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::namespace::Namespace;
13 use crate::require_c_abi_if_c_variadic;
14 use crate::util::common::ErrorReported;
15 use rustc::lint::builtin::AMBIGUOUS_ASSOCIATED_ITEMS;
16 use rustc::session::parse::feature_err;
18 use rustc::traits::astconv_object_safety_violations;
19 use rustc::traits::error_reporting::report_object_safety_error;
20 use rustc::traits::wf::object_region_bounds;
21 use rustc::ty::subst::{self, InternalSubsts, Subst, SubstsRef};
22 use rustc::ty::{self, Const, DefIdTree, ToPredicate, Ty, TyCtxt, TypeFoldable, WithConstness};
23 use rustc::ty::{GenericParamDef, GenericParamDefKind};
24 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
25 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticId};
27 use rustc_hir::def::{CtorOf, DefKind, Res};
28 use rustc_hir::def_id::DefId;
29 use rustc_hir::intravisit::Visitor;
31 use rustc_hir::{ExprKind, GenericArg, GenericArgs};
32 use rustc_span::symbol::sym;
33 use rustc_span::{MultiSpan, Span, DUMMY_SP};
34 use rustc_target::spec::abi;
35 use smallvec::SmallVec;
36 use syntax::ast::{self, Constness};
37 use syntax::util::lev_distance::find_best_match_for_name;
39 use std::collections::BTreeSet;
43 use rustc::mir::interpret::LitToConstInput;
46 pub struct PathSeg(pub DefId, pub usize);
48 pub trait AstConv<'tcx> {
49 fn tcx<'a>(&'a self) -> TyCtxt<'tcx>;
51 fn item_def_id(&self) -> Option<DefId>;
53 fn default_constness_for_trait_bounds(&self) -> Constness;
55 /// Returns predicates in scope of the form `X: Foo`, where `X` is
56 /// a type parameter `X` with the given id `def_id`. This is a
57 /// subset of the full set of predicates.
59 /// This is used for one specific purpose: resolving "short-hand"
60 /// associated type references like `T::Item`. In principle, we
61 /// would do that by first getting the full set of predicates in
62 /// scope and then filtering down to find those that apply to `T`,
63 /// but this can lead to cycle errors. The problem is that we have
64 /// to do this resolution *in order to create the predicates in
65 /// the first place*. Hence, we have this "special pass".
66 fn get_type_parameter_bounds(&self, span: Span, def_id: DefId) -> ty::GenericPredicates<'tcx>;
68 /// Returns the lifetime to use when a lifetime is omitted (and not elided).
69 fn re_infer(&self, param: Option<&ty::GenericParamDef>, span: Span)
70 -> Option<ty::Region<'tcx>>;
72 /// Returns the type to use when a type is omitted.
73 fn ty_infer(&self, param: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx>;
75 /// Returns `true` if `_` is allowed in type signatures in the current context.
76 fn allow_ty_infer(&self) -> bool;
78 /// Returns the const to use when a const is omitted.
82 param: Option<&ty::GenericParamDef>,
84 ) -> &'tcx Const<'tcx>;
86 /// Projecting an associated type from a (potentially)
87 /// higher-ranked trait reference is more complicated, because of
88 /// the possibility of late-bound regions appearing in the
89 /// associated type binding. This is not legal in function
90 /// signatures for that reason. In a function body, we can always
91 /// handle it because we can use inference variables to remove the
92 /// late-bound regions.
93 fn projected_ty_from_poly_trait_ref(
97 item_segment: &hir::PathSegment<'_>,
98 poly_trait_ref: ty::PolyTraitRef<'tcx>,
101 /// Normalize an associated type coming from the user.
102 fn normalize_ty(&self, span: Span, ty: Ty<'tcx>) -> Ty<'tcx>;
104 /// Invoked when we encounter an error from some prior pass
105 /// (e.g., resolve) that is translated into a ty-error. This is
106 /// used to help suppress derived errors typeck might otherwise
108 fn set_tainted_by_errors(&self);
110 fn record_ty(&self, hir_id: hir::HirId, ty: Ty<'tcx>, span: Span);
113 pub enum SizedByDefault {
118 struct ConvertedBinding<'a, 'tcx> {
119 item_name: ast::Ident,
120 kind: ConvertedBindingKind<'a, 'tcx>,
124 enum ConvertedBindingKind<'a, 'tcx> {
126 Constraint(&'a [hir::GenericBound<'a>]),
130 enum GenericArgPosition {
132 Value, // e.g., functions
136 impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
137 pub fn ast_region_to_region(
139 lifetime: &hir::Lifetime,
140 def: Option<&ty::GenericParamDef>,
141 ) -> ty::Region<'tcx> {
142 let tcx = self.tcx();
143 let lifetime_name = |def_id| tcx.hir().name(tcx.hir().as_local_hir_id(def_id).unwrap());
145 let r = match tcx.named_region(lifetime.hir_id) {
146 Some(rl::Region::Static) => tcx.lifetimes.re_static,
148 Some(rl::Region::LateBound(debruijn, id, _)) => {
149 let name = lifetime_name(id);
150 tcx.mk_region(ty::ReLateBound(debruijn, ty::BrNamed(id, name)))
153 Some(rl::Region::LateBoundAnon(debruijn, index)) => {
154 tcx.mk_region(ty::ReLateBound(debruijn, ty::BrAnon(index)))
157 Some(rl::Region::EarlyBound(index, id, _)) => {
158 let name = lifetime_name(id);
159 tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion { def_id: id, index, name }))
162 Some(rl::Region::Free(scope, id)) => {
163 let name = lifetime_name(id);
164 tcx.mk_region(ty::ReFree(ty::FreeRegion {
166 bound_region: ty::BrNamed(id, name),
169 // (*) -- not late-bound, won't change
173 self.re_infer(def, lifetime.span).unwrap_or_else(|| {
174 // This indicates an illegal lifetime
175 // elision. `resolve_lifetime` should have
176 // reported an error in this case -- but if
177 // not, let's error out.
178 tcx.sess.delay_span_bug(lifetime.span, "unelided lifetime in signature");
180 // Supply some dummy value. We don't have an
181 // `re_error`, annoyingly, so use `'static`.
182 tcx.lifetimes.re_static
187 debug!("ast_region_to_region(lifetime={:?}) yields {:?}", lifetime, r);
192 /// Given a path `path` that refers to an item `I` with the declared generics `decl_generics`,
193 /// returns an appropriate set of substitutions for this particular reference to `I`.
194 pub fn ast_path_substs_for_ty(
198 item_segment: &hir::PathSegment<'_>,
199 ) -> SubstsRef<'tcx> {
200 let (substs, assoc_bindings, _) = self.create_substs_for_ast_path(
204 item_segment.generic_args(),
205 item_segment.infer_args,
209 assoc_bindings.first().map(|b| Self::prohibit_assoc_ty_binding(self.tcx(), b.span));
214 /// Report error if there is an explicit type parameter when using `impl Trait`.
217 seg: &hir::PathSegment<'_>,
218 generics: &ty::Generics,
220 let explicit = !seg.infer_args;
221 let impl_trait = generics.params.iter().any(|param| match param.kind {
222 ty::GenericParamDefKind::Type {
223 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
229 if explicit && impl_trait {
234 .filter_map(|arg| match arg {
235 GenericArg::Type(_) => Some(arg.span()),
238 .collect::<Vec<_>>();
240 let mut err = struct_span_err! {
244 "cannot provide explicit generic arguments when `impl Trait` is \
245 used in argument position"
249 err.span_label(span, "explicit generic argument not allowed");
258 /// Checks that the correct number of generic arguments have been provided.
259 /// Used specifically for function calls.
260 pub fn check_generic_arg_count_for_call(
264 seg: &hir::PathSegment<'_>,
265 is_method_call: bool,
267 let empty_args = hir::GenericArgs::none();
268 let suppress_mismatch = Self::check_impl_trait(tcx, seg, &def);
269 Self::check_generic_arg_count(
273 if let Some(ref args) = seg.args { args } else { &empty_args },
274 if is_method_call { GenericArgPosition::MethodCall } else { GenericArgPosition::Value },
275 def.parent.is_none() && def.has_self, // `has_self`
276 seg.infer_args || suppress_mismatch, // `infer_args`
281 /// Checks that the correct number of generic arguments have been provided.
282 /// This is used both for datatypes and function calls.
283 fn check_generic_arg_count(
287 args: &hir::GenericArgs<'_>,
288 position: GenericArgPosition,
291 ) -> (bool, Option<Vec<Span>>) {
292 // At this stage we are guaranteed that the generic arguments are in the correct order, e.g.
293 // that lifetimes will proceed types. So it suffices to check the number of each generic
294 // arguments in order to validate them with respect to the generic parameters.
295 let param_counts = def.own_counts();
296 let arg_counts = args.own_counts();
297 let infer_lifetimes = position != GenericArgPosition::Type && arg_counts.lifetimes == 0;
299 let mut defaults: ty::GenericParamCount = Default::default();
300 for param in &def.params {
302 GenericParamDefKind::Lifetime => {}
303 GenericParamDefKind::Type { has_default, .. } => {
304 defaults.types += has_default as usize
306 GenericParamDefKind::Const => {
307 // FIXME(const_generics:defaults)
312 if position != GenericArgPosition::Type && !args.bindings.is_empty() {
313 AstConv::prohibit_assoc_ty_binding(tcx, args.bindings[0].span);
316 // Prohibit explicit lifetime arguments if late-bound lifetime parameters are present.
317 let mut reported_late_bound_region_err = None;
318 if !infer_lifetimes {
319 if let Some(span_late) = def.has_late_bound_regions {
320 let msg = "cannot specify lifetime arguments explicitly \
321 if late bound lifetime parameters are present";
322 let note = "the late bound lifetime parameter is introduced here";
323 let span = args.args[0].span();
324 if position == GenericArgPosition::Value
325 && arg_counts.lifetimes != param_counts.lifetimes
327 let mut err = tcx.sess.struct_span_err(span, msg);
328 err.span_note(span_late, note);
330 reported_late_bound_region_err = Some(true);
332 let mut multispan = MultiSpan::from_span(span);
333 multispan.push_span_label(span_late, note.to_string());
335 lint::builtin::LATE_BOUND_LIFETIME_ARGUMENTS,
340 reported_late_bound_region_err = Some(false);
345 let check_kind_count = |kind, required, permitted, provided, offset| {
347 "check_kind_count: kind: {} required: {} permitted: {} provided: {} offset: {}",
348 kind, required, permitted, provided, offset
350 // We enforce the following: `required` <= `provided` <= `permitted`.
351 // For kinds without defaults (e.g.., lifetimes), `required == permitted`.
352 // For other kinds (i.e., types), `permitted` may be greater than `required`.
353 if required <= provided && provided <= permitted {
354 return (reported_late_bound_region_err.unwrap_or(false), None);
357 // Unfortunately lifetime and type parameter mismatches are typically styled
358 // differently in diagnostics, which means we have a few cases to consider here.
359 let (bound, quantifier) = if required != permitted {
360 if provided < required {
361 (required, "at least ")
363 // provided > permitted
364 (permitted, "at most ")
370 let mut potential_assoc_types: Option<Vec<Span>> = None;
371 let (spans, label) = if required == permitted && provided > permitted {
372 // In the case when the user has provided too many arguments,
373 // we want to point to the unexpected arguments.
374 let spans: Vec<Span> = args.args[offset + permitted..offset + provided]
376 .map(|arg| arg.span())
378 potential_assoc_types = Some(spans.clone());
379 (spans, format!("unexpected {} argument", kind))
384 "expected {}{} {} argument{}",
393 let mut err = tcx.sess.struct_span_err_with_code(
396 "wrong number of {} arguments: expected {}{}, found {}",
397 kind, quantifier, bound, provided,
399 DiagnosticId::Error("E0107".into()),
402 err.span_label(span, label.as_str());
407 provided > required, // `suppress_error`
408 potential_assoc_types,
412 if reported_late_bound_region_err.is_none()
413 && (!infer_lifetimes || arg_counts.lifetimes > param_counts.lifetimes)
417 param_counts.lifetimes,
418 param_counts.lifetimes,
419 arg_counts.lifetimes,
423 // FIXME(const_generics:defaults)
424 if !infer_args || arg_counts.consts > param_counts.consts {
430 arg_counts.lifetimes + arg_counts.types,
433 // Note that type errors are currently be emitted *after* const errors.
434 if !infer_args || arg_counts.types > param_counts.types - defaults.types - has_self as usize
438 param_counts.types - defaults.types - has_self as usize,
439 param_counts.types - has_self as usize,
441 arg_counts.lifetimes,
444 (reported_late_bound_region_err.unwrap_or(false), None)
448 /// Creates the relevant generic argument substitutions
449 /// corresponding to a set of generic parameters. This is a
450 /// rather complex function. Let us try to explain the role
451 /// of each of its parameters:
453 /// To start, we are given the `def_id` of the thing we are
454 /// creating the substitutions for, and a partial set of
455 /// substitutions `parent_substs`. In general, the substitutions
456 /// for an item begin with substitutions for all the "parents" of
457 /// that item -- e.g., for a method it might include the
458 /// parameters from the impl.
460 /// Therefore, the method begins by walking down these parents,
461 /// starting with the outermost parent and proceed inwards until
462 /// it reaches `def_id`. For each parent `P`, it will check `parent_substs`
463 /// first to see if the parent's substitutions are listed in there. If so,
464 /// we can append those and move on. Otherwise, it invokes the
465 /// three callback functions:
467 /// - `args_for_def_id`: given the `DefId` `P`, supplies back the
468 /// generic arguments that were given to that parent from within
469 /// the path; so e.g., if you have `<T as Foo>::Bar`, the `DefId`
470 /// might refer to the trait `Foo`, and the arguments might be
471 /// `[T]`. The boolean value indicates whether to infer values
472 /// for arguments whose values were not explicitly provided.
473 /// - `provided_kind`: given the generic parameter and the value from `args_for_def_id`,
474 /// instantiate a `GenericArg`.
475 /// - `inferred_kind`: if no parameter was provided, and inference is enabled, then
476 /// creates a suitable inference variable.
477 pub fn create_substs_for_generic_args<'b>(
480 parent_substs: &[subst::GenericArg<'tcx>],
482 self_ty: Option<Ty<'tcx>>,
483 args_for_def_id: impl Fn(DefId) -> (Option<&'b GenericArgs<'b>>, bool),
484 provided_kind: impl Fn(&GenericParamDef, &GenericArg<'_>) -> subst::GenericArg<'tcx>,
485 mut inferred_kind: impl FnMut(
486 Option<&[subst::GenericArg<'tcx>]>,
489 ) -> subst::GenericArg<'tcx>,
490 ) -> SubstsRef<'tcx> {
491 // Collect the segments of the path; we need to substitute arguments
492 // for parameters throughout the entire path (wherever there are
493 // generic parameters).
494 let mut parent_defs = tcx.generics_of(def_id);
495 let count = parent_defs.count();
496 let mut stack = vec![(def_id, parent_defs)];
497 while let Some(def_id) = parent_defs.parent {
498 parent_defs = tcx.generics_of(def_id);
499 stack.push((def_id, parent_defs));
502 // We manually build up the substitution, rather than using convenience
503 // methods in `subst.rs`, so that we can iterate over the arguments and
504 // parameters in lock-step linearly, instead of trying to match each pair.
505 let mut substs: SmallVec<[subst::GenericArg<'tcx>; 8]> = SmallVec::with_capacity(count);
507 // Iterate over each segment of the path.
508 while let Some((def_id, defs)) = stack.pop() {
509 let mut params = defs.params.iter().peekable();
511 // If we have already computed substitutions for parents, we can use those directly.
512 while let Some(¶m) = params.peek() {
513 if let Some(&kind) = parent_substs.get(param.index as usize) {
521 // `Self` is handled first, unless it's been handled in `parent_substs`.
523 if let Some(¶m) = params.peek() {
524 if param.index == 0 {
525 if let GenericParamDefKind::Type { .. } = param.kind {
529 .unwrap_or_else(|| inferred_kind(None, param, true)),
537 // Check whether this segment takes generic arguments and the user has provided any.
538 let (generic_args, infer_args) = args_for_def_id(def_id);
541 generic_args.iter().flat_map(|generic_args| generic_args.args.iter()).peekable();
544 // We're going to iterate through the generic arguments that the user
545 // provided, matching them with the generic parameters we expect.
546 // Mismatches can occur as a result of elided lifetimes, or for malformed
547 // input. We try to handle both sensibly.
548 match (args.peek(), params.peek()) {
549 (Some(&arg), Some(¶m)) => {
550 match (arg, ¶m.kind) {
551 (GenericArg::Lifetime(_), GenericParamDefKind::Lifetime)
552 | (GenericArg::Type(_), GenericParamDefKind::Type { .. })
553 | (GenericArg::Const(_), GenericParamDefKind::Const) => {
554 substs.push(provided_kind(param, arg));
558 (GenericArg::Type(_), GenericParamDefKind::Lifetime)
559 | (GenericArg::Const(_), GenericParamDefKind::Lifetime) => {
560 // We expected a lifetime argument, but got a type or const
561 // argument. That means we're inferring the lifetimes.
562 substs.push(inferred_kind(None, param, infer_args));
566 // We expected one kind of parameter, but the user provided
567 // another. This is an error, but we need to handle it
568 // gracefully so we can report sensible errors.
569 // In this case, we're simply going to infer this argument.
575 // We should never be able to reach this point with well-formed input.
576 // Getting to this point means the user supplied more arguments than
577 // there are parameters.
580 (None, Some(¶m)) => {
581 // If there are fewer arguments than parameters, it means
582 // we're inferring the remaining arguments.
583 substs.push(inferred_kind(Some(&substs), param, infer_args));
587 (None, None) => break,
592 tcx.intern_substs(&substs)
595 /// Given the type/lifetime/const arguments provided to some path (along with
596 /// an implicit `Self`, if this is a trait reference), returns the complete
597 /// set of substitutions. This may involve applying defaulted type parameters.
598 /// Also returns back constriants on associated types.
603 /// T: std::ops::Index<usize, Output = u32>
604 /// ^1 ^^^^^^^^^^^^^^2 ^^^^3 ^^^^^^^^^^^4
607 /// 1. The `self_ty` here would refer to the type `T`.
608 /// 2. The path in question is the path to the trait `std::ops::Index`,
609 /// which will have been resolved to a `def_id`
610 /// 3. The `generic_args` contains info on the `<...>` contents. The `usize` type
611 /// parameters are returned in the `SubstsRef`, the associated type bindings like
612 /// `Output = u32` are returned in the `Vec<ConvertedBinding...>` result.
614 /// Note that the type listing given here is *exactly* what the user provided.
616 /// For (generic) associated types
619 /// <Vec<u8> as Iterable<u8>>::Iter::<'a>
622 /// We have the parent substs are the substs for the parent trait:
623 /// `[Vec<u8>, u8]` and `generic_args` are the arguments for the associated
624 /// type itself: `['a]`. The returned `SubstsRef` concatenates these two
625 /// lists: `[Vec<u8>, u8, 'a]`.
626 fn create_substs_for_ast_path<'a>(
630 parent_substs: &[subst::GenericArg<'tcx>],
631 generic_args: &'a hir::GenericArgs<'_>,
633 self_ty: Option<Ty<'tcx>>,
634 ) -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'a, 'tcx>>, Option<Vec<Span>>) {
635 // If the type is parameterized by this region, then replace this
636 // region with the current anon region binding (in other words,
637 // whatever & would get replaced with).
639 "create_substs_for_ast_path(def_id={:?}, self_ty={:?}, \
641 def_id, self_ty, generic_args
644 let tcx = self.tcx();
645 let generic_params = tcx.generics_of(def_id);
647 if generic_params.has_self {
648 if generic_params.parent.is_some() {
649 // The parent is a trait so it should have at least one subst
650 // for the `Self` type.
651 assert!(!parent_substs.is_empty())
653 // This item (presumably a trait) needs a self-type.
654 assert!(self_ty.is_some());
657 assert!(self_ty.is_none() && parent_substs.is_empty());
660 let (_, potential_assoc_types) = Self::check_generic_arg_count(
665 GenericArgPosition::Type,
670 let is_object = self_ty.map_or(false, |ty| ty == self.tcx().types.trait_object_dummy_self);
671 let default_needs_object_self = |param: &ty::GenericParamDef| {
672 if let GenericParamDefKind::Type { has_default, .. } = param.kind {
673 if is_object && has_default {
674 let self_param = tcx.types.self_param;
675 if tcx.at(span).type_of(param.def_id).walk().any(|ty| ty == self_param) {
676 // There is no suitable inference default for a type parameter
677 // that references self, in an object type.
686 let mut missing_type_params = vec![];
687 let substs = Self::create_substs_for_generic_args(
693 // Provide the generic args, and whether types should be inferred.
694 |_| (Some(generic_args), infer_args),
695 // Provide substitutions for parameters for which (valid) arguments have been provided.
696 |param, arg| match (¶m.kind, arg) {
697 (GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => {
698 self.ast_region_to_region(<, Some(param)).into()
700 (GenericParamDefKind::Type { .. }, GenericArg::Type(ty)) => {
701 self.ast_ty_to_ty(&ty).into()
703 (GenericParamDefKind::Const, GenericArg::Const(ct)) => {
704 self.ast_const_to_const(&ct.value, tcx.type_of(param.def_id)).into()
708 // Provide substitutions for parameters for which arguments are inferred.
709 |substs, param, infer_args| {
711 GenericParamDefKind::Lifetime => tcx.lifetimes.re_static.into(),
712 GenericParamDefKind::Type { has_default, .. } => {
713 if !infer_args && has_default {
714 // No type parameter provided, but a default exists.
716 // If we are converting an object type, then the
717 // `Self` parameter is unknown. However, some of the
718 // other type parameters may reference `Self` in their
719 // defaults. This will lead to an ICE if we are not
721 if default_needs_object_self(param) {
722 missing_type_params.push(param.name.to_string());
725 // This is a default type parameter.
728 tcx.at(span).type_of(param.def_id).subst_spanned(
736 } else if infer_args {
737 // No type parameters were provided, we can infer all.
739 if !default_needs_object_self(param) { Some(param) } else { None };
740 self.ty_infer(param, span).into()
742 // We've already errored above about the mismatch.
746 GenericParamDefKind::Const => {
747 // FIXME(const_generics:defaults)
749 // No const parameters were provided, we can infer all.
750 let ty = tcx.at(span).type_of(param.def_id);
751 self.ct_infer(ty, Some(param), span).into()
753 // We've already errored above about the mismatch.
754 tcx.consts.err.into()
761 self.complain_about_missing_type_params(
765 generic_args.args.is_empty(),
768 // Convert associated-type bindings or constraints into a separate vector.
769 // Example: Given this:
771 // T: Iterator<Item = u32>
773 // The `T` is passed in as a self-type; the `Item = u32` is
774 // not a "type parameter" of the `Iterator` trait, but rather
775 // a restriction on `<T as Iterator>::Item`, so it is passed
777 let assoc_bindings = generic_args
781 let kind = match binding.kind {
782 hir::TypeBindingKind::Equality { ref ty } => {
783 ConvertedBindingKind::Equality(self.ast_ty_to_ty(ty))
785 hir::TypeBindingKind::Constraint { ref bounds } => {
786 ConvertedBindingKind::Constraint(bounds)
789 ConvertedBinding { item_name: binding.ident, kind, span: binding.span }
794 "create_substs_for_ast_path(generic_params={:?}, self_ty={:?}) -> {:?}",
795 generic_params, self_ty, substs
798 (substs, assoc_bindings, potential_assoc_types)
801 crate fn create_substs_for_associated_item(
806 item_segment: &hir::PathSegment<'_>,
807 parent_substs: SubstsRef<'tcx>,
808 ) -> SubstsRef<'tcx> {
809 if tcx.generics_of(item_def_id).params.is_empty() {
810 self.prohibit_generics(slice::from_ref(item_segment));
814 self.create_substs_for_ast_path(
818 item_segment.generic_args(),
819 item_segment.infer_args,
826 /// On missing type parameters, emit an E0393 error and provide a structured suggestion using
827 /// the type parameter's name as a placeholder.
828 fn complain_about_missing_type_params(
830 missing_type_params: Vec<String>,
833 empty_generic_args: bool,
835 if missing_type_params.is_empty() {
839 missing_type_params.iter().map(|n| format!("`{}`", n)).collect::<Vec<_>>().join(", ");
840 let mut err = struct_span_err!(
844 "the type parameter{} {} must be explicitly specified",
845 pluralize!(missing_type_params.len()),
849 self.tcx().def_span(def_id),
851 "type parameter{} {} must be specified for this",
852 pluralize!(missing_type_params.len()),
856 let mut suggested = false;
857 if let (Ok(snippet), true) = (
858 self.tcx().sess.source_map().span_to_snippet(span),
859 // Don't suggest setting the type params if there are some already: the order is
860 // tricky to get right and the user will already know what the syntax is.
863 if snippet.ends_with('>') {
864 // The user wrote `Trait<'a, T>` or similar. To provide an accurate suggestion
865 // we would have to preserve the right order. For now, as clearly the user is
866 // aware of the syntax, we do nothing.
868 // The user wrote `Iterator`, so we don't have a type we can suggest, but at
869 // least we can clue them to the correct syntax `Iterator<Type>`.
873 "set the type parameter{plural} to the desired type{plural}",
874 plural = pluralize!(missing_type_params.len()),
876 format!("{}<{}>", snippet, missing_type_params.join(", ")),
877 Applicability::HasPlaceholders,
886 "missing reference{} to {}",
887 pluralize!(missing_type_params.len()),
893 "because of the default `Self` reference, type parameters must be \
894 specified on object types"
899 /// Instantiates the path for the given trait reference, assuming that it's
900 /// bound to a valid trait type. Returns the `DefId` of the defining trait.
901 /// The type _cannot_ be a type other than a trait type.
903 /// If the `projections` argument is `None`, then assoc type bindings like `Foo<T = X>`
904 /// are disallowed. Otherwise, they are pushed onto the vector given.
905 pub fn instantiate_mono_trait_ref(
907 trait_ref: &hir::TraitRef<'_>,
909 ) -> ty::TraitRef<'tcx> {
910 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
912 self.ast_path_to_mono_trait_ref(
914 trait_ref.trait_def_id(),
916 trait_ref.path.segments.last().unwrap(),
920 /// The given trait-ref must actually be a trait.
921 pub(super) fn instantiate_poly_trait_ref_inner(
923 trait_ref: &hir::TraitRef<'_>,
925 constness: Constness,
927 bounds: &mut Bounds<'tcx>,
929 ) -> Option<Vec<Span>> {
930 let trait_def_id = trait_ref.trait_def_id();
932 debug!("instantiate_poly_trait_ref({:?}, def_id={:?})", trait_ref, trait_def_id);
934 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
936 let path_span = if let [segment] = &trait_ref.path.segments[..] {
937 // FIXME: `trait_ref.path.span` can point to a full path with multiple
938 // segments, even though `trait_ref.path.segments` is of length `1`. Work
939 // around that bug here, even though it should be fixed elsewhere.
940 // This would otherwise cause an invalid suggestion. For an example, look at
941 // `src/test/ui/issues/issue-28344.rs`.
946 let (substs, assoc_bindings, potential_assoc_types) = self.create_substs_for_ast_trait_ref(
950 trait_ref.path.segments.last().unwrap(),
952 let poly_trait_ref = ty::Binder::bind(ty::TraitRef::new(trait_def_id, substs));
954 bounds.trait_bounds.push((poly_trait_ref, span, constness));
956 let mut dup_bindings = FxHashMap::default();
957 for binding in &assoc_bindings {
958 // Specify type to assert that error was already reported in `Err` case.
959 let _: Result<_, ErrorReported> = self.add_predicates_for_ast_type_binding(
960 trait_ref.hir_ref_id,
968 // Okay to ignore `Err` because of `ErrorReported` (see above).
972 "instantiate_poly_trait_ref({:?}, bounds={:?}) -> {:?}",
973 trait_ref, bounds, poly_trait_ref
975 potential_assoc_types
978 /// Given a trait bound like `Debug`, applies that trait bound the given self-type to construct
979 /// a full trait reference. The resulting trait reference is returned. This may also generate
980 /// auxiliary bounds, which are added to `bounds`.
985 /// poly_trait_ref = Iterator<Item = u32>
989 /// this would return `Foo: Iterator` and add `<Foo as Iterator>::Item = u32` into `bounds`.
991 /// **A note on binders:** against our usual convention, there is an implied bounder around
992 /// the `self_ty` and `poly_trait_ref` parameters here. So they may reference bound regions.
993 /// If for example you had `for<'a> Foo<'a>: Bar<'a>`, then the `self_ty` would be `Foo<'a>`
994 /// where `'a` is a bound region at depth 0. Similarly, the `poly_trait_ref` would be
995 /// `Bar<'a>`. The returned poly-trait-ref will have this binder instantiated explicitly,
997 pub fn instantiate_poly_trait_ref(
999 poly_trait_ref: &hir::PolyTraitRef<'_>,
1000 constness: Constness,
1002 bounds: &mut Bounds<'tcx>,
1003 ) -> Option<Vec<Span>> {
1004 self.instantiate_poly_trait_ref_inner(
1005 &poly_trait_ref.trait_ref,
1006 poly_trait_ref.span,
1014 fn ast_path_to_mono_trait_ref(
1017 trait_def_id: DefId,
1019 trait_segment: &hir::PathSegment<'_>,
1020 ) -> ty::TraitRef<'tcx> {
1021 let (substs, assoc_bindings, _) =
1022 self.create_substs_for_ast_trait_ref(span, trait_def_id, self_ty, trait_segment);
1023 assoc_bindings.first().map(|b| AstConv::prohibit_assoc_ty_binding(self.tcx(), b.span));
1024 ty::TraitRef::new(trait_def_id, substs)
1027 /// When the code is using the `Fn` traits directly, instead of the `Fn(A) -> B` syntax, emit
1028 /// an error and attempt to build a reasonable structured suggestion.
1029 fn complain_about_internal_fn_trait(
1032 trait_def_id: DefId,
1033 trait_segment: &'a hir::PathSegment<'a>,
1035 let trait_def = self.tcx().trait_def(trait_def_id);
1037 if !self.tcx().features().unboxed_closures
1038 && trait_segment.generic_args().parenthesized != trait_def.paren_sugar
1040 // For now, require that parenthetical notation be used only with `Fn()` etc.
1041 let (msg, sugg) = if trait_def.paren_sugar {
1043 "the precise format of `Fn`-family traits' type parameters is subject to \
1047 trait_segment.ident,
1051 .and_then(|args| args.args.get(0))
1052 .and_then(|arg| match arg {
1053 hir::GenericArg::Type(ty) => {
1054 Some(print::to_string(print::NO_ANN, |s| s.print_type(ty)))
1058 .unwrap_or_else(|| "()".to_string()),
1063 .filter_map(|b| match (b.ident.as_str() == "Output", &b.kind) {
1064 (true, hir::TypeBindingKind::Equality { ty }) => {
1065 Some(print::to_string(print::NO_ANN, |s| s.print_type(ty)))
1070 .unwrap_or_else(|| "()".to_string()),
1074 ("parenthetical notation is only stable when used with `Fn`-family traits", None)
1076 let sess = &self.tcx().sess.parse_sess;
1077 let mut err = feature_err(sess, sym::unboxed_closures, span, msg);
1078 if let Some(sugg) = sugg {
1079 let msg = "use parenthetical notation instead";
1080 err.span_suggestion(span, msg, sugg, Applicability::MaybeIncorrect);
1086 fn create_substs_for_ast_trait_ref<'a>(
1089 trait_def_id: DefId,
1091 trait_segment: &'a hir::PathSegment<'a>,
1092 ) -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'a, 'tcx>>, Option<Vec<Span>>) {
1093 debug!("create_substs_for_ast_trait_ref(trait_segment={:?})", trait_segment);
1095 self.complain_about_internal_fn_trait(span, trait_def_id, trait_segment);
1097 self.create_substs_for_ast_path(
1101 trait_segment.generic_args(),
1102 trait_segment.infer_args,
1107 fn trait_defines_associated_type_named(
1109 trait_def_id: DefId,
1110 assoc_name: ast::Ident,
1112 self.tcx().associated_items(trait_def_id).any(|item| {
1113 item.kind == ty::AssocKind::Type
1114 && self.tcx().hygienic_eq(assoc_name, item.ident, trait_def_id)
1118 // Returns `true` if a bounds list includes `?Sized`.
1119 pub fn is_unsized(&self, ast_bounds: &[hir::GenericBound<'_>], span: Span) -> bool {
1120 let tcx = self.tcx();
1122 // Try to find an unbound in bounds.
1123 let mut unbound = None;
1124 for ab in ast_bounds {
1125 if let &hir::GenericBound::Trait(ref ptr, hir::TraitBoundModifier::Maybe) = ab {
1126 if unbound.is_none() {
1127 unbound = Some(&ptr.trait_ref);
1133 "type parameter has more than one relaxed default \
1134 bound, only one is supported"
1141 let kind_id = tcx.lang_items().require(SizedTraitLangItem);
1144 // FIXME(#8559) currently requires the unbound to be built-in.
1145 if let Ok(kind_id) = kind_id {
1146 if tpb.path.res != Res::Def(DefKind::Trait, kind_id) {
1149 "default bound relaxed for a type parameter, but \
1150 this does nothing because the given bound is not \
1151 a default; only `?Sized` is supported",
1156 _ if kind_id.is_ok() => {
1159 // No lang item for `Sized`, so we can't add it as a bound.
1166 /// This helper takes a *converted* parameter type (`param_ty`)
1167 /// and an *unconverted* list of bounds:
1170 /// fn foo<T: Debug>
1171 /// ^ ^^^^^ `ast_bounds` parameter, in HIR form
1173 /// `param_ty`, in ty form
1176 /// It adds these `ast_bounds` into the `bounds` structure.
1178 /// **A note on binders:** there is an implied binder around
1179 /// `param_ty` and `ast_bounds`. See `instantiate_poly_trait_ref`
1180 /// for more details.
1184 ast_bounds: &[hir::GenericBound<'_>],
1185 bounds: &mut Bounds<'tcx>,
1187 let mut trait_bounds = Vec::new();
1188 let mut region_bounds = Vec::new();
1190 let constness = self.default_constness_for_trait_bounds();
1191 for ast_bound in ast_bounds {
1193 hir::GenericBound::Trait(ref b, hir::TraitBoundModifier::None) => {
1194 trait_bounds.push((b, constness))
1196 hir::GenericBound::Trait(ref b, hir::TraitBoundModifier::MaybeConst) => {
1197 trait_bounds.push((b, Constness::NotConst))
1199 hir::GenericBound::Trait(_, hir::TraitBoundModifier::Maybe) => {}
1200 hir::GenericBound::Outlives(ref l) => region_bounds.push(l),
1204 for (bound, constness) in trait_bounds {
1205 let _ = self.instantiate_poly_trait_ref(bound, constness, param_ty, bounds);
1208 bounds.region_bounds.extend(
1209 region_bounds.into_iter().map(|r| (self.ast_region_to_region(r, None), r.span)),
1213 /// Translates a list of bounds from the HIR into the `Bounds` data structure.
1214 /// The self-type for the bounds is given by `param_ty`.
1219 /// fn foo<T: Bar + Baz>() { }
1220 /// ^ ^^^^^^^^^ ast_bounds
1224 /// The `sized_by_default` parameter indicates if, in this context, the `param_ty` should be
1225 /// considered `Sized` unless there is an explicit `?Sized` bound. This would be true in the
1226 /// example above, but is not true in supertrait listings like `trait Foo: Bar + Baz`.
1228 /// `span` should be the declaration size of the parameter.
1229 pub fn compute_bounds(
1232 ast_bounds: &[hir::GenericBound<'_>],
1233 sized_by_default: SizedByDefault,
1236 let mut bounds = Bounds::default();
1238 self.add_bounds(param_ty, ast_bounds, &mut bounds);
1239 bounds.trait_bounds.sort_by_key(|(t, _, _)| t.def_id());
1241 bounds.implicitly_sized = if let SizedByDefault::Yes = sized_by_default {
1242 if !self.is_unsized(ast_bounds, span) { Some(span) } else { None }
1250 /// Given an HIR binding like `Item = Foo` or `Item: Foo`, pushes the corresponding predicates
1253 /// **A note on binders:** given something like `T: for<'a> Iterator<Item = &'a u32>`, the
1254 /// `trait_ref` here will be `for<'a> T: Iterator`. The `binding` data however is from *inside*
1255 /// the binder (e.g., `&'a u32`) and hence may reference bound regions.
1256 fn add_predicates_for_ast_type_binding(
1258 hir_ref_id: hir::HirId,
1259 trait_ref: ty::PolyTraitRef<'tcx>,
1260 binding: &ConvertedBinding<'_, 'tcx>,
1261 bounds: &mut Bounds<'tcx>,
1263 dup_bindings: &mut FxHashMap<DefId, Span>,
1265 ) -> Result<(), ErrorReported> {
1266 let tcx = self.tcx();
1269 // Given something like `U: SomeTrait<T = X>`, we want to produce a
1270 // predicate like `<U as SomeTrait>::T = X`. This is somewhat
1271 // subtle in the event that `T` is defined in a supertrait of
1272 // `SomeTrait`, because in that case we need to upcast.
1274 // That is, consider this case:
1277 // trait SubTrait: SuperTrait<int> { }
1278 // trait SuperTrait<A> { type T; }
1280 // ... B: SubTrait<T = foo> ...
1283 // We want to produce `<B as SuperTrait<int>>::T == foo`.
1285 // Find any late-bound regions declared in `ty` that are not
1286 // declared in the trait-ref. These are not well-formed.
1290 // for<'a> <T as Iterator>::Item = &'a str // <-- 'a is bad
1291 // for<'a> <T as FnMut<(&'a u32,)>>::Output = &'a str // <-- 'a is ok
1292 if let ConvertedBindingKind::Equality(ty) = binding.kind {
1293 let late_bound_in_trait_ref =
1294 tcx.collect_constrained_late_bound_regions(&trait_ref);
1295 let late_bound_in_ty =
1296 tcx.collect_referenced_late_bound_regions(&ty::Binder::bind(ty));
1297 debug!("late_bound_in_trait_ref = {:?}", late_bound_in_trait_ref);
1298 debug!("late_bound_in_ty = {:?}", late_bound_in_ty);
1299 for br in late_bound_in_ty.difference(&late_bound_in_trait_ref) {
1300 let br_name = match *br {
1301 ty::BrNamed(_, name) => name,
1305 "anonymous bound region {:?} in binding but not trait ref",
1314 "binding for associated type `{}` references lifetime `{}`, \
1315 which does not appear in the trait input types",
1325 if self.trait_defines_associated_type_named(trait_ref.def_id(), binding.item_name) {
1326 // Simple case: X is defined in the current trait.
1329 // Otherwise, we have to walk through the supertraits to find
1331 self.one_bound_for_assoc_type(
1332 || traits::supertraits(tcx, trait_ref),
1333 || trait_ref.print_only_trait_path().to_string(),
1336 || match binding.kind {
1337 ConvertedBindingKind::Equality(ty) => Some(ty.to_string()),
1343 let (assoc_ident, def_scope) =
1344 tcx.adjust_ident_and_get_scope(binding.item_name, candidate.def_id(), hir_ref_id);
1346 .associated_items(candidate.def_id())
1347 .find(|i| i.kind == ty::AssocKind::Type && i.ident.modern() == assoc_ident)
1348 .expect("missing associated type");
1350 if !assoc_ty.vis.is_accessible_from(def_scope, tcx) {
1351 let msg = format!("associated type `{}` is private", binding.item_name);
1352 tcx.sess.span_err(binding.span, &msg);
1354 tcx.check_stability(assoc_ty.def_id, Some(hir_ref_id), binding.span);
1358 .entry(assoc_ty.def_id)
1359 .and_modify(|prev_span| {
1364 "the value of the associated type `{}` (from trait `{}`) \
1365 is already specified",
1367 tcx.def_path_str(assoc_ty.container.id())
1369 .span_label(binding.span, "re-bound here")
1370 .span_label(*prev_span, format!("`{}` bound here first", binding.item_name))
1373 .or_insert(binding.span);
1376 match binding.kind {
1377 ConvertedBindingKind::Equality(ref ty) => {
1378 // "Desugar" a constraint like `T: Iterator<Item = u32>` this to
1379 // the "projection predicate" for:
1381 // `<T as Iterator>::Item = u32`
1382 bounds.projection_bounds.push((
1383 candidate.map_bound(|trait_ref| ty::ProjectionPredicate {
1384 projection_ty: ty::ProjectionTy::from_ref_and_name(
1394 ConvertedBindingKind::Constraint(ast_bounds) => {
1395 // "Desugar" a constraint like `T: Iterator<Item: Debug>` to
1397 // `<T as Iterator>::Item: Debug`
1399 // Calling `skip_binder` is okay, because `add_bounds` expects the `param_ty`
1400 // parameter to have a skipped binder.
1401 let param_ty = tcx.mk_projection(assoc_ty.def_id, candidate.skip_binder().substs);
1402 self.add_bounds(param_ty, ast_bounds, bounds);
1412 item_segment: &hir::PathSegment<'_>,
1414 let substs = self.ast_path_substs_for_ty(span, did, item_segment);
1415 self.normalize_ty(span, self.tcx().at(span).type_of(did).subst(self.tcx(), substs))
1418 fn conv_object_ty_poly_trait_ref(
1421 trait_bounds: &[hir::PolyTraitRef<'_>],
1422 lifetime: &hir::Lifetime,
1424 let tcx = self.tcx();
1426 let mut bounds = Bounds::default();
1427 let mut potential_assoc_types = Vec::new();
1428 let dummy_self = self.tcx().types.trait_object_dummy_self;
1429 for trait_bound in trait_bounds.iter().rev() {
1430 let cur_potential_assoc_types = self.instantiate_poly_trait_ref(
1432 Constness::NotConst,
1436 potential_assoc_types.extend(cur_potential_assoc_types.into_iter().flatten());
1439 // Expand trait aliases recursively and check that only one regular (non-auto) trait
1440 // is used and no 'maybe' bounds are used.
1441 let expanded_traits = traits::expand_trait_aliases(
1443 bounds.trait_bounds.iter().map(|&(a, b, _)| (a.clone(), b)),
1445 let (mut auto_traits, regular_traits): (Vec<_>, Vec<_>) =
1446 expanded_traits.partition(|i| tcx.trait_is_auto(i.trait_ref().def_id()));
1447 if regular_traits.len() > 1 {
1448 let first_trait = ®ular_traits[0];
1449 let additional_trait = ®ular_traits[1];
1450 let mut err = struct_span_err!(
1452 additional_trait.bottom().1,
1454 "only auto traits can be used as additional traits in a trait object"
1456 additional_trait.label_with_exp_info(
1458 "additional non-auto trait",
1461 first_trait.label_with_exp_info(&mut err, "first non-auto trait", "first use");
1465 if regular_traits.is_empty() && auto_traits.is_empty() {
1470 "at least one trait is required for an object type"
1473 return tcx.types.err;
1476 // Check that there are no gross object safety violations;
1477 // most importantly, that the supertraits don't contain `Self`,
1479 for item in ®ular_traits {
1480 let object_safety_violations =
1481 astconv_object_safety_violations(tcx, item.trait_ref().def_id());
1482 if !object_safety_violations.is_empty() {
1483 report_object_safety_error(
1486 item.trait_ref().def_id(),
1487 object_safety_violations,
1490 return tcx.types.err;
1494 // Use a `BTreeSet` to keep output in a more consistent order.
1495 let mut associated_types: FxHashMap<Span, BTreeSet<DefId>> = FxHashMap::default();
1497 let regular_traits_refs_spans = bounds
1500 .filter(|(trait_ref, _, _)| !tcx.trait_is_auto(trait_ref.def_id()));
1502 for (base_trait_ref, span, constness) in regular_traits_refs_spans {
1503 assert_eq!(constness, ast::Constness::NotConst);
1505 for trait_ref in traits::elaborate_trait_ref(tcx, base_trait_ref) {
1507 "conv_object_ty_poly_trait_ref: observing object predicate `{:?}`",
1511 ty::Predicate::Trait(pred, _) => {
1512 associated_types.entry(span).or_default().extend(
1513 tcx.associated_items(pred.def_id())
1514 .filter(|item| item.kind == ty::AssocKind::Type)
1515 .map(|item| item.def_id),
1518 ty::Predicate::Projection(pred) => {
1519 // A `Self` within the original bound will be substituted with a
1520 // `trait_object_dummy_self`, so check for that.
1521 let references_self = pred.skip_binder().ty.walk().any(|t| t == dummy_self);
1523 // If the projection output contains `Self`, force the user to
1524 // elaborate it explicitly to avoid a lot of complexity.
1526 // The "classicaly useful" case is the following:
1528 // trait MyTrait: FnMut() -> <Self as MyTrait>::MyOutput {
1533 // Here, the user could theoretically write `dyn MyTrait<Output = X>`,
1534 // but actually supporting that would "expand" to an infinitely-long type
1535 // `fix $ τ → dyn MyTrait<MyOutput = X, Output = <τ as MyTrait>::MyOutput`.
1537 // Instead, we force the user to write
1538 // `dyn MyTrait<MyOutput = X, Output = X>`, which is uglier but works. See
1539 // the discussion in #56288 for alternatives.
1540 if !references_self {
1541 // Include projections defined on supertraits.
1542 bounds.projection_bounds.push((pred, span));
1550 for (projection_bound, _) in &bounds.projection_bounds {
1551 for (_, def_ids) in &mut associated_types {
1552 def_ids.remove(&projection_bound.projection_def_id());
1556 self.complain_about_missing_associated_types(
1558 potential_assoc_types,
1562 // De-duplicate auto traits so that, e.g., `dyn Trait + Send + Send` is the same as
1563 // `dyn Trait + Send`.
1564 auto_traits.sort_by_key(|i| i.trait_ref().def_id());
1565 auto_traits.dedup_by_key(|i| i.trait_ref().def_id());
1566 debug!("regular_traits: {:?}", regular_traits);
1567 debug!("auto_traits: {:?}", auto_traits);
1569 // Transform a `PolyTraitRef` into a `PolyExistentialTraitRef` by
1570 // removing the dummy `Self` type (`trait_object_dummy_self`).
1571 let trait_ref_to_existential = |trait_ref: ty::TraitRef<'tcx>| {
1572 if trait_ref.self_ty() != dummy_self {
1573 // FIXME: There appears to be a missing filter on top of `expand_trait_aliases`,
1574 // which picks up non-supertraits where clauses - but also, the object safety
1575 // completely ignores trait aliases, which could be object safety hazards. We
1576 // `delay_span_bug` here to avoid an ICE in stable even when the feature is
1577 // disabled. (#66420)
1578 tcx.sess.delay_span_bug(
1581 "trait_ref_to_existential called on {:?} with non-dummy Self",
1586 ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref)
1589 // Erase the `dummy_self` (`trait_object_dummy_self`) used above.
1590 let existential_trait_refs = regular_traits
1592 .map(|i| i.trait_ref().map_bound(|trait_ref| trait_ref_to_existential(trait_ref)));
1593 let existential_projections = bounds.projection_bounds.iter().map(|(bound, _)| {
1594 bound.map_bound(|b| {
1595 let trait_ref = trait_ref_to_existential(b.projection_ty.trait_ref(tcx));
1596 ty::ExistentialProjection {
1598 item_def_id: b.projection_ty.item_def_id,
1599 substs: trait_ref.substs,
1604 // Calling `skip_binder` is okay because the predicates are re-bound.
1605 let regular_trait_predicates = existential_trait_refs
1606 .map(|trait_ref| ty::ExistentialPredicate::Trait(*trait_ref.skip_binder()));
1607 let auto_trait_predicates = auto_traits
1609 .map(|trait_ref| ty::ExistentialPredicate::AutoTrait(trait_ref.trait_ref().def_id()));
1610 let mut v = regular_trait_predicates
1611 .chain(auto_trait_predicates)
1613 existential_projections
1614 .map(|x| ty::ExistentialPredicate::Projection(*x.skip_binder())),
1616 .collect::<SmallVec<[_; 8]>>();
1617 v.sort_by(|a, b| a.stable_cmp(tcx, b));
1619 let existential_predicates = ty::Binder::bind(tcx.mk_existential_predicates(v.into_iter()));
1621 // Use explicitly-specified region bound.
1622 let region_bound = if !lifetime.is_elided() {
1623 self.ast_region_to_region(lifetime, None)
1625 self.compute_object_lifetime_bound(span, existential_predicates).unwrap_or_else(|| {
1626 if tcx.named_region(lifetime.hir_id).is_some() {
1627 self.ast_region_to_region(lifetime, None)
1629 self.re_infer(None, span).unwrap_or_else(|| {
1634 "the lifetime bound for this object type cannot be deduced \
1635 from context; please supply an explicit bound"
1638 tcx.lifetimes.re_static
1643 debug!("region_bound: {:?}", region_bound);
1645 let ty = tcx.mk_dynamic(existential_predicates, region_bound);
1646 debug!("trait_object_type: {:?}", ty);
1650 /// When there are any missing associated types, emit an E0191 error and attempt to supply a
1651 /// reasonable suggestion on how to write it. For the case of multiple associated types in the
1652 /// same trait bound have the same name (as they come from different super-traits), we instead
1653 /// emit a generic note suggesting using a `where` clause to constraint instead.
1654 fn complain_about_missing_associated_types(
1656 associated_types: FxHashMap<Span, BTreeSet<DefId>>,
1657 potential_assoc_types: Vec<Span>,
1658 trait_bounds: &[hir::PolyTraitRef<'_>],
1660 if !associated_types.values().any(|v| v.len() > 0) {
1663 let tcx = self.tcx();
1664 // FIXME: Marked `mut` so that we can replace the spans further below with a more
1665 // appropriate one, but this should be handled earlier in the span assignment.
1666 let mut associated_types: FxHashMap<Span, Vec<_>> = associated_types
1668 .map(|(span, def_ids)| {
1669 (span, def_ids.into_iter().map(|did| tcx.associated_item(did)).collect())
1672 let mut names = vec![];
1674 // Account for things like `dyn Foo + 'a`, like in tests `issue-22434.rs` and
1675 // `issue-22560.rs`.
1676 let mut trait_bound_spans: Vec<Span> = vec![];
1677 for (span, items) in &associated_types {
1678 if !items.is_empty() {
1679 trait_bound_spans.push(*span);
1681 for assoc_item in items {
1682 let trait_def_id = assoc_item.container.id();
1684 "`{}` (from trait `{}`)",
1686 tcx.def_path_str(trait_def_id),
1691 match (&potential_assoc_types[..], &trait_bounds) {
1692 ([], [bound]) => match &bound.trait_ref.path.segments[..] {
1693 // FIXME: `trait_ref.path.span` can point to a full path with multiple
1694 // segments, even though `trait_ref.path.segments` is of length `1`. Work
1695 // around that bug here, even though it should be fixed elsewhere.
1696 // This would otherwise cause an invalid suggestion. For an example, look at
1697 // `src/test/ui/issues/issue-28344.rs` where instead of the following:
1699 // error[E0191]: the value of the associated type `Output`
1700 // (from trait `std::ops::BitXor`) must be specified
1701 // --> $DIR/issue-28344.rs:4:17
1703 // LL | let x: u8 = BitXor::bitor(0 as u8, 0 as u8);
1704 // | ^^^^^^ help: specify the associated type:
1705 // | `BitXor<Output = Type>`
1709 // error[E0191]: the value of the associated type `Output`
1710 // (from trait `std::ops::BitXor`) must be specified
1711 // --> $DIR/issue-28344.rs:4:17
1713 // LL | let x: u8 = BitXor::bitor(0 as u8, 0 as u8);
1714 // | ^^^^^^^^^^^^^ help: specify the associated type:
1715 // | `BitXor::bitor<Output = Type>`
1716 [segment] if segment.args.is_none() => {
1717 trait_bound_spans = vec![segment.ident.span];
1718 associated_types = associated_types
1720 .map(|(_, items)| (segment.ident.span, items))
1728 trait_bound_spans.sort();
1729 let mut err = struct_span_err!(
1733 "the value of the associated type{} {} must be specified",
1734 pluralize!(names.len()),
1737 let mut suggestions = vec![];
1738 let mut types_count = 0;
1739 let mut where_constraints = vec![];
1740 for (span, assoc_items) in &associated_types {
1741 let mut names: FxHashMap<_, usize> = FxHashMap::default();
1742 for item in assoc_items {
1744 *names.entry(item.ident.name).or_insert(0) += 1;
1746 let mut dupes = false;
1747 for item in assoc_items {
1748 let prefix = if names[&item.ident.name] > 1 {
1749 let trait_def_id = item.container.id();
1751 format!("{}::", tcx.def_path_str(trait_def_id))
1755 if let Some(sp) = tcx.hir().span_if_local(item.def_id) {
1756 err.span_label(sp, format!("`{}{}` defined here", prefix, item.ident));
1759 if potential_assoc_types.len() == assoc_items.len() {
1760 // Only suggest when the amount of missing associated types equals the number of
1761 // extra type arguments present, as that gives us a relatively high confidence
1762 // that the user forgot to give the associtated type's name. The canonical
1763 // example would be trying to use `Iterator<isize>` instead of
1764 // `Iterator<Item = isize>`.
1765 for (potential, item) in potential_assoc_types.iter().zip(assoc_items.iter()) {
1766 if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(*potential) {
1767 suggestions.push((*potential, format!("{} = {}", item.ident, snippet)));
1770 } else if let (Ok(snippet), false) =
1771 (tcx.sess.source_map().span_to_snippet(*span), dupes)
1774 assoc_items.iter().map(|item| format!("{} = Type", item.ident)).collect();
1775 let code = if snippet.ends_with(">") {
1776 // The user wrote `Trait<'a>` or similar and we don't have a type we can
1777 // suggest, but at least we can clue them to the correct syntax
1778 // `Trait<'a, Item = Type>` while accounting for the `<'a>` in the
1780 format!("{}, {}>", &snippet[..snippet.len() - 1], types.join(", "))
1782 // The user wrote `Iterator`, so we don't have a type we can suggest, but at
1783 // least we can clue them to the correct syntax `Iterator<Item = Type>`.
1784 format!("{}<{}>", snippet, types.join(", "))
1786 suggestions.push((*span, code));
1788 where_constraints.push(*span);
1791 let where_msg = "consider introducing a new type parameter, adding `where` constraints \
1792 using the fully-qualified path to the associated types";
1793 if !where_constraints.is_empty() && suggestions.is_empty() {
1794 // If there are duplicates associated type names and a single trait bound do not
1795 // use structured suggestion, it means that there are multiple super-traits with
1796 // the same associated type name.
1797 err.help(where_msg);
1799 if suggestions.len() != 1 {
1800 // We don't need this label if there's an inline suggestion, show otherwise.
1801 for (span, assoc_items) in &associated_types {
1802 let mut names: FxHashMap<_, usize> = FxHashMap::default();
1803 for item in assoc_items {
1805 *names.entry(item.ident.name).or_insert(0) += 1;
1807 let mut label = vec![];
1808 for item in assoc_items {
1809 let postfix = if names[&item.ident.name] > 1 {
1810 let trait_def_id = item.container.id();
1811 format!(" (from trait `{}`)", tcx.def_path_str(trait_def_id))
1815 label.push(format!("`{}`{}", item.ident, postfix));
1817 if !label.is_empty() {
1821 "associated type{} {} must be specified",
1822 pluralize!(label.len()),
1829 if !suggestions.is_empty() {
1830 err.multipart_suggestion(
1831 &format!("specify the associated type{}", pluralize!(types_count)),
1833 Applicability::HasPlaceholders,
1835 if !where_constraints.is_empty() {
1836 err.span_help(where_constraints, where_msg);
1842 fn report_ambiguous_associated_type(
1849 let mut err = struct_span_err!(self.tcx().sess, span, E0223, "ambiguous associated type");
1850 if let (Some(_), Ok(snippet)) = (
1851 self.tcx().sess.confused_type_with_std_module.borrow().get(&span),
1852 self.tcx().sess.source_map().span_to_snippet(span),
1854 err.span_suggestion(
1856 "you are looking for the module in `std`, not the primitive type",
1857 format!("std::{}", snippet),
1858 Applicability::MachineApplicable,
1861 err.span_suggestion(
1863 "use fully-qualified syntax",
1864 format!("<{} as {}>::{}", type_str, trait_str, name),
1865 Applicability::HasPlaceholders,
1871 // Search for a bound on a type parameter which includes the associated item
1872 // given by `assoc_name`. `ty_param_def_id` is the `DefId` of the type parameter
1873 // This function will fail if there are no suitable bounds or there is
1875 fn find_bound_for_assoc_item(
1877 ty_param_def_id: DefId,
1878 assoc_name: ast::Ident,
1880 ) -> Result<ty::PolyTraitRef<'tcx>, ErrorReported> {
1881 let tcx = self.tcx();
1884 "find_bound_for_assoc_item(ty_param_def_id={:?}, assoc_name={:?}, span={:?})",
1885 ty_param_def_id, assoc_name, span,
1888 let predicates = &self.get_type_parameter_bounds(span, ty_param_def_id).predicates;
1890 debug!("find_bound_for_assoc_item: predicates={:#?}", predicates);
1892 let param_hir_id = tcx.hir().as_local_hir_id(ty_param_def_id).unwrap();
1893 let param_name = tcx.hir().ty_param_name(param_hir_id);
1894 self.one_bound_for_assoc_type(
1896 traits::transitive_bounds(
1898 predicates.iter().filter_map(|(p, _)| p.to_opt_poly_trait_ref()),
1901 || param_name.to_string(),
1908 // Checks that `bounds` contains exactly one element and reports appropriate
1909 // errors otherwise.
1910 fn one_bound_for_assoc_type<I>(
1912 all_candidates: impl Fn() -> I,
1913 ty_param_name: impl Fn() -> String,
1914 assoc_name: ast::Ident,
1916 is_equality: impl Fn() -> Option<String>,
1917 ) -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
1919 I: Iterator<Item = ty::PolyTraitRef<'tcx>>,
1921 let mut matching_candidates = all_candidates()
1922 .filter(|r| self.trait_defines_associated_type_named(r.def_id(), assoc_name));
1924 let bound = match matching_candidates.next() {
1925 Some(bound) => bound,
1927 self.complain_about_assoc_type_not_found(
1933 return Err(ErrorReported);
1937 debug!("one_bound_for_assoc_type: bound = {:?}", bound);
1939 if let Some(bound2) = matching_candidates.next() {
1940 debug!("one_bound_for_assoc_type: bound2 = {:?}", bound2);
1942 let is_equality = is_equality();
1943 let bounds = iter::once(bound).chain(iter::once(bound2)).chain(matching_candidates);
1944 let mut err = if is_equality.is_some() {
1945 // More specific Error Index entry.
1950 "ambiguous associated type `{}` in bounds of `{}`",
1959 "ambiguous associated type `{}` in bounds of `{}`",
1964 err.span_label(span, format!("ambiguous associated type `{}`", assoc_name));
1966 let mut where_bounds = vec![];
1967 for bound in bounds {
1968 let bound_span = self
1970 .associated_items(bound.def_id())
1972 item.kind == ty::AssocKind::Type
1973 && self.tcx().hygienic_eq(assoc_name, item.ident, bound.def_id())
1975 .and_then(|item| self.tcx().hir().span_if_local(item.def_id));
1977 if let Some(bound_span) = bound_span {
1981 "ambiguous `{}` from `{}`",
1983 bound.print_only_trait_path(),
1986 if let Some(constraint) = &is_equality {
1987 where_bounds.push(format!(
1988 " T: {trait}::{assoc} = {constraint}",
1989 trait=bound.print_only_trait_path(),
1991 constraint=constraint,
1994 err.span_suggestion(
1996 "use fully qualified syntax to disambiguate",
2000 bound.print_only_trait_path(),
2003 Applicability::MaybeIncorrect,
2008 "associated type `{}` could derive from `{}`",
2010 bound.print_only_trait_path(),
2014 if !where_bounds.is_empty() {
2016 "consider introducing a new type parameter `T` and adding `where` constraints:\
2017 \n where\n T: {},\n{}",
2019 where_bounds.join(",\n"),
2023 if !where_bounds.is_empty() {
2024 return Err(ErrorReported);
2030 fn complain_about_assoc_type_not_found<I>(
2032 all_candidates: impl Fn() -> I,
2033 ty_param_name: &str,
2034 assoc_name: ast::Ident,
2037 I: Iterator<Item = ty::PolyTraitRef<'tcx>>,
2039 // The fallback span is needed because `assoc_name` might be an `Fn()`'s `Output` without a
2040 // valid span, so we point at the whole path segment instead.
2041 let span = if assoc_name.span != DUMMY_SP { assoc_name.span } else { span };
2042 let mut err = struct_span_err!(
2046 "associated type `{}` not found for `{}`",
2051 let all_candidate_names: Vec<_> = all_candidates()
2052 .map(|r| self.tcx().associated_items(r.def_id()))
2055 |item| if item.kind == ty::AssocKind::Type { Some(item.ident.name) } else { None },
2059 if let (Some(suggested_name), true) = (
2060 find_best_match_for_name(all_candidate_names.iter(), &assoc_name.as_str(), None),
2061 assoc_name.span != DUMMY_SP,
2063 err.span_suggestion(
2065 "there is an associated type with a similar name",
2066 suggested_name.to_string(),
2067 Applicability::MaybeIncorrect,
2070 err.span_label(span, format!("associated type `{}` not found", assoc_name));
2076 // Create a type from a path to an associated type.
2077 // For a path `A::B::C::D`, `qself_ty` and `qself_def` are the type and def for `A::B::C`
2078 // and item_segment is the path segment for `D`. We return a type and a def for
2080 // Will fail except for `T::A` and `Self::A`; i.e., if `qself_ty`/`qself_def` are not a type
2081 // parameter or `Self`.
2082 pub fn associated_path_to_ty(
2084 hir_ref_id: hir::HirId,
2088 assoc_segment: &hir::PathSegment<'_>,
2089 permit_variants: bool,
2090 ) -> Result<(Ty<'tcx>, DefKind, DefId), ErrorReported> {
2091 let tcx = self.tcx();
2092 let assoc_ident = assoc_segment.ident;
2094 debug!("associated_path_to_ty: {:?}::{}", qself_ty, assoc_ident);
2096 // Check if we have an enum variant.
2097 let mut variant_resolution = None;
2098 if let ty::Adt(adt_def, _) = qself_ty.kind {
2099 if adt_def.is_enum() {
2100 let variant_def = adt_def
2103 .find(|vd| tcx.hygienic_eq(assoc_ident, vd.ident, adt_def.did));
2104 if let Some(variant_def) = variant_def {
2105 if permit_variants {
2106 tcx.check_stability(variant_def.def_id, Some(hir_ref_id), span);
2107 self.prohibit_generics(slice::from_ref(assoc_segment));
2108 return Ok((qself_ty, DefKind::Variant, variant_def.def_id));
2110 variant_resolution = Some(variant_def.def_id);
2116 // Find the type of the associated item, and the trait where the associated
2117 // item is declared.
2118 let bound = match (&qself_ty.kind, qself_res) {
2119 (_, Res::SelfTy(Some(_), Some(impl_def_id))) => {
2120 // `Self` in an impl of a trait -- we have a concrete self type and a
2122 let trait_ref = match tcx.impl_trait_ref(impl_def_id) {
2123 Some(trait_ref) => trait_ref,
2125 // A cycle error occurred, most likely.
2126 return Err(ErrorReported);
2130 self.one_bound_for_assoc_type(
2131 || traits::supertraits(tcx, ty::Binder::bind(trait_ref)),
2132 || "Self".to_string(),
2138 (&ty::Param(_), Res::SelfTy(Some(param_did), None))
2139 | (&ty::Param(_), Res::Def(DefKind::TyParam, param_did)) => {
2140 self.find_bound_for_assoc_item(param_did, assoc_ident, span)?
2143 if variant_resolution.is_some() {
2144 // Variant in type position
2145 let msg = format!("expected type, found variant `{}`", assoc_ident);
2146 tcx.sess.span_err(span, &msg);
2147 } else if qself_ty.is_enum() {
2148 let mut err = struct_span_err!(
2152 "no variant named `{}` found for enum `{}`",
2157 let adt_def = qself_ty.ty_adt_def().expect("enum is not an ADT");
2158 if let Some(suggested_name) = find_best_match_for_name(
2159 adt_def.variants.iter().map(|variant| &variant.ident.name),
2160 &assoc_ident.as_str(),
2163 err.span_suggestion(
2165 "there is a variant with a similar name",
2166 suggested_name.to_string(),
2167 Applicability::MaybeIncorrect,
2172 format!("variant not found in `{}`", qself_ty),
2176 if let Some(sp) = tcx.hir().span_if_local(adt_def.did) {
2177 let sp = tcx.sess.source_map().def_span(sp);
2178 err.span_label(sp, format!("variant `{}` not found here", assoc_ident));
2182 } else if !qself_ty.references_error() {
2183 // Don't print `TyErr` to the user.
2184 self.report_ambiguous_associated_type(
2186 &qself_ty.to_string(),
2191 return Err(ErrorReported);
2195 let trait_did = bound.def_id();
2196 let (assoc_ident, def_scope) =
2197 tcx.adjust_ident_and_get_scope(assoc_ident, trait_did, hir_ref_id);
2199 .associated_items(trait_did)
2200 .find(|i| Namespace::from(i.kind) == Namespace::Type && i.ident.modern() == assoc_ident)
2201 .expect("missing associated type");
2203 let ty = self.projected_ty_from_poly_trait_ref(span, item.def_id, assoc_segment, bound);
2204 let ty = self.normalize_ty(span, ty);
2206 let kind = DefKind::AssocTy;
2207 if !item.vis.is_accessible_from(def_scope, tcx) {
2208 let msg = format!("{} `{}` is private", kind.descr(item.def_id), assoc_ident);
2209 tcx.sess.span_err(span, &msg);
2211 tcx.check_stability(item.def_id, Some(hir_ref_id), span);
2213 if let Some(variant_def_id) = variant_resolution {
2214 let mut err = tcx.struct_span_lint_hir(
2215 AMBIGUOUS_ASSOCIATED_ITEMS,
2218 "ambiguous associated item",
2221 let mut could_refer_to = |kind: DefKind, def_id, also| {
2222 let note_msg = format!(
2223 "`{}` could{} refer to {} defined here",
2228 err.span_note(tcx.def_span(def_id), ¬e_msg);
2230 could_refer_to(DefKind::Variant, variant_def_id, "");
2231 could_refer_to(kind, item.def_id, " also");
2233 err.span_suggestion(
2235 "use fully-qualified syntax",
2236 format!("<{} as {}>::{}", qself_ty, tcx.item_name(trait_did), assoc_ident),
2237 Applicability::MachineApplicable,
2242 Ok((ty, kind, item.def_id))
2248 opt_self_ty: Option<Ty<'tcx>>,
2250 trait_segment: &hir::PathSegment<'_>,
2251 item_segment: &hir::PathSegment<'_>,
2253 let tcx = self.tcx();
2255 let trait_def_id = tcx.parent(item_def_id).unwrap();
2257 debug!("qpath_to_ty: trait_def_id={:?}", trait_def_id);
2259 let self_ty = if let Some(ty) = opt_self_ty {
2262 let path_str = tcx.def_path_str(trait_def_id);
2264 let def_id = self.item_def_id();
2266 debug!("qpath_to_ty: self.item_def_id()={:?}", def_id);
2268 let parent_def_id = def_id
2269 .and_then(|def_id| tcx.hir().as_local_hir_id(def_id))
2270 .map(|hir_id| tcx.hir().get_parent_did(hir_id));
2272 debug!("qpath_to_ty: parent_def_id={:?}", parent_def_id);
2274 // If the trait in segment is the same as the trait defining the item,
2275 // use the `<Self as ..>` syntax in the error.
2276 let is_part_of_self_trait_constraints = def_id == Some(trait_def_id);
2277 let is_part_of_fn_in_self_trait = parent_def_id == Some(trait_def_id);
2279 let type_name = if is_part_of_self_trait_constraints || is_part_of_fn_in_self_trait {
2285 self.report_ambiguous_associated_type(
2289 item_segment.ident.name,
2291 return tcx.types.err;
2294 debug!("qpath_to_ty: self_type={:?}", self_ty);
2296 let trait_ref = self.ast_path_to_mono_trait_ref(span, trait_def_id, self_ty, trait_segment);
2298 let item_substs = self.create_substs_for_associated_item(
2306 debug!("qpath_to_ty: trait_ref={:?}", trait_ref);
2308 self.normalize_ty(span, tcx.mk_projection(item_def_id, item_substs))
2311 pub fn prohibit_generics<'a, T: IntoIterator<Item = &'a hir::PathSegment<'a>>>(
2315 let mut has_err = false;
2316 for segment in segments {
2317 let (mut err_for_lt, mut err_for_ty, mut err_for_ct) = (false, false, false);
2318 for arg in segment.generic_args().args {
2319 let (span, kind) = match arg {
2320 hir::GenericArg::Lifetime(lt) => {
2326 (lt.span, "lifetime")
2328 hir::GenericArg::Type(ty) => {
2336 hir::GenericArg::Const(ct) => {
2344 let mut err = struct_span_err!(
2348 "{} arguments are not allowed for this type",
2351 err.span_label(span, format!("{} argument not allowed", kind));
2353 if err_for_lt && err_for_ty && err_for_ct {
2357 for binding in segment.generic_args().bindings {
2359 Self::prohibit_assoc_ty_binding(self.tcx(), binding.span);
2366 pub fn prohibit_assoc_ty_binding(tcx: TyCtxt<'_>, span: Span) {
2367 let mut err = struct_span_err!(
2371 "associated type bindings are not allowed here"
2373 err.span_label(span, "associated type not allowed here").emit();
2376 // FIXME(eddyb, varkor) handle type paths here too, not just value ones.
2377 pub fn def_ids_for_value_path_segments(
2379 segments: &[hir::PathSegment<'_>],
2380 self_ty: Option<Ty<'tcx>>,
2384 // We need to extract the type parameters supplied by the user in
2385 // the path `path`. Due to the current setup, this is a bit of a
2386 // tricky-process; the problem is that resolve only tells us the
2387 // end-point of the path resolution, and not the intermediate steps.
2388 // Luckily, we can (at least for now) deduce the intermediate steps
2389 // just from the end-point.
2391 // There are basically five cases to consider:
2393 // 1. Reference to a constructor of a struct:
2395 // struct Foo<T>(...)
2397 // In this case, the parameters are declared in the type space.
2399 // 2. Reference to a constructor of an enum variant:
2401 // enum E<T> { Foo(...) }
2403 // In this case, the parameters are defined in the type space,
2404 // but may be specified either on the type or the variant.
2406 // 3. Reference to a fn item or a free constant:
2410 // In this case, the path will again always have the form
2411 // `a::b::foo::<T>` where only the final segment should have
2412 // type parameters. However, in this case, those parameters are
2413 // declared on a value, and hence are in the `FnSpace`.
2415 // 4. Reference to a method or an associated constant:
2417 // impl<A> SomeStruct<A> {
2421 // Here we can have a path like
2422 // `a::b::SomeStruct::<A>::foo::<B>`, in which case parameters
2423 // may appear in two places. The penultimate segment,
2424 // `SomeStruct::<A>`, contains parameters in TypeSpace, and the
2425 // final segment, `foo::<B>` contains parameters in fn space.
2427 // The first step then is to categorize the segments appropriately.
2429 let tcx = self.tcx();
2431 assert!(!segments.is_empty());
2432 let last = segments.len() - 1;
2434 let mut path_segs = vec![];
2437 // Case 1. Reference to a struct constructor.
2438 DefKind::Ctor(CtorOf::Struct, ..) => {
2439 // Everything but the final segment should have no
2440 // parameters at all.
2441 let generics = tcx.generics_of(def_id);
2442 // Variant and struct constructors use the
2443 // generics of their parent type definition.
2444 let generics_def_id = generics.parent.unwrap_or(def_id);
2445 path_segs.push(PathSeg(generics_def_id, last));
2448 // Case 2. Reference to a variant constructor.
2449 DefKind::Ctor(CtorOf::Variant, ..) | DefKind::Variant => {
2450 let adt_def = self_ty.map(|t| t.ty_adt_def().unwrap());
2451 let (generics_def_id, index) = if let Some(adt_def) = adt_def {
2452 debug_assert!(adt_def.is_enum());
2454 } else if last >= 1 && segments[last - 1].args.is_some() {
2455 // Everything but the penultimate segment should have no
2456 // parameters at all.
2457 let mut def_id = def_id;
2459 // `DefKind::Ctor` -> `DefKind::Variant`
2460 if let DefKind::Ctor(..) = kind {
2461 def_id = tcx.parent(def_id).unwrap()
2464 // `DefKind::Variant` -> `DefKind::Enum`
2465 let enum_def_id = tcx.parent(def_id).unwrap();
2466 (enum_def_id, last - 1)
2468 // FIXME: lint here recommending `Enum::<...>::Variant` form
2469 // instead of `Enum::Variant::<...>` form.
2471 // Everything but the final segment should have no
2472 // parameters at all.
2473 let generics = tcx.generics_of(def_id);
2474 // Variant and struct constructors use the
2475 // generics of their parent type definition.
2476 (generics.parent.unwrap_or(def_id), last)
2478 path_segs.push(PathSeg(generics_def_id, index));
2481 // Case 3. Reference to a top-level value.
2482 DefKind::Fn | DefKind::Const | DefKind::ConstParam | DefKind::Static => {
2483 path_segs.push(PathSeg(def_id, last));
2486 // Case 4. Reference to a method or associated const.
2487 DefKind::Method | DefKind::AssocConst => {
2488 if segments.len() >= 2 {
2489 let generics = tcx.generics_of(def_id);
2490 path_segs.push(PathSeg(generics.parent.unwrap(), last - 1));
2492 path_segs.push(PathSeg(def_id, last));
2495 kind => bug!("unexpected definition kind {:?} for {:?}", kind, def_id),
2498 debug!("path_segs = {:?}", path_segs);
2503 // Check a type `Path` and convert it to a `Ty`.
2506 opt_self_ty: Option<Ty<'tcx>>,
2507 path: &hir::Path<'_>,
2508 permit_variants: bool,
2510 let tcx = self.tcx();
2513 "res_to_ty(res={:?}, opt_self_ty={:?}, path_segments={:?})",
2514 path.res, opt_self_ty, path.segments
2517 let span = path.span;
2519 Res::Def(DefKind::OpaqueTy, did) => {
2520 // Check for desugared `impl Trait`.
2521 assert!(ty::is_impl_trait_defn(tcx, did).is_none());
2522 let item_segment = path.segments.split_last().unwrap();
2523 self.prohibit_generics(item_segment.1);
2524 let substs = self.ast_path_substs_for_ty(span, did, item_segment.0);
2525 self.normalize_ty(span, tcx.mk_opaque(did, substs))
2527 Res::Def(DefKind::Enum, did)
2528 | Res::Def(DefKind::TyAlias, did)
2529 | Res::Def(DefKind::Struct, did)
2530 | Res::Def(DefKind::Union, did)
2531 | Res::Def(DefKind::ForeignTy, did) => {
2532 assert_eq!(opt_self_ty, None);
2533 self.prohibit_generics(path.segments.split_last().unwrap().1);
2534 self.ast_path_to_ty(span, did, path.segments.last().unwrap())
2536 Res::Def(kind @ DefKind::Variant, def_id) if permit_variants => {
2537 // Convert "variant type" as if it were a real type.
2538 // The resulting `Ty` is type of the variant's enum for now.
2539 assert_eq!(opt_self_ty, None);
2542 self.def_ids_for_value_path_segments(&path.segments, None, kind, def_id);
2543 let generic_segs: FxHashSet<_> =
2544 path_segs.iter().map(|PathSeg(_, index)| index).collect();
2545 self.prohibit_generics(path.segments.iter().enumerate().filter_map(
2547 if !generic_segs.contains(&index) { Some(seg) } else { None }
2551 let PathSeg(def_id, index) = path_segs.last().unwrap();
2552 self.ast_path_to_ty(span, *def_id, &path.segments[*index])
2554 Res::Def(DefKind::TyParam, def_id) => {
2555 assert_eq!(opt_self_ty, None);
2556 self.prohibit_generics(path.segments);
2558 let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
2559 let item_id = tcx.hir().get_parent_node(hir_id);
2560 let item_def_id = tcx.hir().local_def_id(item_id);
2561 let generics = tcx.generics_of(item_def_id);
2562 let index = generics.param_def_id_to_index[&def_id];
2563 tcx.mk_ty_param(index, tcx.hir().name(hir_id))
2565 Res::SelfTy(Some(_), None) => {
2566 // `Self` in trait or type alias.
2567 assert_eq!(opt_self_ty, None);
2568 self.prohibit_generics(path.segments);
2569 tcx.types.self_param
2571 Res::SelfTy(_, Some(def_id)) => {
2572 // `Self` in impl (we know the concrete type).
2573 assert_eq!(opt_self_ty, None);
2574 self.prohibit_generics(path.segments);
2575 // Try to evaluate any array length constants.
2576 self.normalize_ty(span, tcx.at(span).type_of(def_id))
2578 Res::Def(DefKind::AssocTy, def_id) => {
2579 debug_assert!(path.segments.len() >= 2);
2580 self.prohibit_generics(&path.segments[..path.segments.len() - 2]);
2585 &path.segments[path.segments.len() - 2],
2586 path.segments.last().unwrap(),
2589 Res::PrimTy(prim_ty) => {
2590 assert_eq!(opt_self_ty, None);
2591 self.prohibit_generics(path.segments);
2593 hir::PrimTy::Bool => tcx.types.bool,
2594 hir::PrimTy::Char => tcx.types.char,
2595 hir::PrimTy::Int(it) => tcx.mk_mach_int(it),
2596 hir::PrimTy::Uint(uit) => tcx.mk_mach_uint(uit),
2597 hir::PrimTy::Float(ft) => tcx.mk_mach_float(ft),
2598 hir::PrimTy::Str => tcx.mk_str(),
2602 self.set_tainted_by_errors();
2603 return self.tcx().types.err;
2605 _ => span_bug!(span, "unexpected resolution: {:?}", path.res),
2609 /// Parses the programmer's textual representation of a type into our
2610 /// internal notion of a type.
2611 pub fn ast_ty_to_ty(&self, ast_ty: &hir::Ty<'_>) -> Ty<'tcx> {
2612 debug!("ast_ty_to_ty(id={:?}, ast_ty={:?} ty_ty={:?})", ast_ty.hir_id, ast_ty, ast_ty.kind);
2614 let tcx = self.tcx();
2616 let result_ty = match ast_ty.kind {
2617 hir::TyKind::Slice(ref ty) => tcx.mk_slice(self.ast_ty_to_ty(&ty)),
2618 hir::TyKind::Ptr(ref mt) => {
2619 tcx.mk_ptr(ty::TypeAndMut { ty: self.ast_ty_to_ty(&mt.ty), mutbl: mt.mutbl })
2621 hir::TyKind::Rptr(ref region, ref mt) => {
2622 let r = self.ast_region_to_region(region, None);
2623 debug!("ast_ty_to_ty: r={:?}", r);
2624 let t = self.ast_ty_to_ty(&mt.ty);
2625 tcx.mk_ref(r, ty::TypeAndMut { ty: t, mutbl: mt.mutbl })
2627 hir::TyKind::Never => tcx.types.never,
2628 hir::TyKind::Tup(ref fields) => {
2629 tcx.mk_tup(fields.iter().map(|t| self.ast_ty_to_ty(&t)))
2631 hir::TyKind::BareFn(ref bf) => {
2632 require_c_abi_if_c_variadic(tcx, &bf.decl, bf.abi, ast_ty.span);
2633 tcx.mk_fn_ptr(self.ty_of_fn(bf.unsafety, bf.abi, &bf.decl, &[], None))
2635 hir::TyKind::TraitObject(ref bounds, ref lifetime) => {
2636 self.conv_object_ty_poly_trait_ref(ast_ty.span, bounds, lifetime)
2638 hir::TyKind::Path(hir::QPath::Resolved(ref maybe_qself, ref path)) => {
2639 debug!("ast_ty_to_ty: maybe_qself={:?} path={:?}", maybe_qself, path);
2640 let opt_self_ty = maybe_qself.as_ref().map(|qself| self.ast_ty_to_ty(qself));
2641 self.res_to_ty(opt_self_ty, path, false)
2643 hir::TyKind::Def(item_id, ref lifetimes) => {
2644 let did = tcx.hir().local_def_id(item_id.id);
2645 self.impl_trait_ty_to_ty(did, lifetimes)
2647 hir::TyKind::Path(hir::QPath::TypeRelative(ref qself, ref segment)) => {
2648 debug!("ast_ty_to_ty: qself={:?} segment={:?}", qself, segment);
2649 let ty = self.ast_ty_to_ty(qself);
2651 let res = if let hir::TyKind::Path(hir::QPath::Resolved(_, ref path)) = qself.kind {
2656 self.associated_path_to_ty(ast_ty.hir_id, ast_ty.span, ty, res, segment, false)
2657 .map(|(ty, _, _)| ty)
2658 .unwrap_or(tcx.types.err)
2660 hir::TyKind::Array(ref ty, ref length) => {
2661 let length = self.ast_const_to_const(length, tcx.types.usize);
2662 let array_ty = tcx.mk_ty(ty::Array(self.ast_ty_to_ty(&ty), length));
2663 self.normalize_ty(ast_ty.span, array_ty)
2665 hir::TyKind::Typeof(ref _e) => {
2670 "`typeof` is a reserved keyword but unimplemented"
2672 .span_label(ast_ty.span, "reserved keyword")
2677 hir::TyKind::Infer => {
2678 // Infer also appears as the type of arguments or return
2679 // values in a ExprKind::Closure, or as
2680 // the type of local variables. Both of these cases are
2681 // handled specially and will not descend into this routine.
2682 self.ty_infer(None, ast_ty.span)
2684 hir::TyKind::Err => tcx.types.err,
2687 debug!("ast_ty_to_ty: result_ty={:?}", result_ty);
2689 self.record_ty(ast_ty.hir_id, result_ty, ast_ty.span);
2693 /// Returns the `DefId` of the constant parameter that the provided expression is a path to.
2694 pub fn const_param_def_id(&self, expr: &hir::Expr<'_>) -> Option<DefId> {
2695 // Unwrap a block, so that e.g. `{ P }` is recognised as a parameter. Const arguments
2696 // currently have to be wrapped in curly brackets, so it's necessary to special-case.
2697 let expr = match &expr.kind {
2698 ExprKind::Block(block, _) if block.stmts.is_empty() && block.expr.is_some() => {
2699 block.expr.as_ref().unwrap()
2705 ExprKind::Path(hir::QPath::Resolved(_, path)) => match path.res {
2706 Res::Def(DefKind::ConstParam, did) => Some(did),
2713 pub fn ast_const_to_const(
2715 ast_const: &hir::AnonConst,
2717 ) -> &'tcx ty::Const<'tcx> {
2718 debug!("ast_const_to_const(id={:?}, ast_const={:?})", ast_const.hir_id, ast_const);
2720 let tcx = self.tcx();
2721 let def_id = tcx.hir().local_def_id(ast_const.hir_id);
2723 let expr = &tcx.hir().body(ast_const.body).value;
2725 let lit_input = match expr.kind {
2726 hir::ExprKind::Lit(ref lit) => Some(LitToConstInput { lit: &lit.node, ty, neg: false }),
2727 hir::ExprKind::Unary(hir::UnOp::UnNeg, ref expr) => match expr.kind {
2728 hir::ExprKind::Lit(ref lit) => {
2729 Some(LitToConstInput { lit: &lit.node, ty, neg: true })
2736 if let Some(lit_input) = lit_input {
2737 // If an error occurred, ignore that it's a literal and leave reporting the error up to
2739 if let Ok(c) = tcx.at(expr.span).lit_to_const(lit_input) {
2744 let kind = if let Some(def_id) = self.const_param_def_id(expr) {
2745 // Find the name and index of the const parameter by indexing the generics of the
2746 // parent item and construct a `ParamConst`.
2747 let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
2748 let item_id = tcx.hir().get_parent_node(hir_id);
2749 let item_def_id = tcx.hir().local_def_id(item_id);
2750 let generics = tcx.generics_of(item_def_id);
2751 let index = generics.param_def_id_to_index[&tcx.hir().local_def_id(hir_id)];
2752 let name = tcx.hir().name(hir_id);
2753 ty::ConstKind::Param(ty::ParamConst::new(index, name))
2755 ty::ConstKind::Unevaluated(def_id, InternalSubsts::identity_for_item(tcx, def_id), None)
2757 tcx.mk_const(ty::Const { val: kind, ty })
2760 pub fn impl_trait_ty_to_ty(
2763 lifetimes: &[hir::GenericArg<'_>],
2765 debug!("impl_trait_ty_to_ty(def_id={:?}, lifetimes={:?})", def_id, lifetimes);
2766 let tcx = self.tcx();
2768 let generics = tcx.generics_of(def_id);
2770 debug!("impl_trait_ty_to_ty: generics={:?}", generics);
2771 let substs = InternalSubsts::for_item(tcx, def_id, |param, _| {
2772 if let Some(i) = (param.index as usize).checked_sub(generics.parent_count) {
2773 // Our own parameters are the resolved lifetimes.
2775 GenericParamDefKind::Lifetime => {
2776 if let hir::GenericArg::Lifetime(lifetime) = &lifetimes[i] {
2777 self.ast_region_to_region(lifetime, None).into()
2785 // Replace all parent lifetimes with `'static`.
2787 GenericParamDefKind::Lifetime => tcx.lifetimes.re_static.into(),
2788 _ => tcx.mk_param_from_def(param),
2792 debug!("impl_trait_ty_to_ty: substs={:?}", substs);
2794 let ty = tcx.mk_opaque(def_id, substs);
2795 debug!("impl_trait_ty_to_ty: {}", ty);
2799 pub fn ty_of_arg(&self, ty: &hir::Ty<'_>, expected_ty: Option<Ty<'tcx>>) -> Ty<'tcx> {
2801 hir::TyKind::Infer if expected_ty.is_some() => {
2802 self.record_ty(ty.hir_id, expected_ty.unwrap(), ty.span);
2803 expected_ty.unwrap()
2805 _ => self.ast_ty_to_ty(ty),
2811 unsafety: hir::Unsafety,
2813 decl: &hir::FnDecl<'_>,
2814 generic_params: &[hir::GenericParam<'_>],
2815 ident_span: Option<Span>,
2816 ) -> ty::PolyFnSig<'tcx> {
2819 let tcx = self.tcx();
2821 // We proactively collect all the infered type params to emit a single error per fn def.
2822 let mut visitor = PlaceholderHirTyCollector::default();
2823 for ty in decl.inputs {
2824 visitor.visit_ty(ty);
2826 let input_tys = decl.inputs.iter().map(|a| self.ty_of_arg(a, None));
2827 let output_ty = match decl.output {
2828 hir::FunctionRetTy::Return(ref output) => {
2829 visitor.visit_ty(output);
2830 self.ast_ty_to_ty(output)
2832 hir::FunctionRetTy::DefaultReturn(..) => tcx.mk_unit(),
2835 debug!("ty_of_fn: output_ty={:?}", output_ty);
2838 ty::Binder::bind(tcx.mk_fn_sig(input_tys, output_ty, decl.c_variadic, unsafety, abi));
2840 if !self.allow_ty_infer() {
2841 // We always collect the spans for placeholder types when evaluating `fn`s, but we
2842 // only want to emit an error complaining about them if infer types (`_`) are not
2843 // allowed. `allow_ty_infer` gates this behavior.
2844 crate::collect::placeholder_type_error(
2846 ident_span.map(|sp| sp.shrink_to_hi()).unwrap_or(DUMMY_SP),
2849 ident_span.is_some(),
2853 // Find any late-bound regions declared in return type that do
2854 // not appear in the arguments. These are not well-formed.
2857 // for<'a> fn() -> &'a str <-- 'a is bad
2858 // for<'a> fn(&'a String) -> &'a str <-- 'a is ok
2859 let inputs = bare_fn_ty.inputs();
2860 let late_bound_in_args =
2861 tcx.collect_constrained_late_bound_regions(&inputs.map_bound(|i| i.to_owned()));
2862 let output = bare_fn_ty.output();
2863 let late_bound_in_ret = tcx.collect_referenced_late_bound_regions(&output);
2864 for br in late_bound_in_ret.difference(&late_bound_in_args) {
2865 let lifetime_name = match *br {
2866 ty::BrNamed(_, name) => format!("lifetime `{}`,", name),
2867 ty::BrAnon(_) | ty::BrEnv => "an anonymous lifetime".to_string(),
2869 let mut err = struct_span_err!(
2873 "return type references {} \
2874 which is not constrained by the fn input types",
2877 if let ty::BrAnon(_) = *br {
2878 // The only way for an anonymous lifetime to wind up
2879 // in the return type but **also** be unconstrained is
2880 // if it only appears in "associated types" in the
2881 // input. See #47511 for an example. In this case,
2882 // though we can easily give a hint that ought to be
2885 "lifetimes appearing in an associated type \
2886 are not considered constrained",
2895 /// Given the bounds on an object, determines what single region bound (if any) we can
2896 /// use to summarize this type. The basic idea is that we will use the bound the user
2897 /// provided, if they provided one, and otherwise search the supertypes of trait bounds
2898 /// for region bounds. It may be that we can derive no bound at all, in which case
2899 /// we return `None`.
2900 fn compute_object_lifetime_bound(
2903 existential_predicates: ty::Binder<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>>,
2904 ) -> Option<ty::Region<'tcx>> // if None, use the default
2906 let tcx = self.tcx();
2908 debug!("compute_opt_region_bound(existential_predicates={:?})", existential_predicates);
2910 // No explicit region bound specified. Therefore, examine trait
2911 // bounds and see if we can derive region bounds from those.
2912 let derived_region_bounds = object_region_bounds(tcx, existential_predicates);
2914 // If there are no derived region bounds, then report back that we
2915 // can find no region bound. The caller will use the default.
2916 if derived_region_bounds.is_empty() {
2920 // If any of the derived region bounds are 'static, that is always
2922 if derived_region_bounds.iter().any(|&r| ty::ReStatic == *r) {
2923 return Some(tcx.lifetimes.re_static);
2926 // Determine whether there is exactly one unique region in the set
2927 // of derived region bounds. If so, use that. Otherwise, report an
2929 let r = derived_region_bounds[0];
2930 if derived_region_bounds[1..].iter().any(|r1| r != *r1) {
2935 "ambiguous lifetime bound, explicit lifetime bound required"
2943 /// Collects together a list of bounds that are applied to some type,
2944 /// after they've been converted into `ty` form (from the HIR
2945 /// representations). These lists of bounds occur in many places in
2949 /// trait Foo: Bar + Baz { }
2950 /// ^^^^^^^^^ supertrait list bounding the `Self` type parameter
2952 /// fn foo<T: Bar + Baz>() { }
2953 /// ^^^^^^^^^ bounding the type parameter `T`
2955 /// impl dyn Bar + Baz
2956 /// ^^^^^^^^^ bounding the forgotten dynamic type
2959 /// Our representation is a bit mixed here -- in some cases, we
2960 /// include the self type (e.g., `trait_bounds`) but in others we do
2961 #[derive(Default, PartialEq, Eq, Clone, Debug)]
2962 pub struct Bounds<'tcx> {
2963 /// A list of region bounds on the (implicit) self type. So if you
2964 /// had `T: 'a + 'b` this might would be a list `['a, 'b]` (but
2965 /// the `T` is not explicitly included).
2966 pub region_bounds: Vec<(ty::Region<'tcx>, Span)>,
2968 /// A list of trait bounds. So if you had `T: Debug` this would be
2969 /// `T: Debug`. Note that the self-type is explicit here.
2970 pub trait_bounds: Vec<(ty::PolyTraitRef<'tcx>, Span, Constness)>,
2972 /// A list of projection equality bounds. So if you had `T:
2973 /// Iterator<Item = u32>` this would include `<T as
2974 /// Iterator>::Item => u32`. Note that the self-type is explicit
2976 pub projection_bounds: Vec<(ty::PolyProjectionPredicate<'tcx>, Span)>,
2978 /// `Some` if there is *no* `?Sized` predicate. The `span`
2979 /// is the location in the source of the `T` declaration which can
2980 /// be cited as the source of the `T: Sized` requirement.
2981 pub implicitly_sized: Option<Span>,
2984 impl<'tcx> Bounds<'tcx> {
2985 /// Converts a bounds list into a flat set of predicates (like
2986 /// where-clauses). Because some of our bounds listings (e.g.,
2987 /// regions) don't include the self-type, you must supply the
2988 /// self-type here (the `param_ty` parameter).
2993 ) -> Vec<(ty::Predicate<'tcx>, Span)> {
2994 // If it could be sized, and is, add the `Sized` predicate.
2995 let sized_predicate = self.implicitly_sized.and_then(|span| {
2996 tcx.lang_items().sized_trait().map(|sized| {
2997 let trait_ref = ty::Binder::bind(ty::TraitRef {
2999 substs: tcx.mk_substs_trait(param_ty, &[]),
3001 (trait_ref.without_const().to_predicate(), span)
3010 .map(|&(region_bound, span)| {
3011 // Account for the binder being introduced below; no need to shift `param_ty`
3012 // because, at present at least, it either only refers to early-bound regions,
3013 // or it's a generic associated type that deliberately has escaping bound vars.
3014 let region_bound = ty::fold::shift_region(tcx, region_bound, 1);
3015 let outlives = ty::OutlivesPredicate(param_ty, region_bound);
3016 (ty::Binder::bind(outlives).to_predicate(), span)
3018 .chain(self.trait_bounds.iter().map(|&(bound_trait_ref, span, constness)| {
3019 let predicate = bound_trait_ref.with_constness(constness).to_predicate();
3023 self.projection_bounds
3025 .map(|&(projection, span)| (projection.to_predicate(), span)),