1 use crate::astconv::AstConv;
2 use crate::bounds::Bounds;
3 use crate::collect::ItemCtxt;
4 use crate::constrained_generic_params as cgp;
5 use hir::{HirId, Node};
6 use rustc_data_structures::fx::FxIndexSet;
8 use rustc_hir::def::DefKind;
9 use rustc_hir::def_id::{DefId, LocalDefId};
10 use rustc_hir::intravisit::{self, Visitor};
11 use rustc_middle::ty::subst::InternalSubsts;
12 use rustc_middle::ty::ToPredicate;
13 use rustc_middle::ty::{self, Ty, TyCtxt};
14 use rustc_span::symbol::{sym, Ident};
15 use rustc_span::{Span, DUMMY_SP};
18 struct OnlySelfBounds(bool);
20 /// Returns a list of all type predicates (explicit and implicit) for the definition with
21 /// ID `def_id`. This includes all predicates returned by `predicates_defined_on`, plus
22 /// `Self: Trait` predicates for traits.
23 pub(super) fn predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericPredicates<'_> {
24 let mut result = tcx.predicates_defined_on(def_id);
26 if tcx.is_trait(def_id) {
27 // For traits, add `Self: Trait` predicate. This is
28 // not part of the predicates that a user writes, but it
29 // is something that one must prove in order to invoke a
30 // method or project an associated type.
32 // In the chalk setup, this predicate is not part of the
33 // "predicates" for a trait item. But it is useful in
34 // rustc because if you directly (e.g.) invoke a trait
35 // method like `Trait::method(...)`, you must naturally
36 // prove that the trait applies to the types that were
37 // used, and adding the predicate into this list ensures
40 // We use a DUMMY_SP here as a way to signal trait bounds that come
41 // from the trait itself that *shouldn't* be shown as the source of
42 // an obligation and instead be skipped. Otherwise we'd use
43 // `tcx.def_span(def_id);`
45 let constness = if tcx.has_attr(def_id, sym::const_trait) {
46 ty::BoundConstness::ConstIfConst
48 ty::BoundConstness::NotConst
51 let span = rustc_span::DUMMY_SP;
53 tcx.arena.alloc_from_iter(result.predicates.iter().copied().chain(std::iter::once((
54 ty::TraitRef::identity(tcx, def_id).with_constness(constness).to_predicate(tcx),
58 debug!("predicates_of(def_id={:?}) = {:?}", def_id, result);
62 /// Returns a list of user-specified type predicates for the definition with ID `def_id`.
63 /// N.B., this does not include any implied/inferred constraints.
64 #[instrument(level = "trace", skip(tcx), ret)]
65 fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericPredicates<'_> {
68 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
69 let node = tcx.hir().get(hir_id);
71 let mut is_trait = None;
72 let mut is_default_impl_trait = None;
74 let icx = ItemCtxt::new(tcx, def_id);
76 const NO_GENERICS: &hir::Generics<'_> = hir::Generics::empty();
78 // We use an `IndexSet` to preserve order of insertion.
79 // Preserving the order of insertion is important here so as not to break UI tests.
80 let mut predicates: FxIndexSet<(ty::Predicate<'_>, Span)> = FxIndexSet::default();
82 let ast_generics = match node {
83 Node::TraitItem(item) => item.generics,
85 Node::ImplItem(item) => item.generics,
87 Node::Item(item) => match item.kind {
88 ItemKind::Impl(ref impl_) => {
89 if impl_.defaultness.is_default() {
90 is_default_impl_trait = tcx.impl_trait_ref(def_id).map(ty::Binder::dummy);
94 ItemKind::Fn(.., ref generics, _)
95 | ItemKind::TyAlias(_, ref generics)
96 | ItemKind::Enum(_, ref generics)
97 | ItemKind::Struct(_, ref generics)
98 | ItemKind::Union(_, ref generics) => *generics,
100 ItemKind::Trait(_, _, ref generics, ..) | ItemKind::TraitAlias(ref generics, _) => {
101 is_trait = Some(ty::TraitRef::identity(tcx, def_id));
104 ItemKind::OpaqueTy(OpaqueTy { ref generics, .. }) => generics,
108 Node::ForeignItem(item) => match item.kind {
109 ForeignItemKind::Static(..) => NO_GENERICS,
110 ForeignItemKind::Fn(_, _, ref generics) => *generics,
111 ForeignItemKind::Type => NO_GENERICS,
117 let generics = tcx.generics_of(def_id);
118 let parent_count = generics.parent_count as u32;
119 let has_own_self = generics.has_self && parent_count == 0;
121 // Below we'll consider the bounds on the type parameters (including `Self`)
122 // and the explicit where-clauses, but to get the full set of predicates
123 // on a trait we need to add in the supertrait bounds and bounds found on
125 if let Some(_trait_ref) = is_trait {
126 predicates.extend(tcx.super_predicates_of(def_id).predicates.iter().cloned());
129 // In default impls, we can assume that the self type implements
132 // default impl Foo for Bar { .. }
134 // we add a default where clause `Foo: Bar`. We do a similar thing for traits
135 // (see below). Recall that a default impl is not itself an impl, but rather a
136 // set of defaults that can be incorporated into another impl.
137 if let Some(trait_ref) = is_default_impl_trait {
138 predicates.insert((trait_ref.without_const().to_predicate(tcx), tcx.def_span(def_id)));
141 // Collect the region predicates that were declared inline as
142 // well. In the case of parameters declared on a fn or method, we
143 // have to be careful to only iterate over early-bound regions.
144 let mut index = parent_count
145 + has_own_self as u32
146 + super::early_bound_lifetimes_from_generics(tcx, ast_generics).count() as u32;
149 trace!(?ast_generics);
152 // Collect the predicates that were written inline by the user on each
153 // type parameter (e.g., `<T: Foo>`).
154 for param in ast_generics.params {
156 // We already dealt with early bound lifetimes above.
157 GenericParamKind::Lifetime { .. } => (),
158 GenericParamKind::Type { .. } => {
159 let name = param.name.ident().name;
160 let param_ty = ty::ParamTy::new(index, name).to_ty(tcx);
163 let mut bounds = Bounds::default();
164 // Params are implicitly sized unless a `?Sized` bound is found
165 <dyn AstConv<'_>>::add_implicitly_sized(
170 Some((param.def_id, ast_generics.predicates)),
174 predicates.extend(bounds.predicates());
177 GenericParamKind::Const { .. } => {
178 // Bounds on const parameters are currently not possible.
185 // Add in the bounds that appear in the where-clause.
186 for predicate in ast_generics.predicates {
188 hir::WherePredicate::BoundPredicate(bound_pred) => {
189 let ty = icx.to_ty(bound_pred.bounded_ty);
190 let bound_vars = icx.tcx.late_bound_vars(bound_pred.hir_id);
192 // Keep the type around in a dummy predicate, in case of no bounds.
193 // That way, `where Ty:` is not a complete noop (see #53696) and `Ty`
194 // is still checked for WF.
195 if bound_pred.bounds.is_empty() {
196 if let ty::Param(_) = ty.kind() {
197 // This is a `where T:`, which can be in the HIR from the
198 // transformation that moves `?Sized` to `T`'s declaration.
199 // We can skip the predicate because type parameters are
200 // trivially WF, but also we *should*, to avoid exposing
201 // users who never wrote `where Type:,` themselves, to
202 // compiler/tooling bugs from not handling WF predicates.
204 let span = bound_pred.bounded_ty.span;
205 let predicate = ty::Binder::bind_with_vars(
206 ty::PredicateKind::WellFormed(ty.into()),
209 predicates.insert((predicate.to_predicate(tcx), span));
213 let mut bounds = Bounds::default();
214 <dyn AstConv<'_>>::add_bounds(
217 bound_pred.bounds.iter(),
221 predicates.extend(bounds.predicates());
224 hir::WherePredicate::RegionPredicate(region_pred) => {
225 let r1 = <dyn AstConv<'_>>::ast_region_to_region(&icx, ®ion_pred.lifetime, None);
226 predicates.extend(region_pred.bounds.iter().map(|bound| {
227 let (r2, span) = match bound {
228 hir::GenericBound::Outlives(lt) => {
229 (<dyn AstConv<'_>>::ast_region_to_region(&icx, lt, None), lt.ident.span)
233 let pred = ty::Binder::dummy(ty::PredicateKind::Clause(
234 ty::Clause::RegionOutlives(ty::OutlivesPredicate(r1, r2)),
236 .to_predicate(icx.tcx);
242 hir::WherePredicate::EqPredicate(..) => {
248 if tcx.features().generic_const_exprs {
249 predicates.extend(const_evaluatable_predicates_of(tcx, def_id.expect_local()));
252 let mut predicates: Vec<_> = predicates.into_iter().collect();
254 // Subtle: before we store the predicates into the tcx, we
255 // sort them so that predicates like `T: Foo<Item=U>` come
256 // before uses of `U`. This avoids false ambiguity errors
257 // in trait checking. See `setup_constraining_predicates`
259 if let Node::Item(&Item { kind: ItemKind::Impl { .. }, .. }) = node {
260 let self_ty = tcx.type_of(def_id);
261 let trait_ref = tcx.impl_trait_ref(def_id);
262 cgp::setup_constraining_predicates(
266 &mut cgp::parameters_for_impl(self_ty, trait_ref),
270 // Opaque types duplicate some of their generic parameters.
271 // We create bi-directional Outlives predicates between the original
272 // and the duplicated parameter, to ensure that they do not get out of sync.
273 if let Node::Item(&Item { kind: ItemKind::OpaqueTy(..), .. }) = node {
274 let opaque_ty_id = tcx.hir().parent_id(hir_id);
275 let opaque_ty_node = tcx.hir().get(opaque_ty_id);
276 let Node::Ty(&Ty { kind: TyKind::OpaqueDef(_, lifetimes, _), .. }) = opaque_ty_node else {
277 bug!("unexpected {opaque_ty_node:?}")
280 for (arg, duplicate) in std::iter::zip(lifetimes, ast_generics.params) {
281 let hir::GenericArg::Lifetime(arg) = arg else { bug!() };
282 let orig_region = <dyn AstConv<'_>>::ast_region_to_region(&icx, &arg, None);
283 if !matches!(orig_region.kind(), ty::ReEarlyBound(..)) {
284 // Only early-bound regions can point to the original generic parameter.
288 let hir::GenericParamKind::Lifetime { .. } = duplicate.kind else { continue };
289 let dup_def = tcx.hir().local_def_id(duplicate.hir_id).to_def_id();
291 let Some(dup_index) = generics.param_def_id_to_index(tcx, dup_def) else { bug!() };
293 let dup_region = tcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion {
296 name: duplicate.name.ident().name,
299 ty::Binder::dummy(ty::PredicateKind::Clause(ty::Clause::RegionOutlives(
300 ty::OutlivesPredicate(orig_region, dup_region),
302 .to_predicate(icx.tcx),
306 ty::Binder::dummy(ty::PredicateKind::Clause(ty::Clause::RegionOutlives(
307 ty::OutlivesPredicate(dup_region, orig_region),
309 .to_predicate(icx.tcx),
316 ty::GenericPredicates {
317 parent: generics.parent,
318 predicates: tcx.arena.alloc_from_iter(predicates),
322 fn const_evaluatable_predicates_of(
325 ) -> FxIndexSet<(ty::Predicate<'_>, Span)> {
326 struct ConstCollector<'tcx> {
328 preds: FxIndexSet<(ty::Predicate<'tcx>, Span)>,
331 impl<'tcx> intravisit::Visitor<'tcx> for ConstCollector<'tcx> {
332 fn visit_anon_const(&mut self, c: &'tcx hir::AnonConst) {
333 let ct = ty::Const::from_anon_const(self.tcx, c.def_id);
334 if let ty::ConstKind::Unevaluated(_) = ct.kind() {
335 let span = self.tcx.def_span(c.def_id);
337 ty::Binder::dummy(ty::PredicateKind::ConstEvaluatable(ct))
338 .to_predicate(self.tcx),
344 fn visit_const_param_default(&mut self, _param: HirId, _ct: &'tcx hir::AnonConst) {
345 // Do not look into const param defaults,
346 // these get checked when they are actually instantiated.
348 // We do not want the following to error:
350 // struct Foo<const N: usize, const M: usize = { N + 1 }>;
351 // struct Bar<const N: usize>(Foo<N, 3>);
355 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
356 let node = tcx.hir().get(hir_id);
358 let mut collector = ConstCollector { tcx, preds: FxIndexSet::default() };
359 if let hir::Node::Item(item) = node && let hir::ItemKind::Impl(ref impl_) = item.kind {
360 if let Some(of_trait) = &impl_.of_trait {
361 debug!("const_evaluatable_predicates_of({:?}): visit impl trait_ref", def_id);
362 collector.visit_trait_ref(of_trait);
365 debug!("const_evaluatable_predicates_of({:?}): visit_self_ty", def_id);
366 collector.visit_ty(impl_.self_ty);
369 if let Some(generics) = node.generics() {
370 debug!("const_evaluatable_predicates_of({:?}): visit_generics", def_id);
371 collector.visit_generics(generics);
374 if let Some(fn_sig) = tcx.hir().fn_sig_by_hir_id(hir_id) {
375 debug!("const_evaluatable_predicates_of({:?}): visit_fn_decl", def_id);
376 collector.visit_fn_decl(fn_sig.decl);
378 debug!("const_evaluatable_predicates_of({:?}) = {:?}", def_id, collector.preds);
383 pub(super) fn trait_explicit_predicates_and_bounds(
386 ) -> ty::GenericPredicates<'_> {
387 assert_eq!(tcx.def_kind(def_id), DefKind::Trait);
388 gather_explicit_predicates_of(tcx, def_id.to_def_id())
391 pub(super) fn explicit_predicates_of<'tcx>(
394 ) -> ty::GenericPredicates<'tcx> {
395 let def_kind = tcx.def_kind(def_id);
396 if let DefKind::Trait = def_kind {
397 // Remove bounds on associated types from the predicates, they will be
398 // returned by `explicit_item_bounds`.
399 let predicates_and_bounds = tcx.trait_explicit_predicates_and_bounds(def_id.expect_local());
400 let trait_identity_substs = InternalSubsts::identity_for_item(tcx, def_id);
402 let is_assoc_item_ty = |ty: Ty<'tcx>| {
403 // For a predicate from a where clause to become a bound on an
405 // * It must use the identity substs of the item.
406 // * We're in the scope of the trait, so we can't name any
407 // parameters of the GAT. That means that all we need to
408 // check are that the substs of the projection are the
409 // identity substs of the trait.
410 // * It must be an associated type for this trait (*not* a
412 if let ty::Alias(ty::Projection, projection) = ty.kind() {
413 projection.substs == trait_identity_substs
414 && tcx.associated_item(projection.def_id).container_id(tcx) == def_id
420 let predicates: Vec<_> = predicates_and_bounds
424 .filter(|(pred, _)| match pred.kind().skip_binder() {
425 ty::PredicateKind::Clause(ty::Clause::Trait(tr)) => !is_assoc_item_ty(tr.self_ty()),
426 ty::PredicateKind::Clause(ty::Clause::Projection(proj)) => {
427 !is_assoc_item_ty(proj.projection_ty.self_ty())
429 ty::PredicateKind::Clause(ty::Clause::TypeOutlives(outlives)) => {
430 !is_assoc_item_ty(outlives.0)
435 if predicates.len() == predicates_and_bounds.predicates.len() {
436 predicates_and_bounds
438 ty::GenericPredicates {
439 parent: predicates_and_bounds.parent,
440 predicates: tcx.arena.alloc_slice(&predicates),
444 if matches!(def_kind, DefKind::AnonConst) && tcx.lazy_normalization() {
445 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
446 let parent_def_id = tcx.hir().get_parent_item(hir_id);
448 if tcx.hir().opt_const_param_default_param_def_id(hir_id).is_some() {
449 // In `generics_of` we set the generics' parent to be our parent's parent which means that
450 // we lose out on the predicates of our actual parent if we dont return those predicates here.
451 // (See comment in `generics_of` for more information on why the parent shenanigans is necessary)
453 // struct Foo<T, const N: usize = { <T as Trait>::ASSOC }>(T) where T: Trait;
454 // ^^^ ^^^^^^^^^^^^^^^^^^^^^^^ the def id we are calling
455 // ^^^ explicit_predicates_of on
456 // parent item we dont have set as the
457 // parent of generics returned by `generics_of`
459 // In the above code we want the anon const to have predicates in its param env for `T: Trait`
460 // and we would be calling `explicit_predicates_of(Foo)` here
461 return tcx.explicit_predicates_of(parent_def_id);
464 let parent_def_kind = tcx.def_kind(parent_def_id);
465 if matches!(parent_def_kind, DefKind::OpaqueTy) {
466 // In `instantiate_identity` we inherit the predicates of our parent.
467 // However, opaque types do not have a parent (see `gather_explicit_predicates_of`), which means
468 // that we lose out on the predicates of our actual parent if we dont return those predicates here.
471 // fn foo<T: Trait>() -> impl Iterator<Output = Another<{ <T as Trait>::ASSOC }> > { todo!() }
472 // ^^^^^^^^^^^^^^^^^^^ the def id we are calling
473 // explicit_predicates_of on
475 // In the above code we want the anon const to have predicates in its param env for `T: Trait`.
476 // However, the anon const cannot inherit predicates from its parent since it's opaque.
478 // To fix this, we call `explicit_predicates_of` directly on `foo`, the parent's parent.
480 // In the above example this is `foo::{opaque#0}` or `impl Iterator`
481 let parent_hir_id = tcx.hir().local_def_id_to_hir_id(parent_def_id.def_id);
483 // In the above example this is the function `foo`
484 let item_def_id = tcx.hir().get_parent_item(parent_hir_id);
486 // In the above code example we would be calling `explicit_predicates_of(foo)` here
487 return tcx.explicit_predicates_of(item_def_id);
490 gather_explicit_predicates_of(tcx, def_id)
494 /// Ensures that the super-predicates of the trait with a `DefId`
495 /// of `trait_def_id` are converted and stored. This also ensures that
496 /// the transitive super-predicates are converted.
497 pub(super) fn super_predicates_of(
500 ) -> ty::GenericPredicates<'_> {
501 tcx.super_predicates_that_define_assoc_type((trait_def_id, None))
504 /// Ensures that the super-predicates of the trait with a `DefId`
505 /// of `trait_def_id` are converted and stored. This also ensures that
506 /// the transitive super-predicates are converted.
507 pub(super) fn super_predicates_that_define_assoc_type(
509 (trait_def_id, assoc_name): (DefId, Option<Ident>),
510 ) -> ty::GenericPredicates<'_> {
511 if trait_def_id.is_local() {
512 debug!("local trait");
513 let trait_hir_id = tcx.hir().local_def_id_to_hir_id(trait_def_id.expect_local());
515 let Node::Item(item) = tcx.hir().get(trait_hir_id) else {
516 bug!("trait_node_id {} is not an item", trait_hir_id);
519 let (generics, bounds) = match item.kind {
520 hir::ItemKind::Trait(.., ref generics, ref supertraits, _) => (generics, supertraits),
521 hir::ItemKind::TraitAlias(ref generics, ref supertraits) => (generics, supertraits),
522 _ => span_bug!(item.span, "super_predicates invoked on non-trait"),
525 let icx = ItemCtxt::new(tcx, trait_def_id);
527 // Convert the bounds that follow the colon, e.g., `Bar + Zed` in `trait Foo: Bar + Zed`.
528 let self_param_ty = tcx.types.self_param;
529 let superbounds1 = if let Some(assoc_name) = assoc_name {
530 <dyn AstConv<'_>>::compute_bounds_that_match_assoc_type(
537 <dyn AstConv<'_>>::compute_bounds(&icx, self_param_ty, bounds)
540 let superbounds1 = superbounds1.predicates();
542 // Convert any explicit superbounds in the where-clause,
543 // e.g., `trait Foo where Self: Bar`.
544 // In the case of trait aliases, however, we include all bounds in the where-clause,
545 // so e.g., `trait Foo = where u32: PartialEq<Self>` would include `u32: PartialEq<Self>`
546 // as one of its "superpredicates".
547 let is_trait_alias = tcx.is_trait_alias(trait_def_id);
548 let superbounds2 = icx.type_parameter_bounds_in_generics(
550 item.owner_id.def_id,
552 OnlySelfBounds(!is_trait_alias),
556 // Combine the two lists to form the complete set of superbounds:
557 let superbounds = &*tcx.arena.alloc_from_iter(superbounds1.into_iter().chain(superbounds2));
558 debug!(?superbounds);
560 // Now require that immediate supertraits are converted,
561 // which will, in turn, reach indirect supertraits.
562 if assoc_name.is_none() {
563 // Now require that immediate supertraits are converted,
564 // which will, in turn, reach indirect supertraits.
565 for &(pred, span) in superbounds {
566 debug!("superbound: {:?}", pred);
567 if let ty::PredicateKind::Clause(ty::Clause::Trait(bound)) =
568 pred.kind().skip_binder()
570 tcx.at(span).super_predicates_of(bound.def_id());
575 ty::GenericPredicates { parent: None, predicates: superbounds }
577 // if `assoc_name` is None, then the query should've been redirected to an
579 assert!(assoc_name.is_some());
580 tcx.super_predicates_of(trait_def_id)
584 /// Returns the predicates defined on `item_def_id` of the form
585 /// `X: Foo` where `X` is the type parameter `def_id`.
586 #[instrument(level = "trace", skip(tcx))]
587 pub(super) fn type_param_predicates(
589 (item_def_id, def_id, assoc_name): (DefId, LocalDefId, Ident),
590 ) -> ty::GenericPredicates<'_> {
593 // In the AST, bounds can derive from two places. Either
594 // written inline like `<T: Foo>` or in a where-clause like
597 let param_id = tcx.hir().local_def_id_to_hir_id(def_id);
598 let param_owner = tcx.hir().ty_param_owner(def_id);
599 let generics = tcx.generics_of(param_owner);
600 let index = generics.param_def_id_to_index[&def_id.to_def_id()];
601 let ty = tcx.mk_ty_param(index, tcx.hir().ty_param_name(def_id));
603 // Don't look for bounds where the type parameter isn't in scope.
604 let parent = if item_def_id == param_owner.to_def_id() {
607 tcx.generics_of(item_def_id).parent
610 let mut result = parent
612 let icx = ItemCtxt::new(tcx, parent);
613 icx.get_type_parameter_bounds(DUMMY_SP, def_id.to_def_id(), assoc_name)
615 .unwrap_or_default();
616 let mut extend = None;
618 let item_hir_id = tcx.hir().local_def_id_to_hir_id(item_def_id.expect_local());
619 let ast_generics = match tcx.hir().get(item_hir_id) {
620 Node::TraitItem(item) => &item.generics,
622 Node::ImplItem(item) => &item.generics,
624 Node::Item(item) => {
626 ItemKind::Fn(.., ref generics, _)
627 | ItemKind::Impl(hir::Impl { ref generics, .. })
628 | ItemKind::TyAlias(_, ref generics)
629 | ItemKind::OpaqueTy(OpaqueTy {
631 origin: hir::OpaqueTyOrigin::TyAlias,
634 | ItemKind::Enum(_, ref generics)
635 | ItemKind::Struct(_, ref generics)
636 | ItemKind::Union(_, ref generics) => generics,
637 ItemKind::Trait(_, _, ref generics, ..) => {
638 // Implied `Self: Trait` and supertrait bounds.
639 if param_id == item_hir_id {
640 let identity_trait_ref = ty::TraitRef::identity(tcx, item_def_id);
642 Some((identity_trait_ref.without_const().to_predicate(tcx), item.span));
650 Node::ForeignItem(item) => match item.kind {
651 ForeignItemKind::Fn(_, _, ref generics) => generics,
658 let icx = ItemCtxt::new(tcx, item_def_id);
659 let extra_predicates = extend.into_iter().chain(
660 icx.type_parameter_bounds_in_generics(
664 OnlySelfBounds(true),
668 .filter(|(predicate, _)| match predicate.kind().skip_binder() {
669 ty::PredicateKind::Clause(ty::Clause::Trait(data)) => data.self_ty().is_param(index),
674 tcx.arena.alloc_from_iter(result.predicates.iter().copied().chain(extra_predicates));
678 impl<'tcx> ItemCtxt<'tcx> {
679 /// Finds bounds from `hir::Generics`. This requires scanning through the
680 /// AST. We do this to avoid having to convert *all* the bounds, which
681 /// would create artificial cycles. Instead, we can only convert the
682 /// bounds for a type parameter `X` if `X::Foo` is used.
683 #[instrument(level = "trace", skip(self, ast_generics))]
684 fn type_parameter_bounds_in_generics(
686 ast_generics: &'tcx hir::Generics<'tcx>,
687 param_def_id: LocalDefId,
689 only_self_bounds: OnlySelfBounds,
690 assoc_name: Option<Ident>,
691 ) -> Vec<(ty::Predicate<'tcx>, Span)> {
695 .filter_map(|wp| match *wp {
696 hir::WherePredicate::BoundPredicate(ref bp) => Some(bp),
700 let bt = if bp.is_param_bound(param_def_id.to_def_id()) {
702 } else if !only_self_bounds.0 {
703 Some(self.to_ty(bp.bounded_ty))
707 let bvars = self.tcx.late_bound_vars(bp.hir_id);
709 bp.bounds.iter().filter_map(move |b| bt.map(|bt| (bt, b, bvars))).filter(
710 |(_, b, _)| match assoc_name {
711 Some(assoc_name) => self.bound_defines_assoc_item(b, assoc_name),
716 .flat_map(|(bt, b, bvars)| predicates_from_bound(self, bt, b, bvars))
720 #[instrument(level = "trace", skip(self))]
721 fn bound_defines_assoc_item(&self, b: &hir::GenericBound<'_>, assoc_name: Ident) -> bool {
723 hir::GenericBound::Trait(poly_trait_ref, _) => {
724 let trait_ref = &poly_trait_ref.trait_ref;
725 if let Some(trait_did) = trait_ref.trait_def_id() {
726 self.tcx.trait_may_define_assoc_type(trait_did, assoc_name)
736 /// Converts a specific `GenericBound` from the AST into a set of
737 /// predicates that apply to the self type. A vector is returned
738 /// because this can be anywhere from zero predicates (`T: ?Sized` adds no
739 /// predicates) to one (`T: Foo`) to many (`T: Bar<X = i32>` adds `T: Bar`
740 /// and `<T as Bar>::X == i32`).
741 fn predicates_from_bound<'tcx>(
742 astconv: &dyn AstConv<'tcx>,
744 bound: &'tcx hir::GenericBound<'tcx>,
745 bound_vars: &'tcx ty::List<ty::BoundVariableKind>,
746 ) -> Vec<(ty::Predicate<'tcx>, Span)> {
747 let mut bounds = Bounds::default();
748 astconv.add_bounds(param_ty, [bound].into_iter(), &mut bounds, bound_vars);
749 bounds.predicates().collect()