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, Session};
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 /// A marker denoting that the generic arguments that were
136 /// provided did not match the respective generic parameters.
137 pub struct GenericArgCountMismatch;
139 impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
140 pub fn ast_region_to_region(
142 lifetime: &hir::Lifetime,
143 def: Option<&ty::GenericParamDef>,
144 ) -> ty::Region<'tcx> {
145 let tcx = self.tcx();
146 let lifetime_name = |def_id| tcx.hir().name(tcx.hir().as_local_hir_id(def_id).unwrap());
148 let r = match tcx.named_region(lifetime.hir_id) {
149 Some(rl::Region::Static) => tcx.lifetimes.re_static,
151 Some(rl::Region::LateBound(debruijn, id, _)) => {
152 let name = lifetime_name(id);
153 tcx.mk_region(ty::ReLateBound(debruijn, ty::BrNamed(id, name)))
156 Some(rl::Region::LateBoundAnon(debruijn, index)) => {
157 tcx.mk_region(ty::ReLateBound(debruijn, ty::BrAnon(index)))
160 Some(rl::Region::EarlyBound(index, id, _)) => {
161 let name = lifetime_name(id);
162 tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion { def_id: id, index, name }))
165 Some(rl::Region::Free(scope, id)) => {
166 let name = lifetime_name(id);
167 tcx.mk_region(ty::ReFree(ty::FreeRegion {
169 bound_region: ty::BrNamed(id, name),
172 // (*) -- not late-bound, won't change
176 self.re_infer(def, lifetime.span).unwrap_or_else(|| {
177 // This indicates an illegal lifetime
178 // elision. `resolve_lifetime` should have
179 // reported an error in this case -- but if
180 // not, let's error out.
181 tcx.sess.delay_span_bug(lifetime.span, "unelided lifetime in signature");
183 // Supply some dummy value. We don't have an
184 // `re_error`, annoyingly, so use `'static`.
185 tcx.lifetimes.re_static
190 debug!("ast_region_to_region(lifetime={:?}) yields {:?}", lifetime, r);
195 /// Given a path `path` that refers to an item `I` with the declared generics `decl_generics`,
196 /// returns an appropriate set of substitutions for this particular reference to `I`.
197 pub fn ast_path_substs_for_ty(
201 item_segment: &hir::PathSegment<'_>,
202 ) -> SubstsRef<'tcx> {
203 let (substs, assoc_bindings, _) = self.create_substs_for_ast_path(
207 item_segment.generic_args(),
208 item_segment.infer_args,
212 assoc_bindings.first().map(|b| Self::prohibit_assoc_ty_binding(self.tcx(), b.span));
217 /// Report error if there is an explicit type parameter when using `impl Trait`.
220 seg: &hir::PathSegment<'_>,
221 generics: &ty::Generics,
223 let explicit = !seg.infer_args;
224 let impl_trait = generics.params.iter().any(|param| match param.kind {
225 ty::GenericParamDefKind::Type {
226 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait),
232 if explicit && impl_trait {
237 .filter_map(|arg| match arg {
238 GenericArg::Type(_) => Some(arg.span()),
241 .collect::<Vec<_>>();
243 let mut err = struct_span_err! {
247 "cannot provide explicit generic arguments when `impl Trait` is \
248 used in argument position"
252 err.span_label(span, "explicit generic argument not allowed");
261 /// Checks that the correct number of generic arguments have been provided.
262 /// Used specifically for function calls.
263 pub fn check_generic_arg_count_for_call(
267 seg: &hir::PathSegment<'_>,
268 is_method_call: bool,
269 ) -> Result<(), GenericArgCountMismatch> {
270 let empty_args = hir::GenericArgs::none();
271 let suppress_mismatch = Self::check_impl_trait(tcx, seg, &def);
272 Self::check_generic_arg_count(
276 if let Some(ref args) = seg.args { args } else { &empty_args },
277 if is_method_call { GenericArgPosition::MethodCall } else { GenericArgPosition::Value },
278 def.parent.is_none() && def.has_self, // `has_self`
279 seg.infer_args || suppress_mismatch, // `infer_args`
284 /// Checks that the correct number of generic arguments have been provided.
285 /// This is used both for datatypes and function calls.
286 fn check_generic_arg_count(
290 args: &hir::GenericArgs<'_>,
291 position: GenericArgPosition,
294 ) -> (Result<(), GenericArgCountMismatch>, Vec<Span>) {
295 // At this stage we are guaranteed that the generic arguments are in the correct order, e.g.
296 // that lifetimes will proceed types. So it suffices to check the number of each generic
297 // arguments in order to validate them with respect to the generic parameters.
298 let param_counts = def.own_counts();
299 let arg_counts = args.own_counts();
300 let infer_lifetimes = position != GenericArgPosition::Type && arg_counts.lifetimes == 0;
302 let mut defaults: ty::GenericParamCount = Default::default();
303 for param in &def.params {
305 GenericParamDefKind::Lifetime => {}
306 GenericParamDefKind::Type { has_default, .. } => {
307 defaults.types += has_default as usize
309 GenericParamDefKind::Const => {
310 // FIXME(const_generics:defaults)
315 if position != GenericArgPosition::Type && !args.bindings.is_empty() {
316 AstConv::prohibit_assoc_ty_binding(tcx, args.bindings[0].span);
319 // Prohibit explicit lifetime arguments if late-bound lifetime parameters are present.
320 let mut reported_late_bound_region_err = false;
321 if !infer_lifetimes {
322 if let Some(span_late) = def.has_late_bound_regions {
323 reported_late_bound_region_err = true;
324 let msg = "cannot specify lifetime arguments explicitly \
325 if late bound lifetime parameters are present";
326 let note = "the late bound lifetime parameter is introduced here";
327 let span = args.args[0].span();
328 if position == GenericArgPosition::Value
329 && arg_counts.lifetimes != param_counts.lifetimes
331 let mut err = tcx.sess.struct_span_err(span, msg);
332 err.span_note(span_late, note);
335 let mut multispan = MultiSpan::from_span(span);
336 multispan.push_span_label(span_late, note.to_string());
337 tcx.struct_span_lint_hir(
338 lint::builtin::LATE_BOUND_LIFETIME_ARGUMENTS,
341 |lint| lint.build(msg).emit(),
347 let check_kind_count =
348 |kind, required, permitted, provided, offset, unexpected_spans: &mut Vec<Span>| {
350 "check_kind_count: kind: {} required: {} permitted: {} provided: {} offset: {}",
351 kind, required, permitted, provided, offset
353 // We enforce the following: `required` <= `provided` <= `permitted`.
354 // For kinds without defaults (e.g.., lifetimes), `required == permitted`.
355 // For other kinds (i.e., types), `permitted` may be greater than `required`.
356 if required <= provided && provided <= permitted {
360 // Unfortunately lifetime and type parameter mismatches are typically styled
361 // differently in diagnostics, which means we have a few cases to consider here.
362 let (bound, quantifier) = if required != permitted {
363 if provided < required {
364 (required, "at least ")
366 // provided > permitted
367 (permitted, "at most ")
373 let (spans, label) = if required == permitted && provided > permitted {
374 // In the case when the user has provided too many arguments,
375 // we want to point to the unexpected arguments.
376 let spans: Vec<Span> = args.args[offset + permitted..offset + provided]
378 .map(|arg| arg.span())
380 unexpected_spans.extend(spans.clone());
381 (spans, format!("unexpected {} argument", kind))
386 "expected {}{} {} argument{}",
395 let mut err = tcx.sess.struct_span_err_with_code(
398 "wrong number of {} arguments: expected {}{}, found {}",
399 kind, quantifier, bound, provided,
401 DiagnosticId::Error("E0107".into()),
404 err.span_label(span, label.as_str());
411 let mut arg_count_mismatch = reported_late_bound_region_err;
412 let mut unexpected_spans = vec![];
414 if !reported_late_bound_region_err
415 && (!infer_lifetimes || arg_counts.lifetimes > param_counts.lifetimes)
417 arg_count_mismatch |= check_kind_count(
419 param_counts.lifetimes,
420 param_counts.lifetimes,
421 arg_counts.lifetimes,
423 &mut unexpected_spans,
426 // FIXME(const_generics:defaults)
427 if !infer_args || arg_counts.consts > param_counts.consts {
428 arg_count_mismatch |= check_kind_count(
433 arg_counts.lifetimes + arg_counts.types,
434 &mut unexpected_spans,
437 // Note that type errors are currently be emitted *after* const errors.
438 if !infer_args || arg_counts.types > param_counts.types - defaults.types - has_self as usize
440 arg_count_mismatch |= check_kind_count(
442 param_counts.types - defaults.types - has_self as usize,
443 param_counts.types - has_self as usize,
445 arg_counts.lifetimes,
446 &mut unexpected_spans,
450 (if arg_count_mismatch { Err(GenericArgCountMismatch) } else { Ok(()) }, unexpected_spans)
453 /// Report an error that a generic argument did not match the generic parameter that was
455 fn generic_arg_mismatch_err(sess: &Session, arg: &GenericArg<'_>, kind: &'static str) {
460 "{} provided when a {} was expected",
467 /// Creates the relevant generic argument substitutions
468 /// corresponding to a set of generic parameters. This is a
469 /// rather complex function. Let us try to explain the role
470 /// of each of its parameters:
472 /// To start, we are given the `def_id` of the thing we are
473 /// creating the substitutions for, and a partial set of
474 /// substitutions `parent_substs`. In general, the substitutions
475 /// for an item begin with substitutions for all the "parents" of
476 /// that item -- e.g., for a method it might include the
477 /// parameters from the impl.
479 /// Therefore, the method begins by walking down these parents,
480 /// starting with the outermost parent and proceed inwards until
481 /// it reaches `def_id`. For each parent `P`, it will check `parent_substs`
482 /// first to see if the parent's substitutions are listed in there. If so,
483 /// we can append those and move on. Otherwise, it invokes the
484 /// three callback functions:
486 /// - `args_for_def_id`: given the `DefId` `P`, supplies back the
487 /// generic arguments that were given to that parent from within
488 /// the path; so e.g., if you have `<T as Foo>::Bar`, the `DefId`
489 /// might refer to the trait `Foo`, and the arguments might be
490 /// `[T]`. The boolean value indicates whether to infer values
491 /// for arguments whose values were not explicitly provided.
492 /// - `provided_kind`: given the generic parameter and the value from `args_for_def_id`,
493 /// instantiate a `GenericArg`.
494 /// - `inferred_kind`: if no parameter was provided, and inference is enabled, then
495 /// creates a suitable inference variable.
496 pub fn create_substs_for_generic_args<'b>(
499 parent_substs: &[subst::GenericArg<'tcx>],
501 self_ty: Option<Ty<'tcx>>,
502 arg_count_correct: Result<(), GenericArgCountMismatch>,
503 args_for_def_id: impl Fn(DefId) -> (Option<&'b GenericArgs<'b>>, bool),
504 provided_kind: impl Fn(&GenericParamDef, &GenericArg<'_>) -> subst::GenericArg<'tcx>,
505 mut inferred_kind: impl FnMut(
506 Option<&[subst::GenericArg<'tcx>]>,
509 ) -> subst::GenericArg<'tcx>,
510 ) -> SubstsRef<'tcx> {
511 // Collect the segments of the path; we need to substitute arguments
512 // for parameters throughout the entire path (wherever there are
513 // generic parameters).
514 let mut parent_defs = tcx.generics_of(def_id);
515 let count = parent_defs.count();
516 let mut stack = vec![(def_id, parent_defs)];
517 while let Some(def_id) = parent_defs.parent {
518 parent_defs = tcx.generics_of(def_id);
519 stack.push((def_id, parent_defs));
522 // We manually build up the substitution, rather than using convenience
523 // methods in `subst.rs`, so that we can iterate over the arguments and
524 // parameters in lock-step linearly, instead of trying to match each pair.
525 let mut substs: SmallVec<[subst::GenericArg<'tcx>; 8]> = SmallVec::with_capacity(count);
526 // Iterate over each segment of the path.
527 while let Some((def_id, defs)) = stack.pop() {
528 let mut params = defs.params.iter().peekable();
530 // If we have already computed substitutions for parents, we can use those directly.
531 while let Some(¶m) = params.peek() {
532 if let Some(&kind) = parent_substs.get(param.index as usize) {
540 // `Self` is handled first, unless it's been handled in `parent_substs`.
542 if let Some(¶m) = params.peek() {
543 if param.index == 0 {
544 if let GenericParamDefKind::Type { .. } = param.kind {
548 .unwrap_or_else(|| inferred_kind(None, param, true)),
556 // Check whether this segment takes generic arguments and the user has provided any.
557 let (generic_args, infer_args) = args_for_def_id(def_id);
560 generic_args.iter().flat_map(|generic_args| generic_args.args.iter()).peekable();
562 // If we encounter a type or const when we expect a lifetime, we infer the lifetimes.
563 // If we later encounter a lifetime, we know that the arguments were provided in the
564 // wrong order. `force_infer_lt` records the type or const that forced lifetimes to be
565 // inferred, so we can use it for diagnostics later.
566 let mut force_infer_lt = None;
569 // We're going to iterate through the generic arguments that the user
570 // provided, matching them with the generic parameters we expect.
571 // Mismatches can occur as a result of elided lifetimes, or for malformed
572 // input. We try to handle both sensibly.
573 match (args.peek(), params.peek()) {
574 (Some(&arg), Some(¶m)) => {
575 match (arg, ¶m.kind) {
576 (GenericArg::Lifetime(_), GenericParamDefKind::Lifetime)
577 | (GenericArg::Type(_), GenericParamDefKind::Type { .. })
578 | (GenericArg::Const(_), GenericParamDefKind::Const) => {
579 substs.push(provided_kind(param, arg));
583 (GenericArg::Type(_), GenericParamDefKind::Lifetime)
584 | (GenericArg::Const(_), GenericParamDefKind::Lifetime) => {
585 // We expected a lifetime argument, but got a type or const
586 // argument. That means we're inferring the lifetimes.
587 substs.push(inferred_kind(None, param, infer_args));
588 force_infer_lt = Some(arg);
592 // We expected one kind of parameter, but the user provided
593 // another. This is an error. However, if we already know that
594 // the arguments don't match up with the parameters, we won't issue
595 // an additional error, as the user already knows what's wrong.
596 if arg_count_correct.is_ok() {
597 Self::generic_arg_mismatch_err(tcx.sess, arg, kind.descr());
600 // We've reported the error, but we want to make sure that this
601 // problem doesn't bubble down and create additional, irrelevant
602 // errors. In this case, we're simply going to ignore the argument
603 // and any following arguments. The rest of the parameters will be
605 while args.next().is_some() {}
610 (Some(&arg), None) => {
611 // We should never be able to reach this point with well-formed input.
612 // There are two situations in which we can encounter this issue.
614 // 1. The number of arguments is incorrect. In this case, an error
615 // will already have been emitted, and we can ignore it. This case
616 // also occurs when late-bound lifetime parameters are present, yet
617 // the lifetime arguments have also been explicitly specified by the
619 // 2. We've inferred some lifetimes, which have been provided later (i.e.
620 // after a type or const). We want to throw an error in this case.
622 if arg_count_correct.is_ok() {
623 let kind = arg.descr();
624 assert_eq!(kind, "lifetime");
626 force_infer_lt.expect("lifetimes ought to have been inferred");
627 Self::generic_arg_mismatch_err(tcx.sess, provided, kind);
633 (None, Some(¶m)) => {
634 // If there are fewer arguments than parameters, it means
635 // we're inferring the remaining arguments.
636 substs.push(inferred_kind(Some(&substs), param, infer_args));
640 (None, None) => break,
645 tcx.intern_substs(&substs)
648 /// Given the type/lifetime/const arguments provided to some path (along with
649 /// an implicit `Self`, if this is a trait reference), returns the complete
650 /// set of substitutions. This may involve applying defaulted type parameters.
651 /// Also returns back constriants on associated types.
656 /// T: std::ops::Index<usize, Output = u32>
657 /// ^1 ^^^^^^^^^^^^^^2 ^^^^3 ^^^^^^^^^^^4
660 /// 1. The `self_ty` here would refer to the type `T`.
661 /// 2. The path in question is the path to the trait `std::ops::Index`,
662 /// which will have been resolved to a `def_id`
663 /// 3. The `generic_args` contains info on the `<...>` contents. The `usize` type
664 /// parameters are returned in the `SubstsRef`, the associated type bindings like
665 /// `Output = u32` are returned in the `Vec<ConvertedBinding...>` result.
667 /// Note that the type listing given here is *exactly* what the user provided.
669 /// For (generic) associated types
672 /// <Vec<u8> as Iterable<u8>>::Iter::<'a>
675 /// We have the parent substs are the substs for the parent trait:
676 /// `[Vec<u8>, u8]` and `generic_args` are the arguments for the associated
677 /// type itself: `['a]`. The returned `SubstsRef` concatenates these two
678 /// lists: `[Vec<u8>, u8, 'a]`.
679 fn create_substs_for_ast_path<'a>(
683 parent_substs: &[subst::GenericArg<'tcx>],
684 generic_args: &'a hir::GenericArgs<'_>,
686 self_ty: Option<Ty<'tcx>>,
687 ) -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'a, 'tcx>>, Vec<Span>) {
688 // If the type is parameterized by this region, then replace this
689 // region with the current anon region binding (in other words,
690 // whatever & would get replaced with).
692 "create_substs_for_ast_path(def_id={:?}, self_ty={:?}, \
694 def_id, self_ty, generic_args
697 let tcx = self.tcx();
698 let generic_params = tcx.generics_of(def_id);
700 if generic_params.has_self {
701 if generic_params.parent.is_some() {
702 // The parent is a trait so it should have at least one subst
703 // for the `Self` type.
704 assert!(!parent_substs.is_empty())
706 // This item (presumably a trait) needs a self-type.
707 assert!(self_ty.is_some());
710 assert!(self_ty.is_none() && parent_substs.is_empty());
713 let (arg_count_correct, potential_assoc_types) = Self::check_generic_arg_count(
718 GenericArgPosition::Type,
723 let is_object = self_ty.map_or(false, |ty| ty == self.tcx().types.trait_object_dummy_self);
724 let default_needs_object_self = |param: &ty::GenericParamDef| {
725 if let GenericParamDefKind::Type { has_default, .. } = param.kind {
726 if is_object && has_default {
727 let self_param = tcx.types.self_param;
728 if tcx.at(span).type_of(param.def_id).walk().any(|ty| ty == self_param) {
729 // There is no suitable inference default for a type parameter
730 // that references self, in an object type.
739 let mut missing_type_params = vec![];
740 let substs = Self::create_substs_for_generic_args(
747 // Provide the generic args, and whether types should be inferred.
750 (Some(generic_args), infer_args)
752 // The last component of this tuple is unimportant.
756 // Provide substitutions for parameters for which (valid) arguments have been provided.
757 |param, arg| match (¶m.kind, arg) {
758 (GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => {
759 self.ast_region_to_region(<, Some(param)).into()
761 (GenericParamDefKind::Type { .. }, GenericArg::Type(ty)) => {
762 self.ast_ty_to_ty(&ty).into()
764 (GenericParamDefKind::Const, GenericArg::Const(ct)) => {
765 self.ast_const_to_const(&ct.value, tcx.type_of(param.def_id)).into()
769 // Provide substitutions for parameters for which arguments are inferred.
770 |substs, param, infer_args| {
772 GenericParamDefKind::Lifetime => tcx.lifetimes.re_static.into(),
773 GenericParamDefKind::Type { has_default, .. } => {
774 if !infer_args && has_default {
775 // No type parameter provided, but a default exists.
777 // If we are converting an object type, then the
778 // `Self` parameter is unknown. However, some of the
779 // other type parameters may reference `Self` in their
780 // defaults. This will lead to an ICE if we are not
782 if default_needs_object_self(param) {
783 missing_type_params.push(param.name.to_string());
786 // This is a default type parameter.
789 tcx.at(span).type_of(param.def_id).subst_spanned(
797 } else if infer_args {
798 // No type parameters were provided, we can infer all.
800 if !default_needs_object_self(param) { Some(param) } else { None };
801 self.ty_infer(param, span).into()
803 // We've already errored above about the mismatch.
807 GenericParamDefKind::Const => {
808 // FIXME(const_generics:defaults)
810 // No const parameters were provided, we can infer all.
811 let ty = tcx.at(span).type_of(param.def_id);
812 self.ct_infer(ty, Some(param), span).into()
814 // We've already errored above about the mismatch.
815 tcx.consts.err.into()
822 self.complain_about_missing_type_params(
826 generic_args.args.is_empty(),
829 // Convert associated-type bindings or constraints into a separate vector.
830 // Example: Given this:
832 // T: Iterator<Item = u32>
834 // The `T` is passed in as a self-type; the `Item = u32` is
835 // not a "type parameter" of the `Iterator` trait, but rather
836 // a restriction on `<T as Iterator>::Item`, so it is passed
838 let assoc_bindings = generic_args
842 let kind = match binding.kind {
843 hir::TypeBindingKind::Equality { ref ty } => {
844 ConvertedBindingKind::Equality(self.ast_ty_to_ty(ty))
846 hir::TypeBindingKind::Constraint { ref bounds } => {
847 ConvertedBindingKind::Constraint(bounds)
850 ConvertedBinding { item_name: binding.ident, kind, span: binding.span }
855 "create_substs_for_ast_path(generic_params={:?}, self_ty={:?}) -> {:?}",
856 generic_params, self_ty, substs
859 (substs, assoc_bindings, potential_assoc_types)
862 crate fn create_substs_for_associated_item(
867 item_segment: &hir::PathSegment<'_>,
868 parent_substs: SubstsRef<'tcx>,
869 ) -> SubstsRef<'tcx> {
870 if tcx.generics_of(item_def_id).params.is_empty() {
871 self.prohibit_generics(slice::from_ref(item_segment));
875 self.create_substs_for_ast_path(
879 item_segment.generic_args(),
880 item_segment.infer_args,
887 /// On missing type parameters, emit an E0393 error and provide a structured suggestion using
888 /// the type parameter's name as a placeholder.
889 fn complain_about_missing_type_params(
891 missing_type_params: Vec<String>,
894 empty_generic_args: bool,
896 if missing_type_params.is_empty() {
900 missing_type_params.iter().map(|n| format!("`{}`", n)).collect::<Vec<_>>().join(", ");
901 let mut err = struct_span_err!(
905 "the type parameter{} {} must be explicitly specified",
906 pluralize!(missing_type_params.len()),
910 self.tcx().def_span(def_id),
912 "type parameter{} {} must be specified for this",
913 pluralize!(missing_type_params.len()),
917 let mut suggested = false;
918 if let (Ok(snippet), true) = (
919 self.tcx().sess.source_map().span_to_snippet(span),
920 // Don't suggest setting the type params if there are some already: the order is
921 // tricky to get right and the user will already know what the syntax is.
924 if snippet.ends_with('>') {
925 // The user wrote `Trait<'a, T>` or similar. To provide an accurate suggestion
926 // we would have to preserve the right order. For now, as clearly the user is
927 // aware of the syntax, we do nothing.
929 // The user wrote `Iterator`, so we don't have a type we can suggest, but at
930 // least we can clue them to the correct syntax `Iterator<Type>`.
934 "set the type parameter{plural} to the desired type{plural}",
935 plural = pluralize!(missing_type_params.len()),
937 format!("{}<{}>", snippet, missing_type_params.join(", ")),
938 Applicability::HasPlaceholders,
947 "missing reference{} to {}",
948 pluralize!(missing_type_params.len()),
954 "because of the default `Self` reference, type parameters must be \
955 specified on object types"
960 /// Instantiates the path for the given trait reference, assuming that it's
961 /// bound to a valid trait type. Returns the `DefId` of the defining trait.
962 /// The type _cannot_ be a type other than a trait type.
964 /// If the `projections` argument is `None`, then assoc type bindings like `Foo<T = X>`
965 /// are disallowed. Otherwise, they are pushed onto the vector given.
966 pub fn instantiate_mono_trait_ref(
968 trait_ref: &hir::TraitRef<'_>,
970 ) -> ty::TraitRef<'tcx> {
971 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
973 self.ast_path_to_mono_trait_ref(
975 trait_ref.trait_def_id(),
977 trait_ref.path.segments.last().unwrap(),
981 /// The given trait-ref must actually be a trait.
982 pub(super) fn instantiate_poly_trait_ref_inner(
984 trait_ref: &hir::TraitRef<'_>,
986 constness: Constness,
988 bounds: &mut Bounds<'tcx>,
991 let trait_def_id = trait_ref.trait_def_id();
993 debug!("instantiate_poly_trait_ref({:?}, def_id={:?})", trait_ref, trait_def_id);
995 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
997 let path_span = if let [segment] = &trait_ref.path.segments[..] {
998 // FIXME: `trait_ref.path.span` can point to a full path with multiple
999 // segments, even though `trait_ref.path.segments` is of length `1`. Work
1000 // around that bug here, even though it should be fixed elsewhere.
1001 // This would otherwise cause an invalid suggestion. For an example, look at
1002 // `src/test/ui/issues/issue-28344.rs`.
1007 let (substs, assoc_bindings, potential_assoc_types) = self.create_substs_for_ast_trait_ref(
1011 trait_ref.path.segments.last().unwrap(),
1013 let poly_trait_ref = ty::Binder::bind(ty::TraitRef::new(trait_def_id, substs));
1015 bounds.trait_bounds.push((poly_trait_ref, span, constness));
1017 let mut dup_bindings = FxHashMap::default();
1018 for binding in &assoc_bindings {
1019 // Specify type to assert that error was already reported in `Err` case.
1020 let _: Result<_, ErrorReported> = self.add_predicates_for_ast_type_binding(
1021 trait_ref.hir_ref_id,
1029 // Okay to ignore `Err` because of `ErrorReported` (see above).
1033 "instantiate_poly_trait_ref({:?}, bounds={:?}) -> {:?}",
1034 trait_ref, bounds, poly_trait_ref
1037 potential_assoc_types
1040 /// Given a trait bound like `Debug`, applies that trait bound the given self-type to construct
1041 /// a full trait reference. The resulting trait reference is returned. This may also generate
1042 /// auxiliary bounds, which are added to `bounds`.
1047 /// poly_trait_ref = Iterator<Item = u32>
1051 /// this would return `Foo: Iterator` and add `<Foo as Iterator>::Item = u32` into `bounds`.
1053 /// **A note on binders:** against our usual convention, there is an implied bounder around
1054 /// the `self_ty` and `poly_trait_ref` parameters here. So they may reference bound regions.
1055 /// If for example you had `for<'a> Foo<'a>: Bar<'a>`, then the `self_ty` would be `Foo<'a>`
1056 /// where `'a` is a bound region at depth 0. Similarly, the `poly_trait_ref` would be
1057 /// `Bar<'a>`. The returned poly-trait-ref will have this binder instantiated explicitly,
1059 pub fn instantiate_poly_trait_ref(
1061 poly_trait_ref: &hir::PolyTraitRef<'_>,
1062 constness: Constness,
1064 bounds: &mut Bounds<'tcx>,
1066 self.instantiate_poly_trait_ref_inner(
1067 &poly_trait_ref.trait_ref,
1068 poly_trait_ref.span,
1076 fn ast_path_to_mono_trait_ref(
1079 trait_def_id: DefId,
1081 trait_segment: &hir::PathSegment<'_>,
1082 ) -> ty::TraitRef<'tcx> {
1083 let (substs, assoc_bindings, _) =
1084 self.create_substs_for_ast_trait_ref(span, trait_def_id, self_ty, trait_segment);
1085 assoc_bindings.first().map(|b| AstConv::prohibit_assoc_ty_binding(self.tcx(), b.span));
1086 ty::TraitRef::new(trait_def_id, substs)
1089 /// When the code is using the `Fn` traits directly, instead of the `Fn(A) -> B` syntax, emit
1090 /// an error and attempt to build a reasonable structured suggestion.
1091 fn complain_about_internal_fn_trait(
1094 trait_def_id: DefId,
1095 trait_segment: &'a hir::PathSegment<'a>,
1097 let trait_def = self.tcx().trait_def(trait_def_id);
1099 if !self.tcx().features().unboxed_closures
1100 && trait_segment.generic_args().parenthesized != trait_def.paren_sugar
1102 // For now, require that parenthetical notation be used only with `Fn()` etc.
1103 let (msg, sugg) = if trait_def.paren_sugar {
1105 "the precise format of `Fn`-family traits' type parameters is subject to \
1109 trait_segment.ident,
1113 .and_then(|args| args.args.get(0))
1114 .and_then(|arg| match arg {
1115 hir::GenericArg::Type(ty) => {
1116 Some(print::to_string(print::NO_ANN, |s| s.print_type(ty)))
1120 .unwrap_or_else(|| "()".to_string()),
1125 .filter_map(|b| match (b.ident.as_str() == "Output", &b.kind) {
1126 (true, hir::TypeBindingKind::Equality { ty }) => {
1127 Some(print::to_string(print::NO_ANN, |s| s.print_type(ty)))
1132 .unwrap_or_else(|| "()".to_string()),
1136 ("parenthetical notation is only stable when used with `Fn`-family traits", None)
1138 let sess = &self.tcx().sess.parse_sess;
1139 let mut err = feature_err(sess, sym::unboxed_closures, span, msg);
1140 if let Some(sugg) = sugg {
1141 let msg = "use parenthetical notation instead";
1142 err.span_suggestion(span, msg, sugg, Applicability::MaybeIncorrect);
1148 fn create_substs_for_ast_trait_ref<'a>(
1151 trait_def_id: DefId,
1153 trait_segment: &'a hir::PathSegment<'a>,
1154 ) -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'a, 'tcx>>, Vec<Span>) {
1155 debug!("create_substs_for_ast_trait_ref(trait_segment={:?})", trait_segment);
1157 self.complain_about_internal_fn_trait(span, trait_def_id, trait_segment);
1159 self.create_substs_for_ast_path(
1163 trait_segment.generic_args(),
1164 trait_segment.infer_args,
1169 fn trait_defines_associated_type_named(
1171 trait_def_id: DefId,
1172 assoc_name: ast::Ident,
1175 .associated_items(trait_def_id)
1176 .find_by_name_and_kind(self.tcx(), assoc_name, ty::AssocKind::Type, trait_def_id)
1180 // Returns `true` if a bounds list includes `?Sized`.
1181 pub fn is_unsized(&self, ast_bounds: &[hir::GenericBound<'_>], span: Span) -> bool {
1182 let tcx = self.tcx();
1184 // Try to find an unbound in bounds.
1185 let mut unbound = None;
1186 for ab in ast_bounds {
1187 if let &hir::GenericBound::Trait(ref ptr, hir::TraitBoundModifier::Maybe) = ab {
1188 if unbound.is_none() {
1189 unbound = Some(&ptr.trait_ref);
1195 "type parameter has more than one relaxed default \
1196 bound, only one is supported"
1203 let kind_id = tcx.lang_items().require(SizedTraitLangItem);
1206 // FIXME(#8559) currently requires the unbound to be built-in.
1207 if let Ok(kind_id) = kind_id {
1208 if tpb.path.res != Res::Def(DefKind::Trait, kind_id) {
1211 "default bound relaxed for a type parameter, but \
1212 this does nothing because the given bound is not \
1213 a default; only `?Sized` is supported",
1218 _ if kind_id.is_ok() => {
1221 // No lang item for `Sized`, so we can't add it as a bound.
1228 /// This helper takes a *converted* parameter type (`param_ty`)
1229 /// and an *unconverted* list of bounds:
1232 /// fn foo<T: Debug>
1233 /// ^ ^^^^^ `ast_bounds` parameter, in HIR form
1235 /// `param_ty`, in ty form
1238 /// It adds these `ast_bounds` into the `bounds` structure.
1240 /// **A note on binders:** there is an implied binder around
1241 /// `param_ty` and `ast_bounds`. See `instantiate_poly_trait_ref`
1242 /// for more details.
1246 ast_bounds: &[hir::GenericBound<'_>],
1247 bounds: &mut Bounds<'tcx>,
1249 let mut trait_bounds = Vec::new();
1250 let mut region_bounds = Vec::new();
1252 let constness = self.default_constness_for_trait_bounds();
1253 for ast_bound in ast_bounds {
1255 hir::GenericBound::Trait(ref b, hir::TraitBoundModifier::None) => {
1256 trait_bounds.push((b, constness))
1258 hir::GenericBound::Trait(ref b, hir::TraitBoundModifier::MaybeConst) => {
1259 trait_bounds.push((b, Constness::NotConst))
1261 hir::GenericBound::Trait(_, hir::TraitBoundModifier::Maybe) => {}
1262 hir::GenericBound::Outlives(ref l) => region_bounds.push(l),
1266 for (bound, constness) in trait_bounds {
1267 let _ = self.instantiate_poly_trait_ref(bound, constness, param_ty, bounds);
1270 bounds.region_bounds.extend(
1271 region_bounds.into_iter().map(|r| (self.ast_region_to_region(r, None), r.span)),
1275 /// Translates a list of bounds from the HIR into the `Bounds` data structure.
1276 /// The self-type for the bounds is given by `param_ty`.
1281 /// fn foo<T: Bar + Baz>() { }
1282 /// ^ ^^^^^^^^^ ast_bounds
1286 /// The `sized_by_default` parameter indicates if, in this context, the `param_ty` should be
1287 /// considered `Sized` unless there is an explicit `?Sized` bound. This would be true in the
1288 /// example above, but is not true in supertrait listings like `trait Foo: Bar + Baz`.
1290 /// `span` should be the declaration size of the parameter.
1291 pub fn compute_bounds(
1294 ast_bounds: &[hir::GenericBound<'_>],
1295 sized_by_default: SizedByDefault,
1298 let mut bounds = Bounds::default();
1300 self.add_bounds(param_ty, ast_bounds, &mut bounds);
1301 bounds.trait_bounds.sort_by_key(|(t, _, _)| t.def_id());
1303 bounds.implicitly_sized = if let SizedByDefault::Yes = sized_by_default {
1304 if !self.is_unsized(ast_bounds, span) { Some(span) } else { None }
1312 /// Given an HIR binding like `Item = Foo` or `Item: Foo`, pushes the corresponding predicates
1315 /// **A note on binders:** given something like `T: for<'a> Iterator<Item = &'a u32>`, the
1316 /// `trait_ref` here will be `for<'a> T: Iterator`. The `binding` data however is from *inside*
1317 /// the binder (e.g., `&'a u32`) and hence may reference bound regions.
1318 fn add_predicates_for_ast_type_binding(
1320 hir_ref_id: hir::HirId,
1321 trait_ref: ty::PolyTraitRef<'tcx>,
1322 binding: &ConvertedBinding<'_, 'tcx>,
1323 bounds: &mut Bounds<'tcx>,
1325 dup_bindings: &mut FxHashMap<DefId, Span>,
1327 ) -> Result<(), ErrorReported> {
1328 let tcx = self.tcx();
1331 // Given something like `U: SomeTrait<T = X>`, we want to produce a
1332 // predicate like `<U as SomeTrait>::T = X`. This is somewhat
1333 // subtle in the event that `T` is defined in a supertrait of
1334 // `SomeTrait`, because in that case we need to upcast.
1336 // That is, consider this case:
1339 // trait SubTrait: SuperTrait<int> { }
1340 // trait SuperTrait<A> { type T; }
1342 // ... B: SubTrait<T = foo> ...
1345 // We want to produce `<B as SuperTrait<int>>::T == foo`.
1347 // Find any late-bound regions declared in `ty` that are not
1348 // declared in the trait-ref. These are not well-formed.
1352 // for<'a> <T as Iterator>::Item = &'a str // <-- 'a is bad
1353 // for<'a> <T as FnMut<(&'a u32,)>>::Output = &'a str // <-- 'a is ok
1354 if let ConvertedBindingKind::Equality(ty) = binding.kind {
1355 let late_bound_in_trait_ref =
1356 tcx.collect_constrained_late_bound_regions(&trait_ref);
1357 let late_bound_in_ty =
1358 tcx.collect_referenced_late_bound_regions(&ty::Binder::bind(ty));
1359 debug!("late_bound_in_trait_ref = {:?}", late_bound_in_trait_ref);
1360 debug!("late_bound_in_ty = {:?}", late_bound_in_ty);
1361 for br in late_bound_in_ty.difference(&late_bound_in_trait_ref) {
1362 let br_name = match *br {
1363 ty::BrNamed(_, name) => name,
1367 "anonymous bound region {:?} in binding but not trait ref",
1372 // FIXME: point at the type params that don't have appropriate lifetimes:
1373 // struct S1<F: for<'a> Fn(&i32, &i32) -> &'a i32>(F);
1374 // ---- ---- ^^^^^^^
1379 "binding for associated type `{}` references lifetime `{}`, \
1380 which does not appear in the trait input types",
1390 if self.trait_defines_associated_type_named(trait_ref.def_id(), binding.item_name) {
1391 // Simple case: X is defined in the current trait.
1394 // Otherwise, we have to walk through the supertraits to find
1396 self.one_bound_for_assoc_type(
1397 || traits::supertraits(tcx, trait_ref),
1398 || trait_ref.print_only_trait_path().to_string(),
1401 || match binding.kind {
1402 ConvertedBindingKind::Equality(ty) => Some(ty.to_string()),
1408 let (assoc_ident, def_scope) =
1409 tcx.adjust_ident_and_get_scope(binding.item_name, candidate.def_id(), hir_ref_id);
1411 // We have already adjusted the item name above, so compare with `ident.modern()` instead
1412 // of calling `filter_by_name_and_kind`.
1414 .associated_items(candidate.def_id())
1415 .filter_by_name_unhygienic(assoc_ident.name)
1416 .find(|i| i.kind == ty::AssocKind::Type && i.ident.modern() == assoc_ident)
1417 .expect("missing associated type");
1419 if !assoc_ty.vis.is_accessible_from(def_scope, tcx) {
1420 let msg = format!("associated type `{}` is private", binding.item_name);
1421 tcx.sess.span_err(binding.span, &msg);
1423 tcx.check_stability(assoc_ty.def_id, Some(hir_ref_id), binding.span);
1427 .entry(assoc_ty.def_id)
1428 .and_modify(|prev_span| {
1433 "the value of the associated type `{}` (from trait `{}`) \
1434 is already specified",
1436 tcx.def_path_str(assoc_ty.container.id())
1438 .span_label(binding.span, "re-bound here")
1439 .span_label(*prev_span, format!("`{}` bound here first", binding.item_name))
1442 .or_insert(binding.span);
1445 match binding.kind {
1446 ConvertedBindingKind::Equality(ref ty) => {
1447 // "Desugar" a constraint like `T: Iterator<Item = u32>` this to
1448 // the "projection predicate" for:
1450 // `<T as Iterator>::Item = u32`
1451 bounds.projection_bounds.push((
1452 candidate.map_bound(|trait_ref| ty::ProjectionPredicate {
1453 projection_ty: ty::ProjectionTy::from_ref_and_name(
1463 ConvertedBindingKind::Constraint(ast_bounds) => {
1464 // "Desugar" a constraint like `T: Iterator<Item: Debug>` to
1466 // `<T as Iterator>::Item: Debug`
1468 // Calling `skip_binder` is okay, because `add_bounds` expects the `param_ty`
1469 // parameter to have a skipped binder.
1470 let param_ty = tcx.mk_projection(assoc_ty.def_id, candidate.skip_binder().substs);
1471 self.add_bounds(param_ty, ast_bounds, bounds);
1481 item_segment: &hir::PathSegment<'_>,
1483 let substs = self.ast_path_substs_for_ty(span, did, item_segment);
1484 self.normalize_ty(span, self.tcx().at(span).type_of(did).subst(self.tcx(), substs))
1487 fn conv_object_ty_poly_trait_ref(
1490 trait_bounds: &[hir::PolyTraitRef<'_>],
1491 lifetime: &hir::Lifetime,
1493 let tcx = self.tcx();
1495 let mut bounds = Bounds::default();
1496 let mut potential_assoc_types = Vec::new();
1497 let dummy_self = self.tcx().types.trait_object_dummy_self;
1498 for trait_bound in trait_bounds.iter().rev() {
1499 let cur_potential_assoc_types = self.instantiate_poly_trait_ref(
1501 Constness::NotConst,
1505 potential_assoc_types.extend(cur_potential_assoc_types.into_iter());
1508 // Expand trait aliases recursively and check that only one regular (non-auto) trait
1509 // is used and no 'maybe' bounds are used.
1510 let expanded_traits =
1511 traits::expand_trait_aliases(tcx, bounds.trait_bounds.iter().map(|&(a, b, _)| (a, b)));
1512 let (mut auto_traits, regular_traits): (Vec<_>, Vec<_>) =
1513 expanded_traits.partition(|i| tcx.trait_is_auto(i.trait_ref().def_id()));
1514 if regular_traits.len() > 1 {
1515 let first_trait = ®ular_traits[0];
1516 let additional_trait = ®ular_traits[1];
1517 let mut err = struct_span_err!(
1519 additional_trait.bottom().1,
1521 "only auto traits can be used as additional traits in a trait object"
1523 additional_trait.label_with_exp_info(
1525 "additional non-auto trait",
1528 first_trait.label_with_exp_info(&mut err, "first non-auto trait", "first use");
1532 if regular_traits.is_empty() && auto_traits.is_empty() {
1537 "at least one trait is required for an object type"
1540 return tcx.types.err;
1543 // Check that there are no gross object safety violations;
1544 // most importantly, that the supertraits don't contain `Self`,
1546 for item in ®ular_traits {
1547 let object_safety_violations =
1548 astconv_object_safety_violations(tcx, item.trait_ref().def_id());
1549 if !object_safety_violations.is_empty() {
1550 report_object_safety_error(
1553 item.trait_ref().def_id(),
1554 object_safety_violations,
1557 return tcx.types.err;
1561 // Use a `BTreeSet` to keep output in a more consistent order.
1562 let mut associated_types: FxHashMap<Span, BTreeSet<DefId>> = FxHashMap::default();
1564 let regular_traits_refs_spans = bounds
1567 .filter(|(trait_ref, _, _)| !tcx.trait_is_auto(trait_ref.def_id()));
1569 for (base_trait_ref, span, constness) in regular_traits_refs_spans {
1570 assert_eq!(constness, Constness::NotConst);
1572 for trait_ref in traits::elaborate_trait_ref(tcx, base_trait_ref) {
1574 "conv_object_ty_poly_trait_ref: observing object predicate `{:?}`",
1578 ty::Predicate::Trait(pred, _) => {
1579 associated_types.entry(span).or_default().extend(
1580 tcx.associated_items(pred.def_id())
1581 .in_definition_order()
1582 .filter(|item| item.kind == ty::AssocKind::Type)
1583 .map(|item| item.def_id),
1586 ty::Predicate::Projection(pred) => {
1587 // A `Self` within the original bound will be substituted with a
1588 // `trait_object_dummy_self`, so check for that.
1589 let references_self = pred.skip_binder().ty.walk().any(|t| t == dummy_self);
1591 // If the projection output contains `Self`, force the user to
1592 // elaborate it explicitly to avoid a lot of complexity.
1594 // The "classicaly useful" case is the following:
1596 // trait MyTrait: FnMut() -> <Self as MyTrait>::MyOutput {
1601 // Here, the user could theoretically write `dyn MyTrait<Output = X>`,
1602 // but actually supporting that would "expand" to an infinitely-long type
1603 // `fix $ τ → dyn MyTrait<MyOutput = X, Output = <τ as MyTrait>::MyOutput`.
1605 // Instead, we force the user to write
1606 // `dyn MyTrait<MyOutput = X, Output = X>`, which is uglier but works. See
1607 // the discussion in #56288 for alternatives.
1608 if !references_self {
1609 // Include projections defined on supertraits.
1610 bounds.projection_bounds.push((pred, span));
1618 for (projection_bound, _) in &bounds.projection_bounds {
1619 for (_, def_ids) in &mut associated_types {
1620 def_ids.remove(&projection_bound.projection_def_id());
1624 self.complain_about_missing_associated_types(
1626 potential_assoc_types,
1630 // De-duplicate auto traits so that, e.g., `dyn Trait + Send + Send` is the same as
1631 // `dyn Trait + Send`.
1632 auto_traits.sort_by_key(|i| i.trait_ref().def_id());
1633 auto_traits.dedup_by_key(|i| i.trait_ref().def_id());
1634 debug!("regular_traits: {:?}", regular_traits);
1635 debug!("auto_traits: {:?}", auto_traits);
1637 // Transform a `PolyTraitRef` into a `PolyExistentialTraitRef` by
1638 // removing the dummy `Self` type (`trait_object_dummy_self`).
1639 let trait_ref_to_existential = |trait_ref: ty::TraitRef<'tcx>| {
1640 if trait_ref.self_ty() != dummy_self {
1641 // FIXME: There appears to be a missing filter on top of `expand_trait_aliases`,
1642 // which picks up non-supertraits where clauses - but also, the object safety
1643 // completely ignores trait aliases, which could be object safety hazards. We
1644 // `delay_span_bug` here to avoid an ICE in stable even when the feature is
1645 // disabled. (#66420)
1646 tcx.sess.delay_span_bug(
1649 "trait_ref_to_existential called on {:?} with non-dummy Self",
1654 ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref)
1657 // Erase the `dummy_self` (`trait_object_dummy_self`) used above.
1658 let existential_trait_refs = regular_traits
1660 .map(|i| i.trait_ref().map_bound(|trait_ref| trait_ref_to_existential(trait_ref)));
1661 let existential_projections = bounds.projection_bounds.iter().map(|(bound, _)| {
1662 bound.map_bound(|b| {
1663 let trait_ref = trait_ref_to_existential(b.projection_ty.trait_ref(tcx));
1664 ty::ExistentialProjection {
1666 item_def_id: b.projection_ty.item_def_id,
1667 substs: trait_ref.substs,
1672 // Calling `skip_binder` is okay because the predicates are re-bound.
1673 let regular_trait_predicates = existential_trait_refs
1674 .map(|trait_ref| ty::ExistentialPredicate::Trait(*trait_ref.skip_binder()));
1675 let auto_trait_predicates = auto_traits
1677 .map(|trait_ref| ty::ExistentialPredicate::AutoTrait(trait_ref.trait_ref().def_id()));
1678 let mut v = regular_trait_predicates
1679 .chain(auto_trait_predicates)
1681 existential_projections
1682 .map(|x| ty::ExistentialPredicate::Projection(*x.skip_binder())),
1684 .collect::<SmallVec<[_; 8]>>();
1685 v.sort_by(|a, b| a.stable_cmp(tcx, b));
1687 let existential_predicates = ty::Binder::bind(tcx.mk_existential_predicates(v.into_iter()));
1689 // Use explicitly-specified region bound.
1690 let region_bound = if !lifetime.is_elided() {
1691 self.ast_region_to_region(lifetime, None)
1693 self.compute_object_lifetime_bound(span, existential_predicates).unwrap_or_else(|| {
1694 if tcx.named_region(lifetime.hir_id).is_some() {
1695 self.ast_region_to_region(lifetime, None)
1697 self.re_infer(None, span).unwrap_or_else(|| {
1702 "the lifetime bound for this object type cannot be deduced \
1703 from context; please supply an explicit bound"
1706 tcx.lifetimes.re_static
1711 debug!("region_bound: {:?}", region_bound);
1713 let ty = tcx.mk_dynamic(existential_predicates, region_bound);
1714 debug!("trait_object_type: {:?}", ty);
1718 /// When there are any missing associated types, emit an E0191 error and attempt to supply a
1719 /// reasonable suggestion on how to write it. For the case of multiple associated types in the
1720 /// same trait bound have the same name (as they come from different super-traits), we instead
1721 /// emit a generic note suggesting using a `where` clause to constraint instead.
1722 fn complain_about_missing_associated_types(
1724 associated_types: FxHashMap<Span, BTreeSet<DefId>>,
1725 potential_assoc_types: Vec<Span>,
1726 trait_bounds: &[hir::PolyTraitRef<'_>],
1728 if !associated_types.values().any(|v| v.len() > 0) {
1731 let tcx = self.tcx();
1732 // FIXME: Marked `mut` so that we can replace the spans further below with a more
1733 // appropriate one, but this should be handled earlier in the span assignment.
1734 let mut associated_types: FxHashMap<Span, Vec<_>> = associated_types
1736 .map(|(span, def_ids)| {
1737 (span, def_ids.into_iter().map(|did| tcx.associated_item(did)).collect())
1740 let mut names = vec![];
1742 // Account for things like `dyn Foo + 'a`, like in tests `issue-22434.rs` and
1743 // `issue-22560.rs`.
1744 let mut trait_bound_spans: Vec<Span> = vec![];
1745 for (span, items) in &associated_types {
1746 if !items.is_empty() {
1747 trait_bound_spans.push(*span);
1749 for assoc_item in items {
1750 let trait_def_id = assoc_item.container.id();
1752 "`{}` (from trait `{}`)",
1754 tcx.def_path_str(trait_def_id),
1759 match (&potential_assoc_types[..], &trait_bounds) {
1760 ([], [bound]) => match &bound.trait_ref.path.segments[..] {
1761 // FIXME: `trait_ref.path.span` can point to a full path with multiple
1762 // segments, even though `trait_ref.path.segments` is of length `1`. Work
1763 // around that bug here, even though it should be fixed elsewhere.
1764 // This would otherwise cause an invalid suggestion. For an example, look at
1765 // `src/test/ui/issues/issue-28344.rs` where instead of the following:
1767 // error[E0191]: the value of the associated type `Output`
1768 // (from trait `std::ops::BitXor`) must be specified
1769 // --> $DIR/issue-28344.rs:4:17
1771 // LL | let x: u8 = BitXor::bitor(0 as u8, 0 as u8);
1772 // | ^^^^^^ help: specify the associated type:
1773 // | `BitXor<Output = Type>`
1777 // error[E0191]: the value of the associated type `Output`
1778 // (from trait `std::ops::BitXor`) must be specified
1779 // --> $DIR/issue-28344.rs:4:17
1781 // LL | let x: u8 = BitXor::bitor(0 as u8, 0 as u8);
1782 // | ^^^^^^^^^^^^^ help: specify the associated type:
1783 // | `BitXor::bitor<Output = Type>`
1784 [segment] if segment.args.is_none() => {
1785 trait_bound_spans = vec![segment.ident.span];
1786 associated_types = associated_types
1788 .map(|(_, items)| (segment.ident.span, items))
1796 trait_bound_spans.sort();
1797 let mut err = struct_span_err!(
1801 "the value of the associated type{} {} must be specified",
1802 pluralize!(names.len()),
1805 let mut suggestions = vec![];
1806 let mut types_count = 0;
1807 let mut where_constraints = vec![];
1808 for (span, assoc_items) in &associated_types {
1809 let mut names: FxHashMap<_, usize> = FxHashMap::default();
1810 for item in assoc_items {
1812 *names.entry(item.ident.name).or_insert(0) += 1;
1814 let mut dupes = false;
1815 for item in assoc_items {
1816 let prefix = if names[&item.ident.name] > 1 {
1817 let trait_def_id = item.container.id();
1819 format!("{}::", tcx.def_path_str(trait_def_id))
1823 if let Some(sp) = tcx.hir().span_if_local(item.def_id) {
1824 err.span_label(sp, format!("`{}{}` defined here", prefix, item.ident));
1827 if potential_assoc_types.len() == assoc_items.len() {
1828 // Only suggest when the amount of missing associated types equals the number of
1829 // extra type arguments present, as that gives us a relatively high confidence
1830 // that the user forgot to give the associtated type's name. The canonical
1831 // example would be trying to use `Iterator<isize>` instead of
1832 // `Iterator<Item = isize>`.
1833 for (potential, item) in potential_assoc_types.iter().zip(assoc_items.iter()) {
1834 if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(*potential) {
1835 suggestions.push((*potential, format!("{} = {}", item.ident, snippet)));
1838 } else if let (Ok(snippet), false) =
1839 (tcx.sess.source_map().span_to_snippet(*span), dupes)
1842 assoc_items.iter().map(|item| format!("{} = Type", item.ident)).collect();
1843 let code = if snippet.ends_with(">") {
1844 // The user wrote `Trait<'a>` or similar and we don't have a type we can
1845 // suggest, but at least we can clue them to the correct syntax
1846 // `Trait<'a, Item = Type>` while accounting for the `<'a>` in the
1848 format!("{}, {}>", &snippet[..snippet.len() - 1], types.join(", "))
1850 // The user wrote `Iterator`, so we don't have a type we can suggest, but at
1851 // least we can clue them to the correct syntax `Iterator<Item = Type>`.
1852 format!("{}<{}>", snippet, types.join(", "))
1854 suggestions.push((*span, code));
1856 where_constraints.push(*span);
1859 let where_msg = "consider introducing a new type parameter, adding `where` constraints \
1860 using the fully-qualified path to the associated types";
1861 if !where_constraints.is_empty() && suggestions.is_empty() {
1862 // If there are duplicates associated type names and a single trait bound do not
1863 // use structured suggestion, it means that there are multiple super-traits with
1864 // the same associated type name.
1865 err.help(where_msg);
1867 if suggestions.len() != 1 {
1868 // We don't need this label if there's an inline suggestion, show otherwise.
1869 for (span, assoc_items) in &associated_types {
1870 let mut names: FxHashMap<_, usize> = FxHashMap::default();
1871 for item in assoc_items {
1873 *names.entry(item.ident.name).or_insert(0) += 1;
1875 let mut label = vec![];
1876 for item in assoc_items {
1877 let postfix = if names[&item.ident.name] > 1 {
1878 let trait_def_id = item.container.id();
1879 format!(" (from trait `{}`)", tcx.def_path_str(trait_def_id))
1883 label.push(format!("`{}`{}", item.ident, postfix));
1885 if !label.is_empty() {
1889 "associated type{} {} must be specified",
1890 pluralize!(label.len()),
1897 if !suggestions.is_empty() {
1898 err.multipart_suggestion(
1899 &format!("specify the associated type{}", pluralize!(types_count)),
1901 Applicability::HasPlaceholders,
1903 if !where_constraints.is_empty() {
1904 err.span_help(where_constraints, where_msg);
1910 fn report_ambiguous_associated_type(
1917 let mut err = struct_span_err!(self.tcx().sess, span, E0223, "ambiguous associated type");
1918 if let (Some(_), Ok(snippet)) = (
1919 self.tcx().sess.confused_type_with_std_module.borrow().get(&span),
1920 self.tcx().sess.source_map().span_to_snippet(span),
1922 err.span_suggestion(
1924 "you are looking for the module in `std`, not the primitive type",
1925 format!("std::{}", snippet),
1926 Applicability::MachineApplicable,
1929 err.span_suggestion(
1931 "use fully-qualified syntax",
1932 format!("<{} as {}>::{}", type_str, trait_str, name),
1933 Applicability::HasPlaceholders,
1939 // Search for a bound on a type parameter which includes the associated item
1940 // given by `assoc_name`. `ty_param_def_id` is the `DefId` of the type parameter
1941 // This function will fail if there are no suitable bounds or there is
1943 fn find_bound_for_assoc_item(
1945 ty_param_def_id: DefId,
1946 assoc_name: ast::Ident,
1948 ) -> Result<ty::PolyTraitRef<'tcx>, ErrorReported> {
1949 let tcx = self.tcx();
1952 "find_bound_for_assoc_item(ty_param_def_id={:?}, assoc_name={:?}, span={:?})",
1953 ty_param_def_id, assoc_name, span,
1956 let predicates = &self.get_type_parameter_bounds(span, ty_param_def_id).predicates;
1958 debug!("find_bound_for_assoc_item: predicates={:#?}", predicates);
1960 let param_hir_id = tcx.hir().as_local_hir_id(ty_param_def_id).unwrap();
1961 let param_name = tcx.hir().ty_param_name(param_hir_id);
1962 self.one_bound_for_assoc_type(
1964 traits::transitive_bounds(
1966 predicates.iter().filter_map(|(p, _)| p.to_opt_poly_trait_ref()),
1969 || param_name.to_string(),
1976 // Checks that `bounds` contains exactly one element and reports appropriate
1977 // errors otherwise.
1978 fn one_bound_for_assoc_type<I>(
1980 all_candidates: impl Fn() -> I,
1981 ty_param_name: impl Fn() -> String,
1982 assoc_name: ast::Ident,
1984 is_equality: impl Fn() -> Option<String>,
1985 ) -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
1987 I: Iterator<Item = ty::PolyTraitRef<'tcx>>,
1989 let mut matching_candidates = all_candidates()
1990 .filter(|r| self.trait_defines_associated_type_named(r.def_id(), assoc_name));
1992 let bound = match matching_candidates.next() {
1993 Some(bound) => bound,
1995 self.complain_about_assoc_type_not_found(
2001 return Err(ErrorReported);
2005 debug!("one_bound_for_assoc_type: bound = {:?}", bound);
2007 if let Some(bound2) = matching_candidates.next() {
2008 debug!("one_bound_for_assoc_type: bound2 = {:?}", bound2);
2010 let is_equality = is_equality();
2011 let bounds = iter::once(bound).chain(iter::once(bound2)).chain(matching_candidates);
2012 let mut err = if is_equality.is_some() {
2013 // More specific Error Index entry.
2018 "ambiguous associated type `{}` in bounds of `{}`",
2027 "ambiguous associated type `{}` in bounds of `{}`",
2032 err.span_label(span, format!("ambiguous associated type `{}`", assoc_name));
2034 let mut where_bounds = vec![];
2035 for bound in bounds {
2036 let bound_id = bound.def_id();
2037 let bound_span = self
2039 .associated_items(bound_id)
2040 .find_by_name_and_kind(self.tcx(), assoc_name, ty::AssocKind::Type, bound_id)
2041 .and_then(|item| self.tcx().hir().span_if_local(item.def_id));
2043 if let Some(bound_span) = bound_span {
2047 "ambiguous `{}` from `{}`",
2049 bound.print_only_trait_path(),
2052 if let Some(constraint) = &is_equality {
2053 where_bounds.push(format!(
2054 " T: {trait}::{assoc} = {constraint}",
2055 trait=bound.print_only_trait_path(),
2057 constraint=constraint,
2060 err.span_suggestion(
2062 "use fully qualified syntax to disambiguate",
2066 bound.print_only_trait_path(),
2069 Applicability::MaybeIncorrect,
2074 "associated type `{}` could derive from `{}`",
2076 bound.print_only_trait_path(),
2080 if !where_bounds.is_empty() {
2082 "consider introducing a new type parameter `T` and adding `where` constraints:\
2083 \n where\n T: {},\n{}",
2085 where_bounds.join(",\n"),
2089 if !where_bounds.is_empty() {
2090 return Err(ErrorReported);
2096 fn complain_about_assoc_type_not_found<I>(
2098 all_candidates: impl Fn() -> I,
2099 ty_param_name: &str,
2100 assoc_name: ast::Ident,
2103 I: Iterator<Item = ty::PolyTraitRef<'tcx>>,
2105 // The fallback span is needed because `assoc_name` might be an `Fn()`'s `Output` without a
2106 // valid span, so we point at the whole path segment instead.
2107 let span = if assoc_name.span != DUMMY_SP { assoc_name.span } else { span };
2108 let mut err = struct_span_err!(
2112 "associated type `{}` not found for `{}`",
2117 let all_candidate_names: Vec<_> = all_candidates()
2118 .map(|r| self.tcx().associated_items(r.def_id()).in_definition_order())
2121 |item| if item.kind == ty::AssocKind::Type { Some(item.ident.name) } else { None },
2125 if let (Some(suggested_name), true) = (
2126 find_best_match_for_name(all_candidate_names.iter(), &assoc_name.as_str(), None),
2127 assoc_name.span != DUMMY_SP,
2129 err.span_suggestion(
2131 "there is an associated type with a similar name",
2132 suggested_name.to_string(),
2133 Applicability::MaybeIncorrect,
2136 err.span_label(span, format!("associated type `{}` not found", assoc_name));
2142 // Create a type from a path to an associated type.
2143 // For a path `A::B::C::D`, `qself_ty` and `qself_def` are the type and def for `A::B::C`
2144 // and item_segment is the path segment for `D`. We return a type and a def for
2146 // Will fail except for `T::A` and `Self::A`; i.e., if `qself_ty`/`qself_def` are not a type
2147 // parameter or `Self`.
2148 pub fn associated_path_to_ty(
2150 hir_ref_id: hir::HirId,
2154 assoc_segment: &hir::PathSegment<'_>,
2155 permit_variants: bool,
2156 ) -> Result<(Ty<'tcx>, DefKind, DefId), ErrorReported> {
2157 let tcx = self.tcx();
2158 let assoc_ident = assoc_segment.ident;
2160 debug!("associated_path_to_ty: {:?}::{}", qself_ty, assoc_ident);
2162 // Check if we have an enum variant.
2163 let mut variant_resolution = None;
2164 if let ty::Adt(adt_def, _) = qself_ty.kind {
2165 if adt_def.is_enum() {
2166 let variant_def = adt_def
2169 .find(|vd| tcx.hygienic_eq(assoc_ident, vd.ident, adt_def.did));
2170 if let Some(variant_def) = variant_def {
2171 if permit_variants {
2172 tcx.check_stability(variant_def.def_id, Some(hir_ref_id), span);
2173 self.prohibit_generics(slice::from_ref(assoc_segment));
2174 return Ok((qself_ty, DefKind::Variant, variant_def.def_id));
2176 variant_resolution = Some(variant_def.def_id);
2182 // Find the type of the associated item, and the trait where the associated
2183 // item is declared.
2184 let bound = match (&qself_ty.kind, qself_res) {
2185 (_, Res::SelfTy(Some(_), Some(impl_def_id))) => {
2186 // `Self` in an impl of a trait -- we have a concrete self type and a
2188 let trait_ref = match tcx.impl_trait_ref(impl_def_id) {
2189 Some(trait_ref) => trait_ref,
2191 // A cycle error occurred, most likely.
2192 return Err(ErrorReported);
2196 self.one_bound_for_assoc_type(
2197 || traits::supertraits(tcx, ty::Binder::bind(trait_ref)),
2198 || "Self".to_string(),
2204 (&ty::Param(_), Res::SelfTy(Some(param_did), None))
2205 | (&ty::Param(_), Res::Def(DefKind::TyParam, param_did)) => {
2206 self.find_bound_for_assoc_item(param_did, assoc_ident, span)?
2209 if variant_resolution.is_some() {
2210 // Variant in type position
2211 let msg = format!("expected type, found variant `{}`", assoc_ident);
2212 tcx.sess.span_err(span, &msg);
2213 } else if qself_ty.is_enum() {
2214 let mut err = struct_span_err!(
2218 "no variant named `{}` found for enum `{}`",
2223 let adt_def = qself_ty.ty_adt_def().expect("enum is not an ADT");
2224 if let Some(suggested_name) = find_best_match_for_name(
2225 adt_def.variants.iter().map(|variant| &variant.ident.name),
2226 &assoc_ident.as_str(),
2229 err.span_suggestion(
2231 "there is a variant with a similar name",
2232 suggested_name.to_string(),
2233 Applicability::MaybeIncorrect,
2238 format!("variant not found in `{}`", qself_ty),
2242 if let Some(sp) = tcx.hir().span_if_local(adt_def.did) {
2243 let sp = tcx.sess.source_map().def_span(sp);
2244 err.span_label(sp, format!("variant `{}` not found here", assoc_ident));
2248 } else if !qself_ty.references_error() {
2249 // Don't print `TyErr` to the user.
2250 self.report_ambiguous_associated_type(
2252 &qself_ty.to_string(),
2257 return Err(ErrorReported);
2261 let trait_did = bound.def_id();
2262 let (assoc_ident, def_scope) =
2263 tcx.adjust_ident_and_get_scope(assoc_ident, trait_did, hir_ref_id);
2265 // We have already adjusted the item name above, so compare with `ident.modern()` instead
2266 // of calling `filter_by_name_and_kind`.
2268 .associated_items(trait_did)
2269 .in_definition_order()
2270 .find(|i| i.kind.namespace() == Namespace::TypeNS && i.ident.modern() == assoc_ident)
2271 .expect("missing associated type");
2273 let ty = self.projected_ty_from_poly_trait_ref(span, item.def_id, assoc_segment, bound);
2274 let ty = self.normalize_ty(span, ty);
2276 let kind = DefKind::AssocTy;
2277 if !item.vis.is_accessible_from(def_scope, tcx) {
2278 let msg = format!("{} `{}` is private", kind.descr(item.def_id), assoc_ident);
2279 tcx.sess.span_err(span, &msg);
2281 tcx.check_stability(item.def_id, Some(hir_ref_id), span);
2283 if let Some(variant_def_id) = variant_resolution {
2284 tcx.struct_span_lint_hir(AMBIGUOUS_ASSOCIATED_ITEMS, hir_ref_id, span, |lint| {
2285 let mut err = lint.build("ambiguous associated item");
2286 let mut could_refer_to = |kind: DefKind, def_id, also| {
2287 let note_msg = format!(
2288 "`{}` could{} refer to the {} defined here",
2293 err.span_note(tcx.def_span(def_id), ¬e_msg);
2296 could_refer_to(DefKind::Variant, variant_def_id, "");
2297 could_refer_to(kind, item.def_id, " also");
2299 err.span_suggestion(
2301 "use fully-qualified syntax",
2302 format!("<{} as {}>::{}", qself_ty, tcx.item_name(trait_did), assoc_ident),
2303 Applicability::MachineApplicable,
2309 Ok((ty, kind, item.def_id))
2315 opt_self_ty: Option<Ty<'tcx>>,
2317 trait_segment: &hir::PathSegment<'_>,
2318 item_segment: &hir::PathSegment<'_>,
2320 let tcx = self.tcx();
2322 let trait_def_id = tcx.parent(item_def_id).unwrap();
2324 debug!("qpath_to_ty: trait_def_id={:?}", trait_def_id);
2326 let self_ty = if let Some(ty) = opt_self_ty {
2329 let path_str = tcx.def_path_str(trait_def_id);
2331 let def_id = self.item_def_id();
2333 debug!("qpath_to_ty: self.item_def_id()={:?}", def_id);
2335 let parent_def_id = def_id
2336 .and_then(|def_id| tcx.hir().as_local_hir_id(def_id))
2337 .map(|hir_id| tcx.hir().get_parent_did(hir_id));
2339 debug!("qpath_to_ty: parent_def_id={:?}", parent_def_id);
2341 // If the trait in segment is the same as the trait defining the item,
2342 // use the `<Self as ..>` syntax in the error.
2343 let is_part_of_self_trait_constraints = def_id == Some(trait_def_id);
2344 let is_part_of_fn_in_self_trait = parent_def_id == Some(trait_def_id);
2346 let type_name = if is_part_of_self_trait_constraints || is_part_of_fn_in_self_trait {
2352 self.report_ambiguous_associated_type(
2356 item_segment.ident.name,
2358 return tcx.types.err;
2361 debug!("qpath_to_ty: self_type={:?}", self_ty);
2363 let trait_ref = self.ast_path_to_mono_trait_ref(span, trait_def_id, self_ty, trait_segment);
2365 let item_substs = self.create_substs_for_associated_item(
2373 debug!("qpath_to_ty: trait_ref={:?}", trait_ref);
2375 self.normalize_ty(span, tcx.mk_projection(item_def_id, item_substs))
2378 pub fn prohibit_generics<'a, T: IntoIterator<Item = &'a hir::PathSegment<'a>>>(
2382 let mut has_err = false;
2383 for segment in segments {
2384 let (mut err_for_lt, mut err_for_ty, mut err_for_ct) = (false, false, false);
2385 for arg in segment.generic_args().args {
2386 let (span, kind) = match arg {
2387 hir::GenericArg::Lifetime(lt) => {
2393 (lt.span, "lifetime")
2395 hir::GenericArg::Type(ty) => {
2403 hir::GenericArg::Const(ct) => {
2411 let mut err = struct_span_err!(
2415 "{} arguments are not allowed for this type",
2418 err.span_label(span, format!("{} argument not allowed", kind));
2420 if err_for_lt && err_for_ty && err_for_ct {
2424 for binding in segment.generic_args().bindings {
2426 Self::prohibit_assoc_ty_binding(self.tcx(), binding.span);
2433 pub fn prohibit_assoc_ty_binding(tcx: TyCtxt<'_>, span: Span) {
2434 let mut err = struct_span_err!(
2438 "associated type bindings are not allowed here"
2440 err.span_label(span, "associated type not allowed here").emit();
2443 // FIXME(eddyb, varkor) handle type paths here too, not just value ones.
2444 pub fn def_ids_for_value_path_segments(
2446 segments: &[hir::PathSegment<'_>],
2447 self_ty: Option<Ty<'tcx>>,
2451 // We need to extract the type parameters supplied by the user in
2452 // the path `path`. Due to the current setup, this is a bit of a
2453 // tricky-process; the problem is that resolve only tells us the
2454 // end-point of the path resolution, and not the intermediate steps.
2455 // Luckily, we can (at least for now) deduce the intermediate steps
2456 // just from the end-point.
2458 // There are basically five cases to consider:
2460 // 1. Reference to a constructor of a struct:
2462 // struct Foo<T>(...)
2464 // In this case, the parameters are declared in the type space.
2466 // 2. Reference to a constructor of an enum variant:
2468 // enum E<T> { Foo(...) }
2470 // In this case, the parameters are defined in the type space,
2471 // but may be specified either on the type or the variant.
2473 // 3. Reference to a fn item or a free constant:
2477 // In this case, the path will again always have the form
2478 // `a::b::foo::<T>` where only the final segment should have
2479 // type parameters. However, in this case, those parameters are
2480 // declared on a value, and hence are in the `FnSpace`.
2482 // 4. Reference to a method or an associated constant:
2484 // impl<A> SomeStruct<A> {
2488 // Here we can have a path like
2489 // `a::b::SomeStruct::<A>::foo::<B>`, in which case parameters
2490 // may appear in two places. The penultimate segment,
2491 // `SomeStruct::<A>`, contains parameters in TypeSpace, and the
2492 // final segment, `foo::<B>` contains parameters in fn space.
2494 // The first step then is to categorize the segments appropriately.
2496 let tcx = self.tcx();
2498 assert!(!segments.is_empty());
2499 let last = segments.len() - 1;
2501 let mut path_segs = vec![];
2504 // Case 1. Reference to a struct constructor.
2505 DefKind::Ctor(CtorOf::Struct, ..) => {
2506 // Everything but the final segment should have no
2507 // parameters at all.
2508 let generics = tcx.generics_of(def_id);
2509 // Variant and struct constructors use the
2510 // generics of their parent type definition.
2511 let generics_def_id = generics.parent.unwrap_or(def_id);
2512 path_segs.push(PathSeg(generics_def_id, last));
2515 // Case 2. Reference to a variant constructor.
2516 DefKind::Ctor(CtorOf::Variant, ..) | DefKind::Variant => {
2517 let adt_def = self_ty.map(|t| t.ty_adt_def().unwrap());
2518 let (generics_def_id, index) = if let Some(adt_def) = adt_def {
2519 debug_assert!(adt_def.is_enum());
2521 } else if last >= 1 && segments[last - 1].args.is_some() {
2522 // Everything but the penultimate segment should have no
2523 // parameters at all.
2524 let mut def_id = def_id;
2526 // `DefKind::Ctor` -> `DefKind::Variant`
2527 if let DefKind::Ctor(..) = kind {
2528 def_id = tcx.parent(def_id).unwrap()
2531 // `DefKind::Variant` -> `DefKind::Enum`
2532 let enum_def_id = tcx.parent(def_id).unwrap();
2533 (enum_def_id, last - 1)
2535 // FIXME: lint here recommending `Enum::<...>::Variant` form
2536 // instead of `Enum::Variant::<...>` form.
2538 // Everything but the final segment should have no
2539 // parameters at all.
2540 let generics = tcx.generics_of(def_id);
2541 // Variant and struct constructors use the
2542 // generics of their parent type definition.
2543 (generics.parent.unwrap_or(def_id), last)
2545 path_segs.push(PathSeg(generics_def_id, index));
2548 // Case 3. Reference to a top-level value.
2549 DefKind::Fn | DefKind::Const | DefKind::ConstParam | DefKind::Static => {
2550 path_segs.push(PathSeg(def_id, last));
2553 // Case 4. Reference to a method or associated const.
2554 DefKind::Method | DefKind::AssocConst => {
2555 if segments.len() >= 2 {
2556 let generics = tcx.generics_of(def_id);
2557 path_segs.push(PathSeg(generics.parent.unwrap(), last - 1));
2559 path_segs.push(PathSeg(def_id, last));
2562 kind => bug!("unexpected definition kind {:?} for {:?}", kind, def_id),
2565 debug!("path_segs = {:?}", path_segs);
2570 // Check a type `Path` and convert it to a `Ty`.
2573 opt_self_ty: Option<Ty<'tcx>>,
2574 path: &hir::Path<'_>,
2575 permit_variants: bool,
2577 let tcx = self.tcx();
2580 "res_to_ty(res={:?}, opt_self_ty={:?}, path_segments={:?})",
2581 path.res, opt_self_ty, path.segments
2584 let span = path.span;
2586 Res::Def(DefKind::OpaqueTy, did) => {
2587 // Check for desugared `impl Trait`.
2588 assert!(ty::is_impl_trait_defn(tcx, did).is_none());
2589 let item_segment = path.segments.split_last().unwrap();
2590 self.prohibit_generics(item_segment.1);
2591 let substs = self.ast_path_substs_for_ty(span, did, item_segment.0);
2592 self.normalize_ty(span, tcx.mk_opaque(did, substs))
2594 Res::Def(DefKind::Enum, did)
2595 | Res::Def(DefKind::TyAlias, did)
2596 | Res::Def(DefKind::Struct, did)
2597 | Res::Def(DefKind::Union, did)
2598 | Res::Def(DefKind::ForeignTy, did) => {
2599 assert_eq!(opt_self_ty, None);
2600 self.prohibit_generics(path.segments.split_last().unwrap().1);
2601 self.ast_path_to_ty(span, did, path.segments.last().unwrap())
2603 Res::Def(kind @ DefKind::Variant, def_id) if permit_variants => {
2604 // Convert "variant type" as if it were a real type.
2605 // The resulting `Ty` is type of the variant's enum for now.
2606 assert_eq!(opt_self_ty, None);
2609 self.def_ids_for_value_path_segments(&path.segments, None, kind, def_id);
2610 let generic_segs: FxHashSet<_> =
2611 path_segs.iter().map(|PathSeg(_, index)| index).collect();
2612 self.prohibit_generics(path.segments.iter().enumerate().filter_map(
2614 if !generic_segs.contains(&index) { Some(seg) } else { None }
2618 let PathSeg(def_id, index) = path_segs.last().unwrap();
2619 self.ast_path_to_ty(span, *def_id, &path.segments[*index])
2621 Res::Def(DefKind::TyParam, def_id) => {
2622 assert_eq!(opt_self_ty, None);
2623 self.prohibit_generics(path.segments);
2625 let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
2626 let item_id = tcx.hir().get_parent_node(hir_id);
2627 let item_def_id = tcx.hir().local_def_id(item_id);
2628 let generics = tcx.generics_of(item_def_id);
2629 let index = generics.param_def_id_to_index[&def_id];
2630 tcx.mk_ty_param(index, tcx.hir().name(hir_id))
2632 Res::SelfTy(Some(_), None) => {
2633 // `Self` in trait or type alias.
2634 assert_eq!(opt_self_ty, None);
2635 self.prohibit_generics(path.segments);
2636 tcx.types.self_param
2638 Res::SelfTy(_, Some(def_id)) => {
2639 // `Self` in impl (we know the concrete type).
2640 assert_eq!(opt_self_ty, None);
2641 self.prohibit_generics(path.segments);
2642 // Try to evaluate any array length constants.
2643 self.normalize_ty(span, tcx.at(span).type_of(def_id))
2645 Res::Def(DefKind::AssocTy, def_id) => {
2646 debug_assert!(path.segments.len() >= 2);
2647 self.prohibit_generics(&path.segments[..path.segments.len() - 2]);
2652 &path.segments[path.segments.len() - 2],
2653 path.segments.last().unwrap(),
2656 Res::PrimTy(prim_ty) => {
2657 assert_eq!(opt_self_ty, None);
2658 self.prohibit_generics(path.segments);
2660 hir::PrimTy::Bool => tcx.types.bool,
2661 hir::PrimTy::Char => tcx.types.char,
2662 hir::PrimTy::Int(it) => tcx.mk_mach_int(it),
2663 hir::PrimTy::Uint(uit) => tcx.mk_mach_uint(uit),
2664 hir::PrimTy::Float(ft) => tcx.mk_mach_float(ft),
2665 hir::PrimTy::Str => tcx.mk_str(),
2669 self.set_tainted_by_errors();
2670 return self.tcx().types.err;
2672 _ => span_bug!(span, "unexpected resolution: {:?}", path.res),
2676 /// Parses the programmer's textual representation of a type into our
2677 /// internal notion of a type.
2678 pub fn ast_ty_to_ty(&self, ast_ty: &hir::Ty<'_>) -> Ty<'tcx> {
2679 debug!("ast_ty_to_ty(id={:?}, ast_ty={:?} ty_ty={:?})", ast_ty.hir_id, ast_ty, ast_ty.kind);
2681 let tcx = self.tcx();
2683 let result_ty = match ast_ty.kind {
2684 hir::TyKind::Slice(ref ty) => tcx.mk_slice(self.ast_ty_to_ty(&ty)),
2685 hir::TyKind::Ptr(ref mt) => {
2686 tcx.mk_ptr(ty::TypeAndMut { ty: self.ast_ty_to_ty(&mt.ty), mutbl: mt.mutbl })
2688 hir::TyKind::Rptr(ref region, ref mt) => {
2689 let r = self.ast_region_to_region(region, None);
2690 debug!("ast_ty_to_ty: r={:?}", r);
2691 let t = self.ast_ty_to_ty(&mt.ty);
2692 tcx.mk_ref(r, ty::TypeAndMut { ty: t, mutbl: mt.mutbl })
2694 hir::TyKind::Never => tcx.types.never,
2695 hir::TyKind::Tup(ref fields) => {
2696 tcx.mk_tup(fields.iter().map(|t| self.ast_ty_to_ty(&t)))
2698 hir::TyKind::BareFn(ref bf) => {
2699 require_c_abi_if_c_variadic(tcx, &bf.decl, bf.abi, ast_ty.span);
2700 tcx.mk_fn_ptr(self.ty_of_fn(bf.unsafety, bf.abi, &bf.decl, &[], None))
2702 hir::TyKind::TraitObject(ref bounds, ref lifetime) => {
2703 self.conv_object_ty_poly_trait_ref(ast_ty.span, bounds, lifetime)
2705 hir::TyKind::Path(hir::QPath::Resolved(ref maybe_qself, ref path)) => {
2706 debug!("ast_ty_to_ty: maybe_qself={:?} path={:?}", maybe_qself, path);
2707 let opt_self_ty = maybe_qself.as_ref().map(|qself| self.ast_ty_to_ty(qself));
2708 self.res_to_ty(opt_self_ty, path, false)
2710 hir::TyKind::Def(item_id, ref lifetimes) => {
2711 let did = tcx.hir().local_def_id(item_id.id);
2712 self.impl_trait_ty_to_ty(did, lifetimes)
2714 hir::TyKind::Path(hir::QPath::TypeRelative(ref qself, ref segment)) => {
2715 debug!("ast_ty_to_ty: qself={:?} segment={:?}", qself, segment);
2716 let ty = self.ast_ty_to_ty(qself);
2718 let res = if let hir::TyKind::Path(hir::QPath::Resolved(_, ref path)) = qself.kind {
2723 self.associated_path_to_ty(ast_ty.hir_id, ast_ty.span, ty, res, segment, false)
2724 .map(|(ty, _, _)| ty)
2725 .unwrap_or(tcx.types.err)
2727 hir::TyKind::Array(ref ty, ref length) => {
2728 let length = self.ast_const_to_const(length, tcx.types.usize);
2729 let array_ty = tcx.mk_ty(ty::Array(self.ast_ty_to_ty(&ty), length));
2730 self.normalize_ty(ast_ty.span, array_ty)
2732 hir::TyKind::Typeof(ref _e) => {
2737 "`typeof` is a reserved keyword but unimplemented"
2739 .span_label(ast_ty.span, "reserved keyword")
2744 hir::TyKind::Infer => {
2745 // Infer also appears as the type of arguments or return
2746 // values in a ExprKind::Closure, or as
2747 // the type of local variables. Both of these cases are
2748 // handled specially and will not descend into this routine.
2749 self.ty_infer(None, ast_ty.span)
2751 hir::TyKind::Err => tcx.types.err,
2754 debug!("ast_ty_to_ty: result_ty={:?}", result_ty);
2756 self.record_ty(ast_ty.hir_id, result_ty, ast_ty.span);
2760 /// Returns the `DefId` of the constant parameter that the provided expression is a path to.
2761 pub fn const_param_def_id(&self, expr: &hir::Expr<'_>) -> Option<DefId> {
2762 // Unwrap a block, so that e.g. `{ P }` is recognised as a parameter. Const arguments
2763 // currently have to be wrapped in curly brackets, so it's necessary to special-case.
2764 let expr = match &expr.kind {
2765 ExprKind::Block(block, _) if block.stmts.is_empty() && block.expr.is_some() => {
2766 block.expr.as_ref().unwrap()
2772 ExprKind::Path(hir::QPath::Resolved(_, path)) => match path.res {
2773 Res::Def(DefKind::ConstParam, did) => Some(did),
2780 pub fn ast_const_to_const(
2782 ast_const: &hir::AnonConst,
2784 ) -> &'tcx ty::Const<'tcx> {
2785 debug!("ast_const_to_const(id={:?}, ast_const={:?})", ast_const.hir_id, ast_const);
2787 let tcx = self.tcx();
2788 let def_id = tcx.hir().local_def_id(ast_const.hir_id);
2790 let expr = &tcx.hir().body(ast_const.body).value;
2792 let lit_input = match expr.kind {
2793 hir::ExprKind::Lit(ref lit) => Some(LitToConstInput { lit: &lit.node, ty, neg: false }),
2794 hir::ExprKind::Unary(hir::UnOp::UnNeg, ref expr) => match expr.kind {
2795 hir::ExprKind::Lit(ref lit) => {
2796 Some(LitToConstInput { lit: &lit.node, ty, neg: true })
2803 if let Some(lit_input) = lit_input {
2804 // If an error occurred, ignore that it's a literal and leave reporting the error up to
2806 if let Ok(c) = tcx.at(expr.span).lit_to_const(lit_input) {
2809 tcx.sess.delay_span_bug(expr.span, "ast_const_to_const: couldn't lit_to_const");
2813 let kind = if let Some(def_id) = self.const_param_def_id(expr) {
2814 // Find the name and index of the const parameter by indexing the generics of the
2815 // parent item and construct a `ParamConst`.
2816 let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
2817 let item_id = tcx.hir().get_parent_node(hir_id);
2818 let item_def_id = tcx.hir().local_def_id(item_id);
2819 let generics = tcx.generics_of(item_def_id);
2820 let index = generics.param_def_id_to_index[&tcx.hir().local_def_id(hir_id)];
2821 let name = tcx.hir().name(hir_id);
2822 ty::ConstKind::Param(ty::ParamConst::new(index, name))
2824 ty::ConstKind::Unevaluated(def_id, InternalSubsts::identity_for_item(tcx, def_id), None)
2826 tcx.mk_const(ty::Const { val: kind, ty })
2829 pub fn impl_trait_ty_to_ty(
2832 lifetimes: &[hir::GenericArg<'_>],
2834 debug!("impl_trait_ty_to_ty(def_id={:?}, lifetimes={:?})", def_id, lifetimes);
2835 let tcx = self.tcx();
2837 let generics = tcx.generics_of(def_id);
2839 debug!("impl_trait_ty_to_ty: generics={:?}", generics);
2840 let substs = InternalSubsts::for_item(tcx, def_id, |param, _| {
2841 if let Some(i) = (param.index as usize).checked_sub(generics.parent_count) {
2842 // Our own parameters are the resolved lifetimes.
2844 GenericParamDefKind::Lifetime => {
2845 if let hir::GenericArg::Lifetime(lifetime) = &lifetimes[i] {
2846 self.ast_region_to_region(lifetime, None).into()
2854 // Replace all parent lifetimes with `'static`.
2856 GenericParamDefKind::Lifetime => tcx.lifetimes.re_static.into(),
2857 _ => tcx.mk_param_from_def(param),
2861 debug!("impl_trait_ty_to_ty: substs={:?}", substs);
2863 let ty = tcx.mk_opaque(def_id, substs);
2864 debug!("impl_trait_ty_to_ty: {}", ty);
2868 pub fn ty_of_arg(&self, ty: &hir::Ty<'_>, expected_ty: Option<Ty<'tcx>>) -> Ty<'tcx> {
2870 hir::TyKind::Infer if expected_ty.is_some() => {
2871 self.record_ty(ty.hir_id, expected_ty.unwrap(), ty.span);
2872 expected_ty.unwrap()
2874 _ => self.ast_ty_to_ty(ty),
2880 unsafety: hir::Unsafety,
2882 decl: &hir::FnDecl<'_>,
2883 generic_params: &[hir::GenericParam<'_>],
2884 ident_span: Option<Span>,
2885 ) -> ty::PolyFnSig<'tcx> {
2888 let tcx = self.tcx();
2890 // We proactively collect all the infered type params to emit a single error per fn def.
2891 let mut visitor = PlaceholderHirTyCollector::default();
2892 for ty in decl.inputs {
2893 visitor.visit_ty(ty);
2895 let input_tys = decl.inputs.iter().map(|a| self.ty_of_arg(a, None));
2896 let output_ty = match decl.output {
2897 hir::FnRetTy::Return(ref output) => {
2898 visitor.visit_ty(output);
2899 self.ast_ty_to_ty(output)
2901 hir::FnRetTy::DefaultReturn(..) => tcx.mk_unit(),
2904 debug!("ty_of_fn: output_ty={:?}", output_ty);
2907 ty::Binder::bind(tcx.mk_fn_sig(input_tys, output_ty, decl.c_variadic, unsafety, abi));
2909 if !self.allow_ty_infer() {
2910 // We always collect the spans for placeholder types when evaluating `fn`s, but we
2911 // only want to emit an error complaining about them if infer types (`_`) are not
2912 // allowed. `allow_ty_infer` gates this behavior.
2913 crate::collect::placeholder_type_error(
2915 ident_span.map(|sp| sp.shrink_to_hi()).unwrap_or(DUMMY_SP),
2918 ident_span.is_some(),
2922 // Find any late-bound regions declared in return type that do
2923 // not appear in the arguments. These are not well-formed.
2926 // for<'a> fn() -> &'a str <-- 'a is bad
2927 // for<'a> fn(&'a String) -> &'a str <-- 'a is ok
2928 let inputs = bare_fn_ty.inputs();
2929 let late_bound_in_args =
2930 tcx.collect_constrained_late_bound_regions(&inputs.map_bound(|i| i.to_owned()));
2931 let output = bare_fn_ty.output();
2932 let late_bound_in_ret = tcx.collect_referenced_late_bound_regions(&output);
2933 for br in late_bound_in_ret.difference(&late_bound_in_args) {
2934 let lifetime_name = match *br {
2935 ty::BrNamed(_, name) => format!("lifetime `{}`,", name),
2936 ty::BrAnon(_) | ty::BrEnv => "an anonymous lifetime".to_string(),
2938 let mut err = struct_span_err!(
2942 "return type references {} \
2943 which is not constrained by the fn input types",
2946 if let ty::BrAnon(_) = *br {
2947 // The only way for an anonymous lifetime to wind up
2948 // in the return type but **also** be unconstrained is
2949 // if it only appears in "associated types" in the
2950 // input. See #47511 for an example. In this case,
2951 // though we can easily give a hint that ought to be
2954 "lifetimes appearing in an associated type \
2955 are not considered constrained",
2964 /// Given the bounds on an object, determines what single region bound (if any) we can
2965 /// use to summarize this type. The basic idea is that we will use the bound the user
2966 /// provided, if they provided one, and otherwise search the supertypes of trait bounds
2967 /// for region bounds. It may be that we can derive no bound at all, in which case
2968 /// we return `None`.
2969 fn compute_object_lifetime_bound(
2972 existential_predicates: ty::Binder<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>>,
2973 ) -> Option<ty::Region<'tcx>> // if None, use the default
2975 let tcx = self.tcx();
2977 debug!("compute_opt_region_bound(existential_predicates={:?})", existential_predicates);
2979 // No explicit region bound specified. Therefore, examine trait
2980 // bounds and see if we can derive region bounds from those.
2981 let derived_region_bounds = object_region_bounds(tcx, existential_predicates);
2983 // If there are no derived region bounds, then report back that we
2984 // can find no region bound. The caller will use the default.
2985 if derived_region_bounds.is_empty() {
2989 // If any of the derived region bounds are 'static, that is always
2991 if derived_region_bounds.iter().any(|&r| ty::ReStatic == *r) {
2992 return Some(tcx.lifetimes.re_static);
2995 // Determine whether there is exactly one unique region in the set
2996 // of derived region bounds. If so, use that. Otherwise, report an
2998 let r = derived_region_bounds[0];
2999 if derived_region_bounds[1..].iter().any(|r1| r != *r1) {
3004 "ambiguous lifetime bound, explicit lifetime bound required"
3012 /// Collects together a list of bounds that are applied to some type,
3013 /// after they've been converted into `ty` form (from the HIR
3014 /// representations). These lists of bounds occur in many places in
3018 /// trait Foo: Bar + Baz { }
3019 /// ^^^^^^^^^ supertrait list bounding the `Self` type parameter
3021 /// fn foo<T: Bar + Baz>() { }
3022 /// ^^^^^^^^^ bounding the type parameter `T`
3024 /// impl dyn Bar + Baz
3025 /// ^^^^^^^^^ bounding the forgotten dynamic type
3028 /// Our representation is a bit mixed here -- in some cases, we
3029 /// include the self type (e.g., `trait_bounds`) but in others we do
3030 #[derive(Default, PartialEq, Eq, Clone, Debug)]
3031 pub struct Bounds<'tcx> {
3032 /// A list of region bounds on the (implicit) self type. So if you
3033 /// had `T: 'a + 'b` this might would be a list `['a, 'b]` (but
3034 /// the `T` is not explicitly included).
3035 pub region_bounds: Vec<(ty::Region<'tcx>, Span)>,
3037 /// A list of trait bounds. So if you had `T: Debug` this would be
3038 /// `T: Debug`. Note that the self-type is explicit here.
3039 pub trait_bounds: Vec<(ty::PolyTraitRef<'tcx>, Span, Constness)>,
3041 /// A list of projection equality bounds. So if you had `T:
3042 /// Iterator<Item = u32>` this would include `<T as
3043 /// Iterator>::Item => u32`. Note that the self-type is explicit
3045 pub projection_bounds: Vec<(ty::PolyProjectionPredicate<'tcx>, Span)>,
3047 /// `Some` if there is *no* `?Sized` predicate. The `span`
3048 /// is the location in the source of the `T` declaration which can
3049 /// be cited as the source of the `T: Sized` requirement.
3050 pub implicitly_sized: Option<Span>,
3053 impl<'tcx> Bounds<'tcx> {
3054 /// Converts a bounds list into a flat set of predicates (like
3055 /// where-clauses). Because some of our bounds listings (e.g.,
3056 /// regions) don't include the self-type, you must supply the
3057 /// self-type here (the `param_ty` parameter).
3062 ) -> Vec<(ty::Predicate<'tcx>, Span)> {
3063 // If it could be sized, and is, add the `Sized` predicate.
3064 let sized_predicate = self.implicitly_sized.and_then(|span| {
3065 tcx.lang_items().sized_trait().map(|sized| {
3066 let trait_ref = ty::Binder::bind(ty::TraitRef {
3068 substs: tcx.mk_substs_trait(param_ty, &[]),
3070 (trait_ref.without_const().to_predicate(), span)
3079 .map(|&(region_bound, span)| {
3080 // Account for the binder being introduced below; no need to shift `param_ty`
3081 // because, at present at least, it either only refers to early-bound regions,
3082 // or it's a generic associated type that deliberately has escaping bound vars.
3083 let region_bound = ty::fold::shift_region(tcx, region_bound, 1);
3084 let outlives = ty::OutlivesPredicate(param_ty, region_bound);
3085 (ty::Binder::bind(outlives).to_predicate(), span)
3087 .chain(self.trait_bounds.iter().map(|&(bound_trait_ref, span, constness)| {
3088 let predicate = bound_trait_ref.with_constness(constness).to_predicate();
3092 self.projection_bounds
3094 .map(|&(projection, span)| (projection.to_predicate(), span)),