1 // ignore-tidy-filelength FIXME(#67418) Split up this file.
2 //! Conversion from AST representation of types to the `ty.rs` representation.
3 //! The main routine here is `ast_ty_to_ty()`; each use is parameterized by an
4 //! instance of `AstConv`.
6 // ignore-tidy-filelength
8 use crate::collect::PlaceholderHirTyCollector;
10 use crate::middle::lang_items::SizedTraitLangItem;
11 use crate::middle::resolve_lifetime as rl;
12 use crate::require_c_abi_if_c_variadic;
13 use crate::util::common::ErrorReported;
14 use rustc::lint::builtin::AMBIGUOUS_ASSOCIATED_ITEMS;
15 use rustc::session::parse::feature_err;
16 use rustc::ty::subst::{self, InternalSubsts, Subst, SubstsRef};
17 use rustc::ty::{self, Const, DefIdTree, ToPredicate, Ty, TyCtxt, TypeFoldable, WithConstness};
18 use rustc::ty::{GenericParamDef, GenericParamDefKind};
19 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
20 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticId};
22 use rustc_hir::def::{CtorOf, DefKind, Namespace, Res};
23 use rustc_hir::def_id::DefId;
24 use rustc_hir::intravisit::Visitor;
26 use rustc_hir::{Constness, ExprKind, GenericArg, GenericArgs};
27 use rustc_infer::traits;
28 use rustc_infer::traits::astconv_object_safety_violations;
29 use rustc_infer::traits::error_reporting::report_object_safety_error;
30 use rustc_infer::traits::wf::object_region_bounds;
31 use rustc_span::symbol::sym;
32 use rustc_span::{MultiSpan, Span, DUMMY_SP};
33 use rustc_target::spec::abi;
34 use smallvec::SmallVec;
36 use syntax::util::lev_distance::find_best_match_for_name;
38 use std::collections::BTreeSet;
42 use rustc::mir::interpret::LitToConstInput;
45 pub struct PathSeg(pub DefId, pub usize);
47 pub trait AstConv<'tcx> {
48 fn tcx<'a>(&'a self) -> TyCtxt<'tcx>;
50 fn item_def_id(&self) -> Option<DefId>;
52 fn default_constness_for_trait_bounds(&self) -> Constness;
54 /// Returns predicates in scope of the form `X: Foo`, where `X` is
55 /// a type parameter `X` with the given id `def_id`. This is a
56 /// subset of the full set of predicates.
58 /// This is used for one specific purpose: resolving "short-hand"
59 /// associated type references like `T::Item`. In principle, we
60 /// would do that by first getting the full set of predicates in
61 /// scope and then filtering down to find those that apply to `T`,
62 /// but this can lead to cycle errors. The problem is that we have
63 /// to do this resolution *in order to create the predicates in
64 /// the first place*. Hence, we have this "special pass".
65 fn get_type_parameter_bounds(&self, span: Span, def_id: DefId) -> ty::GenericPredicates<'tcx>;
67 /// Returns the lifetime to use when a lifetime is omitted (and not elided).
68 fn re_infer(&self, param: Option<&ty::GenericParamDef>, span: Span)
69 -> Option<ty::Region<'tcx>>;
71 /// Returns the type to use when a type is omitted.
72 fn ty_infer(&self, param: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx>;
74 /// Returns `true` if `_` is allowed in type signatures in the current context.
75 fn allow_ty_infer(&self) -> bool;
77 /// Returns the const to use when a const is omitted.
81 param: Option<&ty::GenericParamDef>,
83 ) -> &'tcx Const<'tcx>;
85 /// Projecting an associated type from a (potentially)
86 /// higher-ranked trait reference is more complicated, because of
87 /// the possibility of late-bound regions appearing in the
88 /// associated type binding. This is not legal in function
89 /// signatures for that reason. In a function body, we can always
90 /// handle it because we can use inference variables to remove the
91 /// late-bound regions.
92 fn projected_ty_from_poly_trait_ref(
96 item_segment: &hir::PathSegment<'_>,
97 poly_trait_ref: ty::PolyTraitRef<'tcx>,
100 /// Normalize an associated type coming from the user.
101 fn normalize_ty(&self, span: Span, ty: Ty<'tcx>) -> Ty<'tcx>;
103 /// Invoked when we encounter an error from some prior pass
104 /// (e.g., resolve) that is translated into a ty-error. This is
105 /// used to help suppress derived errors typeck might otherwise
107 fn set_tainted_by_errors(&self);
109 fn record_ty(&self, hir_id: hir::HirId, ty: Ty<'tcx>, span: Span);
112 pub enum SizedByDefault {
117 struct ConvertedBinding<'a, 'tcx> {
118 item_name: ast::Ident,
119 kind: ConvertedBindingKind<'a, 'tcx>,
123 enum ConvertedBindingKind<'a, 'tcx> {
125 Constraint(&'a [hir::GenericBound<'a>]),
129 enum GenericArgPosition {
131 Value, // e.g., functions
135 impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
136 pub fn ast_region_to_region(
138 lifetime: &hir::Lifetime,
139 def: Option<&ty::GenericParamDef>,
140 ) -> ty::Region<'tcx> {
141 let tcx = self.tcx();
142 let lifetime_name = |def_id| tcx.hir().name(tcx.hir().as_local_hir_id(def_id).unwrap());
144 let r = match tcx.named_region(lifetime.hir_id) {
145 Some(rl::Region::Static) => tcx.lifetimes.re_static,
147 Some(rl::Region::LateBound(debruijn, id, _)) => {
148 let name = lifetime_name(id);
149 tcx.mk_region(ty::ReLateBound(debruijn, ty::BrNamed(id, name)))
152 Some(rl::Region::LateBoundAnon(debruijn, index)) => {
153 tcx.mk_region(ty::ReLateBound(debruijn, ty::BrAnon(index)))
156 Some(rl::Region::EarlyBound(index, id, _)) => {
157 let name = lifetime_name(id);
158 tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion { def_id: id, index, name }))
161 Some(rl::Region::Free(scope, id)) => {
162 let name = lifetime_name(id);
163 tcx.mk_region(ty::ReFree(ty::FreeRegion {
165 bound_region: ty::BrNamed(id, name),
168 // (*) -- not late-bound, won't change
172 self.re_infer(def, lifetime.span).unwrap_or_else(|| {
173 // This indicates an illegal lifetime
174 // elision. `resolve_lifetime` should have
175 // reported an error in this case -- but if
176 // not, let's error out.
177 tcx.sess.delay_span_bug(lifetime.span, "unelided lifetime in signature");
179 // Supply some dummy value. We don't have an
180 // `re_error`, annoyingly, so use `'static`.
181 tcx.lifetimes.re_static
186 debug!("ast_region_to_region(lifetime={:?}) yields {:?}", lifetime, r);
191 /// Given a path `path` that refers to an item `I` with the declared generics `decl_generics`,
192 /// returns an appropriate set of substitutions for this particular reference to `I`.
193 pub fn ast_path_substs_for_ty(
197 item_segment: &hir::PathSegment<'_>,
198 ) -> SubstsRef<'tcx> {
199 let (substs, assoc_bindings, _) = self.create_substs_for_ast_path(
203 item_segment.generic_args(),
204 item_segment.infer_args,
208 assoc_bindings.first().map(|b| Self::prohibit_assoc_ty_binding(self.tcx(), b.span));
213 /// Report error if there is an explicit type parameter when using `impl Trait`.
216 seg: &hir::PathSegment<'_>,
217 generics: &ty::Generics,
219 let explicit = !seg.infer_args;
220 let impl_trait = generics.params.iter().any(|param| match param.kind {
221 ty::GenericParamDefKind::Type {
222 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
228 if explicit && impl_trait {
233 .filter_map(|arg| match arg {
234 GenericArg::Type(_) => Some(arg.span()),
237 .collect::<Vec<_>>();
239 let mut err = struct_span_err! {
243 "cannot provide explicit generic arguments when `impl Trait` is \
244 used in argument position"
248 err.span_label(span, "explicit generic argument not allowed");
257 /// Checks that the correct number of generic arguments have been provided.
258 /// Used specifically for function calls.
259 pub fn check_generic_arg_count_for_call(
263 seg: &hir::PathSegment<'_>,
264 is_method_call: bool,
266 let empty_args = hir::GenericArgs::none();
267 let suppress_mismatch = Self::check_impl_trait(tcx, seg, &def);
268 Self::check_generic_arg_count(
272 if let Some(ref args) = seg.args { args } else { &empty_args },
273 if is_method_call { GenericArgPosition::MethodCall } else { GenericArgPosition::Value },
274 def.parent.is_none() && def.has_self, // `has_self`
275 seg.infer_args || suppress_mismatch, // `infer_args`
280 /// Checks that the correct number of generic arguments have been provided.
281 /// This is used both for datatypes and function calls.
282 fn check_generic_arg_count(
286 args: &hir::GenericArgs<'_>,
287 position: GenericArgPosition,
290 ) -> (bool, Option<Vec<Span>>) {
291 // At this stage we are guaranteed that the generic arguments are in the correct order, e.g.
292 // that lifetimes will proceed types. So it suffices to check the number of each generic
293 // arguments in order to validate them with respect to the generic parameters.
294 let param_counts = def.own_counts();
295 let arg_counts = args.own_counts();
296 let infer_lifetimes = position != GenericArgPosition::Type && arg_counts.lifetimes == 0;
298 let mut defaults: ty::GenericParamCount = Default::default();
299 for param in &def.params {
301 GenericParamDefKind::Lifetime => {}
302 GenericParamDefKind::Type { has_default, .. } => {
303 defaults.types += has_default as usize
305 GenericParamDefKind::Const => {
306 // FIXME(const_generics:defaults)
311 if position != GenericArgPosition::Type && !args.bindings.is_empty() {
312 AstConv::prohibit_assoc_ty_binding(tcx, args.bindings[0].span);
315 // Prohibit explicit lifetime arguments if late-bound lifetime parameters are present.
316 let mut reported_late_bound_region_err = None;
317 if !infer_lifetimes {
318 if let Some(span_late) = def.has_late_bound_regions {
319 let msg = "cannot specify lifetime arguments explicitly \
320 if late bound lifetime parameters are present";
321 let note = "the late bound lifetime parameter is introduced here";
322 let span = args.args[0].span();
323 if position == GenericArgPosition::Value
324 && arg_counts.lifetimes != param_counts.lifetimes
326 let mut err = tcx.sess.struct_span_err(span, msg);
327 err.span_note(span_late, note);
329 reported_late_bound_region_err = Some(true);
331 let mut multispan = MultiSpan::from_span(span);
332 multispan.push_span_label(span_late, note.to_string());
333 tcx.struct_span_lint_hir(
334 lint::builtin::LATE_BOUND_LIFETIME_ARGUMENTS,
337 |lint| lint.build(msg).emit(),
339 reported_late_bound_region_err = Some(false);
344 let check_kind_count = |kind, required, permitted, provided, offset| {
346 "check_kind_count: kind: {} required: {} permitted: {} provided: {} offset: {}",
347 kind, required, permitted, provided, offset
349 // We enforce the following: `required` <= `provided` <= `permitted`.
350 // For kinds without defaults (e.g.., lifetimes), `required == permitted`.
351 // For other kinds (i.e., types), `permitted` may be greater than `required`.
352 if required <= provided && provided <= permitted {
353 return (reported_late_bound_region_err.unwrap_or(false), None);
356 // Unfortunately lifetime and type parameter mismatches are typically styled
357 // differently in diagnostics, which means we have a few cases to consider here.
358 let (bound, quantifier) = if required != permitted {
359 if provided < required {
360 (required, "at least ")
362 // provided > permitted
363 (permitted, "at most ")
369 let mut potential_assoc_types: Option<Vec<Span>> = None;
370 let (spans, label) = if required == permitted && provided > permitted {
371 // In the case when the user has provided too many arguments,
372 // we want to point to the unexpected arguments.
373 let spans: Vec<Span> = args.args[offset + permitted..offset + provided]
375 .map(|arg| arg.span())
377 potential_assoc_types = Some(spans.clone());
378 (spans, format!("unexpected {} argument", kind))
383 "expected {}{} {} argument{}",
392 let mut err = tcx.sess.struct_span_err_with_code(
395 "wrong number of {} arguments: expected {}{}, found {}",
396 kind, quantifier, bound, provided,
398 DiagnosticId::Error("E0107".into()),
401 err.span_label(span, label.as_str());
406 provided > required, // `suppress_error`
407 potential_assoc_types,
411 if reported_late_bound_region_err.is_none()
412 && (!infer_lifetimes || arg_counts.lifetimes > param_counts.lifetimes)
416 param_counts.lifetimes,
417 param_counts.lifetimes,
418 arg_counts.lifetimes,
422 // FIXME(const_generics:defaults)
423 if !infer_args || arg_counts.consts > param_counts.consts {
429 arg_counts.lifetimes + arg_counts.types,
432 // Note that type errors are currently be emitted *after* const errors.
433 if !infer_args || arg_counts.types > param_counts.types - defaults.types - has_self as usize
437 param_counts.types - defaults.types - has_self as usize,
438 param_counts.types - has_self as usize,
440 arg_counts.lifetimes,
443 (reported_late_bound_region_err.unwrap_or(false), None)
447 /// Creates the relevant generic argument substitutions
448 /// corresponding to a set of generic parameters. This is a
449 /// rather complex function. Let us try to explain the role
450 /// of each of its parameters:
452 /// To start, we are given the `def_id` of the thing we are
453 /// creating the substitutions for, and a partial set of
454 /// substitutions `parent_substs`. In general, the substitutions
455 /// for an item begin with substitutions for all the "parents" of
456 /// that item -- e.g., for a method it might include the
457 /// parameters from the impl.
459 /// Therefore, the method begins by walking down these parents,
460 /// starting with the outermost parent and proceed inwards until
461 /// it reaches `def_id`. For each parent `P`, it will check `parent_substs`
462 /// first to see if the parent's substitutions are listed in there. If so,
463 /// we can append those and move on. Otherwise, it invokes the
464 /// three callback functions:
466 /// - `args_for_def_id`: given the `DefId` `P`, supplies back the
467 /// generic arguments that were given to that parent from within
468 /// the path; so e.g., if you have `<T as Foo>::Bar`, the `DefId`
469 /// might refer to the trait `Foo`, and the arguments might be
470 /// `[T]`. The boolean value indicates whether to infer values
471 /// for arguments whose values were not explicitly provided.
472 /// - `provided_kind`: given the generic parameter and the value from `args_for_def_id`,
473 /// instantiate a `GenericArg`.
474 /// - `inferred_kind`: if no parameter was provided, and inference is enabled, then
475 /// creates a suitable inference variable.
476 pub fn create_substs_for_generic_args<'b>(
479 parent_substs: &[subst::GenericArg<'tcx>],
481 self_ty: Option<Ty<'tcx>>,
482 args_for_def_id: impl Fn(DefId) -> (Option<&'b GenericArgs<'b>>, bool),
483 provided_kind: impl Fn(&GenericParamDef, &GenericArg<'_>) -> subst::GenericArg<'tcx>,
484 mut inferred_kind: impl FnMut(
485 Option<&[subst::GenericArg<'tcx>]>,
488 ) -> subst::GenericArg<'tcx>,
489 ) -> SubstsRef<'tcx> {
490 // Collect the segments of the path; we need to substitute arguments
491 // for parameters throughout the entire path (wherever there are
492 // generic parameters).
493 let mut parent_defs = tcx.generics_of(def_id);
494 let count = parent_defs.count();
495 let mut stack = vec![(def_id, parent_defs)];
496 while let Some(def_id) = parent_defs.parent {
497 parent_defs = tcx.generics_of(def_id);
498 stack.push((def_id, parent_defs));
501 // We manually build up the substitution, rather than using convenience
502 // methods in `subst.rs`, so that we can iterate over the arguments and
503 // parameters in lock-step linearly, instead of trying to match each pair.
504 let mut substs: SmallVec<[subst::GenericArg<'tcx>; 8]> = SmallVec::with_capacity(count);
506 // Iterate over each segment of the path.
507 while let Some((def_id, defs)) = stack.pop() {
508 let mut params = defs.params.iter().peekable();
510 // If we have already computed substitutions for parents, we can use those directly.
511 while let Some(¶m) = params.peek() {
512 if let Some(&kind) = parent_substs.get(param.index as usize) {
520 // `Self` is handled first, unless it's been handled in `parent_substs`.
522 if let Some(¶m) = params.peek() {
523 if param.index == 0 {
524 if let GenericParamDefKind::Type { .. } = param.kind {
528 .unwrap_or_else(|| inferred_kind(None, param, true)),
536 // Check whether this segment takes generic arguments and the user has provided any.
537 let (generic_args, infer_args) = args_for_def_id(def_id);
540 generic_args.iter().flat_map(|generic_args| generic_args.args.iter()).peekable();
543 // We're going to iterate through the generic arguments that the user
544 // provided, matching them with the generic parameters we expect.
545 // Mismatches can occur as a result of elided lifetimes, or for malformed
546 // input. We try to handle both sensibly.
547 match (args.peek(), params.peek()) {
548 (Some(&arg), Some(¶m)) => {
549 match (arg, ¶m.kind) {
550 (GenericArg::Lifetime(_), GenericParamDefKind::Lifetime)
551 | (GenericArg::Type(_), GenericParamDefKind::Type { .. })
552 | (GenericArg::Const(_), GenericParamDefKind::Const) => {
553 substs.push(provided_kind(param, arg));
557 (GenericArg::Type(_), GenericParamDefKind::Lifetime)
558 | (GenericArg::Const(_), GenericParamDefKind::Lifetime) => {
559 // We expected a lifetime argument, but got a type or const
560 // argument. That means we're inferring the lifetimes.
561 substs.push(inferred_kind(None, param, infer_args));
565 // We expected one kind of parameter, but the user provided
566 // another. This is an error, but we need to handle it
567 // gracefully so we can report sensible errors.
568 // In this case, we're simply going to infer this argument.
574 // We should never be able to reach this point with well-formed input.
575 // Getting to this point means the user supplied more arguments than
576 // there are parameters.
579 (None, Some(¶m)) => {
580 // If there are fewer arguments than parameters, it means
581 // we're inferring the remaining arguments.
582 substs.push(inferred_kind(Some(&substs), param, infer_args));
586 (None, None) => break,
591 tcx.intern_substs(&substs)
594 /// Given the type/lifetime/const arguments provided to some path (along with
595 /// an implicit `Self`, if this is a trait reference), returns the complete
596 /// set of substitutions. This may involve applying defaulted type parameters.
597 /// Also returns back constriants on associated types.
602 /// T: std::ops::Index<usize, Output = u32>
603 /// ^1 ^^^^^^^^^^^^^^2 ^^^^3 ^^^^^^^^^^^4
606 /// 1. The `self_ty` here would refer to the type `T`.
607 /// 2. The path in question is the path to the trait `std::ops::Index`,
608 /// which will have been resolved to a `def_id`
609 /// 3. The `generic_args` contains info on the `<...>` contents. The `usize` type
610 /// parameters are returned in the `SubstsRef`, the associated type bindings like
611 /// `Output = u32` are returned in the `Vec<ConvertedBinding...>` result.
613 /// Note that the type listing given here is *exactly* what the user provided.
615 /// For (generic) associated types
618 /// <Vec<u8> as Iterable<u8>>::Iter::<'a>
621 /// We have the parent substs are the substs for the parent trait:
622 /// `[Vec<u8>, u8]` and `generic_args` are the arguments for the associated
623 /// type itself: `['a]`. The returned `SubstsRef` concatenates these two
624 /// lists: `[Vec<u8>, u8, 'a]`.
625 fn create_substs_for_ast_path<'a>(
629 parent_substs: &[subst::GenericArg<'tcx>],
630 generic_args: &'a hir::GenericArgs<'_>,
632 self_ty: Option<Ty<'tcx>>,
633 ) -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'a, 'tcx>>, Option<Vec<Span>>) {
634 // If the type is parameterized by this region, then replace this
635 // region with the current anon region binding (in other words,
636 // whatever & would get replaced with).
638 "create_substs_for_ast_path(def_id={:?}, self_ty={:?}, \
640 def_id, self_ty, generic_args
643 let tcx = self.tcx();
644 let generic_params = tcx.generics_of(def_id);
646 if generic_params.has_self {
647 if generic_params.parent.is_some() {
648 // The parent is a trait so it should have at least one subst
649 // for the `Self` type.
650 assert!(!parent_substs.is_empty())
652 // This item (presumably a trait) needs a self-type.
653 assert!(self_ty.is_some());
656 assert!(self_ty.is_none() && parent_substs.is_empty());
659 let (_, potential_assoc_types) = Self::check_generic_arg_count(
664 GenericArgPosition::Type,
669 let is_object = self_ty.map_or(false, |ty| ty == self.tcx().types.trait_object_dummy_self);
670 let default_needs_object_self = |param: &ty::GenericParamDef| {
671 if let GenericParamDefKind::Type { has_default, .. } = param.kind {
672 if is_object && has_default {
673 let self_param = tcx.types.self_param;
674 if tcx.at(span).type_of(param.def_id).walk().any(|ty| ty == self_param) {
675 // There is no suitable inference default for a type parameter
676 // that references self, in an object type.
685 let mut missing_type_params = vec![];
686 let substs = Self::create_substs_for_generic_args(
692 // Provide the generic args, and whether types should be inferred.
693 |_| (Some(generic_args), infer_args),
694 // Provide substitutions for parameters for which (valid) arguments have been provided.
695 |param, arg| match (¶m.kind, arg) {
696 (GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => {
697 self.ast_region_to_region(<, Some(param)).into()
699 (GenericParamDefKind::Type { .. }, GenericArg::Type(ty)) => {
700 self.ast_ty_to_ty(&ty).into()
702 (GenericParamDefKind::Const, GenericArg::Const(ct)) => {
703 self.ast_const_to_const(&ct.value, tcx.type_of(param.def_id)).into()
707 // Provide substitutions for parameters for which arguments are inferred.
708 |substs, param, infer_args| {
710 GenericParamDefKind::Lifetime => tcx.lifetimes.re_static.into(),
711 GenericParamDefKind::Type { has_default, .. } => {
712 if !infer_args && has_default {
713 // No type parameter provided, but a default exists.
715 // If we are converting an object type, then the
716 // `Self` parameter is unknown. However, some of the
717 // other type parameters may reference `Self` in their
718 // defaults. This will lead to an ICE if we are not
720 if default_needs_object_self(param) {
721 missing_type_params.push(param.name.to_string());
724 // This is a default type parameter.
727 tcx.at(span).type_of(param.def_id).subst_spanned(
735 } else if infer_args {
736 // No type parameters were provided, we can infer all.
738 if !default_needs_object_self(param) { Some(param) } else { None };
739 self.ty_infer(param, span).into()
741 // We've already errored above about the mismatch.
745 GenericParamDefKind::Const => {
746 // FIXME(const_generics:defaults)
748 // No const parameters were provided, we can infer all.
749 let ty = tcx.at(span).type_of(param.def_id);
750 self.ct_infer(ty, Some(param), span).into()
752 // We've already errored above about the mismatch.
753 tcx.consts.err.into()
760 self.complain_about_missing_type_params(
764 generic_args.args.is_empty(),
767 // Convert associated-type bindings or constraints into a separate vector.
768 // Example: Given this:
770 // T: Iterator<Item = u32>
772 // The `T` is passed in as a self-type; the `Item = u32` is
773 // not a "type parameter" of the `Iterator` trait, but rather
774 // a restriction on `<T as Iterator>::Item`, so it is passed
776 let assoc_bindings = generic_args
780 let kind = match binding.kind {
781 hir::TypeBindingKind::Equality { ref ty } => {
782 ConvertedBindingKind::Equality(self.ast_ty_to_ty(ty))
784 hir::TypeBindingKind::Constraint { ref bounds } => {
785 ConvertedBindingKind::Constraint(bounds)
788 ConvertedBinding { item_name: binding.ident, kind, span: binding.span }
793 "create_substs_for_ast_path(generic_params={:?}, self_ty={:?}) -> {:?}",
794 generic_params, self_ty, substs
797 (substs, assoc_bindings, potential_assoc_types)
800 crate fn create_substs_for_associated_item(
805 item_segment: &hir::PathSegment<'_>,
806 parent_substs: SubstsRef<'tcx>,
807 ) -> SubstsRef<'tcx> {
808 if tcx.generics_of(item_def_id).params.is_empty() {
809 self.prohibit_generics(slice::from_ref(item_segment));
813 self.create_substs_for_ast_path(
817 item_segment.generic_args(),
818 item_segment.infer_args,
825 /// On missing type parameters, emit an E0393 error and provide a structured suggestion using
826 /// the type parameter's name as a placeholder.
827 fn complain_about_missing_type_params(
829 missing_type_params: Vec<String>,
832 empty_generic_args: bool,
834 if missing_type_params.is_empty() {
838 missing_type_params.iter().map(|n| format!("`{}`", n)).collect::<Vec<_>>().join(", ");
839 let mut err = struct_span_err!(
843 "the type parameter{} {} must be explicitly specified",
844 pluralize!(missing_type_params.len()),
848 self.tcx().def_span(def_id),
850 "type parameter{} {} must be specified for this",
851 pluralize!(missing_type_params.len()),
855 let mut suggested = false;
856 if let (Ok(snippet), true) = (
857 self.tcx().sess.source_map().span_to_snippet(span),
858 // Don't suggest setting the type params if there are some already: the order is
859 // tricky to get right and the user will already know what the syntax is.
862 if snippet.ends_with('>') {
863 // The user wrote `Trait<'a, T>` or similar. To provide an accurate suggestion
864 // we would have to preserve the right order. For now, as clearly the user is
865 // aware of the syntax, we do nothing.
867 // The user wrote `Iterator`, so we don't have a type we can suggest, but at
868 // least we can clue them to the correct syntax `Iterator<Type>`.
872 "set the type parameter{plural} to the desired type{plural}",
873 plural = pluralize!(missing_type_params.len()),
875 format!("{}<{}>", snippet, missing_type_params.join(", ")),
876 Applicability::HasPlaceholders,
885 "missing reference{} to {}",
886 pluralize!(missing_type_params.len()),
892 "because of the default `Self` reference, type parameters must be \
893 specified on object types"
898 /// Instantiates the path for the given trait reference, assuming that it's
899 /// bound to a valid trait type. Returns the `DefId` of the defining trait.
900 /// The type _cannot_ be a type other than a trait type.
902 /// If the `projections` argument is `None`, then assoc type bindings like `Foo<T = X>`
903 /// are disallowed. Otherwise, they are pushed onto the vector given.
904 pub fn instantiate_mono_trait_ref(
906 trait_ref: &hir::TraitRef<'_>,
908 ) -> ty::TraitRef<'tcx> {
909 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
911 self.ast_path_to_mono_trait_ref(
913 trait_ref.trait_def_id(),
915 trait_ref.path.segments.last().unwrap(),
919 /// The given trait-ref must actually be a trait.
920 pub(super) fn instantiate_poly_trait_ref_inner(
922 trait_ref: &hir::TraitRef<'_>,
924 constness: Constness,
926 bounds: &mut Bounds<'tcx>,
928 ) -> Option<Vec<Span>> {
929 let trait_def_id = trait_ref.trait_def_id();
931 debug!("instantiate_poly_trait_ref({:?}, def_id={:?})", trait_ref, trait_def_id);
933 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
935 let path_span = if let [segment] = &trait_ref.path.segments[..] {
936 // FIXME: `trait_ref.path.span` can point to a full path with multiple
937 // segments, even though `trait_ref.path.segments` is of length `1`. Work
938 // around that bug here, even though it should be fixed elsewhere.
939 // This would otherwise cause an invalid suggestion. For an example, look at
940 // `src/test/ui/issues/issue-28344.rs`.
945 let (substs, assoc_bindings, potential_assoc_types) = self.create_substs_for_ast_trait_ref(
949 trait_ref.path.segments.last().unwrap(),
951 let poly_trait_ref = ty::Binder::bind(ty::TraitRef::new(trait_def_id, substs));
953 bounds.trait_bounds.push((poly_trait_ref, span, constness));
955 let mut dup_bindings = FxHashMap::default();
956 for binding in &assoc_bindings {
957 // Specify type to assert that error was already reported in `Err` case.
958 let _: Result<_, ErrorReported> = self.add_predicates_for_ast_type_binding(
959 trait_ref.hir_ref_id,
967 // Okay to ignore `Err` because of `ErrorReported` (see above).
971 "instantiate_poly_trait_ref({:?}, bounds={:?}) -> {:?}",
972 trait_ref, bounds, poly_trait_ref
974 potential_assoc_types
977 /// Given a trait bound like `Debug`, applies that trait bound the given self-type to construct
978 /// a full trait reference. The resulting trait reference is returned. This may also generate
979 /// auxiliary bounds, which are added to `bounds`.
984 /// poly_trait_ref = Iterator<Item = u32>
988 /// this would return `Foo: Iterator` and add `<Foo as Iterator>::Item = u32` into `bounds`.
990 /// **A note on binders:** against our usual convention, there is an implied bounder around
991 /// the `self_ty` and `poly_trait_ref` parameters here. So they may reference bound regions.
992 /// If for example you had `for<'a> Foo<'a>: Bar<'a>`, then the `self_ty` would be `Foo<'a>`
993 /// where `'a` is a bound region at depth 0. Similarly, the `poly_trait_ref` would be
994 /// `Bar<'a>`. The returned poly-trait-ref will have this binder instantiated explicitly,
996 pub fn instantiate_poly_trait_ref(
998 poly_trait_ref: &hir::PolyTraitRef<'_>,
999 constness: Constness,
1001 bounds: &mut Bounds<'tcx>,
1002 ) -> Option<Vec<Span>> {
1003 self.instantiate_poly_trait_ref_inner(
1004 &poly_trait_ref.trait_ref,
1005 poly_trait_ref.span,
1013 fn ast_path_to_mono_trait_ref(
1016 trait_def_id: DefId,
1018 trait_segment: &hir::PathSegment<'_>,
1019 ) -> ty::TraitRef<'tcx> {
1020 let (substs, assoc_bindings, _) =
1021 self.create_substs_for_ast_trait_ref(span, trait_def_id, self_ty, trait_segment);
1022 assoc_bindings.first().map(|b| AstConv::prohibit_assoc_ty_binding(self.tcx(), b.span));
1023 ty::TraitRef::new(trait_def_id, substs)
1026 /// When the code is using the `Fn` traits directly, instead of the `Fn(A) -> B` syntax, emit
1027 /// an error and attempt to build a reasonable structured suggestion.
1028 fn complain_about_internal_fn_trait(
1031 trait_def_id: DefId,
1032 trait_segment: &'a hir::PathSegment<'a>,
1034 let trait_def = self.tcx().trait_def(trait_def_id);
1036 if !self.tcx().features().unboxed_closures
1037 && trait_segment.generic_args().parenthesized != trait_def.paren_sugar
1039 // For now, require that parenthetical notation be used only with `Fn()` etc.
1040 let (msg, sugg) = if trait_def.paren_sugar {
1042 "the precise format of `Fn`-family traits' type parameters is subject to \
1046 trait_segment.ident,
1050 .and_then(|args| args.args.get(0))
1051 .and_then(|arg| match arg {
1052 hir::GenericArg::Type(ty) => {
1053 Some(print::to_string(print::NO_ANN, |s| s.print_type(ty)))
1057 .unwrap_or_else(|| "()".to_string()),
1062 .filter_map(|b| match (b.ident.as_str() == "Output", &b.kind) {
1063 (true, hir::TypeBindingKind::Equality { ty }) => {
1064 Some(print::to_string(print::NO_ANN, |s| s.print_type(ty)))
1069 .unwrap_or_else(|| "()".to_string()),
1073 ("parenthetical notation is only stable when used with `Fn`-family traits", None)
1075 let sess = &self.tcx().sess.parse_sess;
1076 let mut err = feature_err(sess, sym::unboxed_closures, span, msg);
1077 if let Some(sugg) = sugg {
1078 let msg = "use parenthetical notation instead";
1079 err.span_suggestion(span, msg, sugg, Applicability::MaybeIncorrect);
1085 fn create_substs_for_ast_trait_ref<'a>(
1088 trait_def_id: DefId,
1090 trait_segment: &'a hir::PathSegment<'a>,
1091 ) -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'a, 'tcx>>, Option<Vec<Span>>) {
1092 debug!("create_substs_for_ast_trait_ref(trait_segment={:?})", trait_segment);
1094 self.complain_about_internal_fn_trait(span, trait_def_id, trait_segment);
1096 self.create_substs_for_ast_path(
1100 trait_segment.generic_args(),
1101 trait_segment.infer_args,
1106 fn trait_defines_associated_type_named(
1108 trait_def_id: DefId,
1109 assoc_name: ast::Ident,
1112 .associated_items(trait_def_id)
1113 .find_by_name_and_kind(self.tcx(), assoc_name, ty::AssocKind::Type, trait_def_id)
1117 // Returns `true` if a bounds list includes `?Sized`.
1118 pub fn is_unsized(&self, ast_bounds: &[hir::GenericBound<'_>], span: Span) -> bool {
1119 let tcx = self.tcx();
1121 // Try to find an unbound in bounds.
1122 let mut unbound = None;
1123 for ab in ast_bounds {
1124 if let &hir::GenericBound::Trait(ref ptr, hir::TraitBoundModifier::Maybe) = ab {
1125 if unbound.is_none() {
1126 unbound = Some(&ptr.trait_ref);
1132 "type parameter has more than one relaxed default \
1133 bound, only one is supported"
1140 let kind_id = tcx.lang_items().require(SizedTraitLangItem);
1143 // FIXME(#8559) currently requires the unbound to be built-in.
1144 if let Ok(kind_id) = kind_id {
1145 if tpb.path.res != Res::Def(DefKind::Trait, kind_id) {
1148 "default bound relaxed for a type parameter, but \
1149 this does nothing because the given bound is not \
1150 a default; only `?Sized` is supported",
1155 _ if kind_id.is_ok() => {
1158 // No lang item for `Sized`, so we can't add it as a bound.
1165 /// This helper takes a *converted* parameter type (`param_ty`)
1166 /// and an *unconverted* list of bounds:
1169 /// fn foo<T: Debug>
1170 /// ^ ^^^^^ `ast_bounds` parameter, in HIR form
1172 /// `param_ty`, in ty form
1175 /// It adds these `ast_bounds` into the `bounds` structure.
1177 /// **A note on binders:** there is an implied binder around
1178 /// `param_ty` and `ast_bounds`. See `instantiate_poly_trait_ref`
1179 /// for more details.
1183 ast_bounds: &[hir::GenericBound<'_>],
1184 bounds: &mut Bounds<'tcx>,
1186 let mut trait_bounds = Vec::new();
1187 let mut region_bounds = Vec::new();
1189 let constness = self.default_constness_for_trait_bounds();
1190 for ast_bound in ast_bounds {
1192 hir::GenericBound::Trait(ref b, hir::TraitBoundModifier::None) => {
1193 trait_bounds.push((b, constness))
1195 hir::GenericBound::Trait(ref b, hir::TraitBoundModifier::MaybeConst) => {
1196 trait_bounds.push((b, Constness::NotConst))
1198 hir::GenericBound::Trait(_, hir::TraitBoundModifier::Maybe) => {}
1199 hir::GenericBound::Outlives(ref l) => region_bounds.push(l),
1203 for (bound, constness) in trait_bounds {
1204 let _ = self.instantiate_poly_trait_ref(bound, constness, param_ty, bounds);
1207 bounds.region_bounds.extend(
1208 region_bounds.into_iter().map(|r| (self.ast_region_to_region(r, None), r.span)),
1212 /// Translates a list of bounds from the HIR into the `Bounds` data structure.
1213 /// The self-type for the bounds is given by `param_ty`.
1218 /// fn foo<T: Bar + Baz>() { }
1219 /// ^ ^^^^^^^^^ ast_bounds
1223 /// The `sized_by_default` parameter indicates if, in this context, the `param_ty` should be
1224 /// considered `Sized` unless there is an explicit `?Sized` bound. This would be true in the
1225 /// example above, but is not true in supertrait listings like `trait Foo: Bar + Baz`.
1227 /// `span` should be the declaration size of the parameter.
1228 pub fn compute_bounds(
1231 ast_bounds: &[hir::GenericBound<'_>],
1232 sized_by_default: SizedByDefault,
1235 let mut bounds = Bounds::default();
1237 self.add_bounds(param_ty, ast_bounds, &mut bounds);
1238 bounds.trait_bounds.sort_by_key(|(t, _, _)| t.def_id());
1240 bounds.implicitly_sized = if let SizedByDefault::Yes = sized_by_default {
1241 if !self.is_unsized(ast_bounds, span) { Some(span) } else { None }
1249 /// Given an HIR binding like `Item = Foo` or `Item: Foo`, pushes the corresponding predicates
1252 /// **A note on binders:** given something like `T: for<'a> Iterator<Item = &'a u32>`, the
1253 /// `trait_ref` here will be `for<'a> T: Iterator`. The `binding` data however is from *inside*
1254 /// the binder (e.g., `&'a u32`) and hence may reference bound regions.
1255 fn add_predicates_for_ast_type_binding(
1257 hir_ref_id: hir::HirId,
1258 trait_ref: ty::PolyTraitRef<'tcx>,
1259 binding: &ConvertedBinding<'_, 'tcx>,
1260 bounds: &mut Bounds<'tcx>,
1262 dup_bindings: &mut FxHashMap<DefId, Span>,
1264 ) -> Result<(), ErrorReported> {
1265 let tcx = self.tcx();
1268 // Given something like `U: SomeTrait<T = X>`, we want to produce a
1269 // predicate like `<U as SomeTrait>::T = X`. This is somewhat
1270 // subtle in the event that `T` is defined in a supertrait of
1271 // `SomeTrait`, because in that case we need to upcast.
1273 // That is, consider this case:
1276 // trait SubTrait: SuperTrait<int> { }
1277 // trait SuperTrait<A> { type T; }
1279 // ... B: SubTrait<T = foo> ...
1282 // We want to produce `<B as SuperTrait<int>>::T == foo`.
1284 // Find any late-bound regions declared in `ty` that are not
1285 // declared in the trait-ref. These are not well-formed.
1289 // for<'a> <T as Iterator>::Item = &'a str // <-- 'a is bad
1290 // for<'a> <T as FnMut<(&'a u32,)>>::Output = &'a str // <-- 'a is ok
1291 if let ConvertedBindingKind::Equality(ty) = binding.kind {
1292 let late_bound_in_trait_ref =
1293 tcx.collect_constrained_late_bound_regions(&trait_ref);
1294 let late_bound_in_ty =
1295 tcx.collect_referenced_late_bound_regions(&ty::Binder::bind(ty));
1296 debug!("late_bound_in_trait_ref = {:?}", late_bound_in_trait_ref);
1297 debug!("late_bound_in_ty = {:?}", late_bound_in_ty);
1298 for br in late_bound_in_ty.difference(&late_bound_in_trait_ref) {
1299 let br_name = match *br {
1300 ty::BrNamed(_, name) => name,
1304 "anonymous bound region {:?} in binding but not trait ref",
1309 // FIXME: point at the type params that don't have appropriate lifetimes:
1310 // struct S1<F: for<'a> Fn(&i32, &i32) -> &'a i32>(F);
1311 // ---- ---- ^^^^^^^
1316 "binding for associated type `{}` references lifetime `{}`, \
1317 which does not appear in the trait input types",
1327 if self.trait_defines_associated_type_named(trait_ref.def_id(), binding.item_name) {
1328 // Simple case: X is defined in the current trait.
1331 // Otherwise, we have to walk through the supertraits to find
1333 self.one_bound_for_assoc_type(
1334 || traits::supertraits(tcx, trait_ref),
1335 || trait_ref.print_only_trait_path().to_string(),
1338 || match binding.kind {
1339 ConvertedBindingKind::Equality(ty) => Some(ty.to_string()),
1345 let (assoc_ident, def_scope) =
1346 tcx.adjust_ident_and_get_scope(binding.item_name, candidate.def_id(), hir_ref_id);
1348 // We have already adjusted the item name above, so compare with `ident.modern()` instead
1349 // of calling `filter_by_name_and_kind`.
1351 .associated_items(candidate.def_id())
1352 .filter_by_name_unhygienic(assoc_ident.name)
1353 .find(|i| i.kind == ty::AssocKind::Type && i.ident.modern() == assoc_ident)
1354 .expect("missing associated type");
1356 if !assoc_ty.vis.is_accessible_from(def_scope, tcx) {
1357 let msg = format!("associated type `{}` is private", binding.item_name);
1358 tcx.sess.span_err(binding.span, &msg);
1360 tcx.check_stability(assoc_ty.def_id, Some(hir_ref_id), binding.span);
1364 .entry(assoc_ty.def_id)
1365 .and_modify(|prev_span| {
1370 "the value of the associated type `{}` (from trait `{}`) \
1371 is already specified",
1373 tcx.def_path_str(assoc_ty.container.id())
1375 .span_label(binding.span, "re-bound here")
1376 .span_label(*prev_span, format!("`{}` bound here first", binding.item_name))
1379 .or_insert(binding.span);
1382 match binding.kind {
1383 ConvertedBindingKind::Equality(ref ty) => {
1384 // "Desugar" a constraint like `T: Iterator<Item = u32>` this to
1385 // the "projection predicate" for:
1387 // `<T as Iterator>::Item = u32`
1388 bounds.projection_bounds.push((
1389 candidate.map_bound(|trait_ref| ty::ProjectionPredicate {
1390 projection_ty: ty::ProjectionTy::from_ref_and_name(
1400 ConvertedBindingKind::Constraint(ast_bounds) => {
1401 // "Desugar" a constraint like `T: Iterator<Item: Debug>` to
1403 // `<T as Iterator>::Item: Debug`
1405 // Calling `skip_binder` is okay, because `add_bounds` expects the `param_ty`
1406 // parameter to have a skipped binder.
1407 let param_ty = tcx.mk_projection(assoc_ty.def_id, candidate.skip_binder().substs);
1408 self.add_bounds(param_ty, ast_bounds, bounds);
1418 item_segment: &hir::PathSegment<'_>,
1420 let substs = self.ast_path_substs_for_ty(span, did, item_segment);
1421 self.normalize_ty(span, self.tcx().at(span).type_of(did).subst(self.tcx(), substs))
1424 fn conv_object_ty_poly_trait_ref(
1427 trait_bounds: &[hir::PolyTraitRef<'_>],
1428 lifetime: &hir::Lifetime,
1430 let tcx = self.tcx();
1432 let mut bounds = Bounds::default();
1433 let mut potential_assoc_types = Vec::new();
1434 let dummy_self = self.tcx().types.trait_object_dummy_self;
1435 for trait_bound in trait_bounds.iter().rev() {
1436 let cur_potential_assoc_types = self.instantiate_poly_trait_ref(
1438 Constness::NotConst,
1442 potential_assoc_types.extend(cur_potential_assoc_types.into_iter().flatten());
1445 // Expand trait aliases recursively and check that only one regular (non-auto) trait
1446 // is used and no 'maybe' bounds are used.
1447 let expanded_traits =
1448 traits::expand_trait_aliases(tcx, bounds.trait_bounds.iter().map(|&(a, b, _)| (a, b)));
1449 let (mut auto_traits, regular_traits): (Vec<_>, Vec<_>) =
1450 expanded_traits.partition(|i| tcx.trait_is_auto(i.trait_ref().def_id()));
1451 if regular_traits.len() > 1 {
1452 let first_trait = ®ular_traits[0];
1453 let additional_trait = ®ular_traits[1];
1454 let mut err = struct_span_err!(
1456 additional_trait.bottom().1,
1458 "only auto traits can be used as additional traits in a trait object"
1460 additional_trait.label_with_exp_info(
1462 "additional non-auto trait",
1465 first_trait.label_with_exp_info(&mut err, "first non-auto trait", "first use");
1469 if regular_traits.is_empty() && auto_traits.is_empty() {
1474 "at least one trait is required for an object type"
1477 return tcx.types.err;
1480 // Check that there are no gross object safety violations;
1481 // most importantly, that the supertraits don't contain `Self`,
1483 for item in ®ular_traits {
1484 let object_safety_violations =
1485 astconv_object_safety_violations(tcx, item.trait_ref().def_id());
1486 if !object_safety_violations.is_empty() {
1487 report_object_safety_error(
1490 item.trait_ref().def_id(),
1491 object_safety_violations,
1494 return tcx.types.err;
1498 // Use a `BTreeSet` to keep output in a more consistent order.
1499 let mut associated_types: FxHashMap<Span, BTreeSet<DefId>> = FxHashMap::default();
1501 let regular_traits_refs_spans = bounds
1504 .filter(|(trait_ref, _, _)| !tcx.trait_is_auto(trait_ref.def_id()));
1506 for (base_trait_ref, span, constness) in regular_traits_refs_spans {
1507 assert_eq!(constness, Constness::NotConst);
1509 for trait_ref in traits::elaborate_trait_ref(tcx, base_trait_ref) {
1511 "conv_object_ty_poly_trait_ref: observing object predicate `{:?}`",
1515 ty::Predicate::Trait(pred, _) => {
1516 associated_types.entry(span).or_default().extend(
1517 tcx.associated_items(pred.def_id())
1518 .in_definition_order()
1519 .filter(|item| item.kind == ty::AssocKind::Type)
1520 .map(|item| item.def_id),
1523 ty::Predicate::Projection(pred) => {
1524 // A `Self` within the original bound will be substituted with a
1525 // `trait_object_dummy_self`, so check for that.
1526 let references_self = pred.skip_binder().ty.walk().any(|t| t == dummy_self);
1528 // If the projection output contains `Self`, force the user to
1529 // elaborate it explicitly to avoid a lot of complexity.
1531 // The "classicaly useful" case is the following:
1533 // trait MyTrait: FnMut() -> <Self as MyTrait>::MyOutput {
1538 // Here, the user could theoretically write `dyn MyTrait<Output = X>`,
1539 // but actually supporting that would "expand" to an infinitely-long type
1540 // `fix $ τ → dyn MyTrait<MyOutput = X, Output = <τ as MyTrait>::MyOutput`.
1542 // Instead, we force the user to write
1543 // `dyn MyTrait<MyOutput = X, Output = X>`, which is uglier but works. See
1544 // the discussion in #56288 for alternatives.
1545 if !references_self {
1546 // Include projections defined on supertraits.
1547 bounds.projection_bounds.push((pred, span));
1555 for (projection_bound, _) in &bounds.projection_bounds {
1556 for (_, def_ids) in &mut associated_types {
1557 def_ids.remove(&projection_bound.projection_def_id());
1561 self.complain_about_missing_associated_types(
1563 potential_assoc_types,
1567 // De-duplicate auto traits so that, e.g., `dyn Trait + Send + Send` is the same as
1568 // `dyn Trait + Send`.
1569 auto_traits.sort_by_key(|i| i.trait_ref().def_id());
1570 auto_traits.dedup_by_key(|i| i.trait_ref().def_id());
1571 debug!("regular_traits: {:?}", regular_traits);
1572 debug!("auto_traits: {:?}", auto_traits);
1574 // Transform a `PolyTraitRef` into a `PolyExistentialTraitRef` by
1575 // removing the dummy `Self` type (`trait_object_dummy_self`).
1576 let trait_ref_to_existential = |trait_ref: ty::TraitRef<'tcx>| {
1577 if trait_ref.self_ty() != dummy_self {
1578 // FIXME: There appears to be a missing filter on top of `expand_trait_aliases`,
1579 // which picks up non-supertraits where clauses - but also, the object safety
1580 // completely ignores trait aliases, which could be object safety hazards. We
1581 // `delay_span_bug` here to avoid an ICE in stable even when the feature is
1582 // disabled. (#66420)
1583 tcx.sess.delay_span_bug(
1586 "trait_ref_to_existential called on {:?} with non-dummy Self",
1591 ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref)
1594 // Erase the `dummy_self` (`trait_object_dummy_self`) used above.
1595 let existential_trait_refs = regular_traits
1597 .map(|i| i.trait_ref().map_bound(|trait_ref| trait_ref_to_existential(trait_ref)));
1598 let existential_projections = bounds.projection_bounds.iter().map(|(bound, _)| {
1599 bound.map_bound(|b| {
1600 let trait_ref = trait_ref_to_existential(b.projection_ty.trait_ref(tcx));
1601 ty::ExistentialProjection {
1603 item_def_id: b.projection_ty.item_def_id,
1604 substs: trait_ref.substs,
1609 // Calling `skip_binder` is okay because the predicates are re-bound.
1610 let regular_trait_predicates = existential_trait_refs
1611 .map(|trait_ref| ty::ExistentialPredicate::Trait(*trait_ref.skip_binder()));
1612 let auto_trait_predicates = auto_traits
1614 .map(|trait_ref| ty::ExistentialPredicate::AutoTrait(trait_ref.trait_ref().def_id()));
1615 let mut v = regular_trait_predicates
1616 .chain(auto_trait_predicates)
1618 existential_projections
1619 .map(|x| ty::ExistentialPredicate::Projection(*x.skip_binder())),
1621 .collect::<SmallVec<[_; 8]>>();
1622 v.sort_by(|a, b| a.stable_cmp(tcx, b));
1624 let existential_predicates = ty::Binder::bind(tcx.mk_existential_predicates(v.into_iter()));
1626 // Use explicitly-specified region bound.
1627 let region_bound = if !lifetime.is_elided() {
1628 self.ast_region_to_region(lifetime, None)
1630 self.compute_object_lifetime_bound(span, existential_predicates).unwrap_or_else(|| {
1631 if tcx.named_region(lifetime.hir_id).is_some() {
1632 self.ast_region_to_region(lifetime, None)
1634 self.re_infer(None, span).unwrap_or_else(|| {
1639 "the lifetime bound for this object type cannot be deduced \
1640 from context; please supply an explicit bound"
1643 tcx.lifetimes.re_static
1648 debug!("region_bound: {:?}", region_bound);
1650 let ty = tcx.mk_dynamic(existential_predicates, region_bound);
1651 debug!("trait_object_type: {:?}", ty);
1655 /// When there are any missing associated types, emit an E0191 error and attempt to supply a
1656 /// reasonable suggestion on how to write it. For the case of multiple associated types in the
1657 /// same trait bound have the same name (as they come from different super-traits), we instead
1658 /// emit a generic note suggesting using a `where` clause to constraint instead.
1659 fn complain_about_missing_associated_types(
1661 associated_types: FxHashMap<Span, BTreeSet<DefId>>,
1662 potential_assoc_types: Vec<Span>,
1663 trait_bounds: &[hir::PolyTraitRef<'_>],
1665 if !associated_types.values().any(|v| v.len() > 0) {
1668 let tcx = self.tcx();
1669 // FIXME: Marked `mut` so that we can replace the spans further below with a more
1670 // appropriate one, but this should be handled earlier in the span assignment.
1671 let mut associated_types: FxHashMap<Span, Vec<_>> = associated_types
1673 .map(|(span, def_ids)| {
1674 (span, def_ids.into_iter().map(|did| tcx.associated_item(did)).collect())
1677 let mut names = vec![];
1679 // Account for things like `dyn Foo + 'a`, like in tests `issue-22434.rs` and
1680 // `issue-22560.rs`.
1681 let mut trait_bound_spans: Vec<Span> = vec![];
1682 for (span, items) in &associated_types {
1683 if !items.is_empty() {
1684 trait_bound_spans.push(*span);
1686 for assoc_item in items {
1687 let trait_def_id = assoc_item.container.id();
1689 "`{}` (from trait `{}`)",
1691 tcx.def_path_str(trait_def_id),
1696 match (&potential_assoc_types[..], &trait_bounds) {
1697 ([], [bound]) => match &bound.trait_ref.path.segments[..] {
1698 // FIXME: `trait_ref.path.span` can point to a full path with multiple
1699 // segments, even though `trait_ref.path.segments` is of length `1`. Work
1700 // around that bug here, even though it should be fixed elsewhere.
1701 // This would otherwise cause an invalid suggestion. For an example, look at
1702 // `src/test/ui/issues/issue-28344.rs` where instead of the following:
1704 // error[E0191]: the value of the associated type `Output`
1705 // (from trait `std::ops::BitXor`) must be specified
1706 // --> $DIR/issue-28344.rs:4:17
1708 // LL | let x: u8 = BitXor::bitor(0 as u8, 0 as u8);
1709 // | ^^^^^^ help: specify the associated type:
1710 // | `BitXor<Output = Type>`
1714 // error[E0191]: the value of the associated type `Output`
1715 // (from trait `std::ops::BitXor`) must be specified
1716 // --> $DIR/issue-28344.rs:4:17
1718 // LL | let x: u8 = BitXor::bitor(0 as u8, 0 as u8);
1719 // | ^^^^^^^^^^^^^ help: specify the associated type:
1720 // | `BitXor::bitor<Output = Type>`
1721 [segment] if segment.args.is_none() => {
1722 trait_bound_spans = vec![segment.ident.span];
1723 associated_types = associated_types
1725 .map(|(_, items)| (segment.ident.span, items))
1733 trait_bound_spans.sort();
1734 let mut err = struct_span_err!(
1738 "the value of the associated type{} {} must be specified",
1739 pluralize!(names.len()),
1742 let mut suggestions = vec![];
1743 let mut types_count = 0;
1744 let mut where_constraints = vec![];
1745 for (span, assoc_items) in &associated_types {
1746 let mut names: FxHashMap<_, usize> = FxHashMap::default();
1747 for item in assoc_items {
1749 *names.entry(item.ident.name).or_insert(0) += 1;
1751 let mut dupes = false;
1752 for item in assoc_items {
1753 let prefix = if names[&item.ident.name] > 1 {
1754 let trait_def_id = item.container.id();
1756 format!("{}::", tcx.def_path_str(trait_def_id))
1760 if let Some(sp) = tcx.hir().span_if_local(item.def_id) {
1761 err.span_label(sp, format!("`{}{}` defined here", prefix, item.ident));
1764 if potential_assoc_types.len() == assoc_items.len() {
1765 // Only suggest when the amount of missing associated types equals the number of
1766 // extra type arguments present, as that gives us a relatively high confidence
1767 // that the user forgot to give the associtated type's name. The canonical
1768 // example would be trying to use `Iterator<isize>` instead of
1769 // `Iterator<Item = isize>`.
1770 for (potential, item) in potential_assoc_types.iter().zip(assoc_items.iter()) {
1771 if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(*potential) {
1772 suggestions.push((*potential, format!("{} = {}", item.ident, snippet)));
1775 } else if let (Ok(snippet), false) =
1776 (tcx.sess.source_map().span_to_snippet(*span), dupes)
1779 assoc_items.iter().map(|item| format!("{} = Type", item.ident)).collect();
1780 let code = if snippet.ends_with(">") {
1781 // The user wrote `Trait<'a>` or similar and we don't have a type we can
1782 // suggest, but at least we can clue them to the correct syntax
1783 // `Trait<'a, Item = Type>` while accounting for the `<'a>` in the
1785 format!("{}, {}>", &snippet[..snippet.len() - 1], types.join(", "))
1787 // The user wrote `Iterator`, so we don't have a type we can suggest, but at
1788 // least we can clue them to the correct syntax `Iterator<Item = Type>`.
1789 format!("{}<{}>", snippet, types.join(", "))
1791 suggestions.push((*span, code));
1793 where_constraints.push(*span);
1796 let where_msg = "consider introducing a new type parameter, adding `where` constraints \
1797 using the fully-qualified path to the associated types";
1798 if !where_constraints.is_empty() && suggestions.is_empty() {
1799 // If there are duplicates associated type names and a single trait bound do not
1800 // use structured suggestion, it means that there are multiple super-traits with
1801 // the same associated type name.
1802 err.help(where_msg);
1804 if suggestions.len() != 1 {
1805 // We don't need this label if there's an inline suggestion, show otherwise.
1806 for (span, assoc_items) in &associated_types {
1807 let mut names: FxHashMap<_, usize> = FxHashMap::default();
1808 for item in assoc_items {
1810 *names.entry(item.ident.name).or_insert(0) += 1;
1812 let mut label = vec![];
1813 for item in assoc_items {
1814 let postfix = if names[&item.ident.name] > 1 {
1815 let trait_def_id = item.container.id();
1816 format!(" (from trait `{}`)", tcx.def_path_str(trait_def_id))
1820 label.push(format!("`{}`{}", item.ident, postfix));
1822 if !label.is_empty() {
1826 "associated type{} {} must be specified",
1827 pluralize!(label.len()),
1834 if !suggestions.is_empty() {
1835 err.multipart_suggestion(
1836 &format!("specify the associated type{}", pluralize!(types_count)),
1838 Applicability::HasPlaceholders,
1840 if !where_constraints.is_empty() {
1841 err.span_help(where_constraints, where_msg);
1847 fn report_ambiguous_associated_type(
1854 let mut err = struct_span_err!(self.tcx().sess, span, E0223, "ambiguous associated type");
1855 if let (Some(_), Ok(snippet)) = (
1856 self.tcx().sess.confused_type_with_std_module.borrow().get(&span),
1857 self.tcx().sess.source_map().span_to_snippet(span),
1859 err.span_suggestion(
1861 "you are looking for the module in `std`, not the primitive type",
1862 format!("std::{}", snippet),
1863 Applicability::MachineApplicable,
1866 err.span_suggestion(
1868 "use fully-qualified syntax",
1869 format!("<{} as {}>::{}", type_str, trait_str, name),
1870 Applicability::HasPlaceholders,
1876 // Search for a bound on a type parameter which includes the associated item
1877 // given by `assoc_name`. `ty_param_def_id` is the `DefId` of the type parameter
1878 // This function will fail if there are no suitable bounds or there is
1880 fn find_bound_for_assoc_item(
1882 ty_param_def_id: DefId,
1883 assoc_name: ast::Ident,
1885 ) -> Result<ty::PolyTraitRef<'tcx>, ErrorReported> {
1886 let tcx = self.tcx();
1889 "find_bound_for_assoc_item(ty_param_def_id={:?}, assoc_name={:?}, span={:?})",
1890 ty_param_def_id, assoc_name, span,
1893 let predicates = &self.get_type_parameter_bounds(span, ty_param_def_id).predicates;
1895 debug!("find_bound_for_assoc_item: predicates={:#?}", predicates);
1897 let param_hir_id = tcx.hir().as_local_hir_id(ty_param_def_id).unwrap();
1898 let param_name = tcx.hir().ty_param_name(param_hir_id);
1899 self.one_bound_for_assoc_type(
1901 traits::transitive_bounds(
1903 predicates.iter().filter_map(|(p, _)| p.to_opt_poly_trait_ref()),
1906 || param_name.to_string(),
1913 // Checks that `bounds` contains exactly one element and reports appropriate
1914 // errors otherwise.
1915 fn one_bound_for_assoc_type<I>(
1917 all_candidates: impl Fn() -> I,
1918 ty_param_name: impl Fn() -> String,
1919 assoc_name: ast::Ident,
1921 is_equality: impl Fn() -> Option<String>,
1922 ) -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
1924 I: Iterator<Item = ty::PolyTraitRef<'tcx>>,
1926 let mut matching_candidates = all_candidates()
1927 .filter(|r| self.trait_defines_associated_type_named(r.def_id(), assoc_name));
1929 let bound = match matching_candidates.next() {
1930 Some(bound) => bound,
1932 self.complain_about_assoc_type_not_found(
1938 return Err(ErrorReported);
1942 debug!("one_bound_for_assoc_type: bound = {:?}", bound);
1944 if let Some(bound2) = matching_candidates.next() {
1945 debug!("one_bound_for_assoc_type: bound2 = {:?}", bound2);
1947 let is_equality = is_equality();
1948 let bounds = iter::once(bound).chain(iter::once(bound2)).chain(matching_candidates);
1949 let mut err = if is_equality.is_some() {
1950 // More specific Error Index entry.
1955 "ambiguous associated type `{}` in bounds of `{}`",
1964 "ambiguous associated type `{}` in bounds of `{}`",
1969 err.span_label(span, format!("ambiguous associated type `{}`", assoc_name));
1971 let mut where_bounds = vec![];
1972 for bound in bounds {
1973 let bound_id = bound.def_id();
1974 let bound_span = self
1976 .associated_items(bound_id)
1977 .find_by_name_and_kind(self.tcx(), assoc_name, ty::AssocKind::Type, bound_id)
1978 .and_then(|item| self.tcx().hir().span_if_local(item.def_id));
1980 if let Some(bound_span) = bound_span {
1984 "ambiguous `{}` from `{}`",
1986 bound.print_only_trait_path(),
1989 if let Some(constraint) = &is_equality {
1990 where_bounds.push(format!(
1991 " T: {trait}::{assoc} = {constraint}",
1992 trait=bound.print_only_trait_path(),
1994 constraint=constraint,
1997 err.span_suggestion(
1999 "use fully qualified syntax to disambiguate",
2003 bound.print_only_trait_path(),
2006 Applicability::MaybeIncorrect,
2011 "associated type `{}` could derive from `{}`",
2013 bound.print_only_trait_path(),
2017 if !where_bounds.is_empty() {
2019 "consider introducing a new type parameter `T` and adding `where` constraints:\
2020 \n where\n T: {},\n{}",
2022 where_bounds.join(",\n"),
2026 if !where_bounds.is_empty() {
2027 return Err(ErrorReported);
2033 fn complain_about_assoc_type_not_found<I>(
2035 all_candidates: impl Fn() -> I,
2036 ty_param_name: &str,
2037 assoc_name: ast::Ident,
2040 I: Iterator<Item = ty::PolyTraitRef<'tcx>>,
2042 // The fallback span is needed because `assoc_name` might be an `Fn()`'s `Output` without a
2043 // valid span, so we point at the whole path segment instead.
2044 let span = if assoc_name.span != DUMMY_SP { assoc_name.span } else { span };
2045 let mut err = struct_span_err!(
2049 "associated type `{}` not found for `{}`",
2054 let all_candidate_names: Vec<_> = all_candidates()
2055 .map(|r| self.tcx().associated_items(r.def_id()).in_definition_order())
2058 |item| if item.kind == ty::AssocKind::Type { Some(item.ident.name) } else { None },
2062 if let (Some(suggested_name), true) = (
2063 find_best_match_for_name(all_candidate_names.iter(), &assoc_name.as_str(), None),
2064 assoc_name.span != DUMMY_SP,
2066 err.span_suggestion(
2068 "there is an associated type with a similar name",
2069 suggested_name.to_string(),
2070 Applicability::MaybeIncorrect,
2073 err.span_label(span, format!("associated type `{}` not found", assoc_name));
2079 // Create a type from a path to an associated type.
2080 // For a path `A::B::C::D`, `qself_ty` and `qself_def` are the type and def for `A::B::C`
2081 // and item_segment is the path segment for `D`. We return a type and a def for
2083 // Will fail except for `T::A` and `Self::A`; i.e., if `qself_ty`/`qself_def` are not a type
2084 // parameter or `Self`.
2085 pub fn associated_path_to_ty(
2087 hir_ref_id: hir::HirId,
2091 assoc_segment: &hir::PathSegment<'_>,
2092 permit_variants: bool,
2093 ) -> Result<(Ty<'tcx>, DefKind, DefId), ErrorReported> {
2094 let tcx = self.tcx();
2095 let assoc_ident = assoc_segment.ident;
2097 debug!("associated_path_to_ty: {:?}::{}", qself_ty, assoc_ident);
2099 // Check if we have an enum variant.
2100 let mut variant_resolution = None;
2101 if let ty::Adt(adt_def, _) = qself_ty.kind {
2102 if adt_def.is_enum() {
2103 let variant_def = adt_def
2106 .find(|vd| tcx.hygienic_eq(assoc_ident, vd.ident, adt_def.did));
2107 if let Some(variant_def) = variant_def {
2108 if permit_variants {
2109 tcx.check_stability(variant_def.def_id, Some(hir_ref_id), span);
2110 self.prohibit_generics(slice::from_ref(assoc_segment));
2111 return Ok((qself_ty, DefKind::Variant, variant_def.def_id));
2113 variant_resolution = Some(variant_def.def_id);
2119 // Find the type of the associated item, and the trait where the associated
2120 // item is declared.
2121 let bound = match (&qself_ty.kind, qself_res) {
2122 (_, Res::SelfTy(Some(_), Some(impl_def_id))) => {
2123 // `Self` in an impl of a trait -- we have a concrete self type and a
2125 let trait_ref = match tcx.impl_trait_ref(impl_def_id) {
2126 Some(trait_ref) => trait_ref,
2128 // A cycle error occurred, most likely.
2129 return Err(ErrorReported);
2133 self.one_bound_for_assoc_type(
2134 || traits::supertraits(tcx, ty::Binder::bind(trait_ref)),
2135 || "Self".to_string(),
2141 (&ty::Param(_), Res::SelfTy(Some(param_did), None))
2142 | (&ty::Param(_), Res::Def(DefKind::TyParam, param_did)) => {
2143 self.find_bound_for_assoc_item(param_did, assoc_ident, span)?
2146 if variant_resolution.is_some() {
2147 // Variant in type position
2148 let msg = format!("expected type, found variant `{}`", assoc_ident);
2149 tcx.sess.span_err(span, &msg);
2150 } else if qself_ty.is_enum() {
2151 let mut err = struct_span_err!(
2155 "no variant named `{}` found for enum `{}`",
2160 let adt_def = qself_ty.ty_adt_def().expect("enum is not an ADT");
2161 if let Some(suggested_name) = find_best_match_for_name(
2162 adt_def.variants.iter().map(|variant| &variant.ident.name),
2163 &assoc_ident.as_str(),
2166 err.span_suggestion(
2168 "there is a variant with a similar name",
2169 suggested_name.to_string(),
2170 Applicability::MaybeIncorrect,
2175 format!("variant not found in `{}`", qself_ty),
2179 if let Some(sp) = tcx.hir().span_if_local(adt_def.did) {
2180 let sp = tcx.sess.source_map().def_span(sp);
2181 err.span_label(sp, format!("variant `{}` not found here", assoc_ident));
2185 } else if !qself_ty.references_error() {
2186 // Don't print `TyErr` to the user.
2187 self.report_ambiguous_associated_type(
2189 &qself_ty.to_string(),
2194 return Err(ErrorReported);
2198 let trait_did = bound.def_id();
2199 let (assoc_ident, def_scope) =
2200 tcx.adjust_ident_and_get_scope(assoc_ident, trait_did, hir_ref_id);
2202 // We have already adjusted the item name above, so compare with `ident.modern()` instead
2203 // of calling `filter_by_name_and_kind`.
2205 .associated_items(trait_did)
2206 .in_definition_order()
2207 .find(|i| i.kind.namespace() == Namespace::TypeNS && i.ident.modern() == assoc_ident)
2208 .expect("missing associated type");
2210 let ty = self.projected_ty_from_poly_trait_ref(span, item.def_id, assoc_segment, bound);
2211 let ty = self.normalize_ty(span, ty);
2213 let kind = DefKind::AssocTy;
2214 if !item.vis.is_accessible_from(def_scope, tcx) {
2215 let msg = format!("{} `{}` is private", kind.descr(item.def_id), assoc_ident);
2216 tcx.sess.span_err(span, &msg);
2218 tcx.check_stability(item.def_id, Some(hir_ref_id), span);
2220 if let Some(variant_def_id) = variant_resolution {
2221 tcx.struct_span_lint_hir(AMBIGUOUS_ASSOCIATED_ITEMS, hir_ref_id, span, |lint| {
2222 let mut err = lint.build("ambiguous associated item");
2223 let mut could_refer_to = |kind: DefKind, def_id, also| {
2224 let note_msg = format!(
2225 "`{}` could{} refer to the {} defined here",
2230 err.span_note(tcx.def_span(def_id), ¬e_msg);
2233 could_refer_to(DefKind::Variant, variant_def_id, "");
2234 could_refer_to(kind, item.def_id, " also");
2236 err.span_suggestion(
2238 "use fully-qualified syntax",
2239 format!("<{} as {}>::{}", qself_ty, tcx.item_name(trait_did), assoc_ident),
2240 Applicability::MachineApplicable,
2246 Ok((ty, kind, item.def_id))
2252 opt_self_ty: Option<Ty<'tcx>>,
2254 trait_segment: &hir::PathSegment<'_>,
2255 item_segment: &hir::PathSegment<'_>,
2257 let tcx = self.tcx();
2259 let trait_def_id = tcx.parent(item_def_id).unwrap();
2261 debug!("qpath_to_ty: trait_def_id={:?}", trait_def_id);
2263 let self_ty = if let Some(ty) = opt_self_ty {
2266 let path_str = tcx.def_path_str(trait_def_id);
2268 let def_id = self.item_def_id();
2270 debug!("qpath_to_ty: self.item_def_id()={:?}", def_id);
2272 let parent_def_id = def_id
2273 .and_then(|def_id| tcx.hir().as_local_hir_id(def_id))
2274 .map(|hir_id| tcx.hir().get_parent_did(hir_id));
2276 debug!("qpath_to_ty: parent_def_id={:?}", parent_def_id);
2278 // If the trait in segment is the same as the trait defining the item,
2279 // use the `<Self as ..>` syntax in the error.
2280 let is_part_of_self_trait_constraints = def_id == Some(trait_def_id);
2281 let is_part_of_fn_in_self_trait = parent_def_id == Some(trait_def_id);
2283 let type_name = if is_part_of_self_trait_constraints || is_part_of_fn_in_self_trait {
2289 self.report_ambiguous_associated_type(
2293 item_segment.ident.name,
2295 return tcx.types.err;
2298 debug!("qpath_to_ty: self_type={:?}", self_ty);
2300 let trait_ref = self.ast_path_to_mono_trait_ref(span, trait_def_id, self_ty, trait_segment);
2302 let item_substs = self.create_substs_for_associated_item(
2310 debug!("qpath_to_ty: trait_ref={:?}", trait_ref);
2312 self.normalize_ty(span, tcx.mk_projection(item_def_id, item_substs))
2315 pub fn prohibit_generics<'a, T: IntoIterator<Item = &'a hir::PathSegment<'a>>>(
2319 let mut has_err = false;
2320 for segment in segments {
2321 let (mut err_for_lt, mut err_for_ty, mut err_for_ct) = (false, false, false);
2322 for arg in segment.generic_args().args {
2323 let (span, kind) = match arg {
2324 hir::GenericArg::Lifetime(lt) => {
2330 (lt.span, "lifetime")
2332 hir::GenericArg::Type(ty) => {
2340 hir::GenericArg::Const(ct) => {
2348 let mut err = struct_span_err!(
2352 "{} arguments are not allowed for this type",
2355 err.span_label(span, format!("{} argument not allowed", kind));
2357 if err_for_lt && err_for_ty && err_for_ct {
2362 // Only emit the first error to avoid overloading the user with error messages.
2363 if let [binding, ..] = segment.generic_args().bindings {
2365 Self::prohibit_assoc_ty_binding(self.tcx(), binding.span);
2371 pub fn prohibit_assoc_ty_binding(tcx: TyCtxt<'_>, span: Span) {
2372 let mut err = struct_span_err!(
2376 "associated type bindings are not allowed here"
2378 err.span_label(span, "associated type not allowed here").emit();
2381 // FIXME(eddyb, varkor) handle type paths here too, not just value ones.
2382 pub fn def_ids_for_value_path_segments(
2384 segments: &[hir::PathSegment<'_>],
2385 self_ty: Option<Ty<'tcx>>,
2389 // We need to extract the type parameters supplied by the user in
2390 // the path `path`. Due to the current setup, this is a bit of a
2391 // tricky-process; the problem is that resolve only tells us the
2392 // end-point of the path resolution, and not the intermediate steps.
2393 // Luckily, we can (at least for now) deduce the intermediate steps
2394 // just from the end-point.
2396 // There are basically five cases to consider:
2398 // 1. Reference to a constructor of a struct:
2400 // struct Foo<T>(...)
2402 // In this case, the parameters are declared in the type space.
2404 // 2. Reference to a constructor of an enum variant:
2406 // enum E<T> { Foo(...) }
2408 // In this case, the parameters are defined in the type space,
2409 // but may be specified either on the type or the variant.
2411 // 3. Reference to a fn item or a free constant:
2415 // In this case, the path will again always have the form
2416 // `a::b::foo::<T>` where only the final segment should have
2417 // type parameters. However, in this case, those parameters are
2418 // declared on a value, and hence are in the `FnSpace`.
2420 // 4. Reference to a method or an associated constant:
2422 // impl<A> SomeStruct<A> {
2426 // Here we can have a path like
2427 // `a::b::SomeStruct::<A>::foo::<B>`, in which case parameters
2428 // may appear in two places. The penultimate segment,
2429 // `SomeStruct::<A>`, contains parameters in TypeSpace, and the
2430 // final segment, `foo::<B>` contains parameters in fn space.
2432 // The first step then is to categorize the segments appropriately.
2434 let tcx = self.tcx();
2436 assert!(!segments.is_empty());
2437 let last = segments.len() - 1;
2439 let mut path_segs = vec![];
2442 // Case 1. Reference to a struct constructor.
2443 DefKind::Ctor(CtorOf::Struct, ..) => {
2444 // Everything but the final segment should have no
2445 // parameters at all.
2446 let generics = tcx.generics_of(def_id);
2447 // Variant and struct constructors use the
2448 // generics of their parent type definition.
2449 let generics_def_id = generics.parent.unwrap_or(def_id);
2450 path_segs.push(PathSeg(generics_def_id, last));
2453 // Case 2. Reference to a variant constructor.
2454 DefKind::Ctor(CtorOf::Variant, ..) | DefKind::Variant => {
2455 let adt_def = self_ty.map(|t| t.ty_adt_def().unwrap());
2456 let (generics_def_id, index) = if let Some(adt_def) = adt_def {
2457 debug_assert!(adt_def.is_enum());
2459 } else if last >= 1 && segments[last - 1].args.is_some() {
2460 // Everything but the penultimate segment should have no
2461 // parameters at all.
2462 let mut def_id = def_id;
2464 // `DefKind::Ctor` -> `DefKind::Variant`
2465 if let DefKind::Ctor(..) = kind {
2466 def_id = tcx.parent(def_id).unwrap()
2469 // `DefKind::Variant` -> `DefKind::Enum`
2470 let enum_def_id = tcx.parent(def_id).unwrap();
2471 (enum_def_id, last - 1)
2473 // FIXME: lint here recommending `Enum::<...>::Variant` form
2474 // instead of `Enum::Variant::<...>` form.
2476 // Everything but the final segment should have no
2477 // parameters at all.
2478 let generics = tcx.generics_of(def_id);
2479 // Variant and struct constructors use the
2480 // generics of their parent type definition.
2481 (generics.parent.unwrap_or(def_id), last)
2483 path_segs.push(PathSeg(generics_def_id, index));
2486 // Case 3. Reference to a top-level value.
2487 DefKind::Fn | DefKind::Const | DefKind::ConstParam | DefKind::Static => {
2488 path_segs.push(PathSeg(def_id, last));
2491 // Case 4. Reference to a method or associated const.
2492 DefKind::Method | DefKind::AssocConst => {
2493 if segments.len() >= 2 {
2494 let generics = tcx.generics_of(def_id);
2495 path_segs.push(PathSeg(generics.parent.unwrap(), last - 1));
2497 path_segs.push(PathSeg(def_id, last));
2500 kind => bug!("unexpected definition kind {:?} for {:?}", kind, def_id),
2503 debug!("path_segs = {:?}", path_segs);
2508 // Check a type `Path` and convert it to a `Ty`.
2511 opt_self_ty: Option<Ty<'tcx>>,
2512 path: &hir::Path<'_>,
2513 permit_variants: bool,
2515 let tcx = self.tcx();
2518 "res_to_ty(res={:?}, opt_self_ty={:?}, path_segments={:?})",
2519 path.res, opt_self_ty, path.segments
2522 let span = path.span;
2524 Res::Def(DefKind::OpaqueTy, did) => {
2525 // Check for desugared `impl Trait`.
2526 assert!(ty::is_impl_trait_defn(tcx, did).is_none());
2527 let item_segment = path.segments.split_last().unwrap();
2528 self.prohibit_generics(item_segment.1);
2529 let substs = self.ast_path_substs_for_ty(span, did, item_segment.0);
2530 self.normalize_ty(span, tcx.mk_opaque(did, substs))
2532 Res::Def(DefKind::Enum, did)
2533 | Res::Def(DefKind::TyAlias, did)
2534 | Res::Def(DefKind::Struct, did)
2535 | Res::Def(DefKind::Union, did)
2536 | Res::Def(DefKind::ForeignTy, did) => {
2537 assert_eq!(opt_self_ty, None);
2538 self.prohibit_generics(path.segments.split_last().unwrap().1);
2539 self.ast_path_to_ty(span, did, path.segments.last().unwrap())
2541 Res::Def(kind @ DefKind::Variant, def_id) if permit_variants => {
2542 // Convert "variant type" as if it were a real type.
2543 // The resulting `Ty` is type of the variant's enum for now.
2544 assert_eq!(opt_self_ty, None);
2547 self.def_ids_for_value_path_segments(&path.segments, None, kind, def_id);
2548 let generic_segs: FxHashSet<_> =
2549 path_segs.iter().map(|PathSeg(_, index)| index).collect();
2550 self.prohibit_generics(path.segments.iter().enumerate().filter_map(
2552 if !generic_segs.contains(&index) { Some(seg) } else { None }
2556 let PathSeg(def_id, index) = path_segs.last().unwrap();
2557 self.ast_path_to_ty(span, *def_id, &path.segments[*index])
2559 Res::Def(DefKind::TyParam, def_id) => {
2560 assert_eq!(opt_self_ty, None);
2561 self.prohibit_generics(path.segments);
2563 let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
2564 let item_id = tcx.hir().get_parent_node(hir_id);
2565 let item_def_id = tcx.hir().local_def_id(item_id);
2566 let generics = tcx.generics_of(item_def_id);
2567 let index = generics.param_def_id_to_index[&def_id];
2568 tcx.mk_ty_param(index, tcx.hir().name(hir_id))
2570 Res::SelfTy(Some(_), None) => {
2571 // `Self` in trait or type alias.
2572 assert_eq!(opt_self_ty, None);
2573 self.prohibit_generics(path.segments);
2574 tcx.types.self_param
2576 Res::SelfTy(_, Some(def_id)) => {
2577 // `Self` in impl (we know the concrete type).
2578 assert_eq!(opt_self_ty, None);
2579 self.prohibit_generics(path.segments);
2580 // Try to evaluate any array length constants.
2581 self.normalize_ty(span, tcx.at(span).type_of(def_id))
2583 Res::Def(DefKind::AssocTy, def_id) => {
2584 debug_assert!(path.segments.len() >= 2);
2585 self.prohibit_generics(&path.segments[..path.segments.len() - 2]);
2590 &path.segments[path.segments.len() - 2],
2591 path.segments.last().unwrap(),
2594 Res::PrimTy(prim_ty) => {
2595 assert_eq!(opt_self_ty, None);
2596 self.prohibit_generics(path.segments);
2598 hir::PrimTy::Bool => tcx.types.bool,
2599 hir::PrimTy::Char => tcx.types.char,
2600 hir::PrimTy::Int(it) => tcx.mk_mach_int(it),
2601 hir::PrimTy::Uint(uit) => tcx.mk_mach_uint(uit),
2602 hir::PrimTy::Float(ft) => tcx.mk_mach_float(ft),
2603 hir::PrimTy::Str => tcx.mk_str(),
2607 self.set_tainted_by_errors();
2608 return self.tcx().types.err;
2610 _ => span_bug!(span, "unexpected resolution: {:?}", path.res),
2614 /// Parses the programmer's textual representation of a type into our
2615 /// internal notion of a type.
2616 pub fn ast_ty_to_ty(&self, ast_ty: &hir::Ty<'_>) -> Ty<'tcx> {
2617 debug!("ast_ty_to_ty(id={:?}, ast_ty={:?} ty_ty={:?})", ast_ty.hir_id, ast_ty, ast_ty.kind);
2619 let tcx = self.tcx();
2621 let result_ty = match ast_ty.kind {
2622 hir::TyKind::Slice(ref ty) => tcx.mk_slice(self.ast_ty_to_ty(&ty)),
2623 hir::TyKind::Ptr(ref mt) => {
2624 tcx.mk_ptr(ty::TypeAndMut { ty: self.ast_ty_to_ty(&mt.ty), mutbl: mt.mutbl })
2626 hir::TyKind::Rptr(ref region, ref mt) => {
2627 let r = self.ast_region_to_region(region, None);
2628 debug!("ast_ty_to_ty: r={:?}", r);
2629 let t = self.ast_ty_to_ty(&mt.ty);
2630 tcx.mk_ref(r, ty::TypeAndMut { ty: t, mutbl: mt.mutbl })
2632 hir::TyKind::Never => tcx.types.never,
2633 hir::TyKind::Tup(ref fields) => {
2634 tcx.mk_tup(fields.iter().map(|t| self.ast_ty_to_ty(&t)))
2636 hir::TyKind::BareFn(ref bf) => {
2637 require_c_abi_if_c_variadic(tcx, &bf.decl, bf.abi, ast_ty.span);
2638 tcx.mk_fn_ptr(self.ty_of_fn(bf.unsafety, bf.abi, &bf.decl, &[], None))
2640 hir::TyKind::TraitObject(ref bounds, ref lifetime) => {
2641 self.conv_object_ty_poly_trait_ref(ast_ty.span, bounds, lifetime)
2643 hir::TyKind::Path(hir::QPath::Resolved(ref maybe_qself, ref path)) => {
2644 debug!("ast_ty_to_ty: maybe_qself={:?} path={:?}", maybe_qself, path);
2645 let opt_self_ty = maybe_qself.as_ref().map(|qself| self.ast_ty_to_ty(qself));
2646 self.res_to_ty(opt_self_ty, path, false)
2648 hir::TyKind::Def(item_id, ref lifetimes) => {
2649 let did = tcx.hir().local_def_id(item_id.id);
2650 self.impl_trait_ty_to_ty(did, lifetimes)
2652 hir::TyKind::Path(hir::QPath::TypeRelative(ref qself, ref segment)) => {
2653 debug!("ast_ty_to_ty: qself={:?} segment={:?}", qself, segment);
2654 let ty = self.ast_ty_to_ty(qself);
2656 let res = if let hir::TyKind::Path(hir::QPath::Resolved(_, ref path)) = qself.kind {
2661 self.associated_path_to_ty(ast_ty.hir_id, ast_ty.span, ty, res, segment, false)
2662 .map(|(ty, _, _)| ty)
2663 .unwrap_or(tcx.types.err)
2665 hir::TyKind::Array(ref ty, ref length) => {
2666 let length = self.ast_const_to_const(length, tcx.types.usize);
2667 let array_ty = tcx.mk_ty(ty::Array(self.ast_ty_to_ty(&ty), length));
2668 self.normalize_ty(ast_ty.span, array_ty)
2670 hir::TyKind::Typeof(ref _e) => {
2675 "`typeof` is a reserved keyword but unimplemented"
2677 .span_label(ast_ty.span, "reserved keyword")
2682 hir::TyKind::Infer => {
2683 // Infer also appears as the type of arguments or return
2684 // values in a ExprKind::Closure, or as
2685 // the type of local variables. Both of these cases are
2686 // handled specially and will not descend into this routine.
2687 self.ty_infer(None, ast_ty.span)
2689 hir::TyKind::Err => tcx.types.err,
2692 debug!("ast_ty_to_ty: result_ty={:?}", result_ty);
2694 self.record_ty(ast_ty.hir_id, result_ty, ast_ty.span);
2698 /// Returns the `DefId` of the constant parameter that the provided expression is a path to.
2699 pub fn const_param_def_id(&self, expr: &hir::Expr<'_>) -> Option<DefId> {
2700 // Unwrap a block, so that e.g. `{ P }` is recognised as a parameter. Const arguments
2701 // currently have to be wrapped in curly brackets, so it's necessary to special-case.
2702 let expr = match &expr.kind {
2703 ExprKind::Block(block, _) if block.stmts.is_empty() && block.expr.is_some() => {
2704 block.expr.as_ref().unwrap()
2710 ExprKind::Path(hir::QPath::Resolved(_, path)) => match path.res {
2711 Res::Def(DefKind::ConstParam, did) => Some(did),
2718 pub fn ast_const_to_const(
2720 ast_const: &hir::AnonConst,
2722 ) -> &'tcx ty::Const<'tcx> {
2723 debug!("ast_const_to_const(id={:?}, ast_const={:?})", ast_const.hir_id, ast_const);
2725 let tcx = self.tcx();
2726 let def_id = tcx.hir().local_def_id(ast_const.hir_id);
2728 let expr = &tcx.hir().body(ast_const.body).value;
2730 let lit_input = match expr.kind {
2731 hir::ExprKind::Lit(ref lit) => Some(LitToConstInput { lit: &lit.node, ty, neg: false }),
2732 hir::ExprKind::Unary(hir::UnOp::UnNeg, ref expr) => match expr.kind {
2733 hir::ExprKind::Lit(ref lit) => {
2734 Some(LitToConstInput { lit: &lit.node, ty, neg: true })
2741 if let Some(lit_input) = lit_input {
2742 // If an error occurred, ignore that it's a literal and leave reporting the error up to
2744 if let Ok(c) = tcx.at(expr.span).lit_to_const(lit_input) {
2747 tcx.sess.delay_span_bug(expr.span, "ast_const_to_const: couldn't lit_to_const");
2751 let kind = if let Some(def_id) = self.const_param_def_id(expr) {
2752 // Find the name and index of the const parameter by indexing the generics of the
2753 // parent item and construct a `ParamConst`.
2754 let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
2755 let item_id = tcx.hir().get_parent_node(hir_id);
2756 let item_def_id = tcx.hir().local_def_id(item_id);
2757 let generics = tcx.generics_of(item_def_id);
2758 let index = generics.param_def_id_to_index[&tcx.hir().local_def_id(hir_id)];
2759 let name = tcx.hir().name(hir_id);
2760 ty::ConstKind::Param(ty::ParamConst::new(index, name))
2762 ty::ConstKind::Unevaluated(def_id, InternalSubsts::identity_for_item(tcx, def_id), None)
2764 tcx.mk_const(ty::Const { val: kind, ty })
2767 pub fn impl_trait_ty_to_ty(
2770 lifetimes: &[hir::GenericArg<'_>],
2772 debug!("impl_trait_ty_to_ty(def_id={:?}, lifetimes={:?})", def_id, lifetimes);
2773 let tcx = self.tcx();
2775 let generics = tcx.generics_of(def_id);
2777 debug!("impl_trait_ty_to_ty: generics={:?}", generics);
2778 let substs = InternalSubsts::for_item(tcx, def_id, |param, _| {
2779 if let Some(i) = (param.index as usize).checked_sub(generics.parent_count) {
2780 // Our own parameters are the resolved lifetimes.
2782 GenericParamDefKind::Lifetime => {
2783 if let hir::GenericArg::Lifetime(lifetime) = &lifetimes[i] {
2784 self.ast_region_to_region(lifetime, None).into()
2792 // Replace all parent lifetimes with `'static`.
2794 GenericParamDefKind::Lifetime => tcx.lifetimes.re_static.into(),
2795 _ => tcx.mk_param_from_def(param),
2799 debug!("impl_trait_ty_to_ty: substs={:?}", substs);
2801 let ty = tcx.mk_opaque(def_id, substs);
2802 debug!("impl_trait_ty_to_ty: {}", ty);
2806 pub fn ty_of_arg(&self, ty: &hir::Ty<'_>, expected_ty: Option<Ty<'tcx>>) -> Ty<'tcx> {
2808 hir::TyKind::Infer if expected_ty.is_some() => {
2809 self.record_ty(ty.hir_id, expected_ty.unwrap(), ty.span);
2810 expected_ty.unwrap()
2812 _ => self.ast_ty_to_ty(ty),
2818 unsafety: hir::Unsafety,
2820 decl: &hir::FnDecl<'_>,
2821 generic_params: &[hir::GenericParam<'_>],
2822 ident_span: Option<Span>,
2823 ) -> ty::PolyFnSig<'tcx> {
2826 let tcx = self.tcx();
2828 // We proactively collect all the infered type params to emit a single error per fn def.
2829 let mut visitor = PlaceholderHirTyCollector::default();
2830 for ty in decl.inputs {
2831 visitor.visit_ty(ty);
2833 let input_tys = decl.inputs.iter().map(|a| self.ty_of_arg(a, None));
2834 let output_ty = match decl.output {
2835 hir::FnRetTy::Return(ref output) => {
2836 visitor.visit_ty(output);
2837 self.ast_ty_to_ty(output)
2839 hir::FnRetTy::DefaultReturn(..) => tcx.mk_unit(),
2842 debug!("ty_of_fn: output_ty={:?}", output_ty);
2845 ty::Binder::bind(tcx.mk_fn_sig(input_tys, output_ty, decl.c_variadic, unsafety, abi));
2847 if !self.allow_ty_infer() {
2848 // We always collect the spans for placeholder types when evaluating `fn`s, but we
2849 // only want to emit an error complaining about them if infer types (`_`) are not
2850 // allowed. `allow_ty_infer` gates this behavior.
2851 crate::collect::placeholder_type_error(
2853 ident_span.map(|sp| sp.shrink_to_hi()).unwrap_or(DUMMY_SP),
2856 ident_span.is_some(),
2860 // Find any late-bound regions declared in return type that do
2861 // not appear in the arguments. These are not well-formed.
2864 // for<'a> fn() -> &'a str <-- 'a is bad
2865 // for<'a> fn(&'a String) -> &'a str <-- 'a is ok
2866 let inputs = bare_fn_ty.inputs();
2867 let late_bound_in_args =
2868 tcx.collect_constrained_late_bound_regions(&inputs.map_bound(|i| i.to_owned()));
2869 let output = bare_fn_ty.output();
2870 let late_bound_in_ret = tcx.collect_referenced_late_bound_regions(&output);
2871 for br in late_bound_in_ret.difference(&late_bound_in_args) {
2872 let lifetime_name = match *br {
2873 ty::BrNamed(_, name) => format!("lifetime `{}`,", name),
2874 ty::BrAnon(_) | ty::BrEnv => "an anonymous lifetime".to_string(),
2876 let mut err = struct_span_err!(
2880 "return type references {} \
2881 which is not constrained by the fn input types",
2884 if let ty::BrAnon(_) = *br {
2885 // The only way for an anonymous lifetime to wind up
2886 // in the return type but **also** be unconstrained is
2887 // if it only appears in "associated types" in the
2888 // input. See #47511 for an example. In this case,
2889 // though we can easily give a hint that ought to be
2892 "lifetimes appearing in an associated type \
2893 are not considered constrained",
2902 /// Given the bounds on an object, determines what single region bound (if any) we can
2903 /// use to summarize this type. The basic idea is that we will use the bound the user
2904 /// provided, if they provided one, and otherwise search the supertypes of trait bounds
2905 /// for region bounds. It may be that we can derive no bound at all, in which case
2906 /// we return `None`.
2907 fn compute_object_lifetime_bound(
2910 existential_predicates: ty::Binder<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>>,
2911 ) -> Option<ty::Region<'tcx>> // if None, use the default
2913 let tcx = self.tcx();
2915 debug!("compute_opt_region_bound(existential_predicates={:?})", existential_predicates);
2917 // No explicit region bound specified. Therefore, examine trait
2918 // bounds and see if we can derive region bounds from those.
2919 let derived_region_bounds = object_region_bounds(tcx, existential_predicates);
2921 // If there are no derived region bounds, then report back that we
2922 // can find no region bound. The caller will use the default.
2923 if derived_region_bounds.is_empty() {
2927 // If any of the derived region bounds are 'static, that is always
2929 if derived_region_bounds.iter().any(|&r| ty::ReStatic == *r) {
2930 return Some(tcx.lifetimes.re_static);
2933 // Determine whether there is exactly one unique region in the set
2934 // of derived region bounds. If so, use that. Otherwise, report an
2936 let r = derived_region_bounds[0];
2937 if derived_region_bounds[1..].iter().any(|r1| r != *r1) {
2942 "ambiguous lifetime bound, explicit lifetime bound required"
2950 /// Collects together a list of bounds that are applied to some type,
2951 /// after they've been converted into `ty` form (from the HIR
2952 /// representations). These lists of bounds occur in many places in
2956 /// trait Foo: Bar + Baz { }
2957 /// ^^^^^^^^^ supertrait list bounding the `Self` type parameter
2959 /// fn foo<T: Bar + Baz>() { }
2960 /// ^^^^^^^^^ bounding the type parameter `T`
2962 /// impl dyn Bar + Baz
2963 /// ^^^^^^^^^ bounding the forgotten dynamic type
2966 /// Our representation is a bit mixed here -- in some cases, we
2967 /// include the self type (e.g., `trait_bounds`) but in others we do
2968 #[derive(Default, PartialEq, Eq, Clone, Debug)]
2969 pub struct Bounds<'tcx> {
2970 /// A list of region bounds on the (implicit) self type. So if you
2971 /// had `T: 'a + 'b` this might would be a list `['a, 'b]` (but
2972 /// the `T` is not explicitly included).
2973 pub region_bounds: Vec<(ty::Region<'tcx>, Span)>,
2975 /// A list of trait bounds. So if you had `T: Debug` this would be
2976 /// `T: Debug`. Note that the self-type is explicit here.
2977 pub trait_bounds: Vec<(ty::PolyTraitRef<'tcx>, Span, Constness)>,
2979 /// A list of projection equality bounds. So if you had `T:
2980 /// Iterator<Item = u32>` this would include `<T as
2981 /// Iterator>::Item => u32`. Note that the self-type is explicit
2983 pub projection_bounds: Vec<(ty::PolyProjectionPredicate<'tcx>, Span)>,
2985 /// `Some` if there is *no* `?Sized` predicate. The `span`
2986 /// is the location in the source of the `T` declaration which can
2987 /// be cited as the source of the `T: Sized` requirement.
2988 pub implicitly_sized: Option<Span>,
2991 impl<'tcx> Bounds<'tcx> {
2992 /// Converts a bounds list into a flat set of predicates (like
2993 /// where-clauses). Because some of our bounds listings (e.g.,
2994 /// regions) don't include the self-type, you must supply the
2995 /// self-type here (the `param_ty` parameter).
3000 ) -> Vec<(ty::Predicate<'tcx>, Span)> {
3001 // If it could be sized, and is, add the `Sized` predicate.
3002 let sized_predicate = self.implicitly_sized.and_then(|span| {
3003 tcx.lang_items().sized_trait().map(|sized| {
3004 let trait_ref = ty::Binder::bind(ty::TraitRef {
3006 substs: tcx.mk_substs_trait(param_ty, &[]),
3008 (trait_ref.without_const().to_predicate(), span)
3017 .map(|&(region_bound, span)| {
3018 // Account for the binder being introduced below; no need to shift `param_ty`
3019 // because, at present at least, it either only refers to early-bound regions,
3020 // or it's a generic associated type that deliberately has escaping bound vars.
3021 let region_bound = ty::fold::shift_region(tcx, region_bound, 1);
3022 let outlives = ty::OutlivesPredicate(param_ty, region_bound);
3023 (ty::Binder::bind(outlives).to_predicate(), span)
3025 .chain(self.trait_bounds.iter().map(|&(bound_trait_ref, span, constness)| {
3026 let predicate = bound_trait_ref.with_constness(constness).to_predicate();
3030 self.projection_bounds
3032 .map(|&(projection, span)| (projection.to_predicate(), span)),