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;
12 use rustc_ast::util::lev_distance::find_best_match_for_name;
13 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
14 use rustc_errors::ErrorReported;
15 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticId, FatalError};
17 use rustc_hir::def::{CtorOf, DefKind, Namespace, Res};
18 use rustc_hir::def_id::DefId;
19 use rustc_hir::intravisit::{walk_generics, Visitor as _};
20 use rustc_hir::lang_items::SizedTraitLangItem;
21 use rustc_hir::{Constness, GenericArg, GenericArgs};
22 use rustc_middle::ty::subst::{self, InternalSubsts, Subst, SubstsRef};
23 use rustc_middle::ty::{
24 self, Const, DefIdTree, ToPredicate, Ty, TyCtxt, TypeFoldable, WithConstness,
26 use rustc_middle::ty::{GenericParamDef, GenericParamDefKind};
27 use rustc_session::lint::builtin::{AMBIGUOUS_ASSOCIATED_ITEMS, LATE_BOUND_LIFETIME_ARGUMENTS};
28 use rustc_session::parse::feature_err;
29 use rustc_session::Session;
30 use rustc_span::symbol::sym;
31 use rustc_span::{MultiSpan, Span, DUMMY_SP};
32 use rustc_target::spec::abi;
33 use rustc_trait_selection::traits;
34 use rustc_trait_selection::traits::astconv_object_safety_violations;
35 use rustc_trait_selection::traits::error_reporting::report_object_safety_error;
36 use rustc_trait_selection::traits::wf::object_region_bounds;
38 use smallvec::SmallVec;
39 use std::collections::BTreeSet;
44 pub struct PathSeg(pub DefId, pub usize);
46 pub trait AstConv<'tcx> {
47 fn tcx<'a>(&'a self) -> TyCtxt<'tcx>;
49 fn item_def_id(&self) -> Option<DefId>;
51 fn default_constness_for_trait_bounds(&self) -> Constness;
53 /// Returns predicates in scope of the form `X: Foo`, where `X` is
54 /// a type parameter `X` with the given id `def_id`. This is a
55 /// subset of the full set of predicates.
57 /// This is used for one specific purpose: resolving "short-hand"
58 /// associated type references like `T::Item`. In principle, we
59 /// would do that by first getting the full set of predicates in
60 /// scope and then filtering down to find those that apply to `T`,
61 /// but this can lead to cycle errors. The problem is that we have
62 /// to do this resolution *in order to create the predicates in
63 /// the first place*. Hence, we have this "special pass".
64 fn get_type_parameter_bounds(&self, span: Span, def_id: DefId) -> ty::GenericPredicates<'tcx>;
66 /// Returns the lifetime to use when a lifetime is omitted (and not elided).
67 fn re_infer(&self, param: Option<&ty::GenericParamDef>, span: Span)
68 -> Option<ty::Region<'tcx>>;
70 /// Returns the type to use when a type is omitted.
71 fn ty_infer(&self, param: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx>;
73 /// Returns `true` if `_` is allowed in type signatures in the current context.
74 fn allow_ty_infer(&self) -> bool;
76 /// Returns the const to use when a const is omitted.
80 param: Option<&ty::GenericParamDef>,
82 ) -> &'tcx Const<'tcx>;
84 /// Projecting an associated type from a (potentially)
85 /// higher-ranked trait reference is more complicated, because of
86 /// the possibility of late-bound regions appearing in the
87 /// associated type binding. This is not legal in function
88 /// signatures for that reason. In a function body, we can always
89 /// handle it because we can use inference variables to remove the
90 /// late-bound regions.
91 fn projected_ty_from_poly_trait_ref(
95 item_segment: &hir::PathSegment<'_>,
96 poly_trait_ref: ty::PolyTraitRef<'tcx>,
99 /// Normalize an associated type coming from the user.
100 fn normalize_ty(&self, span: Span, ty: Ty<'tcx>) -> Ty<'tcx>;
102 /// Invoked when we encounter an error from some prior pass
103 /// (e.g., resolve) that is translated into a ty-error. This is
104 /// used to help suppress derived errors typeck might otherwise
106 fn set_tainted_by_errors(&self);
108 fn record_ty(&self, hir_id: hir::HirId, ty: Ty<'tcx>, span: Span);
111 pub enum SizedByDefault {
116 struct ConvertedBinding<'a, 'tcx> {
117 item_name: ast::Ident,
118 kind: ConvertedBindingKind<'a, 'tcx>,
122 enum ConvertedBindingKind<'a, 'tcx> {
124 Constraint(&'a [hir::GenericBound<'a>]),
128 enum GenericArgPosition {
130 Value, // e.g., functions
134 /// A marker denoting that the generic arguments that were
135 /// provided did not match the respective generic parameters.
136 pub struct GenericArgCountMismatch {
137 /// Indicates whether a fatal error was reported (`Some`), or just a lint (`None`).
138 pub reported: Option<ErrorReported>,
139 /// A list of spans of arguments provided that were not valid.
140 pub invalid_args: Vec<Span>,
143 impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
144 pub fn ast_region_to_region(
146 lifetime: &hir::Lifetime,
147 def: Option<&ty::GenericParamDef>,
148 ) -> ty::Region<'tcx> {
149 let tcx = self.tcx();
150 let lifetime_name = |def_id| tcx.hir().name(tcx.hir().as_local_hir_id(def_id).unwrap());
152 let r = match tcx.named_region(lifetime.hir_id) {
153 Some(rl::Region::Static) => tcx.lifetimes.re_static,
155 Some(rl::Region::LateBound(debruijn, id, _)) => {
156 let name = lifetime_name(id);
157 tcx.mk_region(ty::ReLateBound(debruijn, ty::BrNamed(id, name)))
160 Some(rl::Region::LateBoundAnon(debruijn, index)) => {
161 tcx.mk_region(ty::ReLateBound(debruijn, ty::BrAnon(index)))
164 Some(rl::Region::EarlyBound(index, id, _)) => {
165 let name = lifetime_name(id);
166 tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion { def_id: id, index, name }))
169 Some(rl::Region::Free(scope, id)) => {
170 let name = lifetime_name(id);
171 tcx.mk_region(ty::ReFree(ty::FreeRegion {
173 bound_region: ty::BrNamed(id, name),
176 // (*) -- not late-bound, won't change
180 self.re_infer(def, lifetime.span).unwrap_or_else(|| {
181 // This indicates an illegal lifetime
182 // elision. `resolve_lifetime` should have
183 // reported an error in this case -- but if
184 // not, let's error out.
185 tcx.sess.delay_span_bug(lifetime.span, "unelided lifetime in signature");
187 // Supply some dummy value. We don't have an
188 // `re_error`, annoyingly, so use `'static`.
189 tcx.lifetimes.re_static
194 debug!("ast_region_to_region(lifetime={:?}) yields {:?}", lifetime, r);
199 /// Given a path `path` that refers to an item `I` with the declared generics `decl_generics`,
200 /// returns an appropriate set of substitutions for this particular reference to `I`.
201 pub fn ast_path_substs_for_ty(
205 item_segment: &hir::PathSegment<'_>,
206 ) -> SubstsRef<'tcx> {
207 let (substs, assoc_bindings, _) = self.create_substs_for_ast_path(
211 item_segment.generic_args(),
212 item_segment.infer_args,
216 assoc_bindings.first().map(|b| Self::prohibit_assoc_ty_binding(self.tcx(), b.span));
221 /// Report error if there is an explicit type parameter when using `impl Trait`.
224 seg: &hir::PathSegment<'_>,
225 generics: &ty::Generics,
227 let explicit = !seg.infer_args;
228 let impl_trait = generics.params.iter().any(|param| match param.kind {
229 ty::GenericParamDefKind::Type {
230 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
236 if explicit && impl_trait {
241 .filter_map(|arg| match arg {
242 GenericArg::Type(_) => Some(arg.span()),
245 .collect::<Vec<_>>();
247 let mut err = struct_span_err! {
251 "cannot provide explicit generic arguments when `impl Trait` is \
252 used in argument position"
256 err.span_label(span, "explicit generic argument not allowed");
265 /// Checks that the correct number of generic arguments have been provided.
266 /// Used specifically for function calls.
267 pub fn check_generic_arg_count_for_call(
271 seg: &hir::PathSegment<'_>,
272 is_method_call: bool,
273 ) -> Result<(), GenericArgCountMismatch> {
274 let empty_args = hir::GenericArgs::none();
275 let suppress_mismatch = Self::check_impl_trait(tcx, seg, &def);
276 Self::check_generic_arg_count(
280 if let Some(ref args) = seg.args { args } else { &empty_args },
281 if is_method_call { GenericArgPosition::MethodCall } else { GenericArgPosition::Value },
282 def.parent.is_none() && def.has_self, // `has_self`
283 seg.infer_args || suppress_mismatch, // `infer_args`
287 /// Checks that the correct number of generic arguments have been provided.
288 /// This is used both for datatypes and function calls.
289 fn check_generic_arg_count(
293 args: &hir::GenericArgs<'_>,
294 position: GenericArgPosition,
297 ) -> Result<(), GenericArgCountMismatch> {
298 // At this stage we are guaranteed that the generic arguments are in the correct order, e.g.
299 // that lifetimes will proceed types. So it suffices to check the number of each generic
300 // arguments in order to validate them with respect to the generic parameters.
301 let param_counts = def.own_counts();
302 let arg_counts = args.own_counts();
303 let infer_lifetimes = position != GenericArgPosition::Type && arg_counts.lifetimes == 0;
305 let mut defaults: ty::GenericParamCount = Default::default();
306 for param in &def.params {
308 GenericParamDefKind::Lifetime => {}
309 GenericParamDefKind::Type { has_default, .. } => {
310 defaults.types += has_default as usize
312 GenericParamDefKind::Const => {
313 // FIXME(const_generics:defaults)
318 if position != GenericArgPosition::Type && !args.bindings.is_empty() {
319 AstConv::prohibit_assoc_ty_binding(tcx, args.bindings[0].span);
322 // Prohibit explicit lifetime arguments if late-bound lifetime parameters are present.
323 let mut explicit_lifetimes = Ok(());
324 if !infer_lifetimes {
325 if let Some(span_late) = def.has_late_bound_regions {
326 let msg = "cannot specify lifetime arguments explicitly \
327 if late bound lifetime parameters are present";
328 let note = "the late bound lifetime parameter is introduced here";
329 let span = args.args[0].span();
330 if position == GenericArgPosition::Value
331 && arg_counts.lifetimes != param_counts.lifetimes
333 explicit_lifetimes = Err(true);
334 let mut err = tcx.sess.struct_span_err(span, msg);
335 err.span_note(span_late, note);
338 explicit_lifetimes = Err(false);
339 let mut multispan = MultiSpan::from_span(span);
340 multispan.push_span_label(span_late, note.to_string());
341 tcx.struct_span_lint_hir(
342 LATE_BOUND_LIFETIME_ARGUMENTS,
345 |lint| lint.build(msg).emit(),
351 let check_kind_count =
352 |kind, required, permitted, provided, offset, unexpected_spans: &mut Vec<Span>| {
354 "check_kind_count: kind: {} required: {} permitted: {} provided: {} offset: {}",
355 kind, required, permitted, provided, offset
357 // We enforce the following: `required` <= `provided` <= `permitted`.
358 // For kinds without defaults (e.g.., lifetimes), `required == permitted`.
359 // For other kinds (i.e., types), `permitted` may be greater than `required`.
360 if required <= provided && provided <= permitted {
364 // Unfortunately lifetime and type parameter mismatches are typically styled
365 // differently in diagnostics, which means we have a few cases to consider here.
366 let (bound, quantifier) = if required != permitted {
367 if provided < required {
368 (required, "at least ")
370 // provided > permitted
371 (permitted, "at most ")
377 let (spans, label) = if required == permitted && provided > permitted {
378 // In the case when the user has provided too many arguments,
379 // we want to point to the unexpected arguments.
380 let spans: Vec<Span> = args.args[offset + permitted..offset + provided]
382 .map(|arg| arg.span())
384 unexpected_spans.extend(spans.clone());
385 (spans, format!("unexpected {} argument", kind))
390 "expected {}{} {} argument{}",
399 let mut err = tcx.sess.struct_span_err_with_code(
402 "wrong number of {} arguments: expected {}{}, found {}",
403 kind, quantifier, bound, provided,
405 DiagnosticId::Error("E0107".into()),
408 err.span_label(span, label.as_str());
415 let mut arg_count_correct = explicit_lifetimes;
416 let mut unexpected_spans = vec![];
418 if arg_count_correct.is_ok()
419 && (!infer_lifetimes || arg_counts.lifetimes > param_counts.lifetimes)
421 arg_count_correct = check_kind_count(
423 param_counts.lifetimes,
424 param_counts.lifetimes,
425 arg_counts.lifetimes,
427 &mut unexpected_spans,
429 .and(arg_count_correct);
431 // FIXME(const_generics:defaults)
432 if !infer_args || arg_counts.consts > param_counts.consts {
433 arg_count_correct = check_kind_count(
438 arg_counts.lifetimes + arg_counts.types,
439 &mut unexpected_spans,
441 .and(arg_count_correct);
443 // Note that type errors are currently be emitted *after* const errors.
444 if !infer_args || arg_counts.types > param_counts.types - defaults.types - has_self as usize
446 arg_count_correct = check_kind_count(
448 param_counts.types - defaults.types - has_self as usize,
449 param_counts.types - has_self as usize,
451 arg_counts.lifetimes,
452 &mut unexpected_spans,
454 .and(arg_count_correct);
457 arg_count_correct.map_err(|reported_err| GenericArgCountMismatch {
458 reported: if reported_err { Some(ErrorReported) } else { None },
459 invalid_args: unexpected_spans,
463 /// Report an error that a generic argument did not match the generic parameter that was
465 fn generic_arg_mismatch_err(sess: &Session, arg: &GenericArg<'_>, kind: &'static str) {
466 let mut err = struct_span_err!(
470 "{} provided when a {} was expected",
474 // This note will be true as long as generic parameters are strictly ordered by their kind.
475 err.note(&format!("{} arguments must be provided before {} arguments", kind, arg.descr()));
479 /// Creates the relevant generic argument substitutions
480 /// corresponding to a set of generic parameters. This is a
481 /// rather complex function. Let us try to explain the role
482 /// of each of its parameters:
484 /// To start, we are given the `def_id` of the thing we are
485 /// creating the substitutions for, and a partial set of
486 /// substitutions `parent_substs`. In general, the substitutions
487 /// for an item begin with substitutions for all the "parents" of
488 /// that item -- e.g., for a method it might include the
489 /// parameters from the impl.
491 /// Therefore, the method begins by walking down these parents,
492 /// starting with the outermost parent and proceed inwards until
493 /// it reaches `def_id`. For each parent `P`, it will check `parent_substs`
494 /// first to see if the parent's substitutions are listed in there. If so,
495 /// we can append those and move on. Otherwise, it invokes the
496 /// three callback functions:
498 /// - `args_for_def_id`: given the `DefId` `P`, supplies back the
499 /// generic arguments that were given to that parent from within
500 /// the path; so e.g., if you have `<T as Foo>::Bar`, the `DefId`
501 /// might refer to the trait `Foo`, and the arguments might be
502 /// `[T]`. The boolean value indicates whether to infer values
503 /// for arguments whose values were not explicitly provided.
504 /// - `provided_kind`: given the generic parameter and the value from `args_for_def_id`,
505 /// instantiate a `GenericArg`.
506 /// - `inferred_kind`: if no parameter was provided, and inference is enabled, then
507 /// creates a suitable inference variable.
508 pub fn create_substs_for_generic_args<'b>(
511 parent_substs: &[subst::GenericArg<'tcx>],
513 self_ty: Option<Ty<'tcx>>,
514 arg_count_correct: bool,
515 args_for_def_id: impl Fn(DefId) -> (Option<&'b GenericArgs<'b>>, bool),
516 mut provided_kind: impl FnMut(&GenericParamDef, &GenericArg<'_>) -> subst::GenericArg<'tcx>,
517 mut inferred_kind: impl FnMut(
518 Option<&[subst::GenericArg<'tcx>]>,
521 ) -> subst::GenericArg<'tcx>,
522 ) -> SubstsRef<'tcx> {
523 // Collect the segments of the path; we need to substitute arguments
524 // for parameters throughout the entire path (wherever there are
525 // generic parameters).
526 let mut parent_defs = tcx.generics_of(def_id);
527 let count = parent_defs.count();
528 let mut stack = vec![(def_id, parent_defs)];
529 while let Some(def_id) = parent_defs.parent {
530 parent_defs = tcx.generics_of(def_id);
531 stack.push((def_id, parent_defs));
534 // We manually build up the substitution, rather than using convenience
535 // methods in `subst.rs`, so that we can iterate over the arguments and
536 // parameters in lock-step linearly, instead of trying to match each pair.
537 let mut substs: SmallVec<[subst::GenericArg<'tcx>; 8]> = SmallVec::with_capacity(count);
538 // Iterate over each segment of the path.
539 while let Some((def_id, defs)) = stack.pop() {
540 let mut params = defs.params.iter().peekable();
542 // If we have already computed substitutions for parents, we can use those directly.
543 while let Some(¶m) = params.peek() {
544 if let Some(&kind) = parent_substs.get(param.index as usize) {
552 // `Self` is handled first, unless it's been handled in `parent_substs`.
554 if let Some(¶m) = params.peek() {
555 if param.index == 0 {
556 if let GenericParamDefKind::Type { .. } = param.kind {
560 .unwrap_or_else(|| inferred_kind(None, param, true)),
568 // Check whether this segment takes generic arguments and the user has provided any.
569 let (generic_args, infer_args) = args_for_def_id(def_id);
572 generic_args.iter().flat_map(|generic_args| generic_args.args.iter()).peekable();
574 // If we encounter a type or const when we expect a lifetime, we infer the lifetimes.
575 // If we later encounter a lifetime, we know that the arguments were provided in the
576 // wrong order. `force_infer_lt` records the type or const that forced lifetimes to be
577 // inferred, so we can use it for diagnostics later.
578 let mut force_infer_lt = None;
581 // We're going to iterate through the generic arguments that the user
582 // provided, matching them with the generic parameters we expect.
583 // Mismatches can occur as a result of elided lifetimes, or for malformed
584 // input. We try to handle both sensibly.
585 match (args.peek(), params.peek()) {
586 (Some(&arg), Some(¶m)) => {
587 match (arg, ¶m.kind) {
588 (GenericArg::Lifetime(_), GenericParamDefKind::Lifetime)
589 | (GenericArg::Type(_), GenericParamDefKind::Type { .. })
590 | (GenericArg::Const(_), GenericParamDefKind::Const) => {
591 substs.push(provided_kind(param, arg));
595 (GenericArg::Type(_), GenericParamDefKind::Lifetime)
596 | (GenericArg::Const(_), GenericParamDefKind::Lifetime) => {
597 // We expected a lifetime argument, but got a type or const
598 // argument. That means we're inferring the lifetimes.
599 substs.push(inferred_kind(None, param, infer_args));
600 force_infer_lt = Some(arg);
604 // We expected one kind of parameter, but the user provided
605 // another. This is an error. However, if we already know that
606 // the arguments don't match up with the parameters, we won't issue
607 // an additional error, as the user already knows what's wrong.
608 if arg_count_correct {
609 Self::generic_arg_mismatch_err(tcx.sess, arg, kind.descr());
612 // We've reported the error, but we want to make sure that this
613 // problem doesn't bubble down and create additional, irrelevant
614 // errors. In this case, we're simply going to ignore the argument
615 // and any following arguments. The rest of the parameters will be
617 while args.next().is_some() {}
622 (Some(&arg), None) => {
623 // We should never be able to reach this point with well-formed input.
624 // There are two situations in which we can encounter this issue.
626 // 1. The number of arguments is incorrect. In this case, an error
627 // will already have been emitted, and we can ignore it. This case
628 // also occurs when late-bound lifetime parameters are present, yet
629 // the lifetime arguments have also been explicitly specified by the
631 // 2. We've inferred some lifetimes, which have been provided later (i.e.
632 // after a type or const). We want to throw an error in this case.
634 if arg_count_correct {
635 let kind = arg.descr();
636 assert_eq!(kind, "lifetime");
638 force_infer_lt.expect("lifetimes ought to have been inferred");
639 Self::generic_arg_mismatch_err(tcx.sess, provided, kind);
645 (None, Some(¶m)) => {
646 // If there are fewer arguments than parameters, it means
647 // we're inferring the remaining arguments.
648 substs.push(inferred_kind(Some(&substs), param, infer_args));
652 (None, None) => break,
657 tcx.intern_substs(&substs)
660 /// Given the type/lifetime/const arguments provided to some path (along with
661 /// an implicit `Self`, if this is a trait reference), returns the complete
662 /// set of substitutions. This may involve applying defaulted type parameters.
663 /// Also returns back constraints on associated types.
668 /// T: std::ops::Index<usize, Output = u32>
669 /// ^1 ^^^^^^^^^^^^^^2 ^^^^3 ^^^^^^^^^^^4
672 /// 1. The `self_ty` here would refer to the type `T`.
673 /// 2. The path in question is the path to the trait `std::ops::Index`,
674 /// which will have been resolved to a `def_id`
675 /// 3. The `generic_args` contains info on the `<...>` contents. The `usize` type
676 /// parameters are returned in the `SubstsRef`, the associated type bindings like
677 /// `Output = u32` are returned in the `Vec<ConvertedBinding...>` result.
679 /// Note that the type listing given here is *exactly* what the user provided.
681 /// For (generic) associated types
684 /// <Vec<u8> as Iterable<u8>>::Iter::<'a>
687 /// We have the parent substs are the substs for the parent trait:
688 /// `[Vec<u8>, u8]` and `generic_args` are the arguments for the associated
689 /// type itself: `['a]`. The returned `SubstsRef` concatenates these two
690 /// lists: `[Vec<u8>, u8, 'a]`.
691 fn create_substs_for_ast_path<'a>(
695 parent_substs: &[subst::GenericArg<'tcx>],
696 generic_args: &'a hir::GenericArgs<'_>,
698 self_ty: Option<Ty<'tcx>>,
699 ) -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'a, 'tcx>>, Result<(), GenericArgCountMismatch>)
701 // If the type is parameterized by this region, then replace this
702 // region with the current anon region binding (in other words,
703 // whatever & would get replaced with).
705 "create_substs_for_ast_path(def_id={:?}, self_ty={:?}, \
707 def_id, self_ty, generic_args
710 let tcx = self.tcx();
711 let generic_params = tcx.generics_of(def_id);
713 if generic_params.has_self {
714 if generic_params.parent.is_some() {
715 // The parent is a trait so it should have at least one subst
716 // for the `Self` type.
717 assert!(!parent_substs.is_empty())
719 // This item (presumably a trait) needs a self-type.
720 assert!(self_ty.is_some());
723 assert!(self_ty.is_none() && parent_substs.is_empty());
726 let arg_count_correct = Self::check_generic_arg_count(
731 GenericArgPosition::Type,
736 let is_object = self_ty.map_or(false, |ty| ty == self.tcx().types.trait_object_dummy_self);
737 let default_needs_object_self = |param: &ty::GenericParamDef| {
738 if let GenericParamDefKind::Type { has_default, .. } = param.kind {
739 if is_object && has_default {
740 let default_ty = tcx.at(span).type_of(param.def_id);
741 let self_param = tcx.types.self_param;
742 if default_ty.walk().any(|arg| arg == self_param.into()) {
743 // There is no suitable inference default for a type parameter
744 // that references self, in an object type.
753 let mut missing_type_params = vec![];
754 let mut inferred_params = vec![];
755 let substs = Self::create_substs_for_generic_args(
761 arg_count_correct.is_ok(),
762 // Provide the generic args, and whether types should be inferred.
765 (Some(generic_args), infer_args)
767 // The last component of this tuple is unimportant.
771 // Provide substitutions for parameters for which (valid) arguments have been provided.
772 |param, arg| match (¶m.kind, arg) {
773 (GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => {
774 self.ast_region_to_region(<, Some(param)).into()
776 (GenericParamDefKind::Type { .. }, GenericArg::Type(ty)) => {
777 if let (hir::TyKind::Infer, false) = (&ty.kind, self.allow_ty_infer()) {
778 inferred_params.push(ty.span);
781 self.ast_ty_to_ty(&ty).into()
784 (GenericParamDefKind::Const, GenericArg::Const(ct)) => {
785 let ct_def_id = tcx.hir().local_def_id(ct.value.hir_id).expect_local();
786 ty::Const::from_anon_const(tcx, ct_def_id).into()
790 // Provide substitutions for parameters for which arguments are inferred.
791 |substs, param, infer_args| {
793 GenericParamDefKind::Lifetime => tcx.lifetimes.re_static.into(),
794 GenericParamDefKind::Type { has_default, .. } => {
795 if !infer_args && has_default {
796 // No type parameter provided, but a default exists.
798 // If we are converting an object type, then the
799 // `Self` parameter is unknown. However, some of the
800 // other type parameters may reference `Self` in their
801 // defaults. This will lead to an ICE if we are not
803 if default_needs_object_self(param) {
804 missing_type_params.push(param.name.to_string());
807 // This is a default type parameter.
810 tcx.at(span).type_of(param.def_id).subst_spanned(
818 } else if infer_args {
819 // No type parameters were provided, we can infer all.
821 if !default_needs_object_self(param) { Some(param) } else { None };
822 self.ty_infer(param, span).into()
824 // We've already errored above about the mismatch.
828 GenericParamDefKind::Const => {
829 let ty = tcx.at(span).type_of(param.def_id);
830 // FIXME(const_generics:defaults)
832 // No const parameters were provided, we can infer all.
833 self.ct_infer(ty, Some(param), span).into()
835 // We've already errored above about the mismatch.
836 tcx.mk_const(ty::Const { val: ty::ConstKind::Error, ty }).into()
843 self.complain_about_missing_type_params(
847 generic_args.args.is_empty(),
850 // Convert associated-type bindings or constraints into a separate vector.
851 // Example: Given this:
853 // T: Iterator<Item = u32>
855 // The `T` is passed in as a self-type; the `Item = u32` is
856 // not a "type parameter" of the `Iterator` trait, but rather
857 // a restriction on `<T as Iterator>::Item`, so it is passed
859 let assoc_bindings = generic_args
863 let kind = match binding.kind {
864 hir::TypeBindingKind::Equality { ref ty } => {
865 ConvertedBindingKind::Equality(self.ast_ty_to_ty(ty))
867 hir::TypeBindingKind::Constraint { ref bounds } => {
868 ConvertedBindingKind::Constraint(bounds)
871 ConvertedBinding { item_name: binding.ident, kind, span: binding.span }
876 "create_substs_for_ast_path(generic_params={:?}, self_ty={:?}) -> {:?}",
877 generic_params, self_ty, substs
880 (substs, assoc_bindings, arg_count_correct)
883 crate fn create_substs_for_associated_item(
888 item_segment: &hir::PathSegment<'_>,
889 parent_substs: SubstsRef<'tcx>,
890 ) -> SubstsRef<'tcx> {
891 if tcx.generics_of(item_def_id).params.is_empty() {
892 self.prohibit_generics(slice::from_ref(item_segment));
896 self.create_substs_for_ast_path(
900 item_segment.generic_args(),
901 item_segment.infer_args,
908 /// On missing type parameters, emit an E0393 error and provide a structured suggestion using
909 /// the type parameter's name as a placeholder.
910 fn complain_about_missing_type_params(
912 missing_type_params: Vec<String>,
915 empty_generic_args: bool,
917 if missing_type_params.is_empty() {
921 missing_type_params.iter().map(|n| format!("`{}`", n)).collect::<Vec<_>>().join(", ");
922 let mut err = struct_span_err!(
926 "the type parameter{} {} must be explicitly specified",
927 pluralize!(missing_type_params.len()),
931 self.tcx().def_span(def_id),
933 "type parameter{} {} must be specified for this",
934 pluralize!(missing_type_params.len()),
938 let mut suggested = false;
939 if let (Ok(snippet), true) = (
940 self.tcx().sess.source_map().span_to_snippet(span),
941 // Don't suggest setting the type params if there are some already: the order is
942 // tricky to get right and the user will already know what the syntax is.
945 if snippet.ends_with('>') {
946 // The user wrote `Trait<'a, T>` or similar. To provide an accurate suggestion
947 // we would have to preserve the right order. For now, as clearly the user is
948 // aware of the syntax, we do nothing.
950 // The user wrote `Iterator`, so we don't have a type we can suggest, but at
951 // least we can clue them to the correct syntax `Iterator<Type>`.
955 "set the type parameter{plural} to the desired type{plural}",
956 plural = pluralize!(missing_type_params.len()),
958 format!("{}<{}>", snippet, missing_type_params.join(", ")),
959 Applicability::HasPlaceholders,
968 "missing reference{} to {}",
969 pluralize!(missing_type_params.len()),
975 "because of the default `Self` reference, type parameters must be \
976 specified on object types",
981 /// Instantiates the path for the given trait reference, assuming that it's
982 /// bound to a valid trait type. Returns the `DefId` of the defining trait.
983 /// The type _cannot_ be a type other than a trait type.
985 /// If the `projections` argument is `None`, then assoc type bindings like `Foo<T = X>`
986 /// are disallowed. Otherwise, they are pushed onto the vector given.
987 pub fn instantiate_mono_trait_ref(
989 trait_ref: &hir::TraitRef<'_>,
991 ) -> ty::TraitRef<'tcx> {
992 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
994 self.ast_path_to_mono_trait_ref(
996 trait_ref.trait_def_id().unwrap_or_else(|| FatalError.raise()),
998 trait_ref.path.segments.last().unwrap(),
1002 /// The given trait-ref must actually be a trait.
1003 pub(super) fn instantiate_poly_trait_ref_inner(
1005 trait_ref: &hir::TraitRef<'_>,
1007 constness: Constness,
1009 bounds: &mut Bounds<'tcx>,
1011 ) -> Result<(), GenericArgCountMismatch> {
1012 let trait_def_id = trait_ref.trait_def_id().unwrap_or_else(|| FatalError.raise());
1014 debug!("instantiate_poly_trait_ref({:?}, def_id={:?})", trait_ref, trait_def_id);
1016 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
1018 let path_span = if let [segment] = &trait_ref.path.segments[..] {
1019 // FIXME: `trait_ref.path.span` can point to a full path with multiple
1020 // segments, even though `trait_ref.path.segments` is of length `1`. Work
1021 // around that bug here, even though it should be fixed elsewhere.
1022 // This would otherwise cause an invalid suggestion. For an example, look at
1023 // `src/test/ui/issues/issue-28344.rs`.
1028 let (substs, assoc_bindings, arg_count_correct) = self.create_substs_for_ast_trait_ref(
1032 trait_ref.path.segments.last().unwrap(),
1034 let poly_trait_ref = ty::Binder::bind(ty::TraitRef::new(trait_def_id, substs));
1036 bounds.trait_bounds.push((poly_trait_ref, span, constness));
1038 let mut dup_bindings = FxHashMap::default();
1039 for binding in &assoc_bindings {
1040 // Specify type to assert that error was already reported in `Err` case.
1041 let _: Result<_, ErrorReported> = self.add_predicates_for_ast_type_binding(
1042 trait_ref.hir_ref_id,
1050 // Okay to ignore `Err` because of `ErrorReported` (see above).
1054 "instantiate_poly_trait_ref({:?}, bounds={:?}) -> {:?}",
1055 trait_ref, bounds, poly_trait_ref
1061 /// Given a trait bound like `Debug`, applies that trait bound the given self-type to construct
1062 /// a full trait reference. The resulting trait reference is returned. This may also generate
1063 /// auxiliary bounds, which are added to `bounds`.
1068 /// poly_trait_ref = Iterator<Item = u32>
1072 /// this would return `Foo: Iterator` and add `<Foo as Iterator>::Item = u32` into `bounds`.
1074 /// **A note on binders:** against our usual convention, there is an implied bounder around
1075 /// the `self_ty` and `poly_trait_ref` parameters here. So they may reference bound regions.
1076 /// If for example you had `for<'a> Foo<'a>: Bar<'a>`, then the `self_ty` would be `Foo<'a>`
1077 /// where `'a` is a bound region at depth 0. Similarly, the `poly_trait_ref` would be
1078 /// `Bar<'a>`. The returned poly-trait-ref will have this binder instantiated explicitly,
1080 pub fn instantiate_poly_trait_ref(
1082 poly_trait_ref: &hir::PolyTraitRef<'_>,
1083 constness: Constness,
1085 bounds: &mut Bounds<'tcx>,
1086 ) -> Result<(), GenericArgCountMismatch> {
1087 self.instantiate_poly_trait_ref_inner(
1088 &poly_trait_ref.trait_ref,
1089 poly_trait_ref.span,
1097 fn ast_path_to_mono_trait_ref(
1100 trait_def_id: DefId,
1102 trait_segment: &hir::PathSegment<'_>,
1103 ) -> ty::TraitRef<'tcx> {
1104 let (substs, assoc_bindings, _) =
1105 self.create_substs_for_ast_trait_ref(span, trait_def_id, self_ty, trait_segment);
1106 assoc_bindings.first().map(|b| AstConv::prohibit_assoc_ty_binding(self.tcx(), b.span));
1107 ty::TraitRef::new(trait_def_id, substs)
1110 /// When the code is using the `Fn` traits directly, instead of the `Fn(A) -> B` syntax, emit
1111 /// an error and attempt to build a reasonable structured suggestion.
1112 fn complain_about_internal_fn_trait(
1115 trait_def_id: DefId,
1116 trait_segment: &'a hir::PathSegment<'a>,
1118 let trait_def = self.tcx().trait_def(trait_def_id);
1120 if !self.tcx().features().unboxed_closures
1121 && trait_segment.generic_args().parenthesized != trait_def.paren_sugar
1123 let sess = &self.tcx().sess.parse_sess;
1124 // For now, require that parenthetical notation be used only with `Fn()` etc.
1125 let (msg, sugg) = if trait_def.paren_sugar {
1127 "the precise format of `Fn`-family traits' type parameters is subject to \
1131 trait_segment.ident,
1135 .and_then(|args| args.args.get(0))
1136 .and_then(|arg| match arg {
1137 hir::GenericArg::Type(ty) => {
1138 sess.source_map().span_to_snippet(ty.span).ok()
1142 .unwrap_or_else(|| "()".to_string()),
1147 .filter_map(|b| match (b.ident.as_str() == "Output", &b.kind) {
1148 (true, hir::TypeBindingKind::Equality { ty }) => {
1149 sess.source_map().span_to_snippet(ty.span).ok()
1154 .unwrap_or_else(|| "()".to_string()),
1158 ("parenthetical notation is only stable when used with `Fn`-family traits", None)
1160 let mut err = feature_err(sess, sym::unboxed_closures, span, msg);
1161 if let Some(sugg) = sugg {
1162 let msg = "use parenthetical notation instead";
1163 err.span_suggestion(span, msg, sugg, Applicability::MaybeIncorrect);
1169 fn create_substs_for_ast_trait_ref<'a>(
1172 trait_def_id: DefId,
1174 trait_segment: &'a hir::PathSegment<'a>,
1175 ) -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'a, 'tcx>>, Result<(), GenericArgCountMismatch>)
1177 debug!("create_substs_for_ast_trait_ref(trait_segment={:?})", trait_segment);
1179 self.complain_about_internal_fn_trait(span, trait_def_id, trait_segment);
1181 self.create_substs_for_ast_path(
1185 trait_segment.generic_args(),
1186 trait_segment.infer_args,
1191 fn trait_defines_associated_type_named(
1193 trait_def_id: DefId,
1194 assoc_name: ast::Ident,
1197 .associated_items(trait_def_id)
1198 .find_by_name_and_kind(self.tcx(), assoc_name, ty::AssocKind::Type, trait_def_id)
1202 // Returns `true` if a bounds list includes `?Sized`.
1203 pub fn is_unsized(&self, ast_bounds: &[hir::GenericBound<'_>], span: Span) -> bool {
1204 let tcx = self.tcx();
1206 // Try to find an unbound in bounds.
1207 let mut unbound = None;
1208 for ab in ast_bounds {
1209 if let &hir::GenericBound::Trait(ref ptr, hir::TraitBoundModifier::Maybe) = ab {
1210 if unbound.is_none() {
1211 unbound = Some(&ptr.trait_ref);
1217 "type parameter has more than one relaxed default \
1218 bound, only one is supported"
1225 let kind_id = tcx.lang_items().require(SizedTraitLangItem);
1228 // FIXME(#8559) currently requires the unbound to be built-in.
1229 if let Ok(kind_id) = kind_id {
1230 if tpb.path.res != Res::Def(DefKind::Trait, kind_id) {
1233 "default bound relaxed for a type parameter, but \
1234 this does nothing because the given bound is not \
1235 a default; only `?Sized` is supported",
1240 _ if kind_id.is_ok() => {
1243 // No lang item for `Sized`, so we can't add it as a bound.
1250 /// This helper takes a *converted* parameter type (`param_ty`)
1251 /// and an *unconverted* list of bounds:
1254 /// fn foo<T: Debug>
1255 /// ^ ^^^^^ `ast_bounds` parameter, in HIR form
1257 /// `param_ty`, in ty form
1260 /// It adds these `ast_bounds` into the `bounds` structure.
1262 /// **A note on binders:** there is an implied binder around
1263 /// `param_ty` and `ast_bounds`. See `instantiate_poly_trait_ref`
1264 /// for more details.
1268 ast_bounds: &[hir::GenericBound<'_>],
1269 bounds: &mut Bounds<'tcx>,
1271 let mut trait_bounds = Vec::new();
1272 let mut region_bounds = Vec::new();
1274 let constness = self.default_constness_for_trait_bounds();
1275 for ast_bound in ast_bounds {
1277 hir::GenericBound::Trait(ref b, hir::TraitBoundModifier::None) => {
1278 trait_bounds.push((b, constness))
1280 hir::GenericBound::Trait(ref b, hir::TraitBoundModifier::MaybeConst) => {
1281 trait_bounds.push((b, Constness::NotConst))
1283 hir::GenericBound::Trait(_, hir::TraitBoundModifier::Maybe) => {}
1284 hir::GenericBound::Outlives(ref l) => region_bounds.push(l),
1288 for (bound, constness) in trait_bounds {
1289 let _ = self.instantiate_poly_trait_ref(bound, constness, param_ty, bounds);
1292 bounds.region_bounds.extend(
1293 region_bounds.into_iter().map(|r| (self.ast_region_to_region(r, None), r.span)),
1297 /// Translates a list of bounds from the HIR into the `Bounds` data structure.
1298 /// The self-type for the bounds is given by `param_ty`.
1303 /// fn foo<T: Bar + Baz>() { }
1304 /// ^ ^^^^^^^^^ ast_bounds
1308 /// The `sized_by_default` parameter indicates if, in this context, the `param_ty` should be
1309 /// considered `Sized` unless there is an explicit `?Sized` bound. This would be true in the
1310 /// example above, but is not true in supertrait listings like `trait Foo: Bar + Baz`.
1312 /// `span` should be the declaration size of the parameter.
1313 pub fn compute_bounds(
1316 ast_bounds: &[hir::GenericBound<'_>],
1317 sized_by_default: SizedByDefault,
1320 let mut bounds = Bounds::default();
1322 self.add_bounds(param_ty, ast_bounds, &mut bounds);
1323 bounds.trait_bounds.sort_by_key(|(t, _, _)| t.def_id());
1325 bounds.implicitly_sized = if let SizedByDefault::Yes = sized_by_default {
1326 if !self.is_unsized(ast_bounds, span) { Some(span) } else { None }
1334 /// Given an HIR binding like `Item = Foo` or `Item: Foo`, pushes the corresponding predicates
1337 /// **A note on binders:** given something like `T: for<'a> Iterator<Item = &'a u32>`, the
1338 /// `trait_ref` here will be `for<'a> T: Iterator`. The `binding` data however is from *inside*
1339 /// the binder (e.g., `&'a u32`) and hence may reference bound regions.
1340 fn add_predicates_for_ast_type_binding(
1342 hir_ref_id: hir::HirId,
1343 trait_ref: ty::PolyTraitRef<'tcx>,
1344 binding: &ConvertedBinding<'_, 'tcx>,
1345 bounds: &mut Bounds<'tcx>,
1347 dup_bindings: &mut FxHashMap<DefId, Span>,
1349 ) -> Result<(), ErrorReported> {
1350 let tcx = self.tcx();
1353 // Given something like `U: SomeTrait<T = X>`, we want to produce a
1354 // predicate like `<U as SomeTrait>::T = X`. This is somewhat
1355 // subtle in the event that `T` is defined in a supertrait of
1356 // `SomeTrait`, because in that case we need to upcast.
1358 // That is, consider this case:
1361 // trait SubTrait: SuperTrait<int> { }
1362 // trait SuperTrait<A> { type T; }
1364 // ... B: SubTrait<T = foo> ...
1367 // We want to produce `<B as SuperTrait<int>>::T == foo`.
1369 // Find any late-bound regions declared in `ty` that are not
1370 // declared in the trait-ref. These are not well-formed.
1374 // for<'a> <T as Iterator>::Item = &'a str // <-- 'a is bad
1375 // for<'a> <T as FnMut<(&'a u32,)>>::Output = &'a str // <-- 'a is ok
1376 if let ConvertedBindingKind::Equality(ty) = binding.kind {
1377 let late_bound_in_trait_ref =
1378 tcx.collect_constrained_late_bound_regions(&trait_ref);
1379 let late_bound_in_ty =
1380 tcx.collect_referenced_late_bound_regions(&ty::Binder::bind(ty));
1381 debug!("late_bound_in_trait_ref = {:?}", late_bound_in_trait_ref);
1382 debug!("late_bound_in_ty = {:?}", late_bound_in_ty);
1383 for br in late_bound_in_ty.difference(&late_bound_in_trait_ref) {
1384 let br_name = match *br {
1385 ty::BrNamed(_, name) => name,
1389 "anonymous bound region {:?} in binding but not trait ref",
1394 // FIXME: point at the type params that don't have appropriate lifetimes:
1395 // struct S1<F: for<'a> Fn(&i32, &i32) -> &'a i32>(F);
1396 // ---- ---- ^^^^^^^
1401 "binding for associated type `{}` references lifetime `{}`, \
1402 which does not appear in the trait input types",
1412 if self.trait_defines_associated_type_named(trait_ref.def_id(), binding.item_name) {
1413 // Simple case: X is defined in the current trait.
1416 // Otherwise, we have to walk through the supertraits to find
1418 self.one_bound_for_assoc_type(
1419 || traits::supertraits(tcx, trait_ref),
1420 || trait_ref.print_only_trait_path().to_string(),
1423 || match binding.kind {
1424 ConvertedBindingKind::Equality(ty) => Some(ty.to_string()),
1430 let (assoc_ident, def_scope) =
1431 tcx.adjust_ident_and_get_scope(binding.item_name, candidate.def_id(), hir_ref_id);
1433 // We have already adjusted the item name above, so compare with `ident.normalize_to_macros_2_0()` instead
1434 // of calling `filter_by_name_and_kind`.
1436 .associated_items(candidate.def_id())
1437 .filter_by_name_unhygienic(assoc_ident.name)
1439 i.kind == ty::AssocKind::Type && i.ident.normalize_to_macros_2_0() == assoc_ident
1441 .expect("missing associated type");
1443 if !assoc_ty.vis.is_accessible_from(def_scope, tcx) {
1447 &format!("associated type `{}` is private", binding.item_name),
1449 .span_label(binding.span, "private associated type")
1452 tcx.check_stability(assoc_ty.def_id, Some(hir_ref_id), binding.span);
1456 .entry(assoc_ty.def_id)
1457 .and_modify(|prev_span| {
1462 "the value of the associated type `{}` (from trait `{}`) \
1463 is already specified",
1465 tcx.def_path_str(assoc_ty.container.id())
1467 .span_label(binding.span, "re-bound here")
1468 .span_label(*prev_span, format!("`{}` bound here first", binding.item_name))
1471 .or_insert(binding.span);
1474 match binding.kind {
1475 ConvertedBindingKind::Equality(ref ty) => {
1476 // "Desugar" a constraint like `T: Iterator<Item = u32>` this to
1477 // the "projection predicate" for:
1479 // `<T as Iterator>::Item = u32`
1480 bounds.projection_bounds.push((
1481 candidate.map_bound(|trait_ref| ty::ProjectionPredicate {
1482 projection_ty: ty::ProjectionTy::from_ref_and_name(
1492 ConvertedBindingKind::Constraint(ast_bounds) => {
1493 // "Desugar" a constraint like `T: Iterator<Item: Debug>` to
1495 // `<T as Iterator>::Item: Debug`
1497 // Calling `skip_binder` is okay, because `add_bounds` expects the `param_ty`
1498 // parameter to have a skipped binder.
1499 let param_ty = tcx.mk_projection(assoc_ty.def_id, candidate.skip_binder().substs);
1500 self.add_bounds(param_ty, ast_bounds, bounds);
1510 item_segment: &hir::PathSegment<'_>,
1512 let substs = self.ast_path_substs_for_ty(span, did, item_segment);
1513 self.normalize_ty(span, self.tcx().at(span).type_of(did).subst(self.tcx(), substs))
1516 fn conv_object_ty_poly_trait_ref(
1519 trait_bounds: &[hir::PolyTraitRef<'_>],
1520 lifetime: &hir::Lifetime,
1522 let tcx = self.tcx();
1524 let mut bounds = Bounds::default();
1525 let mut potential_assoc_types = Vec::new();
1526 let dummy_self = self.tcx().types.trait_object_dummy_self;
1527 for trait_bound in trait_bounds.iter().rev() {
1528 if let Err(GenericArgCountMismatch {
1529 invalid_args: cur_potential_assoc_types, ..
1530 }) = self.instantiate_poly_trait_ref(
1532 Constness::NotConst,
1536 potential_assoc_types.extend(cur_potential_assoc_types.into_iter());
1540 // Expand trait aliases recursively and check that only one regular (non-auto) trait
1541 // is used and no 'maybe' bounds are used.
1542 let expanded_traits =
1543 traits::expand_trait_aliases(tcx, bounds.trait_bounds.iter().map(|&(a, b, _)| (a, b)));
1544 let (mut auto_traits, regular_traits): (Vec<_>, Vec<_>) =
1545 expanded_traits.partition(|i| tcx.trait_is_auto(i.trait_ref().def_id()));
1546 if regular_traits.len() > 1 {
1547 let first_trait = ®ular_traits[0];
1548 let additional_trait = ®ular_traits[1];
1549 let mut err = struct_span_err!(
1551 additional_trait.bottom().1,
1553 "only auto traits can be used as additional traits in a trait object"
1555 additional_trait.label_with_exp_info(
1557 "additional non-auto trait",
1560 first_trait.label_with_exp_info(&mut err, "first non-auto trait", "first use");
1564 if regular_traits.is_empty() && auto_traits.is_empty() {
1569 "at least one trait is required for an object type"
1572 return tcx.types.err;
1575 // Check that there are no gross object safety violations;
1576 // most importantly, that the supertraits don't contain `Self`,
1578 for item in ®ular_traits {
1579 let object_safety_violations =
1580 astconv_object_safety_violations(tcx, item.trait_ref().def_id());
1581 if !object_safety_violations.is_empty() {
1582 report_object_safety_error(
1585 item.trait_ref().def_id(),
1586 &object_safety_violations[..],
1589 return tcx.types.err;
1593 // Use a `BTreeSet` to keep output in a more consistent order.
1594 let mut associated_types: FxHashMap<Span, BTreeSet<DefId>> = FxHashMap::default();
1596 let regular_traits_refs_spans = bounds
1599 .filter(|(trait_ref, _, _)| !tcx.trait_is_auto(trait_ref.def_id()));
1601 for (base_trait_ref, span, constness) in regular_traits_refs_spans {
1602 assert_eq!(constness, Constness::NotConst);
1604 for obligation in traits::elaborate_trait_ref(tcx, base_trait_ref) {
1606 "conv_object_ty_poly_trait_ref: observing object predicate `{:?}`",
1607 obligation.predicate
1609 match obligation.predicate {
1610 ty::Predicate::Trait(pred, _) => {
1611 associated_types.entry(span).or_default().extend(
1612 tcx.associated_items(pred.def_id())
1613 .in_definition_order()
1614 .filter(|item| item.kind == ty::AssocKind::Type)
1615 .map(|item| item.def_id),
1618 ty::Predicate::Projection(pred) => {
1619 // A `Self` within the original bound will be substituted with a
1620 // `trait_object_dummy_self`, so check for that.
1621 let references_self =
1622 pred.skip_binder().ty.walk().any(|arg| arg == dummy_self.into());
1624 // If the projection output contains `Self`, force the user to
1625 // elaborate it explicitly to avoid a lot of complexity.
1627 // The "classicaly useful" case is the following:
1629 // trait MyTrait: FnMut() -> <Self as MyTrait>::MyOutput {
1634 // Here, the user could theoretically write `dyn MyTrait<Output = X>`,
1635 // but actually supporting that would "expand" to an infinitely-long type
1636 // `fix $ τ → dyn MyTrait<MyOutput = X, Output = <τ as MyTrait>::MyOutput`.
1638 // Instead, we force the user to write
1639 // `dyn MyTrait<MyOutput = X, Output = X>`, which is uglier but works. See
1640 // the discussion in #56288 for alternatives.
1641 if !references_self {
1642 // Include projections defined on supertraits.
1643 bounds.projection_bounds.push((pred, span));
1651 for (projection_bound, _) in &bounds.projection_bounds {
1652 for def_ids in associated_types.values_mut() {
1653 def_ids.remove(&projection_bound.projection_def_id());
1657 self.complain_about_missing_associated_types(
1659 potential_assoc_types,
1663 // De-duplicate auto traits so that, e.g., `dyn Trait + Send + Send` is the same as
1664 // `dyn Trait + Send`.
1665 auto_traits.sort_by_key(|i| i.trait_ref().def_id());
1666 auto_traits.dedup_by_key(|i| i.trait_ref().def_id());
1667 debug!("regular_traits: {:?}", regular_traits);
1668 debug!("auto_traits: {:?}", auto_traits);
1670 // Transform a `PolyTraitRef` into a `PolyExistentialTraitRef` by
1671 // removing the dummy `Self` type (`trait_object_dummy_self`).
1672 let trait_ref_to_existential = |trait_ref: ty::TraitRef<'tcx>| {
1673 if trait_ref.self_ty() != dummy_self {
1674 // FIXME: There appears to be a missing filter on top of `expand_trait_aliases`,
1675 // which picks up non-supertraits where clauses - but also, the object safety
1676 // completely ignores trait aliases, which could be object safety hazards. We
1677 // `delay_span_bug` here to avoid an ICE in stable even when the feature is
1678 // disabled. (#66420)
1679 tcx.sess.delay_span_bug(
1682 "trait_ref_to_existential called on {:?} with non-dummy Self",
1687 ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref)
1690 // Erase the `dummy_self` (`trait_object_dummy_self`) used above.
1691 let existential_trait_refs =
1692 regular_traits.iter().map(|i| i.trait_ref().map_bound(trait_ref_to_existential));
1693 let existential_projections = bounds.projection_bounds.iter().map(|(bound, _)| {
1694 bound.map_bound(|b| {
1695 let trait_ref = trait_ref_to_existential(b.projection_ty.trait_ref(tcx));
1696 ty::ExistentialProjection {
1698 item_def_id: b.projection_ty.item_def_id,
1699 substs: trait_ref.substs,
1704 // Calling `skip_binder` is okay because the predicates are re-bound.
1705 let regular_trait_predicates = existential_trait_refs
1706 .map(|trait_ref| ty::ExistentialPredicate::Trait(*trait_ref.skip_binder()));
1707 let auto_trait_predicates = auto_traits
1709 .map(|trait_ref| ty::ExistentialPredicate::AutoTrait(trait_ref.trait_ref().def_id()));
1710 let mut v = regular_trait_predicates
1711 .chain(auto_trait_predicates)
1713 existential_projections
1714 .map(|x| ty::ExistentialPredicate::Projection(*x.skip_binder())),
1716 .collect::<SmallVec<[_; 8]>>();
1717 v.sort_by(|a, b| a.stable_cmp(tcx, b));
1719 let existential_predicates = ty::Binder::bind(tcx.mk_existential_predicates(v.into_iter()));
1721 // Use explicitly-specified region bound.
1722 let region_bound = if !lifetime.is_elided() {
1723 self.ast_region_to_region(lifetime, None)
1725 self.compute_object_lifetime_bound(span, existential_predicates).unwrap_or_else(|| {
1726 if tcx.named_region(lifetime.hir_id).is_some() {
1727 self.ast_region_to_region(lifetime, None)
1729 self.re_infer(None, span).unwrap_or_else(|| {
1734 "the lifetime bound for this object type cannot be deduced \
1735 from context; please supply an explicit bound"
1738 tcx.lifetimes.re_static
1743 debug!("region_bound: {:?}", region_bound);
1745 let ty = tcx.mk_dynamic(existential_predicates, region_bound);
1746 debug!("trait_object_type: {:?}", ty);
1750 /// When there are any missing associated types, emit an E0191 error and attempt to supply a
1751 /// reasonable suggestion on how to write it. For the case of multiple associated types in the
1752 /// same trait bound have the same name (as they come from different super-traits), we instead
1753 /// emit a generic note suggesting using a `where` clause to constraint instead.
1754 fn complain_about_missing_associated_types(
1756 associated_types: FxHashMap<Span, BTreeSet<DefId>>,
1757 potential_assoc_types: Vec<Span>,
1758 trait_bounds: &[hir::PolyTraitRef<'_>],
1760 if !associated_types.values().any(|v| !v.is_empty()) {
1763 let tcx = self.tcx();
1764 // FIXME: Marked `mut` so that we can replace the spans further below with a more
1765 // appropriate one, but this should be handled earlier in the span assignment.
1766 let mut associated_types: FxHashMap<Span, Vec<_>> = associated_types
1768 .map(|(span, def_ids)| {
1769 (span, def_ids.into_iter().map(|did| tcx.associated_item(did)).collect())
1772 let mut names = vec![];
1774 // Account for things like `dyn Foo + 'a`, like in tests `issue-22434.rs` and
1775 // `issue-22560.rs`.
1776 let mut trait_bound_spans: Vec<Span> = vec![];
1777 for (span, items) in &associated_types {
1778 if !items.is_empty() {
1779 trait_bound_spans.push(*span);
1781 for assoc_item in items {
1782 let trait_def_id = assoc_item.container.id();
1784 "`{}` (from trait `{}`)",
1786 tcx.def_path_str(trait_def_id),
1790 if let ([], [bound]) = (&potential_assoc_types[..], &trait_bounds) {
1791 match &bound.trait_ref.path.segments[..] {
1792 // FIXME: `trait_ref.path.span` can point to a full path with multiple
1793 // segments, even though `trait_ref.path.segments` is of length `1`. Work
1794 // around that bug here, even though it should be fixed elsewhere.
1795 // This would otherwise cause an invalid suggestion. For an example, look at
1796 // `src/test/ui/issues/issue-28344.rs` where instead of the following:
1798 // error[E0191]: the value of the associated type `Output`
1799 // (from trait `std::ops::BitXor`) must be specified
1800 // --> $DIR/issue-28344.rs:4:17
1802 // LL | let x: u8 = BitXor::bitor(0 as u8, 0 as u8);
1803 // | ^^^^^^ help: specify the associated type:
1804 // | `BitXor<Output = Type>`
1808 // error[E0191]: the value of the associated type `Output`
1809 // (from trait `std::ops::BitXor`) must be specified
1810 // --> $DIR/issue-28344.rs:4:17
1812 // LL | let x: u8 = BitXor::bitor(0 as u8, 0 as u8);
1813 // | ^^^^^^^^^^^^^ help: specify the associated type:
1814 // | `BitXor::bitor<Output = Type>`
1815 [segment] if segment.args.is_none() => {
1816 trait_bound_spans = vec![segment.ident.span];
1817 associated_types = associated_types
1819 .map(|(_, items)| (segment.ident.span, items))
1826 trait_bound_spans.sort();
1827 let mut err = struct_span_err!(
1831 "the value of the associated type{} {} must be specified",
1832 pluralize!(names.len()),
1835 let mut suggestions = vec![];
1836 let mut types_count = 0;
1837 let mut where_constraints = vec![];
1838 for (span, assoc_items) in &associated_types {
1839 let mut names: FxHashMap<_, usize> = FxHashMap::default();
1840 for item in assoc_items {
1842 *names.entry(item.ident.name).or_insert(0) += 1;
1844 let mut dupes = false;
1845 for item in assoc_items {
1846 let prefix = if names[&item.ident.name] > 1 {
1847 let trait_def_id = item.container.id();
1849 format!("{}::", tcx.def_path_str(trait_def_id))
1853 if let Some(sp) = tcx.hir().span_if_local(item.def_id) {
1854 err.span_label(sp, format!("`{}{}` defined here", prefix, item.ident));
1857 if potential_assoc_types.len() == assoc_items.len() {
1858 // Only suggest when the amount of missing associated types equals the number of
1859 // extra type arguments present, as that gives us a relatively high confidence
1860 // that the user forgot to give the associtated type's name. The canonical
1861 // example would be trying to use `Iterator<isize>` instead of
1862 // `Iterator<Item = isize>`.
1863 for (potential, item) in potential_assoc_types.iter().zip(assoc_items.iter()) {
1864 if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(*potential) {
1865 suggestions.push((*potential, format!("{} = {}", item.ident, snippet)));
1868 } else if let (Ok(snippet), false) =
1869 (tcx.sess.source_map().span_to_snippet(*span), dupes)
1872 assoc_items.iter().map(|item| format!("{} = Type", item.ident)).collect();
1873 let code = if snippet.ends_with('>') {
1874 // The user wrote `Trait<'a>` or similar and we don't have a type we can
1875 // suggest, but at least we can clue them to the correct syntax
1876 // `Trait<'a, Item = Type>` while accounting for the `<'a>` in the
1878 format!("{}, {}>", &snippet[..snippet.len() - 1], types.join(", "))
1880 // The user wrote `Iterator`, so we don't have a type we can suggest, but at
1881 // least we can clue them to the correct syntax `Iterator<Item = Type>`.
1882 format!("{}<{}>", snippet, types.join(", "))
1884 suggestions.push((*span, code));
1886 where_constraints.push(*span);
1889 let where_msg = "consider introducing a new type parameter, adding `where` constraints \
1890 using the fully-qualified path to the associated types";
1891 if !where_constraints.is_empty() && suggestions.is_empty() {
1892 // If there are duplicates associated type names and a single trait bound do not
1893 // use structured suggestion, it means that there are multiple super-traits with
1894 // the same associated type name.
1895 err.help(where_msg);
1897 if suggestions.len() != 1 {
1898 // We don't need this label if there's an inline suggestion, show otherwise.
1899 for (span, assoc_items) in &associated_types {
1900 let mut names: FxHashMap<_, usize> = FxHashMap::default();
1901 for item in assoc_items {
1903 *names.entry(item.ident.name).or_insert(0) += 1;
1905 let mut label = vec![];
1906 for item in assoc_items {
1907 let postfix = if names[&item.ident.name] > 1 {
1908 let trait_def_id = item.container.id();
1909 format!(" (from trait `{}`)", tcx.def_path_str(trait_def_id))
1913 label.push(format!("`{}`{}", item.ident, postfix));
1915 if !label.is_empty() {
1919 "associated type{} {} must be specified",
1920 pluralize!(label.len()),
1927 if !suggestions.is_empty() {
1928 err.multipart_suggestion(
1929 &format!("specify the associated type{}", pluralize!(types_count)),
1931 Applicability::HasPlaceholders,
1933 if !where_constraints.is_empty() {
1934 err.span_help(where_constraints, where_msg);
1940 fn report_ambiguous_associated_type(
1947 let mut err = struct_span_err!(self.tcx().sess, span, E0223, "ambiguous associated type");
1948 if let (Some(_), Ok(snippet)) = (
1949 self.tcx().sess.confused_type_with_std_module.borrow().get(&span),
1950 self.tcx().sess.source_map().span_to_snippet(span),
1952 err.span_suggestion(
1954 "you are looking for the module in `std`, not the primitive type",
1955 format!("std::{}", snippet),
1956 Applicability::MachineApplicable,
1959 err.span_suggestion(
1961 "use fully-qualified syntax",
1962 format!("<{} as {}>::{}", type_str, trait_str, name),
1963 Applicability::HasPlaceholders,
1969 // Search for a bound on a type parameter which includes the associated item
1970 // given by `assoc_name`. `ty_param_def_id` is the `DefId` of the type parameter
1971 // This function will fail if there are no suitable bounds or there is
1973 fn find_bound_for_assoc_item(
1975 ty_param_def_id: DefId,
1976 assoc_name: ast::Ident,
1978 ) -> Result<ty::PolyTraitRef<'tcx>, ErrorReported> {
1979 let tcx = self.tcx();
1982 "find_bound_for_assoc_item(ty_param_def_id={:?}, assoc_name={:?}, span={:?})",
1983 ty_param_def_id, assoc_name, span,
1986 let predicates = &self.get_type_parameter_bounds(span, ty_param_def_id).predicates;
1988 debug!("find_bound_for_assoc_item: predicates={:#?}", predicates);
1990 let param_hir_id = tcx.hir().as_local_hir_id(ty_param_def_id).unwrap();
1991 let param_name = tcx.hir().ty_param_name(param_hir_id);
1992 self.one_bound_for_assoc_type(
1994 traits::transitive_bounds(
1996 predicates.iter().filter_map(|(p, _)| p.to_opt_poly_trait_ref()),
1999 || param_name.to_string(),
2006 // Checks that `bounds` contains exactly one element and reports appropriate
2007 // errors otherwise.
2008 fn one_bound_for_assoc_type<I>(
2010 all_candidates: impl Fn() -> I,
2011 ty_param_name: impl Fn() -> String,
2012 assoc_name: ast::Ident,
2014 is_equality: impl Fn() -> Option<String>,
2015 ) -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
2017 I: Iterator<Item = ty::PolyTraitRef<'tcx>>,
2019 let mut matching_candidates = all_candidates()
2020 .filter(|r| self.trait_defines_associated_type_named(r.def_id(), assoc_name));
2022 let bound = match matching_candidates.next() {
2023 Some(bound) => bound,
2025 self.complain_about_assoc_type_not_found(
2031 return Err(ErrorReported);
2035 debug!("one_bound_for_assoc_type: bound = {:?}", bound);
2037 if let Some(bound2) = matching_candidates.next() {
2038 debug!("one_bound_for_assoc_type: bound2 = {:?}", bound2);
2040 let is_equality = is_equality();
2041 let bounds = iter::once(bound).chain(iter::once(bound2)).chain(matching_candidates);
2042 let mut err = if is_equality.is_some() {
2043 // More specific Error Index entry.
2048 "ambiguous associated type `{}` in bounds of `{}`",
2057 "ambiguous associated type `{}` in bounds of `{}`",
2062 err.span_label(span, format!("ambiguous associated type `{}`", assoc_name));
2064 let mut where_bounds = vec![];
2065 for bound in bounds {
2066 let bound_id = bound.def_id();
2067 let bound_span = self
2069 .associated_items(bound_id)
2070 .find_by_name_and_kind(self.tcx(), assoc_name, ty::AssocKind::Type, bound_id)
2071 .and_then(|item| self.tcx().hir().span_if_local(item.def_id));
2073 if let Some(bound_span) = bound_span {
2077 "ambiguous `{}` from `{}`",
2079 bound.print_only_trait_path(),
2082 if let Some(constraint) = &is_equality {
2083 where_bounds.push(format!(
2084 " T: {trait}::{assoc} = {constraint}",
2085 trait=bound.print_only_trait_path(),
2087 constraint=constraint,
2090 err.span_suggestion(
2092 "use fully qualified syntax to disambiguate",
2096 bound.print_only_trait_path(),
2099 Applicability::MaybeIncorrect,
2104 "associated type `{}` could derive from `{}`",
2106 bound.print_only_trait_path(),
2110 if !where_bounds.is_empty() {
2112 "consider introducing a new type parameter `T` and adding `where` constraints:\
2113 \n where\n T: {},\n{}",
2115 where_bounds.join(",\n"),
2119 if !where_bounds.is_empty() {
2120 return Err(ErrorReported);
2126 fn complain_about_assoc_type_not_found<I>(
2128 all_candidates: impl Fn() -> I,
2129 ty_param_name: &str,
2130 assoc_name: ast::Ident,
2133 I: Iterator<Item = ty::PolyTraitRef<'tcx>>,
2135 // The fallback span is needed because `assoc_name` might be an `Fn()`'s `Output` without a
2136 // valid span, so we point at the whole path segment instead.
2137 let span = if assoc_name.span != DUMMY_SP { assoc_name.span } else { span };
2138 let mut err = struct_span_err!(
2142 "associated type `{}` not found for `{}`",
2147 let all_candidate_names: Vec<_> = all_candidates()
2148 .map(|r| self.tcx().associated_items(r.def_id()).in_definition_order())
2151 |item| if item.kind == ty::AssocKind::Type { Some(item.ident.name) } else { None },
2155 if let (Some(suggested_name), true) = (
2156 find_best_match_for_name(all_candidate_names.iter(), &assoc_name.as_str(), None),
2157 assoc_name.span != DUMMY_SP,
2159 err.span_suggestion(
2161 "there is an associated type with a similar name",
2162 suggested_name.to_string(),
2163 Applicability::MaybeIncorrect,
2166 err.span_label(span, format!("associated type `{}` not found", assoc_name));
2172 // Create a type from a path to an associated type.
2173 // For a path `A::B::C::D`, `qself_ty` and `qself_def` are the type and def for `A::B::C`
2174 // and item_segment is the path segment for `D`. We return a type and a def for
2176 // Will fail except for `T::A` and `Self::A`; i.e., if `qself_ty`/`qself_def` are not a type
2177 // parameter or `Self`.
2178 pub fn associated_path_to_ty(
2180 hir_ref_id: hir::HirId,
2184 assoc_segment: &hir::PathSegment<'_>,
2185 permit_variants: bool,
2186 ) -> Result<(Ty<'tcx>, DefKind, DefId), ErrorReported> {
2187 let tcx = self.tcx();
2188 let assoc_ident = assoc_segment.ident;
2190 debug!("associated_path_to_ty: {:?}::{}", qself_ty, assoc_ident);
2192 // Check if we have an enum variant.
2193 let mut variant_resolution = None;
2194 if let ty::Adt(adt_def, _) = qself_ty.kind {
2195 if adt_def.is_enum() {
2196 let variant_def = adt_def
2199 .find(|vd| tcx.hygienic_eq(assoc_ident, vd.ident, adt_def.did));
2200 if let Some(variant_def) = variant_def {
2201 if permit_variants {
2202 tcx.check_stability(variant_def.def_id, Some(hir_ref_id), span);
2203 self.prohibit_generics(slice::from_ref(assoc_segment));
2204 return Ok((qself_ty, DefKind::Variant, variant_def.def_id));
2206 variant_resolution = Some(variant_def.def_id);
2212 // Find the type of the associated item, and the trait where the associated
2213 // item is declared.
2214 let bound = match (&qself_ty.kind, qself_res) {
2215 (_, Res::SelfTy(Some(_), Some(impl_def_id))) => {
2216 // `Self` in an impl of a trait -- we have a concrete self type and a
2218 let trait_ref = match tcx.impl_trait_ref(impl_def_id) {
2219 Some(trait_ref) => trait_ref,
2221 // A cycle error occurred, most likely.
2222 return Err(ErrorReported);
2226 self.one_bound_for_assoc_type(
2227 || traits::supertraits(tcx, ty::Binder::bind(trait_ref)),
2228 || "Self".to_string(),
2234 (&ty::Param(_), Res::SelfTy(Some(param_did), None))
2235 | (&ty::Param(_), Res::Def(DefKind::TyParam, param_did)) => {
2236 self.find_bound_for_assoc_item(param_did, assoc_ident, span)?
2239 if variant_resolution.is_some() {
2240 // Variant in type position
2241 let msg = format!("expected type, found variant `{}`", assoc_ident);
2242 tcx.sess.span_err(span, &msg);
2243 } else if qself_ty.is_enum() {
2244 let mut err = struct_span_err!(
2248 "no variant named `{}` found for enum `{}`",
2253 let adt_def = qself_ty.ty_adt_def().expect("enum is not an ADT");
2254 if let Some(suggested_name) = find_best_match_for_name(
2255 adt_def.variants.iter().map(|variant| &variant.ident.name),
2256 &assoc_ident.as_str(),
2259 err.span_suggestion(
2261 "there is a variant with a similar name",
2262 suggested_name.to_string(),
2263 Applicability::MaybeIncorrect,
2268 format!("variant not found in `{}`", qself_ty),
2272 if let Some(sp) = tcx.hir().span_if_local(adt_def.did) {
2273 let sp = tcx.sess.source_map().guess_head_span(sp);
2274 err.span_label(sp, format!("variant `{}` not found here", assoc_ident));
2278 } else if !qself_ty.references_error() {
2279 // Don't print `TyErr` to the user.
2280 self.report_ambiguous_associated_type(
2282 &qself_ty.to_string(),
2287 return Err(ErrorReported);
2291 let trait_did = bound.def_id();
2292 let (assoc_ident, def_scope) =
2293 tcx.adjust_ident_and_get_scope(assoc_ident, trait_did, hir_ref_id);
2295 // We have already adjusted the item name above, so compare with `ident.normalize_to_macros_2_0()` instead
2296 // of calling `filter_by_name_and_kind`.
2298 .associated_items(trait_did)
2299 .in_definition_order()
2301 i.kind.namespace() == Namespace::TypeNS
2302 && i.ident.normalize_to_macros_2_0() == assoc_ident
2304 .expect("missing associated type");
2306 let ty = self.projected_ty_from_poly_trait_ref(span, item.def_id, assoc_segment, bound);
2307 let ty = self.normalize_ty(span, ty);
2309 let kind = DefKind::AssocTy;
2310 if !item.vis.is_accessible_from(def_scope, tcx) {
2311 let kind = kind.descr(item.def_id);
2312 let msg = format!("{} `{}` is private", kind, assoc_ident);
2314 .struct_span_err(span, &msg)
2315 .span_label(span, &format!("private {}", kind))
2318 tcx.check_stability(item.def_id, Some(hir_ref_id), span);
2320 if let Some(variant_def_id) = variant_resolution {
2321 tcx.struct_span_lint_hir(AMBIGUOUS_ASSOCIATED_ITEMS, hir_ref_id, span, |lint| {
2322 let mut err = lint.build("ambiguous associated item");
2323 let mut could_refer_to = |kind: DefKind, def_id, also| {
2324 let note_msg = format!(
2325 "`{}` could{} refer to the {} defined here",
2330 err.span_note(tcx.def_span(def_id), ¬e_msg);
2333 could_refer_to(DefKind::Variant, variant_def_id, "");
2334 could_refer_to(kind, item.def_id, " also");
2336 err.span_suggestion(
2338 "use fully-qualified syntax",
2339 format!("<{} as {}>::{}", qself_ty, tcx.item_name(trait_did), assoc_ident),
2340 Applicability::MachineApplicable,
2346 Ok((ty, kind, item.def_id))
2352 opt_self_ty: Option<Ty<'tcx>>,
2354 trait_segment: &hir::PathSegment<'_>,
2355 item_segment: &hir::PathSegment<'_>,
2357 let tcx = self.tcx();
2359 let trait_def_id = tcx.parent(item_def_id).unwrap();
2361 debug!("qpath_to_ty: trait_def_id={:?}", trait_def_id);
2363 let self_ty = if let Some(ty) = opt_self_ty {
2366 let path_str = tcx.def_path_str(trait_def_id);
2368 let def_id = self.item_def_id();
2370 debug!("qpath_to_ty: self.item_def_id()={:?}", def_id);
2372 let parent_def_id = def_id
2373 .and_then(|def_id| tcx.hir().as_local_hir_id(def_id))
2374 .map(|hir_id| tcx.hir().get_parent_did(hir_id).to_def_id());
2376 debug!("qpath_to_ty: parent_def_id={:?}", parent_def_id);
2378 // If the trait in segment is the same as the trait defining the item,
2379 // use the `<Self as ..>` syntax in the error.
2380 let is_part_of_self_trait_constraints = def_id == Some(trait_def_id);
2381 let is_part_of_fn_in_self_trait = parent_def_id == Some(trait_def_id);
2383 let type_name = if is_part_of_self_trait_constraints || is_part_of_fn_in_self_trait {
2389 self.report_ambiguous_associated_type(
2393 item_segment.ident.name,
2395 return tcx.types.err;
2398 debug!("qpath_to_ty: self_type={:?}", self_ty);
2400 let trait_ref = self.ast_path_to_mono_trait_ref(span, trait_def_id, self_ty, trait_segment);
2402 let item_substs = self.create_substs_for_associated_item(
2410 debug!("qpath_to_ty: trait_ref={:?}", trait_ref);
2412 self.normalize_ty(span, tcx.mk_projection(item_def_id, item_substs))
2415 pub fn prohibit_generics<'a, T: IntoIterator<Item = &'a hir::PathSegment<'a>>>(
2419 let mut has_err = false;
2420 for segment in segments {
2421 let (mut err_for_lt, mut err_for_ty, mut err_for_ct) = (false, false, false);
2422 for arg in segment.generic_args().args {
2423 let (span, kind) = match arg {
2424 hir::GenericArg::Lifetime(lt) => {
2430 (lt.span, "lifetime")
2432 hir::GenericArg::Type(ty) => {
2440 hir::GenericArg::Const(ct) => {
2449 let mut err = struct_span_err!(
2453 "{} arguments are not allowed for this type",
2456 err.span_label(span, format!("{} argument not allowed", kind));
2458 if err_for_lt && err_for_ty && err_for_ct {
2463 // Only emit the first error to avoid overloading the user with error messages.
2464 if let [binding, ..] = segment.generic_args().bindings {
2466 Self::prohibit_assoc_ty_binding(self.tcx(), binding.span);
2472 pub fn prohibit_assoc_ty_binding(tcx: TyCtxt<'_>, span: Span) {
2473 let mut err = struct_span_err!(
2477 "associated type bindings are not allowed here"
2479 err.span_label(span, "associated type not allowed here").emit();
2482 // FIXME(eddyb, varkor) handle type paths here too, not just value ones.
2483 pub fn def_ids_for_value_path_segments(
2485 segments: &[hir::PathSegment<'_>],
2486 self_ty: Option<Ty<'tcx>>,
2490 // We need to extract the type parameters supplied by the user in
2491 // the path `path`. Due to the current setup, this is a bit of a
2492 // tricky-process; the problem is that resolve only tells us the
2493 // end-point of the path resolution, and not the intermediate steps.
2494 // Luckily, we can (at least for now) deduce the intermediate steps
2495 // just from the end-point.
2497 // There are basically five cases to consider:
2499 // 1. Reference to a constructor of a struct:
2501 // struct Foo<T>(...)
2503 // In this case, the parameters are declared in the type space.
2505 // 2. Reference to a constructor of an enum variant:
2507 // enum E<T> { Foo(...) }
2509 // In this case, the parameters are defined in the type space,
2510 // but may be specified either on the type or the variant.
2512 // 3. Reference to a fn item or a free constant:
2516 // In this case, the path will again always have the form
2517 // `a::b::foo::<T>` where only the final segment should have
2518 // type parameters. However, in this case, those parameters are
2519 // declared on a value, and hence are in the `FnSpace`.
2521 // 4. Reference to a method or an associated constant:
2523 // impl<A> SomeStruct<A> {
2527 // Here we can have a path like
2528 // `a::b::SomeStruct::<A>::foo::<B>`, in which case parameters
2529 // may appear in two places. The penultimate segment,
2530 // `SomeStruct::<A>`, contains parameters in TypeSpace, and the
2531 // final segment, `foo::<B>` contains parameters in fn space.
2533 // The first step then is to categorize the segments appropriately.
2535 let tcx = self.tcx();
2537 assert!(!segments.is_empty());
2538 let last = segments.len() - 1;
2540 let mut path_segs = vec![];
2543 // Case 1. Reference to a struct constructor.
2544 DefKind::Ctor(CtorOf::Struct, ..) => {
2545 // Everything but the final segment should have no
2546 // parameters at all.
2547 let generics = tcx.generics_of(def_id);
2548 // Variant and struct constructors use the
2549 // generics of their parent type definition.
2550 let generics_def_id = generics.parent.unwrap_or(def_id);
2551 path_segs.push(PathSeg(generics_def_id, last));
2554 // Case 2. Reference to a variant constructor.
2555 DefKind::Ctor(CtorOf::Variant, ..) | DefKind::Variant => {
2556 let adt_def = self_ty.map(|t| t.ty_adt_def().unwrap());
2557 let (generics_def_id, index) = if let Some(adt_def) = adt_def {
2558 debug_assert!(adt_def.is_enum());
2560 } else if last >= 1 && segments[last - 1].args.is_some() {
2561 // Everything but the penultimate segment should have no
2562 // parameters at all.
2563 let mut def_id = def_id;
2565 // `DefKind::Ctor` -> `DefKind::Variant`
2566 if let DefKind::Ctor(..) = kind {
2567 def_id = tcx.parent(def_id).unwrap()
2570 // `DefKind::Variant` -> `DefKind::Enum`
2571 let enum_def_id = tcx.parent(def_id).unwrap();
2572 (enum_def_id, last - 1)
2574 // FIXME: lint here recommending `Enum::<...>::Variant` form
2575 // instead of `Enum::Variant::<...>` form.
2577 // Everything but the final segment should have no
2578 // parameters at all.
2579 let generics = tcx.generics_of(def_id);
2580 // Variant and struct constructors use the
2581 // generics of their parent type definition.
2582 (generics.parent.unwrap_or(def_id), last)
2584 path_segs.push(PathSeg(generics_def_id, index));
2587 // Case 3. Reference to a top-level value.
2588 DefKind::Fn | DefKind::Const | DefKind::ConstParam | DefKind::Static => {
2589 path_segs.push(PathSeg(def_id, last));
2592 // Case 4. Reference to a method or associated const.
2593 DefKind::AssocFn | DefKind::AssocConst => {
2594 if segments.len() >= 2 {
2595 let generics = tcx.generics_of(def_id);
2596 path_segs.push(PathSeg(generics.parent.unwrap(), last - 1));
2598 path_segs.push(PathSeg(def_id, last));
2601 kind => bug!("unexpected definition kind {:?} for {:?}", kind, def_id),
2604 debug!("path_segs = {:?}", path_segs);
2609 // Check a type `Path` and convert it to a `Ty`.
2612 opt_self_ty: Option<Ty<'tcx>>,
2613 path: &hir::Path<'_>,
2614 permit_variants: bool,
2616 let tcx = self.tcx();
2619 "res_to_ty(res={:?}, opt_self_ty={:?}, path_segments={:?})",
2620 path.res, opt_self_ty, path.segments
2623 let span = path.span;
2625 Res::Def(DefKind::OpaqueTy, did) => {
2626 // Check for desugared `impl Trait`.
2627 assert!(ty::is_impl_trait_defn(tcx, did).is_none());
2628 let item_segment = path.segments.split_last().unwrap();
2629 self.prohibit_generics(item_segment.1);
2630 let substs = self.ast_path_substs_for_ty(span, did, item_segment.0);
2631 self.normalize_ty(span, tcx.mk_opaque(did, substs))
2633 Res::Def(DefKind::Enum, did)
2634 | Res::Def(DefKind::TyAlias, did)
2635 | Res::Def(DefKind::Struct, did)
2636 | Res::Def(DefKind::Union, did)
2637 | Res::Def(DefKind::ForeignTy, did) => {
2638 assert_eq!(opt_self_ty, None);
2639 self.prohibit_generics(path.segments.split_last().unwrap().1);
2640 self.ast_path_to_ty(span, did, path.segments.last().unwrap())
2642 Res::Def(kind @ DefKind::Variant, def_id) if permit_variants => {
2643 // Convert "variant type" as if it were a real type.
2644 // The resulting `Ty` is type of the variant's enum for now.
2645 assert_eq!(opt_self_ty, None);
2648 self.def_ids_for_value_path_segments(&path.segments, None, kind, def_id);
2649 let generic_segs: FxHashSet<_> =
2650 path_segs.iter().map(|PathSeg(_, index)| index).collect();
2651 self.prohibit_generics(path.segments.iter().enumerate().filter_map(
2653 if !generic_segs.contains(&index) { Some(seg) } else { None }
2657 let PathSeg(def_id, index) = path_segs.last().unwrap();
2658 self.ast_path_to_ty(span, *def_id, &path.segments[*index])
2660 Res::Def(DefKind::TyParam, def_id) => {
2661 assert_eq!(opt_self_ty, None);
2662 self.prohibit_generics(path.segments);
2664 let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
2665 let item_id = tcx.hir().get_parent_node(hir_id);
2666 let item_def_id = tcx.hir().local_def_id(item_id);
2667 let generics = tcx.generics_of(item_def_id);
2668 let index = generics.param_def_id_to_index[&def_id];
2669 tcx.mk_ty_param(index, tcx.hir().name(hir_id))
2671 Res::SelfTy(Some(_), None) => {
2672 // `Self` in trait or type alias.
2673 assert_eq!(opt_self_ty, None);
2674 self.prohibit_generics(path.segments);
2675 tcx.types.self_param
2677 Res::SelfTy(_, Some(def_id)) => {
2678 // `Self` in impl (we know the concrete type).
2679 assert_eq!(opt_self_ty, None);
2680 self.prohibit_generics(path.segments);
2681 // Try to evaluate any array length constants.
2682 self.normalize_ty(span, tcx.at(span).type_of(def_id))
2684 Res::Def(DefKind::AssocTy, def_id) => {
2685 debug_assert!(path.segments.len() >= 2);
2686 self.prohibit_generics(&path.segments[..path.segments.len() - 2]);
2691 &path.segments[path.segments.len() - 2],
2692 path.segments.last().unwrap(),
2695 Res::PrimTy(prim_ty) => {
2696 assert_eq!(opt_self_ty, None);
2697 self.prohibit_generics(path.segments);
2699 hir::PrimTy::Bool => tcx.types.bool,
2700 hir::PrimTy::Char => tcx.types.char,
2701 hir::PrimTy::Int(it) => tcx.mk_mach_int(it),
2702 hir::PrimTy::Uint(uit) => tcx.mk_mach_uint(uit),
2703 hir::PrimTy::Float(ft) => tcx.mk_mach_float(ft),
2704 hir::PrimTy::Str => tcx.mk_str(),
2708 self.set_tainted_by_errors();
2709 self.tcx().types.err
2711 _ => span_bug!(span, "unexpected resolution: {:?}", path.res),
2715 /// Parses the programmer's textual representation of a type into our
2716 /// internal notion of a type.
2717 pub fn ast_ty_to_ty(&self, ast_ty: &hir::Ty<'_>) -> Ty<'tcx> {
2718 debug!("ast_ty_to_ty(id={:?}, ast_ty={:?} ty_ty={:?})", ast_ty.hir_id, ast_ty, ast_ty.kind);
2720 let tcx = self.tcx();
2722 let result_ty = match ast_ty.kind {
2723 hir::TyKind::Slice(ref ty) => tcx.mk_slice(self.ast_ty_to_ty(&ty)),
2724 hir::TyKind::Ptr(ref mt) => {
2725 tcx.mk_ptr(ty::TypeAndMut { ty: self.ast_ty_to_ty(&mt.ty), mutbl: mt.mutbl })
2727 hir::TyKind::Rptr(ref region, ref mt) => {
2728 let r = self.ast_region_to_region(region, None);
2729 debug!("ast_ty_to_ty: r={:?}", r);
2730 let t = self.ast_ty_to_ty(&mt.ty);
2731 tcx.mk_ref(r, ty::TypeAndMut { ty: t, mutbl: mt.mutbl })
2733 hir::TyKind::Never => tcx.types.never,
2734 hir::TyKind::Tup(ref fields) => {
2735 tcx.mk_tup(fields.iter().map(|t| self.ast_ty_to_ty(&t)))
2737 hir::TyKind::BareFn(ref bf) => {
2738 require_c_abi_if_c_variadic(tcx, &bf.decl, bf.abi, ast_ty.span);
2739 tcx.mk_fn_ptr(self.ty_of_fn(
2743 &hir::Generics::empty(),
2747 hir::TyKind::TraitObject(ref bounds, ref lifetime) => {
2748 self.conv_object_ty_poly_trait_ref(ast_ty.span, bounds, lifetime)
2750 hir::TyKind::Path(hir::QPath::Resolved(ref maybe_qself, ref path)) => {
2751 debug!("ast_ty_to_ty: maybe_qself={:?} path={:?}", maybe_qself, path);
2752 let opt_self_ty = maybe_qself.as_ref().map(|qself| self.ast_ty_to_ty(qself));
2753 self.res_to_ty(opt_self_ty, path, false)
2755 hir::TyKind::Def(item_id, ref lifetimes) => {
2756 let did = tcx.hir().local_def_id(item_id.id);
2757 self.impl_trait_ty_to_ty(did, lifetimes)
2759 hir::TyKind::Path(hir::QPath::TypeRelative(ref qself, ref segment)) => {
2760 debug!("ast_ty_to_ty: qself={:?} segment={:?}", qself, segment);
2761 let ty = self.ast_ty_to_ty(qself);
2763 let res = if let hir::TyKind::Path(hir::QPath::Resolved(_, ref path)) = qself.kind {
2768 self.associated_path_to_ty(ast_ty.hir_id, ast_ty.span, ty, res, segment, false)
2769 .map(|(ty, _, _)| ty)
2770 .unwrap_or(tcx.types.err)
2772 hir::TyKind::Array(ref ty, ref length) => {
2773 let length_def_id = tcx.hir().local_def_id(length.hir_id).expect_local();
2774 let length = ty::Const::from_anon_const(tcx, length_def_id);
2775 let array_ty = tcx.mk_ty(ty::Array(self.ast_ty_to_ty(&ty), length));
2776 self.normalize_ty(ast_ty.span, array_ty)
2778 hir::TyKind::Typeof(ref _e) => {
2783 "`typeof` is a reserved keyword but unimplemented"
2785 .span_label(ast_ty.span, "reserved keyword")
2790 hir::TyKind::Infer => {
2791 // Infer also appears as the type of arguments or return
2792 // values in a ExprKind::Closure, or as
2793 // the type of local variables. Both of these cases are
2794 // handled specially and will not descend into this routine.
2795 self.ty_infer(None, ast_ty.span)
2797 hir::TyKind::Err => tcx.types.err,
2800 debug!("ast_ty_to_ty: result_ty={:?}", result_ty);
2802 self.record_ty(ast_ty.hir_id, result_ty, ast_ty.span);
2806 pub fn impl_trait_ty_to_ty(
2809 lifetimes: &[hir::GenericArg<'_>],
2811 debug!("impl_trait_ty_to_ty(def_id={:?}, lifetimes={:?})", def_id, lifetimes);
2812 let tcx = self.tcx();
2814 let generics = tcx.generics_of(def_id);
2816 debug!("impl_trait_ty_to_ty: generics={:?}", generics);
2817 let substs = InternalSubsts::for_item(tcx, def_id, |param, _| {
2818 if let Some(i) = (param.index as usize).checked_sub(generics.parent_count) {
2819 // Our own parameters are the resolved lifetimes.
2821 GenericParamDefKind::Lifetime => {
2822 if let hir::GenericArg::Lifetime(lifetime) = &lifetimes[i] {
2823 self.ast_region_to_region(lifetime, None).into()
2831 // Replace all parent lifetimes with `'static`.
2833 GenericParamDefKind::Lifetime => tcx.lifetimes.re_static.into(),
2834 _ => tcx.mk_param_from_def(param),
2838 debug!("impl_trait_ty_to_ty: substs={:?}", substs);
2840 let ty = tcx.mk_opaque(def_id, substs);
2841 debug!("impl_trait_ty_to_ty: {}", ty);
2845 pub fn ty_of_arg(&self, ty: &hir::Ty<'_>, expected_ty: Option<Ty<'tcx>>) -> Ty<'tcx> {
2847 hir::TyKind::Infer if expected_ty.is_some() => {
2848 self.record_ty(ty.hir_id, expected_ty.unwrap(), ty.span);
2849 expected_ty.unwrap()
2851 _ => self.ast_ty_to_ty(ty),
2857 unsafety: hir::Unsafety,
2859 decl: &hir::FnDecl<'_>,
2860 generics: &hir::Generics<'_>,
2861 ident_span: Option<Span>,
2862 ) -> ty::PolyFnSig<'tcx> {
2865 let tcx = self.tcx();
2867 // We proactively collect all the inferred type params to emit a single error per fn def.
2868 let mut visitor = PlaceholderHirTyCollector::default();
2869 for ty in decl.inputs {
2870 visitor.visit_ty(ty);
2872 walk_generics(&mut visitor, generics);
2874 let input_tys = decl.inputs.iter().map(|a| self.ty_of_arg(a, None));
2875 let output_ty = match decl.output {
2876 hir::FnRetTy::Return(ref output) => {
2877 visitor.visit_ty(output);
2878 self.ast_ty_to_ty(output)
2880 hir::FnRetTy::DefaultReturn(..) => tcx.mk_unit(),
2883 debug!("ty_of_fn: output_ty={:?}", output_ty);
2886 ty::Binder::bind(tcx.mk_fn_sig(input_tys, output_ty, decl.c_variadic, unsafety, abi));
2888 if let (false, Some(ident_span)) = (self.allow_ty_infer(), ident_span) {
2889 // We always collect the spans for placeholder types when evaluating `fn`s, but we
2890 // only want to emit an error complaining about them if infer types (`_`) are not
2891 // allowed. `allow_ty_infer` gates this behavior. We check for the presence of
2892 // `ident_span` to not emit an error twice when we have `fn foo(_: fn() -> _)`.
2893 crate::collect::placeholder_type_error(
2895 ident_span.shrink_to_hi(),
2896 &generics.params[..],
2902 // Find any late-bound regions declared in return type that do
2903 // not appear in the arguments. These are not well-formed.
2906 // for<'a> fn() -> &'a str <-- 'a is bad
2907 // for<'a> fn(&'a String) -> &'a str <-- 'a is ok
2908 let inputs = bare_fn_ty.inputs();
2909 let late_bound_in_args =
2910 tcx.collect_constrained_late_bound_regions(&inputs.map_bound(|i| i.to_owned()));
2911 let output = bare_fn_ty.output();
2912 let late_bound_in_ret = tcx.collect_referenced_late_bound_regions(&output);
2913 for br in late_bound_in_ret.difference(&late_bound_in_args) {
2914 let lifetime_name = match *br {
2915 ty::BrNamed(_, name) => format!("lifetime `{}`,", name),
2916 ty::BrAnon(_) | ty::BrEnv => "an anonymous lifetime".to_string(),
2918 let mut err = struct_span_err!(
2922 "return type references {} which is not constrained by the fn input types",
2925 if let ty::BrAnon(_) = *br {
2926 // The only way for an anonymous lifetime to wind up
2927 // in the return type but **also** be unconstrained is
2928 // if it only appears in "associated types" in the
2929 // input. See #47511 for an example. In this case,
2930 // though we can easily give a hint that ought to be
2933 "lifetimes appearing in an associated type are not considered constrained",
2942 /// Given the bounds on an object, determines what single region bound (if any) we can
2943 /// use to summarize this type. The basic idea is that we will use the bound the user
2944 /// provided, if they provided one, and otherwise search the supertypes of trait bounds
2945 /// for region bounds. It may be that we can derive no bound at all, in which case
2946 /// we return `None`.
2947 fn compute_object_lifetime_bound(
2950 existential_predicates: ty::Binder<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>>,
2951 ) -> Option<ty::Region<'tcx>> // if None, use the default
2953 let tcx = self.tcx();
2955 debug!("compute_opt_region_bound(existential_predicates={:?})", existential_predicates);
2957 // No explicit region bound specified. Therefore, examine trait
2958 // bounds and see if we can derive region bounds from those.
2959 let derived_region_bounds = object_region_bounds(tcx, existential_predicates);
2961 // If there are no derived region bounds, then report back that we
2962 // can find no region bound. The caller will use the default.
2963 if derived_region_bounds.is_empty() {
2967 // If any of the derived region bounds are 'static, that is always
2969 if derived_region_bounds.iter().any(|&r| ty::ReStatic == *r) {
2970 return Some(tcx.lifetimes.re_static);
2973 // Determine whether there is exactly one unique region in the set
2974 // of derived region bounds. If so, use that. Otherwise, report an
2976 let r = derived_region_bounds[0];
2977 if derived_region_bounds[1..].iter().any(|r1| r != *r1) {
2982 "ambiguous lifetime bound, explicit lifetime bound required"
2990 /// Collects together a list of bounds that are applied to some type,
2991 /// after they've been converted into `ty` form (from the HIR
2992 /// representations). These lists of bounds occur in many places in
2996 /// trait Foo: Bar + Baz { }
2997 /// ^^^^^^^^^ supertrait list bounding the `Self` type parameter
2999 /// fn foo<T: Bar + Baz>() { }
3000 /// ^^^^^^^^^ bounding the type parameter `T`
3002 /// impl dyn Bar + Baz
3003 /// ^^^^^^^^^ bounding the forgotten dynamic type
3006 /// Our representation is a bit mixed here -- in some cases, we
3007 /// include the self type (e.g., `trait_bounds`) but in others we do
3008 #[derive(Default, PartialEq, Eq, Clone, Debug)]
3009 pub struct Bounds<'tcx> {
3010 /// A list of region bounds on the (implicit) self type. So if you
3011 /// had `T: 'a + 'b` this might would be a list `['a, 'b]` (but
3012 /// the `T` is not explicitly included).
3013 pub region_bounds: Vec<(ty::Region<'tcx>, Span)>,
3015 /// A list of trait bounds. So if you had `T: Debug` this would be
3016 /// `T: Debug`. Note that the self-type is explicit here.
3017 pub trait_bounds: Vec<(ty::PolyTraitRef<'tcx>, Span, Constness)>,
3019 /// A list of projection equality bounds. So if you had `T:
3020 /// Iterator<Item = u32>` this would include `<T as
3021 /// Iterator>::Item => u32`. Note that the self-type is explicit
3023 pub projection_bounds: Vec<(ty::PolyProjectionPredicate<'tcx>, Span)>,
3025 /// `Some` if there is *no* `?Sized` predicate. The `span`
3026 /// is the location in the source of the `T` declaration which can
3027 /// be cited as the source of the `T: Sized` requirement.
3028 pub implicitly_sized: Option<Span>,
3031 impl<'tcx> Bounds<'tcx> {
3032 /// Converts a bounds list into a flat set of predicates (like
3033 /// where-clauses). Because some of our bounds listings (e.g.,
3034 /// regions) don't include the self-type, you must supply the
3035 /// self-type here (the `param_ty` parameter).
3040 ) -> Vec<(ty::Predicate<'tcx>, Span)> {
3041 // If it could be sized, and is, add the `Sized` predicate.
3042 let sized_predicate = self.implicitly_sized.and_then(|span| {
3043 tcx.lang_items().sized_trait().map(|sized| {
3044 let trait_ref = ty::Binder::bind(ty::TraitRef {
3046 substs: tcx.mk_substs_trait(param_ty, &[]),
3048 (trait_ref.without_const().to_predicate(), span)
3057 .map(|&(region_bound, span)| {
3058 // Account for the binder being introduced below; no need to shift `param_ty`
3059 // because, at present at least, it either only refers to early-bound regions,
3060 // or it's a generic associated type that deliberately has escaping bound vars.
3061 let region_bound = ty::fold::shift_region(tcx, region_bound, 1);
3062 let outlives = ty::OutlivesPredicate(param_ty, region_bound);
3063 (ty::Binder::bind(outlives).to_predicate(), span)
3065 .chain(self.trait_bounds.iter().map(|&(bound_trait_ref, span, constness)| {
3066 let predicate = bound_trait_ref.with_constness(constness).to_predicate();
3070 self.projection_bounds
3072 .map(|&(projection, span)| (projection.to_predicate(), span)),