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 errors::{Applicability, DiagnosticId};
6 use crate::hir::{self, GenericArg, GenericArgs, ExprKind};
7 use crate::hir::def::Def;
8 use crate::hir::def_id::DefId;
9 use crate::hir::HirVec;
11 use crate::middle::resolve_lifetime as rl;
12 use crate::namespace::Namespace;
13 use rustc::lint::builtin::AMBIGUOUS_ASSOCIATED_ITEMS;
15 use rustc::ty::{self, Ty, TyCtxt, ToPredicate, TypeFoldable};
16 use rustc::ty::{GenericParamDef, GenericParamDefKind};
17 use rustc::ty::subst::{Kind, Subst, InternalSubsts, SubstsRef};
18 use rustc::ty::wf::object_region_bounds;
19 use rustc::mir::interpret::ConstValue;
20 use rustc_data_structures::sync::Lrc;
21 use rustc_target::spec::abi;
22 use crate::require_c_abi_if_c_variadic;
23 use smallvec::SmallVec;
25 use syntax::feature_gate::{GateIssue, emit_feature_err};
27 use syntax::util::lev_distance::find_best_match_for_name;
28 use syntax_pos::{DUMMY_SP, Span, MultiSpan};
29 use crate::util::common::ErrorReported;
30 use crate::util::nodemap::FxHashMap;
32 use std::collections::BTreeSet;
36 use super::{check_type_alias_enum_variants_enabled};
37 use rustc_data_structures::fx::FxHashSet;
40 pub struct PathSeg(pub DefId, pub usize);
42 pub trait AstConv<'gcx, 'tcx> {
43 fn tcx<'a>(&'a self) -> TyCtxt<'a, 'gcx, 'tcx>;
45 /// Returns the set of bounds in scope for the type parameter with
47 fn get_type_parameter_bounds(&self, span: Span, def_id: DefId)
48 -> Lrc<ty::GenericPredicates<'tcx>>;
50 /// What lifetime should we use when a lifetime is omitted (and not elided)?
51 fn re_infer(&self, span: Span, _def: Option<&ty::GenericParamDef>)
52 -> Option<ty::Region<'tcx>>;
54 /// What type should we use when a type is omitted?
55 fn ty_infer(&self, span: Span) -> Ty<'tcx>;
57 /// Same as ty_infer, but with a known type parameter definition.
58 fn ty_infer_for_def(&self,
59 _def: &ty::GenericParamDef,
60 span: Span) -> Ty<'tcx> {
64 /// Projecting an associated type from a (potentially)
65 /// higher-ranked trait reference is more complicated, because of
66 /// the possibility of late-bound regions appearing in the
67 /// associated type binding. This is not legal in function
68 /// signatures for that reason. In a function body, we can always
69 /// handle it because we can use inference variables to remove the
70 /// late-bound regions.
71 fn projected_ty_from_poly_trait_ref(&self,
74 poly_trait_ref: ty::PolyTraitRef<'tcx>)
77 /// Normalize an associated type coming from the user.
78 fn normalize_ty(&self, span: Span, ty: Ty<'tcx>) -> Ty<'tcx>;
80 /// Invoked when we encounter an error from some prior pass
81 /// (e.g., resolve) that is translated into a ty-error. This is
82 /// used to help suppress derived errors typeck might otherwise
84 fn set_tainted_by_errors(&self);
86 fn record_ty(&self, hir_id: hir::HirId, ty: Ty<'tcx>, span: Span);
89 struct ConvertedBinding<'tcx> {
90 item_name: ast::Ident,
96 enum GenericArgPosition {
98 Value, // e.g., functions
102 /// Dummy type used for the `Self` of a `TraitRef` created for converting
103 /// a trait object, and which gets removed in `ExistentialTraitRef`.
104 /// This type must not appear anywhere in other converted types.
105 const TRAIT_OBJECT_DUMMY_SELF: ty::TyKind<'static> = ty::Infer(ty::FreshTy(0));
107 impl<'o, 'gcx: 'tcx, 'tcx> dyn AstConv<'gcx, 'tcx> + 'o {
108 pub fn ast_region_to_region(&self,
109 lifetime: &hir::Lifetime,
110 def: Option<&ty::GenericParamDef>)
113 let tcx = self.tcx();
114 let lifetime_name = |def_id| {
115 tcx.hir().name_by_hir_id(tcx.hir().as_local_hir_id(def_id).unwrap()).as_interned_str()
118 let r = match tcx.named_region(lifetime.hir_id) {
119 Some(rl::Region::Static) => {
123 Some(rl::Region::LateBound(debruijn, id, _)) => {
124 let name = lifetime_name(id);
125 tcx.mk_region(ty::ReLateBound(debruijn,
126 ty::BrNamed(id, name)))
129 Some(rl::Region::LateBoundAnon(debruijn, index)) => {
130 tcx.mk_region(ty::ReLateBound(debruijn, ty::BrAnon(index)))
133 Some(rl::Region::EarlyBound(index, id, _)) => {
134 let name = lifetime_name(id);
135 tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion {
142 Some(rl::Region::Free(scope, id)) => {
143 let name = lifetime_name(id);
144 tcx.mk_region(ty::ReFree(ty::FreeRegion {
146 bound_region: ty::BrNamed(id, name)
149 // (*) -- not late-bound, won't change
153 self.re_infer(lifetime.span, def)
155 // This indicates an illegal lifetime
156 // elision. `resolve_lifetime` should have
157 // reported an error in this case -- but if
158 // not, let's error out.
159 tcx.sess.delay_span_bug(lifetime.span, "unelided lifetime in signature");
161 // Supply some dummy value. We don't have an
162 // `re_error`, annoyingly, so use `'static`.
168 debug!("ast_region_to_region(lifetime={:?}) yields {:?}",
175 /// Given a path `path` that refers to an item `I` with the declared generics `decl_generics`,
176 /// returns an appropriate set of substitutions for this particular reference to `I`.
177 pub fn ast_path_substs_for_ty(&self,
180 item_segment: &hir::PathSegment)
183 let (substs, assoc_bindings, _) = item_segment.with_generic_args(|generic_args| {
184 self.create_substs_for_ast_path(
188 item_segment.infer_types,
193 assoc_bindings.first().map(|b| Self::prohibit_assoc_ty_binding(self.tcx(), b.span));
198 /// Report error if there is an explicit type parameter when using `impl Trait`.
200 tcx: TyCtxt<'_, '_, '_>,
202 seg: &hir::PathSegment,
203 generics: &ty::Generics,
205 let explicit = !seg.infer_types;
206 let impl_trait = generics.params.iter().any(|param| match param.kind {
207 ty::GenericParamDefKind::Type {
208 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait), ..
213 if explicit && impl_trait {
214 let mut err = struct_span_err! {
218 "cannot provide explicit type parameters when `impl Trait` is \
219 used in argument position."
228 /// Checks that the correct number of generic arguments have been provided.
229 /// Used specifically for function calls.
230 pub fn check_generic_arg_count_for_call(
231 tcx: TyCtxt<'_, '_, '_>,
234 seg: &hir::PathSegment,
235 is_method_call: bool,
237 let empty_args = P(hir::GenericArgs {
238 args: HirVec::new(), bindings: HirVec::new(), parenthesized: false,
240 let suppress_mismatch = Self::check_impl_trait(tcx, span, seg, &def);
241 Self::check_generic_arg_count(
245 if let Some(ref args) = seg.args {
251 GenericArgPosition::MethodCall
253 GenericArgPosition::Value
255 def.parent.is_none() && def.has_self, // `has_self`
256 seg.infer_types || suppress_mismatch, // `infer_types`
260 /// Checks that the correct number of generic arguments have been provided.
261 /// This is used both for datatypes and function calls.
262 fn check_generic_arg_count(
263 tcx: TyCtxt<'_, '_, '_>,
266 args: &hir::GenericArgs,
267 position: GenericArgPosition,
270 ) -> (bool, Option<Vec<Span>>) {
271 // At this stage we are guaranteed that the generic arguments are in the correct order, e.g.
272 // that lifetimes will proceed types. So it suffices to check the number of each generic
273 // arguments in order to validate them with respect to the generic parameters.
274 let param_counts = def.own_counts();
275 let arg_counts = args.own_counts();
276 let infer_lifetimes = position != GenericArgPosition::Type && arg_counts.lifetimes == 0;
277 let infer_consts = position != GenericArgPosition::Type && arg_counts.consts == 0;
279 let mut defaults: ty::GenericParamCount = Default::default();
280 for param in &def.params {
282 GenericParamDefKind::Lifetime => {}
283 GenericParamDefKind::Type { has_default, .. } => {
284 defaults.types += has_default as usize
286 GenericParamDefKind::Const => {
287 // FIXME(const_generics:defaults)
292 if position != GenericArgPosition::Type && !args.bindings.is_empty() {
293 AstConv::prohibit_assoc_ty_binding(tcx, args.bindings[0].span);
296 // Prohibit explicit lifetime arguments if late-bound lifetime parameters are present.
297 if !infer_lifetimes {
298 if let Some(span_late) = def.has_late_bound_regions {
299 let msg = "cannot specify lifetime arguments explicitly \
300 if late bound lifetime parameters are present";
301 let note = "the late bound lifetime parameter is introduced here";
302 let span = args.args[0].span();
303 if position == GenericArgPosition::Value
304 && arg_counts.lifetimes != param_counts.lifetimes {
305 let mut err = tcx.sess.struct_span_err(span, msg);
306 err.span_note(span_late, note);
310 let mut multispan = MultiSpan::from_span(span);
311 multispan.push_span_label(span_late, note.to_string());
312 tcx.lint_hir(lint::builtin::LATE_BOUND_LIFETIME_ARGUMENTS,
313 args.args[0].id(), multispan, msg);
314 return (false, None);
319 let check_kind_count = |kind, required, permitted, provided, offset| {
321 "check_kind_count: kind: {} required: {} permitted: {} provided: {} offset: {}",
328 // We enforce the following: `required` <= `provided` <= `permitted`.
329 // For kinds without defaults (i.e., lifetimes), `required == permitted`.
330 // For other kinds (i.e., types), `permitted` may be greater than `required`.
331 if required <= provided && provided <= permitted {
332 return (false, None);
335 // Unfortunately lifetime and type parameter mismatches are typically styled
336 // differently in diagnostics, which means we have a few cases to consider here.
337 let (bound, quantifier) = if required != permitted {
338 if provided < required {
339 (required, "at least ")
340 } else { // provided > permitted
341 (permitted, "at most ")
347 let mut potential_assoc_types: Option<Vec<Span>> = None;
348 let (spans, label) = if required == permitted && provided > permitted {
349 // In the case when the user has provided too many arguments,
350 // we want to point to the unexpected arguments.
351 let spans: Vec<Span> = args.args[offset+permitted .. offset+provided]
353 .map(|arg| arg.span())
355 potential_assoc_types = Some(spans.clone());
356 (spans, format!( "unexpected {} argument", kind))
358 (vec![span], format!(
359 "expected {}{} {} argument{}",
363 if bound != 1 { "s" } else { "" },
367 let mut err = tcx.sess.struct_span_err_with_code(
370 "wrong number of {} arguments: expected {}{}, found {}",
376 DiagnosticId::Error("E0107".into())
379 err.span_label(span, label.as_str());
383 (provided > required, // `suppress_error`
384 potential_assoc_types)
387 if !infer_lifetimes || arg_counts.lifetimes > param_counts.lifetimes {
390 param_counts.lifetimes,
391 param_counts.lifetimes,
392 arg_counts.lifetimes,
396 // FIXME(const_generics:defaults)
397 if !infer_consts || arg_counts.consts > param_counts.consts {
403 arg_counts.lifetimes + arg_counts.types,
406 // Note that type errors are currently be emitted *after* const errors.
408 || arg_counts.types > param_counts.types - defaults.types - has_self as usize {
411 param_counts.types - defaults.types - has_self as usize,
412 param_counts.types - has_self as usize,
414 arg_counts.lifetimes,
421 /// Creates the relevant generic argument substitutions
422 /// corresponding to a set of generic parameters. This is a
423 /// rather complex function. Let us try to explain the role
424 /// of each of its parameters:
426 /// To start, we are given the `def_id` of the thing we are
427 /// creating the substitutions for, and a partial set of
428 /// substitutions `parent_substs`. In general, the substitutions
429 /// for an item begin with substitutions for all the "parents" of
430 /// that item -- e.g., for a method it might include the
431 /// parameters from the impl.
433 /// Therefore, the method begins by walking down these parents,
434 /// starting with the outermost parent and proceed inwards until
435 /// it reaches `def_id`. For each parent `P`, it will check `parent_substs`
436 /// first to see if the parent's substitutions are listed in there. If so,
437 /// we can append those and move on. Otherwise, it invokes the
438 /// three callback functions:
440 /// - `args_for_def_id`: given the `DefId` `P`, supplies back the
441 /// generic arguments that were given to that parent from within
442 /// the path; so e.g., if you have `<T as Foo>::Bar`, the `DefId`
443 /// might refer to the trait `Foo`, and the arguments might be
444 /// `[T]`. The boolean value indicates whether to infer values
445 /// for arguments whose values were not explicitly provided.
446 /// - `provided_kind`: given the generic parameter and the value from `args_for_def_id`,
447 /// instantiate a `Kind`.
448 /// - `inferred_kind`: if no parameter was provided, and inference is enabled, then
449 /// creates a suitable inference variable.
450 pub fn create_substs_for_generic_args<'a, 'b>(
451 tcx: TyCtxt<'a, 'gcx, 'tcx>,
453 parent_substs: &[Kind<'tcx>],
455 self_ty: Option<Ty<'tcx>>,
456 args_for_def_id: impl Fn(DefId) -> (Option<&'b GenericArgs>, bool),
457 provided_kind: impl Fn(&GenericParamDef, &GenericArg) -> Kind<'tcx>,
458 inferred_kind: impl Fn(Option<&[Kind<'tcx>]>, &GenericParamDef, bool) -> Kind<'tcx>,
459 ) -> SubstsRef<'tcx> {
460 // Collect the segments of the path; we need to substitute arguments
461 // for parameters throughout the entire path (wherever there are
462 // generic parameters).
463 let mut parent_defs = tcx.generics_of(def_id);
464 let count = parent_defs.count();
465 let mut stack = vec![(def_id, parent_defs)];
466 while let Some(def_id) = parent_defs.parent {
467 parent_defs = tcx.generics_of(def_id);
468 stack.push((def_id, parent_defs));
471 // We manually build up the substitution, rather than using convenience
472 // methods in `subst.rs`, so that we can iterate over the arguments and
473 // parameters in lock-step linearly, instead of trying to match each pair.
474 let mut substs: SmallVec<[Kind<'tcx>; 8]> = SmallVec::with_capacity(count);
476 // Iterate over each segment of the path.
477 while let Some((def_id, defs)) = stack.pop() {
478 let mut params = defs.params.iter().peekable();
480 // If we have already computed substitutions for parents, we can use those directly.
481 while let Some(¶m) = params.peek() {
482 if let Some(&kind) = parent_substs.get(param.index as usize) {
490 // `Self` is handled first, unless it's been handled in `parent_substs`.
492 if let Some(¶m) = params.peek() {
493 if param.index == 0 {
494 if let GenericParamDefKind::Type { .. } = param.kind {
495 substs.push(self_ty.map(|ty| ty.into())
496 .unwrap_or_else(|| inferred_kind(None, param, true)));
503 // Check whether this segment takes generic arguments and the user has provided any.
504 let (generic_args, infer_types) = args_for_def_id(def_id);
506 let mut args = generic_args.iter().flat_map(|generic_args| generic_args.args.iter())
510 // We're going to iterate through the generic arguments that the user
511 // provided, matching them with the generic parameters we expect.
512 // Mismatches can occur as a result of elided lifetimes, or for malformed
513 // input. We try to handle both sensibly.
514 match (args.peek(), params.peek()) {
515 (Some(&arg), Some(¶m)) => {
516 match (arg, ¶m.kind) {
517 (GenericArg::Lifetime(_), GenericParamDefKind::Lifetime)
518 | (GenericArg::Type(_), GenericParamDefKind::Type { .. })
519 | (GenericArg::Const(_), GenericParamDefKind::Const) => {
520 substs.push(provided_kind(param, arg));
524 (GenericArg::Type(_), GenericParamDefKind::Lifetime)
525 | (GenericArg::Const(_), GenericParamDefKind::Lifetime) => {
526 // We expected a lifetime argument, but got a type or const
527 // argument. That means we're inferring the lifetimes.
528 substs.push(inferred_kind(None, param, infer_types));
532 // We expected one kind of parameter, but the user provided
533 // another. This is an error, but we need to handle it
534 // gracefully so we can report sensible errors.
535 // In this case, we're simply going to infer this argument.
541 // We should never be able to reach this point with well-formed input.
542 // Getting to this point means the user supplied more arguments than
543 // there are parameters.
546 (None, Some(¶m)) => {
547 // If there are fewer arguments than parameters, it means
548 // we're inferring the remaining arguments.
549 substs.push(inferred_kind(Some(&substs), param, infer_types));
553 (None, None) => break,
558 tcx.intern_substs(&substs)
561 /// Given the type/region arguments provided to some path (along with
562 /// an implicit `Self`, if this is a trait reference) returns the complete
563 /// set of substitutions. This may involve applying defaulted type parameters.
565 /// Note that the type listing given here is *exactly* what the user provided.
566 fn create_substs_for_ast_path(&self,
569 generic_args: &hir::GenericArgs,
571 self_ty: Option<Ty<'tcx>>)
572 -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'tcx>>, Option<Vec<Span>>)
574 // If the type is parameterized by this region, then replace this
575 // region with the current anon region binding (in other words,
576 // whatever & would get replaced with).
577 debug!("create_substs_for_ast_path(def_id={:?}, self_ty={:?}, \
579 def_id, self_ty, generic_args);
581 let tcx = self.tcx();
582 let generic_params = tcx.generics_of(def_id);
584 // If a self-type was declared, one should be provided.
585 assert_eq!(generic_params.has_self, self_ty.is_some());
587 let has_self = generic_params.has_self;
588 let (_, potential_assoc_types) = Self::check_generic_arg_count(
593 GenericArgPosition::Type,
598 let is_object = self_ty.map_or(false, |ty| ty.sty == TRAIT_OBJECT_DUMMY_SELF);
599 let default_needs_object_self = |param: &ty::GenericParamDef| {
600 if let GenericParamDefKind::Type { has_default, .. } = param.kind {
601 if is_object && has_default {
602 if tcx.at(span).type_of(param.def_id).has_self_ty() {
603 // There is no suitable inference default for a type parameter
604 // that references self, in an object type.
613 let substs = Self::create_substs_for_generic_args(
619 // Provide the generic args, and whether types should be inferred.
620 |_| (Some(generic_args), infer_types),
621 // Provide substitutions for parameters for which (valid) arguments have been provided.
623 match (¶m.kind, arg) {
624 (GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => {
625 self.ast_region_to_region(<, Some(param)).into()
627 (GenericParamDefKind::Type { .. }, GenericArg::Type(ty)) => {
628 self.ast_ty_to_ty(&ty).into()
630 (GenericParamDefKind::Const, GenericArg::Const(ct)) => {
631 self.ast_const_to_const(&ct.value, tcx.type_of(param.def_id)).into()
636 // Provide substitutions for parameters for which arguments are inferred.
637 |substs, param, infer_types| {
639 GenericParamDefKind::Lifetime => tcx.types.re_static.into(),
640 GenericParamDefKind::Type { has_default, .. } => {
641 if !infer_types && has_default {
642 // No type parameter provided, but a default exists.
644 // If we are converting an object type, then the
645 // `Self` parameter is unknown. However, some of the
646 // other type parameters may reference `Self` in their
647 // defaults. This will lead to an ICE if we are not
649 if default_needs_object_self(param) {
650 struct_span_err!(tcx.sess, span, E0393,
651 "the type parameter `{}` must be explicitly \
655 format!("missing reference to `{}`", param.name))
656 .note(&format!("because of the default `Self` reference, \
657 type parameters must be specified on object \
662 // This is a default type parameter.
665 tcx.at(span).type_of(param.def_id)
666 .subst_spanned(tcx, substs.unwrap(), Some(span))
669 } else if infer_types {
670 // No type parameters were provided, we can infer all.
671 if !default_needs_object_self(param) {
672 self.ty_infer_for_def(param, span).into()
674 self.ty_infer(span).into()
677 // We've already errored above about the mismatch.
681 GenericParamDefKind::Const => {
682 // FIXME(const_generics:defaults)
683 // We've already errored above about the mismatch.
690 let assoc_bindings = generic_args.bindings.iter().map(|binding| {
692 item_name: binding.ident,
693 ty: self.ast_ty_to_ty(&binding.ty),
698 debug!("create_substs_for_ast_path(generic_params={:?}, self_ty={:?}) -> {:?}",
699 generic_params, self_ty, substs);
701 (substs, assoc_bindings, potential_assoc_types)
704 /// Instantiates the path for the given trait reference, assuming that it's
705 /// bound to a valid trait type. Returns the def_id for the defining trait.
706 /// The type _cannot_ be a type other than a trait type.
708 /// If the `projections` argument is `None`, then assoc type bindings like `Foo<T = X>`
709 /// are disallowed. Otherwise, they are pushed onto the vector given.
710 pub fn instantiate_mono_trait_ref(&self,
711 trait_ref: &hir::TraitRef,
713 -> ty::TraitRef<'tcx>
715 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
717 self.ast_path_to_mono_trait_ref(trait_ref.path.span,
718 trait_ref.trait_def_id(),
720 trait_ref.path.segments.last().unwrap())
723 /// The given trait-ref must actually be a trait.
724 pub(super) fn instantiate_poly_trait_ref_inner(&self,
725 trait_ref: &hir::TraitRef,
727 poly_projections: &mut Vec<(ty::PolyProjectionPredicate<'tcx>, Span)>,
729 -> (ty::PolyTraitRef<'tcx>, Option<Vec<Span>>)
731 let trait_def_id = trait_ref.trait_def_id();
733 debug!("instantiate_poly_trait_ref({:?}, def_id={:?})", trait_ref, trait_def_id);
735 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
737 let (substs, assoc_bindings, potential_assoc_types) = self.create_substs_for_ast_trait_ref(
741 trait_ref.path.segments.last().unwrap(),
743 let poly_trait_ref = ty::Binder::bind(ty::TraitRef::new(trait_def_id, substs));
745 let mut dup_bindings = FxHashMap::default();
746 poly_projections.extend(assoc_bindings.iter().filter_map(|binding| {
747 // specify type to assert that error was already reported in Err case:
748 let predicate: Result<_, ErrorReported> =
749 self.ast_type_binding_to_poly_projection_predicate(
750 trait_ref.hir_ref_id, poly_trait_ref, binding, speculative, &mut dup_bindings);
751 // okay to ignore Err because of ErrorReported (see above)
752 Some((predicate.ok()?, binding.span))
755 debug!("instantiate_poly_trait_ref({:?}, projections={:?}) -> {:?}",
756 trait_ref, poly_projections, poly_trait_ref);
757 (poly_trait_ref, potential_assoc_types)
760 pub fn instantiate_poly_trait_ref(&self,
761 poly_trait_ref: &hir::PolyTraitRef,
763 poly_projections: &mut Vec<(ty::PolyProjectionPredicate<'tcx>, Span)>)
764 -> (ty::PolyTraitRef<'tcx>, Option<Vec<Span>>)
766 self.instantiate_poly_trait_ref_inner(&poly_trait_ref.trait_ref, self_ty,
767 poly_projections, false)
770 fn ast_path_to_mono_trait_ref(&self,
774 trait_segment: &hir::PathSegment)
775 -> ty::TraitRef<'tcx>
777 let (substs, assoc_bindings, _) =
778 self.create_substs_for_ast_trait_ref(span,
782 assoc_bindings.first().map(|b| AstConv::prohibit_assoc_ty_binding(self.tcx(), b.span));
783 ty::TraitRef::new(trait_def_id, substs)
786 fn create_substs_for_ast_trait_ref(
791 trait_segment: &hir::PathSegment,
792 ) -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'tcx>>, Option<Vec<Span>>) {
793 debug!("create_substs_for_ast_trait_ref(trait_segment={:?})",
796 let trait_def = self.tcx().trait_def(trait_def_id);
798 if !self.tcx().features().unboxed_closures &&
799 trait_segment.with_generic_args(|generic_args| generic_args.parenthesized)
800 != trait_def.paren_sugar {
801 // For now, require that parenthetical notation be used only with `Fn()` etc.
802 let msg = if trait_def.paren_sugar {
803 "the precise format of `Fn`-family traits' type parameters is subject to change. \
804 Use parenthetical notation (Fn(Foo, Bar) -> Baz) instead"
806 "parenthetical notation is only stable when used with `Fn`-family traits"
808 emit_feature_err(&self.tcx().sess.parse_sess, "unboxed_closures",
809 span, GateIssue::Language, msg);
812 trait_segment.with_generic_args(|generic_args| {
813 self.create_substs_for_ast_path(span,
816 trait_segment.infer_types,
821 fn trait_defines_associated_type_named(&self,
823 assoc_name: ast::Ident)
826 self.tcx().associated_items(trait_def_id).any(|item| {
827 item.kind == ty::AssociatedKind::Type &&
828 self.tcx().hygienic_eq(assoc_name, item.ident, trait_def_id)
832 fn ast_type_binding_to_poly_projection_predicate(
834 hir_ref_id: hir::HirId,
835 trait_ref: ty::PolyTraitRef<'tcx>,
836 binding: &ConvertedBinding<'tcx>,
838 dup_bindings: &mut FxHashMap<DefId, Span>)
839 -> Result<ty::PolyProjectionPredicate<'tcx>, ErrorReported>
841 let tcx = self.tcx();
844 // Given something like `U: SomeTrait<T = X>`, we want to produce a
845 // predicate like `<U as SomeTrait>::T = X`. This is somewhat
846 // subtle in the event that `T` is defined in a supertrait of
847 // `SomeTrait`, because in that case we need to upcast.
849 // That is, consider this case:
852 // trait SubTrait: SuperTrait<int> { }
853 // trait SuperTrait<A> { type T; }
855 // ... B : SubTrait<T=foo> ...
858 // We want to produce `<B as SuperTrait<int>>::T == foo`.
860 // Find any late-bound regions declared in `ty` that are not
861 // declared in the trait-ref. These are not wellformed.
865 // for<'a> <T as Iterator>::Item = &'a str // <-- 'a is bad
866 // for<'a> <T as FnMut<(&'a u32,)>>::Output = &'a str // <-- 'a is ok
867 let late_bound_in_trait_ref = tcx.collect_constrained_late_bound_regions(&trait_ref);
868 let late_bound_in_ty =
869 tcx.collect_referenced_late_bound_regions(&ty::Binder::bind(binding.ty));
870 debug!("late_bound_in_trait_ref = {:?}", late_bound_in_trait_ref);
871 debug!("late_bound_in_ty = {:?}", late_bound_in_ty);
872 for br in late_bound_in_ty.difference(&late_bound_in_trait_ref) {
873 let br_name = match *br {
874 ty::BrNamed(_, name) => name,
878 "anonymous bound region {:?} in binding but not trait ref",
882 struct_span_err!(tcx.sess,
885 "binding for associated type `{}` references lifetime `{}`, \
886 which does not appear in the trait input types",
887 binding.item_name, br_name)
892 let candidate = if self.trait_defines_associated_type_named(trait_ref.def_id(),
894 // Simple case: X is defined in the current trait.
897 // Otherwise, we have to walk through the supertraits to find
899 let candidates = traits::supertraits(tcx, trait_ref).filter(|r| {
900 self.trait_defines_associated_type_named(r.def_id(), binding.item_name)
902 self.one_bound_for_assoc_type(candidates, &trait_ref.to_string(),
903 binding.item_name, binding.span)
906 let (assoc_ident, def_scope) =
907 tcx.adjust_ident(binding.item_name, candidate.def_id(), hir_ref_id);
908 let assoc_ty = tcx.associated_items(candidate.def_id()).find(|i| {
909 i.kind == ty::AssociatedKind::Type && i.ident.modern() == assoc_ident
910 }).expect("missing associated type");
912 if !assoc_ty.vis.is_accessible_from(def_scope, tcx) {
913 let msg = format!("associated type `{}` is private", binding.item_name);
914 tcx.sess.span_err(binding.span, &msg);
916 tcx.check_stability(assoc_ty.def_id, Some(hir_ref_id), binding.span);
919 dup_bindings.entry(assoc_ty.def_id)
920 .and_modify(|prev_span| {
921 struct_span_err!(self.tcx().sess, binding.span, E0719,
922 "the value of the associated type `{}` (from the trait `{}`) \
923 is already specified",
925 tcx.item_path_str(assoc_ty.container.id()))
926 .span_label(binding.span, "re-bound here")
927 .span_label(*prev_span, format!("`{}` bound here first", binding.item_name))
930 .or_insert(binding.span);
933 Ok(candidate.map_bound(|trait_ref| {
934 ty::ProjectionPredicate {
935 projection_ty: ty::ProjectionTy::from_ref_and_name(
945 fn ast_path_to_ty(&self,
948 item_segment: &hir::PathSegment)
951 let substs = self.ast_path_substs_for_ty(span, did, item_segment);
954 self.tcx().at(span).type_of(did).subst(self.tcx(), substs)
958 /// Transform a `PolyTraitRef` into a `PolyExistentialTraitRef` by
959 /// removing the dummy `Self` type (`TRAIT_OBJECT_DUMMY_SELF`).
960 fn trait_ref_to_existential(&self, trait_ref: ty::TraitRef<'tcx>)
961 -> ty::ExistentialTraitRef<'tcx> {
962 assert_eq!(trait_ref.self_ty().sty, TRAIT_OBJECT_DUMMY_SELF);
963 ty::ExistentialTraitRef::erase_self_ty(self.tcx(), trait_ref)
966 fn conv_object_ty_poly_trait_ref(&self,
968 trait_bounds: &[hir::PolyTraitRef],
969 lifetime: &hir::Lifetime)
972 let tcx = self.tcx();
974 if trait_bounds.is_empty() {
975 span_err!(tcx.sess, span, E0224,
976 "at least one non-builtin trait is required for an object type");
977 return tcx.types.err;
980 let mut projection_bounds = Vec::new();
981 let dummy_self = tcx.mk_ty(TRAIT_OBJECT_DUMMY_SELF);
982 let (principal, potential_assoc_types) = self.instantiate_poly_trait_ref(
985 &mut projection_bounds,
987 debug!("principal: {:?}", principal);
989 for trait_bound in trait_bounds[1..].iter() {
990 // sanity check for non-principal trait bounds
991 self.instantiate_poly_trait_ref(trait_bound,
996 let (mut auto_traits, trait_bounds) = split_auto_traits(tcx, &trait_bounds[1..]);
998 if !trait_bounds.is_empty() {
999 let b = &trait_bounds[0];
1000 let span = b.trait_ref.path.span;
1001 struct_span_err!(self.tcx().sess, span, E0225,
1002 "only auto traits can be used as additional traits in a trait object")
1003 .span_label(span, "non-auto additional trait")
1007 // Check that there are no gross object safety violations;
1008 // most importantly, that the supertraits don't contain `Self`,
1010 let object_safety_violations =
1011 tcx.global_tcx().astconv_object_safety_violations(principal.def_id());
1012 if !object_safety_violations.is_empty() {
1013 tcx.report_object_safety_error(
1014 span, principal.def_id(), object_safety_violations)
1016 return tcx.types.err;
1019 // Use a `BTreeSet` to keep output in a more consistent order.
1020 let mut associated_types = BTreeSet::default();
1022 for tr in traits::elaborate_trait_ref(tcx, principal) {
1023 debug!("conv_object_ty_poly_trait_ref: observing object predicate `{:?}`", tr);
1025 ty::Predicate::Trait(pred) => {
1026 associated_types.extend(tcx.associated_items(pred.def_id())
1027 .filter(|item| item.kind == ty::AssociatedKind::Type)
1028 .map(|item| item.def_id));
1030 ty::Predicate::Projection(pred) => {
1031 // A `Self` within the original bound will be substituted with a
1032 // `TRAIT_OBJECT_DUMMY_SELF`, so check for that.
1033 let references_self =
1034 pred.skip_binder().ty.walk().any(|t| t == dummy_self);
1036 // If the projection output contains `Self`, force the user to
1037 // elaborate it explicitly to avoid a bunch of complexity.
1039 // The "classicaly useful" case is the following:
1041 // trait MyTrait: FnMut() -> <Self as MyTrait>::MyOutput {
1046 // Here, the user could theoretically write `dyn MyTrait<Output=X>`,
1047 // but actually supporting that would "expand" to an infinitely-long type
1048 // `fix $ τ → dyn MyTrait<MyOutput=X, Output=<τ as MyTrait>::MyOutput`.
1050 // Instead, we force the user to write `dyn MyTrait<MyOutput=X, Output=X>`,
1051 // which is uglier but works. See the discussion in #56288 for alternatives.
1052 if !references_self {
1053 // Include projections defined on supertraits,
1054 projection_bounds.push((pred, DUMMY_SP))
1061 for (projection_bound, _) in &projection_bounds {
1062 associated_types.remove(&projection_bound.projection_def_id());
1065 if !associated_types.is_empty() {
1066 let names = associated_types.iter().map(|item_def_id| {
1067 let assoc_item = tcx.associated_item(*item_def_id);
1068 let trait_def_id = assoc_item.container.id();
1070 "`{}` (from the trait `{}`)",
1072 tcx.item_path_str(trait_def_id),
1074 }).collect::<Vec<_>>().join(", ");
1075 let mut err = struct_span_err!(
1079 "the value of the associated type{} {} must be specified",
1080 if associated_types.len() == 1 { "" } else { "s" },
1083 let mut suggest = false;
1084 let mut potential_assoc_types_spans = vec![];
1085 if let Some(potential_assoc_types) = potential_assoc_types {
1086 if potential_assoc_types.len() == associated_types.len() {
1087 // Only suggest when the amount of missing associated types is equals to the
1088 // extra type arguments present, as that gives us a relatively high confidence
1089 // that the user forgot to give the associtated type's name. The canonical
1090 // example would be trying to use `Iterator<isize>` instead of
1091 // `Iterator<Item=isize>`.
1093 potential_assoc_types_spans = potential_assoc_types;
1096 let mut suggestions = vec![];
1097 for (i, item_def_id) in associated_types.iter().enumerate() {
1098 let assoc_item = tcx.associated_item(*item_def_id);
1101 format!("associated type `{}` must be specified", assoc_item.ident),
1103 if item_def_id.is_local() {
1105 tcx.def_span(*item_def_id),
1106 format!("`{}` defined here", assoc_item.ident),
1110 if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(
1111 potential_assoc_types_spans[i],
1114 potential_assoc_types_spans[i],
1115 format!("{} = {}", assoc_item.ident, snippet),
1120 if !suggestions.is_empty() {
1121 let msg = format!("if you meant to specify the associated {}, write",
1122 if suggestions.len() == 1 { "type" } else { "types" });
1123 err.multipart_suggestion(
1126 Applicability::MaybeIncorrect,
1132 // Erase the `dummy_self` (`TRAIT_OBJECT_DUMMY_SELF`) used above.
1133 let existential_principal = principal.map_bound(|trait_ref| {
1134 self.trait_ref_to_existential(trait_ref)
1136 let existential_projections = projection_bounds.iter().map(|(bound, _)| {
1137 bound.map_bound(|b| {
1138 let trait_ref = self.trait_ref_to_existential(b.projection_ty.trait_ref(tcx));
1139 ty::ExistentialProjection {
1141 item_def_id: b.projection_ty.item_def_id,
1142 substs: trait_ref.substs,
1147 // Dedup auto traits so that `dyn Trait + Send + Send` is the same as `dyn Trait + Send`.
1149 auto_traits.dedup();
1151 // Calling `skip_binder` is okay, because the predicates are re-bound.
1152 let principal = if tcx.trait_is_auto(existential_principal.def_id()) {
1153 ty::ExistentialPredicate::AutoTrait(existential_principal.def_id())
1155 ty::ExistentialPredicate::Trait(*existential_principal.skip_binder())
1158 iter::once(principal)
1159 .chain(auto_traits.into_iter().map(ty::ExistentialPredicate::AutoTrait))
1160 .chain(existential_projections
1161 .map(|x| ty::ExistentialPredicate::Projection(*x.skip_binder())))
1162 .collect::<SmallVec<[_; 8]>>();
1163 v.sort_by(|a, b| a.stable_cmp(tcx, b));
1165 let existential_predicates = ty::Binder::bind(tcx.mk_existential_predicates(v.into_iter()));
1167 // Use explicitly-specified region bound.
1168 let region_bound = if !lifetime.is_elided() {
1169 self.ast_region_to_region(lifetime, None)
1171 self.compute_object_lifetime_bound(span, existential_predicates).unwrap_or_else(|| {
1172 if tcx.named_region(lifetime.hir_id).is_some() {
1173 self.ast_region_to_region(lifetime, None)
1175 self.re_infer(span, None).unwrap_or_else(|| {
1176 span_err!(tcx.sess, span, E0228,
1177 "the lifetime bound for this object type cannot be deduced \
1178 from context; please supply an explicit bound");
1185 debug!("region_bound: {:?}", region_bound);
1187 let ty = tcx.mk_dynamic(existential_predicates, region_bound);
1188 debug!("trait_object_type: {:?}", ty);
1192 fn report_ambiguous_associated_type(&self,
1197 struct_span_err!(self.tcx().sess, span, E0223, "ambiguous associated type")
1200 "use fully-qualified syntax",
1201 format!("<{} as {}>::{}", type_str, trait_str, name),
1202 Applicability::HasPlaceholders
1206 // Search for a bound on a type parameter which includes the associated item
1207 // given by `assoc_name`. `ty_param_def_id` is the `DefId` for the type parameter
1208 // This function will fail if there are no suitable bounds or there is
1210 fn find_bound_for_assoc_item(&self,
1211 ty_param_def_id: DefId,
1212 assoc_name: ast::Ident,
1214 -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
1216 let tcx = self.tcx();
1218 let predicates = &self.get_type_parameter_bounds(span, ty_param_def_id).predicates;
1219 let bounds = predicates.iter().filter_map(|(p, _)| p.to_opt_poly_trait_ref());
1221 // Check that there is exactly one way to find an associated type with the
1223 let suitable_bounds = traits::transitive_bounds(tcx, bounds)
1224 .filter(|b| self.trait_defines_associated_type_named(b.def_id(), assoc_name));
1226 let param_hir_id = tcx.hir().as_local_hir_id(ty_param_def_id).unwrap();
1227 let param_name = tcx.hir().ty_param_name(param_hir_id);
1228 self.one_bound_for_assoc_type(suitable_bounds,
1229 ¶m_name.as_str(),
1234 // Checks that `bounds` contains exactly one element and reports appropriate
1235 // errors otherwise.
1236 fn one_bound_for_assoc_type<I>(&self,
1238 ty_param_name: &str,
1239 assoc_name: ast::Ident,
1241 -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
1242 where I: Iterator<Item=ty::PolyTraitRef<'tcx>>
1244 let bound = match bounds.next() {
1245 Some(bound) => bound,
1247 struct_span_err!(self.tcx().sess, span, E0220,
1248 "associated type `{}` not found for `{}`",
1251 .span_label(span, format!("associated type `{}` not found", assoc_name))
1253 return Err(ErrorReported);
1257 if let Some(bound2) = bounds.next() {
1258 let bounds = iter::once(bound).chain(iter::once(bound2)).chain(bounds);
1259 let mut err = struct_span_err!(
1260 self.tcx().sess, span, E0221,
1261 "ambiguous associated type `{}` in bounds of `{}`",
1264 err.span_label(span, format!("ambiguous associated type `{}`", assoc_name));
1266 for bound in bounds {
1267 let bound_span = self.tcx().associated_items(bound.def_id()).find(|item| {
1268 item.kind == ty::AssociatedKind::Type &&
1269 self.tcx().hygienic_eq(assoc_name, item.ident, bound.def_id())
1271 .and_then(|item| self.tcx().hir().span_if_local(item.def_id));
1273 if let Some(span) = bound_span {
1274 err.span_label(span, format!("ambiguous `{}` from `{}`",
1278 span_note!(&mut err, span,
1279 "associated type `{}` could derive from `{}`",
1290 // Create a type from a path to an associated type.
1291 // For a path `A::B::C::D`, `qself_ty` and `qself_def` are the type and def for `A::B::C`
1292 // and item_segment is the path segment for `D`. We return a type and a def for
1294 // Will fail except for `T::A` and `Self::A`; i.e., if `qself_ty`/`qself_def` are not a type
1295 // parameter or `Self`.
1296 pub fn associated_path_to_ty(
1298 hir_ref_id: hir::HirId,
1302 assoc_segment: &hir::PathSegment,
1303 permit_variants: bool,
1304 ) -> (Ty<'tcx>, Def) {
1305 let tcx = self.tcx();
1306 let assoc_ident = assoc_segment.ident;
1308 debug!("associated_path_to_ty: {:?}::{}", qself_ty, assoc_ident);
1310 self.prohibit_generics(slice::from_ref(assoc_segment));
1312 // Check if we have an enum variant.
1313 let mut variant_resolution = None;
1314 if let ty::Adt(adt_def, _) = qself_ty.sty {
1315 if adt_def.is_enum() {
1316 let variant_def = adt_def.variants.iter().find(|vd| {
1317 tcx.hygienic_eq(assoc_ident, vd.ident, adt_def.did)
1319 if let Some(variant_def) = variant_def {
1320 let def = Def::Variant(variant_def.did);
1321 if permit_variants {
1322 check_type_alias_enum_variants_enabled(tcx, span);
1323 tcx.check_stability(variant_def.did, Some(hir_ref_id), span);
1324 return (qself_ty, def);
1326 variant_resolution = Some(def);
1332 // Find the type of the associated item, and the trait where the associated
1333 // item is declared.
1334 let bound = match (&qself_ty.sty, qself_def) {
1335 (_, Def::SelfTy(Some(_), Some(impl_def_id))) => {
1336 // `Self` in an impl of a trait -- we have a concrete self type and a
1338 let trait_ref = match tcx.impl_trait_ref(impl_def_id) {
1339 Some(trait_ref) => trait_ref,
1341 // A cycle error occurred, most likely.
1342 return (tcx.types.err, Def::Err);
1346 let candidates = traits::supertraits(tcx, ty::Binder::bind(trait_ref))
1347 .filter(|r| self.trait_defines_associated_type_named(r.def_id(), assoc_ident));
1349 match self.one_bound_for_assoc_type(candidates, "Self", assoc_ident, span) {
1351 Err(ErrorReported) => return (tcx.types.err, Def::Err),
1354 (&ty::Param(_), Def::SelfTy(Some(param_did), None)) |
1355 (&ty::Param(_), Def::TyParam(param_did)) => {
1356 match self.find_bound_for_assoc_item(param_did, assoc_ident, span) {
1358 Err(ErrorReported) => return (tcx.types.err, Def::Err),
1362 if variant_resolution.is_some() {
1363 // Variant in type position
1364 let msg = format!("expected type, found variant `{}`", assoc_ident);
1365 tcx.sess.span_err(span, &msg);
1366 } else if qself_ty.is_enum() {
1367 // Report as incorrect enum variant rather than ambiguous type.
1368 let mut err = tcx.sess.struct_span_err(
1370 &format!("no variant `{}` on enum `{}`", &assoc_ident.as_str(), qself_ty),
1372 // Check if it was a typo.
1373 let adt_def = qself_ty.ty_adt_def().expect("enum is not an ADT");
1374 if let Some(suggested_name) = find_best_match_for_name(
1375 adt_def.variants.iter().map(|variant| &variant.ident.name),
1376 &assoc_ident.as_str(),
1379 err.span_suggestion(
1382 format!("{}::{}", qself_ty, suggested_name),
1383 Applicability::MaybeIncorrect,
1386 err.span_label(span, "unknown variant");
1389 } else if !qself_ty.references_error() {
1390 // Don't print `TyErr` to the user.
1391 self.report_ambiguous_associated_type(span,
1392 &qself_ty.to_string(),
1394 &assoc_ident.as_str());
1396 return (tcx.types.err, Def::Err);
1400 let trait_did = bound.def_id();
1401 let (assoc_ident, def_scope) = tcx.adjust_ident(assoc_ident, trait_did, hir_ref_id);
1402 let item = tcx.associated_items(trait_did).find(|i| {
1403 Namespace::from(i.kind) == Namespace::Type &&
1404 i.ident.modern() == assoc_ident
1405 }).expect("missing associated type");
1407 let ty = self.projected_ty_from_poly_trait_ref(span, item.def_id, bound);
1408 let ty = self.normalize_ty(span, ty);
1410 let def = Def::AssociatedTy(item.def_id);
1411 if !item.vis.is_accessible_from(def_scope, tcx) {
1412 let msg = format!("{} `{}` is private", def.kind_name(), assoc_ident);
1413 tcx.sess.span_err(span, &msg);
1415 tcx.check_stability(item.def_id, Some(hir_ref_id), span);
1417 if let Some(variant_def) = variant_resolution {
1418 let mut err = tcx.struct_span_lint_hir(
1419 AMBIGUOUS_ASSOCIATED_ITEMS,
1422 "ambiguous associated item",
1425 let mut could_refer_to = |def: Def, also| {
1426 let note_msg = format!("`{}` could{} refer to {} defined here",
1427 assoc_ident, also, def.kind_name());
1428 err.span_note(tcx.def_span(def.def_id()), ¬e_msg);
1430 could_refer_to(variant_def, "");
1431 could_refer_to(def, " also");
1433 err.span_suggestion(
1435 "use fully-qualified syntax",
1436 format!("<{} as {}>::{}", qself_ty, "Trait", assoc_ident),
1437 Applicability::HasPlaceholders,
1444 fn qpath_to_ty(&self,
1446 opt_self_ty: Option<Ty<'tcx>>,
1448 trait_segment: &hir::PathSegment,
1449 item_segment: &hir::PathSegment)
1452 let tcx = self.tcx();
1453 let trait_def_id = tcx.parent_def_id(item_def_id).unwrap();
1455 self.prohibit_generics(slice::from_ref(item_segment));
1457 let self_ty = if let Some(ty) = opt_self_ty {
1460 let path_str = tcx.item_path_str(trait_def_id);
1461 self.report_ambiguous_associated_type(span,
1464 &item_segment.ident.as_str());
1465 return tcx.types.err;
1468 debug!("qpath_to_ty: self_type={:?}", self_ty);
1470 let trait_ref = self.ast_path_to_mono_trait_ref(span,
1475 debug!("qpath_to_ty: trait_ref={:?}", trait_ref);
1477 self.normalize_ty(span, tcx.mk_projection(item_def_id, trait_ref.substs))
1480 pub fn prohibit_generics<'a, T: IntoIterator<Item = &'a hir::PathSegment>>(
1481 &self, segments: T) -> bool {
1482 let mut has_err = false;
1483 for segment in segments {
1484 segment.with_generic_args(|generic_args| {
1485 let (mut err_for_lt, mut err_for_ty, mut err_for_ct) = (false, false, false);
1486 for arg in &generic_args.args {
1487 let (mut span_err, span, kind) = match arg {
1488 // FIXME(varkor): unify E0109, E0110 and E0111.
1489 hir::GenericArg::Lifetime(lt) => {
1490 if err_for_lt { continue }
1493 (struct_span_err!(self.tcx().sess, lt.span, E0110,
1494 "lifetime arguments are not allowed on this entity"),
1498 hir::GenericArg::Type(ty) => {
1499 if err_for_ty { continue }
1502 (struct_span_err!(self.tcx().sess, ty.span, E0109,
1503 "type arguments are not allowed on this entity"),
1507 hir::GenericArg::Const(ct) => {
1508 if err_for_ct { continue }
1510 (struct_span_err!(self.tcx().sess, ct.span, E0111,
1511 "const parameters are not allowed on this type"),
1516 span_err.span_label(span, format!("{} argument not allowed", kind))
1518 if err_for_lt && err_for_ty && err_for_ct {
1522 for binding in &generic_args.bindings {
1524 Self::prohibit_assoc_ty_binding(self.tcx(), binding.span);
1532 pub fn prohibit_assoc_ty_binding(tcx: TyCtxt<'_, '_, '_>, span: Span) {
1533 let mut err = struct_span_err!(tcx.sess, span, E0229,
1534 "associated type bindings are not allowed here");
1535 err.span_label(span, "associated type not allowed here").emit();
1538 pub fn def_ids_for_path_segments(&self,
1539 segments: &[hir::PathSegment],
1540 self_ty: Option<Ty<'tcx>>,
1543 // We need to extract the type parameters supplied by the user in
1544 // the path `path`. Due to the current setup, this is a bit of a
1545 // tricky-process; the problem is that resolve only tells us the
1546 // end-point of the path resolution, and not the intermediate steps.
1547 // Luckily, we can (at least for now) deduce the intermediate steps
1548 // just from the end-point.
1550 // There are basically five cases to consider:
1552 // 1. Reference to a constructor of a struct:
1554 // struct Foo<T>(...)
1556 // In this case, the parameters are declared in the type space.
1558 // 2. Reference to a constructor of an enum variant:
1560 // enum E<T> { Foo(...) }
1562 // In this case, the parameters are defined in the type space,
1563 // but may be specified either on the type or the variant.
1565 // 3. Reference to a fn item or a free constant:
1569 // In this case, the path will again always have the form
1570 // `a::b::foo::<T>` where only the final segment should have
1571 // type parameters. However, in this case, those parameters are
1572 // declared on a value, and hence are in the `FnSpace`.
1574 // 4. Reference to a method or an associated constant:
1576 // impl<A> SomeStruct<A> {
1580 // Here we can have a path like
1581 // `a::b::SomeStruct::<A>::foo::<B>`, in which case parameters
1582 // may appear in two places. The penultimate segment,
1583 // `SomeStruct::<A>`, contains parameters in TypeSpace, and the
1584 // final segment, `foo::<B>` contains parameters in fn space.
1586 // 5. Reference to a local variable
1588 // Local variables can't have any type parameters.
1590 // The first step then is to categorize the segments appropriately.
1592 let tcx = self.tcx();
1594 assert!(!segments.is_empty());
1595 let last = segments.len() - 1;
1597 let mut path_segs = vec![];
1600 // Case 1. Reference to a struct constructor.
1601 Def::StructCtor(def_id, ..) |
1602 Def::SelfCtor(.., def_id) => {
1603 // Everything but the final segment should have no
1604 // parameters at all.
1605 let generics = tcx.generics_of(def_id);
1606 // Variant and struct constructors use the
1607 // generics of their parent type definition.
1608 let generics_def_id = generics.parent.unwrap_or(def_id);
1609 path_segs.push(PathSeg(generics_def_id, last));
1612 // Case 2. Reference to a variant constructor.
1613 Def::Variant(def_id) |
1614 Def::VariantCtor(def_id, ..) => {
1615 let adt_def = self_ty.map(|t| t.ty_adt_def().unwrap());
1616 let (generics_def_id, index) = if let Some(adt_def) = adt_def {
1617 debug_assert!(adt_def.is_enum());
1619 } else if last >= 1 && segments[last - 1].args.is_some() {
1620 // Everything but the penultimate segment should have no
1621 // parameters at all.
1622 let enum_def_id = tcx.parent_def_id(def_id).unwrap();
1623 (enum_def_id, last - 1)
1625 // FIXME: lint here recommending `Enum::<...>::Variant` form
1626 // instead of `Enum::Variant::<...>` form.
1628 // Everything but the final segment should have no
1629 // parameters at all.
1630 let generics = tcx.generics_of(def_id);
1631 // Variant and struct constructors use the
1632 // generics of their parent type definition.
1633 (generics.parent.unwrap_or(def_id), last)
1635 path_segs.push(PathSeg(generics_def_id, index));
1638 // Case 3. Reference to a top-level value.
1640 Def::Const(def_id) |
1641 Def::ConstParam(def_id) |
1642 Def::Static(def_id, _) => {
1643 path_segs.push(PathSeg(def_id, last));
1646 // Case 4. Reference to a method or associated const.
1647 Def::Method(def_id) |
1648 Def::AssociatedConst(def_id) => {
1649 if segments.len() >= 2 {
1650 let generics = tcx.generics_of(def_id);
1651 path_segs.push(PathSeg(generics.parent.unwrap(), last - 1));
1653 path_segs.push(PathSeg(def_id, last));
1656 // Case 5. Local variable, no generics.
1657 Def::Local(..) | Def::Upvar(..) => {}
1659 _ => bug!("unexpected definition: {:?}", def),
1662 debug!("path_segs = {:?}", path_segs);
1667 // Check a type `Path` and convert it to a `Ty`.
1668 pub fn def_to_ty(&self,
1669 opt_self_ty: Option<Ty<'tcx>>,
1671 permit_variants: bool)
1673 let tcx = self.tcx();
1675 debug!("def_to_ty(def={:?}, opt_self_ty={:?}, path_segments={:?})",
1676 path.def, opt_self_ty, path.segments);
1678 let span = path.span;
1680 Def::Existential(did) => {
1681 // Check for desugared impl trait.
1682 assert!(ty::is_impl_trait_defn(tcx, did).is_none());
1683 let item_segment = path.segments.split_last().unwrap();
1684 self.prohibit_generics(item_segment.1);
1685 let substs = self.ast_path_substs_for_ty(span, did, item_segment.0);
1688 tcx.mk_opaque(did, substs),
1691 Def::Enum(did) | Def::TyAlias(did) | Def::Struct(did) |
1692 Def::Union(did) | Def::ForeignTy(did) => {
1693 assert_eq!(opt_self_ty, None);
1694 self.prohibit_generics(path.segments.split_last().unwrap().1);
1695 self.ast_path_to_ty(span, did, path.segments.last().unwrap())
1697 Def::Variant(_) if permit_variants => {
1698 // Convert "variant type" as if it were a real type.
1699 // The resulting `Ty` is type of the variant's enum for now.
1700 assert_eq!(opt_self_ty, None);
1702 let path_segs = self.def_ids_for_path_segments(&path.segments, None, path.def);
1703 let generic_segs: FxHashSet<_> =
1704 path_segs.iter().map(|PathSeg(_, index)| index).collect();
1705 self.prohibit_generics(path.segments.iter().enumerate().filter_map(|(index, seg)| {
1706 if !generic_segs.contains(&index) {
1713 let PathSeg(def_id, index) = path_segs.last().unwrap();
1714 self.ast_path_to_ty(span, *def_id, &path.segments[*index])
1716 Def::TyParam(did) => {
1717 assert_eq!(opt_self_ty, None);
1718 self.prohibit_generics(&path.segments);
1720 let hir_id = tcx.hir().as_local_hir_id(did).unwrap();
1721 let item_id = tcx.hir().get_parent_node_by_hir_id(hir_id);
1722 let item_def_id = tcx.hir().local_def_id_from_hir_id(item_id);
1723 let generics = tcx.generics_of(item_def_id);
1724 let index = generics.param_def_id_to_index[
1725 &tcx.hir().local_def_id_from_hir_id(hir_id)];
1726 tcx.mk_ty_param(index, tcx.hir().name_by_hir_id(hir_id).as_interned_str())
1728 Def::SelfTy(_, Some(def_id)) => {
1729 // `Self` in impl (we know the concrete type).
1730 assert_eq!(opt_self_ty, None);
1731 self.prohibit_generics(&path.segments);
1732 // Try to evaluate any array length constants
1733 self.normalize_ty(span, tcx.at(span).type_of(def_id))
1735 Def::SelfTy(Some(_), None) => {
1737 assert_eq!(opt_self_ty, None);
1738 self.prohibit_generics(&path.segments);
1741 Def::AssociatedTy(def_id) => {
1742 debug_assert!(path.segments.len() >= 2);
1743 self.prohibit_generics(&path.segments[..path.segments.len() - 2]);
1744 self.qpath_to_ty(span,
1747 &path.segments[path.segments.len() - 2],
1748 path.segments.last().unwrap())
1750 Def::PrimTy(prim_ty) => {
1751 assert_eq!(opt_self_ty, None);
1752 self.prohibit_generics(&path.segments);
1754 hir::Bool => tcx.types.bool,
1755 hir::Char => tcx.types.char,
1756 hir::Int(it) => tcx.mk_mach_int(it),
1757 hir::Uint(uit) => tcx.mk_mach_uint(uit),
1758 hir::Float(ft) => tcx.mk_mach_float(ft),
1759 hir::Str => tcx.mk_str()
1763 self.set_tainted_by_errors();
1764 return self.tcx().types.err;
1766 _ => span_bug!(span, "unexpected definition: {:?}", path.def)
1770 /// Parses the programmer's textual representation of a type into our
1771 /// internal notion of a type.
1772 pub fn ast_ty_to_ty(&self, ast_ty: &hir::Ty) -> Ty<'tcx> {
1773 debug!("ast_ty_to_ty(id={:?}, ast_ty={:?} ty_ty={:?})",
1774 ast_ty.hir_id, ast_ty, ast_ty.node);
1776 let tcx = self.tcx();
1778 let result_ty = match ast_ty.node {
1779 hir::TyKind::Slice(ref ty) => {
1780 tcx.mk_slice(self.ast_ty_to_ty(&ty))
1782 hir::TyKind::Ptr(ref mt) => {
1783 tcx.mk_ptr(ty::TypeAndMut {
1784 ty: self.ast_ty_to_ty(&mt.ty),
1788 hir::TyKind::Rptr(ref region, ref mt) => {
1789 let r = self.ast_region_to_region(region, None);
1790 debug!("Ref r={:?}", r);
1791 let t = self.ast_ty_to_ty(&mt.ty);
1792 tcx.mk_ref(r, ty::TypeAndMut {ty: t, mutbl: mt.mutbl})
1794 hir::TyKind::Never => {
1797 hir::TyKind::Tup(ref fields) => {
1798 tcx.mk_tup(fields.iter().map(|t| self.ast_ty_to_ty(&t)))
1800 hir::TyKind::BareFn(ref bf) => {
1801 require_c_abi_if_c_variadic(tcx, &bf.decl, bf.abi, ast_ty.span);
1802 tcx.mk_fn_ptr(self.ty_of_fn(bf.unsafety, bf.abi, &bf.decl))
1804 hir::TyKind::TraitObject(ref bounds, ref lifetime) => {
1805 self.conv_object_ty_poly_trait_ref(ast_ty.span, bounds, lifetime)
1807 hir::TyKind::Path(hir::QPath::Resolved(ref maybe_qself, ref path)) => {
1808 debug!("ast_ty_to_ty: maybe_qself={:?} path={:?}", maybe_qself, path);
1809 let opt_self_ty = maybe_qself.as_ref().map(|qself| {
1810 self.ast_ty_to_ty(qself)
1812 self.def_to_ty(opt_self_ty, path, false)
1814 hir::TyKind::Def(item_id, ref lifetimes) => {
1815 let did = tcx.hir().local_def_id(item_id.id);
1816 self.impl_trait_ty_to_ty(did, lifetimes)
1818 hir::TyKind::Path(hir::QPath::TypeRelative(ref qself, ref segment)) => {
1819 debug!("ast_ty_to_ty: qself={:?} segment={:?}", qself, segment);
1820 let ty = self.ast_ty_to_ty(qself);
1822 let def = if let hir::TyKind::Path(hir::QPath::Resolved(_, ref path)) = qself.node {
1827 self.associated_path_to_ty(ast_ty.hir_id, ast_ty.span, ty, def, segment, false).0
1829 hir::TyKind::Array(ref ty, ref length) => {
1830 let length = self.ast_const_to_const(length, tcx.types.usize);
1831 let array_ty = tcx.mk_ty(ty::Array(self.ast_ty_to_ty(&ty), length));
1832 self.normalize_ty(ast_ty.span, array_ty)
1834 hir::TyKind::Typeof(ref _e) => {
1835 struct_span_err!(tcx.sess, ast_ty.span, E0516,
1836 "`typeof` is a reserved keyword but unimplemented")
1837 .span_label(ast_ty.span, "reserved keyword")
1842 hir::TyKind::Infer => {
1843 // Infer also appears as the type of arguments or return
1844 // values in a ExprKind::Closure, or as
1845 // the type of local variables. Both of these cases are
1846 // handled specially and will not descend into this routine.
1847 self.ty_infer(ast_ty.span)
1849 hir::TyKind::Err => {
1852 hir::TyKind::CVarArgs(lt) => {
1853 let va_list_did = match tcx.lang_items().va_list() {
1855 None => span_bug!(ast_ty.span,
1856 "`va_list` lang item required for variadics"),
1858 let region = self.ast_region_to_region(<, None);
1859 tcx.type_of(va_list_did).subst(tcx, &[region.into()])
1863 self.record_ty(ast_ty.hir_id, result_ty, ast_ty.span);
1867 pub fn ast_const_to_const(
1869 ast_const: &hir::AnonConst,
1871 ) -> &'tcx ty::LazyConst<'tcx> {
1872 debug!("ast_const_to_const(id={:?}, ast_const={:?})", ast_const.hir_id, ast_const);
1874 let tcx = self.tcx();
1875 let def_id = tcx.hir().local_def_id_from_hir_id(ast_const.hir_id);
1877 let mut lazy_const = ty::LazyConst::Unevaluated(
1879 InternalSubsts::identity_for_item(tcx, def_id),
1882 let expr = &tcx.hir().body(ast_const.body).value;
1883 if let ExprKind::Path(ref qpath) = expr.node {
1884 if let hir::QPath::Resolved(_, ref path) = qpath {
1885 if let Def::ConstParam(def_id) = path.def {
1886 let node_id = tcx.hir().as_local_node_id(def_id).unwrap();
1887 let item_id = tcx.hir().get_parent_node(node_id);
1888 let item_def_id = tcx.hir().local_def_id(item_id);
1889 let generics = tcx.generics_of(item_def_id);
1890 let index = generics.param_def_id_to_index[&tcx.hir().local_def_id(node_id)];
1891 let name = tcx.hir().name(node_id).as_interned_str();
1892 lazy_const = ty::LazyConst::Evaluated(ty::Const {
1893 val: ConstValue::Param(ty::ParamConst::new(index, name)),
1900 tcx.mk_lazy_const(lazy_const)
1903 pub fn impl_trait_ty_to_ty(
1906 lifetimes: &[hir::GenericArg],
1908 debug!("impl_trait_ty_to_ty(def_id={:?}, lifetimes={:?})", def_id, lifetimes);
1909 let tcx = self.tcx();
1911 let generics = tcx.generics_of(def_id);
1913 debug!("impl_trait_ty_to_ty: generics={:?}", generics);
1914 let substs = InternalSubsts::for_item(tcx, def_id, |param, _| {
1915 if let Some(i) = (param.index as usize).checked_sub(generics.parent_count) {
1916 // Our own parameters are the resolved lifetimes.
1918 GenericParamDefKind::Lifetime => {
1919 if let hir::GenericArg::Lifetime(lifetime) = &lifetimes[i] {
1920 self.ast_region_to_region(lifetime, None).into()
1928 // Replace all parent lifetimes with 'static.
1930 GenericParamDefKind::Lifetime => {
1931 tcx.types.re_static.into()
1933 _ => tcx.mk_param_from_def(param)
1937 debug!("impl_trait_ty_to_ty: final substs = {:?}", substs);
1939 let ty = tcx.mk_opaque(def_id, substs);
1940 debug!("impl_trait_ty_to_ty: {}", ty);
1944 pub fn ty_of_arg(&self,
1946 expected_ty: Option<Ty<'tcx>>)
1950 hir::TyKind::Infer if expected_ty.is_some() => {
1951 self.record_ty(ty.hir_id, expected_ty.unwrap(), ty.span);
1952 expected_ty.unwrap()
1954 _ => self.ast_ty_to_ty(ty),
1958 pub fn ty_of_fn(&self,
1959 unsafety: hir::Unsafety,
1962 -> ty::PolyFnSig<'tcx> {
1965 let tcx = self.tcx();
1967 decl.inputs.iter().map(|a| self.ty_of_arg(a, None));
1969 let output_ty = match decl.output {
1970 hir::Return(ref output) => self.ast_ty_to_ty(output),
1971 hir::DefaultReturn(..) => tcx.mk_unit(),
1974 debug!("ty_of_fn: output_ty={:?}", output_ty);
1976 let bare_fn_ty = ty::Binder::bind(tcx.mk_fn_sig(
1984 // Find any late-bound regions declared in return type that do
1985 // not appear in the arguments. These are not well-formed.
1988 // for<'a> fn() -> &'a str <-- 'a is bad
1989 // for<'a> fn(&'a String) -> &'a str <-- 'a is ok
1990 let inputs = bare_fn_ty.inputs();
1991 let late_bound_in_args = tcx.collect_constrained_late_bound_regions(
1992 &inputs.map_bound(|i| i.to_owned()));
1993 let output = bare_fn_ty.output();
1994 let late_bound_in_ret = tcx.collect_referenced_late_bound_regions(&output);
1995 for br in late_bound_in_ret.difference(&late_bound_in_args) {
1996 let lifetime_name = match *br {
1997 ty::BrNamed(_, name) => format!("lifetime `{}`,", name),
1998 ty::BrAnon(_) | ty::BrFresh(_) | ty::BrEnv => "an anonymous lifetime".to_string(),
2000 let mut err = struct_span_err!(tcx.sess,
2003 "return type references {} \
2004 which is not constrained by the fn input types",
2006 if let ty::BrAnon(_) = *br {
2007 // The only way for an anonymous lifetime to wind up
2008 // in the return type but **also** be unconstrained is
2009 // if it only appears in "associated types" in the
2010 // input. See #47511 for an example. In this case,
2011 // though we can easily give a hint that ought to be
2013 err.note("lifetimes appearing in an associated type \
2014 are not considered constrained");
2022 /// Given the bounds on an object, determines what single region bound (if any) we can
2023 /// use to summarize this type. The basic idea is that we will use the bound the user
2024 /// provided, if they provided one, and otherwise search the supertypes of trait bounds
2025 /// for region bounds. It may be that we can derive no bound at all, in which case
2026 /// we return `None`.
2027 fn compute_object_lifetime_bound(&self,
2029 existential_predicates: ty::Binder<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>>)
2030 -> Option<ty::Region<'tcx>> // if None, use the default
2032 let tcx = self.tcx();
2034 debug!("compute_opt_region_bound(existential_predicates={:?})",
2035 existential_predicates);
2037 // No explicit region bound specified. Therefore, examine trait
2038 // bounds and see if we can derive region bounds from those.
2039 let derived_region_bounds =
2040 object_region_bounds(tcx, existential_predicates);
2042 // If there are no derived region bounds, then report back that we
2043 // can find no region bound. The caller will use the default.
2044 if derived_region_bounds.is_empty() {
2048 // If any of the derived region bounds are 'static, that is always
2050 if derived_region_bounds.iter().any(|&r| ty::ReStatic == *r) {
2051 return Some(tcx.types.re_static);
2054 // Determine whether there is exactly one unique region in the set
2055 // of derived region bounds. If so, use that. Otherwise, report an
2057 let r = derived_region_bounds[0];
2058 if derived_region_bounds[1..].iter().any(|r1| r != *r1) {
2059 span_err!(tcx.sess, span, E0227,
2060 "ambiguous lifetime bound, explicit lifetime bound required");
2066 /// Divides a list of general trait bounds into two groups: auto traits (e.g., Sync and Send) and
2067 /// the remaining general trait bounds.
2068 fn split_auto_traits<'a, 'b, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
2069 trait_bounds: &'b [hir::PolyTraitRef])
2070 -> (Vec<DefId>, Vec<&'b hir::PolyTraitRef>)
2072 let (auto_traits, trait_bounds): (Vec<_>, _) = trait_bounds.iter().partition(|bound| {
2073 // Checks whether `trait_did` is an auto trait and adds it to `auto_traits` if so.
2074 match bound.trait_ref.path.def {
2075 Def::Trait(trait_did) if tcx.trait_is_auto(trait_did) => {
2082 let auto_traits = auto_traits.into_iter().map(|tr| {
2083 if let Def::Trait(trait_did) = tr.trait_ref.path.def {
2088 }).collect::<Vec<_>>();
2090 (auto_traits, trait_bounds)
2093 // A helper struct for conveniently grouping a set of bounds which we pass to
2094 // and return from functions in multiple places.
2095 #[derive(PartialEq, Eq, Clone, Debug)]
2096 pub struct Bounds<'tcx> {
2097 pub region_bounds: Vec<(ty::Region<'tcx>, Span)>,
2098 pub implicitly_sized: Option<Span>,
2099 pub trait_bounds: Vec<(ty::PolyTraitRef<'tcx>, Span)>,
2100 pub projection_bounds: Vec<(ty::PolyProjectionPredicate<'tcx>, Span)>,
2103 impl<'a, 'gcx, 'tcx> Bounds<'tcx> {
2104 pub fn predicates(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>, param_ty: Ty<'tcx>)
2105 -> Vec<(ty::Predicate<'tcx>, Span)>
2107 // If it could be sized, and is, add the sized predicate.
2108 let sized_predicate = self.implicitly_sized.and_then(|span| {
2109 tcx.lang_items().sized_trait().map(|sized| {
2110 let trait_ref = ty::TraitRef {
2112 substs: tcx.mk_substs_trait(param_ty, &[])
2114 (trait_ref.to_predicate(), span)
2118 sized_predicate.into_iter().chain(
2119 self.region_bounds.iter().map(|&(region_bound, span)| {
2120 // Account for the binder being introduced below; no need to shift `param_ty`
2121 // because, at present at least, it can only refer to early-bound regions.
2122 let region_bound = ty::fold::shift_region(tcx, region_bound, 1);
2123 let outlives = ty::OutlivesPredicate(param_ty, region_bound);
2124 (ty::Binder::dummy(outlives).to_predicate(), span)
2126 self.trait_bounds.iter().map(|&(bound_trait_ref, span)| {
2127 (bound_trait_ref.to_predicate(), span)
2130 self.projection_bounds.iter().map(|&(projection, span)| {
2131 (projection.to_predicate(), span)