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, 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 = false;
317 if !infer_lifetimes {
318 if let Some(span_late) = def.has_late_bound_regions {
319 reported_late_bound_region_err = true;
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);
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(),
343 let check_kind_count =
344 |kind, required, permitted, provided, offset, unexpected_spans: &mut Vec<Span>| {
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 {
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 (spans, label) = if required == permitted && provided > permitted {
370 // In the case when the user has provided too many arguments,
371 // we want to point to the unexpected arguments.
372 let spans: Vec<Span> = args.args[offset + permitted..offset + provided]
374 .map(|arg| arg.span())
376 unexpected_spans.extend(spans.clone());
377 (spans, format!("unexpected {} argument", kind))
382 "expected {}{} {} argument{}",
391 let mut err = tcx.sess.struct_span_err_with_code(
394 "wrong number of {} arguments: expected {}{}, found {}",
395 kind, quantifier, bound, provided,
397 DiagnosticId::Error("E0107".into()),
400 err.span_label(span, label.as_str());
407 let mut arg_count_mismatch = reported_late_bound_region_err;
408 let mut unexpected_spans = vec![];
410 if !reported_late_bound_region_err
411 && (!infer_lifetimes || arg_counts.lifetimes > param_counts.lifetimes)
413 arg_count_mismatch |= check_kind_count(
415 param_counts.lifetimes,
416 param_counts.lifetimes,
417 arg_counts.lifetimes,
419 &mut unexpected_spans,
422 // FIXME(const_generics:defaults)
423 if !infer_args || arg_counts.consts > param_counts.consts {
424 arg_count_mismatch |= check_kind_count(
429 arg_counts.lifetimes + arg_counts.types,
430 &mut unexpected_spans,
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
436 arg_count_mismatch |= check_kind_count(
438 param_counts.types - defaults.types - has_self as usize,
439 param_counts.types - has_self as usize,
441 arg_counts.lifetimes,
442 &mut unexpected_spans,
446 (arg_count_mismatch, unexpected_spans)
449 /// Creates the relevant generic argument substitutions
450 /// corresponding to a set of generic parameters. This is a
451 /// rather complex function. Let us try to explain the role
452 /// of each of its parameters:
454 /// To start, we are given the `def_id` of the thing we are
455 /// creating the substitutions for, and a partial set of
456 /// substitutions `parent_substs`. In general, the substitutions
457 /// for an item begin with substitutions for all the "parents" of
458 /// that item -- e.g., for a method it might include the
459 /// parameters from the impl.
461 /// Therefore, the method begins by walking down these parents,
462 /// starting with the outermost parent and proceed inwards until
463 /// it reaches `def_id`. For each parent `P`, it will check `parent_substs`
464 /// first to see if the parent's substitutions are listed in there. If so,
465 /// we can append those and move on. Otherwise, it invokes the
466 /// three callback functions:
468 /// - `args_for_def_id`: given the `DefId` `P`, supplies back the
469 /// generic arguments that were given to that parent from within
470 /// the path; so e.g., if you have `<T as Foo>::Bar`, the `DefId`
471 /// might refer to the trait `Foo`, and the arguments might be
472 /// `[T]`. The boolean value indicates whether to infer values
473 /// for arguments whose values were not explicitly provided.
474 /// - `provided_kind`: given the generic parameter and the value from `args_for_def_id`,
475 /// instantiate a `GenericArg`.
476 /// - `inferred_kind`: if no parameter was provided, and inference is enabled, then
477 /// creates a suitable inference variable.
478 pub fn create_substs_for_generic_args<'b>(
481 parent_substs: &[subst::GenericArg<'tcx>],
483 self_ty: Option<Ty<'tcx>>,
484 args_for_def_id: impl Fn(DefId) -> (Option<&'b GenericArgs<'b>>, bool),
485 provided_kind: impl Fn(&GenericParamDef, &GenericArg<'_>) -> subst::GenericArg<'tcx>,
486 mut inferred_kind: impl FnMut(
487 Option<&[subst::GenericArg<'tcx>]>,
490 ) -> subst::GenericArg<'tcx>,
491 ) -> SubstsRef<'tcx> {
492 // Collect the segments of the path; we need to substitute arguments
493 // for parameters throughout the entire path (wherever there are
494 // generic parameters).
495 let mut parent_defs = tcx.generics_of(def_id);
496 let count = parent_defs.count();
497 let mut stack = vec![(def_id, parent_defs)];
498 while let Some(def_id) = parent_defs.parent {
499 parent_defs = tcx.generics_of(def_id);
500 stack.push((def_id, parent_defs));
503 // We manually build up the substitution, rather than using convenience
504 // methods in `subst.rs`, so that we can iterate over the arguments and
505 // parameters in lock-step linearly, instead of trying to match each pair.
506 let mut substs: SmallVec<[subst::GenericArg<'tcx>; 8]> = SmallVec::with_capacity(count);
508 // Iterate over each segment of the path.
509 while let Some((def_id, defs)) = stack.pop() {
510 let mut params = defs.params.iter().peekable();
512 // If we have already computed substitutions for parents, we can use those directly.
513 while let Some(¶m) = params.peek() {
514 if let Some(&kind) = parent_substs.get(param.index as usize) {
522 // `Self` is handled first, unless it's been handled in `parent_substs`.
524 if let Some(¶m) = params.peek() {
525 if param.index == 0 {
526 if let GenericParamDefKind::Type { .. } = param.kind {
530 .unwrap_or_else(|| inferred_kind(None, param, true)),
538 // Check whether this segment takes generic arguments and the user has provided any.
539 let (generic_args, infer_args) = args_for_def_id(def_id);
542 generic_args.iter().flat_map(|generic_args| generic_args.args.iter()).peekable();
545 // We're going to iterate through the generic arguments that the user
546 // provided, matching them with the generic parameters we expect.
547 // Mismatches can occur as a result of elided lifetimes, or for malformed
548 // input. We try to handle both sensibly.
549 match (args.peek(), params.peek()) {
550 (Some(&arg), Some(¶m)) => {
551 match (arg, ¶m.kind) {
552 (GenericArg::Lifetime(_), GenericParamDefKind::Lifetime)
553 | (GenericArg::Type(_), GenericParamDefKind::Type { .. })
554 | (GenericArg::Const(_), GenericParamDefKind::Const) => {
555 substs.push(provided_kind(param, arg));
559 (GenericArg::Type(_), GenericParamDefKind::Lifetime)
560 | (GenericArg::Const(_), GenericParamDefKind::Lifetime) => {
561 // We expected a lifetime argument, but got a type or const
562 // argument. That means we're inferring the lifetimes.
563 substs.push(inferred_kind(None, param, infer_args));
567 // We expected one kind of parameter, but the user provided
568 // another. This is an error, but we need to handle it
569 // gracefully so we can report sensible errors.
570 // In this case, we're simply going to infer this argument.
576 // We should never be able to reach this point with well-formed input.
577 // Getting to this point means the user supplied more arguments than
578 // there are parameters.
581 (None, Some(¶m)) => {
582 // If there are fewer arguments than parameters, it means
583 // we're inferring the remaining arguments.
584 substs.push(inferred_kind(Some(&substs), param, infer_args));
588 (None, None) => break,
593 tcx.intern_substs(&substs)
596 /// Given the type/lifetime/const arguments provided to some path (along with
597 /// an implicit `Self`, if this is a trait reference), returns the complete
598 /// set of substitutions. This may involve applying defaulted type parameters.
599 /// Also returns back constriants on associated types.
604 /// T: std::ops::Index<usize, Output = u32>
605 /// ^1 ^^^^^^^^^^^^^^2 ^^^^3 ^^^^^^^^^^^4
608 /// 1. The `self_ty` here would refer to the type `T`.
609 /// 2. The path in question is the path to the trait `std::ops::Index`,
610 /// which will have been resolved to a `def_id`
611 /// 3. The `generic_args` contains info on the `<...>` contents. The `usize` type
612 /// parameters are returned in the `SubstsRef`, the associated type bindings like
613 /// `Output = u32` are returned in the `Vec<ConvertedBinding...>` result.
615 /// Note that the type listing given here is *exactly* what the user provided.
617 /// For (generic) associated types
620 /// <Vec<u8> as Iterable<u8>>::Iter::<'a>
623 /// We have the parent substs are the substs for the parent trait:
624 /// `[Vec<u8>, u8]` and `generic_args` are the arguments for the associated
625 /// type itself: `['a]`. The returned `SubstsRef` concatenates these two
626 /// lists: `[Vec<u8>, u8, 'a]`.
627 fn create_substs_for_ast_path<'a>(
631 parent_substs: &[subst::GenericArg<'tcx>],
632 generic_args: &'a hir::GenericArgs<'_>,
634 self_ty: Option<Ty<'tcx>>,
635 ) -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'a, 'tcx>>, Vec<Span>) {
636 // If the type is parameterized by this region, then replace this
637 // region with the current anon region binding (in other words,
638 // whatever & would get replaced with).
640 "create_substs_for_ast_path(def_id={:?}, self_ty={:?}, \
642 def_id, self_ty, generic_args
645 let tcx = self.tcx();
646 let generic_params = tcx.generics_of(def_id);
648 if generic_params.has_self {
649 if generic_params.parent.is_some() {
650 // The parent is a trait so it should have at least one subst
651 // for the `Self` type.
652 assert!(!parent_substs.is_empty())
654 // This item (presumably a trait) needs a self-type.
655 assert!(self_ty.is_some());
658 assert!(self_ty.is_none() && parent_substs.is_empty());
661 let (_, potential_assoc_types) = Self::check_generic_arg_count(
666 GenericArgPosition::Type,
671 let is_object = self_ty.map_or(false, |ty| ty == self.tcx().types.trait_object_dummy_self);
672 let default_needs_object_self = |param: &ty::GenericParamDef| {
673 if let GenericParamDefKind::Type { has_default, .. } = param.kind {
674 if is_object && has_default {
675 let self_param = tcx.types.self_param;
676 if tcx.at(span).type_of(param.def_id).walk().any(|ty| ty == self_param) {
677 // There is no suitable inference default for a type parameter
678 // that references self, in an object type.
687 let mut missing_type_params = vec![];
688 let substs = Self::create_substs_for_generic_args(
694 // Provide the generic args, and whether types should be inferred.
697 (Some(generic_args), infer_args)
699 // The last component of this tuple is unimportant.
703 // Provide substitutions for parameters for which (valid) arguments have been provided.
704 |param, arg| match (¶m.kind, arg) {
705 (GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => {
706 self.ast_region_to_region(<, Some(param)).into()
708 (GenericParamDefKind::Type { .. }, GenericArg::Type(ty)) => {
709 self.ast_ty_to_ty(&ty).into()
711 (GenericParamDefKind::Const, GenericArg::Const(ct)) => {
712 self.ast_const_to_const(&ct.value, tcx.type_of(param.def_id)).into()
716 // Provide substitutions for parameters for which arguments are inferred.
717 |substs, param, infer_args| {
719 GenericParamDefKind::Lifetime => tcx.lifetimes.re_static.into(),
720 GenericParamDefKind::Type { has_default, .. } => {
721 if !infer_args && has_default {
722 // No type parameter provided, but a default exists.
724 // If we are converting an object type, then the
725 // `Self` parameter is unknown. However, some of the
726 // other type parameters may reference `Self` in their
727 // defaults. This will lead to an ICE if we are not
729 if default_needs_object_self(param) {
730 missing_type_params.push(param.name.to_string());
733 // This is a default type parameter.
736 tcx.at(span).type_of(param.def_id).subst_spanned(
744 } else if infer_args {
745 // No type parameters were provided, we can infer all.
747 if !default_needs_object_self(param) { Some(param) } else { None };
748 self.ty_infer(param, span).into()
750 // We've already errored above about the mismatch.
754 GenericParamDefKind::Const => {
755 // FIXME(const_generics:defaults)
757 // No const parameters were provided, we can infer all.
758 let ty = tcx.at(span).type_of(param.def_id);
759 self.ct_infer(ty, Some(param), span).into()
761 // We've already errored above about the mismatch.
762 tcx.consts.err.into()
769 self.complain_about_missing_type_params(
773 generic_args.args.is_empty(),
776 // Convert associated-type bindings or constraints into a separate vector.
777 // Example: Given this:
779 // T: Iterator<Item = u32>
781 // The `T` is passed in as a self-type; the `Item = u32` is
782 // not a "type parameter" of the `Iterator` trait, but rather
783 // a restriction on `<T as Iterator>::Item`, so it is passed
785 let assoc_bindings = generic_args
789 let kind = match binding.kind {
790 hir::TypeBindingKind::Equality { ref ty } => {
791 ConvertedBindingKind::Equality(self.ast_ty_to_ty(ty))
793 hir::TypeBindingKind::Constraint { ref bounds } => {
794 ConvertedBindingKind::Constraint(bounds)
797 ConvertedBinding { item_name: binding.ident, kind, span: binding.span }
802 "create_substs_for_ast_path(generic_params={:?}, self_ty={:?}) -> {:?}",
803 generic_params, self_ty, substs
806 (substs, assoc_bindings, potential_assoc_types)
809 crate fn create_substs_for_associated_item(
814 item_segment: &hir::PathSegment<'_>,
815 parent_substs: SubstsRef<'tcx>,
816 ) -> SubstsRef<'tcx> {
817 if tcx.generics_of(item_def_id).params.is_empty() {
818 self.prohibit_generics(slice::from_ref(item_segment));
822 self.create_substs_for_ast_path(
826 item_segment.generic_args(),
827 item_segment.infer_args,
834 /// On missing type parameters, emit an E0393 error and provide a structured suggestion using
835 /// the type parameter's name as a placeholder.
836 fn complain_about_missing_type_params(
838 missing_type_params: Vec<String>,
841 empty_generic_args: bool,
843 if missing_type_params.is_empty() {
847 missing_type_params.iter().map(|n| format!("`{}`", n)).collect::<Vec<_>>().join(", ");
848 let mut err = struct_span_err!(
852 "the type parameter{} {} must be explicitly specified",
853 pluralize!(missing_type_params.len()),
857 self.tcx().def_span(def_id),
859 "type parameter{} {} must be specified for this",
860 pluralize!(missing_type_params.len()),
864 let mut suggested = false;
865 if let (Ok(snippet), true) = (
866 self.tcx().sess.source_map().span_to_snippet(span),
867 // Don't suggest setting the type params if there are some already: the order is
868 // tricky to get right and the user will already know what the syntax is.
871 if snippet.ends_with('>') {
872 // The user wrote `Trait<'a, T>` or similar. To provide an accurate suggestion
873 // we would have to preserve the right order. For now, as clearly the user is
874 // aware of the syntax, we do nothing.
876 // The user wrote `Iterator`, so we don't have a type we can suggest, but at
877 // least we can clue them to the correct syntax `Iterator<Type>`.
881 "set the type parameter{plural} to the desired type{plural}",
882 plural = pluralize!(missing_type_params.len()),
884 format!("{}<{}>", snippet, missing_type_params.join(", ")),
885 Applicability::HasPlaceholders,
894 "missing reference{} to {}",
895 pluralize!(missing_type_params.len()),
901 "because of the default `Self` reference, type parameters must be \
902 specified on object types"
907 /// Instantiates the path for the given trait reference, assuming that it's
908 /// bound to a valid trait type. Returns the `DefId` of the defining trait.
909 /// The type _cannot_ be a type other than a trait type.
911 /// If the `projections` argument is `None`, then assoc type bindings like `Foo<T = X>`
912 /// are disallowed. Otherwise, they are pushed onto the vector given.
913 pub fn instantiate_mono_trait_ref(
915 trait_ref: &hir::TraitRef<'_>,
917 ) -> ty::TraitRef<'tcx> {
918 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
920 self.ast_path_to_mono_trait_ref(
922 trait_ref.trait_def_id(),
924 trait_ref.path.segments.last().unwrap(),
928 /// The given trait-ref must actually be a trait.
929 pub(super) fn instantiate_poly_trait_ref_inner(
931 trait_ref: &hir::TraitRef<'_>,
933 constness: Constness,
935 bounds: &mut Bounds<'tcx>,
938 let trait_def_id = trait_ref.trait_def_id();
940 debug!("instantiate_poly_trait_ref({:?}, def_id={:?})", trait_ref, trait_def_id);
942 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
944 let path_span = if let [segment] = &trait_ref.path.segments[..] {
945 // FIXME: `trait_ref.path.span` can point to a full path with multiple
946 // segments, even though `trait_ref.path.segments` is of length `1`. Work
947 // around that bug here, even though it should be fixed elsewhere.
948 // This would otherwise cause an invalid suggestion. For an example, look at
949 // `src/test/ui/issues/issue-28344.rs`.
954 let (substs, assoc_bindings, potential_assoc_types) = self.create_substs_for_ast_trait_ref(
958 trait_ref.path.segments.last().unwrap(),
960 let poly_trait_ref = ty::Binder::bind(ty::TraitRef::new(trait_def_id, substs));
962 bounds.trait_bounds.push((poly_trait_ref, span, constness));
964 let mut dup_bindings = FxHashMap::default();
965 for binding in &assoc_bindings {
966 // Specify type to assert that error was already reported in `Err` case.
967 let _: Result<_, ErrorReported> = self.add_predicates_for_ast_type_binding(
968 trait_ref.hir_ref_id,
976 // Okay to ignore `Err` because of `ErrorReported` (see above).
980 "instantiate_poly_trait_ref({:?}, bounds={:?}) -> {:?}",
981 trait_ref, bounds, poly_trait_ref
984 potential_assoc_types
987 /// Given a trait bound like `Debug`, applies that trait bound the given self-type to construct
988 /// a full trait reference. The resulting trait reference is returned. This may also generate
989 /// auxiliary bounds, which are added to `bounds`.
994 /// poly_trait_ref = Iterator<Item = u32>
998 /// this would return `Foo: Iterator` and add `<Foo as Iterator>::Item = u32` into `bounds`.
1000 /// **A note on binders:** against our usual convention, there is an implied bounder around
1001 /// the `self_ty` and `poly_trait_ref` parameters here. So they may reference bound regions.
1002 /// If for example you had `for<'a> Foo<'a>: Bar<'a>`, then the `self_ty` would be `Foo<'a>`
1003 /// where `'a` is a bound region at depth 0. Similarly, the `poly_trait_ref` would be
1004 /// `Bar<'a>`. The returned poly-trait-ref will have this binder instantiated explicitly,
1006 pub fn instantiate_poly_trait_ref(
1008 poly_trait_ref: &hir::PolyTraitRef<'_>,
1009 constness: Constness,
1011 bounds: &mut Bounds<'tcx>,
1013 self.instantiate_poly_trait_ref_inner(
1014 &poly_trait_ref.trait_ref,
1015 poly_trait_ref.span,
1023 fn ast_path_to_mono_trait_ref(
1026 trait_def_id: DefId,
1028 trait_segment: &hir::PathSegment<'_>,
1029 ) -> ty::TraitRef<'tcx> {
1030 let (substs, assoc_bindings, _) =
1031 self.create_substs_for_ast_trait_ref(span, trait_def_id, self_ty, trait_segment);
1032 assoc_bindings.first().map(|b| AstConv::prohibit_assoc_ty_binding(self.tcx(), b.span));
1033 ty::TraitRef::new(trait_def_id, substs)
1036 /// When the code is using the `Fn` traits directly, instead of the `Fn(A) -> B` syntax, emit
1037 /// an error and attempt to build a reasonable structured suggestion.
1038 fn complain_about_internal_fn_trait(
1041 trait_def_id: DefId,
1042 trait_segment: &'a hir::PathSegment<'a>,
1044 let trait_def = self.tcx().trait_def(trait_def_id);
1046 if !self.tcx().features().unboxed_closures
1047 && trait_segment.generic_args().parenthesized != trait_def.paren_sugar
1049 // For now, require that parenthetical notation be used only with `Fn()` etc.
1050 let (msg, sugg) = if trait_def.paren_sugar {
1052 "the precise format of `Fn`-family traits' type parameters is subject to \
1056 trait_segment.ident,
1060 .and_then(|args| args.args.get(0))
1061 .and_then(|arg| match arg {
1062 hir::GenericArg::Type(ty) => {
1063 Some(print::to_string(print::NO_ANN, |s| s.print_type(ty)))
1067 .unwrap_or_else(|| "()".to_string()),
1072 .filter_map(|b| match (b.ident.as_str() == "Output", &b.kind) {
1073 (true, hir::TypeBindingKind::Equality { ty }) => {
1074 Some(print::to_string(print::NO_ANN, |s| s.print_type(ty)))
1079 .unwrap_or_else(|| "()".to_string()),
1083 ("parenthetical notation is only stable when used with `Fn`-family traits", None)
1085 let sess = &self.tcx().sess.parse_sess;
1086 let mut err = feature_err(sess, sym::unboxed_closures, span, msg);
1087 if let Some(sugg) = sugg {
1088 let msg = "use parenthetical notation instead";
1089 err.span_suggestion(span, msg, sugg, Applicability::MaybeIncorrect);
1095 fn create_substs_for_ast_trait_ref<'a>(
1098 trait_def_id: DefId,
1100 trait_segment: &'a hir::PathSegment<'a>,
1101 ) -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'a, 'tcx>>, Vec<Span>) {
1102 debug!("create_substs_for_ast_trait_ref(trait_segment={:?})", trait_segment);
1104 self.complain_about_internal_fn_trait(span, trait_def_id, trait_segment);
1106 self.create_substs_for_ast_path(
1110 trait_segment.generic_args(),
1111 trait_segment.infer_args,
1116 fn trait_defines_associated_type_named(
1118 trait_def_id: DefId,
1119 assoc_name: ast::Ident,
1122 .associated_items(trait_def_id)
1123 .find_by_name_and_kind(self.tcx(), assoc_name, ty::AssocKind::Type, trait_def_id)
1127 // Returns `true` if a bounds list includes `?Sized`.
1128 pub fn is_unsized(&self, ast_bounds: &[hir::GenericBound<'_>], span: Span) -> bool {
1129 let tcx = self.tcx();
1131 // Try to find an unbound in bounds.
1132 let mut unbound = None;
1133 for ab in ast_bounds {
1134 if let &hir::GenericBound::Trait(ref ptr, hir::TraitBoundModifier::Maybe) = ab {
1135 if unbound.is_none() {
1136 unbound = Some(&ptr.trait_ref);
1142 "type parameter has more than one relaxed default \
1143 bound, only one is supported"
1150 let kind_id = tcx.lang_items().require(SizedTraitLangItem);
1153 // FIXME(#8559) currently requires the unbound to be built-in.
1154 if let Ok(kind_id) = kind_id {
1155 if tpb.path.res != Res::Def(DefKind::Trait, kind_id) {
1158 "default bound relaxed for a type parameter, but \
1159 this does nothing because the given bound is not \
1160 a default; only `?Sized` is supported",
1165 _ if kind_id.is_ok() => {
1168 // No lang item for `Sized`, so we can't add it as a bound.
1175 /// This helper takes a *converted* parameter type (`param_ty`)
1176 /// and an *unconverted* list of bounds:
1179 /// fn foo<T: Debug>
1180 /// ^ ^^^^^ `ast_bounds` parameter, in HIR form
1182 /// `param_ty`, in ty form
1185 /// It adds these `ast_bounds` into the `bounds` structure.
1187 /// **A note on binders:** there is an implied binder around
1188 /// `param_ty` and `ast_bounds`. See `instantiate_poly_trait_ref`
1189 /// for more details.
1193 ast_bounds: &[hir::GenericBound<'_>],
1194 bounds: &mut Bounds<'tcx>,
1196 let mut trait_bounds = Vec::new();
1197 let mut region_bounds = Vec::new();
1199 let constness = self.default_constness_for_trait_bounds();
1200 for ast_bound in ast_bounds {
1202 hir::GenericBound::Trait(ref b, hir::TraitBoundModifier::None) => {
1203 trait_bounds.push((b, constness))
1205 hir::GenericBound::Trait(ref b, hir::TraitBoundModifier::MaybeConst) => {
1206 trait_bounds.push((b, Constness::NotConst))
1208 hir::GenericBound::Trait(_, hir::TraitBoundModifier::Maybe) => {}
1209 hir::GenericBound::Outlives(ref l) => region_bounds.push(l),
1213 for (bound, constness) in trait_bounds {
1214 let _ = self.instantiate_poly_trait_ref(bound, constness, param_ty, bounds);
1217 bounds.region_bounds.extend(
1218 region_bounds.into_iter().map(|r| (self.ast_region_to_region(r, None), r.span)),
1222 /// Translates a list of bounds from the HIR into the `Bounds` data structure.
1223 /// The self-type for the bounds is given by `param_ty`.
1228 /// fn foo<T: Bar + Baz>() { }
1229 /// ^ ^^^^^^^^^ ast_bounds
1233 /// The `sized_by_default` parameter indicates if, in this context, the `param_ty` should be
1234 /// considered `Sized` unless there is an explicit `?Sized` bound. This would be true in the
1235 /// example above, but is not true in supertrait listings like `trait Foo: Bar + Baz`.
1237 /// `span` should be the declaration size of the parameter.
1238 pub fn compute_bounds(
1241 ast_bounds: &[hir::GenericBound<'_>],
1242 sized_by_default: SizedByDefault,
1245 let mut bounds = Bounds::default();
1247 self.add_bounds(param_ty, ast_bounds, &mut bounds);
1248 bounds.trait_bounds.sort_by_key(|(t, _, _)| t.def_id());
1250 bounds.implicitly_sized = if let SizedByDefault::Yes = sized_by_default {
1251 if !self.is_unsized(ast_bounds, span) { Some(span) } else { None }
1259 /// Given an HIR binding like `Item = Foo` or `Item: Foo`, pushes the corresponding predicates
1262 /// **A note on binders:** given something like `T: for<'a> Iterator<Item = &'a u32>`, the
1263 /// `trait_ref` here will be `for<'a> T: Iterator`. The `binding` data however is from *inside*
1264 /// the binder (e.g., `&'a u32`) and hence may reference bound regions.
1265 fn add_predicates_for_ast_type_binding(
1267 hir_ref_id: hir::HirId,
1268 trait_ref: ty::PolyTraitRef<'tcx>,
1269 binding: &ConvertedBinding<'_, 'tcx>,
1270 bounds: &mut Bounds<'tcx>,
1272 dup_bindings: &mut FxHashMap<DefId, Span>,
1274 ) -> Result<(), ErrorReported> {
1275 let tcx = self.tcx();
1278 // Given something like `U: SomeTrait<T = X>`, we want to produce a
1279 // predicate like `<U as SomeTrait>::T = X`. This is somewhat
1280 // subtle in the event that `T` is defined in a supertrait of
1281 // `SomeTrait`, because in that case we need to upcast.
1283 // That is, consider this case:
1286 // trait SubTrait: SuperTrait<int> { }
1287 // trait SuperTrait<A> { type T; }
1289 // ... B: SubTrait<T = foo> ...
1292 // We want to produce `<B as SuperTrait<int>>::T == foo`.
1294 // Find any late-bound regions declared in `ty` that are not
1295 // declared in the trait-ref. These are not well-formed.
1299 // for<'a> <T as Iterator>::Item = &'a str // <-- 'a is bad
1300 // for<'a> <T as FnMut<(&'a u32,)>>::Output = &'a str // <-- 'a is ok
1301 if let ConvertedBindingKind::Equality(ty) = binding.kind {
1302 let late_bound_in_trait_ref =
1303 tcx.collect_constrained_late_bound_regions(&trait_ref);
1304 let late_bound_in_ty =
1305 tcx.collect_referenced_late_bound_regions(&ty::Binder::bind(ty));
1306 debug!("late_bound_in_trait_ref = {:?}", late_bound_in_trait_ref);
1307 debug!("late_bound_in_ty = {:?}", late_bound_in_ty);
1308 for br in late_bound_in_ty.difference(&late_bound_in_trait_ref) {
1309 let br_name = match *br {
1310 ty::BrNamed(_, name) => name,
1314 "anonymous bound region {:?} in binding but not trait ref",
1319 // FIXME: point at the type params that don't have appropriate lifetimes:
1320 // struct S1<F: for<'a> Fn(&i32, &i32) -> &'a i32>(F);
1321 // ---- ---- ^^^^^^^
1326 "binding for associated type `{}` references lifetime `{}`, \
1327 which does not appear in the trait input types",
1337 if self.trait_defines_associated_type_named(trait_ref.def_id(), binding.item_name) {
1338 // Simple case: X is defined in the current trait.
1341 // Otherwise, we have to walk through the supertraits to find
1343 self.one_bound_for_assoc_type(
1344 || traits::supertraits(tcx, trait_ref),
1345 || trait_ref.print_only_trait_path().to_string(),
1348 || match binding.kind {
1349 ConvertedBindingKind::Equality(ty) => Some(ty.to_string()),
1355 let (assoc_ident, def_scope) =
1356 tcx.adjust_ident_and_get_scope(binding.item_name, candidate.def_id(), hir_ref_id);
1358 // We have already adjusted the item name above, so compare with `ident.modern()` instead
1359 // of calling `filter_by_name_and_kind`.
1361 .associated_items(candidate.def_id())
1362 .filter_by_name_unhygienic(assoc_ident.name)
1363 .find(|i| i.kind == ty::AssocKind::Type && i.ident.modern() == assoc_ident)
1364 .expect("missing associated type");
1366 if !assoc_ty.vis.is_accessible_from(def_scope, tcx) {
1367 let msg = format!("associated type `{}` is private", binding.item_name);
1368 tcx.sess.span_err(binding.span, &msg);
1370 tcx.check_stability(assoc_ty.def_id, Some(hir_ref_id), binding.span);
1374 .entry(assoc_ty.def_id)
1375 .and_modify(|prev_span| {
1380 "the value of the associated type `{}` (from trait `{}`) \
1381 is already specified",
1383 tcx.def_path_str(assoc_ty.container.id())
1385 .span_label(binding.span, "re-bound here")
1386 .span_label(*prev_span, format!("`{}` bound here first", binding.item_name))
1389 .or_insert(binding.span);
1392 match binding.kind {
1393 ConvertedBindingKind::Equality(ref ty) => {
1394 // "Desugar" a constraint like `T: Iterator<Item = u32>` this to
1395 // the "projection predicate" for:
1397 // `<T as Iterator>::Item = u32`
1398 bounds.projection_bounds.push((
1399 candidate.map_bound(|trait_ref| ty::ProjectionPredicate {
1400 projection_ty: ty::ProjectionTy::from_ref_and_name(
1410 ConvertedBindingKind::Constraint(ast_bounds) => {
1411 // "Desugar" a constraint like `T: Iterator<Item: Debug>` to
1413 // `<T as Iterator>::Item: Debug`
1415 // Calling `skip_binder` is okay, because `add_bounds` expects the `param_ty`
1416 // parameter to have a skipped binder.
1417 let param_ty = tcx.mk_projection(assoc_ty.def_id, candidate.skip_binder().substs);
1418 self.add_bounds(param_ty, ast_bounds, bounds);
1428 item_segment: &hir::PathSegment<'_>,
1430 let substs = self.ast_path_substs_for_ty(span, did, item_segment);
1431 self.normalize_ty(span, self.tcx().at(span).type_of(did).subst(self.tcx(), substs))
1434 fn conv_object_ty_poly_trait_ref(
1437 trait_bounds: &[hir::PolyTraitRef<'_>],
1438 lifetime: &hir::Lifetime,
1440 let tcx = self.tcx();
1442 let mut bounds = Bounds::default();
1443 let mut potential_assoc_types = Vec::new();
1444 let dummy_self = self.tcx().types.trait_object_dummy_self;
1445 for trait_bound in trait_bounds.iter().rev() {
1446 let cur_potential_assoc_types = self.instantiate_poly_trait_ref(
1448 Constness::NotConst,
1452 potential_assoc_types.extend(cur_potential_assoc_types.into_iter());
1455 // Expand trait aliases recursively and check that only one regular (non-auto) trait
1456 // is used and no 'maybe' bounds are used.
1457 let expanded_traits =
1458 traits::expand_trait_aliases(tcx, bounds.trait_bounds.iter().map(|&(a, b, _)| (a, b)));
1459 let (mut auto_traits, regular_traits): (Vec<_>, Vec<_>) =
1460 expanded_traits.partition(|i| tcx.trait_is_auto(i.trait_ref().def_id()));
1461 if regular_traits.len() > 1 {
1462 let first_trait = ®ular_traits[0];
1463 let additional_trait = ®ular_traits[1];
1464 let mut err = struct_span_err!(
1466 additional_trait.bottom().1,
1468 "only auto traits can be used as additional traits in a trait object"
1470 additional_trait.label_with_exp_info(
1472 "additional non-auto trait",
1475 first_trait.label_with_exp_info(&mut err, "first non-auto trait", "first use");
1479 if regular_traits.is_empty() && auto_traits.is_empty() {
1484 "at least one trait is required for an object type"
1487 return tcx.types.err;
1490 // Check that there are no gross object safety violations;
1491 // most importantly, that the supertraits don't contain `Self`,
1493 for item in ®ular_traits {
1494 let object_safety_violations =
1495 astconv_object_safety_violations(tcx, item.trait_ref().def_id());
1496 if !object_safety_violations.is_empty() {
1497 report_object_safety_error(
1500 item.trait_ref().def_id(),
1501 object_safety_violations,
1504 return tcx.types.err;
1508 // Use a `BTreeSet` to keep output in a more consistent order.
1509 let mut associated_types: FxHashMap<Span, BTreeSet<DefId>> = FxHashMap::default();
1511 let regular_traits_refs_spans = bounds
1514 .filter(|(trait_ref, _, _)| !tcx.trait_is_auto(trait_ref.def_id()));
1516 for (base_trait_ref, span, constness) in regular_traits_refs_spans {
1517 assert_eq!(constness, Constness::NotConst);
1519 for trait_ref in traits::elaborate_trait_ref(tcx, base_trait_ref) {
1521 "conv_object_ty_poly_trait_ref: observing object predicate `{:?}`",
1525 ty::Predicate::Trait(pred, _) => {
1526 associated_types.entry(span).or_default().extend(
1527 tcx.associated_items(pred.def_id())
1528 .in_definition_order()
1529 .filter(|item| item.kind == ty::AssocKind::Type)
1530 .map(|item| item.def_id),
1533 ty::Predicate::Projection(pred) => {
1534 // A `Self` within the original bound will be substituted with a
1535 // `trait_object_dummy_self`, so check for that.
1536 let references_self = pred.skip_binder().ty.walk().any(|t| t == dummy_self);
1538 // If the projection output contains `Self`, force the user to
1539 // elaborate it explicitly to avoid a lot of complexity.
1541 // The "classicaly useful" case is the following:
1543 // trait MyTrait: FnMut() -> <Self as MyTrait>::MyOutput {
1548 // Here, the user could theoretically write `dyn MyTrait<Output = X>`,
1549 // but actually supporting that would "expand" to an infinitely-long type
1550 // `fix $ τ → dyn MyTrait<MyOutput = X, Output = <τ as MyTrait>::MyOutput`.
1552 // Instead, we force the user to write
1553 // `dyn MyTrait<MyOutput = X, Output = X>`, which is uglier but works. See
1554 // the discussion in #56288 for alternatives.
1555 if !references_self {
1556 // Include projections defined on supertraits.
1557 bounds.projection_bounds.push((pred, span));
1565 for (projection_bound, _) in &bounds.projection_bounds {
1566 for (_, def_ids) in &mut associated_types {
1567 def_ids.remove(&projection_bound.projection_def_id());
1571 self.complain_about_missing_associated_types(
1573 potential_assoc_types,
1577 // De-duplicate auto traits so that, e.g., `dyn Trait + Send + Send` is the same as
1578 // `dyn Trait + Send`.
1579 auto_traits.sort_by_key(|i| i.trait_ref().def_id());
1580 auto_traits.dedup_by_key(|i| i.trait_ref().def_id());
1581 debug!("regular_traits: {:?}", regular_traits);
1582 debug!("auto_traits: {:?}", auto_traits);
1584 // Transform a `PolyTraitRef` into a `PolyExistentialTraitRef` by
1585 // removing the dummy `Self` type (`trait_object_dummy_self`).
1586 let trait_ref_to_existential = |trait_ref: ty::TraitRef<'tcx>| {
1587 if trait_ref.self_ty() != dummy_self {
1588 // FIXME: There appears to be a missing filter on top of `expand_trait_aliases`,
1589 // which picks up non-supertraits where clauses - but also, the object safety
1590 // completely ignores trait aliases, which could be object safety hazards. We
1591 // `delay_span_bug` here to avoid an ICE in stable even when the feature is
1592 // disabled. (#66420)
1593 tcx.sess.delay_span_bug(
1596 "trait_ref_to_existential called on {:?} with non-dummy Self",
1601 ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref)
1604 // Erase the `dummy_self` (`trait_object_dummy_self`) used above.
1605 let existential_trait_refs = regular_traits
1607 .map(|i| i.trait_ref().map_bound(|trait_ref| trait_ref_to_existential(trait_ref)));
1608 let existential_projections = bounds.projection_bounds.iter().map(|(bound, _)| {
1609 bound.map_bound(|b| {
1610 let trait_ref = trait_ref_to_existential(b.projection_ty.trait_ref(tcx));
1611 ty::ExistentialProjection {
1613 item_def_id: b.projection_ty.item_def_id,
1614 substs: trait_ref.substs,
1619 // Calling `skip_binder` is okay because the predicates are re-bound.
1620 let regular_trait_predicates = existential_trait_refs
1621 .map(|trait_ref| ty::ExistentialPredicate::Trait(*trait_ref.skip_binder()));
1622 let auto_trait_predicates = auto_traits
1624 .map(|trait_ref| ty::ExistentialPredicate::AutoTrait(trait_ref.trait_ref().def_id()));
1625 let mut v = regular_trait_predicates
1626 .chain(auto_trait_predicates)
1628 existential_projections
1629 .map(|x| ty::ExistentialPredicate::Projection(*x.skip_binder())),
1631 .collect::<SmallVec<[_; 8]>>();
1632 v.sort_by(|a, b| a.stable_cmp(tcx, b));
1634 let existential_predicates = ty::Binder::bind(tcx.mk_existential_predicates(v.into_iter()));
1636 // Use explicitly-specified region bound.
1637 let region_bound = if !lifetime.is_elided() {
1638 self.ast_region_to_region(lifetime, None)
1640 self.compute_object_lifetime_bound(span, existential_predicates).unwrap_or_else(|| {
1641 if tcx.named_region(lifetime.hir_id).is_some() {
1642 self.ast_region_to_region(lifetime, None)
1644 self.re_infer(None, span).unwrap_or_else(|| {
1649 "the lifetime bound for this object type cannot be deduced \
1650 from context; please supply an explicit bound"
1653 tcx.lifetimes.re_static
1658 debug!("region_bound: {:?}", region_bound);
1660 let ty = tcx.mk_dynamic(existential_predicates, region_bound);
1661 debug!("trait_object_type: {:?}", ty);
1665 /// When there are any missing associated types, emit an E0191 error and attempt to supply a
1666 /// reasonable suggestion on how to write it. For the case of multiple associated types in the
1667 /// same trait bound have the same name (as they come from different super-traits), we instead
1668 /// emit a generic note suggesting using a `where` clause to constraint instead.
1669 fn complain_about_missing_associated_types(
1671 associated_types: FxHashMap<Span, BTreeSet<DefId>>,
1672 potential_assoc_types: Vec<Span>,
1673 trait_bounds: &[hir::PolyTraitRef<'_>],
1675 if !associated_types.values().any(|v| v.len() > 0) {
1678 let tcx = self.tcx();
1679 // FIXME: Marked `mut` so that we can replace the spans further below with a more
1680 // appropriate one, but this should be handled earlier in the span assignment.
1681 let mut associated_types: FxHashMap<Span, Vec<_>> = associated_types
1683 .map(|(span, def_ids)| {
1684 (span, def_ids.into_iter().map(|did| tcx.associated_item(did)).collect())
1687 let mut names = vec![];
1689 // Account for things like `dyn Foo + 'a`, like in tests `issue-22434.rs` and
1690 // `issue-22560.rs`.
1691 let mut trait_bound_spans: Vec<Span> = vec![];
1692 for (span, items) in &associated_types {
1693 if !items.is_empty() {
1694 trait_bound_spans.push(*span);
1696 for assoc_item in items {
1697 let trait_def_id = assoc_item.container.id();
1699 "`{}` (from trait `{}`)",
1701 tcx.def_path_str(trait_def_id),
1706 match (&potential_assoc_types[..], &trait_bounds) {
1707 ([], [bound]) => match &bound.trait_ref.path.segments[..] {
1708 // FIXME: `trait_ref.path.span` can point to a full path with multiple
1709 // segments, even though `trait_ref.path.segments` is of length `1`. Work
1710 // around that bug here, even though it should be fixed elsewhere.
1711 // This would otherwise cause an invalid suggestion. For an example, look at
1712 // `src/test/ui/issues/issue-28344.rs` where instead of the following:
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<Output = Type>`
1724 // error[E0191]: the value of the associated type `Output`
1725 // (from trait `std::ops::BitXor`) must be specified
1726 // --> $DIR/issue-28344.rs:4:17
1728 // LL | let x: u8 = BitXor::bitor(0 as u8, 0 as u8);
1729 // | ^^^^^^^^^^^^^ help: specify the associated type:
1730 // | `BitXor::bitor<Output = Type>`
1731 [segment] if segment.args.is_none() => {
1732 trait_bound_spans = vec![segment.ident.span];
1733 associated_types = associated_types
1735 .map(|(_, items)| (segment.ident.span, items))
1743 trait_bound_spans.sort();
1744 let mut err = struct_span_err!(
1748 "the value of the associated type{} {} must be specified",
1749 pluralize!(names.len()),
1752 let mut suggestions = vec![];
1753 let mut types_count = 0;
1754 let mut where_constraints = vec![];
1755 for (span, assoc_items) in &associated_types {
1756 let mut names: FxHashMap<_, usize> = FxHashMap::default();
1757 for item in assoc_items {
1759 *names.entry(item.ident.name).or_insert(0) += 1;
1761 let mut dupes = false;
1762 for item in assoc_items {
1763 let prefix = if names[&item.ident.name] > 1 {
1764 let trait_def_id = item.container.id();
1766 format!("{}::", tcx.def_path_str(trait_def_id))
1770 if let Some(sp) = tcx.hir().span_if_local(item.def_id) {
1771 err.span_label(sp, format!("`{}{}` defined here", prefix, item.ident));
1774 if potential_assoc_types.len() == assoc_items.len() {
1775 // Only suggest when the amount of missing associated types equals the number of
1776 // extra type arguments present, as that gives us a relatively high confidence
1777 // that the user forgot to give the associtated type's name. The canonical
1778 // example would be trying to use `Iterator<isize>` instead of
1779 // `Iterator<Item = isize>`.
1780 for (potential, item) in potential_assoc_types.iter().zip(assoc_items.iter()) {
1781 if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(*potential) {
1782 suggestions.push((*potential, format!("{} = {}", item.ident, snippet)));
1785 } else if let (Ok(snippet), false) =
1786 (tcx.sess.source_map().span_to_snippet(*span), dupes)
1789 assoc_items.iter().map(|item| format!("{} = Type", item.ident)).collect();
1790 let code = if snippet.ends_with(">") {
1791 // The user wrote `Trait<'a>` or similar and we don't have a type we can
1792 // suggest, but at least we can clue them to the correct syntax
1793 // `Trait<'a, Item = Type>` while accounting for the `<'a>` in the
1795 format!("{}, {}>", &snippet[..snippet.len() - 1], types.join(", "))
1797 // The user wrote `Iterator`, so we don't have a type we can suggest, but at
1798 // least we can clue them to the correct syntax `Iterator<Item = Type>`.
1799 format!("{}<{}>", snippet, types.join(", "))
1801 suggestions.push((*span, code));
1803 where_constraints.push(*span);
1806 let where_msg = "consider introducing a new type parameter, adding `where` constraints \
1807 using the fully-qualified path to the associated types";
1808 if !where_constraints.is_empty() && suggestions.is_empty() {
1809 // If there are duplicates associated type names and a single trait bound do not
1810 // use structured suggestion, it means that there are multiple super-traits with
1811 // the same associated type name.
1812 err.help(where_msg);
1814 if suggestions.len() != 1 {
1815 // We don't need this label if there's an inline suggestion, show otherwise.
1816 for (span, assoc_items) in &associated_types {
1817 let mut names: FxHashMap<_, usize> = FxHashMap::default();
1818 for item in assoc_items {
1820 *names.entry(item.ident.name).or_insert(0) += 1;
1822 let mut label = vec![];
1823 for item in assoc_items {
1824 let postfix = if names[&item.ident.name] > 1 {
1825 let trait_def_id = item.container.id();
1826 format!(" (from trait `{}`)", tcx.def_path_str(trait_def_id))
1830 label.push(format!("`{}`{}", item.ident, postfix));
1832 if !label.is_empty() {
1836 "associated type{} {} must be specified",
1837 pluralize!(label.len()),
1844 if !suggestions.is_empty() {
1845 err.multipart_suggestion(
1846 &format!("specify the associated type{}", pluralize!(types_count)),
1848 Applicability::HasPlaceholders,
1850 if !where_constraints.is_empty() {
1851 err.span_help(where_constraints, where_msg);
1857 fn report_ambiguous_associated_type(
1864 let mut err = struct_span_err!(self.tcx().sess, span, E0223, "ambiguous associated type");
1865 if let (Some(_), Ok(snippet)) = (
1866 self.tcx().sess.confused_type_with_std_module.borrow().get(&span),
1867 self.tcx().sess.source_map().span_to_snippet(span),
1869 err.span_suggestion(
1871 "you are looking for the module in `std`, not the primitive type",
1872 format!("std::{}", snippet),
1873 Applicability::MachineApplicable,
1876 err.span_suggestion(
1878 "use fully-qualified syntax",
1879 format!("<{} as {}>::{}", type_str, trait_str, name),
1880 Applicability::HasPlaceholders,
1886 // Search for a bound on a type parameter which includes the associated item
1887 // given by `assoc_name`. `ty_param_def_id` is the `DefId` of the type parameter
1888 // This function will fail if there are no suitable bounds or there is
1890 fn find_bound_for_assoc_item(
1892 ty_param_def_id: DefId,
1893 assoc_name: ast::Ident,
1895 ) -> Result<ty::PolyTraitRef<'tcx>, ErrorReported> {
1896 let tcx = self.tcx();
1899 "find_bound_for_assoc_item(ty_param_def_id={:?}, assoc_name={:?}, span={:?})",
1900 ty_param_def_id, assoc_name, span,
1903 let predicates = &self.get_type_parameter_bounds(span, ty_param_def_id).predicates;
1905 debug!("find_bound_for_assoc_item: predicates={:#?}", predicates);
1907 let param_hir_id = tcx.hir().as_local_hir_id(ty_param_def_id).unwrap();
1908 let param_name = tcx.hir().ty_param_name(param_hir_id);
1909 self.one_bound_for_assoc_type(
1911 traits::transitive_bounds(
1913 predicates.iter().filter_map(|(p, _)| p.to_opt_poly_trait_ref()),
1916 || param_name.to_string(),
1923 // Checks that `bounds` contains exactly one element and reports appropriate
1924 // errors otherwise.
1925 fn one_bound_for_assoc_type<I>(
1927 all_candidates: impl Fn() -> I,
1928 ty_param_name: impl Fn() -> String,
1929 assoc_name: ast::Ident,
1931 is_equality: impl Fn() -> Option<String>,
1932 ) -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
1934 I: Iterator<Item = ty::PolyTraitRef<'tcx>>,
1936 let mut matching_candidates = all_candidates()
1937 .filter(|r| self.trait_defines_associated_type_named(r.def_id(), assoc_name));
1939 let bound = match matching_candidates.next() {
1940 Some(bound) => bound,
1942 self.complain_about_assoc_type_not_found(
1948 return Err(ErrorReported);
1952 debug!("one_bound_for_assoc_type: bound = {:?}", bound);
1954 if let Some(bound2) = matching_candidates.next() {
1955 debug!("one_bound_for_assoc_type: bound2 = {:?}", bound2);
1957 let is_equality = is_equality();
1958 let bounds = iter::once(bound).chain(iter::once(bound2)).chain(matching_candidates);
1959 let mut err = if is_equality.is_some() {
1960 // More specific Error Index entry.
1965 "ambiguous associated type `{}` in bounds of `{}`",
1974 "ambiguous associated type `{}` in bounds of `{}`",
1979 err.span_label(span, format!("ambiguous associated type `{}`", assoc_name));
1981 let mut where_bounds = vec![];
1982 for bound in bounds {
1983 let bound_id = bound.def_id();
1984 let bound_span = self
1986 .associated_items(bound_id)
1987 .find_by_name_and_kind(self.tcx(), assoc_name, ty::AssocKind::Type, bound_id)
1988 .and_then(|item| self.tcx().hir().span_if_local(item.def_id));
1990 if let Some(bound_span) = bound_span {
1994 "ambiguous `{}` from `{}`",
1996 bound.print_only_trait_path(),
1999 if let Some(constraint) = &is_equality {
2000 where_bounds.push(format!(
2001 " T: {trait}::{assoc} = {constraint}",
2002 trait=bound.print_only_trait_path(),
2004 constraint=constraint,
2007 err.span_suggestion(
2009 "use fully qualified syntax to disambiguate",
2013 bound.print_only_trait_path(),
2016 Applicability::MaybeIncorrect,
2021 "associated type `{}` could derive from `{}`",
2023 bound.print_only_trait_path(),
2027 if !where_bounds.is_empty() {
2029 "consider introducing a new type parameter `T` and adding `where` constraints:\
2030 \n where\n T: {},\n{}",
2032 where_bounds.join(",\n"),
2036 if !where_bounds.is_empty() {
2037 return Err(ErrorReported);
2043 fn complain_about_assoc_type_not_found<I>(
2045 all_candidates: impl Fn() -> I,
2046 ty_param_name: &str,
2047 assoc_name: ast::Ident,
2050 I: Iterator<Item = ty::PolyTraitRef<'tcx>>,
2052 // The fallback span is needed because `assoc_name` might be an `Fn()`'s `Output` without a
2053 // valid span, so we point at the whole path segment instead.
2054 let span = if assoc_name.span != DUMMY_SP { assoc_name.span } else { span };
2055 let mut err = struct_span_err!(
2059 "associated type `{}` not found for `{}`",
2064 let all_candidate_names: Vec<_> = all_candidates()
2065 .map(|r| self.tcx().associated_items(r.def_id()).in_definition_order())
2068 |item| if item.kind == ty::AssocKind::Type { Some(item.ident.name) } else { None },
2072 if let (Some(suggested_name), true) = (
2073 find_best_match_for_name(all_candidate_names.iter(), &assoc_name.as_str(), None),
2074 assoc_name.span != DUMMY_SP,
2076 err.span_suggestion(
2078 "there is an associated type with a similar name",
2079 suggested_name.to_string(),
2080 Applicability::MaybeIncorrect,
2083 err.span_label(span, format!("associated type `{}` not found", assoc_name));
2089 // Create a type from a path to an associated type.
2090 // For a path `A::B::C::D`, `qself_ty` and `qself_def` are the type and def for `A::B::C`
2091 // and item_segment is the path segment for `D`. We return a type and a def for
2093 // Will fail except for `T::A` and `Self::A`; i.e., if `qself_ty`/`qself_def` are not a type
2094 // parameter or `Self`.
2095 pub fn associated_path_to_ty(
2097 hir_ref_id: hir::HirId,
2101 assoc_segment: &hir::PathSegment<'_>,
2102 permit_variants: bool,
2103 ) -> Result<(Ty<'tcx>, DefKind, DefId), ErrorReported> {
2104 let tcx = self.tcx();
2105 let assoc_ident = assoc_segment.ident;
2107 debug!("associated_path_to_ty: {:?}::{}", qself_ty, assoc_ident);
2109 // Check if we have an enum variant.
2110 let mut variant_resolution = None;
2111 if let ty::Adt(adt_def, _) = qself_ty.kind {
2112 if adt_def.is_enum() {
2113 let variant_def = adt_def
2116 .find(|vd| tcx.hygienic_eq(assoc_ident, vd.ident, adt_def.did));
2117 if let Some(variant_def) = variant_def {
2118 if permit_variants {
2119 tcx.check_stability(variant_def.def_id, Some(hir_ref_id), span);
2120 self.prohibit_generics(slice::from_ref(assoc_segment));
2121 return Ok((qself_ty, DefKind::Variant, variant_def.def_id));
2123 variant_resolution = Some(variant_def.def_id);
2129 // Find the type of the associated item, and the trait where the associated
2130 // item is declared.
2131 let bound = match (&qself_ty.kind, qself_res) {
2132 (_, Res::SelfTy(Some(_), Some(impl_def_id))) => {
2133 // `Self` in an impl of a trait -- we have a concrete self type and a
2135 let trait_ref = match tcx.impl_trait_ref(impl_def_id) {
2136 Some(trait_ref) => trait_ref,
2138 // A cycle error occurred, most likely.
2139 return Err(ErrorReported);
2143 self.one_bound_for_assoc_type(
2144 || traits::supertraits(tcx, ty::Binder::bind(trait_ref)),
2145 || "Self".to_string(),
2151 (&ty::Param(_), Res::SelfTy(Some(param_did), None))
2152 | (&ty::Param(_), Res::Def(DefKind::TyParam, param_did)) => {
2153 self.find_bound_for_assoc_item(param_did, assoc_ident, span)?
2156 if variant_resolution.is_some() {
2157 // Variant in type position
2158 let msg = format!("expected type, found variant `{}`", assoc_ident);
2159 tcx.sess.span_err(span, &msg);
2160 } else if qself_ty.is_enum() {
2161 let mut err = struct_span_err!(
2165 "no variant named `{}` found for enum `{}`",
2170 let adt_def = qself_ty.ty_adt_def().expect("enum is not an ADT");
2171 if let Some(suggested_name) = find_best_match_for_name(
2172 adt_def.variants.iter().map(|variant| &variant.ident.name),
2173 &assoc_ident.as_str(),
2176 err.span_suggestion(
2178 "there is a variant with a similar name",
2179 suggested_name.to_string(),
2180 Applicability::MaybeIncorrect,
2185 format!("variant not found in `{}`", qself_ty),
2189 if let Some(sp) = tcx.hir().span_if_local(adt_def.did) {
2190 let sp = tcx.sess.source_map().def_span(sp);
2191 err.span_label(sp, format!("variant `{}` not found here", assoc_ident));
2195 } else if !qself_ty.references_error() {
2196 // Don't print `TyErr` to the user.
2197 self.report_ambiguous_associated_type(
2199 &qself_ty.to_string(),
2204 return Err(ErrorReported);
2208 let trait_did = bound.def_id();
2209 let (assoc_ident, def_scope) =
2210 tcx.adjust_ident_and_get_scope(assoc_ident, trait_did, hir_ref_id);
2212 // We have already adjusted the item name above, so compare with `ident.modern()` instead
2213 // of calling `filter_by_name_and_kind`.
2215 .associated_items(trait_did)
2216 .in_definition_order()
2217 .find(|i| i.kind.namespace() == Namespace::TypeNS && i.ident.modern() == assoc_ident)
2218 .expect("missing associated type");
2220 let ty = self.projected_ty_from_poly_trait_ref(span, item.def_id, assoc_segment, bound);
2221 let ty = self.normalize_ty(span, ty);
2223 let kind = DefKind::AssocTy;
2224 if !item.vis.is_accessible_from(def_scope, tcx) {
2225 let msg = format!("{} `{}` is private", kind.descr(item.def_id), assoc_ident);
2226 tcx.sess.span_err(span, &msg);
2228 tcx.check_stability(item.def_id, Some(hir_ref_id), span);
2230 if let Some(variant_def_id) = variant_resolution {
2231 tcx.struct_span_lint_hir(AMBIGUOUS_ASSOCIATED_ITEMS, hir_ref_id, span, |lint| {
2232 let mut err = lint.build("ambiguous associated item");
2233 let mut could_refer_to = |kind: DefKind, def_id, also| {
2234 let note_msg = format!(
2235 "`{}` could{} refer to the {} defined here",
2240 err.span_note(tcx.def_span(def_id), ¬e_msg);
2243 could_refer_to(DefKind::Variant, variant_def_id, "");
2244 could_refer_to(kind, item.def_id, " also");
2246 err.span_suggestion(
2248 "use fully-qualified syntax",
2249 format!("<{} as {}>::{}", qself_ty, tcx.item_name(trait_did), assoc_ident),
2250 Applicability::MachineApplicable,
2256 Ok((ty, kind, item.def_id))
2262 opt_self_ty: Option<Ty<'tcx>>,
2264 trait_segment: &hir::PathSegment<'_>,
2265 item_segment: &hir::PathSegment<'_>,
2267 let tcx = self.tcx();
2269 let trait_def_id = tcx.parent(item_def_id).unwrap();
2271 debug!("qpath_to_ty: trait_def_id={:?}", trait_def_id);
2273 let self_ty = if let Some(ty) = opt_self_ty {
2276 let path_str = tcx.def_path_str(trait_def_id);
2278 let def_id = self.item_def_id();
2280 debug!("qpath_to_ty: self.item_def_id()={:?}", def_id);
2282 let parent_def_id = def_id
2283 .and_then(|def_id| tcx.hir().as_local_hir_id(def_id))
2284 .map(|hir_id| tcx.hir().get_parent_did(hir_id));
2286 debug!("qpath_to_ty: parent_def_id={:?}", parent_def_id);
2288 // If the trait in segment is the same as the trait defining the item,
2289 // use the `<Self as ..>` syntax in the error.
2290 let is_part_of_self_trait_constraints = def_id == Some(trait_def_id);
2291 let is_part_of_fn_in_self_trait = parent_def_id == Some(trait_def_id);
2293 let type_name = if is_part_of_self_trait_constraints || is_part_of_fn_in_self_trait {
2299 self.report_ambiguous_associated_type(
2303 item_segment.ident.name,
2305 return tcx.types.err;
2308 debug!("qpath_to_ty: self_type={:?}", self_ty);
2310 let trait_ref = self.ast_path_to_mono_trait_ref(span, trait_def_id, self_ty, trait_segment);
2312 let item_substs = self.create_substs_for_associated_item(
2320 debug!("qpath_to_ty: trait_ref={:?}", trait_ref);
2322 self.normalize_ty(span, tcx.mk_projection(item_def_id, item_substs))
2325 pub fn prohibit_generics<'a, T: IntoIterator<Item = &'a hir::PathSegment<'a>>>(
2329 let mut has_err = false;
2330 for segment in segments {
2331 let (mut err_for_lt, mut err_for_ty, mut err_for_ct) = (false, false, false);
2332 for arg in segment.generic_args().args {
2333 let (span, kind) = match arg {
2334 hir::GenericArg::Lifetime(lt) => {
2340 (lt.span, "lifetime")
2342 hir::GenericArg::Type(ty) => {
2350 hir::GenericArg::Const(ct) => {
2358 let mut err = struct_span_err!(
2362 "{} arguments are not allowed for this type",
2365 err.span_label(span, format!("{} argument not allowed", kind));
2367 if err_for_lt && err_for_ty && err_for_ct {
2371 for binding in segment.generic_args().bindings {
2373 Self::prohibit_assoc_ty_binding(self.tcx(), binding.span);
2380 pub fn prohibit_assoc_ty_binding(tcx: TyCtxt<'_>, span: Span) {
2381 let mut err = struct_span_err!(
2385 "associated type bindings are not allowed here"
2387 err.span_label(span, "associated type not allowed here").emit();
2390 // FIXME(eddyb, varkor) handle type paths here too, not just value ones.
2391 pub fn def_ids_for_value_path_segments(
2393 segments: &[hir::PathSegment<'_>],
2394 self_ty: Option<Ty<'tcx>>,
2398 // We need to extract the type parameters supplied by the user in
2399 // the path `path`. Due to the current setup, this is a bit of a
2400 // tricky-process; the problem is that resolve only tells us the
2401 // end-point of the path resolution, and not the intermediate steps.
2402 // Luckily, we can (at least for now) deduce the intermediate steps
2403 // just from the end-point.
2405 // There are basically five cases to consider:
2407 // 1. Reference to a constructor of a struct:
2409 // struct Foo<T>(...)
2411 // In this case, the parameters are declared in the type space.
2413 // 2. Reference to a constructor of an enum variant:
2415 // enum E<T> { Foo(...) }
2417 // In this case, the parameters are defined in the type space,
2418 // but may be specified either on the type or the variant.
2420 // 3. Reference to a fn item or a free constant:
2424 // In this case, the path will again always have the form
2425 // `a::b::foo::<T>` where only the final segment should have
2426 // type parameters. However, in this case, those parameters are
2427 // declared on a value, and hence are in the `FnSpace`.
2429 // 4. Reference to a method or an associated constant:
2431 // impl<A> SomeStruct<A> {
2435 // Here we can have a path like
2436 // `a::b::SomeStruct::<A>::foo::<B>`, in which case parameters
2437 // may appear in two places. The penultimate segment,
2438 // `SomeStruct::<A>`, contains parameters in TypeSpace, and the
2439 // final segment, `foo::<B>` contains parameters in fn space.
2441 // The first step then is to categorize the segments appropriately.
2443 let tcx = self.tcx();
2445 assert!(!segments.is_empty());
2446 let last = segments.len() - 1;
2448 let mut path_segs = vec![];
2451 // Case 1. Reference to a struct constructor.
2452 DefKind::Ctor(CtorOf::Struct, ..) => {
2453 // Everything but the final segment should have no
2454 // parameters at all.
2455 let generics = tcx.generics_of(def_id);
2456 // Variant and struct constructors use the
2457 // generics of their parent type definition.
2458 let generics_def_id = generics.parent.unwrap_or(def_id);
2459 path_segs.push(PathSeg(generics_def_id, last));
2462 // Case 2. Reference to a variant constructor.
2463 DefKind::Ctor(CtorOf::Variant, ..) | DefKind::Variant => {
2464 let adt_def = self_ty.map(|t| t.ty_adt_def().unwrap());
2465 let (generics_def_id, index) = if let Some(adt_def) = adt_def {
2466 debug_assert!(adt_def.is_enum());
2468 } else if last >= 1 && segments[last - 1].args.is_some() {
2469 // Everything but the penultimate segment should have no
2470 // parameters at all.
2471 let mut def_id = def_id;
2473 // `DefKind::Ctor` -> `DefKind::Variant`
2474 if let DefKind::Ctor(..) = kind {
2475 def_id = tcx.parent(def_id).unwrap()
2478 // `DefKind::Variant` -> `DefKind::Enum`
2479 let enum_def_id = tcx.parent(def_id).unwrap();
2480 (enum_def_id, last - 1)
2482 // FIXME: lint here recommending `Enum::<...>::Variant` form
2483 // instead of `Enum::Variant::<...>` form.
2485 // Everything but the final segment should have no
2486 // parameters at all.
2487 let generics = tcx.generics_of(def_id);
2488 // Variant and struct constructors use the
2489 // generics of their parent type definition.
2490 (generics.parent.unwrap_or(def_id), last)
2492 path_segs.push(PathSeg(generics_def_id, index));
2495 // Case 3. Reference to a top-level value.
2496 DefKind::Fn | DefKind::Const | DefKind::ConstParam | DefKind::Static => {
2497 path_segs.push(PathSeg(def_id, last));
2500 // Case 4. Reference to a method or associated const.
2501 DefKind::Method | DefKind::AssocConst => {
2502 if segments.len() >= 2 {
2503 let generics = tcx.generics_of(def_id);
2504 path_segs.push(PathSeg(generics.parent.unwrap(), last - 1));
2506 path_segs.push(PathSeg(def_id, last));
2509 kind => bug!("unexpected definition kind {:?} for {:?}", kind, def_id),
2512 debug!("path_segs = {:?}", path_segs);
2517 // Check a type `Path` and convert it to a `Ty`.
2520 opt_self_ty: Option<Ty<'tcx>>,
2521 path: &hir::Path<'_>,
2522 permit_variants: bool,
2524 let tcx = self.tcx();
2527 "res_to_ty(res={:?}, opt_self_ty={:?}, path_segments={:?})",
2528 path.res, opt_self_ty, path.segments
2531 let span = path.span;
2533 Res::Def(DefKind::OpaqueTy, did) => {
2534 // Check for desugared `impl Trait`.
2535 assert!(ty::is_impl_trait_defn(tcx, did).is_none());
2536 let item_segment = path.segments.split_last().unwrap();
2537 self.prohibit_generics(item_segment.1);
2538 let substs = self.ast_path_substs_for_ty(span, did, item_segment.0);
2539 self.normalize_ty(span, tcx.mk_opaque(did, substs))
2541 Res::Def(DefKind::Enum, did)
2542 | Res::Def(DefKind::TyAlias, did)
2543 | Res::Def(DefKind::Struct, did)
2544 | Res::Def(DefKind::Union, did)
2545 | Res::Def(DefKind::ForeignTy, did) => {
2546 assert_eq!(opt_self_ty, None);
2547 self.prohibit_generics(path.segments.split_last().unwrap().1);
2548 self.ast_path_to_ty(span, did, path.segments.last().unwrap())
2550 Res::Def(kind @ DefKind::Variant, def_id) if permit_variants => {
2551 // Convert "variant type" as if it were a real type.
2552 // The resulting `Ty` is type of the variant's enum for now.
2553 assert_eq!(opt_self_ty, None);
2556 self.def_ids_for_value_path_segments(&path.segments, None, kind, def_id);
2557 let generic_segs: FxHashSet<_> =
2558 path_segs.iter().map(|PathSeg(_, index)| index).collect();
2559 self.prohibit_generics(path.segments.iter().enumerate().filter_map(
2561 if !generic_segs.contains(&index) { Some(seg) } else { None }
2565 let PathSeg(def_id, index) = path_segs.last().unwrap();
2566 self.ast_path_to_ty(span, *def_id, &path.segments[*index])
2568 Res::Def(DefKind::TyParam, def_id) => {
2569 assert_eq!(opt_self_ty, None);
2570 self.prohibit_generics(path.segments);
2572 let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
2573 let item_id = tcx.hir().get_parent_node(hir_id);
2574 let item_def_id = tcx.hir().local_def_id(item_id);
2575 let generics = tcx.generics_of(item_def_id);
2576 let index = generics.param_def_id_to_index[&def_id];
2577 tcx.mk_ty_param(index, tcx.hir().name(hir_id))
2579 Res::SelfTy(Some(_), None) => {
2580 // `Self` in trait or type alias.
2581 assert_eq!(opt_self_ty, None);
2582 self.prohibit_generics(path.segments);
2583 tcx.types.self_param
2585 Res::SelfTy(_, Some(def_id)) => {
2586 // `Self` in impl (we know the concrete type).
2587 assert_eq!(opt_self_ty, None);
2588 self.prohibit_generics(path.segments);
2589 // Try to evaluate any array length constants.
2590 self.normalize_ty(span, tcx.at(span).type_of(def_id))
2592 Res::Def(DefKind::AssocTy, def_id) => {
2593 debug_assert!(path.segments.len() >= 2);
2594 self.prohibit_generics(&path.segments[..path.segments.len() - 2]);
2599 &path.segments[path.segments.len() - 2],
2600 path.segments.last().unwrap(),
2603 Res::PrimTy(prim_ty) => {
2604 assert_eq!(opt_self_ty, None);
2605 self.prohibit_generics(path.segments);
2607 hir::PrimTy::Bool => tcx.types.bool,
2608 hir::PrimTy::Char => tcx.types.char,
2609 hir::PrimTy::Int(it) => tcx.mk_mach_int(it),
2610 hir::PrimTy::Uint(uit) => tcx.mk_mach_uint(uit),
2611 hir::PrimTy::Float(ft) => tcx.mk_mach_float(ft),
2612 hir::PrimTy::Str => tcx.mk_str(),
2616 self.set_tainted_by_errors();
2617 return self.tcx().types.err;
2619 _ => span_bug!(span, "unexpected resolution: {:?}", path.res),
2623 /// Parses the programmer's textual representation of a type into our
2624 /// internal notion of a type.
2625 pub fn ast_ty_to_ty(&self, ast_ty: &hir::Ty<'_>) -> Ty<'tcx> {
2626 debug!("ast_ty_to_ty(id={:?}, ast_ty={:?} ty_ty={:?})", ast_ty.hir_id, ast_ty, ast_ty.kind);
2628 let tcx = self.tcx();
2630 let result_ty = match ast_ty.kind {
2631 hir::TyKind::Slice(ref ty) => tcx.mk_slice(self.ast_ty_to_ty(&ty)),
2632 hir::TyKind::Ptr(ref mt) => {
2633 tcx.mk_ptr(ty::TypeAndMut { ty: self.ast_ty_to_ty(&mt.ty), mutbl: mt.mutbl })
2635 hir::TyKind::Rptr(ref region, ref mt) => {
2636 let r = self.ast_region_to_region(region, None);
2637 debug!("ast_ty_to_ty: r={:?}", r);
2638 let t = self.ast_ty_to_ty(&mt.ty);
2639 tcx.mk_ref(r, ty::TypeAndMut { ty: t, mutbl: mt.mutbl })
2641 hir::TyKind::Never => tcx.types.never,
2642 hir::TyKind::Tup(ref fields) => {
2643 tcx.mk_tup(fields.iter().map(|t| self.ast_ty_to_ty(&t)))
2645 hir::TyKind::BareFn(ref bf) => {
2646 require_c_abi_if_c_variadic(tcx, &bf.decl, bf.abi, ast_ty.span);
2647 tcx.mk_fn_ptr(self.ty_of_fn(bf.unsafety, bf.abi, &bf.decl, &[], None))
2649 hir::TyKind::TraitObject(ref bounds, ref lifetime) => {
2650 self.conv_object_ty_poly_trait_ref(ast_ty.span, bounds, lifetime)
2652 hir::TyKind::Path(hir::QPath::Resolved(ref maybe_qself, ref path)) => {
2653 debug!("ast_ty_to_ty: maybe_qself={:?} path={:?}", maybe_qself, path);
2654 let opt_self_ty = maybe_qself.as_ref().map(|qself| self.ast_ty_to_ty(qself));
2655 self.res_to_ty(opt_self_ty, path, false)
2657 hir::TyKind::Def(item_id, ref lifetimes) => {
2658 let did = tcx.hir().local_def_id(item_id.id);
2659 self.impl_trait_ty_to_ty(did, lifetimes)
2661 hir::TyKind::Path(hir::QPath::TypeRelative(ref qself, ref segment)) => {
2662 debug!("ast_ty_to_ty: qself={:?} segment={:?}", qself, segment);
2663 let ty = self.ast_ty_to_ty(qself);
2665 let res = if let hir::TyKind::Path(hir::QPath::Resolved(_, ref path)) = qself.kind {
2670 self.associated_path_to_ty(ast_ty.hir_id, ast_ty.span, ty, res, segment, false)
2671 .map(|(ty, _, _)| ty)
2672 .unwrap_or(tcx.types.err)
2674 hir::TyKind::Array(ref ty, ref length) => {
2675 let length = self.ast_const_to_const(length, tcx.types.usize);
2676 let array_ty = tcx.mk_ty(ty::Array(self.ast_ty_to_ty(&ty), length));
2677 self.normalize_ty(ast_ty.span, array_ty)
2679 hir::TyKind::Typeof(ref _e) => {
2684 "`typeof` is a reserved keyword but unimplemented"
2686 .span_label(ast_ty.span, "reserved keyword")
2691 hir::TyKind::Infer => {
2692 // Infer also appears as the type of arguments or return
2693 // values in a ExprKind::Closure, or as
2694 // the type of local variables. Both of these cases are
2695 // handled specially and will not descend into this routine.
2696 self.ty_infer(None, ast_ty.span)
2698 hir::TyKind::Err => tcx.types.err,
2701 debug!("ast_ty_to_ty: result_ty={:?}", result_ty);
2703 self.record_ty(ast_ty.hir_id, result_ty, ast_ty.span);
2707 /// Returns the `DefId` of the constant parameter that the provided expression is a path to.
2708 pub fn const_param_def_id(&self, expr: &hir::Expr<'_>) -> Option<DefId> {
2709 // Unwrap a block, so that e.g. `{ P }` is recognised as a parameter. Const arguments
2710 // currently have to be wrapped in curly brackets, so it's necessary to special-case.
2711 let expr = match &expr.kind {
2712 ExprKind::Block(block, _) if block.stmts.is_empty() && block.expr.is_some() => {
2713 block.expr.as_ref().unwrap()
2719 ExprKind::Path(hir::QPath::Resolved(_, path)) => match path.res {
2720 Res::Def(DefKind::ConstParam, did) => Some(did),
2727 pub fn ast_const_to_const(
2729 ast_const: &hir::AnonConst,
2731 ) -> &'tcx ty::Const<'tcx> {
2732 debug!("ast_const_to_const(id={:?}, ast_const={:?})", ast_const.hir_id, ast_const);
2734 let tcx = self.tcx();
2735 let def_id = tcx.hir().local_def_id(ast_const.hir_id);
2737 let expr = &tcx.hir().body(ast_const.body).value;
2739 let lit_input = match expr.kind {
2740 hir::ExprKind::Lit(ref lit) => Some(LitToConstInput { lit: &lit.node, ty, neg: false }),
2741 hir::ExprKind::Unary(hir::UnOp::UnNeg, ref expr) => match expr.kind {
2742 hir::ExprKind::Lit(ref lit) => {
2743 Some(LitToConstInput { lit: &lit.node, ty, neg: true })
2750 if let Some(lit_input) = lit_input {
2751 // If an error occurred, ignore that it's a literal and leave reporting the error up to
2753 if let Ok(c) = tcx.at(expr.span).lit_to_const(lit_input) {
2756 tcx.sess.delay_span_bug(expr.span, "ast_const_to_const: couldn't lit_to_const");
2760 let kind = if let Some(def_id) = self.const_param_def_id(expr) {
2761 // Find the name and index of the const parameter by indexing the generics of the
2762 // parent item and construct a `ParamConst`.
2763 let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
2764 let item_id = tcx.hir().get_parent_node(hir_id);
2765 let item_def_id = tcx.hir().local_def_id(item_id);
2766 let generics = tcx.generics_of(item_def_id);
2767 let index = generics.param_def_id_to_index[&tcx.hir().local_def_id(hir_id)];
2768 let name = tcx.hir().name(hir_id);
2769 ty::ConstKind::Param(ty::ParamConst::new(index, name))
2771 ty::ConstKind::Unevaluated(def_id, InternalSubsts::identity_for_item(tcx, def_id), None)
2773 tcx.mk_const(ty::Const { val: kind, ty })
2776 pub fn impl_trait_ty_to_ty(
2779 lifetimes: &[hir::GenericArg<'_>],
2781 debug!("impl_trait_ty_to_ty(def_id={:?}, lifetimes={:?})", def_id, lifetimes);
2782 let tcx = self.tcx();
2784 let generics = tcx.generics_of(def_id);
2786 debug!("impl_trait_ty_to_ty: generics={:?}", generics);
2787 let substs = InternalSubsts::for_item(tcx, def_id, |param, _| {
2788 if let Some(i) = (param.index as usize).checked_sub(generics.parent_count) {
2789 // Our own parameters are the resolved lifetimes.
2791 GenericParamDefKind::Lifetime => {
2792 if let hir::GenericArg::Lifetime(lifetime) = &lifetimes[i] {
2793 self.ast_region_to_region(lifetime, None).into()
2801 // Replace all parent lifetimes with `'static`.
2803 GenericParamDefKind::Lifetime => tcx.lifetimes.re_static.into(),
2804 _ => tcx.mk_param_from_def(param),
2808 debug!("impl_trait_ty_to_ty: substs={:?}", substs);
2810 let ty = tcx.mk_opaque(def_id, substs);
2811 debug!("impl_trait_ty_to_ty: {}", ty);
2815 pub fn ty_of_arg(&self, ty: &hir::Ty<'_>, expected_ty: Option<Ty<'tcx>>) -> Ty<'tcx> {
2817 hir::TyKind::Infer if expected_ty.is_some() => {
2818 self.record_ty(ty.hir_id, expected_ty.unwrap(), ty.span);
2819 expected_ty.unwrap()
2821 _ => self.ast_ty_to_ty(ty),
2827 unsafety: hir::Unsafety,
2829 decl: &hir::FnDecl<'_>,
2830 generic_params: &[hir::GenericParam<'_>],
2831 ident_span: Option<Span>,
2832 ) -> ty::PolyFnSig<'tcx> {
2835 let tcx = self.tcx();
2837 // We proactively collect all the infered type params to emit a single error per fn def.
2838 let mut visitor = PlaceholderHirTyCollector::default();
2839 for ty in decl.inputs {
2840 visitor.visit_ty(ty);
2842 let input_tys = decl.inputs.iter().map(|a| self.ty_of_arg(a, None));
2843 let output_ty = match decl.output {
2844 hir::FnRetTy::Return(ref output) => {
2845 visitor.visit_ty(output);
2846 self.ast_ty_to_ty(output)
2848 hir::FnRetTy::DefaultReturn(..) => tcx.mk_unit(),
2851 debug!("ty_of_fn: output_ty={:?}", output_ty);
2854 ty::Binder::bind(tcx.mk_fn_sig(input_tys, output_ty, decl.c_variadic, unsafety, abi));
2856 if !self.allow_ty_infer() {
2857 // We always collect the spans for placeholder types when evaluating `fn`s, but we
2858 // only want to emit an error complaining about them if infer types (`_`) are not
2859 // allowed. `allow_ty_infer` gates this behavior.
2860 crate::collect::placeholder_type_error(
2862 ident_span.map(|sp| sp.shrink_to_hi()).unwrap_or(DUMMY_SP),
2865 ident_span.is_some(),
2869 // Find any late-bound regions declared in return type that do
2870 // not appear in the arguments. These are not well-formed.
2873 // for<'a> fn() -> &'a str <-- 'a is bad
2874 // for<'a> fn(&'a String) -> &'a str <-- 'a is ok
2875 let inputs = bare_fn_ty.inputs();
2876 let late_bound_in_args =
2877 tcx.collect_constrained_late_bound_regions(&inputs.map_bound(|i| i.to_owned()));
2878 let output = bare_fn_ty.output();
2879 let late_bound_in_ret = tcx.collect_referenced_late_bound_regions(&output);
2880 for br in late_bound_in_ret.difference(&late_bound_in_args) {
2881 let lifetime_name = match *br {
2882 ty::BrNamed(_, name) => format!("lifetime `{}`,", name),
2883 ty::BrAnon(_) | ty::BrEnv => "an anonymous lifetime".to_string(),
2885 let mut err = struct_span_err!(
2889 "return type references {} \
2890 which is not constrained by the fn input types",
2893 if let ty::BrAnon(_) = *br {
2894 // The only way for an anonymous lifetime to wind up
2895 // in the return type but **also** be unconstrained is
2896 // if it only appears in "associated types" in the
2897 // input. See #47511 for an example. In this case,
2898 // though we can easily give a hint that ought to be
2901 "lifetimes appearing in an associated type \
2902 are not considered constrained",
2911 /// Given the bounds on an object, determines what single region bound (if any) we can
2912 /// use to summarize this type. The basic idea is that we will use the bound the user
2913 /// provided, if they provided one, and otherwise search the supertypes of trait bounds
2914 /// for region bounds. It may be that we can derive no bound at all, in which case
2915 /// we return `None`.
2916 fn compute_object_lifetime_bound(
2919 existential_predicates: ty::Binder<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>>,
2920 ) -> Option<ty::Region<'tcx>> // if None, use the default
2922 let tcx = self.tcx();
2924 debug!("compute_opt_region_bound(existential_predicates={:?})", existential_predicates);
2926 // No explicit region bound specified. Therefore, examine trait
2927 // bounds and see if we can derive region bounds from those.
2928 let derived_region_bounds = object_region_bounds(tcx, existential_predicates);
2930 // If there are no derived region bounds, then report back that we
2931 // can find no region bound. The caller will use the default.
2932 if derived_region_bounds.is_empty() {
2936 // If any of the derived region bounds are 'static, that is always
2938 if derived_region_bounds.iter().any(|&r| ty::ReStatic == *r) {
2939 return Some(tcx.lifetimes.re_static);
2942 // Determine whether there is exactly one unique region in the set
2943 // of derived region bounds. If so, use that. Otherwise, report an
2945 let r = derived_region_bounds[0];
2946 if derived_region_bounds[1..].iter().any(|r1| r != *r1) {
2951 "ambiguous lifetime bound, explicit lifetime bound required"
2959 /// Collects together a list of bounds that are applied to some type,
2960 /// after they've been converted into `ty` form (from the HIR
2961 /// representations). These lists of bounds occur in many places in
2965 /// trait Foo: Bar + Baz { }
2966 /// ^^^^^^^^^ supertrait list bounding the `Self` type parameter
2968 /// fn foo<T: Bar + Baz>() { }
2969 /// ^^^^^^^^^ bounding the type parameter `T`
2971 /// impl dyn Bar + Baz
2972 /// ^^^^^^^^^ bounding the forgotten dynamic type
2975 /// Our representation is a bit mixed here -- in some cases, we
2976 /// include the self type (e.g., `trait_bounds`) but in others we do
2977 #[derive(Default, PartialEq, Eq, Clone, Debug)]
2978 pub struct Bounds<'tcx> {
2979 /// A list of region bounds on the (implicit) self type. So if you
2980 /// had `T: 'a + 'b` this might would be a list `['a, 'b]` (but
2981 /// the `T` is not explicitly included).
2982 pub region_bounds: Vec<(ty::Region<'tcx>, Span)>,
2984 /// A list of trait bounds. So if you had `T: Debug` this would be
2985 /// `T: Debug`. Note that the self-type is explicit here.
2986 pub trait_bounds: Vec<(ty::PolyTraitRef<'tcx>, Span, Constness)>,
2988 /// A list of projection equality bounds. So if you had `T:
2989 /// Iterator<Item = u32>` this would include `<T as
2990 /// Iterator>::Item => u32`. Note that the self-type is explicit
2992 pub projection_bounds: Vec<(ty::PolyProjectionPredicate<'tcx>, Span)>,
2994 /// `Some` if there is *no* `?Sized` predicate. The `span`
2995 /// is the location in the source of the `T` declaration which can
2996 /// be cited as the source of the `T: Sized` requirement.
2997 pub implicitly_sized: Option<Span>,
3000 impl<'tcx> Bounds<'tcx> {
3001 /// Converts a bounds list into a flat set of predicates (like
3002 /// where-clauses). Because some of our bounds listings (e.g.,
3003 /// regions) don't include the self-type, you must supply the
3004 /// self-type here (the `param_ty` parameter).
3009 ) -> Vec<(ty::Predicate<'tcx>, Span)> {
3010 // If it could be sized, and is, add the `Sized` predicate.
3011 let sized_predicate = self.implicitly_sized.and_then(|span| {
3012 tcx.lang_items().sized_trait().map(|sized| {
3013 let trait_ref = ty::Binder::bind(ty::TraitRef {
3015 substs: tcx.mk_substs_trait(param_ty, &[]),
3017 (trait_ref.without_const().to_predicate(), span)
3026 .map(|&(region_bound, span)| {
3027 // Account for the binder being introduced below; no need to shift `param_ty`
3028 // because, at present at least, it either only refers to early-bound regions,
3029 // or it's a generic associated type that deliberately has escaping bound vars.
3030 let region_bound = ty::fold::shift_region(tcx, region_bound, 1);
3031 let outlives = ty::OutlivesPredicate(param_ty, region_bound);
3032 (ty::Binder::bind(outlives).to_predicate(), span)
3034 .chain(self.trait_bounds.iter().map(|&(bound_trait_ref, span, constness)| {
3035 let predicate = bound_trait_ref.with_constness(constness).to_predicate();
3039 self.projection_bounds
3041 .map(|&(projection, span)| (projection.to_predicate(), span)),