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;
9 use crate::middle::resolve_lifetime as rl;
10 use crate::require_c_abi_if_c_variadic;
11 use rustc_ast::{util::lev_distance::find_best_match_for_name, ParamKindOrd};
12 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
13 use rustc_errors::ErrorReported;
14 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticId, FatalError};
16 use rustc_hir::def::{CtorOf, DefKind, Namespace, Res};
17 use rustc_hir::def_id::{DefId, LocalDefId};
18 use rustc_hir::intravisit::{walk_generics, Visitor as _};
19 use rustc_hir::lang_items::SizedTraitLangItem;
20 use rustc_hir::{Constness, GenericArg, GenericArgs};
21 use rustc_middle::ty::subst::{self, InternalSubsts, Subst, SubstsRef};
22 use rustc_middle::ty::{
23 self, Const, DefIdTree, ToPredicate, Ty, TyCtxt, TypeFoldable, WithConstness,
25 use rustc_middle::ty::{GenericParamDef, GenericParamDefKind};
26 use rustc_session::lint::builtin::{AMBIGUOUS_ASSOCIATED_ITEMS, LATE_BOUND_LIFETIME_ARGUMENTS};
27 use rustc_session::parse::feature_err;
28 use rustc_session::Session;
29 use rustc_span::symbol::{kw, sym, Ident, Symbol};
30 use rustc_span::{MultiSpan, Span, DUMMY_SP};
31 use rustc_target::spec::abi;
32 use rustc_trait_selection::traits;
33 use rustc_trait_selection::traits::astconv_object_safety_violations;
34 use rustc_trait_selection::traits::error_reporting::report_object_safety_error;
35 use rustc_trait_selection::traits::wf::object_region_bounds;
37 use smallvec::SmallVec;
38 use std::collections::BTreeSet;
43 pub struct PathSeg(pub DefId, pub usize);
45 pub trait AstConv<'tcx> {
46 fn tcx<'a>(&'a self) -> TyCtxt<'tcx>;
48 fn item_def_id(&self) -> Option<DefId>;
50 fn default_constness_for_trait_bounds(&self) -> Constness;
52 /// Returns predicates in scope of the form `X: Foo`, where `X` is
53 /// a type parameter `X` with the given id `def_id`. This is a
54 /// subset of the full set of predicates.
56 /// This is used for one specific purpose: resolving "short-hand"
57 /// associated type references like `T::Item`. In principle, we
58 /// would do that by first getting the full set of predicates in
59 /// scope and then filtering down to find those that apply to `T`,
60 /// but this can lead to cycle errors. The problem is that we have
61 /// to do this resolution *in order to create the predicates in
62 /// the first place*. Hence, we have this "special pass".
63 fn get_type_parameter_bounds(&self, span: Span, def_id: DefId) -> ty::GenericPredicates<'tcx>;
65 /// Returns the lifetime to use when a lifetime is omitted (and not elided).
66 fn re_infer(&self, param: Option<&ty::GenericParamDef>, span: Span)
67 -> Option<ty::Region<'tcx>>;
69 /// Returns the type to use when a type is omitted.
70 fn ty_infer(&self, param: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx>;
72 /// Returns `true` if `_` is allowed in type signatures in the current context.
73 fn allow_ty_infer(&self) -> bool;
75 /// Returns the const to use when a const is omitted.
79 param: Option<&ty::GenericParamDef>,
81 ) -> &'tcx Const<'tcx>;
83 /// Projecting an associated type from a (potentially)
84 /// higher-ranked trait reference is more complicated, because of
85 /// the possibility of late-bound regions appearing in the
86 /// associated type binding. This is not legal in function
87 /// signatures for that reason. In a function body, we can always
88 /// handle it because we can use inference variables to remove the
89 /// late-bound regions.
90 fn projected_ty_from_poly_trait_ref(
94 item_segment: &hir::PathSegment<'_>,
95 poly_trait_ref: ty::PolyTraitRef<'tcx>,
98 /// Normalize an associated type coming from the user.
99 fn normalize_ty(&self, span: Span, ty: Ty<'tcx>) -> Ty<'tcx>;
101 /// Invoked when we encounter an error from some prior pass
102 /// (e.g., resolve) that is translated into a ty-error. This is
103 /// used to help suppress derived errors typeck might otherwise
105 fn set_tainted_by_errors(&self);
107 fn record_ty(&self, hir_id: hir::HirId, ty: Ty<'tcx>, span: Span);
110 pub enum SizedByDefault {
115 struct ConvertedBinding<'a, 'tcx> {
117 kind: ConvertedBindingKind<'a, 'tcx>,
121 enum ConvertedBindingKind<'a, 'tcx> {
123 Constraint(&'a [hir::GenericBound<'a>]),
126 /// New-typed boolean indicating whether explicit late-bound lifetimes
127 /// are present in a set of generic arguments.
129 /// For example if we have some method `fn f<'a>(&'a self)` implemented
130 /// for some type `T`, although `f` is generic in the lifetime `'a`, `'a`
131 /// is late-bound so should not be provided explicitly. Thus, if `f` is
132 /// instantiated with some generic arguments providing `'a` explicitly,
133 /// we taint those arguments with `ExplicitLateBound::Yes` so that we
134 /// can provide an appropriate diagnostic later.
135 #[derive(Copy, Clone, PartialEq)]
136 pub enum ExplicitLateBound {
141 #[derive(Copy, Clone, PartialEq)]
142 enum GenericArgPosition {
144 Value, // e.g., functions
148 /// A marker denoting that the generic arguments that were
149 /// provided did not match the respective generic parameters.
150 #[derive(Clone, Default)]
151 pub struct GenericArgCountMismatch {
152 /// Indicates whether a fatal error was reported (`Some`), or just a lint (`None`).
153 pub reported: Option<ErrorReported>,
154 /// A list of spans of arguments provided that were not valid.
155 pub invalid_args: Vec<Span>,
158 /// Decorates the result of a generic argument count mismatch
159 /// check with whether explicit late bounds were provided.
161 pub struct GenericArgCountResult {
162 pub explicit_late_bound: ExplicitLateBound,
163 pub correct: Result<(), GenericArgCountMismatch>,
166 impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
167 pub fn ast_region_to_region(
169 lifetime: &hir::Lifetime,
170 def: Option<&ty::GenericParamDef>,
171 ) -> ty::Region<'tcx> {
172 let tcx = self.tcx();
173 let lifetime_name = |def_id| tcx.hir().name(tcx.hir().local_def_id_to_hir_id(def_id));
175 let r = match tcx.named_region(lifetime.hir_id) {
176 Some(rl::Region::Static) => tcx.lifetimes.re_static,
178 Some(rl::Region::LateBound(debruijn, id, _)) => {
179 let name = lifetime_name(id.expect_local());
180 tcx.mk_region(ty::ReLateBound(debruijn, ty::BrNamed(id, name)))
183 Some(rl::Region::LateBoundAnon(debruijn, index)) => {
184 tcx.mk_region(ty::ReLateBound(debruijn, ty::BrAnon(index)))
187 Some(rl::Region::EarlyBound(index, id, _)) => {
188 let name = lifetime_name(id.expect_local());
189 tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion { def_id: id, index, name }))
192 Some(rl::Region::Free(scope, id)) => {
193 let name = lifetime_name(id.expect_local());
194 tcx.mk_region(ty::ReFree(ty::FreeRegion {
196 bound_region: ty::BrNamed(id, name),
199 // (*) -- not late-bound, won't change
203 self.re_infer(def, lifetime.span).unwrap_or_else(|| {
204 // This indicates an illegal lifetime
205 // elision. `resolve_lifetime` should have
206 // reported an error in this case -- but if
207 // not, let's error out.
208 tcx.sess.delay_span_bug(lifetime.span, "unelided lifetime in signature");
210 // Supply some dummy value. We don't have an
211 // `re_error`, annoyingly, so use `'static`.
212 tcx.lifetimes.re_static
217 debug!("ast_region_to_region(lifetime={:?}) yields {:?}", lifetime, r);
222 /// Given a path `path` that refers to an item `I` with the declared generics `decl_generics`,
223 /// returns an appropriate set of substitutions for this particular reference to `I`.
224 pub fn ast_path_substs_for_ty(
228 item_segment: &hir::PathSegment<'_>,
229 ) -> SubstsRef<'tcx> {
230 let (substs, assoc_bindings, _) = self.create_substs_for_ast_path(
234 item_segment.generic_args(),
235 item_segment.infer_args,
239 if let Some(b) = assoc_bindings.first() {
240 Self::prohibit_assoc_ty_binding(self.tcx(), b.span);
246 /// Report error if there is an explicit type parameter when using `impl Trait`.
249 seg: &hir::PathSegment<'_>,
250 generics: &ty::Generics,
252 let explicit = !seg.infer_args;
253 let impl_trait = generics.params.iter().any(|param| match param.kind {
254 ty::GenericParamDefKind::Type {
255 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
261 if explicit && impl_trait {
266 .filter_map(|arg| match arg {
267 GenericArg::Type(_) => Some(arg.span()),
270 .collect::<Vec<_>>();
272 let mut err = struct_span_err! {
276 "cannot provide explicit generic arguments when `impl Trait` is \
277 used in argument position"
281 err.span_label(span, "explicit generic argument not allowed");
290 /// Checks that the correct number of generic arguments have been provided.
291 /// Used specifically for function calls.
292 pub fn check_generic_arg_count_for_call(
296 seg: &hir::PathSegment<'_>,
297 is_method_call: bool,
298 ) -> GenericArgCountResult {
299 let empty_args = hir::GenericArgs::none();
300 let suppress_mismatch = Self::check_impl_trait(tcx, seg, &def);
301 Self::check_generic_arg_count(
305 if let Some(ref args) = seg.args { args } else { &empty_args },
306 if is_method_call { GenericArgPosition::MethodCall } else { GenericArgPosition::Value },
307 def.parent.is_none() && def.has_self, // `has_self`
308 seg.infer_args || suppress_mismatch, // `infer_args`
312 /// Checks that the correct number of generic arguments have been provided.
313 /// This is used both for datatypes and function calls.
314 fn check_generic_arg_count(
318 args: &hir::GenericArgs<'_>,
319 position: GenericArgPosition,
322 ) -> GenericArgCountResult {
323 // At this stage we are guaranteed that the generic arguments are in the correct order, e.g.
324 // that lifetimes will proceed types. So it suffices to check the number of each generic
325 // arguments in order to validate them with respect to the generic parameters.
326 let param_counts = def.own_counts();
327 let arg_counts = args.own_counts();
328 let infer_lifetimes = position != GenericArgPosition::Type && arg_counts.lifetimes == 0;
330 let mut defaults: ty::GenericParamCount = Default::default();
331 for param in &def.params {
333 GenericParamDefKind::Lifetime => {}
334 GenericParamDefKind::Type { has_default, .. } => {
335 defaults.types += has_default as usize
337 GenericParamDefKind::Const => {
338 // FIXME(const_generics:defaults)
343 if position != GenericArgPosition::Type && !args.bindings.is_empty() {
344 AstConv::prohibit_assoc_ty_binding(tcx, args.bindings[0].span);
347 let explicit_late_bound =
348 Self::prohibit_explicit_late_bound_lifetimes(tcx, def, args, position);
350 let check_kind_count = |kind,
355 unexpected_spans: &mut Vec<Span>,
358 "check_kind_count: kind: {} required: {} permitted: {} provided: {} offset: {}",
359 kind, required, permitted, provided, offset
361 // We enforce the following: `required` <= `provided` <= `permitted`.
362 // For kinds without defaults (e.g.., lifetimes), `required == permitted`.
363 // For other kinds (i.e., types), `permitted` may be greater than `required`.
364 if required <= provided && provided <= permitted {
372 // Unfortunately lifetime and type parameter mismatches are typically styled
373 // differently in diagnostics, which means we have a few cases to consider here.
374 let (bound, quantifier) = if required != permitted {
375 if provided < required {
376 (required, "at least ")
378 // provided > permitted
379 (permitted, "at most ")
385 let (spans, label) = if required == permitted && provided > permitted {
386 // In the case when the user has provided too many arguments,
387 // we want to point to the unexpected arguments.
388 let spans: Vec<Span> = args.args[offset + permitted..offset + provided]
390 .map(|arg| arg.span())
392 unexpected_spans.extend(spans.clone());
393 (spans, format!("unexpected {} argument", kind))
398 "expected {}{} {} argument{}",
407 let mut err = tcx.sess.struct_span_err_with_code(
410 "wrong number of {} arguments: expected {}{}, found {}",
411 kind, quantifier, bound, provided,
413 DiagnosticId::Error("E0107".into()),
416 err.span_label(span, label.as_str());
423 let mut arg_count_correct = Ok(());
424 let mut unexpected_spans = vec![];
426 if !infer_lifetimes || arg_counts.lifetimes > param_counts.lifetimes {
427 arg_count_correct = check_kind_count(
429 param_counts.lifetimes,
430 param_counts.lifetimes,
431 arg_counts.lifetimes,
433 &mut unexpected_spans,
434 explicit_late_bound == ExplicitLateBound::Yes,
436 .and(arg_count_correct);
438 // FIXME(const_generics:defaults)
439 if !infer_args || arg_counts.consts > param_counts.consts {
440 arg_count_correct = check_kind_count(
445 arg_counts.lifetimes + arg_counts.types,
446 &mut unexpected_spans,
449 .and(arg_count_correct);
451 // Note that type errors are currently be emitted *after* const errors.
452 if !infer_args || arg_counts.types > param_counts.types - defaults.types - has_self as usize
454 arg_count_correct = check_kind_count(
456 param_counts.types - defaults.types - has_self as usize,
457 param_counts.types - has_self as usize,
459 arg_counts.lifetimes,
460 &mut unexpected_spans,
463 .and(arg_count_correct);
466 GenericArgCountResult {
468 correct: arg_count_correct.map_err(|reported_err| GenericArgCountMismatch {
469 reported: if reported_err { Some(ErrorReported) } else { None },
470 invalid_args: unexpected_spans,
475 /// Report an error that a generic argument did not match the generic parameter that was
477 fn generic_arg_mismatch_err(
479 arg: &GenericArg<'_>,
483 let mut err = struct_span_err!(
487 "{} provided when a {} was expected",
492 let unordered = sess.features_untracked().const_generics;
493 let kind_ord = match kind {
494 "lifetime" => ParamKindOrd::Lifetime,
495 "type" => ParamKindOrd::Type,
496 "constant" => ParamKindOrd::Const { unordered },
497 // It's more concise to match on the string representation, though it means
498 // the match is non-exhaustive.
499 _ => bug!("invalid generic parameter kind {}", kind),
501 let arg_ord = match arg {
502 GenericArg::Lifetime(_) => ParamKindOrd::Lifetime,
503 GenericArg::Type(_) => ParamKindOrd::Type,
504 GenericArg::Const(_) => ParamKindOrd::Const { unordered },
507 // This note is only true when generic parameters are strictly ordered by their kind.
508 if kind_ord.cmp(&arg_ord) != core::cmp::Ordering::Equal {
510 if kind_ord < arg_ord { (kind, arg.descr()) } else { (arg.descr(), kind) };
511 err.note(&format!("{} arguments must be provided before {} arguments", first, last));
512 if let Some(help) = help {
520 /// Creates the relevant generic argument substitutions
521 /// corresponding to a set of generic parameters. This is a
522 /// rather complex function. Let us try to explain the role
523 /// of each of its parameters:
525 /// To start, we are given the `def_id` of the thing we are
526 /// creating the substitutions for, and a partial set of
527 /// substitutions `parent_substs`. In general, the substitutions
528 /// for an item begin with substitutions for all the "parents" of
529 /// that item -- e.g., for a method it might include the
530 /// parameters from the impl.
532 /// Therefore, the method begins by walking down these parents,
533 /// starting with the outermost parent and proceed inwards until
534 /// it reaches `def_id`. For each parent `P`, it will check `parent_substs`
535 /// first to see if the parent's substitutions are listed in there. If so,
536 /// we can append those and move on. Otherwise, it invokes the
537 /// three callback functions:
539 /// - `args_for_def_id`: given the `DefId` `P`, supplies back the
540 /// generic arguments that were given to that parent from within
541 /// the path; so e.g., if you have `<T as Foo>::Bar`, the `DefId`
542 /// might refer to the trait `Foo`, and the arguments might be
543 /// `[T]`. The boolean value indicates whether to infer values
544 /// for arguments whose values were not explicitly provided.
545 /// - `provided_kind`: given the generic parameter and the value from `args_for_def_id`,
546 /// instantiate a `GenericArg`.
547 /// - `inferred_kind`: if no parameter was provided, and inference is enabled, then
548 /// creates a suitable inference variable.
549 pub fn create_substs_for_generic_args<'b>(
552 parent_substs: &[subst::GenericArg<'tcx>],
554 self_ty: Option<Ty<'tcx>>,
555 arg_count: GenericArgCountResult,
556 args_for_def_id: impl Fn(DefId) -> (Option<&'b GenericArgs<'b>>, bool),
557 mut provided_kind: impl FnMut(&GenericParamDef, &GenericArg<'_>) -> subst::GenericArg<'tcx>,
558 mut inferred_kind: impl FnMut(
559 Option<&[subst::GenericArg<'tcx>]>,
562 ) -> subst::GenericArg<'tcx>,
563 ) -> SubstsRef<'tcx> {
564 // Collect the segments of the path; we need to substitute arguments
565 // for parameters throughout the entire path (wherever there are
566 // generic parameters).
567 let mut parent_defs = tcx.generics_of(def_id);
568 let count = parent_defs.count();
569 let mut stack = vec![(def_id, parent_defs)];
570 while let Some(def_id) = parent_defs.parent {
571 parent_defs = tcx.generics_of(def_id);
572 stack.push((def_id, parent_defs));
575 // We manually build up the substitution, rather than using convenience
576 // methods in `subst.rs`, so that we can iterate over the arguments and
577 // parameters in lock-step linearly, instead of trying to match each pair.
578 let mut substs: SmallVec<[subst::GenericArg<'tcx>; 8]> = SmallVec::with_capacity(count);
579 // Iterate over each segment of the path.
580 while let Some((def_id, defs)) = stack.pop() {
581 let mut params = defs.params.iter().peekable();
583 // If we have already computed substitutions for parents, we can use those directly.
584 while let Some(¶m) = params.peek() {
585 if let Some(&kind) = parent_substs.get(param.index as usize) {
593 // `Self` is handled first, unless it's been handled in `parent_substs`.
595 if let Some(¶m) = params.peek() {
596 if param.index == 0 {
597 if let GenericParamDefKind::Type { .. } = param.kind {
601 .unwrap_or_else(|| inferred_kind(None, param, true)),
609 // Check whether this segment takes generic arguments and the user has provided any.
610 let (generic_args, infer_args) = args_for_def_id(def_id);
613 generic_args.iter().flat_map(|generic_args| generic_args.args.iter()).peekable();
615 // If we encounter a type or const when we expect a lifetime, we infer the lifetimes.
616 // If we later encounter a lifetime, we know that the arguments were provided in the
617 // wrong order. `force_infer_lt` records the type or const that forced lifetimes to be
618 // inferred, so we can use it for diagnostics later.
619 let mut force_infer_lt = None;
622 // We're going to iterate through the generic arguments that the user
623 // provided, matching them with the generic parameters we expect.
624 // Mismatches can occur as a result of elided lifetimes, or for malformed
625 // input. We try to handle both sensibly.
626 match (args.peek(), params.peek()) {
627 (Some(&arg), Some(¶m)) => {
628 match (arg, ¶m.kind, arg_count.explicit_late_bound) {
629 (GenericArg::Lifetime(_), GenericParamDefKind::Lifetime, _)
630 | (GenericArg::Type(_), GenericParamDefKind::Type { .. }, _)
631 | (GenericArg::Const(_), GenericParamDefKind::Const, _) => {
632 substs.push(provided_kind(param, arg));
637 GenericArg::Type(_) | GenericArg::Const(_),
638 GenericParamDefKind::Lifetime,
641 // We expected a lifetime argument, but got a type or const
642 // argument. That means we're inferring the lifetimes.
643 substs.push(inferred_kind(None, param, infer_args));
644 force_infer_lt = Some(arg);
647 (GenericArg::Lifetime(_), _, ExplicitLateBound::Yes) => {
648 // We've come across a lifetime when we expected something else in
649 // the presence of explicit late bounds. This is most likely
650 // due to the presence of the explicit bound so we're just going to
655 // We expected one kind of parameter, but the user provided
656 // another. This is an error. However, if we already know that
657 // the arguments don't match up with the parameters, we won't issue
658 // an additional error, as the user already knows what's wrong.
659 if arg_count.correct.is_ok()
660 && arg_count.explicit_late_bound == ExplicitLateBound::No
662 // We're going to iterate over the parameters to sort them out, and
663 // show that order to the user as a possible order for the parameters
664 let mut param_types_present = defs
671 GenericParamDefKind::Lifetime => {
672 ParamKindOrd::Lifetime
674 GenericParamDefKind::Type { .. } => {
677 GenericParamDefKind::Const => {
678 ParamKindOrd::Const {
681 .features_untracked()
689 .collect::<Vec<(ParamKindOrd, GenericParamDef)>>();
690 param_types_present.sort_by_key(|(ord, _)| *ord);
691 let (mut param_types_present, ordered_params): (
693 Vec<GenericParamDef>,
694 ) = param_types_present.into_iter().unzip();
695 param_types_present.dedup();
697 Self::generic_arg_mismatch_err(
702 "reorder the arguments: {}: `<{}>`",
705 .map(|ord| format!("{}s", ord.to_string()))
706 .collect::<Vec<String>>()
710 .filter_map(|param| {
711 if param.name == kw::SelfUpper {
714 Some(param.name.to_string())
717 .collect::<Vec<String>>()
723 // We've reported the error, but we want to make sure that this
724 // problem doesn't bubble down and create additional, irrelevant
725 // errors. In this case, we're simply going to ignore the argument
726 // and any following arguments. The rest of the parameters will be
728 while args.next().is_some() {}
733 (Some(&arg), None) => {
734 // We should never be able to reach this point with well-formed input.
735 // There are three situations in which we can encounter this issue.
737 // 1. The number of arguments is incorrect. In this case, an error
738 // will already have been emitted, and we can ignore it.
739 // 2. There are late-bound lifetime parameters present, yet the
740 // lifetime arguments have also been explicitly specified by the
742 // 3. We've inferred some lifetimes, which have been provided later (i.e.
743 // after a type or const). We want to throw an error in this case.
745 if arg_count.correct.is_ok()
746 && arg_count.explicit_late_bound == ExplicitLateBound::No
748 let kind = arg.descr();
749 assert_eq!(kind, "lifetime");
751 force_infer_lt.expect("lifetimes ought to have been inferred");
752 Self::generic_arg_mismatch_err(tcx.sess, provided, kind, None);
758 (None, Some(¶m)) => {
759 // If there are fewer arguments than parameters, it means
760 // we're inferring the remaining arguments.
761 substs.push(inferred_kind(Some(&substs), param, infer_args));
765 (None, None) => break,
770 tcx.intern_substs(&substs)
773 /// Given the type/lifetime/const arguments provided to some path (along with
774 /// an implicit `Self`, if this is a trait reference), returns the complete
775 /// set of substitutions. This may involve applying defaulted type parameters.
776 /// Also returns back constraints on associated types.
781 /// T: std::ops::Index<usize, Output = u32>
782 /// ^1 ^^^^^^^^^^^^^^2 ^^^^3 ^^^^^^^^^^^4
785 /// 1. The `self_ty` here would refer to the type `T`.
786 /// 2. The path in question is the path to the trait `std::ops::Index`,
787 /// which will have been resolved to a `def_id`
788 /// 3. The `generic_args` contains info on the `<...>` contents. The `usize` type
789 /// parameters are returned in the `SubstsRef`, the associated type bindings like
790 /// `Output = u32` are returned in the `Vec<ConvertedBinding...>` result.
792 /// Note that the type listing given here is *exactly* what the user provided.
794 /// For (generic) associated types
797 /// <Vec<u8> as Iterable<u8>>::Iter::<'a>
800 /// We have the parent substs are the substs for the parent trait:
801 /// `[Vec<u8>, u8]` and `generic_args` are the arguments for the associated
802 /// type itself: `['a]`. The returned `SubstsRef` concatenates these two
803 /// lists: `[Vec<u8>, u8, 'a]`.
804 fn create_substs_for_ast_path<'a>(
808 parent_substs: &[subst::GenericArg<'tcx>],
809 generic_args: &'a hir::GenericArgs<'_>,
811 self_ty: Option<Ty<'tcx>>,
812 ) -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'a, 'tcx>>, GenericArgCountResult) {
813 // If the type is parameterized by this region, then replace this
814 // region with the current anon region binding (in other words,
815 // whatever & would get replaced with).
817 "create_substs_for_ast_path(def_id={:?}, self_ty={:?}, \
819 def_id, self_ty, generic_args
822 let tcx = self.tcx();
823 let generic_params = tcx.generics_of(def_id);
825 if generic_params.has_self {
826 if generic_params.parent.is_some() {
827 // The parent is a trait so it should have at least one subst
828 // for the `Self` type.
829 assert!(!parent_substs.is_empty())
831 // This item (presumably a trait) needs a self-type.
832 assert!(self_ty.is_some());
835 assert!(self_ty.is_none() && parent_substs.is_empty());
838 let arg_count = Self::check_generic_arg_count(
843 GenericArgPosition::Type,
848 let is_object = self_ty.map_or(false, |ty| ty == self.tcx().types.trait_object_dummy_self);
849 let default_needs_object_self = |param: &ty::GenericParamDef| {
850 if let GenericParamDefKind::Type { has_default, .. } = param.kind {
851 if is_object && has_default {
852 let default_ty = tcx.at(span).type_of(param.def_id);
853 let self_param = tcx.types.self_param;
854 if default_ty.walk().any(|arg| arg == self_param.into()) {
855 // There is no suitable inference default for a type parameter
856 // that references self, in an object type.
865 let mut missing_type_params = vec![];
866 let mut inferred_params = vec![];
867 let substs = Self::create_substs_for_generic_args(
874 // Provide the generic args, and whether types should be inferred.
877 (Some(generic_args), infer_args)
879 // The last component of this tuple is unimportant.
883 // Provide substitutions for parameters for which (valid) arguments have been provided.
884 |param, arg| match (¶m.kind, arg) {
885 (GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => {
886 self.ast_region_to_region(<, Some(param)).into()
888 (GenericParamDefKind::Type { .. }, GenericArg::Type(ty)) => {
889 if let (hir::TyKind::Infer, false) = (&ty.kind, self.allow_ty_infer()) {
890 inferred_params.push(ty.span);
891 tcx.ty_error().into()
893 self.ast_ty_to_ty(&ty).into()
896 (GenericParamDefKind::Const, GenericArg::Const(ct)) => {
897 ty::Const::from_opt_const_arg_anon_const(
899 ty::WithOptConstParam {
900 did: tcx.hir().local_def_id(ct.value.hir_id),
901 const_param_did: Some(param.def_id),
908 // Provide substitutions for parameters for which arguments are inferred.
909 |substs, param, infer_args| {
911 GenericParamDefKind::Lifetime => tcx.lifetimes.re_static.into(),
912 GenericParamDefKind::Type { has_default, .. } => {
913 if !infer_args && has_default {
914 // No type parameter provided, but a default exists.
916 // If we are converting an object type, then the
917 // `Self` parameter is unknown. However, some of the
918 // other type parameters may reference `Self` in their
919 // defaults. This will lead to an ICE if we are not
921 if default_needs_object_self(param) {
922 missing_type_params.push(param.name.to_string());
923 tcx.ty_error().into()
925 // This is a default type parameter.
928 tcx.at(span).type_of(param.def_id).subst_spanned(
936 } else if infer_args {
937 // No type parameters were provided, we can infer all.
939 if !default_needs_object_self(param) { Some(param) } else { None };
940 self.ty_infer(param, span).into()
942 // We've already errored above about the mismatch.
943 tcx.ty_error().into()
946 GenericParamDefKind::Const => {
947 let ty = tcx.at(span).type_of(param.def_id);
948 // FIXME(const_generics:defaults)
950 // No const parameters were provided, we can infer all.
951 self.ct_infer(ty, Some(param), span).into()
953 // We've already errored above about the mismatch.
954 tcx.const_error(ty).into()
961 self.complain_about_missing_type_params(
965 generic_args.args.is_empty(),
968 // Convert associated-type bindings or constraints into a separate vector.
969 // Example: Given this:
971 // T: Iterator<Item = u32>
973 // The `T` is passed in as a self-type; the `Item = u32` is
974 // not a "type parameter" of the `Iterator` trait, but rather
975 // a restriction on `<T as Iterator>::Item`, so it is passed
977 let assoc_bindings = generic_args
981 let kind = match binding.kind {
982 hir::TypeBindingKind::Equality { ref ty } => {
983 ConvertedBindingKind::Equality(self.ast_ty_to_ty(ty))
985 hir::TypeBindingKind::Constraint { ref bounds } => {
986 ConvertedBindingKind::Constraint(bounds)
989 ConvertedBinding { item_name: binding.ident, kind, span: binding.span }
994 "create_substs_for_ast_path(generic_params={:?}, self_ty={:?}) -> {:?}",
995 generic_params, self_ty, substs
998 (substs, assoc_bindings, arg_count)
1001 crate fn create_substs_for_associated_item(
1006 item_segment: &hir::PathSegment<'_>,
1007 parent_substs: SubstsRef<'tcx>,
1008 ) -> SubstsRef<'tcx> {
1009 if tcx.generics_of(item_def_id).params.is_empty() {
1010 self.prohibit_generics(slice::from_ref(item_segment));
1014 self.create_substs_for_ast_path(
1018 item_segment.generic_args(),
1019 item_segment.infer_args,
1026 /// On missing type parameters, emit an E0393 error and provide a structured suggestion using
1027 /// the type parameter's name as a placeholder.
1028 fn complain_about_missing_type_params(
1030 missing_type_params: Vec<String>,
1033 empty_generic_args: bool,
1035 if missing_type_params.is_empty() {
1039 missing_type_params.iter().map(|n| format!("`{}`", n)).collect::<Vec<_>>().join(", ");
1040 let mut err = struct_span_err!(
1044 "the type parameter{} {} must be explicitly specified",
1045 pluralize!(missing_type_params.len()),
1049 self.tcx().def_span(def_id),
1051 "type parameter{} {} must be specified for this",
1052 pluralize!(missing_type_params.len()),
1056 let mut suggested = false;
1057 if let (Ok(snippet), true) = (
1058 self.tcx().sess.source_map().span_to_snippet(span),
1059 // Don't suggest setting the type params if there are some already: the order is
1060 // tricky to get right and the user will already know what the syntax is.
1063 if snippet.ends_with('>') {
1064 // The user wrote `Trait<'a, T>` or similar. To provide an accurate suggestion
1065 // we would have to preserve the right order. For now, as clearly the user is
1066 // aware of the syntax, we do nothing.
1068 // The user wrote `Iterator`, so we don't have a type we can suggest, but at
1069 // least we can clue them to the correct syntax `Iterator<Type>`.
1070 err.span_suggestion(
1073 "set the type parameter{plural} to the desired type{plural}",
1074 plural = pluralize!(missing_type_params.len()),
1076 format!("{}<{}>", snippet, missing_type_params.join(", ")),
1077 Applicability::HasPlaceholders,
1086 "missing reference{} to {}",
1087 pluralize!(missing_type_params.len()),
1093 "because of the default `Self` reference, type parameters must be \
1094 specified on object types",
1099 /// Instantiates the path for the given trait reference, assuming that it's
1100 /// bound to a valid trait type. Returns the `DefId` of the defining trait.
1101 /// The type _cannot_ be a type other than a trait type.
1103 /// If the `projections` argument is `None`, then assoc type bindings like `Foo<T = X>`
1104 /// are disallowed. Otherwise, they are pushed onto the vector given.
1105 pub fn instantiate_mono_trait_ref(
1107 trait_ref: &hir::TraitRef<'_>,
1109 ) -> ty::TraitRef<'tcx> {
1110 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
1112 self.ast_path_to_mono_trait_ref(
1113 trait_ref.path.span,
1114 trait_ref.trait_def_id().unwrap_or_else(|| FatalError.raise()),
1116 trait_ref.path.segments.last().unwrap(),
1120 /// The given trait-ref must actually be a trait.
1121 pub(super) fn instantiate_poly_trait_ref_inner(
1123 trait_ref: &hir::TraitRef<'_>,
1125 constness: Constness,
1127 bounds: &mut Bounds<'tcx>,
1129 ) -> GenericArgCountResult {
1130 let trait_def_id = trait_ref.trait_def_id().unwrap_or_else(|| FatalError.raise());
1132 debug!("instantiate_poly_trait_ref({:?}, def_id={:?})", trait_ref, trait_def_id);
1134 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
1136 let (substs, assoc_bindings, arg_count) = self.create_substs_for_ast_trait_ref(
1137 trait_ref.path.span,
1140 trait_ref.path.segments.last().unwrap(),
1142 let poly_trait_ref = ty::Binder::bind(ty::TraitRef::new(trait_def_id, substs));
1144 bounds.trait_bounds.push((poly_trait_ref, span, constness));
1146 let mut dup_bindings = FxHashMap::default();
1147 for binding in &assoc_bindings {
1148 // Specify type to assert that error was already reported in `Err` case.
1149 let _: Result<_, ErrorReported> = self.add_predicates_for_ast_type_binding(
1150 trait_ref.hir_ref_id,
1158 // Okay to ignore `Err` because of `ErrorReported` (see above).
1162 "instantiate_poly_trait_ref({:?}, bounds={:?}) -> {:?}",
1163 trait_ref, bounds, poly_trait_ref
1169 /// Given a trait bound like `Debug`, applies that trait bound the given self-type to construct
1170 /// a full trait reference. The resulting trait reference is returned. This may also generate
1171 /// auxiliary bounds, which are added to `bounds`.
1176 /// poly_trait_ref = Iterator<Item = u32>
1180 /// this would return `Foo: Iterator` and add `<Foo as Iterator>::Item = u32` into `bounds`.
1182 /// **A note on binders:** against our usual convention, there is an implied bounder around
1183 /// the `self_ty` and `poly_trait_ref` parameters here. So they may reference bound regions.
1184 /// If for example you had `for<'a> Foo<'a>: Bar<'a>`, then the `self_ty` would be `Foo<'a>`
1185 /// where `'a` is a bound region at depth 0. Similarly, the `poly_trait_ref` would be
1186 /// `Bar<'a>`. The returned poly-trait-ref will have this binder instantiated explicitly,
1188 pub fn instantiate_poly_trait_ref(
1190 poly_trait_ref: &hir::PolyTraitRef<'_>,
1191 constness: Constness,
1193 bounds: &mut Bounds<'tcx>,
1194 ) -> GenericArgCountResult {
1195 self.instantiate_poly_trait_ref_inner(
1196 &poly_trait_ref.trait_ref,
1197 poly_trait_ref.span,
1205 pub fn instantiate_lang_item_trait_ref(
1207 lang_item: hir::LangItem,
1210 args: &GenericArgs<'_>,
1212 bounds: &mut Bounds<'tcx>,
1214 let trait_def_id = self.tcx().require_lang_item(lang_item, Some(span));
1216 let (substs, assoc_bindings, _) =
1217 self.create_substs_for_ast_path(span, trait_def_id, &[], args, false, Some(self_ty));
1218 let poly_trait_ref = ty::Binder::bind(ty::TraitRef::new(trait_def_id, substs));
1219 bounds.trait_bounds.push((poly_trait_ref, span, Constness::NotConst));
1221 let mut dup_bindings = FxHashMap::default();
1222 for binding in assoc_bindings {
1223 let _: Result<_, ErrorReported> = self.add_predicates_for_ast_type_binding(
1235 fn ast_path_to_mono_trait_ref(
1238 trait_def_id: DefId,
1240 trait_segment: &hir::PathSegment<'_>,
1241 ) -> ty::TraitRef<'tcx> {
1242 let (substs, assoc_bindings, _) =
1243 self.create_substs_for_ast_trait_ref(span, trait_def_id, self_ty, trait_segment);
1244 if let Some(b) = assoc_bindings.first() {
1245 AstConv::prohibit_assoc_ty_binding(self.tcx(), b.span);
1247 ty::TraitRef::new(trait_def_id, substs)
1250 /// When the code is using the `Fn` traits directly, instead of the `Fn(A) -> B` syntax, emit
1251 /// an error and attempt to build a reasonable structured suggestion.
1252 fn complain_about_internal_fn_trait(
1255 trait_def_id: DefId,
1256 trait_segment: &'a hir::PathSegment<'a>,
1258 let trait_def = self.tcx().trait_def(trait_def_id);
1260 if !self.tcx().features().unboxed_closures
1261 && trait_segment.generic_args().parenthesized != trait_def.paren_sugar
1263 let sess = &self.tcx().sess.parse_sess;
1264 // For now, require that parenthetical notation be used only with `Fn()` etc.
1265 let (msg, sugg) = if trait_def.paren_sugar {
1267 "the precise format of `Fn`-family traits' type parameters is subject to \
1271 trait_segment.ident,
1275 .and_then(|args| args.args.get(0))
1276 .and_then(|arg| match arg {
1277 hir::GenericArg::Type(ty) => match ty.kind {
1278 hir::TyKind::Tup(t) => t
1280 .map(|e| sess.source_map().span_to_snippet(e.span))
1281 .collect::<Result<Vec<_>, _>>()
1282 .map(|a| a.join(", ")),
1283 _ => sess.source_map().span_to_snippet(ty.span),
1285 .map(|s| format!("({})", s))
1289 .unwrap_or_else(|| "()".to_string()),
1294 .find_map(|b| match (b.ident.name == sym::Output, &b.kind) {
1295 (true, hir::TypeBindingKind::Equality { ty }) => {
1296 sess.source_map().span_to_snippet(ty.span).ok()
1300 .unwrap_or_else(|| "()".to_string()),
1304 ("parenthetical notation is only stable when used with `Fn`-family traits", None)
1306 let mut err = feature_err(sess, sym::unboxed_closures, span, msg);
1307 if let Some(sugg) = sugg {
1308 let msg = "use parenthetical notation instead";
1309 err.span_suggestion(span, msg, sugg, Applicability::MaybeIncorrect);
1315 fn create_substs_for_ast_trait_ref<'a>(
1318 trait_def_id: DefId,
1320 trait_segment: &'a hir::PathSegment<'a>,
1321 ) -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'a, 'tcx>>, GenericArgCountResult) {
1322 debug!("create_substs_for_ast_trait_ref(trait_segment={:?})", trait_segment);
1324 self.complain_about_internal_fn_trait(span, trait_def_id, trait_segment);
1326 self.create_substs_for_ast_path(
1330 trait_segment.generic_args(),
1331 trait_segment.infer_args,
1336 fn trait_defines_associated_type_named(&self, trait_def_id: DefId, assoc_name: Ident) -> bool {
1338 .associated_items(trait_def_id)
1339 .find_by_name_and_kind(self.tcx(), assoc_name, ty::AssocKind::Type, trait_def_id)
1343 // Returns `true` if a bounds list includes `?Sized`.
1344 pub fn is_unsized(&self, ast_bounds: &[hir::GenericBound<'_>], span: Span) -> bool {
1345 let tcx = self.tcx();
1347 // Try to find an unbound in bounds.
1348 let mut unbound = None;
1349 for ab in ast_bounds {
1350 if let &hir::GenericBound::Trait(ref ptr, hir::TraitBoundModifier::Maybe) = ab {
1351 if unbound.is_none() {
1352 unbound = Some(&ptr.trait_ref);
1358 "type parameter has more than one relaxed default \
1359 bound, only one is supported"
1366 let kind_id = tcx.lang_items().require(SizedTraitLangItem);
1369 // FIXME(#8559) currently requires the unbound to be built-in.
1370 if let Ok(kind_id) = kind_id {
1371 if tpb.path.res != Res::Def(DefKind::Trait, kind_id) {
1374 "default bound relaxed for a type parameter, but \
1375 this does nothing because the given bound is not \
1376 a default; only `?Sized` is supported",
1381 _ if kind_id.is_ok() => {
1384 // No lang item for `Sized`, so we can't add it as a bound.
1391 /// This helper takes a *converted* parameter type (`param_ty`)
1392 /// and an *unconverted* list of bounds:
1395 /// fn foo<T: Debug>
1396 /// ^ ^^^^^ `ast_bounds` parameter, in HIR form
1398 /// `param_ty`, in ty form
1401 /// It adds these `ast_bounds` into the `bounds` structure.
1403 /// **A note on binders:** there is an implied binder around
1404 /// `param_ty` and `ast_bounds`. See `instantiate_poly_trait_ref`
1405 /// for more details.
1409 ast_bounds: &[hir::GenericBound<'_>],
1410 bounds: &mut Bounds<'tcx>,
1412 let mut trait_bounds = Vec::new();
1413 let mut region_bounds = Vec::new();
1415 let constness = self.default_constness_for_trait_bounds();
1416 for ast_bound in ast_bounds {
1418 hir::GenericBound::Trait(ref b, hir::TraitBoundModifier::None) => {
1419 trait_bounds.push((b, constness))
1421 hir::GenericBound::Trait(ref b, hir::TraitBoundModifier::MaybeConst) => {
1422 trait_bounds.push((b, Constness::NotConst))
1424 hir::GenericBound::Trait(_, hir::TraitBoundModifier::Maybe) => {}
1425 hir::GenericBound::LangItemTrait(lang_item, span, hir_id, args) => self
1426 .instantiate_lang_item_trait_ref(
1427 lang_item, span, hir_id, args, param_ty, bounds,
1429 hir::GenericBound::Outlives(ref l) => region_bounds.push(l),
1433 for (bound, constness) in trait_bounds {
1434 let _ = self.instantiate_poly_trait_ref(bound, constness, param_ty, bounds);
1437 bounds.region_bounds.extend(
1438 region_bounds.into_iter().map(|r| (self.ast_region_to_region(r, None), r.span)),
1442 /// Translates a list of bounds from the HIR into the `Bounds` data structure.
1443 /// The self-type for the bounds is given by `param_ty`.
1448 /// fn foo<T: Bar + Baz>() { }
1449 /// ^ ^^^^^^^^^ ast_bounds
1453 /// The `sized_by_default` parameter indicates if, in this context, the `param_ty` should be
1454 /// considered `Sized` unless there is an explicit `?Sized` bound. This would be true in the
1455 /// example above, but is not true in supertrait listings like `trait Foo: Bar + Baz`.
1457 /// `span` should be the declaration size of the parameter.
1458 pub fn compute_bounds(
1461 ast_bounds: &[hir::GenericBound<'_>],
1462 sized_by_default: SizedByDefault,
1465 let mut bounds = Bounds::default();
1467 self.add_bounds(param_ty, ast_bounds, &mut bounds);
1468 bounds.trait_bounds.sort_by_key(|(t, _, _)| t.def_id());
1470 bounds.implicitly_sized = if let SizedByDefault::Yes = sized_by_default {
1471 if !self.is_unsized(ast_bounds, span) { Some(span) } else { None }
1479 /// Given an HIR binding like `Item = Foo` or `Item: Foo`, pushes the corresponding predicates
1482 /// **A note on binders:** given something like `T: for<'a> Iterator<Item = &'a u32>`, the
1483 /// `trait_ref` here will be `for<'a> T: Iterator`. The `binding` data however is from *inside*
1484 /// the binder (e.g., `&'a u32`) and hence may reference bound regions.
1485 fn add_predicates_for_ast_type_binding(
1487 hir_ref_id: hir::HirId,
1488 trait_ref: ty::PolyTraitRef<'tcx>,
1489 binding: &ConvertedBinding<'_, 'tcx>,
1490 bounds: &mut Bounds<'tcx>,
1492 dup_bindings: &mut FxHashMap<DefId, Span>,
1494 ) -> Result<(), ErrorReported> {
1495 let tcx = self.tcx();
1498 // Given something like `U: SomeTrait<T = X>`, we want to produce a
1499 // predicate like `<U as SomeTrait>::T = X`. This is somewhat
1500 // subtle in the event that `T` is defined in a supertrait of
1501 // `SomeTrait`, because in that case we need to upcast.
1503 // That is, consider this case:
1506 // trait SubTrait: SuperTrait<i32> { }
1507 // trait SuperTrait<A> { type T; }
1509 // ... B: SubTrait<T = foo> ...
1512 // We want to produce `<B as SuperTrait<i32>>::T == foo`.
1514 // Find any late-bound regions declared in `ty` that are not
1515 // declared in the trait-ref. These are not well-formed.
1519 // for<'a> <T as Iterator>::Item = &'a str // <-- 'a is bad
1520 // for<'a> <T as FnMut<(&'a u32,)>>::Output = &'a str // <-- 'a is ok
1521 if let ConvertedBindingKind::Equality(ty) = binding.kind {
1522 let late_bound_in_trait_ref =
1523 tcx.collect_constrained_late_bound_regions(&trait_ref);
1524 let late_bound_in_ty =
1525 tcx.collect_referenced_late_bound_regions(&ty::Binder::bind(ty));
1526 debug!("late_bound_in_trait_ref = {:?}", late_bound_in_trait_ref);
1527 debug!("late_bound_in_ty = {:?}", late_bound_in_ty);
1529 // FIXME: point at the type params that don't have appropriate lifetimes:
1530 // struct S1<F: for<'a> Fn(&i32, &i32) -> &'a i32>(F);
1531 // ---- ---- ^^^^^^^
1532 self.validate_late_bound_regions(
1533 late_bound_in_trait_ref,
1540 "binding for associated type `{}` references {}, \
1541 which does not appear in the trait input types",
1551 if self.trait_defines_associated_type_named(trait_ref.def_id(), binding.item_name) {
1552 // Simple case: X is defined in the current trait.
1555 // Otherwise, we have to walk through the supertraits to find
1557 self.one_bound_for_assoc_type(
1558 || traits::supertraits(tcx, trait_ref),
1559 || trait_ref.print_only_trait_path().to_string(),
1562 || match binding.kind {
1563 ConvertedBindingKind::Equality(ty) => Some(ty.to_string()),
1569 let (assoc_ident, def_scope) =
1570 tcx.adjust_ident_and_get_scope(binding.item_name, candidate.def_id(), hir_ref_id);
1572 // We have already adjusted the item name above, so compare with `ident.normalize_to_macros_2_0()` instead
1573 // of calling `filter_by_name_and_kind`.
1575 .associated_items(candidate.def_id())
1576 .filter_by_name_unhygienic(assoc_ident.name)
1578 i.kind == ty::AssocKind::Type && i.ident.normalize_to_macros_2_0() == assoc_ident
1580 .expect("missing associated type");
1582 if !assoc_ty.vis.is_accessible_from(def_scope, tcx) {
1586 &format!("associated type `{}` is private", binding.item_name),
1588 .span_label(binding.span, "private associated type")
1591 tcx.check_stability(assoc_ty.def_id, Some(hir_ref_id), binding.span);
1595 .entry(assoc_ty.def_id)
1596 .and_modify(|prev_span| {
1601 "the value of the associated type `{}` (from trait `{}`) \
1602 is already specified",
1604 tcx.def_path_str(assoc_ty.container.id())
1606 .span_label(binding.span, "re-bound here")
1607 .span_label(*prev_span, format!("`{}` bound here first", binding.item_name))
1610 .or_insert(binding.span);
1613 match binding.kind {
1614 ConvertedBindingKind::Equality(ref ty) => {
1615 // "Desugar" a constraint like `T: Iterator<Item = u32>` this to
1616 // the "projection predicate" for:
1618 // `<T as Iterator>::Item = u32`
1619 bounds.projection_bounds.push((
1620 candidate.map_bound(|trait_ref| ty::ProjectionPredicate {
1621 projection_ty: ty::ProjectionTy::from_ref_and_name(
1631 ConvertedBindingKind::Constraint(ast_bounds) => {
1632 // "Desugar" a constraint like `T: Iterator<Item: Debug>` to
1634 // `<T as Iterator>::Item: Debug`
1636 // Calling `skip_binder` is okay, because `add_bounds` expects the `param_ty`
1637 // parameter to have a skipped binder.
1638 let param_ty = tcx.mk_projection(assoc_ty.def_id, candidate.skip_binder().substs);
1639 self.add_bounds(param_ty, ast_bounds, bounds);
1649 item_segment: &hir::PathSegment<'_>,
1651 let substs = self.ast_path_substs_for_ty(span, did, item_segment);
1652 self.normalize_ty(span, self.tcx().at(span).type_of(did).subst(self.tcx(), substs))
1655 fn conv_object_ty_poly_trait_ref(
1658 trait_bounds: &[hir::PolyTraitRef<'_>],
1659 lifetime: &hir::Lifetime,
1662 let tcx = self.tcx();
1664 let mut bounds = Bounds::default();
1665 let mut potential_assoc_types = Vec::new();
1666 let dummy_self = self.tcx().types.trait_object_dummy_self;
1667 for trait_bound in trait_bounds.iter().rev() {
1668 if let GenericArgCountResult {
1670 Err(GenericArgCountMismatch { invalid_args: cur_potential_assoc_types, .. }),
1672 } = self.instantiate_poly_trait_ref(
1674 Constness::NotConst,
1678 potential_assoc_types.extend(cur_potential_assoc_types.into_iter());
1682 // Expand trait aliases recursively and check that only one regular (non-auto) trait
1683 // is used and no 'maybe' bounds are used.
1684 let expanded_traits =
1685 traits::expand_trait_aliases(tcx, bounds.trait_bounds.iter().map(|&(a, b, _)| (a, b)));
1686 let (mut auto_traits, regular_traits): (Vec<_>, Vec<_>) =
1687 expanded_traits.partition(|i| tcx.trait_is_auto(i.trait_ref().def_id()));
1688 if regular_traits.len() > 1 {
1689 let first_trait = ®ular_traits[0];
1690 let additional_trait = ®ular_traits[1];
1691 let mut err = struct_span_err!(
1693 additional_trait.bottom().1,
1695 "only auto traits can be used as additional traits in a trait object"
1697 additional_trait.label_with_exp_info(
1699 "additional non-auto trait",
1702 first_trait.label_with_exp_info(&mut err, "first non-auto trait", "first use");
1704 "consider creating a new trait with all of these as super-traits and using that \
1705 trait here instead: `trait NewTrait: {} {{}}`",
1708 .map(|t| t.trait_ref().print_only_trait_path().to_string())
1709 .collect::<Vec<_>>()
1713 "auto-traits like `Send` and `Sync` are traits that have special properties; \
1714 for more information on them, visit \
1715 <https://doc.rust-lang.org/reference/special-types-and-traits.html#auto-traits>",
1720 if regular_traits.is_empty() && auto_traits.is_empty() {
1725 "at least one trait is required for an object type"
1728 return tcx.ty_error();
1731 // Check that there are no gross object safety violations;
1732 // most importantly, that the supertraits don't contain `Self`,
1734 for item in ®ular_traits {
1735 let object_safety_violations =
1736 astconv_object_safety_violations(tcx, item.trait_ref().def_id());
1737 if !object_safety_violations.is_empty() {
1738 report_object_safety_error(
1741 item.trait_ref().def_id(),
1742 &object_safety_violations[..],
1745 return tcx.ty_error();
1749 // Use a `BTreeSet` to keep output in a more consistent order.
1750 let mut associated_types: FxHashMap<Span, BTreeSet<DefId>> = FxHashMap::default();
1752 let regular_traits_refs_spans = bounds
1755 .filter(|(trait_ref, _, _)| !tcx.trait_is_auto(trait_ref.def_id()));
1757 for (base_trait_ref, span, constness) in regular_traits_refs_spans {
1758 assert_eq!(constness, Constness::NotConst);
1760 for obligation in traits::elaborate_trait_ref(tcx, base_trait_ref) {
1762 "conv_object_ty_poly_trait_ref: observing object predicate `{:?}`",
1763 obligation.predicate
1766 match obligation.predicate.skip_binders() {
1767 ty::PredicateAtom::Trait(pred, _) => {
1768 let pred = ty::Binder::bind(pred);
1769 associated_types.entry(span).or_default().extend(
1770 tcx.associated_items(pred.def_id())
1771 .in_definition_order()
1772 .filter(|item| item.kind == ty::AssocKind::Type)
1773 .map(|item| item.def_id),
1776 ty::PredicateAtom::Projection(pred) => {
1777 let pred = ty::Binder::bind(pred);
1778 // A `Self` within the original bound will be substituted with a
1779 // `trait_object_dummy_self`, so check for that.
1780 let references_self =
1781 pred.skip_binder().ty.walk().any(|arg| arg == dummy_self.into());
1783 // If the projection output contains `Self`, force the user to
1784 // elaborate it explicitly to avoid a lot of complexity.
1786 // The "classicaly useful" case is the following:
1788 // trait MyTrait: FnMut() -> <Self as MyTrait>::MyOutput {
1793 // Here, the user could theoretically write `dyn MyTrait<Output = X>`,
1794 // but actually supporting that would "expand" to an infinitely-long type
1795 // `fix $ τ → dyn MyTrait<MyOutput = X, Output = <τ as MyTrait>::MyOutput`.
1797 // Instead, we force the user to write
1798 // `dyn MyTrait<MyOutput = X, Output = X>`, which is uglier but works. See
1799 // the discussion in #56288 for alternatives.
1800 if !references_self {
1801 // Include projections defined on supertraits.
1802 bounds.projection_bounds.push((pred, span));
1810 for (projection_bound, _) in &bounds.projection_bounds {
1811 for def_ids in associated_types.values_mut() {
1812 def_ids.remove(&projection_bound.projection_def_id());
1816 self.complain_about_missing_associated_types(
1818 potential_assoc_types,
1822 // De-duplicate auto traits so that, e.g., `dyn Trait + Send + Send` is the same as
1823 // `dyn Trait + Send`.
1824 auto_traits.sort_by_key(|i| i.trait_ref().def_id());
1825 auto_traits.dedup_by_key(|i| i.trait_ref().def_id());
1826 debug!("regular_traits: {:?}", regular_traits);
1827 debug!("auto_traits: {:?}", auto_traits);
1829 // Transform a `PolyTraitRef` into a `PolyExistentialTraitRef` by
1830 // removing the dummy `Self` type (`trait_object_dummy_self`).
1831 let trait_ref_to_existential = |trait_ref: ty::TraitRef<'tcx>| {
1832 if trait_ref.self_ty() != dummy_self {
1833 // FIXME: There appears to be a missing filter on top of `expand_trait_aliases`,
1834 // which picks up non-supertraits where clauses - but also, the object safety
1835 // completely ignores trait aliases, which could be object safety hazards. We
1836 // `delay_span_bug` here to avoid an ICE in stable even when the feature is
1837 // disabled. (#66420)
1838 tcx.sess.delay_span_bug(
1841 "trait_ref_to_existential called on {:?} with non-dummy Self",
1846 ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref)
1849 // Erase the `dummy_self` (`trait_object_dummy_self`) used above.
1850 let existential_trait_refs =
1851 regular_traits.iter().map(|i| i.trait_ref().map_bound(trait_ref_to_existential));
1852 let existential_projections = bounds.projection_bounds.iter().map(|(bound, _)| {
1853 bound.map_bound(|b| {
1854 let trait_ref = trait_ref_to_existential(b.projection_ty.trait_ref(tcx));
1855 ty::ExistentialProjection {
1857 item_def_id: b.projection_ty.item_def_id,
1858 substs: trait_ref.substs,
1863 // Calling `skip_binder` is okay because the predicates are re-bound.
1864 let regular_trait_predicates = existential_trait_refs
1865 .map(|trait_ref| ty::ExistentialPredicate::Trait(trait_ref.skip_binder()));
1866 let auto_trait_predicates = auto_traits
1868 .map(|trait_ref| ty::ExistentialPredicate::AutoTrait(trait_ref.trait_ref().def_id()));
1869 let mut v = regular_trait_predicates
1870 .chain(auto_trait_predicates)
1872 existential_projections
1873 .map(|x| ty::ExistentialPredicate::Projection(x.skip_binder())),
1875 .collect::<SmallVec<[_; 8]>>();
1876 v.sort_by(|a, b| a.stable_cmp(tcx, b));
1878 let existential_predicates = ty::Binder::bind(tcx.mk_existential_predicates(v.into_iter()));
1880 // Use explicitly-specified region bound.
1881 let region_bound = if !lifetime.is_elided() {
1882 self.ast_region_to_region(lifetime, None)
1884 self.compute_object_lifetime_bound(span, existential_predicates).unwrap_or_else(|| {
1885 if tcx.named_region(lifetime.hir_id).is_some() {
1886 self.ast_region_to_region(lifetime, None)
1888 self.re_infer(None, span).unwrap_or_else(|| {
1889 let mut err = struct_span_err!(
1893 "the lifetime bound for this object type cannot be deduced \
1894 from context; please supply an explicit bound"
1897 // We will have already emitted an error E0106 complaining about a
1898 // missing named lifetime in `&dyn Trait`, so we elide this one.
1903 tcx.lifetimes.re_static
1908 debug!("region_bound: {:?}", region_bound);
1910 let ty = tcx.mk_dynamic(existential_predicates, region_bound);
1911 debug!("trait_object_type: {:?}", ty);
1915 /// When there are any missing associated types, emit an E0191 error and attempt to supply a
1916 /// reasonable suggestion on how to write it. For the case of multiple associated types in the
1917 /// same trait bound have the same name (as they come from different super-traits), we instead
1918 /// emit a generic note suggesting using a `where` clause to constraint instead.
1919 fn complain_about_missing_associated_types(
1921 associated_types: FxHashMap<Span, BTreeSet<DefId>>,
1922 potential_assoc_types: Vec<Span>,
1923 trait_bounds: &[hir::PolyTraitRef<'_>],
1925 if associated_types.values().all(|v| v.is_empty()) {
1928 let tcx = self.tcx();
1929 // FIXME: Marked `mut` so that we can replace the spans further below with a more
1930 // appropriate one, but this should be handled earlier in the span assignment.
1931 let mut associated_types: FxHashMap<Span, Vec<_>> = associated_types
1933 .map(|(span, def_ids)| {
1934 (span, def_ids.into_iter().map(|did| tcx.associated_item(did)).collect())
1937 let mut names = vec![];
1939 // Account for things like `dyn Foo + 'a`, like in tests `issue-22434.rs` and
1940 // `issue-22560.rs`.
1941 let mut trait_bound_spans: Vec<Span> = vec![];
1942 for (span, items) in &associated_types {
1943 if !items.is_empty() {
1944 trait_bound_spans.push(*span);
1946 for assoc_item in items {
1947 let trait_def_id = assoc_item.container.id();
1949 "`{}` (from trait `{}`)",
1951 tcx.def_path_str(trait_def_id),
1955 if let ([], [bound]) = (&potential_assoc_types[..], &trait_bounds) {
1956 match &bound.trait_ref.path.segments[..] {
1957 // FIXME: `trait_ref.path.span` can point to a full path with multiple
1958 // segments, even though `trait_ref.path.segments` is of length `1`. Work
1959 // around that bug here, even though it should be fixed elsewhere.
1960 // This would otherwise cause an invalid suggestion. For an example, look at
1961 // `src/test/ui/issues/issue-28344.rs` where instead of the following:
1963 // error[E0191]: the value of the associated type `Output`
1964 // (from trait `std::ops::BitXor`) must be specified
1965 // --> $DIR/issue-28344.rs:4:17
1967 // LL | let x: u8 = BitXor::bitor(0 as u8, 0 as u8);
1968 // | ^^^^^^ help: specify the associated type:
1969 // | `BitXor<Output = Type>`
1973 // error[E0191]: the value of the associated type `Output`
1974 // (from trait `std::ops::BitXor`) must be specified
1975 // --> $DIR/issue-28344.rs:4:17
1977 // LL | let x: u8 = BitXor::bitor(0 as u8, 0 as u8);
1978 // | ^^^^^^^^^^^^^ help: specify the associated type:
1979 // | `BitXor::bitor<Output = Type>`
1980 [segment] if segment.args.is_none() => {
1981 trait_bound_spans = vec![segment.ident.span];
1982 associated_types = associated_types
1984 .map(|(_, items)| (segment.ident.span, items))
1991 trait_bound_spans.sort();
1992 let mut err = struct_span_err!(
1996 "the value of the associated type{} {} must be specified",
1997 pluralize!(names.len()),
2000 let mut suggestions = vec![];
2001 let mut types_count = 0;
2002 let mut where_constraints = vec![];
2003 for (span, assoc_items) in &associated_types {
2004 let mut names: FxHashMap<_, usize> = FxHashMap::default();
2005 for item in assoc_items {
2007 *names.entry(item.ident.name).or_insert(0) += 1;
2009 let mut dupes = false;
2010 for item in assoc_items {
2011 let prefix = if names[&item.ident.name] > 1 {
2012 let trait_def_id = item.container.id();
2014 format!("{}::", tcx.def_path_str(trait_def_id))
2018 if let Some(sp) = tcx.hir().span_if_local(item.def_id) {
2019 err.span_label(sp, format!("`{}{}` defined here", prefix, item.ident));
2022 if potential_assoc_types.len() == assoc_items.len() {
2023 // Only suggest when the amount of missing associated types equals the number of
2024 // extra type arguments present, as that gives us a relatively high confidence
2025 // that the user forgot to give the associtated type's name. The canonical
2026 // example would be trying to use `Iterator<isize>` instead of
2027 // `Iterator<Item = isize>`.
2028 for (potential, item) in potential_assoc_types.iter().zip(assoc_items.iter()) {
2029 if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(*potential) {
2030 suggestions.push((*potential, format!("{} = {}", item.ident, snippet)));
2033 } else if let (Ok(snippet), false) =
2034 (tcx.sess.source_map().span_to_snippet(*span), dupes)
2037 assoc_items.iter().map(|item| format!("{} = Type", item.ident)).collect();
2038 let code = if snippet.ends_with('>') {
2039 // The user wrote `Trait<'a>` or similar and we don't have a type we can
2040 // suggest, but at least we can clue them to the correct syntax
2041 // `Trait<'a, Item = Type>` while accounting for the `<'a>` in the
2043 format!("{}, {}>", &snippet[..snippet.len() - 1], types.join(", "))
2045 // The user wrote `Iterator`, so we don't have a type we can suggest, but at
2046 // least we can clue them to the correct syntax `Iterator<Item = Type>`.
2047 format!("{}<{}>", snippet, types.join(", "))
2049 suggestions.push((*span, code));
2051 where_constraints.push(*span);
2054 let where_msg = "consider introducing a new type parameter, adding `where` constraints \
2055 using the fully-qualified path to the associated types";
2056 if !where_constraints.is_empty() && suggestions.is_empty() {
2057 // If there are duplicates associated type names and a single trait bound do not
2058 // use structured suggestion, it means that there are multiple super-traits with
2059 // the same associated type name.
2060 err.help(where_msg);
2062 if suggestions.len() != 1 {
2063 // We don't need this label if there's an inline suggestion, show otherwise.
2064 for (span, assoc_items) in &associated_types {
2065 let mut names: FxHashMap<_, usize> = FxHashMap::default();
2066 for item in assoc_items {
2068 *names.entry(item.ident.name).or_insert(0) += 1;
2070 let mut label = vec![];
2071 for item in assoc_items {
2072 let postfix = if names[&item.ident.name] > 1 {
2073 let trait_def_id = item.container.id();
2074 format!(" (from trait `{}`)", tcx.def_path_str(trait_def_id))
2078 label.push(format!("`{}`{}", item.ident, postfix));
2080 if !label.is_empty() {
2084 "associated type{} {} must be specified",
2085 pluralize!(label.len()),
2092 if !suggestions.is_empty() {
2093 err.multipart_suggestion(
2094 &format!("specify the associated type{}", pluralize!(types_count)),
2096 Applicability::HasPlaceholders,
2098 if !where_constraints.is_empty() {
2099 err.span_help(where_constraints, where_msg);
2105 fn report_ambiguous_associated_type(
2112 let mut err = struct_span_err!(self.tcx().sess, span, E0223, "ambiguous associated type");
2113 if let (Some(_), Ok(snippet)) = (
2114 self.tcx().sess.confused_type_with_std_module.borrow().get(&span),
2115 self.tcx().sess.source_map().span_to_snippet(span),
2117 err.span_suggestion(
2119 "you are looking for the module in `std`, not the primitive type",
2120 format!("std::{}", snippet),
2121 Applicability::MachineApplicable,
2124 err.span_suggestion(
2126 "use fully-qualified syntax",
2127 format!("<{} as {}>::{}", type_str, trait_str, name),
2128 Applicability::HasPlaceholders,
2134 // Search for a bound on a type parameter which includes the associated item
2135 // given by `assoc_name`. `ty_param_def_id` is the `DefId` of the type parameter
2136 // This function will fail if there are no suitable bounds or there is
2138 fn find_bound_for_assoc_item(
2140 ty_param_def_id: LocalDefId,
2143 ) -> Result<ty::PolyTraitRef<'tcx>, ErrorReported> {
2144 let tcx = self.tcx();
2147 "find_bound_for_assoc_item(ty_param_def_id={:?}, assoc_name={:?}, span={:?})",
2148 ty_param_def_id, assoc_name, span,
2152 &self.get_type_parameter_bounds(span, ty_param_def_id.to_def_id()).predicates;
2154 debug!("find_bound_for_assoc_item: predicates={:#?}", predicates);
2156 let param_hir_id = tcx.hir().local_def_id_to_hir_id(ty_param_def_id);
2157 let param_name = tcx.hir().ty_param_name(param_hir_id);
2158 self.one_bound_for_assoc_type(
2160 traits::transitive_bounds(
2162 predicates.iter().filter_map(|(p, _)| p.to_opt_poly_trait_ref()),
2165 || param_name.to_string(),
2172 // Checks that `bounds` contains exactly one element and reports appropriate
2173 // errors otherwise.
2174 fn one_bound_for_assoc_type<I>(
2176 all_candidates: impl Fn() -> I,
2177 ty_param_name: impl Fn() -> String,
2180 is_equality: impl Fn() -> Option<String>,
2181 ) -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
2183 I: Iterator<Item = ty::PolyTraitRef<'tcx>>,
2185 let mut matching_candidates = all_candidates()
2186 .filter(|r| self.trait_defines_associated_type_named(r.def_id(), assoc_name));
2188 let bound = match matching_candidates.next() {
2189 Some(bound) => bound,
2191 self.complain_about_assoc_type_not_found(
2197 return Err(ErrorReported);
2201 debug!("one_bound_for_assoc_type: bound = {:?}", bound);
2203 if let Some(bound2) = matching_candidates.next() {
2204 debug!("one_bound_for_assoc_type: bound2 = {:?}", bound2);
2206 let is_equality = is_equality();
2207 let bounds = iter::once(bound).chain(iter::once(bound2)).chain(matching_candidates);
2208 let mut err = if is_equality.is_some() {
2209 // More specific Error Index entry.
2214 "ambiguous associated type `{}` in bounds of `{}`",
2223 "ambiguous associated type `{}` in bounds of `{}`",
2228 err.span_label(span, format!("ambiguous associated type `{}`", assoc_name));
2230 let mut where_bounds = vec![];
2231 for bound in bounds {
2232 let bound_id = bound.def_id();
2233 let bound_span = self
2235 .associated_items(bound_id)
2236 .find_by_name_and_kind(self.tcx(), assoc_name, ty::AssocKind::Type, bound_id)
2237 .and_then(|item| self.tcx().hir().span_if_local(item.def_id));
2239 if let Some(bound_span) = bound_span {
2243 "ambiguous `{}` from `{}`",
2245 bound.print_only_trait_path(),
2248 if let Some(constraint) = &is_equality {
2249 where_bounds.push(format!(
2250 " T: {trait}::{assoc} = {constraint}",
2251 trait=bound.print_only_trait_path(),
2253 constraint=constraint,
2256 err.span_suggestion(
2258 "use fully qualified syntax to disambiguate",
2262 bound.print_only_trait_path(),
2265 Applicability::MaybeIncorrect,
2270 "associated type `{}` could derive from `{}`",
2272 bound.print_only_trait_path(),
2276 if !where_bounds.is_empty() {
2278 "consider introducing a new type parameter `T` and adding `where` constraints:\
2279 \n where\n T: {},\n{}",
2281 where_bounds.join(",\n"),
2285 if !where_bounds.is_empty() {
2286 return Err(ErrorReported);
2292 fn complain_about_assoc_type_not_found<I>(
2294 all_candidates: impl Fn() -> I,
2295 ty_param_name: &str,
2299 I: Iterator<Item = ty::PolyTraitRef<'tcx>>,
2301 // The fallback span is needed because `assoc_name` might be an `Fn()`'s `Output` without a
2302 // valid span, so we point at the whole path segment instead.
2303 let span = if assoc_name.span != DUMMY_SP { assoc_name.span } else { span };
2304 let mut err = struct_span_err!(
2308 "associated type `{}` not found for `{}`",
2313 let all_candidate_names: Vec<_> = all_candidates()
2314 .map(|r| self.tcx().associated_items(r.def_id()).in_definition_order())
2317 |item| if item.kind == ty::AssocKind::Type { Some(item.ident.name) } else { None },
2321 if let (Some(suggested_name), true) = (
2322 find_best_match_for_name(all_candidate_names.iter(), assoc_name.name, None),
2323 assoc_name.span != DUMMY_SP,
2325 err.span_suggestion(
2327 "there is an associated type with a similar name",
2328 suggested_name.to_string(),
2329 Applicability::MaybeIncorrect,
2332 err.span_label(span, format!("associated type `{}` not found", assoc_name));
2338 // Create a type from a path to an associated type.
2339 // For a path `A::B::C::D`, `qself_ty` and `qself_def` are the type and def for `A::B::C`
2340 // and item_segment is the path segment for `D`. We return a type and a def for
2342 // Will fail except for `T::A` and `Self::A`; i.e., if `qself_ty`/`qself_def` are not a type
2343 // parameter or `Self`.
2344 pub fn associated_path_to_ty(
2346 hir_ref_id: hir::HirId,
2350 assoc_segment: &hir::PathSegment<'_>,
2351 permit_variants: bool,
2352 ) -> Result<(Ty<'tcx>, DefKind, DefId), ErrorReported> {
2353 let tcx = self.tcx();
2354 let assoc_ident = assoc_segment.ident;
2356 debug!("associated_path_to_ty: {:?}::{}", qself_ty, assoc_ident);
2358 // Check if we have an enum variant.
2359 let mut variant_resolution = None;
2360 if let ty::Adt(adt_def, _) = qself_ty.kind {
2361 if adt_def.is_enum() {
2362 let variant_def = adt_def
2365 .find(|vd| tcx.hygienic_eq(assoc_ident, vd.ident, adt_def.did));
2366 if let Some(variant_def) = variant_def {
2367 if permit_variants {
2368 tcx.check_stability(variant_def.def_id, Some(hir_ref_id), span);
2369 self.prohibit_generics(slice::from_ref(assoc_segment));
2370 return Ok((qself_ty, DefKind::Variant, variant_def.def_id));
2372 variant_resolution = Some(variant_def.def_id);
2378 // Find the type of the associated item, and the trait where the associated
2379 // item is declared.
2380 let bound = match (&qself_ty.kind, qself_res) {
2381 (_, Res::SelfTy(Some(_), Some(impl_def_id))) => {
2382 // `Self` in an impl of a trait -- we have a concrete self type and a
2384 let trait_ref = match tcx.impl_trait_ref(impl_def_id) {
2385 Some(trait_ref) => trait_ref,
2387 // A cycle error occurred, most likely.
2388 return Err(ErrorReported);
2392 self.one_bound_for_assoc_type(
2393 || traits::supertraits(tcx, ty::Binder::bind(trait_ref)),
2394 || "Self".to_string(),
2402 Res::SelfTy(Some(param_did), None) | Res::Def(DefKind::TyParam, param_did),
2403 ) => self.find_bound_for_assoc_item(param_did.expect_local(), assoc_ident, span)?,
2405 if variant_resolution.is_some() {
2406 // Variant in type position
2407 let msg = format!("expected type, found variant `{}`", assoc_ident);
2408 tcx.sess.span_err(span, &msg);
2409 } else if qself_ty.is_enum() {
2410 let mut err = struct_span_err!(
2414 "no variant named `{}` found for enum `{}`",
2419 let adt_def = qself_ty.ty_adt_def().expect("enum is not an ADT");
2420 if let Some(suggested_name) = find_best_match_for_name(
2421 adt_def.variants.iter().map(|variant| &variant.ident.name),
2425 err.span_suggestion(
2427 "there is a variant with a similar name",
2428 suggested_name.to_string(),
2429 Applicability::MaybeIncorrect,
2434 format!("variant not found in `{}`", qself_ty),
2438 if let Some(sp) = tcx.hir().span_if_local(adt_def.did) {
2439 let sp = tcx.sess.source_map().guess_head_span(sp);
2440 err.span_label(sp, format!("variant `{}` not found here", assoc_ident));
2444 } else if !qself_ty.references_error() {
2445 // Don't print `TyErr` to the user.
2446 self.report_ambiguous_associated_type(
2448 &qself_ty.to_string(),
2453 return Err(ErrorReported);
2457 let trait_did = bound.def_id();
2458 let (assoc_ident, def_scope) =
2459 tcx.adjust_ident_and_get_scope(assoc_ident, trait_did, hir_ref_id);
2461 // We have already adjusted the item name above, so compare with `ident.normalize_to_macros_2_0()` instead
2462 // of calling `filter_by_name_and_kind`.
2464 .associated_items(trait_did)
2465 .in_definition_order()
2467 i.kind.namespace() == Namespace::TypeNS
2468 && i.ident.normalize_to_macros_2_0() == assoc_ident
2470 .expect("missing associated type");
2472 let ty = self.projected_ty_from_poly_trait_ref(span, item.def_id, assoc_segment, bound);
2473 let ty = self.normalize_ty(span, ty);
2475 let kind = DefKind::AssocTy;
2476 if !item.vis.is_accessible_from(def_scope, tcx) {
2477 let kind = kind.descr(item.def_id);
2478 let msg = format!("{} `{}` is private", kind, assoc_ident);
2480 .struct_span_err(span, &msg)
2481 .span_label(span, &format!("private {}", kind))
2484 tcx.check_stability(item.def_id, Some(hir_ref_id), span);
2486 if let Some(variant_def_id) = variant_resolution {
2487 tcx.struct_span_lint_hir(AMBIGUOUS_ASSOCIATED_ITEMS, hir_ref_id, span, |lint| {
2488 let mut err = lint.build("ambiguous associated item");
2489 let mut could_refer_to = |kind: DefKind, def_id, also| {
2490 let note_msg = format!(
2491 "`{}` could{} refer to the {} defined here",
2496 err.span_note(tcx.def_span(def_id), ¬e_msg);
2499 could_refer_to(DefKind::Variant, variant_def_id, "");
2500 could_refer_to(kind, item.def_id, " also");
2502 err.span_suggestion(
2504 "use fully-qualified syntax",
2505 format!("<{} as {}>::{}", qself_ty, tcx.item_name(trait_did), assoc_ident),
2506 Applicability::MachineApplicable,
2512 Ok((ty, kind, item.def_id))
2518 opt_self_ty: Option<Ty<'tcx>>,
2520 trait_segment: &hir::PathSegment<'_>,
2521 item_segment: &hir::PathSegment<'_>,
2523 let tcx = self.tcx();
2525 let trait_def_id = tcx.parent(item_def_id).unwrap();
2527 debug!("qpath_to_ty: trait_def_id={:?}", trait_def_id);
2529 let self_ty = if let Some(ty) = opt_self_ty {
2532 let path_str = tcx.def_path_str(trait_def_id);
2534 let def_id = self.item_def_id();
2536 debug!("qpath_to_ty: self.item_def_id()={:?}", def_id);
2538 let parent_def_id = def_id
2539 .and_then(|def_id| {
2540 def_id.as_local().map(|def_id| tcx.hir().local_def_id_to_hir_id(def_id))
2542 .map(|hir_id| tcx.hir().get_parent_did(hir_id).to_def_id());
2544 debug!("qpath_to_ty: parent_def_id={:?}", parent_def_id);
2546 // If the trait in segment is the same as the trait defining the item,
2547 // use the `<Self as ..>` syntax in the error.
2548 let is_part_of_self_trait_constraints = def_id == Some(trait_def_id);
2549 let is_part_of_fn_in_self_trait = parent_def_id == Some(trait_def_id);
2551 let type_name = if is_part_of_self_trait_constraints || is_part_of_fn_in_self_trait {
2557 self.report_ambiguous_associated_type(
2561 item_segment.ident.name,
2563 return tcx.ty_error();
2566 debug!("qpath_to_ty: self_type={:?}", self_ty);
2568 let trait_ref = self.ast_path_to_mono_trait_ref(span, trait_def_id, self_ty, trait_segment);
2570 let item_substs = self.create_substs_for_associated_item(
2578 debug!("qpath_to_ty: trait_ref={:?}", trait_ref);
2580 self.normalize_ty(span, tcx.mk_projection(item_def_id, item_substs))
2583 pub fn prohibit_generics<'a, T: IntoIterator<Item = &'a hir::PathSegment<'a>>>(
2587 let mut has_err = false;
2588 for segment in segments {
2589 let (mut err_for_lt, mut err_for_ty, mut err_for_ct) = (false, false, false);
2590 for arg in segment.generic_args().args {
2591 let (span, kind) = match arg {
2592 hir::GenericArg::Lifetime(lt) => {
2598 (lt.span, "lifetime")
2600 hir::GenericArg::Type(ty) => {
2608 hir::GenericArg::Const(ct) => {
2617 let mut err = struct_span_err!(
2621 "{} arguments are not allowed for this type",
2624 err.span_label(span, format!("{} argument not allowed", kind));
2626 if err_for_lt && err_for_ty && err_for_ct {
2631 // Only emit the first error to avoid overloading the user with error messages.
2632 if let [binding, ..] = segment.generic_args().bindings {
2634 Self::prohibit_assoc_ty_binding(self.tcx(), binding.span);
2640 pub fn prohibit_assoc_ty_binding(tcx: TyCtxt<'_>, span: Span) {
2641 let mut err = struct_span_err!(
2645 "associated type bindings are not allowed here"
2647 err.span_label(span, "associated type not allowed here").emit();
2650 /// Prohibits explicit lifetime arguments if late-bound lifetime parameters
2651 /// are present. This is used both for datatypes and function calls.
2652 fn prohibit_explicit_late_bound_lifetimes(
2655 args: &hir::GenericArgs<'_>,
2656 position: GenericArgPosition,
2657 ) -> ExplicitLateBound {
2658 let param_counts = def.own_counts();
2659 let arg_counts = args.own_counts();
2660 let infer_lifetimes = position != GenericArgPosition::Type && arg_counts.lifetimes == 0;
2662 if infer_lifetimes {
2663 ExplicitLateBound::No
2664 } else if let Some(span_late) = def.has_late_bound_regions {
2665 let msg = "cannot specify lifetime arguments explicitly \
2666 if late bound lifetime parameters are present";
2667 let note = "the late bound lifetime parameter is introduced here";
2668 let span = args.args[0].span();
2669 if position == GenericArgPosition::Value
2670 && arg_counts.lifetimes != param_counts.lifetimes
2672 let mut err = tcx.sess.struct_span_err(span, msg);
2673 err.span_note(span_late, note);
2676 let mut multispan = MultiSpan::from_span(span);
2677 multispan.push_span_label(span_late, note.to_string());
2678 tcx.struct_span_lint_hir(
2679 LATE_BOUND_LIFETIME_ARGUMENTS,
2682 |lint| lint.build(msg).emit(),
2685 ExplicitLateBound::Yes
2687 ExplicitLateBound::No
2691 // FIXME(eddyb, varkor) handle type paths here too, not just value ones.
2692 pub fn def_ids_for_value_path_segments(
2694 segments: &[hir::PathSegment<'_>],
2695 self_ty: Option<Ty<'tcx>>,
2699 // We need to extract the type parameters supplied by the user in
2700 // the path `path`. Due to the current setup, this is a bit of a
2701 // tricky-process; the problem is that resolve only tells us the
2702 // end-point of the path resolution, and not the intermediate steps.
2703 // Luckily, we can (at least for now) deduce the intermediate steps
2704 // just from the end-point.
2706 // There are basically five cases to consider:
2708 // 1. Reference to a constructor of a struct:
2710 // struct Foo<T>(...)
2712 // In this case, the parameters are declared in the type space.
2714 // 2. Reference to a constructor of an enum variant:
2716 // enum E<T> { Foo(...) }
2718 // In this case, the parameters are defined in the type space,
2719 // but may be specified either on the type or the variant.
2721 // 3. Reference to a fn item or a free constant:
2725 // In this case, the path will again always have the form
2726 // `a::b::foo::<T>` where only the final segment should have
2727 // type parameters. However, in this case, those parameters are
2728 // declared on a value, and hence are in the `FnSpace`.
2730 // 4. Reference to a method or an associated constant:
2732 // impl<A> SomeStruct<A> {
2736 // Here we can have a path like
2737 // `a::b::SomeStruct::<A>::foo::<B>`, in which case parameters
2738 // may appear in two places. The penultimate segment,
2739 // `SomeStruct::<A>`, contains parameters in TypeSpace, and the
2740 // final segment, `foo::<B>` contains parameters in fn space.
2742 // The first step then is to categorize the segments appropriately.
2744 let tcx = self.tcx();
2746 assert!(!segments.is_empty());
2747 let last = segments.len() - 1;
2749 let mut path_segs = vec![];
2752 // Case 1. Reference to a struct constructor.
2753 DefKind::Ctor(CtorOf::Struct, ..) => {
2754 // Everything but the final segment should have no
2755 // parameters at all.
2756 let generics = tcx.generics_of(def_id);
2757 // Variant and struct constructors use the
2758 // generics of their parent type definition.
2759 let generics_def_id = generics.parent.unwrap_or(def_id);
2760 path_segs.push(PathSeg(generics_def_id, last));
2763 // Case 2. Reference to a variant constructor.
2764 DefKind::Ctor(CtorOf::Variant, ..) | DefKind::Variant => {
2765 let adt_def = self_ty.map(|t| t.ty_adt_def().unwrap());
2766 let (generics_def_id, index) = if let Some(adt_def) = adt_def {
2767 debug_assert!(adt_def.is_enum());
2769 } else if last >= 1 && segments[last - 1].args.is_some() {
2770 // Everything but the penultimate segment should have no
2771 // parameters at all.
2772 let mut def_id = def_id;
2774 // `DefKind::Ctor` -> `DefKind::Variant`
2775 if let DefKind::Ctor(..) = kind {
2776 def_id = tcx.parent(def_id).unwrap()
2779 // `DefKind::Variant` -> `DefKind::Enum`
2780 let enum_def_id = tcx.parent(def_id).unwrap();
2781 (enum_def_id, last - 1)
2783 // FIXME: lint here recommending `Enum::<...>::Variant` form
2784 // instead of `Enum::Variant::<...>` form.
2786 // Everything but the final segment should have no
2787 // parameters at all.
2788 let generics = tcx.generics_of(def_id);
2789 // Variant and struct constructors use the
2790 // generics of their parent type definition.
2791 (generics.parent.unwrap_or(def_id), last)
2793 path_segs.push(PathSeg(generics_def_id, index));
2796 // Case 3. Reference to a top-level value.
2797 DefKind::Fn | DefKind::Const | DefKind::ConstParam | DefKind::Static => {
2798 path_segs.push(PathSeg(def_id, last));
2801 // Case 4. Reference to a method or associated const.
2802 DefKind::AssocFn | DefKind::AssocConst => {
2803 if segments.len() >= 2 {
2804 let generics = tcx.generics_of(def_id);
2805 path_segs.push(PathSeg(generics.parent.unwrap(), last - 1));
2807 path_segs.push(PathSeg(def_id, last));
2810 kind => bug!("unexpected definition kind {:?} for {:?}", kind, def_id),
2813 debug!("path_segs = {:?}", path_segs);
2818 // Check a type `Path` and convert it to a `Ty`.
2821 opt_self_ty: Option<Ty<'tcx>>,
2822 path: &hir::Path<'_>,
2823 permit_variants: bool,
2825 let tcx = self.tcx();
2828 "res_to_ty(res={:?}, opt_self_ty={:?}, path_segments={:?})",
2829 path.res, opt_self_ty, path.segments
2832 let span = path.span;
2834 Res::Def(DefKind::OpaqueTy, did) => {
2835 // Check for desugared `impl Trait`.
2836 assert!(ty::is_impl_trait_defn(tcx, did).is_none());
2837 let item_segment = path.segments.split_last().unwrap();
2838 self.prohibit_generics(item_segment.1);
2839 let substs = self.ast_path_substs_for_ty(span, did, item_segment.0);
2840 self.normalize_ty(span, tcx.mk_opaque(did, substs))
2847 | DefKind::ForeignTy,
2850 assert_eq!(opt_self_ty, None);
2851 self.prohibit_generics(path.segments.split_last().unwrap().1);
2852 self.ast_path_to_ty(span, did, path.segments.last().unwrap())
2854 Res::Def(kind @ DefKind::Variant, def_id) if permit_variants => {
2855 // Convert "variant type" as if it were a real type.
2856 // The resulting `Ty` is type of the variant's enum for now.
2857 assert_eq!(opt_self_ty, None);
2860 self.def_ids_for_value_path_segments(&path.segments, None, kind, def_id);
2861 let generic_segs: FxHashSet<_> =
2862 path_segs.iter().map(|PathSeg(_, index)| index).collect();
2863 self.prohibit_generics(path.segments.iter().enumerate().filter_map(
2865 if !generic_segs.contains(&index) { Some(seg) } else { None }
2869 let PathSeg(def_id, index) = path_segs.last().unwrap();
2870 self.ast_path_to_ty(span, *def_id, &path.segments[*index])
2872 Res::Def(DefKind::TyParam, def_id) => {
2873 assert_eq!(opt_self_ty, None);
2874 self.prohibit_generics(path.segments);
2876 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
2877 let item_id = tcx.hir().get_parent_node(hir_id);
2878 let item_def_id = tcx.hir().local_def_id(item_id);
2879 let generics = tcx.generics_of(item_def_id);
2880 let index = generics.param_def_id_to_index[&def_id];
2881 tcx.mk_ty_param(index, tcx.hir().name(hir_id))
2883 Res::SelfTy(Some(_), None) => {
2884 // `Self` in trait or type alias.
2885 assert_eq!(opt_self_ty, None);
2886 self.prohibit_generics(path.segments);
2887 tcx.types.self_param
2889 Res::SelfTy(_, Some(def_id)) => {
2890 // `Self` in impl (we know the concrete type).
2891 assert_eq!(opt_self_ty, None);
2892 self.prohibit_generics(path.segments);
2893 // Try to evaluate any array length constants.
2894 self.normalize_ty(span, tcx.at(span).type_of(def_id))
2896 Res::Def(DefKind::AssocTy, def_id) => {
2897 debug_assert!(path.segments.len() >= 2);
2898 self.prohibit_generics(&path.segments[..path.segments.len() - 2]);
2903 &path.segments[path.segments.len() - 2],
2904 path.segments.last().unwrap(),
2907 Res::PrimTy(prim_ty) => {
2908 assert_eq!(opt_self_ty, None);
2909 self.prohibit_generics(path.segments);
2911 hir::PrimTy::Bool => tcx.types.bool,
2912 hir::PrimTy::Char => tcx.types.char,
2913 hir::PrimTy::Int(it) => tcx.mk_mach_int(it),
2914 hir::PrimTy::Uint(uit) => tcx.mk_mach_uint(uit),
2915 hir::PrimTy::Float(ft) => tcx.mk_mach_float(ft),
2916 hir::PrimTy::Str => tcx.types.str_,
2920 self.set_tainted_by_errors();
2921 self.tcx().ty_error()
2923 _ => span_bug!(span, "unexpected resolution: {:?}", path.res),
2927 /// Parses the programmer's textual representation of a type into our
2928 /// internal notion of a type.
2929 pub fn ast_ty_to_ty(&self, ast_ty: &hir::Ty<'_>) -> Ty<'tcx> {
2930 self.ast_ty_to_ty_inner(ast_ty, false)
2933 /// Turns a `hir::Ty` into a `Ty`. For diagnostics' purposes we keep track of whether trait
2934 /// objects are borrowed like `&dyn Trait` to avoid emitting redundant errors.
2935 fn ast_ty_to_ty_inner(&self, ast_ty: &hir::Ty<'_>, borrowed: bool) -> Ty<'tcx> {
2936 debug!("ast_ty_to_ty(id={:?}, ast_ty={:?} ty_ty={:?})", ast_ty.hir_id, ast_ty, ast_ty.kind);
2938 let tcx = self.tcx();
2940 let result_ty = match ast_ty.kind {
2941 hir::TyKind::Slice(ref ty) => tcx.mk_slice(self.ast_ty_to_ty(&ty)),
2942 hir::TyKind::Ptr(ref mt) => {
2943 tcx.mk_ptr(ty::TypeAndMut { ty: self.ast_ty_to_ty(&mt.ty), mutbl: mt.mutbl })
2945 hir::TyKind::Rptr(ref region, ref mt) => {
2946 let r = self.ast_region_to_region(region, None);
2947 debug!("ast_ty_to_ty: r={:?}", r);
2948 let t = self.ast_ty_to_ty_inner(&mt.ty, true);
2949 tcx.mk_ref(r, ty::TypeAndMut { ty: t, mutbl: mt.mutbl })
2951 hir::TyKind::Never => tcx.types.never,
2952 hir::TyKind::Tup(ref fields) => {
2953 tcx.mk_tup(fields.iter().map(|t| self.ast_ty_to_ty(&t)))
2955 hir::TyKind::BareFn(ref bf) => {
2956 require_c_abi_if_c_variadic(tcx, &bf.decl, bf.abi, ast_ty.span);
2957 tcx.mk_fn_ptr(self.ty_of_fn(
2961 &hir::Generics::empty(),
2965 hir::TyKind::TraitObject(ref bounds, ref lifetime) => {
2966 self.conv_object_ty_poly_trait_ref(ast_ty.span, bounds, lifetime, borrowed)
2968 hir::TyKind::Path(hir::QPath::Resolved(ref maybe_qself, ref path)) => {
2969 debug!("ast_ty_to_ty: maybe_qself={:?} path={:?}", maybe_qself, path);
2970 let opt_self_ty = maybe_qself.as_ref().map(|qself| self.ast_ty_to_ty(qself));
2971 self.res_to_ty(opt_self_ty, path, false)
2973 hir::TyKind::OpaqueDef(item_id, ref lifetimes) => {
2974 let opaque_ty = tcx.hir().expect_item(item_id.id);
2975 let def_id = tcx.hir().local_def_id(item_id.id).to_def_id();
2977 match opaque_ty.kind {
2978 hir::ItemKind::OpaqueTy(hir::OpaqueTy { impl_trait_fn, .. }) => {
2979 self.impl_trait_ty_to_ty(def_id, lifetimes, impl_trait_fn.is_some())
2981 ref i => bug!("`impl Trait` pointed to non-opaque type?? {:#?}", i),
2984 hir::TyKind::Path(hir::QPath::TypeRelative(ref qself, ref segment)) => {
2985 debug!("ast_ty_to_ty: qself={:?} segment={:?}", qself, segment);
2986 let ty = self.ast_ty_to_ty(qself);
2988 let res = if let hir::TyKind::Path(hir::QPath::Resolved(_, ref path)) = qself.kind {
2993 self.associated_path_to_ty(ast_ty.hir_id, ast_ty.span, ty, res, segment, false)
2994 .map(|(ty, _, _)| ty)
2995 .unwrap_or_else(|_| tcx.ty_error())
2997 hir::TyKind::Path(hir::QPath::LangItem(lang_item, span)) => {
2998 let def_id = tcx.require_lang_item(lang_item, Some(span));
2999 let (substs, _, _) = self.create_substs_for_ast_path(
3003 &GenericArgs::none(),
3007 self.normalize_ty(span, tcx.at(span).type_of(def_id).subst(tcx, substs))
3009 hir::TyKind::Array(ref ty, ref length) => {
3010 let length_def_id = tcx.hir().local_def_id(length.hir_id);
3011 let length = ty::Const::from_anon_const(tcx, length_def_id);
3012 let array_ty = tcx.mk_ty(ty::Array(self.ast_ty_to_ty(&ty), length));
3013 self.normalize_ty(ast_ty.span, array_ty)
3015 hir::TyKind::Typeof(ref _e) => {
3020 "`typeof` is a reserved keyword but unimplemented"
3022 .span_label(ast_ty.span, "reserved keyword")
3027 hir::TyKind::Infer => {
3028 // Infer also appears as the type of arguments or return
3029 // values in a ExprKind::Closure, or as
3030 // the type of local variables. Both of these cases are
3031 // handled specially and will not descend into this routine.
3032 self.ty_infer(None, ast_ty.span)
3034 hir::TyKind::Err => tcx.ty_error(),
3037 debug!("ast_ty_to_ty: result_ty={:?}", result_ty);
3039 self.record_ty(ast_ty.hir_id, result_ty, ast_ty.span);
3043 pub fn impl_trait_ty_to_ty(
3046 lifetimes: &[hir::GenericArg<'_>],
3047 replace_parent_lifetimes: bool,
3049 debug!("impl_trait_ty_to_ty(def_id={:?}, lifetimes={:?})", def_id, lifetimes);
3050 let tcx = self.tcx();
3052 let generics = tcx.generics_of(def_id);
3054 debug!("impl_trait_ty_to_ty: generics={:?}", generics);
3055 let substs = InternalSubsts::for_item(tcx, def_id, |param, _| {
3056 if let Some(i) = (param.index as usize).checked_sub(generics.parent_count) {
3057 // Our own parameters are the resolved lifetimes.
3059 GenericParamDefKind::Lifetime => {
3060 if let hir::GenericArg::Lifetime(lifetime) = &lifetimes[i] {
3061 self.ast_region_to_region(lifetime, None).into()
3070 // For RPIT (return position impl trait), only lifetimes
3071 // mentioned in the impl Trait predicate are captured by
3072 // the opaque type, so the lifetime parameters from the
3073 // parent item need to be replaced with `'static`.
3075 // For `impl Trait` in the types of statics, constants,
3076 // locals and type aliases. These capture all parent
3077 // lifetimes, so they can use their identity subst.
3078 GenericParamDefKind::Lifetime if replace_parent_lifetimes => {
3079 tcx.lifetimes.re_static.into()
3081 _ => tcx.mk_param_from_def(param),
3085 debug!("impl_trait_ty_to_ty: substs={:?}", substs);
3087 let ty = tcx.mk_opaque(def_id, substs);
3088 debug!("impl_trait_ty_to_ty: {}", ty);
3092 pub fn ty_of_arg(&self, ty: &hir::Ty<'_>, expected_ty: Option<Ty<'tcx>>) -> Ty<'tcx> {
3094 hir::TyKind::Infer if expected_ty.is_some() => {
3095 self.record_ty(ty.hir_id, expected_ty.unwrap(), ty.span);
3096 expected_ty.unwrap()
3098 _ => self.ast_ty_to_ty(ty),
3104 unsafety: hir::Unsafety,
3106 decl: &hir::FnDecl<'_>,
3107 generics: &hir::Generics<'_>,
3108 ident_span: Option<Span>,
3109 ) -> ty::PolyFnSig<'tcx> {
3112 let tcx = self.tcx();
3114 // We proactively collect all the inferred type params to emit a single error per fn def.
3115 let mut visitor = PlaceholderHirTyCollector::default();
3116 for ty in decl.inputs {
3117 visitor.visit_ty(ty);
3119 walk_generics(&mut visitor, generics);
3121 let input_tys = decl.inputs.iter().map(|a| self.ty_of_arg(a, None));
3122 let output_ty = match decl.output {
3123 hir::FnRetTy::Return(ref output) => {
3124 visitor.visit_ty(output);
3125 self.ast_ty_to_ty(output)
3127 hir::FnRetTy::DefaultReturn(..) => tcx.mk_unit(),
3130 debug!("ty_of_fn: output_ty={:?}", output_ty);
3133 ty::Binder::bind(tcx.mk_fn_sig(input_tys, output_ty, decl.c_variadic, unsafety, abi));
3135 if !self.allow_ty_infer() {
3136 // We always collect the spans for placeholder types when evaluating `fn`s, but we
3137 // only want to emit an error complaining about them if infer types (`_`) are not
3138 // allowed. `allow_ty_infer` gates this behavior. We check for the presence of
3139 // `ident_span` to not emit an error twice when we have `fn foo(_: fn() -> _)`.
3140 crate::collect::placeholder_type_error(
3142 ident_span.map(|sp| sp.shrink_to_hi()),
3143 &generics.params[..],
3149 // Find any late-bound regions declared in return type that do
3150 // not appear in the arguments. These are not well-formed.
3153 // for<'a> fn() -> &'a str <-- 'a is bad
3154 // for<'a> fn(&'a String) -> &'a str <-- 'a is ok
3155 let inputs = bare_fn_ty.inputs();
3156 let late_bound_in_args =
3157 tcx.collect_constrained_late_bound_regions(&inputs.map_bound(|i| i.to_owned()));
3158 let output = bare_fn_ty.output();
3159 let late_bound_in_ret = tcx.collect_referenced_late_bound_regions(&output);
3161 self.validate_late_bound_regions(late_bound_in_args, late_bound_in_ret, |br_name| {
3166 "return type references {}, which is not constrained by the fn input types",
3174 fn validate_late_bound_regions(
3176 constrained_regions: FxHashSet<ty::BoundRegion>,
3177 referenced_regions: FxHashSet<ty::BoundRegion>,
3178 generate_err: impl Fn(&str) -> rustc_errors::DiagnosticBuilder<'tcx>,
3180 for br in referenced_regions.difference(&constrained_regions) {
3181 let br_name = match *br {
3182 ty::BrNamed(_, name) => format!("lifetime `{}`", name),
3183 ty::BrAnon(_) | ty::BrEnv => "an anonymous lifetime".to_string(),
3186 let mut err = generate_err(&br_name);
3188 if let ty::BrAnon(_) = *br {
3189 // The only way for an anonymous lifetime to wind up
3190 // in the return type but **also** be unconstrained is
3191 // if it only appears in "associated types" in the
3192 // input. See #47511 and #62200 for examples. In this case,
3193 // though we can easily give a hint that ought to be
3196 "lifetimes appearing in an associated type are not considered constrained",
3204 /// Given the bounds on an object, determines what single region bound (if any) we can
3205 /// use to summarize this type. The basic idea is that we will use the bound the user
3206 /// provided, if they provided one, and otherwise search the supertypes of trait bounds
3207 /// for region bounds. It may be that we can derive no bound at all, in which case
3208 /// we return `None`.
3209 fn compute_object_lifetime_bound(
3212 existential_predicates: ty::Binder<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>>,
3213 ) -> Option<ty::Region<'tcx>> // if None, use the default
3215 let tcx = self.tcx();
3217 debug!("compute_opt_region_bound(existential_predicates={:?})", existential_predicates);
3219 // No explicit region bound specified. Therefore, examine trait
3220 // bounds and see if we can derive region bounds from those.
3221 let derived_region_bounds = object_region_bounds(tcx, existential_predicates);
3223 // If there are no derived region bounds, then report back that we
3224 // can find no region bound. The caller will use the default.
3225 if derived_region_bounds.is_empty() {
3229 // If any of the derived region bounds are 'static, that is always
3231 if derived_region_bounds.iter().any(|&r| ty::ReStatic == *r) {
3232 return Some(tcx.lifetimes.re_static);
3235 // Determine whether there is exactly one unique region in the set
3236 // of derived region bounds. If so, use that. Otherwise, report an
3238 let r = derived_region_bounds[0];
3239 if derived_region_bounds[1..].iter().any(|r1| r != *r1) {
3244 "ambiguous lifetime bound, explicit lifetime bound required"
3252 /// Collects together a list of bounds that are applied to some type,
3253 /// after they've been converted into `ty` form (from the HIR
3254 /// representations). These lists of bounds occur in many places in
3258 /// trait Foo: Bar + Baz { }
3259 /// ^^^^^^^^^ supertrait list bounding the `Self` type parameter
3261 /// fn foo<T: Bar + Baz>() { }
3262 /// ^^^^^^^^^ bounding the type parameter `T`
3264 /// impl dyn Bar + Baz
3265 /// ^^^^^^^^^ bounding the forgotten dynamic type
3268 /// Our representation is a bit mixed here -- in some cases, we
3269 /// include the self type (e.g., `trait_bounds`) but in others we do
3270 #[derive(Default, PartialEq, Eq, Clone, Debug)]
3271 pub struct Bounds<'tcx> {
3272 /// A list of region bounds on the (implicit) self type. So if you
3273 /// had `T: 'a + 'b` this might would be a list `['a, 'b]` (but
3274 /// the `T` is not explicitly included).
3275 pub region_bounds: Vec<(ty::Region<'tcx>, Span)>,
3277 /// A list of trait bounds. So if you had `T: Debug` this would be
3278 /// `T: Debug`. Note that the self-type is explicit here.
3279 pub trait_bounds: Vec<(ty::PolyTraitRef<'tcx>, Span, Constness)>,
3281 /// A list of projection equality bounds. So if you had `T:
3282 /// Iterator<Item = u32>` this would include `<T as
3283 /// Iterator>::Item => u32`. Note that the self-type is explicit
3285 pub projection_bounds: Vec<(ty::PolyProjectionPredicate<'tcx>, Span)>,
3287 /// `Some` if there is *no* `?Sized` predicate. The `span`
3288 /// is the location in the source of the `T` declaration which can
3289 /// be cited as the source of the `T: Sized` requirement.
3290 pub implicitly_sized: Option<Span>,
3293 impl<'tcx> Bounds<'tcx> {
3294 /// Converts a bounds list into a flat set of predicates (like
3295 /// where-clauses). Because some of our bounds listings (e.g.,
3296 /// regions) don't include the self-type, you must supply the
3297 /// self-type here (the `param_ty` parameter).
3302 ) -> Vec<(ty::Predicate<'tcx>, Span)> {
3303 // If it could be sized, and is, add the `Sized` predicate.
3304 let sized_predicate = self.implicitly_sized.and_then(|span| {
3305 tcx.lang_items().sized_trait().map(|sized| {
3306 let trait_ref = ty::Binder::bind(ty::TraitRef {
3308 substs: tcx.mk_substs_trait(param_ty, &[]),
3310 (trait_ref.without_const().to_predicate(tcx), span)
3319 .map(|&(region_bound, span)| {
3320 // Account for the binder being introduced below; no need to shift `param_ty`
3321 // because, at present at least, it either only refers to early-bound regions,
3322 // or it's a generic associated type that deliberately has escaping bound vars.
3323 let region_bound = ty::fold::shift_region(tcx, region_bound, 1);
3324 let outlives = ty::OutlivesPredicate(param_ty, region_bound);
3325 (ty::Binder::bind(outlives).to_predicate(tcx), span)
3327 .chain(self.trait_bounds.iter().map(|&(bound_trait_ref, span, constness)| {
3328 let predicate = bound_trait_ref.with_constness(constness).to_predicate(tcx);
3332 self.projection_bounds
3334 .map(|&(projection, span)| (projection.to_predicate(tcx), span)),