1 //! Conversion from AST representation of types to the `ty.rs` representation.
2 //! The main routine here is `ast_ty_to_ty()`; each use is parameterized by an
3 //! instance of `AstConv`.
5 use crate::collect::PlaceholderHirTyCollector;
7 use crate::middle::lang_items::SizedTraitLangItem;
8 use crate::middle::resolve_lifetime as rl;
9 use crate::namespace::Namespace;
10 use crate::require_c_abi_if_c_variadic;
11 use crate::util::common::ErrorReported;
12 use errors::{Applicability, DiagnosticId};
13 use rustc::hir::intravisit::Visitor;
14 use rustc::lint::builtin::AMBIGUOUS_ASSOCIATED_ITEMS;
16 use rustc::ty::subst::{self, InternalSubsts, Subst, SubstsRef};
17 use rustc::ty::wf::object_region_bounds;
18 use rustc::ty::{self, Const, DefIdTree, ToPredicate, Ty, TyCtxt, TypeFoldable};
19 use rustc::ty::{GenericParamDef, GenericParamDefKind};
20 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
22 use rustc_hir::def::{CtorOf, DefKind, Res};
23 use rustc_hir::def_id::DefId;
25 use rustc_hir::{ExprKind, GenericArg, GenericArgs};
26 use rustc_span::symbol::sym;
27 use rustc_span::{MultiSpan, Span, DUMMY_SP};
28 use rustc_target::spec::abi;
29 use smallvec::SmallVec;
31 use syntax::errors::pluralize;
32 use syntax::feature_gate::feature_err;
33 use syntax::util::lev_distance::find_best_match_for_name;
35 use std::collections::BTreeSet;
39 use rustc_error_codes::*;
42 pub struct PathSeg(pub DefId, pub usize);
44 pub trait AstConv<'tcx> {
45 fn tcx<'a>(&'a self) -> TyCtxt<'tcx>;
47 fn item_def_id(&self) -> Option<DefId>;
49 /// Returns predicates in scope of the form `X: Foo`, where `X` is
50 /// a type parameter `X` with the given id `def_id`. This is a
51 /// subset of the full set of predicates.
53 /// This is used for one specific purpose: resolving "short-hand"
54 /// associated type references like `T::Item`. In principle, we
55 /// would do that by first getting the full set of predicates in
56 /// scope and then filtering down to find those that apply to `T`,
57 /// but this can lead to cycle errors. The problem is that we have
58 /// to do this resolution *in order to create the predicates in
59 /// the first place*. Hence, we have this "special pass".
60 fn get_type_parameter_bounds(&self, span: Span, def_id: DefId) -> ty::GenericPredicates<'tcx>;
62 /// Returns the lifetime to use when a lifetime is omitted (and not elided).
63 fn re_infer(&self, param: Option<&ty::GenericParamDef>, span: Span)
64 -> Option<ty::Region<'tcx>>;
66 /// Returns the type to use when a type is omitted.
67 fn ty_infer(&self, param: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx>;
69 /// Returns `true` if `_` is allowed in type signatures in the current context.
70 fn allow_ty_infer(&self) -> bool;
72 /// Returns the const to use when a const is omitted.
76 param: Option<&ty::GenericParamDef>,
78 ) -> &'tcx Const<'tcx>;
80 /// Projecting an associated type from a (potentially)
81 /// higher-ranked trait reference is more complicated, because of
82 /// the possibility of late-bound regions appearing in the
83 /// associated type binding. This is not legal in function
84 /// signatures for that reason. In a function body, we can always
85 /// handle it because we can use inference variables to remove the
86 /// late-bound regions.
87 fn projected_ty_from_poly_trait_ref(
91 item_segment: &hir::PathSegment<'_>,
92 poly_trait_ref: ty::PolyTraitRef<'tcx>,
95 /// Normalize an associated type coming from the user.
96 fn normalize_ty(&self, span: Span, ty: Ty<'tcx>) -> Ty<'tcx>;
98 /// Invoked when we encounter an error from some prior pass
99 /// (e.g., resolve) that is translated into a ty-error. This is
100 /// used to help suppress derived errors typeck might otherwise
102 fn set_tainted_by_errors(&self);
104 fn record_ty(&self, hir_id: hir::HirId, ty: Ty<'tcx>, span: Span);
107 pub enum SizedByDefault {
112 struct ConvertedBinding<'a, 'tcx> {
113 item_name: ast::Ident,
114 kind: ConvertedBindingKind<'a, 'tcx>,
118 enum ConvertedBindingKind<'a, 'tcx> {
120 Constraint(&'a [hir::GenericBound<'a>]),
124 enum GenericArgPosition {
126 Value, // e.g., functions
130 impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
131 pub fn ast_region_to_region(
133 lifetime: &hir::Lifetime,
134 def: Option<&ty::GenericParamDef>,
135 ) -> ty::Region<'tcx> {
136 let tcx = self.tcx();
137 let lifetime_name = |def_id| tcx.hir().name(tcx.hir().as_local_hir_id(def_id).unwrap());
139 let r = match tcx.named_region(lifetime.hir_id) {
140 Some(rl::Region::Static) => tcx.lifetimes.re_static,
142 Some(rl::Region::LateBound(debruijn, id, _)) => {
143 let name = lifetime_name(id);
144 tcx.mk_region(ty::ReLateBound(debruijn, ty::BrNamed(id, name)))
147 Some(rl::Region::LateBoundAnon(debruijn, index)) => {
148 tcx.mk_region(ty::ReLateBound(debruijn, ty::BrAnon(index)))
151 Some(rl::Region::EarlyBound(index, id, _)) => {
152 let name = lifetime_name(id);
153 tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion { def_id: id, index, name }))
156 Some(rl::Region::Free(scope, id)) => {
157 let name = lifetime_name(id);
158 tcx.mk_region(ty::ReFree(ty::FreeRegion {
160 bound_region: ty::BrNamed(id, name),
163 // (*) -- not late-bound, won't change
167 self.re_infer(def, lifetime.span).unwrap_or_else(|| {
168 // This indicates an illegal lifetime
169 // elision. `resolve_lifetime` should have
170 // reported an error in this case -- but if
171 // not, let's error out.
172 tcx.sess.delay_span_bug(lifetime.span, "unelided lifetime in signature");
174 // Supply some dummy value. We don't have an
175 // `re_error`, annoyingly, so use `'static`.
176 tcx.lifetimes.re_static
181 debug!("ast_region_to_region(lifetime={:?}) yields {:?}", lifetime, r);
186 /// Given a path `path` that refers to an item `I` with the declared generics `decl_generics`,
187 /// returns an appropriate set of substitutions for this particular reference to `I`.
188 pub fn ast_path_substs_for_ty(
192 item_segment: &hir::PathSegment<'_>,
193 ) -> SubstsRef<'tcx> {
194 let (substs, assoc_bindings, _) = self.create_substs_for_ast_path(
198 item_segment.generic_args(),
199 item_segment.infer_args,
203 assoc_bindings.first().map(|b| Self::prohibit_assoc_ty_binding(self.tcx(), b.span));
208 /// Report error if there is an explicit type parameter when using `impl Trait`.
211 seg: &hir::PathSegment<'_>,
212 generics: &ty::Generics,
214 let explicit = !seg.infer_args;
215 let impl_trait = generics.params.iter().any(|param| match param.kind {
216 ty::GenericParamDefKind::Type {
217 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
223 if explicit && impl_trait {
228 .filter_map(|arg| match arg {
229 GenericArg::Type(_) => Some(arg.span()),
232 .collect::<Vec<_>>();
234 let mut err = struct_span_err! {
238 "cannot provide explicit generic arguments when `impl Trait` is \
239 used in argument position"
243 err.span_label(span, "explicit generic argument not allowed");
252 /// Checks that the correct number of generic arguments have been provided.
253 /// Used specifically for function calls.
254 pub fn check_generic_arg_count_for_call(
258 seg: &hir::PathSegment<'_>,
259 is_method_call: bool,
261 let empty_args = hir::GenericArgs::none();
262 let suppress_mismatch = Self::check_impl_trait(tcx, seg, &def);
263 Self::check_generic_arg_count(
267 if let Some(ref args) = seg.args { args } else { &empty_args },
268 if is_method_call { GenericArgPosition::MethodCall } else { GenericArgPosition::Value },
269 def.parent.is_none() && def.has_self, // `has_self`
270 seg.infer_args || suppress_mismatch, // `infer_args`
275 /// Checks that the correct number of generic arguments have been provided.
276 /// This is used both for datatypes and function calls.
277 fn check_generic_arg_count(
281 args: &hir::GenericArgs<'_>,
282 position: GenericArgPosition,
285 ) -> (bool, Option<Vec<Span>>) {
286 // At this stage we are guaranteed that the generic arguments are in the correct order, e.g.
287 // that lifetimes will proceed types. So it suffices to check the number of each generic
288 // arguments in order to validate them with respect to the generic parameters.
289 let param_counts = def.own_counts();
290 let arg_counts = args.own_counts();
291 let infer_lifetimes = position != GenericArgPosition::Type && arg_counts.lifetimes == 0;
293 let mut defaults: ty::GenericParamCount = Default::default();
294 for param in &def.params {
296 GenericParamDefKind::Lifetime => {}
297 GenericParamDefKind::Type { has_default, .. } => {
298 defaults.types += has_default as usize
300 GenericParamDefKind::Const => {
301 // FIXME(const_generics:defaults)
306 if position != GenericArgPosition::Type && !args.bindings.is_empty() {
307 AstConv::prohibit_assoc_ty_binding(tcx, args.bindings[0].span);
310 // Prohibit explicit lifetime arguments if late-bound lifetime parameters are present.
311 let mut reported_late_bound_region_err = None;
312 if !infer_lifetimes {
313 if let Some(span_late) = def.has_late_bound_regions {
314 let msg = "cannot specify lifetime arguments explicitly \
315 if late bound lifetime parameters are present";
316 let note = "the late bound lifetime parameter is introduced here";
317 let span = args.args[0].span();
318 if position == GenericArgPosition::Value
319 && arg_counts.lifetimes != param_counts.lifetimes
321 let mut err = tcx.sess.struct_span_err(span, msg);
322 err.span_note(span_late, note);
324 reported_late_bound_region_err = Some(true);
326 let mut multispan = MultiSpan::from_span(span);
327 multispan.push_span_label(span_late, note.to_string());
329 lint::builtin::LATE_BOUND_LIFETIME_ARGUMENTS,
334 reported_late_bound_region_err = Some(false);
339 let check_kind_count = |kind, required, permitted, provided, offset| {
341 "check_kind_count: kind: {} required: {} permitted: {} provided: {} offset: {}",
342 kind, required, permitted, provided, offset
344 // We enforce the following: `required` <= `provided` <= `permitted`.
345 // For kinds without defaults (e.g.., lifetimes), `required == permitted`.
346 // For other kinds (i.e., types), `permitted` may be greater than `required`.
347 if required <= provided && provided <= permitted {
348 return (reported_late_bound_region_err.unwrap_or(false), None);
351 // Unfortunately lifetime and type parameter mismatches are typically styled
352 // differently in diagnostics, which means we have a few cases to consider here.
353 let (bound, quantifier) = if required != permitted {
354 if provided < required {
355 (required, "at least ")
357 // provided > permitted
358 (permitted, "at most ")
364 let mut potential_assoc_types: Option<Vec<Span>> = None;
365 let (spans, label) = if required == permitted && provided > permitted {
366 // In the case when the user has provided too many arguments,
367 // we want to point to the unexpected arguments.
368 let spans: Vec<Span> = args.args[offset + permitted..offset + provided]
370 .map(|arg| arg.span())
372 potential_assoc_types = Some(spans.clone());
373 (spans, format!("unexpected {} argument", kind))
378 "expected {}{} {} argument{}",
387 let mut err = tcx.sess.struct_span_err_with_code(
390 "wrong number of {} arguments: expected {}{}, found {}",
391 kind, quantifier, bound, provided,
393 DiagnosticId::Error("E0107".into()),
396 err.span_label(span, label.as_str());
401 provided > required, // `suppress_error`
402 potential_assoc_types,
406 if reported_late_bound_region_err.is_none()
407 && (!infer_lifetimes || arg_counts.lifetimes > param_counts.lifetimes)
411 param_counts.lifetimes,
412 param_counts.lifetimes,
413 arg_counts.lifetimes,
417 // FIXME(const_generics:defaults)
418 if !infer_args || arg_counts.consts > param_counts.consts {
424 arg_counts.lifetimes + arg_counts.types,
427 // Note that type errors are currently be emitted *after* const errors.
428 if !infer_args || arg_counts.types > param_counts.types - defaults.types - has_self as usize
432 param_counts.types - defaults.types - has_self as usize,
433 param_counts.types - has_self as usize,
435 arg_counts.lifetimes,
438 (reported_late_bound_region_err.unwrap_or(false), None)
442 /// Creates the relevant generic argument substitutions
443 /// corresponding to a set of generic parameters. This is a
444 /// rather complex function. Let us try to explain the role
445 /// of each of its parameters:
447 /// To start, we are given the `def_id` of the thing we are
448 /// creating the substitutions for, and a partial set of
449 /// substitutions `parent_substs`. In general, the substitutions
450 /// for an item begin with substitutions for all the "parents" of
451 /// that item -- e.g., for a method it might include the
452 /// parameters from the impl.
454 /// Therefore, the method begins by walking down these parents,
455 /// starting with the outermost parent and proceed inwards until
456 /// it reaches `def_id`. For each parent `P`, it will check `parent_substs`
457 /// first to see if the parent's substitutions are listed in there. If so,
458 /// we can append those and move on. Otherwise, it invokes the
459 /// three callback functions:
461 /// - `args_for_def_id`: given the `DefId` `P`, supplies back the
462 /// generic arguments that were given to that parent from within
463 /// the path; so e.g., if you have `<T as Foo>::Bar`, the `DefId`
464 /// might refer to the trait `Foo`, and the arguments might be
465 /// `[T]`. The boolean value indicates whether to infer values
466 /// for arguments whose values were not explicitly provided.
467 /// - `provided_kind`: given the generic parameter and the value from `args_for_def_id`,
468 /// instantiate a `GenericArg`.
469 /// - `inferred_kind`: if no parameter was provided, and inference is enabled, then
470 /// creates a suitable inference variable.
471 pub fn create_substs_for_generic_args<'b>(
474 parent_substs: &[subst::GenericArg<'tcx>],
476 self_ty: Option<Ty<'tcx>>,
477 args_for_def_id: impl Fn(DefId) -> (Option<&'b GenericArgs<'b>>, bool),
478 provided_kind: impl Fn(&GenericParamDef, &GenericArg<'_>) -> subst::GenericArg<'tcx>,
479 mut inferred_kind: impl FnMut(
480 Option<&[subst::GenericArg<'tcx>]>,
483 ) -> subst::GenericArg<'tcx>,
484 ) -> SubstsRef<'tcx> {
485 // Collect the segments of the path; we need to substitute arguments
486 // for parameters throughout the entire path (wherever there are
487 // generic parameters).
488 let mut parent_defs = tcx.generics_of(def_id);
489 let count = parent_defs.count();
490 let mut stack = vec![(def_id, parent_defs)];
491 while let Some(def_id) = parent_defs.parent {
492 parent_defs = tcx.generics_of(def_id);
493 stack.push((def_id, parent_defs));
496 // We manually build up the substitution, rather than using convenience
497 // methods in `subst.rs`, so that we can iterate over the arguments and
498 // parameters in lock-step linearly, instead of trying to match each pair.
499 let mut substs: SmallVec<[subst::GenericArg<'tcx>; 8]> = SmallVec::with_capacity(count);
501 // Iterate over each segment of the path.
502 while let Some((def_id, defs)) = stack.pop() {
503 let mut params = defs.params.iter().peekable();
505 // If we have already computed substitutions for parents, we can use those directly.
506 while let Some(¶m) = params.peek() {
507 if let Some(&kind) = parent_substs.get(param.index as usize) {
515 // `Self` is handled first, unless it's been handled in `parent_substs`.
517 if let Some(¶m) = params.peek() {
518 if param.index == 0 {
519 if let GenericParamDefKind::Type { .. } = param.kind {
523 .unwrap_or_else(|| inferred_kind(None, param, true)),
531 // Check whether this segment takes generic arguments and the user has provided any.
532 let (generic_args, infer_args) = args_for_def_id(def_id);
535 generic_args.iter().flat_map(|generic_args| generic_args.args.iter()).peekable();
538 // We're going to iterate through the generic arguments that the user
539 // provided, matching them with the generic parameters we expect.
540 // Mismatches can occur as a result of elided lifetimes, or for malformed
541 // input. We try to handle both sensibly.
542 match (args.peek(), params.peek()) {
543 (Some(&arg), Some(¶m)) => {
544 match (arg, ¶m.kind) {
545 (GenericArg::Lifetime(_), GenericParamDefKind::Lifetime)
546 | (GenericArg::Type(_), GenericParamDefKind::Type { .. })
547 | (GenericArg::Const(_), GenericParamDefKind::Const) => {
548 substs.push(provided_kind(param, arg));
552 (GenericArg::Type(_), GenericParamDefKind::Lifetime)
553 | (GenericArg::Const(_), GenericParamDefKind::Lifetime) => {
554 // We expected a lifetime argument, but got a type or const
555 // argument. That means we're inferring the lifetimes.
556 substs.push(inferred_kind(None, param, infer_args));
560 // We expected one kind of parameter, but the user provided
561 // another. This is an error, but we need to handle it
562 // gracefully so we can report sensible errors.
563 // In this case, we're simply going to infer this argument.
569 // We should never be able to reach this point with well-formed input.
570 // Getting to this point means the user supplied more arguments than
571 // there are parameters.
574 (None, Some(¶m)) => {
575 // If there are fewer arguments than parameters, it means
576 // we're inferring the remaining arguments.
577 substs.push(inferred_kind(Some(&substs), param, infer_args));
581 (None, None) => break,
586 tcx.intern_substs(&substs)
589 /// Given the type/lifetime/const arguments provided to some path (along with
590 /// an implicit `Self`, if this is a trait reference), returns the complete
591 /// set of substitutions. This may involve applying defaulted type parameters.
592 /// Also returns back constriants on associated types.
597 /// T: std::ops::Index<usize, Output = u32>
598 /// ^1 ^^^^^^^^^^^^^^2 ^^^^3 ^^^^^^^^^^^4
601 /// 1. The `self_ty` here would refer to the type `T`.
602 /// 2. The path in question is the path to the trait `std::ops::Index`,
603 /// which will have been resolved to a `def_id`
604 /// 3. The `generic_args` contains info on the `<...>` contents. The `usize` type
605 /// parameters are returned in the `SubstsRef`, the associated type bindings like
606 /// `Output = u32` are returned in the `Vec<ConvertedBinding...>` result.
608 /// Note that the type listing given here is *exactly* what the user provided.
610 /// For (generic) associated types
613 /// <Vec<u8> as Iterable<u8>>::Iter::<'a>
616 /// We have the parent substs are the substs for the parent trait:
617 /// `[Vec<u8>, u8]` and `generic_args` are the arguments for the associated
618 /// type itself: `['a]`. The returned `SubstsRef` concatenates these two
619 /// lists: `[Vec<u8>, u8, 'a]`.
620 fn create_substs_for_ast_path<'a>(
624 parent_substs: &[subst::GenericArg<'tcx>],
625 generic_args: &'a hir::GenericArgs<'_>,
627 self_ty: Option<Ty<'tcx>>,
628 ) -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'a, 'tcx>>, Option<Vec<Span>>) {
629 // If the type is parameterized by this region, then replace this
630 // region with the current anon region binding (in other words,
631 // whatever & would get replaced with).
633 "create_substs_for_ast_path(def_id={:?}, self_ty={:?}, \
635 def_id, self_ty, generic_args
638 let tcx = self.tcx();
639 let generic_params = tcx.generics_of(def_id);
641 if generic_params.has_self {
642 if generic_params.parent.is_some() {
643 // The parent is a trait so it should have at least one subst
644 // for the `Self` type.
645 assert!(!parent_substs.is_empty())
647 // This item (presumably a trait) needs a self-type.
648 assert!(self_ty.is_some());
651 assert!(self_ty.is_none() && parent_substs.is_empty());
654 let (_, potential_assoc_types) = Self::check_generic_arg_count(
659 GenericArgPosition::Type,
664 let is_object = self_ty.map_or(false, |ty| ty == self.tcx().types.trait_object_dummy_self);
665 let default_needs_object_self = |param: &ty::GenericParamDef| {
666 if let GenericParamDefKind::Type { has_default, .. } = param.kind {
667 if is_object && has_default {
668 let self_param = tcx.types.self_param;
669 if tcx.at(span).type_of(param.def_id).walk().any(|ty| ty == self_param) {
670 // There is no suitable inference default for a type parameter
671 // that references self, in an object type.
680 let mut missing_type_params = vec![];
681 let substs = Self::create_substs_for_generic_args(
687 // Provide the generic args, and whether types should be inferred.
688 |_| (Some(generic_args), infer_args),
689 // Provide substitutions for parameters for which (valid) arguments have been provided.
690 |param, arg| match (¶m.kind, arg) {
691 (GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => {
692 self.ast_region_to_region(<, Some(param)).into()
694 (GenericParamDefKind::Type { .. }, GenericArg::Type(ty)) => {
695 self.ast_ty_to_ty(&ty).into()
697 (GenericParamDefKind::Const, GenericArg::Const(ct)) => {
698 self.ast_const_to_const(&ct.value, tcx.type_of(param.def_id)).into()
702 // Provide substitutions for parameters for which arguments are inferred.
703 |substs, param, infer_args| {
705 GenericParamDefKind::Lifetime => tcx.lifetimes.re_static.into(),
706 GenericParamDefKind::Type { has_default, .. } => {
707 if !infer_args && has_default {
708 // No type parameter provided, but a default exists.
710 // If we are converting an object type, then the
711 // `Self` parameter is unknown. However, some of the
712 // other type parameters may reference `Self` in their
713 // defaults. This will lead to an ICE if we are not
715 if default_needs_object_self(param) {
716 missing_type_params.push(param.name.to_string());
719 // This is a default type parameter.
722 tcx.at(span).type_of(param.def_id).subst_spanned(
730 } else if infer_args {
731 // No type parameters were provided, we can infer all.
733 if !default_needs_object_self(param) { Some(param) } else { None };
734 self.ty_infer(param, span).into()
736 // We've already errored above about the mismatch.
740 GenericParamDefKind::Const => {
741 // FIXME(const_generics:defaults)
743 // No const parameters were provided, we can infer all.
744 let ty = tcx.at(span).type_of(param.def_id);
745 self.ct_infer(ty, Some(param), span).into()
747 // We've already errored above about the mismatch.
748 tcx.consts.err.into()
755 self.complain_about_missing_type_params(
759 generic_args.args.is_empty(),
762 // Convert associated-type bindings or constraints into a separate vector.
763 // Example: Given this:
765 // T: Iterator<Item = u32>
767 // The `T` is passed in as a self-type; the `Item = u32` is
768 // not a "type parameter" of the `Iterator` trait, but rather
769 // a restriction on `<T as Iterator>::Item`, so it is passed
771 let assoc_bindings = generic_args
775 let kind = match binding.kind {
776 hir::TypeBindingKind::Equality { ref ty } => {
777 ConvertedBindingKind::Equality(self.ast_ty_to_ty(ty))
779 hir::TypeBindingKind::Constraint { ref bounds } => {
780 ConvertedBindingKind::Constraint(bounds)
783 ConvertedBinding { item_name: binding.ident, kind, span: binding.span }
788 "create_substs_for_ast_path(generic_params={:?}, self_ty={:?}) -> {:?}",
789 generic_params, self_ty, substs
792 (substs, assoc_bindings, potential_assoc_types)
795 crate fn create_substs_for_associated_item(
800 item_segment: &hir::PathSegment<'_>,
801 parent_substs: SubstsRef<'tcx>,
802 ) -> SubstsRef<'tcx> {
803 if tcx.generics_of(item_def_id).params.is_empty() {
804 self.prohibit_generics(slice::from_ref(item_segment));
808 self.create_substs_for_ast_path(
812 item_segment.generic_args(),
813 item_segment.infer_args,
820 /// On missing type parameters, emit an E0393 error and provide a structured suggestion using
821 /// the type parameter's name as a placeholder.
822 fn complain_about_missing_type_params(
824 missing_type_params: Vec<String>,
827 empty_generic_args: bool,
829 if missing_type_params.is_empty() {
833 missing_type_params.iter().map(|n| format!("`{}`", n)).collect::<Vec<_>>().join(", ");
834 let mut err = struct_span_err!(
838 "the type parameter{} {} must be explicitly specified",
839 pluralize!(missing_type_params.len()),
843 self.tcx().def_span(def_id),
845 "type parameter{} {} must be specified for this",
846 pluralize!(missing_type_params.len()),
850 let mut suggested = false;
851 if let (Ok(snippet), true) = (
852 self.tcx().sess.source_map().span_to_snippet(span),
853 // Don't suggest setting the type params if there are some already: the order is
854 // tricky to get right and the user will already know what the syntax is.
857 if snippet.ends_with('>') {
858 // The user wrote `Trait<'a, T>` or similar. To provide an accurate suggestion
859 // we would have to preserve the right order. For now, as clearly the user is
860 // aware of the syntax, we do nothing.
862 // The user wrote `Iterator`, so we don't have a type we can suggest, but at
863 // least we can clue them to the correct syntax `Iterator<Type>`.
867 "set the type parameter{plural} to the desired type{plural}",
868 plural = pluralize!(missing_type_params.len()),
870 format!("{}<{}>", snippet, missing_type_params.join(", ")),
871 Applicability::HasPlaceholders,
880 "missing reference{} to {}",
881 pluralize!(missing_type_params.len()),
887 "because of the default `Self` reference, type parameters must be \
888 specified on object types"
893 /// Instantiates the path for the given trait reference, assuming that it's
894 /// bound to a valid trait type. Returns the `DefId` of the defining trait.
895 /// The type _cannot_ be a type other than a trait type.
897 /// If the `projections` argument is `None`, then assoc type bindings like `Foo<T = X>`
898 /// are disallowed. Otherwise, they are pushed onto the vector given.
899 pub fn instantiate_mono_trait_ref(
901 trait_ref: &hir::TraitRef<'_>,
903 ) -> ty::TraitRef<'tcx> {
904 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
906 self.ast_path_to_mono_trait_ref(
908 trait_ref.trait_def_id(),
910 trait_ref.path.segments.last().unwrap(),
914 /// The given trait-ref must actually be a trait.
915 pub(super) fn instantiate_poly_trait_ref_inner(
917 trait_ref: &hir::TraitRef<'_>,
920 bounds: &mut Bounds<'tcx>,
922 ) -> Option<Vec<Span>> {
923 let trait_def_id = trait_ref.trait_def_id();
925 debug!("instantiate_poly_trait_ref({:?}, def_id={:?})", trait_ref, trait_def_id);
927 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
929 let path_span = if let [segment] = &trait_ref.path.segments[..] {
930 // FIXME: `trait_ref.path.span` can point to a full path with multiple
931 // segments, even though `trait_ref.path.segments` is of length `1`. Work
932 // around that bug here, even though it should be fixed elsewhere.
933 // This would otherwise cause an invalid suggestion. For an example, look at
934 // `src/test/ui/issues/issue-28344.rs`.
939 let (substs, assoc_bindings, potential_assoc_types) = self.create_substs_for_ast_trait_ref(
943 trait_ref.path.segments.last().unwrap(),
945 let poly_trait_ref = ty::Binder::bind(ty::TraitRef::new(trait_def_id, substs));
947 bounds.trait_bounds.push((poly_trait_ref, span));
949 let mut dup_bindings = FxHashMap::default();
950 for binding in &assoc_bindings {
951 // Specify type to assert that error was already reported in `Err` case.
952 let _: Result<_, ErrorReported> = self.add_predicates_for_ast_type_binding(
953 trait_ref.hir_ref_id,
961 // Okay to ignore `Err` because of `ErrorReported` (see above).
965 "instantiate_poly_trait_ref({:?}, bounds={:?}) -> {:?}",
966 trait_ref, bounds, poly_trait_ref
968 potential_assoc_types
971 /// Given a trait bound like `Debug`, applies that trait bound the given self-type to construct
972 /// a full trait reference. The resulting trait reference is returned. This may also generate
973 /// auxiliary bounds, which are added to `bounds`.
978 /// poly_trait_ref = Iterator<Item = u32>
982 /// this would return `Foo: Iterator` and add `<Foo as Iterator>::Item = u32` into `bounds`.
984 /// **A note on binders:** against our usual convention, there is an implied bounder around
985 /// the `self_ty` and `poly_trait_ref` parameters here. So they may reference bound regions.
986 /// If for example you had `for<'a> Foo<'a>: Bar<'a>`, then the `self_ty` would be `Foo<'a>`
987 /// where `'a` is a bound region at depth 0. Similarly, the `poly_trait_ref` would be
988 /// `Bar<'a>`. The returned poly-trait-ref will have this binder instantiated explicitly,
990 pub fn instantiate_poly_trait_ref(
992 poly_trait_ref: &hir::PolyTraitRef<'_>,
994 bounds: &mut Bounds<'tcx>,
995 ) -> Option<Vec<Span>> {
996 self.instantiate_poly_trait_ref_inner(
997 &poly_trait_ref.trait_ref,
1005 fn ast_path_to_mono_trait_ref(
1008 trait_def_id: DefId,
1010 trait_segment: &hir::PathSegment<'_>,
1011 ) -> ty::TraitRef<'tcx> {
1012 let (substs, assoc_bindings, _) =
1013 self.create_substs_for_ast_trait_ref(span, trait_def_id, self_ty, trait_segment);
1014 assoc_bindings.first().map(|b| AstConv::prohibit_assoc_ty_binding(self.tcx(), b.span));
1015 ty::TraitRef::new(trait_def_id, substs)
1018 /// When the code is using the `Fn` traits directly, instead of the `Fn(A) -> B` syntax, emit
1019 /// an error and attempt to build a reasonable structured suggestion.
1020 fn complain_about_internal_fn_trait(
1023 trait_def_id: DefId,
1024 trait_segment: &'a hir::PathSegment<'a>,
1026 let trait_def = self.tcx().trait_def(trait_def_id);
1028 if !self.tcx().features().unboxed_closures
1029 && trait_segment.generic_args().parenthesized != trait_def.paren_sugar
1031 // For now, require that parenthetical notation be used only with `Fn()` etc.
1032 let (msg, sugg) = if trait_def.paren_sugar {
1034 "the precise format of `Fn`-family traits' type parameters is subject to \
1038 trait_segment.ident,
1042 .and_then(|args| args.args.get(0))
1043 .and_then(|arg| match arg {
1044 hir::GenericArg::Type(ty) => {
1045 Some(print::to_string(print::NO_ANN, |s| s.print_type(ty)))
1049 .unwrap_or_else(|| "()".to_string()),
1054 .filter_map(|b| match (b.ident.as_str() == "Output", &b.kind) {
1055 (true, hir::TypeBindingKind::Equality { ty }) => {
1056 Some(print::to_string(print::NO_ANN, |s| s.print_type(ty)))
1061 .unwrap_or_else(|| "()".to_string()),
1065 ("parenthetical notation is only stable when used with `Fn`-family traits", None)
1067 let sess = &self.tcx().sess.parse_sess;
1068 let mut err = feature_err(sess, sym::unboxed_closures, span, msg);
1069 if let Some(sugg) = sugg {
1070 let msg = "use parenthetical notation instead";
1071 err.span_suggestion(span, msg, sugg, Applicability::MaybeIncorrect);
1077 fn create_substs_for_ast_trait_ref<'a>(
1080 trait_def_id: DefId,
1082 trait_segment: &'a hir::PathSegment<'a>,
1083 ) -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'a, 'tcx>>, Option<Vec<Span>>) {
1084 debug!("create_substs_for_ast_trait_ref(trait_segment={:?})", trait_segment);
1086 self.complain_about_internal_fn_trait(span, trait_def_id, trait_segment);
1088 self.create_substs_for_ast_path(
1092 trait_segment.generic_args(),
1093 trait_segment.infer_args,
1098 fn trait_defines_associated_type_named(
1100 trait_def_id: DefId,
1101 assoc_name: ast::Ident,
1103 self.tcx().associated_items(trait_def_id).any(|item| {
1104 item.kind == ty::AssocKind::Type
1105 && self.tcx().hygienic_eq(assoc_name, item.ident, trait_def_id)
1109 // Returns `true` if a bounds list includes `?Sized`.
1110 pub fn is_unsized(&self, ast_bounds: &[hir::GenericBound<'_>], span: Span) -> bool {
1111 let tcx = self.tcx();
1113 // Try to find an unbound in bounds.
1114 let mut unbound = None;
1115 for ab in ast_bounds {
1116 if let &hir::GenericBound::Trait(ref ptr, hir::TraitBoundModifier::Maybe) = ab {
1117 if unbound.is_none() {
1118 unbound = Some(&ptr.trait_ref);
1124 "type parameter has more than one relaxed default \
1125 bound, only one is supported"
1131 let kind_id = tcx.lang_items().require(SizedTraitLangItem);
1134 // FIXME(#8559) currently requires the unbound to be built-in.
1135 if let Ok(kind_id) = kind_id {
1136 if tpb.path.res != Res::Def(DefKind::Trait, kind_id) {
1139 "default bound relaxed for a type parameter, but \
1140 this does nothing because the given bound is not \
1141 a default; only `?Sized` is supported",
1146 _ if kind_id.is_ok() => {
1149 // No lang item for `Sized`, so we can't add it as a bound.
1156 /// This helper takes a *converted* parameter type (`param_ty`)
1157 /// and an *unconverted* list of bounds:
1160 /// fn foo<T: Debug>
1161 /// ^ ^^^^^ `ast_bounds` parameter, in HIR form
1163 /// `param_ty`, in ty form
1166 /// It adds these `ast_bounds` into the `bounds` structure.
1168 /// **A note on binders:** there is an implied binder around
1169 /// `param_ty` and `ast_bounds`. See `instantiate_poly_trait_ref`
1170 /// for more details.
1174 ast_bounds: &[hir::GenericBound<'_>],
1175 bounds: &mut Bounds<'tcx>,
1177 let mut trait_bounds = Vec::new();
1178 let mut region_bounds = Vec::new();
1180 for ast_bound in ast_bounds {
1182 hir::GenericBound::Trait(ref b, hir::TraitBoundModifier::None) => {
1183 trait_bounds.push(b)
1185 hir::GenericBound::Trait(_, hir::TraitBoundModifier::Maybe) => {}
1186 hir::GenericBound::Outlives(ref l) => region_bounds.push(l),
1190 for bound in trait_bounds {
1191 let _ = self.instantiate_poly_trait_ref(bound, param_ty, bounds);
1194 bounds.region_bounds.extend(
1195 region_bounds.into_iter().map(|r| (self.ast_region_to_region(r, None), r.span)),
1199 /// Translates a list of bounds from the HIR into the `Bounds` data structure.
1200 /// The self-type for the bounds is given by `param_ty`.
1205 /// fn foo<T: Bar + Baz>() { }
1206 /// ^ ^^^^^^^^^ ast_bounds
1210 /// The `sized_by_default` parameter indicates if, in this context, the `param_ty` should be
1211 /// considered `Sized` unless there is an explicit `?Sized` bound. This would be true in the
1212 /// example above, but is not true in supertrait listings like `trait Foo: Bar + Baz`.
1214 /// `span` should be the declaration size of the parameter.
1215 pub fn compute_bounds(
1218 ast_bounds: &[hir::GenericBound<'_>],
1219 sized_by_default: SizedByDefault,
1222 let mut bounds = Bounds::default();
1224 self.add_bounds(param_ty, ast_bounds, &mut bounds);
1225 bounds.trait_bounds.sort_by_key(|(t, _)| t.def_id());
1227 bounds.implicitly_sized = if let SizedByDefault::Yes = sized_by_default {
1228 if !self.is_unsized(ast_bounds, span) { Some(span) } else { None }
1236 /// Given an HIR binding like `Item = Foo` or `Item: Foo`, pushes the corresponding predicates
1239 /// **A note on binders:** given something like `T: for<'a> Iterator<Item = &'a u32>`, the
1240 /// `trait_ref` here will be `for<'a> T: Iterator`. The `binding` data however is from *inside*
1241 /// the binder (e.g., `&'a u32`) and hence may reference bound regions.
1242 fn add_predicates_for_ast_type_binding(
1244 hir_ref_id: hir::HirId,
1245 trait_ref: ty::PolyTraitRef<'tcx>,
1246 binding: &ConvertedBinding<'_, 'tcx>,
1247 bounds: &mut Bounds<'tcx>,
1249 dup_bindings: &mut FxHashMap<DefId, Span>,
1251 ) -> Result<(), ErrorReported> {
1252 let tcx = self.tcx();
1255 // Given something like `U: SomeTrait<T = X>`, we want to produce a
1256 // predicate like `<U as SomeTrait>::T = X`. This is somewhat
1257 // subtle in the event that `T` is defined in a supertrait of
1258 // `SomeTrait`, because in that case we need to upcast.
1260 // That is, consider this case:
1263 // trait SubTrait: SuperTrait<int> { }
1264 // trait SuperTrait<A> { type T; }
1266 // ... B: SubTrait<T = foo> ...
1269 // We want to produce `<B as SuperTrait<int>>::T == foo`.
1271 // Find any late-bound regions declared in `ty` that are not
1272 // declared in the trait-ref. These are not well-formed.
1276 // for<'a> <T as Iterator>::Item = &'a str // <-- 'a is bad
1277 // for<'a> <T as FnMut<(&'a u32,)>>::Output = &'a str // <-- 'a is ok
1278 if let ConvertedBindingKind::Equality(ty) = binding.kind {
1279 let late_bound_in_trait_ref =
1280 tcx.collect_constrained_late_bound_regions(&trait_ref);
1281 let late_bound_in_ty =
1282 tcx.collect_referenced_late_bound_regions(&ty::Binder::bind(ty));
1283 debug!("late_bound_in_trait_ref = {:?}", late_bound_in_trait_ref);
1284 debug!("late_bound_in_ty = {:?}", late_bound_in_ty);
1285 for br in late_bound_in_ty.difference(&late_bound_in_trait_ref) {
1286 let br_name = match *br {
1287 ty::BrNamed(_, name) => name,
1291 "anonymous bound region {:?} in binding but not trait ref",
1300 "binding for associated type `{}` references lifetime `{}`, \
1301 which does not appear in the trait input types",
1311 if self.trait_defines_associated_type_named(trait_ref.def_id(), binding.item_name) {
1312 // Simple case: X is defined in the current trait.
1315 // Otherwise, we have to walk through the supertraits to find
1317 self.one_bound_for_assoc_type(
1318 || traits::supertraits(tcx, trait_ref),
1319 &trait_ref.print_only_trait_path().to_string(),
1322 match binding.kind {
1323 ConvertedBindingKind::Equality(ty) => Some(ty.to_string()),
1329 let (assoc_ident, def_scope) =
1330 tcx.adjust_ident_and_get_scope(binding.item_name, candidate.def_id(), hir_ref_id);
1332 .associated_items(candidate.def_id())
1333 .find(|i| i.kind == ty::AssocKind::Type && i.ident.modern() == assoc_ident)
1334 .expect("missing associated type");
1336 if !assoc_ty.vis.is_accessible_from(def_scope, tcx) {
1337 let msg = format!("associated type `{}` is private", binding.item_name);
1338 tcx.sess.span_err(binding.span, &msg);
1340 tcx.check_stability(assoc_ty.def_id, Some(hir_ref_id), binding.span);
1344 .entry(assoc_ty.def_id)
1345 .and_modify(|prev_span| {
1350 "the value of the associated type `{}` (from trait `{}`) \
1351 is already specified",
1353 tcx.def_path_str(assoc_ty.container.id())
1355 .span_label(binding.span, "re-bound here")
1356 .span_label(*prev_span, format!("`{}` bound here first", binding.item_name))
1359 .or_insert(binding.span);
1362 match binding.kind {
1363 ConvertedBindingKind::Equality(ref ty) => {
1364 // "Desugar" a constraint like `T: Iterator<Item = u32>` this to
1365 // the "projection predicate" for:
1367 // `<T as Iterator>::Item = u32`
1368 bounds.projection_bounds.push((
1369 candidate.map_bound(|trait_ref| ty::ProjectionPredicate {
1370 projection_ty: ty::ProjectionTy::from_ref_and_name(
1380 ConvertedBindingKind::Constraint(ast_bounds) => {
1381 // "Desugar" a constraint like `T: Iterator<Item: Debug>` to
1383 // `<T as Iterator>::Item: Debug`
1385 // Calling `skip_binder` is okay, because `add_bounds` expects the `param_ty`
1386 // parameter to have a skipped binder.
1387 let param_ty = tcx.mk_projection(assoc_ty.def_id, candidate.skip_binder().substs);
1388 self.add_bounds(param_ty, ast_bounds, bounds);
1398 item_segment: &hir::PathSegment<'_>,
1400 let substs = self.ast_path_substs_for_ty(span, did, item_segment);
1401 self.normalize_ty(span, self.tcx().at(span).type_of(did).subst(self.tcx(), substs))
1404 fn conv_object_ty_poly_trait_ref(
1407 trait_bounds: &[hir::PolyTraitRef<'_>],
1408 lifetime: &hir::Lifetime,
1410 let tcx = self.tcx();
1412 let mut bounds = Bounds::default();
1413 let mut potential_assoc_types = Vec::new();
1414 let dummy_self = self.tcx().types.trait_object_dummy_self;
1415 for trait_bound in trait_bounds.iter().rev() {
1416 let cur_potential_assoc_types =
1417 self.instantiate_poly_trait_ref(trait_bound, dummy_self, &mut bounds);
1418 potential_assoc_types.extend(cur_potential_assoc_types.into_iter().flatten());
1421 // Expand trait aliases recursively and check that only one regular (non-auto) trait
1422 // is used and no 'maybe' bounds are used.
1423 let expanded_traits =
1424 traits::expand_trait_aliases(tcx, bounds.trait_bounds.iter().cloned());
1425 let (mut auto_traits, regular_traits): (Vec<_>, Vec<_>) =
1426 expanded_traits.partition(|i| tcx.trait_is_auto(i.trait_ref().def_id()));
1427 if regular_traits.len() > 1 {
1428 let first_trait = ®ular_traits[0];
1429 let additional_trait = ®ular_traits[1];
1430 let mut err = struct_span_err!(
1432 additional_trait.bottom().1,
1434 "only auto traits can be used as additional traits in a trait object"
1436 additional_trait.label_with_exp_info(
1438 "additional non-auto trait",
1441 first_trait.label_with_exp_info(&mut err, "first non-auto trait", "first use");
1445 if regular_traits.is_empty() && auto_traits.is_empty() {
1446 span_err!(tcx.sess, span, E0224, "at least one trait is required for an object type");
1447 return tcx.types.err;
1450 // Check that there are no gross object safety violations;
1451 // most importantly, that the supertraits don't contain `Self`,
1453 for item in ®ular_traits {
1454 let object_safety_violations =
1455 tcx.astconv_object_safety_violations(item.trait_ref().def_id());
1456 if !object_safety_violations.is_empty() {
1457 tcx.report_object_safety_error(
1459 item.trait_ref().def_id(),
1460 object_safety_violations,
1463 return tcx.types.err;
1467 // Use a `BTreeSet` to keep output in a more consistent order.
1468 let mut associated_types: FxHashMap<Span, BTreeSet<DefId>> = FxHashMap::default();
1470 let regular_traits_refs_spans = bounds
1473 .filter(|(trait_ref, _)| !tcx.trait_is_auto(trait_ref.def_id()));
1475 for (base_trait_ref, span) in regular_traits_refs_spans {
1476 for trait_ref in traits::elaborate_trait_ref(tcx, base_trait_ref) {
1478 "conv_object_ty_poly_trait_ref: observing object predicate `{:?}`",
1482 ty::Predicate::Trait(pred) => {
1483 associated_types.entry(span).or_default().extend(
1484 tcx.associated_items(pred.def_id())
1485 .filter(|item| item.kind == ty::AssocKind::Type)
1486 .map(|item| item.def_id),
1489 ty::Predicate::Projection(pred) => {
1490 // A `Self` within the original bound will be substituted with a
1491 // `trait_object_dummy_self`, so check for that.
1492 let references_self = pred.skip_binder().ty.walk().any(|t| t == dummy_self);
1494 // If the projection output contains `Self`, force the user to
1495 // elaborate it explicitly to avoid a lot of complexity.
1497 // The "classicaly useful" case is the following:
1499 // trait MyTrait: FnMut() -> <Self as MyTrait>::MyOutput {
1504 // Here, the user could theoretically write `dyn MyTrait<Output = X>`,
1505 // but actually supporting that would "expand" to an infinitely-long type
1506 // `fix $ τ → dyn MyTrait<MyOutput = X, Output = <τ as MyTrait>::MyOutput`.
1508 // Instead, we force the user to write
1509 // `dyn MyTrait<MyOutput = X, Output = X>`, which is uglier but works. See
1510 // the discussion in #56288 for alternatives.
1511 if !references_self {
1512 // Include projections defined on supertraits.
1513 bounds.projection_bounds.push((pred, span));
1521 for (projection_bound, _) in &bounds.projection_bounds {
1522 for (_, def_ids) in &mut associated_types {
1523 def_ids.remove(&projection_bound.projection_def_id());
1527 self.complain_about_missing_associated_types(
1529 potential_assoc_types,
1533 // De-duplicate auto traits so that, e.g., `dyn Trait + Send + Send` is the same as
1534 // `dyn Trait + Send`.
1535 auto_traits.sort_by_key(|i| i.trait_ref().def_id());
1536 auto_traits.dedup_by_key(|i| i.trait_ref().def_id());
1537 debug!("regular_traits: {:?}", regular_traits);
1538 debug!("auto_traits: {:?}", auto_traits);
1540 // Transform a `PolyTraitRef` into a `PolyExistentialTraitRef` by
1541 // removing the dummy `Self` type (`trait_object_dummy_self`).
1542 let trait_ref_to_existential = |trait_ref: ty::TraitRef<'tcx>| {
1543 if trait_ref.self_ty() != dummy_self {
1544 // FIXME: There appears to be a missing filter on top of `expand_trait_aliases`,
1545 // which picks up non-supertraits where clauses - but also, the object safety
1546 // completely ignores trait aliases, which could be object safety hazards. We
1547 // `delay_span_bug` here to avoid an ICE in stable even when the feature is
1548 // disabled. (#66420)
1549 tcx.sess.delay_span_bug(
1552 "trait_ref_to_existential called on {:?} with non-dummy Self",
1557 ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref)
1560 // Erase the `dummy_self` (`trait_object_dummy_self`) used above.
1561 let existential_trait_refs = regular_traits
1563 .map(|i| i.trait_ref().map_bound(|trait_ref| trait_ref_to_existential(trait_ref)));
1564 let existential_projections = bounds.projection_bounds.iter().map(|(bound, _)| {
1565 bound.map_bound(|b| {
1566 let trait_ref = trait_ref_to_existential(b.projection_ty.trait_ref(tcx));
1567 ty::ExistentialProjection {
1569 item_def_id: b.projection_ty.item_def_id,
1570 substs: trait_ref.substs,
1575 // Calling `skip_binder` is okay because the predicates are re-bound.
1576 let regular_trait_predicates = existential_trait_refs
1577 .map(|trait_ref| ty::ExistentialPredicate::Trait(*trait_ref.skip_binder()));
1578 let auto_trait_predicates = auto_traits
1580 .map(|trait_ref| ty::ExistentialPredicate::AutoTrait(trait_ref.trait_ref().def_id()));
1581 let mut v = regular_trait_predicates
1582 .chain(auto_trait_predicates)
1584 existential_projections
1585 .map(|x| ty::ExistentialPredicate::Projection(*x.skip_binder())),
1587 .collect::<SmallVec<[_; 8]>>();
1588 v.sort_by(|a, b| a.stable_cmp(tcx, b));
1590 let existential_predicates = ty::Binder::bind(tcx.mk_existential_predicates(v.into_iter()));
1592 // Use explicitly-specified region bound.
1593 let region_bound = if !lifetime.is_elided() {
1594 self.ast_region_to_region(lifetime, None)
1596 self.compute_object_lifetime_bound(span, existential_predicates).unwrap_or_else(|| {
1597 if tcx.named_region(lifetime.hir_id).is_some() {
1598 self.ast_region_to_region(lifetime, None)
1600 self.re_infer(None, span).unwrap_or_else(|| {
1605 "the lifetime bound for this object type cannot be deduced \
1606 from context; please supply an explicit bound"
1608 tcx.lifetimes.re_static
1613 debug!("region_bound: {:?}", region_bound);
1615 let ty = tcx.mk_dynamic(existential_predicates, region_bound);
1616 debug!("trait_object_type: {:?}", ty);
1620 /// When there are any missing associated types, emit an E0191 error and attempt to supply a
1621 /// reasonable suggestion on how to write it. For the case of multiple associated types in the
1622 /// same trait bound have the same name (as they come from different super-traits), we instead
1623 /// emit a generic note suggesting using a `where` clause to constraint instead.
1624 fn complain_about_missing_associated_types(
1626 associated_types: FxHashMap<Span, BTreeSet<DefId>>,
1627 potential_assoc_types: Vec<Span>,
1628 trait_bounds: &[hir::PolyTraitRef<'_>],
1630 if !associated_types.values().any(|v| v.len() > 0) {
1633 let tcx = self.tcx();
1634 // FIXME: Marked `mut` so that we can replace the spans further below with a more
1635 // appropriate one, but this should be handled earlier in the span assignment.
1636 let mut associated_types: FxHashMap<Span, Vec<_>> = associated_types
1638 .map(|(span, def_ids)| {
1639 (span, def_ids.into_iter().map(|did| tcx.associated_item(did)).collect())
1642 let mut names = vec![];
1644 // Account for things like `dyn Foo + 'a`, like in tests `issue-22434.rs` and
1645 // `issue-22560.rs`.
1646 let mut trait_bound_spans: Vec<Span> = vec![];
1647 for (span, items) in &associated_types {
1648 if !items.is_empty() {
1649 trait_bound_spans.push(*span);
1651 for assoc_item in items {
1652 let trait_def_id = assoc_item.container.id();
1654 "`{}` (from trait `{}`)",
1656 tcx.def_path_str(trait_def_id),
1661 match (&potential_assoc_types[..], &trait_bounds) {
1662 ([], [bound]) => match &bound.trait_ref.path.segments[..] {
1663 // FIXME: `trait_ref.path.span` can point to a full path with multiple
1664 // segments, even though `trait_ref.path.segments` is of length `1`. Work
1665 // around that bug here, even though it should be fixed elsewhere.
1666 // This would otherwise cause an invalid suggestion. For an example, look at
1667 // `src/test/ui/issues/issue-28344.rs` where instead of the following:
1669 // error[E0191]: the value of the associated type `Output`
1670 // (from trait `std::ops::BitXor`) must be specified
1671 // --> $DIR/issue-28344.rs:4:17
1673 // LL | let x: u8 = BitXor::bitor(0 as u8, 0 as u8);
1674 // | ^^^^^^ help: specify the associated type:
1675 // | `BitXor<Output = Type>`
1679 // error[E0191]: the value of the associated type `Output`
1680 // (from trait `std::ops::BitXor`) must be specified
1681 // --> $DIR/issue-28344.rs:4:17
1683 // LL | let x: u8 = BitXor::bitor(0 as u8, 0 as u8);
1684 // | ^^^^^^^^^^^^^ help: specify the associated type:
1685 // | `BitXor::bitor<Output = Type>`
1686 [segment] if segment.args.is_none() => {
1687 trait_bound_spans = vec![segment.ident.span];
1688 associated_types = associated_types
1690 .map(|(_, items)| (segment.ident.span, items))
1698 trait_bound_spans.sort();
1699 let mut err = struct_span_err!(
1703 "the value of the associated type{} {} must be specified",
1704 pluralize!(names.len()),
1707 let mut suggestions = vec![];
1708 let mut types_count = 0;
1709 let mut where_constraints = vec![];
1710 for (span, assoc_items) in &associated_types {
1711 let mut names: FxHashMap<_, usize> = FxHashMap::default();
1712 for item in assoc_items {
1714 *names.entry(item.ident.name).or_insert(0) += 1;
1716 let mut dupes = false;
1717 for item in assoc_items {
1718 let prefix = if names[&item.ident.name] > 1 {
1719 let trait_def_id = item.container.id();
1721 format!("{}::", tcx.def_path_str(trait_def_id))
1725 if let Some(sp) = tcx.hir().span_if_local(item.def_id) {
1726 err.span_label(sp, format!("`{}{}` defined here", prefix, item.ident));
1729 if potential_assoc_types.len() == assoc_items.len() {
1730 // Only suggest when the amount of missing associated types equals the number of
1731 // extra type arguments present, as that gives us a relatively high confidence
1732 // that the user forgot to give the associtated type's name. The canonical
1733 // example would be trying to use `Iterator<isize>` instead of
1734 // `Iterator<Item = isize>`.
1735 for (potential, item) in potential_assoc_types.iter().zip(assoc_items.iter()) {
1736 if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(*potential) {
1737 suggestions.push((*potential, format!("{} = {}", item.ident, snippet)));
1740 } else if let (Ok(snippet), false) =
1741 (tcx.sess.source_map().span_to_snippet(*span), dupes)
1744 assoc_items.iter().map(|item| format!("{} = Type", item.ident)).collect();
1745 let code = if snippet.ends_with(">") {
1746 // The user wrote `Trait<'a>` or similar and we don't have a type we can
1747 // suggest, but at least we can clue them to the correct syntax
1748 // `Trait<'a, Item = Type>` while accounting for the `<'a>` in the
1750 format!("{}, {}>", &snippet[..snippet.len() - 1], types.join(", "))
1752 // The user wrote `Iterator`, so we don't have a type we can suggest, but at
1753 // least we can clue them to the correct syntax `Iterator<Item = Type>`.
1754 format!("{}<{}>", snippet, types.join(", "))
1756 suggestions.push((*span, code));
1758 where_constraints.push(*span);
1761 let where_msg = "consider introducing a new type parameter, adding `where` constraints \
1762 using the fully-qualified path to the associated types";
1763 if !where_constraints.is_empty() && suggestions.is_empty() {
1764 // If there are duplicates associated type names and a single trait bound do not
1765 // use structured suggestion, it means that there are multiple super-traits with
1766 // the same associated type name.
1767 err.help(where_msg);
1769 if suggestions.len() != 1 {
1770 // We don't need this label if there's an inline suggestion, show otherwise.
1771 for (span, assoc_items) in &associated_types {
1772 let mut names: FxHashMap<_, usize> = FxHashMap::default();
1773 for item in assoc_items {
1775 *names.entry(item.ident.name).or_insert(0) += 1;
1777 let mut label = vec![];
1778 for item in assoc_items {
1779 let postfix = if names[&item.ident.name] > 1 {
1780 let trait_def_id = item.container.id();
1781 format!(" (from trait `{}`)", tcx.def_path_str(trait_def_id))
1785 label.push(format!("`{}`{}", item.ident, postfix));
1787 if !label.is_empty() {
1791 "associated type{} {} must be specified",
1792 pluralize!(label.len()),
1799 if !suggestions.is_empty() {
1800 err.multipart_suggestion(
1801 &format!("specify the associated type{}", pluralize!(types_count)),
1803 Applicability::HasPlaceholders,
1805 if !where_constraints.is_empty() {
1806 err.span_help(where_constraints, where_msg);
1812 fn report_ambiguous_associated_type(
1819 let mut err = struct_span_err!(self.tcx().sess, span, E0223, "ambiguous associated type");
1820 if let (Some(_), Ok(snippet)) = (
1821 self.tcx().sess.confused_type_with_std_module.borrow().get(&span),
1822 self.tcx().sess.source_map().span_to_snippet(span),
1824 err.span_suggestion(
1826 "you are looking for the module in `std`, not the primitive type",
1827 format!("std::{}", snippet),
1828 Applicability::MachineApplicable,
1831 err.span_suggestion(
1833 "use fully-qualified syntax",
1834 format!("<{} as {}>::{}", type_str, trait_str, name),
1835 Applicability::HasPlaceholders,
1841 // Search for a bound on a type parameter which includes the associated item
1842 // given by `assoc_name`. `ty_param_def_id` is the `DefId` of the type parameter
1843 // This function will fail if there are no suitable bounds or there is
1845 fn find_bound_for_assoc_item(
1847 ty_param_def_id: DefId,
1848 assoc_name: ast::Ident,
1850 ) -> Result<ty::PolyTraitRef<'tcx>, ErrorReported> {
1851 let tcx = self.tcx();
1854 "find_bound_for_assoc_item(ty_param_def_id={:?}, assoc_name={:?}, span={:?})",
1855 ty_param_def_id, assoc_name, span,
1858 let predicates = &self.get_type_parameter_bounds(span, ty_param_def_id).predicates;
1860 debug!("find_bound_for_assoc_item: predicates={:#?}", predicates);
1862 let param_hir_id = tcx.hir().as_local_hir_id(ty_param_def_id).unwrap();
1863 let param_name = tcx.hir().ty_param_name(param_hir_id);
1864 self.one_bound_for_assoc_type(
1866 traits::transitive_bounds(
1868 predicates.iter().filter_map(|(p, _)| p.to_opt_poly_trait_ref()),
1871 ¶m_name.as_str(),
1878 // Checks that `bounds` contains exactly one element and reports appropriate
1879 // errors otherwise.
1880 fn one_bound_for_assoc_type<I>(
1882 all_candidates: impl Fn() -> I,
1883 ty_param_name: &str,
1884 assoc_name: ast::Ident,
1886 is_equality: Option<String>,
1887 ) -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
1889 I: Iterator<Item = ty::PolyTraitRef<'tcx>>,
1891 let mut matching_candidates = all_candidates()
1892 .filter(|r| self.trait_defines_associated_type_named(r.def_id(), assoc_name));
1894 let bound = match matching_candidates.next() {
1895 Some(bound) => bound,
1897 self.complain_about_assoc_type_not_found(
1903 return Err(ErrorReported);
1907 debug!("one_bound_for_assoc_type: bound = {:?}", bound);
1909 if let Some(bound2) = matching_candidates.next() {
1910 debug!("one_bound_for_assoc_type: bound2 = {:?}", bound2);
1912 let bounds = iter::once(bound).chain(iter::once(bound2)).chain(matching_candidates);
1913 let mut err = if is_equality.is_some() {
1914 // More specific Error Index entry.
1919 "ambiguous associated type `{}` in bounds of `{}`",
1928 "ambiguous associated type `{}` in bounds of `{}`",
1933 err.span_label(span, format!("ambiguous associated type `{}`", assoc_name));
1935 let mut where_bounds = vec![];
1936 for bound in bounds {
1937 let bound_span = self
1939 .associated_items(bound.def_id())
1941 item.kind == ty::AssocKind::Type
1942 && self.tcx().hygienic_eq(assoc_name, item.ident, bound.def_id())
1944 .and_then(|item| self.tcx().hir().span_if_local(item.def_id));
1946 if let Some(bound_span) = bound_span {
1950 "ambiguous `{}` from `{}`",
1952 bound.print_only_trait_path(),
1955 if let Some(constraint) = &is_equality {
1956 where_bounds.push(format!(
1957 " T: {trait}::{assoc} = {constraint}",
1958 trait=bound.print_only_trait_path(),
1960 constraint=constraint,
1963 err.span_suggestion(
1965 "use fully qualified syntax to disambiguate",
1969 bound.print_only_trait_path(),
1972 Applicability::MaybeIncorrect,
1977 "associated type `{}` could derive from `{}`",
1979 bound.print_only_trait_path(),
1983 if !where_bounds.is_empty() {
1985 "consider introducing a new type parameter `T` and adding `where` constraints:\
1986 \n where\n T: {},\n{}",
1988 where_bounds.join(",\n"),
1992 if !where_bounds.is_empty() {
1993 return Err(ErrorReported);
1999 fn complain_about_assoc_type_not_found<I>(
2001 all_candidates: impl Fn() -> I,
2002 ty_param_name: &str,
2003 assoc_name: ast::Ident,
2006 I: Iterator<Item = ty::PolyTraitRef<'tcx>>,
2008 // The fallback span is needed because `assoc_name` might be an `Fn()`'s `Output` without a
2009 // valid span, so we point at the whole path segment instead.
2010 let span = if assoc_name.span != DUMMY_SP { assoc_name.span } else { span };
2011 let mut err = struct_span_err!(
2015 "associated type `{}` not found for `{}`",
2020 let all_candidate_names: Vec<_> = all_candidates()
2021 .map(|r| self.tcx().associated_items(r.def_id()))
2024 |item| if item.kind == ty::AssocKind::Type { Some(item.ident.name) } else { None },
2028 if let (Some(suggested_name), true) = (
2029 find_best_match_for_name(all_candidate_names.iter(), &assoc_name.as_str(), None),
2030 assoc_name.span != DUMMY_SP,
2032 err.span_suggestion(
2034 "there is an associated type with a similar name",
2035 suggested_name.to_string(),
2036 Applicability::MaybeIncorrect,
2039 err.span_label(span, format!("associated type `{}` not found", assoc_name));
2045 // Create a type from a path to an associated type.
2046 // For a path `A::B::C::D`, `qself_ty` and `qself_def` are the type and def for `A::B::C`
2047 // and item_segment is the path segment for `D`. We return a type and a def for
2049 // Will fail except for `T::A` and `Self::A`; i.e., if `qself_ty`/`qself_def` are not a type
2050 // parameter or `Self`.
2051 pub fn associated_path_to_ty(
2053 hir_ref_id: hir::HirId,
2057 assoc_segment: &hir::PathSegment<'_>,
2058 permit_variants: bool,
2059 ) -> Result<(Ty<'tcx>, DefKind, DefId), ErrorReported> {
2060 let tcx = self.tcx();
2061 let assoc_ident = assoc_segment.ident;
2063 debug!("associated_path_to_ty: {:?}::{}", qself_ty, assoc_ident);
2065 // Check if we have an enum variant.
2066 let mut variant_resolution = None;
2067 if let ty::Adt(adt_def, _) = qself_ty.kind {
2068 if adt_def.is_enum() {
2069 let variant_def = adt_def
2072 .find(|vd| tcx.hygienic_eq(assoc_ident, vd.ident, adt_def.did));
2073 if let Some(variant_def) = variant_def {
2074 if permit_variants {
2075 tcx.check_stability(variant_def.def_id, Some(hir_ref_id), span);
2076 self.prohibit_generics(slice::from_ref(assoc_segment));
2077 return Ok((qself_ty, DefKind::Variant, variant_def.def_id));
2079 variant_resolution = Some(variant_def.def_id);
2085 // Find the type of the associated item, and the trait where the associated
2086 // item is declared.
2087 let bound = match (&qself_ty.kind, qself_res) {
2088 (_, Res::SelfTy(Some(_), Some(impl_def_id))) => {
2089 // `Self` in an impl of a trait -- we have a concrete self type and a
2091 let trait_ref = match tcx.impl_trait_ref(impl_def_id) {
2092 Some(trait_ref) => trait_ref,
2094 // A cycle error occurred, most likely.
2095 return Err(ErrorReported);
2099 self.one_bound_for_assoc_type(
2100 || traits::supertraits(tcx, ty::Binder::bind(trait_ref)),
2107 (&ty::Param(_), Res::SelfTy(Some(param_did), None))
2108 | (&ty::Param(_), Res::Def(DefKind::TyParam, param_did)) => {
2109 self.find_bound_for_assoc_item(param_did, assoc_ident, span)?
2112 if variant_resolution.is_some() {
2113 // Variant in type position
2114 let msg = format!("expected type, found variant `{}`", assoc_ident);
2115 tcx.sess.span_err(span, &msg);
2116 } else if qself_ty.is_enum() {
2117 let mut err = tcx.sess.struct_span_err(
2119 &format!("no variant `{}` in enum `{}`", assoc_ident, qself_ty),
2122 let adt_def = qself_ty.ty_adt_def().expect("enum is not an ADT");
2123 if let Some(suggested_name) = find_best_match_for_name(
2124 adt_def.variants.iter().map(|variant| &variant.ident.name),
2125 &assoc_ident.as_str(),
2128 err.span_suggestion(
2130 "there is a variant with a similar name",
2131 suggested_name.to_string(),
2132 Applicability::MaybeIncorrect,
2137 format!("variant not found in `{}`", qself_ty),
2141 if let Some(sp) = tcx.hir().span_if_local(adt_def.did) {
2142 let sp = tcx.sess.source_map().def_span(sp);
2143 err.span_label(sp, format!("variant `{}` not found here", assoc_ident));
2147 } else if !qself_ty.references_error() {
2148 // Don't print `TyErr` to the user.
2149 self.report_ambiguous_associated_type(
2151 &qself_ty.to_string(),
2156 return Err(ErrorReported);
2160 let trait_did = bound.def_id();
2161 let (assoc_ident, def_scope) =
2162 tcx.adjust_ident_and_get_scope(assoc_ident, trait_did, hir_ref_id);
2164 .associated_items(trait_did)
2165 .find(|i| Namespace::from(i.kind) == Namespace::Type && i.ident.modern() == assoc_ident)
2166 .expect("missing associated type");
2168 let ty = self.projected_ty_from_poly_trait_ref(span, item.def_id, assoc_segment, bound);
2169 let ty = self.normalize_ty(span, ty);
2171 let kind = DefKind::AssocTy;
2172 if !item.vis.is_accessible_from(def_scope, tcx) {
2173 let msg = format!("{} `{}` is private", kind.descr(item.def_id), assoc_ident);
2174 tcx.sess.span_err(span, &msg);
2176 tcx.check_stability(item.def_id, Some(hir_ref_id), span);
2178 if let Some(variant_def_id) = variant_resolution {
2179 let mut err = tcx.struct_span_lint_hir(
2180 AMBIGUOUS_ASSOCIATED_ITEMS,
2183 "ambiguous associated item",
2186 let mut could_refer_to = |kind: DefKind, def_id, also| {
2187 let note_msg = format!(
2188 "`{}` could{} refer to {} defined here",
2193 err.span_note(tcx.def_span(def_id), ¬e_msg);
2195 could_refer_to(DefKind::Variant, variant_def_id, "");
2196 could_refer_to(kind, item.def_id, " also");
2198 err.span_suggestion(
2200 "use fully-qualified syntax",
2201 format!("<{} as {}>::{}", qself_ty, tcx.item_name(trait_did), assoc_ident),
2202 Applicability::MachineApplicable,
2207 Ok((ty, kind, item.def_id))
2213 opt_self_ty: Option<Ty<'tcx>>,
2215 trait_segment: &hir::PathSegment<'_>,
2216 item_segment: &hir::PathSegment<'_>,
2218 let tcx = self.tcx();
2220 let trait_def_id = tcx.parent(item_def_id).unwrap();
2222 debug!("qpath_to_ty: trait_def_id={:?}", trait_def_id);
2224 let self_ty = if let Some(ty) = opt_self_ty {
2227 let path_str = tcx.def_path_str(trait_def_id);
2229 let def_id = self.item_def_id();
2231 debug!("qpath_to_ty: self.item_def_id()={:?}", def_id);
2233 let parent_def_id = def_id
2234 .and_then(|def_id| tcx.hir().as_local_hir_id(def_id))
2235 .map(|hir_id| tcx.hir().get_parent_did(hir_id));
2237 debug!("qpath_to_ty: parent_def_id={:?}", parent_def_id);
2239 // If the trait in segment is the same as the trait defining the item,
2240 // use the `<Self as ..>` syntax in the error.
2241 let is_part_of_self_trait_constraints = def_id == Some(trait_def_id);
2242 let is_part_of_fn_in_self_trait = parent_def_id == Some(trait_def_id);
2244 let type_name = if is_part_of_self_trait_constraints || is_part_of_fn_in_self_trait {
2250 self.report_ambiguous_associated_type(
2254 item_segment.ident.name,
2256 return tcx.types.err;
2259 debug!("qpath_to_ty: self_type={:?}", self_ty);
2261 let trait_ref = self.ast_path_to_mono_trait_ref(span, trait_def_id, self_ty, trait_segment);
2263 let item_substs = self.create_substs_for_associated_item(
2271 debug!("qpath_to_ty: trait_ref={:?}", trait_ref);
2273 self.normalize_ty(span, tcx.mk_projection(item_def_id, item_substs))
2276 pub fn prohibit_generics<'a, T: IntoIterator<Item = &'a hir::PathSegment<'a>>>(
2280 let mut has_err = false;
2281 for segment in segments {
2282 let (mut err_for_lt, mut err_for_ty, mut err_for_ct) = (false, false, false);
2283 for arg in segment.generic_args().args {
2284 let (span, kind) = match arg {
2285 hir::GenericArg::Lifetime(lt) => {
2291 (lt.span, "lifetime")
2293 hir::GenericArg::Type(ty) => {
2301 hir::GenericArg::Const(ct) => {
2309 let mut err = struct_span_err!(
2313 "{} arguments are not allowed for this type",
2316 err.span_label(span, format!("{} argument not allowed", kind));
2318 if err_for_lt && err_for_ty && err_for_ct {
2322 for binding in segment.generic_args().bindings {
2324 Self::prohibit_assoc_ty_binding(self.tcx(), binding.span);
2331 pub fn prohibit_assoc_ty_binding(tcx: TyCtxt<'_>, span: Span) {
2332 let mut err = struct_span_err!(
2336 "associated type bindings are not allowed here"
2338 err.span_label(span, "associated type not allowed here").emit();
2341 // FIXME(eddyb, varkor) handle type paths here too, not just value ones.
2342 pub fn def_ids_for_value_path_segments(
2344 segments: &[hir::PathSegment<'_>],
2345 self_ty: Option<Ty<'tcx>>,
2349 // We need to extract the type parameters supplied by the user in
2350 // the path `path`. Due to the current setup, this is a bit of a
2351 // tricky-process; the problem is that resolve only tells us the
2352 // end-point of the path resolution, and not the intermediate steps.
2353 // Luckily, we can (at least for now) deduce the intermediate steps
2354 // just from the end-point.
2356 // There are basically five cases to consider:
2358 // 1. Reference to a constructor of a struct:
2360 // struct Foo<T>(...)
2362 // In this case, the parameters are declared in the type space.
2364 // 2. Reference to a constructor of an enum variant:
2366 // enum E<T> { Foo(...) }
2368 // In this case, the parameters are defined in the type space,
2369 // but may be specified either on the type or the variant.
2371 // 3. Reference to a fn item or a free constant:
2375 // In this case, the path will again always have the form
2376 // `a::b::foo::<T>` where only the final segment should have
2377 // type parameters. However, in this case, those parameters are
2378 // declared on a value, and hence are in the `FnSpace`.
2380 // 4. Reference to a method or an associated constant:
2382 // impl<A> SomeStruct<A> {
2386 // Here we can have a path like
2387 // `a::b::SomeStruct::<A>::foo::<B>`, in which case parameters
2388 // may appear in two places. The penultimate segment,
2389 // `SomeStruct::<A>`, contains parameters in TypeSpace, and the
2390 // final segment, `foo::<B>` contains parameters in fn space.
2392 // The first step then is to categorize the segments appropriately.
2394 let tcx = self.tcx();
2396 assert!(!segments.is_empty());
2397 let last = segments.len() - 1;
2399 let mut path_segs = vec![];
2402 // Case 1. Reference to a struct constructor.
2403 DefKind::Ctor(CtorOf::Struct, ..) => {
2404 // Everything but the final segment should have no
2405 // parameters at all.
2406 let generics = tcx.generics_of(def_id);
2407 // Variant and struct constructors use the
2408 // generics of their parent type definition.
2409 let generics_def_id = generics.parent.unwrap_or(def_id);
2410 path_segs.push(PathSeg(generics_def_id, last));
2413 // Case 2. Reference to a variant constructor.
2414 DefKind::Ctor(CtorOf::Variant, ..) | DefKind::Variant => {
2415 let adt_def = self_ty.map(|t| t.ty_adt_def().unwrap());
2416 let (generics_def_id, index) = if let Some(adt_def) = adt_def {
2417 debug_assert!(adt_def.is_enum());
2419 } else if last >= 1 && segments[last - 1].args.is_some() {
2420 // Everything but the penultimate segment should have no
2421 // parameters at all.
2422 let mut def_id = def_id;
2424 // `DefKind::Ctor` -> `DefKind::Variant`
2425 if let DefKind::Ctor(..) = kind {
2426 def_id = tcx.parent(def_id).unwrap()
2429 // `DefKind::Variant` -> `DefKind::Enum`
2430 let enum_def_id = tcx.parent(def_id).unwrap();
2431 (enum_def_id, last - 1)
2433 // FIXME: lint here recommending `Enum::<...>::Variant` form
2434 // instead of `Enum::Variant::<...>` form.
2436 // Everything but the final segment should have no
2437 // parameters at all.
2438 let generics = tcx.generics_of(def_id);
2439 // Variant and struct constructors use the
2440 // generics of their parent type definition.
2441 (generics.parent.unwrap_or(def_id), last)
2443 path_segs.push(PathSeg(generics_def_id, index));
2446 // Case 3. Reference to a top-level value.
2447 DefKind::Fn | DefKind::Const | DefKind::ConstParam | DefKind::Static => {
2448 path_segs.push(PathSeg(def_id, last));
2451 // Case 4. Reference to a method or associated const.
2452 DefKind::Method | DefKind::AssocConst => {
2453 if segments.len() >= 2 {
2454 let generics = tcx.generics_of(def_id);
2455 path_segs.push(PathSeg(generics.parent.unwrap(), last - 1));
2457 path_segs.push(PathSeg(def_id, last));
2460 kind => bug!("unexpected definition kind {:?} for {:?}", kind, def_id),
2463 debug!("path_segs = {:?}", path_segs);
2468 // Check a type `Path` and convert it to a `Ty`.
2471 opt_self_ty: Option<Ty<'tcx>>,
2472 path: &hir::Path<'_>,
2473 permit_variants: bool,
2475 let tcx = self.tcx();
2478 "res_to_ty(res={:?}, opt_self_ty={:?}, path_segments={:?})",
2479 path.res, opt_self_ty, path.segments
2482 let span = path.span;
2484 Res::Def(DefKind::OpaqueTy, did) => {
2485 // Check for desugared `impl Trait`.
2486 assert!(ty::is_impl_trait_defn(tcx, did).is_none());
2487 let item_segment = path.segments.split_last().unwrap();
2488 self.prohibit_generics(item_segment.1);
2489 let substs = self.ast_path_substs_for_ty(span, did, item_segment.0);
2490 self.normalize_ty(span, tcx.mk_opaque(did, substs))
2492 Res::Def(DefKind::Enum, did)
2493 | Res::Def(DefKind::TyAlias, did)
2494 | Res::Def(DefKind::Struct, did)
2495 | Res::Def(DefKind::Union, did)
2496 | Res::Def(DefKind::ForeignTy, did) => {
2497 assert_eq!(opt_self_ty, None);
2498 self.prohibit_generics(path.segments.split_last().unwrap().1);
2499 self.ast_path_to_ty(span, did, path.segments.last().unwrap())
2501 Res::Def(kind @ DefKind::Variant, def_id) if permit_variants => {
2502 // Convert "variant type" as if it were a real type.
2503 // The resulting `Ty` is type of the variant's enum for now.
2504 assert_eq!(opt_self_ty, None);
2507 self.def_ids_for_value_path_segments(&path.segments, None, kind, def_id);
2508 let generic_segs: FxHashSet<_> =
2509 path_segs.iter().map(|PathSeg(_, index)| index).collect();
2510 self.prohibit_generics(path.segments.iter().enumerate().filter_map(
2512 if !generic_segs.contains(&index) { Some(seg) } else { None }
2516 let PathSeg(def_id, index) = path_segs.last().unwrap();
2517 self.ast_path_to_ty(span, *def_id, &path.segments[*index])
2519 Res::Def(DefKind::TyParam, def_id) => {
2520 assert_eq!(opt_self_ty, None);
2521 self.prohibit_generics(path.segments);
2523 let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
2524 let item_id = tcx.hir().get_parent_node(hir_id);
2525 let item_def_id = tcx.hir().local_def_id(item_id);
2526 let generics = tcx.generics_of(item_def_id);
2527 let index = generics.param_def_id_to_index[&def_id];
2528 tcx.mk_ty_param(index, tcx.hir().name(hir_id))
2530 Res::SelfTy(Some(_), None) => {
2531 // `Self` in trait or type alias.
2532 assert_eq!(opt_self_ty, None);
2533 self.prohibit_generics(path.segments);
2534 tcx.types.self_param
2536 Res::SelfTy(_, Some(def_id)) => {
2537 // `Self` in impl (we know the concrete type).
2538 assert_eq!(opt_self_ty, None);
2539 self.prohibit_generics(path.segments);
2540 // Try to evaluate any array length constants.
2541 self.normalize_ty(span, tcx.at(span).type_of(def_id))
2543 Res::Def(DefKind::AssocTy, def_id) => {
2544 debug_assert!(path.segments.len() >= 2);
2545 self.prohibit_generics(&path.segments[..path.segments.len() - 2]);
2550 &path.segments[path.segments.len() - 2],
2551 path.segments.last().unwrap(),
2554 Res::PrimTy(prim_ty) => {
2555 assert_eq!(opt_self_ty, None);
2556 self.prohibit_generics(path.segments);
2558 hir::PrimTy::Bool => tcx.types.bool,
2559 hir::PrimTy::Char => tcx.types.char,
2560 hir::PrimTy::Int(it) => tcx.mk_mach_int(it),
2561 hir::PrimTy::Uint(uit) => tcx.mk_mach_uint(uit),
2562 hir::PrimTy::Float(ft) => tcx.mk_mach_float(ft),
2563 hir::PrimTy::Str => tcx.mk_str(),
2567 self.set_tainted_by_errors();
2568 return self.tcx().types.err;
2570 _ => span_bug!(span, "unexpected resolution: {:?}", path.res),
2574 /// Parses the programmer's textual representation of a type into our
2575 /// internal notion of a type.
2576 pub fn ast_ty_to_ty(&self, ast_ty: &hir::Ty<'_>) -> Ty<'tcx> {
2577 debug!("ast_ty_to_ty(id={:?}, ast_ty={:?} ty_ty={:?})", ast_ty.hir_id, ast_ty, ast_ty.kind);
2579 let tcx = self.tcx();
2581 let result_ty = match ast_ty.kind {
2582 hir::TyKind::Slice(ref ty) => tcx.mk_slice(self.ast_ty_to_ty(&ty)),
2583 hir::TyKind::Ptr(ref mt) => {
2584 tcx.mk_ptr(ty::TypeAndMut { ty: self.ast_ty_to_ty(&mt.ty), mutbl: mt.mutbl })
2586 hir::TyKind::Rptr(ref region, ref mt) => {
2587 let r = self.ast_region_to_region(region, None);
2588 debug!("ast_ty_to_ty: r={:?}", r);
2589 let t = self.ast_ty_to_ty(&mt.ty);
2590 tcx.mk_ref(r, ty::TypeAndMut { ty: t, mutbl: mt.mutbl })
2592 hir::TyKind::Never => tcx.types.never,
2593 hir::TyKind::Tup(ref fields) => {
2594 tcx.mk_tup(fields.iter().map(|t| self.ast_ty_to_ty(&t)))
2596 hir::TyKind::BareFn(ref bf) => {
2597 require_c_abi_if_c_variadic(tcx, &bf.decl, bf.abi, ast_ty.span);
2598 tcx.mk_fn_ptr(self.ty_of_fn(bf.unsafety, bf.abi, &bf.decl, &[], None))
2600 hir::TyKind::TraitObject(ref bounds, ref lifetime) => {
2601 self.conv_object_ty_poly_trait_ref(ast_ty.span, bounds, lifetime)
2603 hir::TyKind::Path(hir::QPath::Resolved(ref maybe_qself, ref path)) => {
2604 debug!("ast_ty_to_ty: maybe_qself={:?} path={:?}", maybe_qself, path);
2605 let opt_self_ty = maybe_qself.as_ref().map(|qself| self.ast_ty_to_ty(qself));
2606 self.res_to_ty(opt_self_ty, path, false)
2608 hir::TyKind::Def(item_id, ref lifetimes) => {
2609 let did = tcx.hir().local_def_id(item_id.id);
2610 self.impl_trait_ty_to_ty(did, lifetimes)
2612 hir::TyKind::Path(hir::QPath::TypeRelative(ref qself, ref segment)) => {
2613 debug!("ast_ty_to_ty: qself={:?} segment={:?}", qself, segment);
2614 let ty = self.ast_ty_to_ty(qself);
2616 let res = if let hir::TyKind::Path(hir::QPath::Resolved(_, ref path)) = qself.kind {
2621 self.associated_path_to_ty(ast_ty.hir_id, ast_ty.span, ty, res, segment, false)
2622 .map(|(ty, _, _)| ty)
2623 .unwrap_or(tcx.types.err)
2625 hir::TyKind::Array(ref ty, ref length) => {
2626 let length = self.ast_const_to_const(length, tcx.types.usize);
2627 let array_ty = tcx.mk_ty(ty::Array(self.ast_ty_to_ty(&ty), length));
2628 self.normalize_ty(ast_ty.span, array_ty)
2630 hir::TyKind::Typeof(ref _e) => {
2635 "`typeof` is a reserved keyword but unimplemented"
2637 .span_label(ast_ty.span, "reserved keyword")
2642 hir::TyKind::Infer => {
2643 // Infer also appears as the type of arguments or return
2644 // values in a ExprKind::Closure, or as
2645 // the type of local variables. Both of these cases are
2646 // handled specially and will not descend into this routine.
2647 self.ty_infer(None, ast_ty.span)
2649 hir::TyKind::Err => tcx.types.err,
2652 debug!("ast_ty_to_ty: result_ty={:?}", result_ty);
2654 self.record_ty(ast_ty.hir_id, result_ty, ast_ty.span);
2658 /// Returns the `DefId` of the constant parameter that the provided expression is a path to.
2659 pub fn const_param_def_id(&self, expr: &hir::Expr<'_>) -> Option<DefId> {
2660 // Unwrap a block, so that e.g. `{ P }` is recognised as a parameter. Const arguments
2661 // currently have to be wrapped in curly brackets, so it's necessary to special-case.
2662 let expr = match &expr.kind {
2663 ExprKind::Block(block, _) if block.stmts.is_empty() && block.expr.is_some() => {
2664 block.expr.as_ref().unwrap()
2670 ExprKind::Path(hir::QPath::Resolved(_, path)) => match path.res {
2671 Res::Def(DefKind::ConstParam, did) => Some(did),
2678 pub fn ast_const_to_const(
2680 ast_const: &hir::AnonConst,
2682 ) -> &'tcx ty::Const<'tcx> {
2683 debug!("ast_const_to_const(id={:?}, ast_const={:?})", ast_const.hir_id, ast_const);
2685 let tcx = self.tcx();
2686 let def_id = tcx.hir().local_def_id(ast_const.hir_id);
2688 let mut const_ = ty::Const {
2689 val: ty::ConstKind::Unevaluated(def_id, InternalSubsts::identity_for_item(tcx, def_id)),
2693 let expr = &tcx.hir().body(ast_const.body).value;
2694 if let Some(def_id) = self.const_param_def_id(expr) {
2695 // Find the name and index of the const parameter by indexing the generics of the
2696 // parent item and construct a `ParamConst`.
2697 let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
2698 let item_id = tcx.hir().get_parent_node(hir_id);
2699 let item_def_id = tcx.hir().local_def_id(item_id);
2700 let generics = tcx.generics_of(item_def_id);
2701 let index = generics.param_def_id_to_index[&tcx.hir().local_def_id(hir_id)];
2702 let name = tcx.hir().name(hir_id);
2703 const_.val = ty::ConstKind::Param(ty::ParamConst::new(index, name));
2706 tcx.mk_const(const_)
2709 pub fn impl_trait_ty_to_ty(
2712 lifetimes: &[hir::GenericArg<'_>],
2714 debug!("impl_trait_ty_to_ty(def_id={:?}, lifetimes={:?})", def_id, lifetimes);
2715 let tcx = self.tcx();
2717 let generics = tcx.generics_of(def_id);
2719 debug!("impl_trait_ty_to_ty: generics={:?}", generics);
2720 let substs = InternalSubsts::for_item(tcx, def_id, |param, _| {
2721 if let Some(i) = (param.index as usize).checked_sub(generics.parent_count) {
2722 // Our own parameters are the resolved lifetimes.
2724 GenericParamDefKind::Lifetime => {
2725 if let hir::GenericArg::Lifetime(lifetime) = &lifetimes[i] {
2726 self.ast_region_to_region(lifetime, None).into()
2734 // Replace all parent lifetimes with `'static`.
2736 GenericParamDefKind::Lifetime => tcx.lifetimes.re_static.into(),
2737 _ => tcx.mk_param_from_def(param),
2741 debug!("impl_trait_ty_to_ty: substs={:?}", substs);
2743 let ty = tcx.mk_opaque(def_id, substs);
2744 debug!("impl_trait_ty_to_ty: {}", ty);
2748 pub fn ty_of_arg(&self, ty: &hir::Ty<'_>, expected_ty: Option<Ty<'tcx>>) -> Ty<'tcx> {
2750 hir::TyKind::Infer if expected_ty.is_some() => {
2751 self.record_ty(ty.hir_id, expected_ty.unwrap(), ty.span);
2752 expected_ty.unwrap()
2754 _ => self.ast_ty_to_ty(ty),
2760 unsafety: hir::Unsafety,
2762 decl: &hir::FnDecl<'_>,
2763 generic_params: &[hir::GenericParam<'_>],
2764 ident_span: Option<Span>,
2765 ) -> ty::PolyFnSig<'tcx> {
2768 let tcx = self.tcx();
2770 // We proactively collect all the infered type params to emit a single error per fn def.
2771 let mut visitor = PlaceholderHirTyCollector::default();
2772 for ty in decl.inputs {
2773 visitor.visit_ty(ty);
2775 let input_tys = decl.inputs.iter().map(|a| self.ty_of_arg(a, None));
2776 let output_ty = match decl.output {
2777 hir::FunctionRetTy::Return(ref output) => {
2778 visitor.visit_ty(output);
2779 self.ast_ty_to_ty(output)
2781 hir::FunctionRetTy::DefaultReturn(..) => tcx.mk_unit(),
2784 debug!("ty_of_fn: output_ty={:?}", output_ty);
2787 ty::Binder::bind(tcx.mk_fn_sig(input_tys, output_ty, decl.c_variadic, unsafety, abi));
2789 if !self.allow_ty_infer() {
2790 // We always collect the spans for placeholder types when evaluating `fn`s, but we
2791 // only want to emit an error complaining about them if infer types (`_`) are not
2792 // allowed. `allow_ty_infer` gates this behavior.
2793 crate::collect::placeholder_type_error(
2795 ident_span.unwrap_or(DUMMY_SP),
2798 ident_span.is_some(),
2802 // Find any late-bound regions declared in return type that do
2803 // not appear in the arguments. These are not well-formed.
2806 // for<'a> fn() -> &'a str <-- 'a is bad
2807 // for<'a> fn(&'a String) -> &'a str <-- 'a is ok
2808 let inputs = bare_fn_ty.inputs();
2809 let late_bound_in_args =
2810 tcx.collect_constrained_late_bound_regions(&inputs.map_bound(|i| i.to_owned()));
2811 let output = bare_fn_ty.output();
2812 let late_bound_in_ret = tcx.collect_referenced_late_bound_regions(&output);
2813 for br in late_bound_in_ret.difference(&late_bound_in_args) {
2814 let lifetime_name = match *br {
2815 ty::BrNamed(_, name) => format!("lifetime `{}`,", name),
2816 ty::BrAnon(_) | ty::BrEnv => "an anonymous lifetime".to_string(),
2818 let mut err = struct_span_err!(
2822 "return type references {} \
2823 which is not constrained by the fn input types",
2826 if let ty::BrAnon(_) = *br {
2827 // The only way for an anonymous lifetime to wind up
2828 // in the return type but **also** be unconstrained is
2829 // if it only appears in "associated types" in the
2830 // input. See #47511 for an example. In this case,
2831 // though we can easily give a hint that ought to be
2834 "lifetimes appearing in an associated type \
2835 are not considered constrained",
2844 /// Given the bounds on an object, determines what single region bound (if any) we can
2845 /// use to summarize this type. The basic idea is that we will use the bound the user
2846 /// provided, if they provided one, and otherwise search the supertypes of trait bounds
2847 /// for region bounds. It may be that we can derive no bound at all, in which case
2848 /// we return `None`.
2849 fn compute_object_lifetime_bound(
2852 existential_predicates: ty::Binder<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>>,
2853 ) -> Option<ty::Region<'tcx>> // if None, use the default
2855 let tcx = self.tcx();
2857 debug!("compute_opt_region_bound(existential_predicates={:?})", existential_predicates);
2859 // No explicit region bound specified. Therefore, examine trait
2860 // bounds and see if we can derive region bounds from those.
2861 let derived_region_bounds = object_region_bounds(tcx, existential_predicates);
2863 // If there are no derived region bounds, then report back that we
2864 // can find no region bound. The caller will use the default.
2865 if derived_region_bounds.is_empty() {
2869 // If any of the derived region bounds are 'static, that is always
2871 if derived_region_bounds.iter().any(|&r| ty::ReStatic == *r) {
2872 return Some(tcx.lifetimes.re_static);
2875 // Determine whether there is exactly one unique region in the set
2876 // of derived region bounds. If so, use that. Otherwise, report an
2878 let r = derived_region_bounds[0];
2879 if derived_region_bounds[1..].iter().any(|r1| r != *r1) {
2884 "ambiguous lifetime bound, explicit lifetime bound required"
2891 /// Collects together a list of bounds that are applied to some type,
2892 /// after they've been converted into `ty` form (from the HIR
2893 /// representations). These lists of bounds occur in many places in
2897 /// trait Foo: Bar + Baz { }
2898 /// ^^^^^^^^^ supertrait list bounding the `Self` type parameter
2900 /// fn foo<T: Bar + Baz>() { }
2901 /// ^^^^^^^^^ bounding the type parameter `T`
2903 /// impl dyn Bar + Baz
2904 /// ^^^^^^^^^ bounding the forgotten dynamic type
2907 /// Our representation is a bit mixed here -- in some cases, we
2908 /// include the self type (e.g., `trait_bounds`) but in others we do
2909 #[derive(Default, PartialEq, Eq, Clone, Debug)]
2910 pub struct Bounds<'tcx> {
2911 /// A list of region bounds on the (implicit) self type. So if you
2912 /// had `T: 'a + 'b` this might would be a list `['a, 'b]` (but
2913 /// the `T` is not explicitly included).
2914 pub region_bounds: Vec<(ty::Region<'tcx>, Span)>,
2916 /// A list of trait bounds. So if you had `T: Debug` this would be
2917 /// `T: Debug`. Note that the self-type is explicit here.
2918 pub trait_bounds: Vec<(ty::PolyTraitRef<'tcx>, Span)>,
2920 /// A list of projection equality bounds. So if you had `T:
2921 /// Iterator<Item = u32>` this would include `<T as
2922 /// Iterator>::Item => u32`. Note that the self-type is explicit
2924 pub projection_bounds: Vec<(ty::PolyProjectionPredicate<'tcx>, Span)>,
2926 /// `Some` if there is *no* `?Sized` predicate. The `span`
2927 /// is the location in the source of the `T` declaration which can
2928 /// be cited as the source of the `T: Sized` requirement.
2929 pub implicitly_sized: Option<Span>,
2932 impl<'tcx> Bounds<'tcx> {
2933 /// Converts a bounds list into a flat set of predicates (like
2934 /// where-clauses). Because some of our bounds listings (e.g.,
2935 /// regions) don't include the self-type, you must supply the
2936 /// self-type here (the `param_ty` parameter).
2941 ) -> Vec<(ty::Predicate<'tcx>, Span)> {
2942 // If it could be sized, and is, add the `Sized` predicate.
2943 let sized_predicate = self.implicitly_sized.and_then(|span| {
2944 tcx.lang_items().sized_trait().map(|sized| {
2945 let trait_ref = ty::Binder::bind(ty::TraitRef {
2947 substs: tcx.mk_substs_trait(param_ty, &[]),
2949 (trait_ref.to_predicate(), span)
2958 .map(|&(region_bound, span)| {
2959 // Account for the binder being introduced below; no need to shift `param_ty`
2960 // because, at present at least, it either only refers to early-bound regions,
2961 // or it's a generic associated type that deliberately has escaping bound vars.
2962 let region_bound = ty::fold::shift_region(tcx, region_bound, 1);
2963 let outlives = ty::OutlivesPredicate(param_ty, region_bound);
2964 (ty::Binder::bind(outlives).to_predicate(), span)
2969 .map(|&(bound_trait_ref, span)| (bound_trait_ref.to_predicate(), span)),
2972 self.projection_bounds
2974 .map(|&(projection, span)| (projection.to_predicate(), span)),