949 plural = pluralize!(missing_type_params.len()),
951 format!("{}<{}>", snippet, missing_type_params.join(", ")),
952 Applicability::HasPlaceholders,
961 "missing reference{} to {}",
962 pluralize!(missing_type_params.len()),
968 "because of the default `Self` reference, type parameters must be \
969 specified on object types"
974 /// Instantiates the path for the given trait reference, assuming that it's
975 /// bound to a valid trait type. Returns the `DefId` of the defining trait.
976 /// The type _cannot_ be a type other than a trait type.
978 /// If the `projections` argument is `None`, then assoc type bindings like `Foo<T = X>`
979 /// are disallowed. Otherwise, they are pushed onto the vector given.
980 pub fn instantiate_mono_trait_ref(
982 trait_ref: &hir::TraitRef<'_>,
984 ) -> ty::TraitRef<'tcx> {
985 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
987 self.ast_path_to_mono_trait_ref(
989 trait_ref.trait_def_id(),
991 trait_ref.path.segments.last().unwrap(),
995 /// The given trait-ref must actually be a trait.
996 pub(super) fn instantiate_poly_trait_ref_inner(
998 trait_ref: &hir::TraitRef<'_>,
1000 constness: Constness,
1002 bounds: &mut Bounds<'tcx>,
1004 ) -> Result<(), GenericArgCountMismatch> {
1005 let trait_def_id = trait_ref.trait_def_id();
1007 debug!("instantiate_poly_trait_ref({:?}, def_id={:?})", trait_ref, trait_def_id);
1009 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
1011 let path_span = if let [segment] = &trait_ref.path.segments[..] {
1012 // FIXME: `trait_ref.path.span` can point to a full path with multiple
1013 // segments, even though `trait_ref.path.segments` is of length `1`. Work
1014 // around that bug here, even though it should be fixed elsewhere.
1015 // This would otherwise cause an invalid suggestion. For an example, look at
1016 // `src/test/ui/issues/issue-28344.rs`.
1021 let (substs, assoc_bindings, arg_count_correct) = self.create_substs_for_ast_trait_ref(
1025 trait_ref.path.segments.last().unwrap(),
1027 let poly_trait_ref = ty::Binder::bind(ty::TraitRef::new(trait_def_id, substs));
1029 bounds.trait_bounds.push((poly_trait_ref, span, constness));
1031 let mut dup_bindings = FxHashMap::default();
1032 for binding in &assoc_bindings {
1033 // Specify type to assert that error was already reported in `Err` case.
1034 let _: Result<_, ErrorReported> = self.add_predicates_for_ast_type_binding(
1035 trait_ref.hir_ref_id,
1043 // Okay to ignore `Err` because of `ErrorReported` (see above).
1047 "instantiate_poly_trait_ref({:?}, bounds={:?}) -> {:?}",
1048 trait_ref, bounds, poly_trait_ref
1054 /// Given a trait bound like `Debug`, applies that trait bound the given self-type to construct
1055 /// a full trait reference. The resulting trait reference is returned. This may also generate
1056 /// auxiliary bounds, which are added to `bounds`.
1061 /// poly_trait_ref = Iterator<Item = u32>
1065 /// this would return `Foo: Iterator` and add `<Foo as Iterator>::Item = u32` into `bounds`.
1067 /// **A note on binders:** against our usual convention, there is an implied bounder around
1068 /// the `self_ty` and `poly_trait_ref` parameters here. So they may reference bound regions.
1069 /// If for example you had `for<'a> Foo<'a>: Bar<'a>`, then the `self_ty` would be `Foo<'a>`
1070 /// where `'a` is a bound region at depth 0. Similarly, the `poly_trait_ref` would be
1071 /// `Bar<'a>`. The returned poly-trait-ref will have this binder instantiated explicitly,
1073 pub fn instantiate_poly_trait_ref(
1075 poly_trait_ref: &hir::PolyTraitRef<'_>,
1076 constness: Constness,
1078 bounds: &mut Bounds<'tcx>,
1079 ) -> Result<(), GenericArgCountMismatch> {
1080 self.instantiate_poly_trait_ref_inner(
1081 &poly_trait_ref.trait_ref,
1082 poly_trait_ref.span,
1090 fn ast_path_to_mono_trait_ref(
1093 trait_def_id: DefId,
1095 trait_segment: &hir::PathSegment<'_>,
1096 ) -> ty::TraitRef<'tcx> {
1097 let (substs, assoc_bindings, _) =
1098 self.create_substs_for_ast_trait_ref(span, trait_def_id, self_ty, trait_segment);
1099 assoc_bindings.first().map(|b| AstConv::prohibit_assoc_ty_binding(self.tcx(), b.span));
1100 ty::TraitRef::new(trait_def_id, substs)
1103 /// When the code is using the `Fn` traits directly, instead of the `Fn(A) -> B` syntax, emit
1104 /// an error and attempt to build a reasonable structured suggestion.
1105 fn complain_about_internal_fn_trait(
1108 trait_def_id: DefId,
1109 trait_segment: &'a hir::PathSegment<'a>,
1111 let trait_def = self.tcx().trait_def(trait_def_id);
1113 if !self.tcx().features().unboxed_closures
1114 && trait_segment.generic_args().parenthesized != trait_def.paren_sugar
1116 // For now, require that parenthetical notation be used only with `Fn()` etc.
1117 let (msg, sugg) = if trait_def.paren_sugar {
1119 "the precise format of `Fn`-family traits' type parameters is subject to \
1123 trait_segment.ident,
1127 .and_then(|args| args.args.get(0))
1128 .and_then(|arg| match arg {
1129 hir::GenericArg::Type(ty) => {
1130 Some(print::to_string(print::NO_ANN, |s| s.print_type(ty)))
1134 .unwrap_or_else(|| "()".to_string()),
1139 .filter_map(|b| match (b.ident.as_str() == "Output", &b.kind) {
1140 (true, hir::TypeBindingKind::Equality { ty }) => {
1141 Some(print::to_string(print::NO_ANN, |s| s.print_type(ty)))
1146 .unwrap_or_else(|| "()".to_string()),
1150 ("parenthetical notation is only stable when used with `Fn`-family traits", None)
1152 let sess = &self.tcx().sess.parse_sess;
1153 let mut err = feature_err(sess, sym::unboxed_closures, span, msg);
1154 if let Some(sugg) = sugg {
1155 let msg = "use parenthetical notation instead";
1156 err.span_suggestion(span, msg, sugg, Applicability::MaybeIncorrect);
1162 fn create_substs_for_ast_trait_ref<'a>(
1165 trait_def_id: DefId,
1167 trait_segment: &'a hir::PathSegment<'a>,
1168 ) -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'a, 'tcx>>, Result<(), GenericArgCountMismatch>)
1170 debug!("create_substs_for_ast_trait_ref(trait_segment={:?})", trait_segment);
1172 self.complain_about_internal_fn_trait(span, trait_def_id, trait_segment);
1174 self.create_substs_for_ast_path(
1178 trait_segment.generic_args(),
1179 trait_segment.infer_args,
1184 fn trait_defines_associated_type_named(
1186 trait_def_id: DefId,
1187 assoc_name: ast::Ident,
1190 .associated_items(trait_def_id)
1191 .find_by_name_and_kind(self.tcx(), assoc_name, ty::AssocKind::Type, trait_def_id)
1195 // Returns `true` if a bounds list includes `?Sized`.
1196 pub fn is_unsized(&self, ast_bounds: &[hir::GenericBound<'_>], span: Span) -> bool {
1197 let tcx = self.tcx();
1199 // Try to find an unbound in bounds.
1200 let mut unbound = None;
1201 for ab in ast_bounds {
1202 if let &hir::GenericBound::Trait(ref ptr, hir::TraitBoundModifier::Maybe) = ab {
1203 if unbound.is_none() {
1204 unbound = Some(&ptr.trait_ref);
1210 "type parameter has more than one relaxed default \
1211 bound, only one is supported"
1218 let kind_id = tcx.lang_items().require(SizedTraitLangItem);
1221 // FIXME(#8559) currently requires the unbound to be built-in.
1222 if let Ok(kind_id) = kind_id {
1223 if tpb.path.res != Res::Def(DefKind::Trait, kind_id) {
1226 "default bound relaxed for a type parameter, but \
1227 this does nothing because the given bound is not \
1228 a default; only `?Sized` is supported",
1233 _ if kind_id.is_ok() => {
1236 // No lang item for `Sized`, so we can't add it as a bound.
1243 /// This helper takes a *converted* parameter type (`param_ty`)
1244 /// and an *unconverted* list of bounds:
1247 /// fn foo<T: Debug>
1248 /// ^ ^^^^^ `ast_bounds` parameter, in HIR form
1250 /// `param_ty`, in ty form
1253 /// It adds these `ast_bounds` into the `bounds` structure.
1255 /// **A note on binders:** there is an implied binder around
1256 /// `param_ty` and `ast_bounds`. See `instantiate_poly_trait_ref`
1257 /// for more details.
1261 ast_bounds: &[hir::GenericBound<'_>],
1262 bounds: &mut Bounds<'tcx>,
1264 let mut trait_bounds = Vec::new();
1265 let mut region_bounds = Vec::new();
1267 let constness = self.default_constness_for_trait_bounds();
1268 for ast_bound in ast_bounds {
1270 hir::GenericBound::Trait(ref b, hir::TraitBoundModifier::None) => {
1271 trait_bounds.push((b, constness))
1273 hir::GenericBound::Trait(ref b, hir::TraitBoundModifier::MaybeConst) => {
1274 trait_bounds.push((b, Constness::NotConst))
1276 hir::GenericBound::Trait(_, hir::TraitBoundModifier::Maybe) => {}
1277 hir::GenericBound::Outlives(ref l) => region_bounds.push(l),
1281 for (bound, constness) in trait_bounds {
1282 let _ = self.instantiate_poly_trait_ref(bound, constness, param_ty, bounds);
1285 bounds.region_bounds.extend(
1286 region_bounds.into_iter().map(|r| (self.ast_region_to_region(r, None), r.span)),
1290 /// Translates a list of bounds from the HIR into the `Bounds` data structure.
1291 /// The self-type for the bounds is given by `param_ty`.
1296 /// fn foo<T: Bar + Baz>() { }
1297 /// ^ ^^^^^^^^^ ast_bounds
1301 /// The `sized_by_default` parameter indicates if, in this context, the `param_ty` should be
1302 /// considered `Sized` unless there is an explicit `?Sized` bound. This would be true in the
1303 /// example above, but is not true in supertrait listings like `trait Foo: Bar + Baz`.
1305 /// `span` should be the declaration size of the parameter.
1306 pub fn compute_bounds(
1309 ast_bounds: &[hir::GenericBound<'_>],
1310 sized_by_default: SizedByDefault,
1313 let mut bounds = Bounds::default();
1315 self.add_bounds(param_ty, ast_bounds, &mut bounds);
1316 bounds.trait_bounds.sort_by_key(|(t, _, _)| t.def_id());
1318 bounds.implicitly_sized = if let SizedByDefault::Yes = sized_by_default {
1319 if !self.is_unsized(ast_bounds, span) { Some(span) } else { None }
1327 /// Given an HIR binding like `Item = Foo` or `Item: Foo`, pushes the corresponding predicates
1330 /// **A note on binders:** given something like `T: for<'a> Iterator<Item = &'a u32>`, the
1331 /// `trait_ref` here will be `for<'a> T: Iterator`. The `binding` data however is from *inside*
1332 /// the binder (e.g., `&'a u32`) and hence may reference bound regions.
1333 fn add_predicates_for_ast_type_binding(
1335 hir_ref_id: hir::HirId,
1336 trait_ref: ty::PolyTraitRef<'tcx>,
1337 binding: &ConvertedBinding<'_, 'tcx>,
1338 bounds: &mut Bounds<'tcx>,
1340 dup_bindings: &mut FxHashMap<DefId, Span>,
1342 ) -> Result<(), ErrorReported> {
1343 let tcx = self.tcx();
1346 // Given something like `U: SomeTrait<T = X>`, we want to produce a
1347 // predicate like `<U as SomeTrait>::T = X`. This is somewhat
1348 // subtle in the event that `T` is defined in a supertrait of
1349 // `SomeTrait`, because in that case we need to upcast.
1351 // That is, consider this case:
1354 // trait SubTrait: SuperTrait<int> { }
1355 // trait SuperTrait<A> { type T; }
1357 // ... B: SubTrait<T = foo> ...
1360 // We want to produce `<B as SuperTrait<int>>::T == foo`.
1362 // Find any late-bound regions declared in `ty` that are not
1363 // declared in the trait-ref. These are not well-formed.
1367 // for<'a> <T as Iterator>::Item = &'a str // <-- 'a is bad
1368 // for<'a> <T as FnMut<(&'a u32,)>>::Output = &'a str // <-- 'a is ok
1369 if let ConvertedBindingKind::Equality(ty) = binding.kind {
1370 let late_bound_in_trait_ref =
1371 tcx.collect_constrained_late_bound_regions(&trait_ref);
1372 let late_bound_in_ty =
1373 tcx.collect_referenced_late_bound_regions(&ty::Binder::bind(ty));
1374 debug!("late_bound_in_trait_ref = {:?}", late_bound_in_trait_ref);
1375 debug!("late_bound_in_ty = {:?}", late_bound_in_ty);
1376 for br in late_bound_in_ty.difference(&late_bound_in_trait_ref) {
1377 let br_name = match *br {
1378 ty::BrNamed(_, name) => name,
1382 "anonymous bound region {:?} in binding but not trait ref",
1387 // FIXME: point at the type params that don't have appropriate lifetimes:
1388 // struct S1<F: for<'a> Fn(&i32, &i32) -> &'a i32>(F);
1389 // ---- ---- ^^^^^^^
1394 "binding for associated type `{}` references lifetime `{}`, \
1395 which does not appear in the trait input types",
1405 if self.trait_defines_associated_type_named(trait_ref.def_id(), binding.item_name) {
1406 // Simple case: X is defined in the current trait.
1409 // Otherwise, we have to walk through the supertraits to find
1411 self.one_bound_for_assoc_type(
1412 || traits::supertraits(tcx, trait_ref),
1413 || trait_ref.print_only_trait_path().to_string(),
1416 || match binding.kind {
1417 ConvertedBindingKind::Equality(ty) => Some(ty.to_string()),
1423 let (assoc_ident, def_scope) =
1424 tcx.adjust_ident_and_get_scope(binding.item_name, candidate.def_id(), hir_ref_id);
1426 // We have already adjusted the item name above, so compare with `ident.modern()` instead
1427 // of calling `filter_by_name_and_kind`.
1429 .associated_items(candidate.def_id())
1430 .filter_by_name_unhygienic(assoc_ident.name)
1431 .find(|i| i.kind == ty::AssocKind::Type && i.ident.modern() == assoc_ident)
1432 .expect("missing associated type");
1434 if !assoc_ty.vis.is_accessible_from(def_scope, tcx) {
1435 let msg = format!("associated type `{}` is private", binding.item_name);
1436 tcx.sess.span_err(binding.span, &msg);
1438 tcx.check_stability(assoc_ty.def_id, Some(hir_ref_id), binding.span);
1442 .entry(assoc_ty.def_id)
1443 .and_modify(|prev_span| {
1448 "the value of the associated type `{}` (from trait `{}`) \
1449 is already specified",
1451 tcx.def_path_str(assoc_ty.container.id())
1453 .span_label(binding.span, "re-bound here")
1454 .span_label(*prev_span, format!("`{}` bound here first", binding.item_name))
1457 .or_insert(binding.span);
1460 match binding.kind {
1461 ConvertedBindingKind::Equality(ref ty) => {
1462 // "Desugar" a constraint like `T: Iterator<Item = u32>` this to
1463 // the "projection predicate" for:
1465 // `<T as Iterator>::Item = u32`
1466 bounds.projection_bounds.push((
1467 candidate.map_bound(|trait_ref| ty::ProjectionPredicate {
1468 projection_ty: ty::ProjectionTy::from_ref_and_name(
1478 ConvertedBindingKind::Constraint(ast_bounds) => {
1479 // "Desugar" a constraint like `T: Iterator<Item: Debug>` to
1481 // `<T as Iterator>::Item: Debug`
1483 // Calling `skip_binder` is okay, because `add_bounds` expects the `param_ty`
1484 // parameter to have a skipped binder.
1485 let param_ty = tcx.mk_projection(assoc_ty.def_id, candidate.skip_binder().substs);
1486 self.add_bounds(param_ty, ast_bounds, bounds);
1496 item_segment: &hir::PathSegment<'_>,
1498 let substs = self.ast_path_substs_for_ty(span, did, item_segment);
1499 self.normalize_ty(span, self.tcx().at(span).type_of(did).subst(self.tcx(), substs))
1502 fn conv_object_ty_poly_trait_ref(
1505 trait_bounds: &[hir::PolyTraitRef<'_>],
1506 lifetime: &hir::Lifetime,
1508 let tcx = self.tcx();
1510 let mut bounds = Bounds::default();
1511 let mut potential_assoc_types = Vec::new();
1512 let dummy_self = self.tcx().types.trait_object_dummy_self;
1513 for trait_bound in trait_bounds.iter().rev() {
1514 if let Err(GenericArgCountMismatch {
1515 invalid_args: cur_potential_assoc_types, ..
1516 }) = self.instantiate_poly_trait_ref(
1518 Constness::NotConst,
1522 potential_assoc_types.extend(cur_potential_assoc_types.into_iter());
1526 // Expand trait aliases recursively and check that only one regular (non-auto) trait
1527 // is used and no 'maybe' bounds are used.
1528 let expanded_traits =
1529 traits::expand_trait_aliases(tcx, bounds.trait_bounds.iter().map(|&(a, b, _)| (a, b)));
1530 let (mut auto_traits, regular_traits): (Vec<_>, Vec<_>) =
1531 expanded_traits.partition(|i| tcx.trait_is_auto(i.trait_ref().def_id()));
1532 if regular_traits.len() > 1 {
1533 let first_trait = ®ular_traits[0];
1534 let additional_trait = ®ular_traits[1];
1535 let mut err = struct_span_err!(
1537 additional_trait.bottom().1,
1539 "only auto traits can be used as additional traits in a trait object"
1541 additional_trait.label_with_exp_info(
1543 "additional non-auto trait",
1546 first_trait.label_with_exp_info(&mut err, "first non-auto trait", "first use");
1550 if regular_traits.is_empty() && auto_traits.is_empty() {
1555 "at least one trait is required for an object type"
1558 return tcx.types.err;
1561 // Check that there are no gross object safety violations;
1562 // most importantly, that the supertraits don't contain `Self`,
1564 for item in ®ular_traits {
1565 let object_safety_violations =
1566 astconv_object_safety_violations(tcx, item.trait_ref().def_id());
1567 if !object_safety_violations.is_empty() {
1568 report_object_safety_error(
1571 item.trait_ref().def_id(),
1572 object_safety_violations,
1575 return tcx.types.err;
1579 // Use a `BTreeSet` to keep output in a more consistent order.
1580 let mut associated_types: FxHashMap<Span, BTreeSet<DefId>> = FxHashMap::default();
1582 let regular_traits_refs_spans = bounds
1585 .filter(|(trait_ref, _, _)| !tcx.trait_is_auto(trait_ref.def_id()));
1587 for (base_trait_ref, span, constness) in regular_traits_refs_spans {
1588 assert_eq!(constness, Constness::NotConst);
1590 for trait_ref in traits::elaborate_trait_ref(tcx, base_trait_ref) {
1592 "conv_object_ty_poly_trait_ref: observing object predicate `{:?}`",
1596 ty::Predicate::Trait(pred, _) => {
1597 associated_types.entry(span).or_default().extend(
1598 tcx.associated_items(pred.def_id())
1599 .in_definition_order()
1600 .filter(|item| item.kind == ty::AssocKind::Type)
1601 .map(|item| item.def_id),
1604 ty::Predicate::Projection(pred) => {
1605 // A `Self` within the original bound will be substituted with a
1606 // `trait_object_dummy_self`, so check for that.
1607 let references_self = pred.skip_binder().ty.walk().any(|t| t == dummy_self);
1609 // If the projection output contains `Self`, force the user to
1610 // elaborate it explicitly to avoid a lot of complexity.
1612 // The "classicaly useful" case is the following:
1614 // trait MyTrait: FnMut() -> <Self as MyTrait>::MyOutput {
1619 // Here, the user could theoretically write `dyn MyTrait<Output = X>`,
1620 // but actually supporting that would "expand" to an infinitely-long type
1621 // `fix $ τ → dyn MyTrait<MyOutput = X, Output = <τ as MyTrait>::MyOutput`.
1623 // Instead, we force the user to write
1624 // `dyn MyTrait<MyOutput = X, Output = X>`, which is uglier but works. See
1625 // the discussion in #56288 for alternatives.
1626 if !references_self {
1627 // Include projections defined on supertraits.
1628 bounds.projection_bounds.push((pred, span));
1636 for (projection_bound, _) in &bounds.projection_bounds {
1637 for (_, def_ids) in &mut associated_types {
1638 def_ids.remove(&projection_bound.projection_def_id());
1642 self.complain_about_missing_associated_types(
1644 potential_assoc_types,
1648 // De-duplicate auto traits so that, e.g., `dyn Trait + Send + Send` is the same as
1649 // `dyn Trait + Send`.
1650 auto_traits.sort_by_key(|i| i.trait_ref().def_id());
1651 auto_traits.dedup_by_key(|i| i.trait_ref().def_id());
1652 debug!("regular_traits: {:?}", regular_traits);
1653 debug!("auto_traits: {:?}", auto_traits);
1655 // Transform a `PolyTraitRef` into a `PolyExistentialTraitRef` by
1656 // removing the dummy `Self` type (`trait_object_dummy_self`).
1657 let trait_ref_to_existential = |trait_ref: ty::TraitRef<'tcx>| {
1658 if trait_ref.self_ty() != dummy_self {
1659 // FIXME: There appears to be a missing filter on top of `expand_trait_aliases`,
1660 // which picks up non-supertraits where clauses - but also, the object safety
1661 // completely ignores trait aliases, which could be object safety hazards. We
1662 // `delay_span_bug` here to avoid an ICE in stable even when the feature is
1663 // disabled. (#66420)
1664 tcx.sess.delay_span_bug(
1667 "trait_ref_to_existential called on {:?} with non-dummy Self",
1672 ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref)
1675 // Erase the `dummy_self` (`trait_object_dummy_self`) used above.
1676 let existential_trait_refs = regular_traits
1678 .map(|i| i.trait_ref().map_bound(|trait_ref| trait_ref_to_existential(trait_ref)));
1679 let existential_projections = bounds.projection_bounds.iter().map(|(bound, _)| {
1680 bound.map_bound(|b| {
1681 let trait_ref = trait_ref_to_existential(b.projection_ty.trait_ref(tcx));
1682 ty::ExistentialProjection {
1684 item_def_id: b.projection_ty.item_def_id,
1685 substs: trait_ref.substs,
1690 // Calling `skip_binder` is okay because the predicates are re-bound.
1691 let regular_trait_predicates = existential_trait_refs
1692 .map(|trait_ref| ty::ExistentialPredicate::Trait(*trait_ref.skip_binder()));
1693 let auto_trait_predicates = auto_traits
1695 .map(|trait_ref| ty::ExistentialPredicate::AutoTrait(trait_ref.trait_ref().def_id()));
1696 let mut v = regular_trait_predicates
1697 .chain(auto_trait_predicates)
1699 existential_projections
1700 .map(|x| ty::ExistentialPredicate::Projection(*x.skip_binder())),
1702 .collect::<SmallVec<[_; 8]>>();
1703 v.sort_by(|a, b| a.stable_cmp(tcx, b));
1705 let existential_predicates = ty::Binder::bind(tcx.mk_existential_predicates(v.into_iter()));
1707 // Use explicitly-specified region bound.
1708 let region_bound = if !lifetime.is_elided() {
1709 self.ast_region_to_region(lifetime, None)
1711 self.compute_object_lifetime_bound(span, existential_predicates).unwrap_or_else(|| {
1712 if tcx.named_region(lifetime.hir_id).is_some() {
1713 self.ast_region_to_region(lifetime, None)
1715 self.re_infer(None, span).unwrap_or_else(|| {
1720 "the lifetime bound for this object type cannot be deduced \
1721 from context; please supply an explicit bound"
1724 tcx.lifetimes.re_static
1729 debug!("region_bound: {:?}", region_bound);
1731 let ty = tcx.mk_dynamic(existential_predicates, region_bound);
1732 debug!("trait_object_type: {:?}", ty);
1736 /// When there are any missing associated types, emit an E0191 error and attempt to supply a
1737 /// reasonable suggestion on how to write it. For the case of multiple associated types in the
1738 /// same trait bound have the same name (as they come from different super-traits), we instead
1739 /// emit a generic note suggesting using a `where` clause to constraint instead.
1740 fn complain_about_missing_associated_types(
1742 associated_types: FxHashMap<Span, BTreeSet<DefId>>,
1743 potential_assoc_types: Vec<Span>,
1744 trait_bounds: &[hir::PolyTraitRef<'_>],
1746 if !associated_types.values().any(|v| v.len() > 0) {
1749 let tcx = self.tcx();
1750 // FIXME: Marked `mut` so that we can replace the spans further below with a more
1751 // appropriate one, but this should be handled earlier in the span assignment.
1752 let mut associated_types: FxHashMap<Span, Vec<_>> = associated_types
1754 .map(|(span, def_ids)| {
1755 (span, def_ids.into_iter().map(|did| tcx.associated_item(did)).collect())
1758 let mut names = vec![];
1760 // Account for things like `dyn Foo + 'a`, like in tests `issue-22434.rs` and
1761 // `issue-22560.rs`.
1762 let mut trait_bound_spans: Vec<Span> = vec![];
1763 for (span, items) in &associated_types {
1764 if !items.is_empty() {
1765 trait_bound_spans.push(*span);
1767 for assoc_item in items {
1768 let trait_def_id = assoc_item.container.id();
1770 "`{}` (from trait `{}`)",
1772 tcx.def_path_str(trait_def_id),
1777 match (&potential_assoc_types[..], &trait_bounds) {
1778 ([], [bound]) => match &bound.trait_ref.path.segments[..] {
1779 // FIXME: `trait_ref.path.span` can point to a full path with multiple
1780 // segments, even though `trait_ref.path.segments` is of length `1`. Work
1781 // around that bug here, even though it should be fixed elsewhere.
1782 // This would otherwise cause an invalid suggestion. For an example, look at
1783 // `src/test/ui/issues/issue-28344.rs` where instead of the following:
1785 // error[E0191]: the value of the associated type `Output`
1786 // (from trait `std::ops::BitXor`) must be specified
1787 // --> $DIR/issue-28344.rs:4:17
1789 // LL | let x: u8 = BitXor::bitor(0 as u8, 0 as u8);
1790 // | ^^^^^^ help: specify the associated type:
1791 // | `BitXor<Output = Type>`
1795 // error[E0191]: the value of the associated type `Output`
1796 // (from trait `std::ops::BitXor`) must be specified
1797 // --> $DIR/issue-28344.rs:4:17
1799 // LL | let x: u8 = BitXor::bitor(0 as u8, 0 as u8);
1800 // | ^^^^^^^^^^^^^ help: specify the associated type:
1801 // | `BitXor::bitor<Output = Type>`
1802 [segment] if segment.args.is_none() => {
1803 trait_bound_spans = vec![segment.ident.span];
1804 associated_types = associated_types
1806 .map(|(_, items)| (segment.ident.span, items))
1814 trait_bound_spans.sort();
1815 let mut err = struct_span_err!(
1819 "the value of the associated type{} {} must be specified",
1820 pluralize!(names.len()),
1823 let mut suggestions = vec![];
1824 let mut types_count = 0;
1825 let mut where_constraints = vec![];
1826 for (span, assoc_items) in &associated_types {
1827 let mut names: FxHashMap<_, usize> = FxHashMap::default();
1828 for item in assoc_items {
1830 *names.entry(item.ident.name).or_insert(0) += 1;
1832 let mut dupes = false;
1833 for item in assoc_items {
1834 let prefix = if names[&item.ident.name] > 1 {
1835 let trait_def_id = item.container.id();
1837 format!("{}::", tcx.def_path_str(trait_def_id))
1841 if let Some(sp) = tcx.hir().span_if_local(item.def_id) {
1842 err.span_label(sp, format!("`{}{}` defined here", prefix, item.ident));
1845 if potential_assoc_types.len() == assoc_items.len() {
1846 // Only suggest when the amount of missing associated types equals the number of
1847 // extra type arguments present, as that gives us a relatively high confidence
1848 // that the user forgot to give the associtated type's name. The canonical
1849 // example would be trying to use `Iterator<isize>` instead of
1850 // `Iterator<Item = isize>`.
1851 for (potential, item) in potential_assoc_types.iter().zip(assoc_items.iter()) {
1852 if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(*potential) {
1853 suggestions.push((*potential, format!("{} = {}", item.ident, snippet)));
1856 } else if let (Ok(snippet), false) =
1857 (tcx.sess.source_map().span_to_snippet(*span), dupes)
1860 assoc_items.iter().map(|item| format!("{} = Type", item.ident)).collect();
1861 let code = if snippet.ends_with(">") {
1862 // The user wrote `Trait<'a>` or similar and we don't have a type we can
1863 // suggest, but at least we can clue them to the correct syntax
1864 // `Trait<'a, Item = Type>` while accounting for the `<'a>` in the
1866 format!("{}, {}>", &snippet[..snippet.len() - 1], types.join(", "))
1868 // The user wrote `Iterator`, so we don't have a type we can suggest, but at
1869 // least we can clue them to the correct syntax `Iterator<Item = Type>`.
1870 format!("{}<{}>", snippet, types.join(", "))
1872 suggestions.push((*span, code));
1874 where_constraints.push(*span);
1877 let where_msg = "consider introducing a new type parameter, adding `where` constraints \
1878 using the fully-qualified path to the associated types";
1879 if !where_constraints.is_empty() && suggestions.is_empty() {
1880 // If there are duplicates associated type names and a single trait bound do not
1881 // use structured suggestion, it means that there are multiple super-traits with
1882 // the same associated type name.
1883 err.help(where_msg);
1885 if suggestions.len() != 1 {
1886 // We don't need this label if there's an inline suggestion, show otherwise.
1887 for (span, assoc_items) in &associated_types {
1888 let mut names: FxHashMap<_, usize> = FxHashMap::default();
1889 for item in assoc_items {
1891 *names.entry(item.ident.name).or_insert(0) += 1;
1893 let mut label = vec![];
1894 for item in assoc_items {
1895 let postfix = if names[&item.ident.name] > 1 {
1896 let trait_def_id = item.container.id();
1897 format!(" (from trait `{}`)", tcx.def_path_str(trait_def_id))
1901 label.push(format!("`{}`{}", item.ident, postfix));
1903 if !label.is_empty() {
1907 "associated type{} {} must be specified",
1908 pluralize!(label.len()),
1915 if !suggestions.is_empty() {
1916 err.multipart_suggestion(
1917 &format!("specify the associated type{}", pluralize!(types_count)),
1919 Applicability::HasPlaceholders,
1921 if !where_constraints.is_empty() {
1922 err.span_help(where_constraints, where_msg);
1928 fn report_ambiguous_associated_type(
1935 let mut err = struct_span_err!(self.tcx().sess, span, E0223, "ambiguous associated type");
1936 if let (Some(_), Ok(snippet)) = (
1937 self.tcx().sess.confused_type_with_std_module.borrow().get(&span),
1938 self.tcx().sess.source_map().span_to_snippet(span),
1940 err.span_suggestion(
1942 "you are looking for the module in `std`, not the primitive type",
1943 format!("std::{}", snippet),
1944 Applicability::MachineApplicable,
1947 err.span_suggestion(
1949 "use fully-qualified syntax",
1950 format!("<{} as {}>::{}", type_str, trait_str, name),
1951 Applicability::HasPlaceholders,
1957 // Search for a bound on a type parameter which includes the associated item
1958 // given by `assoc_name`. `ty_param_def_id` is the `DefId` of the type parameter
1959 // This function will fail if there are no suitable bounds or there is
1961 fn find_bound_for_assoc_item(
1963 ty_param_def_id: DefId,
1964 assoc_name: ast::Ident,
1966 ) -> Result<ty::PolyTraitRef<'tcx>, ErrorReported> {
1967 let tcx = self.tcx();
1970 "find_bound_for_assoc_item(ty_param_def_id={:?}, assoc_name={:?}, span={:?})",
1971 ty_param_def_id, assoc_name, span,
1974 let predicates = &self.get_type_parameter_bounds(span, ty_param_def_id).predicates;
1976 debug!("find_bound_for_assoc_item: predicates={:#?}", predicates);
1978 let param_hir_id = tcx.hir().as_local_hir_id(ty_param_def_id).unwrap();
1979 let param_name = tcx.hir().ty_param_name(param_hir_id);
1980 self.one_bound_for_assoc_type(
1982 traits::transitive_bounds(
1984 predicates.iter().filter_map(|(p, _)| p.to_opt_poly_trait_ref()),
1987 || param_name.to_string(),
1994 // Checks that `bounds` contains exactly one element and reports appropriate
1995 // errors otherwise.
1996 fn one_bound_for_assoc_type<I>(
1998 all_candidates: impl Fn() -> I,
1999 ty_param_name: impl Fn() -> String,
2000 assoc_name: ast::Ident,
2002 is_equality: impl Fn() -> Option<String>,
2003 ) -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
2005 I: Iterator<Item = ty::PolyTraitRef<'tcx>>,
2007 let mut matching_candidates = all_candidates()
2008 .filter(|r| self.trait_defines_associated_type_named(r.def_id(), assoc_name));
2010 let bound = match matching_candidates.next() {
2011 Some(bound) => bound,
2013 self.complain_about_assoc_type_not_found(
2019 return Err(ErrorReported);
2023 debug!("one_bound_for_assoc_type: bound = {:?}", bound);
2025 if let Some(bound2) = matching_candidates.next() {
2026 debug!("one_bound_for_assoc_type: bound2 = {:?}", bound2);
2028 let is_equality = is_equality();
2029 let bounds = iter::once(bound).chain(iter::once(bound2)).chain(matching_candidates);
2030 let mut err = if is_equality.is_some() {
2031 // More specific Error Index entry.
2036 "ambiguous associated type `{}` in bounds of `{}`",
2045 "ambiguous associated type `{}` in bounds of `{}`",
2050 err.span_label(span, format!("ambiguous associated type `{}`", assoc_name));
2052 let mut where_bounds = vec![];
2053 for bound in bounds {
2054 let bound_id = bound.def_id();
2055 let bound_span = self
2057 .associated_items(bound_id)
2058 .find_by_name_and_kind(self.tcx(), assoc_name, ty::AssocKind::Type, bound_id)
2059 .and_then(|item| self.tcx().hir().span_if_local(item.def_id));
2061 if let Some(bound_span) = bound_span {
2065 "ambiguous `{}` from `{}`",
2067 bound.print_only_trait_path(),
2070 if let Some(constraint) = &is_equality {
2071 where_bounds.push(format!(
2072 " T: {trait}::{assoc} = {constraint}",
2073 trait=bound.print_only_trait_path(),
2075 constraint=constraint,
2078 err.span_suggestion(
2080 "use fully qualified syntax to disambiguate",
2084 bound.print_only_trait_path(),
2087 Applicability::MaybeIncorrect,
2092 "associated type `{}` could derive from `{}`",
2094 bound.print_only_trait_path(),
2098 if !where_bounds.is_empty() {
2100 "consider introducing a new type parameter `T` and adding `where` constraints:\
2101 \n where\n T: {},\n{}",
2103 where_bounds.join(",\n"),
2107 if !where_bounds.is_empty() {
2108 return Err(ErrorReported);
2114 fn complain_about_assoc_type_not_found<I>(
2116 all_candidates: impl Fn() -> I,
2117 ty_param_name: &str,
2118 assoc_name: ast::Ident,
2121 I: Iterator<Item = ty::PolyTraitRef<'tcx>>,
2123 // The fallback span is needed because `assoc_name` might be an `Fn()`'s `Output` without a
2124 // valid span, so we point at the whole path segment instead.
2125 let span = if assoc_name.span != DUMMY_SP { assoc_name.span } else { span };
2126 let mut err = struct_span_err!(
2130 "associated type `{}` not found for `{}`",
2135 let all_candidate_names: Vec<_> = all_candidates()
2136 .map(|r| self.tcx().associated_items(r.def_id()).in_definition_order())
2139 |item| if item.kind == ty::AssocKind::Type { Some(item.ident.name) } else { None },
2143 if let (Some(suggested_name), true) = (
2144 find_best_match_for_name(all_candidate_names.iter(), &assoc_name.as_str(), None),
2145 assoc_name.span != DUMMY_SP,
2147 err.span_suggestion(
2149 "there is an associated type with a similar name",
2150 suggested_name.to_string(),
2151 Applicability::MaybeIncorrect,
2154 err.span_label(span, format!("associated type `{}` not found", assoc_name));
2160 // Create a type from a path to an associated type.
2161 // For a path `A::B::C::D`, `qself_ty` and `qself_def` are the type and def for `A::B::C`
2162 // and item_segment is the path segment for `D`. We return a type and a def for
2164 // Will fail except for `T::A` and `Self::A`; i.e., if `qself_ty`/`qself_def` are not a type
2165 // parameter or `Self`.
2166 pub fn associated_path_to_ty(
2168 hir_ref_id: hir::HirId,
2172 assoc_segment: &hir::PathSegment<'_>,
2173 permit_variants: bool,
2174 ) -> Result<(Ty<'tcx>, DefKind, DefId), ErrorReported> {
2175 let tcx = self.tcx();
2176 let assoc_ident = assoc_segment.ident;
2178 debug!("associated_path_to_ty: {:?}::{}", qself_ty, assoc_ident);
2180 // Check if we have an enum variant.
2181 let mut variant_resolution = None;
2182 if let ty::Adt(adt_def, _) = qself_ty.kind {
2183 if adt_def.is_enum() {
2184 let variant_def = adt_def
2187 .find(|vd| tcx.hygienic_eq(assoc_ident, vd.ident, adt_def.did));
2188 if let Some(variant_def) = variant_def {
2189 if permit_variants {
2190 tcx.check_stability(variant_def.def_id, Some(hir_ref_id), span);
2191 self.prohibit_generics(slice::from_ref(assoc_segment));
2192 return Ok((qself_ty, DefKind::Variant, variant_def.def_id));
2194 variant_resolution = Some(variant_def.def_id);
2200 // Find the type of the associated item, and the trait where the associated
2201 // item is declared.
2202 let bound = match (&qself_ty.kind, qself_res) {
2203 (_, Res::SelfTy(Some(_), Some(impl_def_id))) => {
2204 // `Self` in an impl of a trait -- we have a concrete self type and a
2206 let trait_ref = match tcx.impl_trait_ref(impl_def_id) {
2207 Some(trait_ref) => trait_ref,
2209 // A cycle error occurred, most likely.
2210 return Err(ErrorReported);
2214 self.one_bound_for_assoc_type(
2215 || traits::supertraits(tcx, ty::Binder::bind(trait_ref)),
2216 || "Self".to_string(),
2222 (&ty::Param(_), Res::SelfTy(Some(param_did), None))
2223 | (&ty::Param(_), Res::Def(DefKind::TyParam, param_did)) => {
2224 self.find_bound_for_assoc_item(param_did, assoc_ident, span)?
2227 if variant_resolution.is_some() {
2228 // Variant in type position
2229 let msg = format!("expected type, found variant `{}`", assoc_ident);
2230 tcx.sess.span_err(span, &msg);
2231 } else if qself_ty.is_enum() {
2232 let mut err = struct_span_err!(
2236 "no variant named `{}` found for enum `{}`",
2241 let adt_def = qself_ty.ty_adt_def().expect("enum is not an ADT");
2242 if let Some(suggested_name) = find_best_match_for_name(
2243 adt_def.variants.iter().map(|variant| &variant.ident.name),
2244 &assoc_ident.as_str(),
2247 err.span_suggestion(
2249 "there is a variant with a similar name",
2250 suggested_name.to_string(),
2251 Applicability::MaybeIncorrect,
2256 format!("variant not found in `{}`", qself_ty),
2260 if let Some(sp) = tcx.hir().span_if_local(adt_def.did) {
2261 let sp = tcx.sess.source_map().def_span(sp);
2262 err.span_label(sp, format!("variant `{}` not found here", assoc_ident));
2266 } else if !qself_ty.references_error() {
2267 // Don't print `TyErr` to the user.
2268 self.report_ambiguous_associated_type(
2270 &qself_ty.to_string(),
2275 return Err(ErrorReported);
2279 let trait_did = bound.def_id();
2280 let (assoc_ident, def_scope) =
2281 tcx.adjust_ident_and_get_scope(assoc_ident, trait_did, hir_ref_id);
2283 // We have already adjusted the item name above, so compare with `ident.modern()` instead
2284 // of calling `filter_by_name_and_kind`.
2286 .associated_items(trait_did)
2287 .in_definition_order()
2288 .find(|i| i.kind.namespace() == Namespace::TypeNS && i.ident.modern() == assoc_ident)
2289 .expect("missing associated type");
2291 let ty = self.projected_ty_from_poly_trait_ref(span, item.def_id, assoc_segment, bound);
2292 let ty = self.normalize_ty(span, ty);
2294 let kind = DefKind::AssocTy;
2295 if !item.vis.is_accessible_from(def_scope, tcx) {
2296 let msg = format!("{} `{}` is private", kind.descr(item.def_id), assoc_ident);
2297 tcx.sess.span_err(span, &msg);
2299 tcx.check_stability(item.def_id, Some(hir_ref_id), span);
2301 if let Some(variant_def_id) = variant_resolution {
2302 tcx.struct_span_lint_hir(AMBIGUOUS_ASSOCIATED_ITEMS, hir_ref_id, span, |lint| {
2303 let mut err = lint.build("ambiguous associated item");
2304 let mut could_refer_to = |kind: DefKind, def_id, also| {
2305 let note_msg = format!(
2306 "`{}` could{} refer to the {} defined here",
2311 err.span_note(tcx.def_span(def_id), ¬e_msg);
2314 could_refer_to(DefKind::Variant, variant_def_id, "");
2315 could_refer_to(kind, item.def_id, " also");
2317 err.span_suggestion(
2319 "use fully-qualified syntax",
2320 format!("<{} as {}>::{}", qself_ty, tcx.item_name(trait_did), assoc_ident),
2321 Applicability::MachineApplicable,
2327 Ok((ty, kind, item.def_id))
2333 opt_self_ty: Option<Ty<'tcx>>,
2335 trait_segment: &hir::PathSegment<'_>,
2336 item_segment: &hir::PathSegment<'_>,
2338 let tcx = self.tcx();
2340 let trait_def_id = tcx.parent(item_def_id).unwrap();
2342 debug!("qpath_to_ty: trait_def_id={:?}", trait_def_id);
2344 let self_ty = if let Some(ty) = opt_self_ty {
2347 let path_str = tcx.def_path_str(trait_def_id);
2349 let def_id = self.item_def_id();
2351 debug!("qpath_to_ty: self.item_def_id()={:?}", def_id);
2353 let parent_def_id = def_id
2354 .and_then(|def_id| tcx.hir().as_local_hir_id(def_id))
2355 .map(|hir_id| tcx.hir().get_parent_did(hir_id));
2357 debug!("qpath_to_ty: parent_def_id={:?}", parent_def_id);
2359 // If the trait in segment is the same as the trait defining the item,
2360 // use the `<Self as ..>` syntax in the error.
2361 let is_part_of_self_trait_constraints = def_id == Some(trait_def_id);
2362 let is_part_of_fn_in_self_trait = parent_def_id == Some(trait_def_id);
2364 let type_name = if is_part_of_self_trait_constraints || is_part_of_fn_in_self_trait {
2370 self.report_ambiguous_associated_type(
2374 item_segment.ident.name,
2376 return tcx.types.err;
2379 debug!("qpath_to_ty: self_type={:?}", self_ty);
2381 let trait_ref = self.ast_path_to_mono_trait_ref(span, trait_def_id, self_ty, trait_segment);
2383 let item_substs = self.create_substs_for_associated_item(
2391 debug!("qpath_to_ty: trait_ref={:?}", trait_ref);
2393 self.normalize_ty(span, tcx.mk_projection(item_def_id, item_substs))
2396 pub fn prohibit_generics<'a, T: IntoIterator<Item = &'a hir::PathSegment<'a>>>(
2400 let mut has_err = false;
2401 for segment in segments {
2402 let (mut err_for_lt, mut err_for_ty, mut err_for_ct) = (false, false, false);
2403 for arg in segment.generic_args().args {
2404 let (span, kind) = match arg {
2405 hir::GenericArg::Lifetime(lt) => {
2411 (lt.span, "lifetime")
2413 hir::GenericArg::Type(ty) => {
2421 hir::GenericArg::Const(ct) => {
2429 let mut err = struct_span_err!(
2433 "{} arguments are not allowed for this type",
2436 err.span_label(span, format!("{} argument not allowed", kind));
2438 if err_for_lt && err_for_ty && err_for_ct {
2442 for binding in segment.generic_args().bindings {
2444 Self::prohibit_assoc_ty_binding(self.tcx(), binding.span);
2451 pub fn prohibit_assoc_ty_binding(tcx: TyCtxt<'_>, span: Span) {
2452 let mut err = struct_span_err!(
2456 "associated type bindings are not allowed here"
2458 err.span_label(span, "associated type not allowed here").emit();
2461 // FIXME(eddyb, varkor) handle type paths here too, not just value ones.
2462 pub fn def_ids_for_value_path_segments(
2464 segments: &[hir::PathSegment<'_>],
2465 self_ty: Option<Ty<'tcx>>,
2469 // We need to extract the type parameters supplied by the user in
2470 // the path `path`. Due to the current setup, this is a bit of a
2471 // tricky-process; the problem is that resolve only tells us the
2472 // end-point of the path resolution, and not the intermediate steps.
2473 // Luckily, we can (at least for now) deduce the intermediate steps
2474 // just from the end-point.
2476 // There are basically five cases to consider:
2478 // 1. Reference to a constructor of a struct:
2480 // struct Foo<T>(...)
2482 // In this case, the parameters are declared in the type space.
2484 // 2. Reference to a constructor of an enum variant:
2486 // enum E<T> { Foo(...) }
2488 // In this case, the parameters are defined in the type space,
2489 // but may be specified either on the type or the variant.
2491 // 3. Reference to a fn item or a free constant:
2495 // In this case, the path will again always have the form
2496 // `a::b::foo::<T>` where only the final segment should have
2497 // type parameters. However, in this case, those parameters are
2498 // declared on a value, and hence are in the `FnSpace`.
2500 // 4. Reference to a method or an associated constant:
2502 // impl<A> SomeStruct<A> {
2506 // Here we can have a path like
2507 // `a::b::SomeStruct::<A>::foo::<B>`, in which case parameters
2508 // may appear in two places. The penultimate segment,
2509 // `SomeStruct::<A>`, contains parameters in TypeSpace, and the
2510 // final segment, `foo::<B>` contains parameters in fn space.
2512 // The first step then is to categorize the segments appropriately.
2514 let tcx = self.tcx();
2516 assert!(!segments.is_empty());
2517 let last = segments.len() - 1;
2519 let mut path_segs = vec![];
2522 // Case 1. Reference to a struct constructor.
2523 DefKind::Ctor(CtorOf::Struct, ..) => {
2524 // Everything but the final segment should have no
2525 // parameters at all.
2526 let generics = tcx.generics_of(def_id);
2527 // Variant and struct constructors use the
2528 // generics of their parent type definition.
2529 let generics_def_id = generics.parent.unwrap_or(def_id);
2530 path_segs.push(PathSeg(generics_def_id, last));
2533 // Case 2. Reference to a variant constructor.
2534 DefKind::Ctor(CtorOf::Variant, ..) | DefKind::Variant => {
2535 let adt_def = self_ty.map(|t| t.ty_adt_def().unwrap());
2536 let (generics_def_id, index) = if let Some(adt_def) = adt_def {
2537 debug_assert!(adt_def.is_enum());
2539 } else if last >= 1 && segments[last - 1].args.is_some() {
2540 // Everything but the penultimate segment should have no
2541 // parameters at all.
2542 let mut def_id = def_id;
2544 // `DefKind::Ctor` -> `DefKind::Variant`
2545 if let DefKind::Ctor(..) = kind {
2546 def_id = tcx.parent(def_id).unwrap()
2549 // `DefKind::Variant` -> `DefKind::Enum`
2550 let enum_def_id = tcx.parent(def_id).unwrap();
2551 (enum_def_id, last - 1)
2553 // FIXME: lint here recommending `Enum::<...>::Variant` form
2554 // instead of `Enum::Variant::<...>` form.
2556 // Everything but the final segment should have no
2557 // parameters at all.
2558 let generics = tcx.generics_of(def_id);
2559 // Variant and struct constructors use the
2560 // generics of their parent type definition.
2561 (generics.parent.unwrap_or(def_id), last)
2563 path_segs.push(PathSeg(generics_def_id, index));
2566 // Case 3. Reference to a top-level value.
2567 DefKind::Fn | DefKind::Const | DefKind::ConstParam | DefKind::Static => {
2568 path_segs.push(PathSeg(def_id, last));
2571 // Case 4. Reference to a method or associated const.
2572 DefKind::Method | DefKind::AssocConst => {
2573 if segments.len() >= 2 {
2574 let generics = tcx.generics_of(def_id);
2575 path_segs.push(PathSeg(generics.parent.unwrap(), last - 1));
2577 path_segs.push(PathSeg(def_id, last));
2580 kind => bug!("unexpected definition kind {:?} for {:?}", kind, def_id),
2583 debug!("path_segs = {:?}", path_segs);
2588 // Check a type `Path` and convert it to a `Ty`.
2591 opt_self_ty: Option<Ty<'tcx>>,
2592 path: &hir::Path<'_>,
2593 permit_variants: bool,
2595 let tcx = self.tcx();
2598 "res_to_ty(res={:?}, opt_self_ty={:?}, path_segments={:?})",
2599 path.res, opt_self_ty, path.segments
2602 let span = path.span;
2604 Res::Def(DefKind::OpaqueTy, did) => {
2605 // Check for desugared `impl Trait`.
2606 assert!(ty::is_impl_trait_defn(tcx, did).is_none());
2607 let item_segment = path.segments.split_last().unwrap();
2608 self.prohibit_generics(item_segment.1);
2609 let substs = self.ast_path_substs_for_ty(span, did, item_segment.0);
2610 self.normalize_ty(span, tcx.mk_opaque(did, substs))
2612 Res::Def(DefKind::Enum, did)
2613 | Res::Def(DefKind::TyAlias, did)
2614 | Res::Def(DefKind::Struct, did)
2615 | Res::Def(DefKind::Union, did)
2616 | Res::Def(DefKind::ForeignTy, did) => {
2617 assert_eq!(opt_self_ty, None);
2618 self.prohibit_generics(path.segments.split_last().unwrap().1);
2619 self.ast_path_to_ty(span, did, path.segments.last().unwrap())
2621 Res::Def(kind @ DefKind::Variant, def_id) if permit_variants => {
2622 // Convert "variant type" as if it were a real type.
2623 // The resulting `Ty` is type of the variant's enum for now.
2624 assert_eq!(opt_self_ty, None);
2627 self.def_ids_for_value_path_segments(&path.segments, None, kind, def_id);
2628 let generic_segs: FxHashSet<_> =
2629 path_segs.iter().map(|PathSeg(_, index)| index).collect();
2630 self.prohibit_generics(path.segments.iter().enumerate().filter_map(
2632 if !generic_segs.contains(&index) { Some(seg) } else { None }
2636 let PathSeg(def_id, index) = path_segs.last().unwrap();
2637 self.ast_path_to_ty(span, *def_id, &path.segments[*index])
2639 Res::Def(DefKind::TyParam, def_id) => {
2640 assert_eq!(opt_self_ty, None);
2641 self.prohibit_generics(path.segments);
2643 let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
2644 let item_id = tcx.hir().get_parent_node(hir_id);
2645 let item_def_id = tcx.hir().local_def_id(item_id);
2646 let generics = tcx.generics_of(item_def_id);
2647 let index = generics.param_def_id_to_index[&def_id];
2648 tcx.mk_ty_param(index, tcx.hir().name(hir_id))
2650 Res::SelfTy(Some(_), None) => {
2651 // `Self` in trait or type alias.
2652 assert_eq!(opt_self_ty, None);
2653 self.prohibit_generics(path.segments);
2654 tcx.types.self_param
2656 Res::SelfTy(_, Some(def_id)) => {
2657 // `Self` in impl (we know the concrete type).
2658 assert_eq!(opt_self_ty, None);
2659 self.prohibit_generics(path.segments);
2660 // Try to evaluate any array length constants.
2661 self.normalize_ty(span, tcx.at(span).type_of(def_id))
2663 Res::Def(DefKind::AssocTy, def_id) => {
2664 debug_assert!(path.segments.len() >= 2);
2665 self.prohibit_generics(&path.segments[..path.segments.len() - 2]);
2670 &path.segments[path.segments.len() - 2],
2671 path.segments.last().unwrap(),
2674 Res::PrimTy(prim_ty) => {
2675 assert_eq!(opt_self_ty, None);
2676 self.prohibit_generics(path.segments);
2678 hir::PrimTy::Bool => tcx.types.bool,
2679 hir::PrimTy::Char => tcx.types.char,
2680 hir::PrimTy::Int(it) => tcx.mk_mach_int(it),
2681 hir::PrimTy::Uint(uit) => tcx.mk_mach_uint(uit),
2682 hir::PrimTy::Float(ft) => tcx.mk_mach_float(ft),
2683 hir::PrimTy::Str => tcx.mk_str(),
2687 self.set_tainted_by_errors();
2688 return self.tcx().types.err;
2690 _ => span_bug!(span, "unexpected resolution: {:?}", path.res),
2694 /// Parses the programmer's textual representation of a type into our
2695 /// internal notion of a type.
2696 pub fn ast_ty_to_ty(&self, ast_ty: &hir::Ty<'_>) -> Ty<'tcx> {
2697 debug!("ast_ty_to_ty(id={:?}, ast_ty={:?} ty_ty={:?})", ast_ty.hir_id, ast_ty, ast_ty.kind);
2699 let tcx = self.tcx();
2701 let result_ty = match ast_ty.kind {
2702 hir::TyKind::Slice(ref ty) => tcx.mk_slice(self.ast_ty_to_ty(&ty)),
2703 hir::TyKind::Ptr(ref mt) => {
2704 tcx.mk_ptr(ty::TypeAndMut { ty: self.ast_ty_to_ty(&mt.ty), mutbl: mt.mutbl })
2706 hir::TyKind::Rptr(ref region, ref mt) => {
2707 let r = self.ast_region_to_region(region, None);
2708 debug!("ast_ty_to_ty: r={:?}", r);
2709 let t = self.ast_ty_to_ty(&mt.ty);
2710 tcx.mk_ref(r, ty::TypeAndMut { ty: t, mutbl: mt.mutbl })
2712 hir::TyKind::Never => tcx.types.never,
2713 hir::TyKind::Tup(ref fields) => {
2714 tcx.mk_tup(fields.iter().map(|t| self.ast_ty_to_ty(&t)))
2716 hir::TyKind::BareFn(ref bf) => {
2717 require_c_abi_if_c_variadic(tcx, &bf.decl, bf.abi, ast_ty.span);
2718 tcx.mk_fn_ptr(self.ty_of_fn(bf.unsafety, bf.abi, &bf.decl, &[], None))
2720 hir::TyKind::TraitObject(ref bounds, ref lifetime) => {
2721 self.conv_object_ty_poly_trait_ref(ast_ty.span, bounds, lifetime)
2723 hir::TyKind::Path(hir::QPath::Resolved(ref maybe_qself, ref path)) => {
2724 debug!("ast_ty_to_ty: maybe_qself={:?} path={:?}", maybe_qself, path);
2725 let opt_self_ty = maybe_qself.as_ref().map(|qself| self.ast_ty_to_ty(qself));
2726 self.res_to_ty(opt_self_ty, path, false)
2728 hir::TyKind::Def(item_id, ref lifetimes) => {
2729 let did = tcx.hir().local_def_id(item_id.id);
2730 self.impl_trait_ty_to_ty(did, lifetimes)
2732 hir::TyKind::Path(hir::QPath::TypeRelative(ref qself, ref segment)) => {
2733 debug!("ast_ty_to_ty: qself={:?} segment={:?}", qself, segment);
2734 let ty = self.ast_ty_to_ty(qself);
2736 let res = if let hir::TyKind::Path(hir::QPath::Resolved(_, ref path)) = qself.kind {
2741 self.associated_path_to_ty(ast_ty.hir_id, ast_ty.span, ty, res, segment, false)
2742 .map(|(ty, _, _)| ty)
2743 .unwrap_or(tcx.types.err)
2745 hir::TyKind::Array(ref ty, ref length) => {
2746 let length = self.ast_const_to_const(length, tcx.types.usize);
2747 let array_ty = tcx.mk_ty(ty::Array(self.ast_ty_to_ty(&ty), length));
2748 self.normalize_ty(ast_ty.span, array_ty)
2750 hir::TyKind::Typeof(ref _e) => {
2755 "`typeof` is a reserved keyword but unimplemented"
2757 .span_label(ast_ty.span, "reserved keyword")
2762 hir::TyKind::Infer => {
2763 // Infer also appears as the type of arguments or return
2764 // values in a ExprKind::Closure, or as
2765 // the type of local variables. Both of these cases are
2766 // handled specially and will not descend into this routine.
2767 self.ty_infer(None, ast_ty.span)
2769 hir::TyKind::Err => tcx.types.err,
2772 debug!("ast_ty_to_ty: result_ty={:?}", result_ty);
2774 self.record_ty(ast_ty.hir_id, result_ty, ast_ty.span);
2778 /// Returns the `DefId` of the constant parameter that the provided expression is a path to.
2779 pub fn const_param_def_id(&self, expr: &hir::Expr<'_>) -> Option<DefId> {
2780 // Unwrap a block, so that e.g. `{ P }` is recognised as a parameter. Const arguments
2781 // currently have to be wrapped in curly brackets, so it's necessary to special-case.
2782 let expr = match &expr.kind {
2783 ExprKind::Block(block, _) if block.stmts.is_empty() && block.expr.is_some() => {
2784 block.expr.as_ref().unwrap()
2790 ExprKind::Path(hir::QPath::Resolved(_, path)) => match path.res {
2791 Res::Def(DefKind::ConstParam, did) => Some(did),
2798 pub fn ast_const_to_const(
2800 ast_const: &hir::AnonConst,
2802 ) -> &'tcx ty::Const<'tcx> {
2803 debug!("ast_const_to_const(id={:?}, ast_const={:?})", ast_const.hir_id, ast_const);
2805 let tcx = self.tcx();
2806 let def_id = tcx.hir().local_def_id(ast_const.hir_id);
2808 let expr = &tcx.hir().body(ast_const.body).value;
2810 let lit_input = match expr.kind {
2811 hir::ExprKind::Lit(ref lit) => Some(LitToConstInput { lit: &lit.node, ty, neg: false }),
2812 hir::ExprKind::Unary(hir::UnOp::UnNeg, ref expr) => match expr.kind {
2813 hir::ExprKind::Lit(ref lit) => {
2814 Some(LitToConstInput { lit: &lit.node, ty, neg: true })
2821 if let Some(lit_input) = lit_input {
2822 // If an error occurred, ignore that it's a literal and leave reporting the error up to
2824 if let Ok(c) = tcx.at(expr.span).lit_to_const(lit_input) {
2827 tcx.sess.delay_span_bug(expr.span, "ast_const_to_const: couldn't lit_to_const");
2831 let kind = if let Some(def_id) = self.const_param_def_id(expr) {
2832 // Find the name and index of the const parameter by indexing the generics of the
2833 // parent item and construct a `ParamConst`.
2834 let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
2835 let item_id = tcx.hir().get_parent_node(hir_id);
2836 let item_def_id = tcx.hir().local_def_id(item_id);
2837 let generics = tcx.generics_of(item_def_id);
2838 let index = generics.param_def_id_to_index[&tcx.hir().local_def_id(hir_id)];
2839 let name = tcx.hir().name(hir_id);
2840 ty::ConstKind::Param(ty::ParamConst::new(index, name))
2842 ty::ConstKind::Unevaluated(def_id, InternalSubsts::identity_for_item(tcx, def_id), None)
2844 tcx.mk_const(ty::Const { val: kind, ty })
2847 pub fn impl_trait_ty_to_ty(
2850 lifetimes: &[hir::GenericArg<'_>],
2852 debug!("impl_trait_ty_to_ty(def_id={:?}, lifetimes={:?})", def_id, lifetimes);
2853 let tcx = self.tcx();
2855 let generics = tcx.generics_of(def_id);
2857 debug!("impl_trait_ty_to_ty: generics={:?}", generics);
2858 let substs = InternalSubsts::for_item(tcx, def_id, |param, _| {
2859 if let Some(i) = (param.index as usize).checked_sub(generics.parent_count) {
2860 // Our own parameters are the resolved lifetimes.
2862 GenericParamDefKind::Lifetime => {
2863 if let hir::GenericArg::Lifetime(lifetime) = &lifetimes[i] {
2864 self.ast_region_to_region(lifetime, None).into()
2872 // Replace all parent lifetimes with `'static`.
2874 GenericParamDefKind::Lifetime => tcx.lifetimes.re_static.into(),
2875 _ => tcx.mk_param_from_def(param),
2879 debug!("impl_trait_ty_to_ty: substs={:?}", substs);
2881 let ty = tcx.mk_opaque(def_id, substs);
2882 debug!("impl_trait_ty_to_ty: {}", ty);
2886 pub fn ty_of_arg(&self, ty: &hir::Ty<'_>, expected_ty: Option<Ty<'tcx>>) -> Ty<'tcx> {
2888 hir::TyKind::Infer if expected_ty.is_some() => {
2889 self.record_ty(ty.hir_id, expected_ty.unwrap(), ty.span);
2890 expected_ty.unwrap()
2892 _ => self.ast_ty_to_ty(ty),
2898 unsafety: hir::Unsafety,
2900 decl: &hir::FnDecl<'_>,
2901 generic_params: &[hir::GenericParam<'_>],
2902 ident_span: Option<Span>,
2903 ) -> ty::PolyFnSig<'tcx> {
2906 let tcx = self.tcx();
2908 // We proactively collect all the infered type params to emit a single error per fn def.
2909 let mut visitor = PlaceholderHirTyCollector::default();
2910 for ty in decl.inputs {
2911 visitor.visit_ty(ty);
2913 let input_tys = decl.inputs.iter().map(|a| self.ty_of_arg(a, None));
2914 let output_ty = match decl.output {
2915 hir::FnRetTy::Return(ref output) => {
2916 visitor.visit_ty(output);
2917 self.ast_ty_to_ty(output)
2919 hir::FnRetTy::DefaultReturn(..) => tcx.mk_unit(),
2922 debug!("ty_of_fn: output_ty={:?}", output_ty);
2925 ty::Binder::bind(tcx.mk_fn_sig(input_tys, output_ty, decl.c_variadic, unsafety, abi));
2927 if !self.allow_ty_infer() {
2928 // We always collect the spans for placeholder types when evaluating `fn`s, but we
2929 // only want to emit an error complaining about them if infer types (`_`) are not
2930 // allowed. `allow_ty_infer` gates this behavior.
2931 crate::collect::placeholder_type_error(
2933 ident_span.map(|sp| sp.shrink_to_hi()).unwrap_or(DUMMY_SP),
2936 ident_span.is_some(),
2940 // Find any late-bound regions declared in return type that do
2941 // not appear in the arguments. These are not well-formed.
2944 // for<'a> fn() -> &'a str <-- 'a is bad
2945 // for<'a> fn(&'a String) -> &'a str <-- 'a is ok
2946 let inputs = bare_fn_ty.inputs();
2947 let late_bound_in_args =
2948 tcx.collect_constrained_late_bound_regions(&inputs.map_bound(|i| i.to_owned()));
2949 let output = bare_fn_ty.output();
2950 let late_bound_in_ret = tcx.collect_referenced_late_bound_regions(&output);
2951 for br in late_bound_in_ret.difference(&late_bound_in_args) {
2952 let lifetime_name = match *br {
2953 ty::BrNamed(_, name) => format!("lifetime `{}`,", name),
2954 ty::BrAnon(_) | ty::BrEnv => "an anonymous lifetime".to_string(),
2956 let mut err = struct_span_err!(
2960 "return type references {} \
2961 which is not constrained by the fn input types",
2964 if let ty::BrAnon(_) = *br {
2965 // The only way for an anonymous lifetime to wind up
2966 // in the return type but **also** be unconstrained is
2967 // if it only appears in "associated types" in the
2968 // input. See #47511 for an example. In this case,
2969 // though we can easily give a hint that ought to be
2972 "lifetimes appearing in an associated type \
2973 are not considered constrained",
2982 /// Given the bounds on an object, determines what single region bound (if any) we can
2983 /// use to summarize this type. The basic idea is that we will use the bound the user
2984 /// provided, if they provided one, and otherwise search the supertypes of trait bounds
2985 /// for region bounds. It may be that we can derive no bound at all, in which case
2986 /// we return `None`.
2987 fn compute_object_lifetime_bound(
2990 existential_predicates: ty::Binder<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>>,
2991 ) -> Option<ty::Region<'tcx>> // if None, use the default
2993 let tcx = self.tcx();
2995 debug!("compute_opt_region_bound(existential_predicates={:?})", existential_predicates);
2997 // No explicit region bound specified. Therefore, examine trait
2998 // bounds and see if we can derive region bounds from those.
2999 let derived_region_bounds = object_region_bounds(tcx, existential_predicates);
3001 // If there are no derived region bounds, then report back that we
3002 // can find no region bound. The caller will use the default.
3003 if derived_region_bounds.is_empty() {
3007 // If any of the derived region bounds are 'static, that is always
3009 if derived_region_bounds.iter().any(|&r| ty::ReStatic == *r) {
3010 return Some(tcx.lifetimes.re_static);
3013 // Determine whether there is exactly one unique region in the set
3014 // of derived region bounds. If so, use that. Otherwise, report an
3016 let r = derived_region_bounds[0];
3017 if derived_region_bounds[1..].iter().any(|r1| r != *r1) {
3022 "ambiguous lifetime bound, explicit lifetime bound required"
3030 /// Collects together a list of bounds that are applied to some type,
3031 /// after they've been converted into `ty` form (from the HIR
3032 /// representations). These lists of bounds occur in many places in
3036 /// trait Foo: Bar + Baz { }
3037 /// ^^^^^^^^^ supertrait list bounding the `Self` type parameter
3039 /// fn foo<T: Bar + Baz>() { }
3040 /// ^^^^^^^^^ bounding the type parameter `T`
3042 /// impl dyn Bar + Baz
3043 /// ^^^^^^^^^ bounding the forgotten dynamic type
3046 /// Our representation is a bit mixed here -- in some cases, we
3047 /// include the self type (e.g., `trait_bounds`) but in others we do
3048 #[derive(Default, PartialEq, Eq, Clone, Debug)]
3049 pub struct Bounds<'tcx> {
3050 /// A list of region bounds on the (implicit) self type. So if you
3051 /// had `T: 'a + 'b` this might would be a list `['a, 'b]` (but
3052 /// the `T` is not explicitly included).
3053 pub region_bounds: Vec<(ty::Region<'tcx>, Span)>,
3055 /// A list of trait bounds. So if you had `T: Debug` this would be
3056 /// `T: Debug`. Note that the self-type is explicit here.
3057 pub trait_bounds: Vec<(ty::PolyTraitRef<'tcx>, Span, Constness)>,
3059 /// A list of projection equality bounds. So if you had `T:
3060 /// Iterator<Item = u32>` this would include `<T as
3061 /// Iterator>::Item => u32`. Note that the self-type is explicit
3063 pub projection_bounds: Vec<(ty::PolyProjectionPredicate<'tcx>, Span)>,
3065 /// `Some` if there is *no* `?Sized` predicate. The `span`
3066 /// is the location in the source of the `T` declaration which can
3067 /// be cited as the source of the `T: Sized` requirement.
3068 pub implicitly_sized: Option<Span>,
3071 impl<'tcx> Bounds<'tcx> {
3072 /// Converts a bounds list into a flat set of predicates (like
3073 /// where-clauses). Because some of our bounds listings (e.g.,
3074 /// regions) don't include the self-type, you must supply the
3075 /// self-type here (the `param_ty` parameter).
3080 ) -> Vec<(ty::Predicate<'tcx>, Span)> {
3081 // If it could be sized, and is, add the `Sized` predicate.
3082 let sized_predicate = self.implicitly_sized.and_then(|span| {
3083 tcx.lang_items().sized_trait().map(|sized| {
3084 let trait_ref = ty::Binder::bind(ty::TraitRef {
3086 substs: tcx.mk_substs_trait(param_ty, &[]),
3088 (trait_ref.without_const().to_predicate(), span)
3097 .map(|&(region_bound, span)| {
3098 // Account for the binder being introduced below; no need to shift `param_ty`
3099 // because, at present at least, it either only refers to early-bound regions,
3100 // or it's a generic associated type that deliberately has escaping bound vars.
3101 let region_bound = ty::fold::shift_region(tcx, region_bound, 1);
3102 let outlives = ty::OutlivesPredicate(param_ty, region_bound);
3103 (ty::Binder::bind(outlives).to_predicate(), span)
3105 .chain(self.trait_bounds.iter().map(|&(bound_trait_ref, span, constness)| {
3106 let predicate = bound_trait_ref.with_constness(constness).to_predicate();
3110 self.projection_bounds
3112 .map(|&(projection, span)| (projection.to_predicate(), span)),