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::{CtorOf, 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, DefIdTree, 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 impl<'o, 'gcx: 'tcx, 'tcx> dyn AstConv<'gcx, 'tcx> + 'o {
103 pub fn ast_region_to_region(&self,
104 lifetime: &hir::Lifetime,
105 def: Option<&ty::GenericParamDef>)
108 let tcx = self.tcx();
109 let lifetime_name = |def_id| {
110 tcx.hir().name_by_hir_id(tcx.hir().as_local_hir_id(def_id).unwrap()).as_interned_str()
113 let r = match tcx.named_region(lifetime.hir_id) {
114 Some(rl::Region::Static) => {
118 Some(rl::Region::LateBound(debruijn, id, _)) => {
119 let name = lifetime_name(id);
120 tcx.mk_region(ty::ReLateBound(debruijn,
121 ty::BrNamed(id, name)))
124 Some(rl::Region::LateBoundAnon(debruijn, index)) => {
125 tcx.mk_region(ty::ReLateBound(debruijn, ty::BrAnon(index)))
128 Some(rl::Region::EarlyBound(index, id, _)) => {
129 let name = lifetime_name(id);
130 tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion {
137 Some(rl::Region::Free(scope, id)) => {
138 let name = lifetime_name(id);
139 tcx.mk_region(ty::ReFree(ty::FreeRegion {
141 bound_region: ty::BrNamed(id, name)
144 // (*) -- not late-bound, won't change
148 self.re_infer(lifetime.span, def)
150 // This indicates an illegal lifetime
151 // elision. `resolve_lifetime` should have
152 // reported an error in this case -- but if
153 // not, let's error out.
154 tcx.sess.delay_span_bug(lifetime.span, "unelided lifetime in signature");
156 // Supply some dummy value. We don't have an
157 // `re_error`, annoyingly, so use `'static`.
163 debug!("ast_region_to_region(lifetime={:?}) yields {:?}",
170 /// Given a path `path` that refers to an item `I` with the declared generics `decl_generics`,
171 /// returns an appropriate set of substitutions for this particular reference to `I`.
172 pub fn ast_path_substs_for_ty(&self,
175 item_segment: &hir::PathSegment)
178 let (substs, assoc_bindings, _) = item_segment.with_generic_args(|generic_args| {
179 self.create_substs_for_ast_path(
183 item_segment.infer_types,
188 assoc_bindings.first().map(|b| Self::prohibit_assoc_ty_binding(self.tcx(), b.span));
193 /// Report error if there is an explicit type parameter when using `impl Trait`.
195 tcx: TyCtxt<'_, '_, '_>,
197 seg: &hir::PathSegment,
198 generics: &ty::Generics,
200 let explicit = !seg.infer_types;
201 let impl_trait = generics.params.iter().any(|param| match param.kind {
202 ty::GenericParamDefKind::Type {
203 synthetic: Some(hir::SyntheticTyParamKind::ImplTrait), ..
208 if explicit && impl_trait {
209 let mut err = struct_span_err! {
213 "cannot provide explicit type parameters when `impl Trait` is \
214 used in argument position."
223 /// Checks that the correct number of generic arguments have been provided.
224 /// Used specifically for function calls.
225 pub fn check_generic_arg_count_for_call(
226 tcx: TyCtxt<'_, '_, '_>,
229 seg: &hir::PathSegment,
230 is_method_call: bool,
232 let empty_args = P(hir::GenericArgs {
233 args: HirVec::new(), bindings: HirVec::new(), parenthesized: false,
235 let suppress_mismatch = Self::check_impl_trait(tcx, span, seg, &def);
236 Self::check_generic_arg_count(
240 if let Some(ref args) = seg.args {
246 GenericArgPosition::MethodCall
248 GenericArgPosition::Value
250 def.parent.is_none() && def.has_self, // `has_self`
251 seg.infer_types || suppress_mismatch, // `infer_types`
255 /// Checks that the correct number of generic arguments have been provided.
256 /// This is used both for datatypes and function calls.
257 fn check_generic_arg_count(
258 tcx: TyCtxt<'_, '_, '_>,
261 args: &hir::GenericArgs,
262 position: GenericArgPosition,
265 ) -> (bool, Option<Vec<Span>>) {
266 // At this stage we are guaranteed that the generic arguments are in the correct order, e.g.
267 // that lifetimes will proceed types. So it suffices to check the number of each generic
268 // arguments in order to validate them with respect to the generic parameters.
269 let param_counts = def.own_counts();
270 let arg_counts = args.own_counts();
271 let infer_lifetimes = position != GenericArgPosition::Type && arg_counts.lifetimes == 0;
272 let infer_consts = position != GenericArgPosition::Type && arg_counts.consts == 0;
274 let mut defaults: ty::GenericParamCount = Default::default();
275 for param in &def.params {
277 GenericParamDefKind::Lifetime => {}
278 GenericParamDefKind::Type { has_default, .. } => {
279 defaults.types += has_default as usize
281 GenericParamDefKind::Const => {
282 // FIXME(const_generics:defaults)
287 if position != GenericArgPosition::Type && !args.bindings.is_empty() {
288 AstConv::prohibit_assoc_ty_binding(tcx, args.bindings[0].span);
291 // Prohibit explicit lifetime arguments if late-bound lifetime parameters are present.
292 if !infer_lifetimes {
293 if let Some(span_late) = def.has_late_bound_regions {
294 let msg = "cannot specify lifetime arguments explicitly \
295 if late bound lifetime parameters are present";
296 let note = "the late bound lifetime parameter is introduced here";
297 let span = args.args[0].span();
298 if position == GenericArgPosition::Value
299 && arg_counts.lifetimes != param_counts.lifetimes {
300 let mut err = tcx.sess.struct_span_err(span, msg);
301 err.span_note(span_late, note);
305 let mut multispan = MultiSpan::from_span(span);
306 multispan.push_span_label(span_late, note.to_string());
307 tcx.lint_hir(lint::builtin::LATE_BOUND_LIFETIME_ARGUMENTS,
308 args.args[0].id(), multispan, msg);
309 return (false, None);
314 let check_kind_count = |kind, required, permitted, provided, offset| {
316 "check_kind_count: kind: {} required: {} permitted: {} provided: {} offset: {}",
323 // We enforce the following: `required` <= `provided` <= `permitted`.
324 // For kinds without defaults (i.e., lifetimes), `required == permitted`.
325 // For other kinds (i.e., types), `permitted` may be greater than `required`.
326 if required <= provided && provided <= permitted {
327 return (false, None);
330 // Unfortunately lifetime and type parameter mismatches are typically styled
331 // differently in diagnostics, which means we have a few cases to consider here.
332 let (bound, quantifier) = if required != permitted {
333 if provided < required {
334 (required, "at least ")
335 } else { // provided > permitted
336 (permitted, "at most ")
342 let mut potential_assoc_types: Option<Vec<Span>> = None;
343 let (spans, label) = if required == permitted && provided > permitted {
344 // In the case when the user has provided too many arguments,
345 // we want to point to the unexpected arguments.
346 let spans: Vec<Span> = args.args[offset+permitted .. offset+provided]
348 .map(|arg| arg.span())
350 potential_assoc_types = Some(spans.clone());
351 (spans, format!( "unexpected {} argument", kind))
353 (vec![span], format!(
354 "expected {}{} {} argument{}",
358 if bound != 1 { "s" } else { "" },
362 let mut err = tcx.sess.struct_span_err_with_code(
365 "wrong number of {} arguments: expected {}{}, found {}",
371 DiagnosticId::Error("E0107".into())
374 err.span_label(span, label.as_str());
378 (provided > required, // `suppress_error`
379 potential_assoc_types)
382 if !infer_lifetimes || arg_counts.lifetimes > param_counts.lifetimes {
385 param_counts.lifetimes,
386 param_counts.lifetimes,
387 arg_counts.lifetimes,
391 // FIXME(const_generics:defaults)
392 if !infer_consts || arg_counts.consts > param_counts.consts {
398 arg_counts.lifetimes + arg_counts.types,
401 // Note that type errors are currently be emitted *after* const errors.
403 || arg_counts.types > param_counts.types - defaults.types - has_self as usize {
406 param_counts.types - defaults.types - has_self as usize,
407 param_counts.types - has_self as usize,
409 arg_counts.lifetimes,
416 /// Creates the relevant generic argument substitutions
417 /// corresponding to a set of generic parameters. This is a
418 /// rather complex function. Let us try to explain the role
419 /// of each of its parameters:
421 /// To start, we are given the `def_id` of the thing we are
422 /// creating the substitutions for, and a partial set of
423 /// substitutions `parent_substs`. In general, the substitutions
424 /// for an item begin with substitutions for all the "parents" of
425 /// that item -- e.g., for a method it might include the
426 /// parameters from the impl.
428 /// Therefore, the method begins by walking down these parents,
429 /// starting with the outermost parent and proceed inwards until
430 /// it reaches `def_id`. For each parent `P`, it will check `parent_substs`
431 /// first to see if the parent's substitutions are listed in there. If so,
432 /// we can append those and move on. Otherwise, it invokes the
433 /// three callback functions:
435 /// - `args_for_def_id`: given the `DefId` `P`, supplies back the
436 /// generic arguments that were given to that parent from within
437 /// the path; so e.g., if you have `<T as Foo>::Bar`, the `DefId`
438 /// might refer to the trait `Foo`, and the arguments might be
439 /// `[T]`. The boolean value indicates whether to infer values
440 /// for arguments whose values were not explicitly provided.
441 /// - `provided_kind`: given the generic parameter and the value from `args_for_def_id`,
442 /// instantiate a `Kind`.
443 /// - `inferred_kind`: if no parameter was provided, and inference is enabled, then
444 /// creates a suitable inference variable.
445 pub fn create_substs_for_generic_args<'a, 'b>(
446 tcx: TyCtxt<'a, 'gcx, 'tcx>,
448 parent_substs: &[Kind<'tcx>],
450 self_ty: Option<Ty<'tcx>>,
451 args_for_def_id: impl Fn(DefId) -> (Option<&'b GenericArgs>, bool),
452 provided_kind: impl Fn(&GenericParamDef, &GenericArg) -> Kind<'tcx>,
453 inferred_kind: impl Fn(Option<&[Kind<'tcx>]>, &GenericParamDef, bool) -> Kind<'tcx>,
454 ) -> SubstsRef<'tcx> {
455 // Collect the segments of the path; we need to substitute arguments
456 // for parameters throughout the entire path (wherever there are
457 // generic parameters).
458 let mut parent_defs = tcx.generics_of(def_id);
459 let count = parent_defs.count();
460 let mut stack = vec![(def_id, parent_defs)];
461 while let Some(def_id) = parent_defs.parent {
462 parent_defs = tcx.generics_of(def_id);
463 stack.push((def_id, parent_defs));
466 // We manually build up the substitution, rather than using convenience
467 // methods in `subst.rs`, so that we can iterate over the arguments and
468 // parameters in lock-step linearly, instead of trying to match each pair.
469 let mut substs: SmallVec<[Kind<'tcx>; 8]> = SmallVec::with_capacity(count);
471 // Iterate over each segment of the path.
472 while let Some((def_id, defs)) = stack.pop() {
473 let mut params = defs.params.iter().peekable();
475 // If we have already computed substitutions for parents, we can use those directly.
476 while let Some(¶m) = params.peek() {
477 if let Some(&kind) = parent_substs.get(param.index as usize) {
485 // `Self` is handled first, unless it's been handled in `parent_substs`.
487 if let Some(¶m) = params.peek() {
488 if param.index == 0 {
489 if let GenericParamDefKind::Type { .. } = param.kind {
490 substs.push(self_ty.map(|ty| ty.into())
491 .unwrap_or_else(|| inferred_kind(None, param, true)));
498 // Check whether this segment takes generic arguments and the user has provided any.
499 let (generic_args, infer_types) = args_for_def_id(def_id);
501 let mut args = generic_args.iter().flat_map(|generic_args| generic_args.args.iter())
505 // We're going to iterate through the generic arguments that the user
506 // provided, matching them with the generic parameters we expect.
507 // Mismatches can occur as a result of elided lifetimes, or for malformed
508 // input. We try to handle both sensibly.
509 match (args.peek(), params.peek()) {
510 (Some(&arg), Some(¶m)) => {
511 match (arg, ¶m.kind) {
512 (GenericArg::Lifetime(_), GenericParamDefKind::Lifetime)
513 | (GenericArg::Type(_), GenericParamDefKind::Type { .. })
514 | (GenericArg::Const(_), GenericParamDefKind::Const) => {
515 substs.push(provided_kind(param, arg));
519 (GenericArg::Type(_), GenericParamDefKind::Lifetime)
520 | (GenericArg::Const(_), GenericParamDefKind::Lifetime) => {
521 // We expected a lifetime argument, but got a type or const
522 // argument. That means we're inferring the lifetimes.
523 substs.push(inferred_kind(None, param, infer_types));
527 // We expected one kind of parameter, but the user provided
528 // another. This is an error, but we need to handle it
529 // gracefully so we can report sensible errors.
530 // In this case, we're simply going to infer this argument.
536 // We should never be able to reach this point with well-formed input.
537 // Getting to this point means the user supplied more arguments than
538 // there are parameters.
541 (None, Some(¶m)) => {
542 // If there are fewer arguments than parameters, it means
543 // we're inferring the remaining arguments.
544 substs.push(inferred_kind(Some(&substs), param, infer_types));
548 (None, None) => break,
553 tcx.intern_substs(&substs)
556 /// Given the type/region arguments provided to some path (along with
557 /// an implicit `Self`, if this is a trait reference) returns the complete
558 /// set of substitutions. This may involve applying defaulted type parameters.
560 /// Note that the type listing given here is *exactly* what the user provided.
561 fn create_substs_for_ast_path(&self,
564 generic_args: &hir::GenericArgs,
566 self_ty: Option<Ty<'tcx>>)
567 -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'tcx>>, Option<Vec<Span>>)
569 // If the type is parameterized by this region, then replace this
570 // region with the current anon region binding (in other words,
571 // whatever & would get replaced with).
572 debug!("create_substs_for_ast_path(def_id={:?}, self_ty={:?}, \
574 def_id, self_ty, generic_args);
576 let tcx = self.tcx();
577 let generic_params = tcx.generics_of(def_id);
579 // If a self-type was declared, one should be provided.
580 assert_eq!(generic_params.has_self, self_ty.is_some());
582 let has_self = generic_params.has_self;
583 let (_, potential_assoc_types) = Self::check_generic_arg_count(
588 GenericArgPosition::Type,
593 let is_object = self_ty.map_or(false, |ty| {
594 ty.sty == self.tcx().types.trait_object_dummy_self.sty
596 let default_needs_object_self = |param: &ty::GenericParamDef| {
597 if let GenericParamDefKind::Type { has_default, .. } = param.kind {
598 if is_object && has_default {
599 if tcx.at(span).type_of(param.def_id).has_self_ty() {
600 // There is no suitable inference default for a type parameter
601 // that references self, in an object type.
610 let substs = Self::create_substs_for_generic_args(
616 // Provide the generic args, and whether types should be inferred.
617 |_| (Some(generic_args), infer_types),
618 // Provide substitutions for parameters for which (valid) arguments have been provided.
620 match (¶m.kind, arg) {
621 (GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => {
622 self.ast_region_to_region(<, Some(param)).into()
624 (GenericParamDefKind::Type { .. }, GenericArg::Type(ty)) => {
625 self.ast_ty_to_ty(&ty).into()
627 (GenericParamDefKind::Const, GenericArg::Const(ct)) => {
628 self.ast_const_to_const(&ct.value, tcx.type_of(param.def_id)).into()
633 // Provide substitutions for parameters for which arguments are inferred.
634 |substs, param, infer_types| {
636 GenericParamDefKind::Lifetime => tcx.types.re_static.into(),
637 GenericParamDefKind::Type { has_default, .. } => {
638 if !infer_types && has_default {
639 // No type parameter provided, but a default exists.
641 // If we are converting an object type, then the
642 // `Self` parameter is unknown. However, some of the
643 // other type parameters may reference `Self` in their
644 // defaults. This will lead to an ICE if we are not
646 if default_needs_object_self(param) {
647 struct_span_err!(tcx.sess, span, E0393,
648 "the type parameter `{}` must be explicitly \
652 format!("missing reference to `{}`", param.name))
653 .note(&format!("because of the default `Self` reference, \
654 type parameters must be specified on object \
659 // This is a default type parameter.
662 tcx.at(span).type_of(param.def_id)
663 .subst_spanned(tcx, substs.unwrap(), Some(span))
666 } else if infer_types {
667 // No type parameters were provided, we can infer all.
668 if !default_needs_object_self(param) {
669 self.ty_infer_for_def(param, span).into()
671 self.ty_infer(span).into()
674 // We've already errored above about the mismatch.
678 GenericParamDefKind::Const => {
679 // FIXME(const_generics:defaults)
680 // We've already errored above about the mismatch.
687 let assoc_bindings = generic_args.bindings.iter().map(|binding| {
689 item_name: binding.ident,
690 ty: self.ast_ty_to_ty(&binding.ty),
695 debug!("create_substs_for_ast_path(generic_params={:?}, self_ty={:?}) -> {:?}",
696 generic_params, self_ty, substs);
698 (substs, assoc_bindings, potential_assoc_types)
701 /// Instantiates the path for the given trait reference, assuming that it's
702 /// bound to a valid trait type. Returns the def_id for the defining trait.
703 /// The type _cannot_ be a type other than a trait type.
705 /// If the `projections` argument is `None`, then assoc type bindings like `Foo<T = X>`
706 /// are disallowed. Otherwise, they are pushed onto the vector given.
707 pub fn instantiate_mono_trait_ref(&self,
708 trait_ref: &hir::TraitRef,
710 -> ty::TraitRef<'tcx>
712 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
714 self.ast_path_to_mono_trait_ref(trait_ref.path.span,
715 trait_ref.trait_def_id(),
717 trait_ref.path.segments.last().unwrap())
720 /// The given trait-ref must actually be a trait.
721 pub(super) fn instantiate_poly_trait_ref_inner(&self,
722 trait_ref: &hir::TraitRef,
724 poly_projections: &mut Vec<(ty::PolyProjectionPredicate<'tcx>, Span)>,
726 -> (ty::PolyTraitRef<'tcx>, Option<Vec<Span>>)
728 let trait_def_id = trait_ref.trait_def_id();
730 debug!("instantiate_poly_trait_ref({:?}, def_id={:?})", trait_ref, trait_def_id);
732 self.prohibit_generics(trait_ref.path.segments.split_last().unwrap().1);
734 let (substs, assoc_bindings, potential_assoc_types) = self.create_substs_for_ast_trait_ref(
738 trait_ref.path.segments.last().unwrap(),
740 let poly_trait_ref = ty::Binder::bind(ty::TraitRef::new(trait_def_id, substs));
742 let mut dup_bindings = FxHashMap::default();
743 poly_projections.extend(assoc_bindings.iter().filter_map(|binding| {
744 // specify type to assert that error was already reported in Err case:
745 let predicate: Result<_, ErrorReported> =
746 self.ast_type_binding_to_poly_projection_predicate(
747 trait_ref.hir_ref_id, poly_trait_ref, binding, speculative, &mut dup_bindings);
748 // okay to ignore Err because of ErrorReported (see above)
749 Some((predicate.ok()?, binding.span))
752 debug!("instantiate_poly_trait_ref({:?}, projections={:?}) -> {:?}",
753 trait_ref, poly_projections, poly_trait_ref);
754 (poly_trait_ref, potential_assoc_types)
757 pub fn instantiate_poly_trait_ref(&self,
758 poly_trait_ref: &hir::PolyTraitRef,
760 poly_projections: &mut Vec<(ty::PolyProjectionPredicate<'tcx>, Span)>)
761 -> (ty::PolyTraitRef<'tcx>, Option<Vec<Span>>)
763 self.instantiate_poly_trait_ref_inner(&poly_trait_ref.trait_ref, self_ty,
764 poly_projections, false)
767 fn ast_path_to_mono_trait_ref(&self,
771 trait_segment: &hir::PathSegment)
772 -> ty::TraitRef<'tcx>
774 let (substs, assoc_bindings, _) =
775 self.create_substs_for_ast_trait_ref(span,
779 assoc_bindings.first().map(|b| AstConv::prohibit_assoc_ty_binding(self.tcx(), b.span));
780 ty::TraitRef::new(trait_def_id, substs)
783 fn create_substs_for_ast_trait_ref(
788 trait_segment: &hir::PathSegment,
789 ) -> (SubstsRef<'tcx>, Vec<ConvertedBinding<'tcx>>, Option<Vec<Span>>) {
790 debug!("create_substs_for_ast_trait_ref(trait_segment={:?})",
793 let trait_def = self.tcx().trait_def(trait_def_id);
795 if !self.tcx().features().unboxed_closures &&
796 trait_segment.with_generic_args(|generic_args| generic_args.parenthesized)
797 != trait_def.paren_sugar {
798 // For now, require that parenthetical notation be used only with `Fn()` etc.
799 let msg = if trait_def.paren_sugar {
800 "the precise format of `Fn`-family traits' type parameters is subject to change. \
801 Use parenthetical notation (Fn(Foo, Bar) -> Baz) instead"
803 "parenthetical notation is only stable when used with `Fn`-family traits"
805 emit_feature_err(&self.tcx().sess.parse_sess, "unboxed_closures",
806 span, GateIssue::Language, msg);
809 trait_segment.with_generic_args(|generic_args| {
810 self.create_substs_for_ast_path(span,
813 trait_segment.infer_types,
818 fn trait_defines_associated_type_named(&self,
820 assoc_name: ast::Ident)
823 self.tcx().associated_items(trait_def_id).any(|item| {
824 item.kind == ty::AssociatedKind::Type &&
825 self.tcx().hygienic_eq(assoc_name, item.ident, trait_def_id)
829 fn ast_type_binding_to_poly_projection_predicate(
831 hir_ref_id: hir::HirId,
832 trait_ref: ty::PolyTraitRef<'tcx>,
833 binding: &ConvertedBinding<'tcx>,
835 dup_bindings: &mut FxHashMap<DefId, Span>)
836 -> Result<ty::PolyProjectionPredicate<'tcx>, ErrorReported>
838 let tcx = self.tcx();
841 // Given something like `U: SomeTrait<T = X>`, we want to produce a
842 // predicate like `<U as SomeTrait>::T = X`. This is somewhat
843 // subtle in the event that `T` is defined in a supertrait of
844 // `SomeTrait`, because in that case we need to upcast.
846 // That is, consider this case:
849 // trait SubTrait: SuperTrait<int> { }
850 // trait SuperTrait<A> { type T; }
852 // ... B : SubTrait<T=foo> ...
855 // We want to produce `<B as SuperTrait<int>>::T == foo`.
857 // Find any late-bound regions declared in `ty` that are not
858 // declared in the trait-ref. These are not wellformed.
862 // for<'a> <T as Iterator>::Item = &'a str // <-- 'a is bad
863 // for<'a> <T as FnMut<(&'a u32,)>>::Output = &'a str // <-- 'a is ok
864 let late_bound_in_trait_ref = tcx.collect_constrained_late_bound_regions(&trait_ref);
865 let late_bound_in_ty =
866 tcx.collect_referenced_late_bound_regions(&ty::Binder::bind(binding.ty));
867 debug!("late_bound_in_trait_ref = {:?}", late_bound_in_trait_ref);
868 debug!("late_bound_in_ty = {:?}", late_bound_in_ty);
869 for br in late_bound_in_ty.difference(&late_bound_in_trait_ref) {
870 let br_name = match *br {
871 ty::BrNamed(_, name) => name,
875 "anonymous bound region {:?} in binding but not trait ref",
879 struct_span_err!(tcx.sess,
882 "binding for associated type `{}` references lifetime `{}`, \
883 which does not appear in the trait input types",
884 binding.item_name, br_name)
889 let candidate = if self.trait_defines_associated_type_named(trait_ref.def_id(),
891 // Simple case: X is defined in the current trait.
894 // Otherwise, we have to walk through the supertraits to find
896 let candidates = traits::supertraits(tcx, trait_ref).filter(|r| {
897 self.trait_defines_associated_type_named(r.def_id(), binding.item_name)
899 self.one_bound_for_assoc_type(candidates, &trait_ref.to_string(),
900 binding.item_name, binding.span)
903 let (assoc_ident, def_scope) =
904 tcx.adjust_ident(binding.item_name, candidate.def_id(), hir_ref_id);
905 let assoc_ty = tcx.associated_items(candidate.def_id()).find(|i| {
906 i.kind == ty::AssociatedKind::Type && i.ident.modern() == assoc_ident
907 }).expect("missing associated type");
909 if !assoc_ty.vis.is_accessible_from(def_scope, tcx) {
910 let msg = format!("associated type `{}` is private", binding.item_name);
911 tcx.sess.span_err(binding.span, &msg);
913 tcx.check_stability(assoc_ty.def_id, Some(hir_ref_id), binding.span);
916 dup_bindings.entry(assoc_ty.def_id)
917 .and_modify(|prev_span| {
918 struct_span_err!(self.tcx().sess, binding.span, E0719,
919 "the value of the associated type `{}` (from the trait `{}`) \
920 is already specified",
922 tcx.def_path_str(assoc_ty.container.id()))
923 .span_label(binding.span, "re-bound here")
924 .span_label(*prev_span, format!("`{}` bound here first", binding.item_name))
927 .or_insert(binding.span);
930 Ok(candidate.map_bound(|trait_ref| {
931 ty::ProjectionPredicate {
932 projection_ty: ty::ProjectionTy::from_ref_and_name(
942 fn ast_path_to_ty(&self,
945 item_segment: &hir::PathSegment)
948 let substs = self.ast_path_substs_for_ty(span, did, item_segment);
951 self.tcx().at(span).type_of(did).subst(self.tcx(), substs)
955 /// Transform a `PolyTraitRef` into a `PolyExistentialTraitRef` by
956 /// removing the dummy `Self` type (`trait_object_dummy_self`).
957 fn trait_ref_to_existential(&self, trait_ref: ty::TraitRef<'tcx>)
958 -> ty::ExistentialTraitRef<'tcx> {
959 if trait_ref.self_ty().sty != self.tcx().types.trait_object_dummy_self.sty {
960 bug!("trait_ref_to_existential called on {:?} with non-dummy Self", trait_ref);
962 ty::ExistentialTraitRef::erase_self_ty(self.tcx(), trait_ref)
965 fn conv_object_ty_poly_trait_ref(&self,
967 trait_bounds: &[hir::PolyTraitRef],
968 lifetime: &hir::Lifetime)
971 let tcx = self.tcx();
973 if trait_bounds.is_empty() {
974 span_err!(tcx.sess, span, E0224,
975 "at least one non-builtin trait is required for an object type");
976 return tcx.types.err;
979 let mut projection_bounds = Vec::new();
980 let dummy_self = self.tcx().types.trait_object_dummy_self;
981 let (principal, potential_assoc_types) = self.instantiate_poly_trait_ref(
984 &mut projection_bounds,
986 debug!("principal: {:?}", principal);
988 for trait_bound in trait_bounds[1..].iter() {
989 // sanity check for non-principal trait bounds
990 self.instantiate_poly_trait_ref(trait_bound,
995 let (mut auto_traits, trait_bounds) = split_auto_traits(tcx, &trait_bounds[1..]);
997 if !trait_bounds.is_empty() {
998 let b = &trait_bounds[0];
999 let span = b.trait_ref.path.span;
1000 struct_span_err!(self.tcx().sess, span, E0225,
1001 "only auto traits can be used as additional traits in a trait object")
1002 .span_label(span, "non-auto additional trait")
1006 // Check that there are no gross object safety violations;
1007 // most importantly, that the supertraits don't contain `Self`,
1009 let object_safety_violations =
1010 tcx.global_tcx().astconv_object_safety_violations(principal.def_id());
1011 if !object_safety_violations.is_empty() {
1012 tcx.report_object_safety_error(span, principal.def_id(), object_safety_violations)
1013 .map(|mut err| err.emit());
1014 return tcx.types.err;
1017 // Use a `BTreeSet` to keep output in a more consistent order.
1018 let mut associated_types = BTreeSet::default();
1020 for tr in traits::elaborate_trait_ref(tcx, principal) {
1021 debug!("conv_object_ty_poly_trait_ref: observing object predicate `{:?}`", tr);
1023 ty::Predicate::Trait(pred) => {
1024 associated_types.extend(tcx.associated_items(pred.def_id())
1025 .filter(|item| item.kind == ty::AssociatedKind::Type)
1026 .map(|item| item.def_id));
1028 ty::Predicate::Projection(pred) => {
1029 // A `Self` within the original bound will be substituted with a
1030 // `trait_object_dummy_self`, so check for that.
1031 let references_self =
1032 pred.skip_binder().ty.walk().any(|t| t == dummy_self);
1034 // If the projection output contains `Self`, force the user to
1035 // elaborate it explicitly to avoid a bunch of complexity.
1037 // The "classicaly useful" case is the following:
1039 // trait MyTrait: FnMut() -> <Self as MyTrait>::MyOutput {
1044 // Here, the user could theoretically write `dyn MyTrait<Output=X>`,
1045 // but actually supporting that would "expand" to an infinitely-long type
1046 // `fix $ τ → dyn MyTrait<MyOutput=X, Output=<τ as MyTrait>::MyOutput`.
1048 // Instead, we force the user to write `dyn MyTrait<MyOutput=X, Output=X>`,
1049 // which is uglier but works. See the discussion in #56288 for alternatives.
1050 if !references_self {
1051 // Include projections defined on supertraits,
1052 projection_bounds.push((pred, DUMMY_SP))
1059 for (projection_bound, _) in &projection_bounds {
1060 associated_types.remove(&projection_bound.projection_def_id());
1063 if !associated_types.is_empty() {
1064 let names = associated_types.iter().map(|item_def_id| {
1065 let assoc_item = tcx.associated_item(*item_def_id);
1066 let trait_def_id = assoc_item.container.id();
1068 "`{}` (from the trait `{}`)",
1070 tcx.def_path_str(trait_def_id),
1072 }).collect::<Vec<_>>().join(", ");
1073 let mut err = struct_span_err!(
1077 "the value of the associated type{} {} must be specified",
1078 if associated_types.len() == 1 { "" } else { "s" },
1081 let mut suggest = false;
1082 let mut potential_assoc_types_spans = vec![];
1083 if let Some(potential_assoc_types) = potential_assoc_types {
1084 if potential_assoc_types.len() == associated_types.len() {
1085 // Only suggest when the amount of missing associated types is equals to the
1086 // extra type arguments present, as that gives us a relatively high confidence
1087 // that the user forgot to give the associtated type's name. The canonical
1088 // example would be trying to use `Iterator<isize>` instead of
1089 // `Iterator<Item=isize>`.
1091 potential_assoc_types_spans = potential_assoc_types;
1094 let mut suggestions = vec![];
1095 for (i, item_def_id) in associated_types.iter().enumerate() {
1096 let assoc_item = tcx.associated_item(*item_def_id);
1099 format!("associated type `{}` must be specified", assoc_item.ident),
1101 if item_def_id.is_local() {
1103 tcx.def_span(*item_def_id),
1104 format!("`{}` defined here", assoc_item.ident),
1108 if let Ok(snippet) = tcx.sess.source_map().span_to_snippet(
1109 potential_assoc_types_spans[i],
1112 potential_assoc_types_spans[i],
1113 format!("{} = {}", assoc_item.ident, snippet),
1118 if !suggestions.is_empty() {
1119 let msg = format!("if you meant to specify the associated {}, write",
1120 if suggestions.len() == 1 { "type" } else { "types" });
1121 err.multipart_suggestion(
1124 Applicability::MaybeIncorrect,
1130 // Erase the `dummy_self` (`trait_object_dummy_self`) used above.
1131 let existential_principal = principal.map_bound(|trait_ref| {
1132 self.trait_ref_to_existential(trait_ref)
1134 let existential_projections = projection_bounds.iter().map(|(bound, _)| {
1135 bound.map_bound(|b| {
1136 let trait_ref = self.trait_ref_to_existential(b.projection_ty.trait_ref(tcx));
1137 ty::ExistentialProjection {
1139 item_def_id: b.projection_ty.item_def_id,
1140 substs: trait_ref.substs,
1145 // Dedup auto traits so that `dyn Trait + Send + Send` is the same as `dyn Trait + Send`.
1147 auto_traits.dedup();
1149 // Calling `skip_binder` is okay, because the predicates are re-bound.
1150 let principal = if tcx.trait_is_auto(existential_principal.def_id()) {
1151 ty::ExistentialPredicate::AutoTrait(existential_principal.def_id())
1153 ty::ExistentialPredicate::Trait(*existential_principal.skip_binder())
1156 iter::once(principal)
1157 .chain(auto_traits.into_iter().map(ty::ExistentialPredicate::AutoTrait))
1158 .chain(existential_projections
1159 .map(|x| ty::ExistentialPredicate::Projection(*x.skip_binder())))
1160 .collect::<SmallVec<[_; 8]>>();
1161 v.sort_by(|a, b| a.stable_cmp(tcx, b));
1163 let existential_predicates = ty::Binder::bind(tcx.mk_existential_predicates(v.into_iter()));
1165 // Use explicitly-specified region bound.
1166 let region_bound = if !lifetime.is_elided() {
1167 self.ast_region_to_region(lifetime, None)
1169 self.compute_object_lifetime_bound(span, existential_predicates).unwrap_or_else(|| {
1170 if tcx.named_region(lifetime.hir_id).is_some() {
1171 self.ast_region_to_region(lifetime, None)
1173 self.re_infer(span, None).unwrap_or_else(|| {
1174 span_err!(tcx.sess, span, E0228,
1175 "the lifetime bound for this object type cannot be deduced \
1176 from context; please supply an explicit bound");
1183 debug!("region_bound: {:?}", region_bound);
1185 let ty = tcx.mk_dynamic(existential_predicates, region_bound);
1186 debug!("trait_object_type: {:?}", ty);
1190 fn report_ambiguous_associated_type(&self,
1195 struct_span_err!(self.tcx().sess, span, E0223, "ambiguous associated type")
1198 "use fully-qualified syntax",
1199 format!("<{} as {}>::{}", type_str, trait_str, name),
1200 Applicability::HasPlaceholders
1204 // Search for a bound on a type parameter which includes the associated item
1205 // given by `assoc_name`. `ty_param_def_id` is the `DefId` for the type parameter
1206 // This function will fail if there are no suitable bounds or there is
1208 fn find_bound_for_assoc_item(&self,
1209 ty_param_def_id: DefId,
1210 assoc_name: ast::Ident,
1212 -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
1214 let tcx = self.tcx();
1216 let predicates = &self.get_type_parameter_bounds(span, ty_param_def_id).predicates;
1217 let bounds = predicates.iter().filter_map(|(p, _)| p.to_opt_poly_trait_ref());
1219 // Check that there is exactly one way to find an associated type with the
1221 let suitable_bounds = traits::transitive_bounds(tcx, bounds)
1222 .filter(|b| self.trait_defines_associated_type_named(b.def_id(), assoc_name));
1224 let param_hir_id = tcx.hir().as_local_hir_id(ty_param_def_id).unwrap();
1225 let param_name = tcx.hir().ty_param_name(param_hir_id);
1226 self.one_bound_for_assoc_type(suitable_bounds,
1227 ¶m_name.as_str(),
1232 // Checks that `bounds` contains exactly one element and reports appropriate
1233 // errors otherwise.
1234 fn one_bound_for_assoc_type<I>(&self,
1236 ty_param_name: &str,
1237 assoc_name: ast::Ident,
1239 -> Result<ty::PolyTraitRef<'tcx>, ErrorReported>
1240 where I: Iterator<Item=ty::PolyTraitRef<'tcx>>
1242 let bound = match bounds.next() {
1243 Some(bound) => bound,
1245 struct_span_err!(self.tcx().sess, span, E0220,
1246 "associated type `{}` not found for `{}`",
1249 .span_label(span, format!("associated type `{}` not found", assoc_name))
1251 return Err(ErrorReported);
1255 if let Some(bound2) = bounds.next() {
1256 let bounds = iter::once(bound).chain(iter::once(bound2)).chain(bounds);
1257 let mut err = struct_span_err!(
1258 self.tcx().sess, span, E0221,
1259 "ambiguous associated type `{}` in bounds of `{}`",
1262 err.span_label(span, format!("ambiguous associated type `{}`", assoc_name));
1264 for bound in bounds {
1265 let bound_span = self.tcx().associated_items(bound.def_id()).find(|item| {
1266 item.kind == ty::AssociatedKind::Type &&
1267 self.tcx().hygienic_eq(assoc_name, item.ident, bound.def_id())
1269 .and_then(|item| self.tcx().hir().span_if_local(item.def_id));
1271 if let Some(span) = bound_span {
1272 err.span_label(span, format!("ambiguous `{}` from `{}`",
1276 span_note!(&mut err, span,
1277 "associated type `{}` could derive from `{}`",
1288 // Create a type from a path to an associated type.
1289 // For a path `A::B::C::D`, `qself_ty` and `qself_def` are the type and def for `A::B::C`
1290 // and item_segment is the path segment for `D`. We return a type and a def for
1292 // Will fail except for `T::A` and `Self::A`; i.e., if `qself_ty`/`qself_def` are not a type
1293 // parameter or `Self`.
1294 pub fn associated_path_to_ty(
1296 hir_ref_id: hir::HirId,
1300 assoc_segment: &hir::PathSegment,
1301 permit_variants: bool,
1302 ) -> (Ty<'tcx>, Def) {
1303 let tcx = self.tcx();
1304 let assoc_ident = assoc_segment.ident;
1306 debug!("associated_path_to_ty: {:?}::{}", qself_ty, assoc_ident);
1308 self.prohibit_generics(slice::from_ref(assoc_segment));
1310 // Check if we have an enum variant.
1311 let mut variant_resolution = None;
1312 if let ty::Adt(adt_def, _) = qself_ty.sty {
1313 if adt_def.is_enum() {
1314 let variant_def = adt_def.variants.iter().find(|vd| {
1315 tcx.hygienic_eq(assoc_ident, vd.ident, adt_def.did)
1317 if let Some(variant_def) = variant_def {
1318 let def = Def::Variant(variant_def.def_id);
1319 if permit_variants {
1320 check_type_alias_enum_variants_enabled(tcx, span);
1321 tcx.check_stability(variant_def.def_id, Some(hir_ref_id), span);
1322 return (qself_ty, def);
1324 variant_resolution = Some(def);
1330 // Find the type of the associated item, and the trait where the associated
1331 // item is declared.
1332 let bound = match (&qself_ty.sty, qself_def) {
1333 (_, Def::SelfTy(Some(_), Some(impl_def_id))) => {
1334 // `Self` in an impl of a trait -- we have a concrete self type and a
1336 let trait_ref = match tcx.impl_trait_ref(impl_def_id) {
1337 Some(trait_ref) => trait_ref,
1339 // A cycle error occurred, most likely.
1340 return (tcx.types.err, Def::Err);
1344 let candidates = traits::supertraits(tcx, ty::Binder::bind(trait_ref))
1345 .filter(|r| self.trait_defines_associated_type_named(r.def_id(), assoc_ident));
1347 match self.one_bound_for_assoc_type(candidates, "Self", assoc_ident, span) {
1349 Err(ErrorReported) => return (tcx.types.err, Def::Err),
1352 (&ty::Param(_), Def::SelfTy(Some(param_did), None)) |
1353 (&ty::Param(_), Def::TyParam(param_did)) => {
1354 match self.find_bound_for_assoc_item(param_did, assoc_ident, span) {
1356 Err(ErrorReported) => return (tcx.types.err, Def::Err),
1360 if variant_resolution.is_some() {
1361 // Variant in type position
1362 let msg = format!("expected type, found variant `{}`", assoc_ident);
1363 tcx.sess.span_err(span, &msg);
1364 } else if qself_ty.is_enum() {
1365 // Report as incorrect enum variant rather than ambiguous type.
1366 let mut err = tcx.sess.struct_span_err(
1368 &format!("no variant `{}` on enum `{}`", &assoc_ident.as_str(), qself_ty),
1370 // Check if it was a typo.
1371 let adt_def = qself_ty.ty_adt_def().expect("enum is not an ADT");
1372 if let Some(suggested_name) = find_best_match_for_name(
1373 adt_def.variants.iter().map(|variant| &variant.ident.name),
1374 &assoc_ident.as_str(),
1377 err.span_suggestion(
1380 format!("{}::{}", qself_ty, suggested_name),
1381 Applicability::MaybeIncorrect,
1384 err.span_label(span, "unknown variant");
1387 } else if !qself_ty.references_error() {
1388 // Don't print `TyErr` to the user.
1389 self.report_ambiguous_associated_type(span,
1390 &qself_ty.to_string(),
1392 &assoc_ident.as_str());
1394 return (tcx.types.err, Def::Err);
1398 let trait_did = bound.def_id();
1399 let (assoc_ident, def_scope) = tcx.adjust_ident(assoc_ident, trait_did, hir_ref_id);
1400 let item = tcx.associated_items(trait_did).find(|i| {
1401 Namespace::from(i.kind) == Namespace::Type &&
1402 i.ident.modern() == assoc_ident
1403 }).expect("missing associated type");
1405 let ty = self.projected_ty_from_poly_trait_ref(span, item.def_id, bound);
1406 let ty = self.normalize_ty(span, ty);
1408 let def = Def::AssociatedTy(item.def_id);
1409 if !item.vis.is_accessible_from(def_scope, tcx) {
1410 let msg = format!("{} `{}` is private", def.kind_name(), assoc_ident);
1411 tcx.sess.span_err(span, &msg);
1413 tcx.check_stability(item.def_id, Some(hir_ref_id), span);
1415 if let Some(variant_def) = variant_resolution {
1416 let mut err = tcx.struct_span_lint_hir(
1417 AMBIGUOUS_ASSOCIATED_ITEMS,
1420 "ambiguous associated item",
1423 let mut could_refer_to = |def: Def, also| {
1424 let note_msg = format!("`{}` could{} refer to {} defined here",
1425 assoc_ident, also, def.kind_name());
1426 err.span_note(tcx.def_span(def.def_id()), ¬e_msg);
1428 could_refer_to(variant_def, "");
1429 could_refer_to(def, " also");
1431 err.span_suggestion(
1433 "use fully-qualified syntax",
1434 format!("<{} as {}>::{}", qself_ty, "Trait", assoc_ident),
1435 Applicability::HasPlaceholders,
1442 fn qpath_to_ty(&self,
1444 opt_self_ty: Option<Ty<'tcx>>,
1446 trait_segment: &hir::PathSegment,
1447 item_segment: &hir::PathSegment)
1450 let tcx = self.tcx();
1451 let trait_def_id = tcx.parent(item_def_id).unwrap();
1453 self.prohibit_generics(slice::from_ref(item_segment));
1455 let self_ty = if let Some(ty) = opt_self_ty {
1458 let path_str = tcx.def_path_str(trait_def_id);
1459 self.report_ambiguous_associated_type(span,
1462 &item_segment.ident.as_str());
1463 return tcx.types.err;
1466 debug!("qpath_to_ty: self_type={:?}", self_ty);
1468 let trait_ref = self.ast_path_to_mono_trait_ref(span,
1473 debug!("qpath_to_ty: trait_ref={:?}", trait_ref);
1475 self.normalize_ty(span, tcx.mk_projection(item_def_id, trait_ref.substs))
1478 pub fn prohibit_generics<'a, T: IntoIterator<Item = &'a hir::PathSegment>>(
1479 &self, segments: T) -> bool {
1480 let mut has_err = false;
1481 for segment in segments {
1482 segment.with_generic_args(|generic_args| {
1483 let (mut err_for_lt, mut err_for_ty, mut err_for_ct) = (false, false, false);
1484 for arg in &generic_args.args {
1485 let (span, kind) = match arg {
1486 hir::GenericArg::Lifetime(lt) => {
1487 if err_for_lt { continue }
1490 (lt.span, "lifetime")
1492 hir::GenericArg::Type(ty) => {
1493 if err_for_ty { continue }
1498 hir::GenericArg::Const(ct) => {
1499 if err_for_ct { continue }
1504 let mut err = struct_span_err!(
1508 "{} arguments are not allowed for this type",
1511 err.span_label(span, format!("{} argument not allowed", kind));
1513 if err_for_lt && err_for_ty && err_for_ct {
1517 for binding in &generic_args.bindings {
1519 Self::prohibit_assoc_ty_binding(self.tcx(), binding.span);
1527 pub fn prohibit_assoc_ty_binding(tcx: TyCtxt<'_, '_, '_>, span: Span) {
1528 let mut err = struct_span_err!(tcx.sess, span, E0229,
1529 "associated type bindings are not allowed here");
1530 err.span_label(span, "associated type not allowed here").emit();
1533 pub fn def_ids_for_path_segments(&self,
1534 segments: &[hir::PathSegment],
1535 self_ty: Option<Ty<'tcx>>,
1538 // We need to extract the type parameters supplied by the user in
1539 // the path `path`. Due to the current setup, this is a bit of a
1540 // tricky-process; the problem is that resolve only tells us the
1541 // end-point of the path resolution, and not the intermediate steps.
1542 // Luckily, we can (at least for now) deduce the intermediate steps
1543 // just from the end-point.
1545 // There are basically five cases to consider:
1547 // 1. Reference to a constructor of a struct:
1549 // struct Foo<T>(...)
1551 // In this case, the parameters are declared in the type space.
1553 // 2. Reference to a constructor of an enum variant:
1555 // enum E<T> { Foo(...) }
1557 // In this case, the parameters are defined in the type space,
1558 // but may be specified either on the type or the variant.
1560 // 3. Reference to a fn item or a free constant:
1564 // In this case, the path will again always have the form
1565 // `a::b::foo::<T>` where only the final segment should have
1566 // type parameters. However, in this case, those parameters are
1567 // declared on a value, and hence are in the `FnSpace`.
1569 // 4. Reference to a method or an associated constant:
1571 // impl<A> SomeStruct<A> {
1575 // Here we can have a path like
1576 // `a::b::SomeStruct::<A>::foo::<B>`, in which case parameters
1577 // may appear in two places. The penultimate segment,
1578 // `SomeStruct::<A>`, contains parameters in TypeSpace, and the
1579 // final segment, `foo::<B>` contains parameters in fn space.
1581 // 5. Reference to a local variable
1583 // Local variables can't have any type parameters.
1585 // The first step then is to categorize the segments appropriately.
1587 let tcx = self.tcx();
1589 assert!(!segments.is_empty());
1590 let last = segments.len() - 1;
1592 let mut path_segs = vec![];
1595 // Case 1. Reference to a struct constructor.
1596 Def::Ctor(def_id, CtorOf::Struct, ..) |
1597 Def::SelfCtor(.., def_id) => {
1598 // Everything but the final segment should have no
1599 // parameters at all.
1600 let generics = tcx.generics_of(def_id);
1601 // Variant and struct constructors use the
1602 // generics of their parent type definition.
1603 let generics_def_id = generics.parent.unwrap_or(def_id);
1604 path_segs.push(PathSeg(generics_def_id, last));
1607 // Case 2. Reference to a variant constructor.
1608 Def::Ctor(def_id, CtorOf::Variant, ..) | Def::Variant(def_id, ..) => {
1609 let adt_def = self_ty.map(|t| t.ty_adt_def().unwrap());
1610 let (generics_def_id, index) = if let Some(adt_def) = adt_def {
1611 debug_assert!(adt_def.is_enum());
1613 } else if last >= 1 && segments[last - 1].args.is_some() {
1614 // Everything but the penultimate segment should have no
1615 // parameters at all.
1616 let mut def_id = def_id;
1618 // `Def::Ctor` -> `Def::Variant`
1619 if let Def::Ctor(..) = def {
1620 def_id = tcx.parent(def_id).unwrap()
1623 // `Def::Variant` -> `Def::Item` (enum)
1624 let enum_def_id = tcx.parent(def_id).unwrap();
1625 (enum_def_id, last - 1)
1627 // FIXME: lint here recommending `Enum::<...>::Variant` form
1628 // instead of `Enum::Variant::<...>` form.
1630 // Everything but the final segment should have no
1631 // parameters at all.
1632 let generics = tcx.generics_of(def_id);
1633 // Variant and struct constructors use the
1634 // generics of their parent type definition.
1635 (generics.parent.unwrap_or(def_id), last)
1637 path_segs.push(PathSeg(generics_def_id, index));
1640 // Case 3. Reference to a top-level value.
1642 Def::Const(def_id) |
1643 Def::ConstParam(def_id) |
1644 Def::Static(def_id, _) => {
1645 path_segs.push(PathSeg(def_id, last));
1648 // Case 4. Reference to a method or associated const.
1649 Def::Method(def_id) |
1650 Def::AssociatedConst(def_id) => {
1651 if segments.len() >= 2 {
1652 let generics = tcx.generics_of(def_id);
1653 path_segs.push(PathSeg(generics.parent.unwrap(), last - 1));
1655 path_segs.push(PathSeg(def_id, last));
1658 // Case 5. Local variable, no generics.
1659 Def::Local(..) | Def::Upvar(..) => {}
1661 _ => bug!("unexpected definition: {:?}", def),
1664 debug!("path_segs = {:?}", path_segs);
1669 // Check a type `Path` and convert it to a `Ty`.
1670 pub fn def_to_ty(&self,
1671 opt_self_ty: Option<Ty<'tcx>>,
1673 permit_variants: bool)
1675 let tcx = self.tcx();
1677 debug!("def_to_ty(def={:?}, opt_self_ty={:?}, path_segments={:?})",
1678 path.def, opt_self_ty, path.segments);
1680 let span = path.span;
1682 Def::Existential(did) => {
1683 // Check for desugared impl trait.
1684 assert!(ty::is_impl_trait_defn(tcx, did).is_none());
1685 let item_segment = path.segments.split_last().unwrap();
1686 self.prohibit_generics(item_segment.1);
1687 let substs = self.ast_path_substs_for_ty(span, did, item_segment.0);
1690 tcx.mk_opaque(did, substs),
1693 Def::Enum(did) | Def::TyAlias(did) | Def::Struct(did) |
1694 Def::Union(did) | Def::ForeignTy(did) => {
1695 assert_eq!(opt_self_ty, None);
1696 self.prohibit_generics(path.segments.split_last().unwrap().1);
1697 self.ast_path_to_ty(span, did, path.segments.last().unwrap())
1699 Def::Variant(_) if permit_variants => {
1700 // Convert "variant type" as if it were a real type.
1701 // The resulting `Ty` is type of the variant's enum for now.
1702 assert_eq!(opt_self_ty, None);
1704 let path_segs = self.def_ids_for_path_segments(&path.segments, None, path.def);
1705 let generic_segs: FxHashSet<_> =
1706 path_segs.iter().map(|PathSeg(_, index)| index).collect();
1707 self.prohibit_generics(path.segments.iter().enumerate().filter_map(|(index, seg)| {
1708 if !generic_segs.contains(&index) {
1715 let PathSeg(def_id, index) = path_segs.last().unwrap();
1716 self.ast_path_to_ty(span, *def_id, &path.segments[*index])
1718 Def::TyParam(did) => {
1719 assert_eq!(opt_self_ty, None);
1720 self.prohibit_generics(&path.segments);
1722 let hir_id = tcx.hir().as_local_hir_id(did).unwrap();
1723 let item_id = tcx.hir().get_parent_node_by_hir_id(hir_id);
1724 let item_def_id = tcx.hir().local_def_id_from_hir_id(item_id);
1725 let generics = tcx.generics_of(item_def_id);
1726 let index = generics.param_def_id_to_index[
1727 &tcx.hir().local_def_id_from_hir_id(hir_id)];
1728 tcx.mk_ty_param(index, tcx.hir().name_by_hir_id(hir_id).as_interned_str())
1730 Def::SelfTy(_, Some(def_id)) => {
1731 // `Self` in impl (we know the concrete type).
1732 assert_eq!(opt_self_ty, None);
1733 self.prohibit_generics(&path.segments);
1734 // Try to evaluate any array length constants
1735 self.normalize_ty(span, tcx.at(span).type_of(def_id))
1737 Def::SelfTy(Some(_), None) => {
1739 assert_eq!(opt_self_ty, None);
1740 self.prohibit_generics(&path.segments);
1743 Def::AssociatedTy(def_id) => {
1744 debug_assert!(path.segments.len() >= 2);
1745 self.prohibit_generics(&path.segments[..path.segments.len() - 2]);
1746 self.qpath_to_ty(span,
1749 &path.segments[path.segments.len() - 2],
1750 path.segments.last().unwrap())
1752 Def::PrimTy(prim_ty) => {
1753 assert_eq!(opt_self_ty, None);
1754 self.prohibit_generics(&path.segments);
1756 hir::Bool => tcx.types.bool,
1757 hir::Char => tcx.types.char,
1758 hir::Int(it) => tcx.mk_mach_int(it),
1759 hir::Uint(uit) => tcx.mk_mach_uint(uit),
1760 hir::Float(ft) => tcx.mk_mach_float(ft),
1761 hir::Str => tcx.mk_str()
1765 self.set_tainted_by_errors();
1766 return self.tcx().types.err;
1768 _ => span_bug!(span, "unexpected definition: {:?}", path.def)
1772 /// Parses the programmer's textual representation of a type into our
1773 /// internal notion of a type.
1774 pub fn ast_ty_to_ty(&self, ast_ty: &hir::Ty) -> Ty<'tcx> {
1775 debug!("ast_ty_to_ty(id={:?}, ast_ty={:?} ty_ty={:?})",
1776 ast_ty.hir_id, ast_ty, ast_ty.node);
1778 let tcx = self.tcx();
1780 let result_ty = match ast_ty.node {
1781 hir::TyKind::Slice(ref ty) => {
1782 tcx.mk_slice(self.ast_ty_to_ty(&ty))
1784 hir::TyKind::Ptr(ref mt) => {
1785 tcx.mk_ptr(ty::TypeAndMut {
1786 ty: self.ast_ty_to_ty(&mt.ty),
1790 hir::TyKind::Rptr(ref region, ref mt) => {
1791 let r = self.ast_region_to_region(region, None);
1792 debug!("Ref r={:?}", r);
1793 let t = self.ast_ty_to_ty(&mt.ty);
1794 tcx.mk_ref(r, ty::TypeAndMut {ty: t, mutbl: mt.mutbl})
1796 hir::TyKind::Never => {
1799 hir::TyKind::Tup(ref fields) => {
1800 tcx.mk_tup(fields.iter().map(|t| self.ast_ty_to_ty(&t)))
1802 hir::TyKind::BareFn(ref bf) => {
1803 require_c_abi_if_c_variadic(tcx, &bf.decl, bf.abi, ast_ty.span);
1804 tcx.mk_fn_ptr(self.ty_of_fn(bf.unsafety, bf.abi, &bf.decl))
1806 hir::TyKind::TraitObject(ref bounds, ref lifetime) => {
1807 self.conv_object_ty_poly_trait_ref(ast_ty.span, bounds, lifetime)
1809 hir::TyKind::Path(hir::QPath::Resolved(ref maybe_qself, ref path)) => {
1810 debug!("ast_ty_to_ty: maybe_qself={:?} path={:?}", maybe_qself, path);
1811 let opt_self_ty = maybe_qself.as_ref().map(|qself| {
1812 self.ast_ty_to_ty(qself)
1814 self.def_to_ty(opt_self_ty, path, false)
1816 hir::TyKind::Def(item_id, ref lifetimes) => {
1817 let did = tcx.hir().local_def_id_from_hir_id(item_id.id);
1818 self.impl_trait_ty_to_ty(did, lifetimes)
1820 hir::TyKind::Path(hir::QPath::TypeRelative(ref qself, ref segment)) => {
1821 debug!("ast_ty_to_ty: qself={:?} segment={:?}", qself, segment);
1822 let ty = self.ast_ty_to_ty(qself);
1824 let def = if let hir::TyKind::Path(hir::QPath::Resolved(_, ref path)) = qself.node {
1829 self.associated_path_to_ty(ast_ty.hir_id, ast_ty.span, ty, def, segment, false).0
1831 hir::TyKind::Array(ref ty, ref length) => {
1832 let length = self.ast_const_to_const(length, tcx.types.usize);
1833 let array_ty = tcx.mk_ty(ty::Array(self.ast_ty_to_ty(&ty), length));
1834 self.normalize_ty(ast_ty.span, array_ty)
1836 hir::TyKind::Typeof(ref _e) => {
1837 struct_span_err!(tcx.sess, ast_ty.span, E0516,
1838 "`typeof` is a reserved keyword but unimplemented")
1839 .span_label(ast_ty.span, "reserved keyword")
1844 hir::TyKind::Infer => {
1845 // Infer also appears as the type of arguments or return
1846 // values in a ExprKind::Closure, or as
1847 // the type of local variables. Both of these cases are
1848 // handled specially and will not descend into this routine.
1849 self.ty_infer(ast_ty.span)
1851 hir::TyKind::Err => {
1854 hir::TyKind::CVarArgs(lt) => {
1855 let va_list_did = match tcx.lang_items().va_list() {
1857 None => span_bug!(ast_ty.span,
1858 "`va_list` lang item required for variadics"),
1860 let region = self.ast_region_to_region(<, None);
1861 tcx.type_of(va_list_did).subst(tcx, &[region.into()])
1865 self.record_ty(ast_ty.hir_id, result_ty, ast_ty.span);
1869 pub fn ast_const_to_const(
1871 ast_const: &hir::AnonConst,
1873 ) -> &'tcx ty::Const<'tcx> {
1874 debug!("ast_const_to_const(id={:?}, ast_const={:?})", ast_const.hir_id, ast_const);
1876 let tcx = self.tcx();
1877 let def_id = tcx.hir().local_def_id_from_hir_id(ast_const.hir_id);
1879 let mut const_ = ty::Const {
1880 val: ConstValue::Unevaluated(
1882 InternalSubsts::identity_for_item(tcx, def_id),
1887 let expr = &tcx.hir().body(ast_const.body).value;
1888 if let ExprKind::Path(ref qpath) = expr.node {
1889 if let hir::QPath::Resolved(_, ref path) = qpath {
1890 if let Def::ConstParam(def_id) = path.def {
1891 let node_id = tcx.hir().as_local_node_id(def_id).unwrap();
1892 let item_id = tcx.hir().get_parent_node(node_id);
1893 let item_def_id = tcx.hir().local_def_id(item_id);
1894 let generics = tcx.generics_of(item_def_id);
1895 let index = generics.param_def_id_to_index[&tcx.hir().local_def_id(node_id)];
1896 let name = tcx.hir().name(node_id).as_interned_str();
1897 const_.val = ConstValue::Param(ty::ParamConst::new(index, name));
1902 tcx.mk_const(const_)
1905 pub fn impl_trait_ty_to_ty(
1908 lifetimes: &[hir::GenericArg],
1910 debug!("impl_trait_ty_to_ty(def_id={:?}, lifetimes={:?})", def_id, lifetimes);
1911 let tcx = self.tcx();
1913 let generics = tcx.generics_of(def_id);
1915 debug!("impl_trait_ty_to_ty: generics={:?}", generics);
1916 let substs = InternalSubsts::for_item(tcx, def_id, |param, _| {
1917 if let Some(i) = (param.index as usize).checked_sub(generics.parent_count) {
1918 // Our own parameters are the resolved lifetimes.
1920 GenericParamDefKind::Lifetime => {
1921 if let hir::GenericArg::Lifetime(lifetime) = &lifetimes[i] {
1922 self.ast_region_to_region(lifetime, None).into()
1930 // Replace all parent lifetimes with 'static.
1932 GenericParamDefKind::Lifetime => {
1933 tcx.types.re_static.into()
1935 _ => tcx.mk_param_from_def(param)
1939 debug!("impl_trait_ty_to_ty: final substs = {:?}", substs);
1941 let ty = tcx.mk_opaque(def_id, substs);
1942 debug!("impl_trait_ty_to_ty: {}", ty);
1946 pub fn ty_of_arg(&self,
1948 expected_ty: Option<Ty<'tcx>>)
1952 hir::TyKind::Infer if expected_ty.is_some() => {
1953 self.record_ty(ty.hir_id, expected_ty.unwrap(), ty.span);
1954 expected_ty.unwrap()
1956 _ => self.ast_ty_to_ty(ty),
1960 pub fn ty_of_fn(&self,
1961 unsafety: hir::Unsafety,
1964 -> ty::PolyFnSig<'tcx> {
1967 let tcx = self.tcx();
1969 decl.inputs.iter().map(|a| self.ty_of_arg(a, None));
1971 let output_ty = match decl.output {
1972 hir::Return(ref output) => self.ast_ty_to_ty(output),
1973 hir::DefaultReturn(..) => tcx.mk_unit(),
1976 debug!("ty_of_fn: output_ty={:?}", output_ty);
1978 let bare_fn_ty = ty::Binder::bind(tcx.mk_fn_sig(
1986 // Find any late-bound regions declared in return type that do
1987 // not appear in the arguments. These are not well-formed.
1990 // for<'a> fn() -> &'a str <-- 'a is bad
1991 // for<'a> fn(&'a String) -> &'a str <-- 'a is ok
1992 let inputs = bare_fn_ty.inputs();
1993 let late_bound_in_args = tcx.collect_constrained_late_bound_regions(
1994 &inputs.map_bound(|i| i.to_owned()));
1995 let output = bare_fn_ty.output();
1996 let late_bound_in_ret = tcx.collect_referenced_late_bound_regions(&output);
1997 for br in late_bound_in_ret.difference(&late_bound_in_args) {
1998 let lifetime_name = match *br {
1999 ty::BrNamed(_, name) => format!("lifetime `{}`,", name),
2000 ty::BrAnon(_) | ty::BrFresh(_) | ty::BrEnv => "an anonymous lifetime".to_string(),
2002 let mut err = struct_span_err!(tcx.sess,
2005 "return type references {} \
2006 which is not constrained by the fn input types",
2008 if let ty::BrAnon(_) = *br {
2009 // The only way for an anonymous lifetime to wind up
2010 // in the return type but **also** be unconstrained is
2011 // if it only appears in "associated types" in the
2012 // input. See #47511 for an example. In this case,
2013 // though we can easily give a hint that ought to be
2015 err.note("lifetimes appearing in an associated type \
2016 are not considered constrained");
2024 /// Given the bounds on an object, determines what single region bound (if any) we can
2025 /// use to summarize this type. The basic idea is that we will use the bound the user
2026 /// provided, if they provided one, and otherwise search the supertypes of trait bounds
2027 /// for region bounds. It may be that we can derive no bound at all, in which case
2028 /// we return `None`.
2029 fn compute_object_lifetime_bound(&self,
2031 existential_predicates: ty::Binder<&'tcx ty::List<ty::ExistentialPredicate<'tcx>>>)
2032 -> Option<ty::Region<'tcx>> // if None, use the default
2034 let tcx = self.tcx();
2036 debug!("compute_opt_region_bound(existential_predicates={:?})",
2037 existential_predicates);
2039 // No explicit region bound specified. Therefore, examine trait
2040 // bounds and see if we can derive region bounds from those.
2041 let derived_region_bounds =
2042 object_region_bounds(tcx, existential_predicates);
2044 // If there are no derived region bounds, then report back that we
2045 // can find no region bound. The caller will use the default.
2046 if derived_region_bounds.is_empty() {
2050 // If any of the derived region bounds are 'static, that is always
2052 if derived_region_bounds.iter().any(|&r| ty::ReStatic == *r) {
2053 return Some(tcx.types.re_static);
2056 // Determine whether there is exactly one unique region in the set
2057 // of derived region bounds. If so, use that. Otherwise, report an
2059 let r = derived_region_bounds[0];
2060 if derived_region_bounds[1..].iter().any(|r1| r != *r1) {
2061 span_err!(tcx.sess, span, E0227,
2062 "ambiguous lifetime bound, explicit lifetime bound required");
2068 /// Divides a list of general trait bounds into two groups: auto traits (e.g., Sync and Send) and
2069 /// the remaining general trait bounds.
2070 fn split_auto_traits<'a, 'b, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
2071 trait_bounds: &'b [hir::PolyTraitRef])
2072 -> (Vec<DefId>, Vec<&'b hir::PolyTraitRef>)
2074 let (auto_traits, trait_bounds): (Vec<_>, _) = trait_bounds.iter().partition(|bound| {
2075 // Checks whether `trait_did` is an auto trait and adds it to `auto_traits` if so.
2076 match bound.trait_ref.path.def {
2077 Def::Trait(trait_did) if tcx.trait_is_auto(trait_did) => {
2084 let auto_traits = auto_traits.into_iter().map(|tr| {
2085 if let Def::Trait(trait_did) = tr.trait_ref.path.def {
2090 }).collect::<Vec<_>>();
2092 (auto_traits, trait_bounds)
2095 // A helper struct for conveniently grouping a set of bounds which we pass to
2096 // and return from functions in multiple places.
2097 #[derive(PartialEq, Eq, Clone, Debug)]
2098 pub struct Bounds<'tcx> {
2099 pub region_bounds: Vec<(ty::Region<'tcx>, Span)>,
2100 pub implicitly_sized: Option<Span>,
2101 pub trait_bounds: Vec<(ty::PolyTraitRef<'tcx>, Span)>,
2102 pub projection_bounds: Vec<(ty::PolyProjectionPredicate<'tcx>, Span)>,
2105 impl<'a, 'gcx, 'tcx> Bounds<'tcx> {
2106 pub fn predicates(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>, param_ty: Ty<'tcx>)
2107 -> Vec<(ty::Predicate<'tcx>, Span)>
2109 // If it could be sized, and is, add the sized predicate.
2110 let sized_predicate = self.implicitly_sized.and_then(|span| {
2111 tcx.lang_items().sized_trait().map(|sized| {
2112 let trait_ref = ty::TraitRef {
2114 substs: tcx.mk_substs_trait(param_ty, &[])
2116 (trait_ref.to_predicate(), span)
2120 sized_predicate.into_iter().chain(
2121 self.region_bounds.iter().map(|&(region_bound, span)| {
2122 // Account for the binder being introduced below; no need to shift `param_ty`
2123 // because, at present at least, it can only refer to early-bound regions.
2124 let region_bound = ty::fold::shift_region(tcx, region_bound, 1);
2125 let outlives = ty::OutlivesPredicate(param_ty, region_bound);
2126 (ty::Binder::dummy(outlives).to_predicate(), span)
2128 self.trait_bounds.iter().map(|&(bound_trait_ref, span)| {
2129 (bound_trait_ref.to_predicate(), span)
2132 self.projection_bounds.iter().map(|&(projection, span)| {
2133 (projection.to_predicate(), span)