1 //! Methods for lowering the HIR to types. There are two main cases here:
3 //! - Lowering a type reference like `&usize` or `Option<foo::bar::Baz>` to a
4 //! type: The entry point for this is `Ty::from_hir`.
5 //! - Building the type for an item: This happens through the `type_for_def` query.
7 //! This usually involves resolving names, collecting generic arguments etc.
8 use std::{iter, sync::Arc};
11 use chalk_ir::{cast::Cast, Mutability, Safety};
14 builtin_type::BuiltinType,
15 generics::{TypeParamProvenance, WherePredicate, WherePredicateTypeTarget},
16 path::{GenericArg, Path, PathSegment, PathSegments},
17 resolver::{HasResolver, Resolver, TypeNs},
18 type_ref::{TraitRef as HirTraitRef, TypeBound, TypeRef},
19 AdtId, AssocContainerId, AssocItemId, ConstId, ConstParamId, EnumId, EnumVariantId, FunctionId,
20 GenericDefId, HasModule, ImplId, LocalFieldId, Lookup, StaticId, StructId, TraitId,
21 TypeAliasId, TypeParamId, UnionId, VariantId,
23 use hir_expand::name::Name;
24 use la_arena::ArenaMap;
25 use smallvec::SmallVec;
30 dummy_usize_const, static_lifetime, to_assoc_type_id, to_chalk_trait_id, to_placeholder_idx,
31 traits::chalk::{Interner, ToChalk},
33 all_super_trait_refs, associated_type_by_name_including_super_traits, generics, Generics,
35 AliasEq, AliasTy, Binders, BoundVar, CallableSig, DebruijnIndex, DynTy, FnPointer, FnSig,
36 FnSubst, ImplTraitId, OpaqueTy, PolyFnSig, ProjectionTy, QuantifiedWhereClause,
37 QuantifiedWhereClauses, ReturnTypeImplTrait, ReturnTypeImplTraits, Substitution,
38 TraitEnvironment, TraitRef, Ty, TyBuilder, TyKind, TypeWalk, WhereClause,
42 pub struct TyLoweringContext<'a> {
43 pub db: &'a dyn HirDatabase,
44 pub resolver: &'a Resolver,
45 in_binders: DebruijnIndex,
46 /// Note: Conceptually, it's thinkable that we could be in a location where
47 /// some type params should be represented as placeholders, and others
48 /// should be converted to variables. I think in practice, this isn't
49 /// possible currently, so this should be fine for now.
50 pub type_param_mode: TypeParamLoweringMode,
51 pub impl_trait_mode: ImplTraitLoweringMode,
52 impl_trait_counter: std::cell::Cell<u16>,
53 /// When turning `impl Trait` into opaque types, we have to collect the
54 /// bounds at the same time to get the IDs correct (without becoming too
55 /// complicated). I don't like using interior mutability (as for the
56 /// counter), but I've tried and failed to make the lifetimes work for
57 /// passing around a `&mut TyLoweringContext`. The core problem is that
58 /// we're grouping the mutable data (the counter and this field) together
59 /// with the immutable context (the references to the DB and resolver).
60 /// Splitting this up would be a possible fix.
61 opaque_type_data: std::cell::RefCell<Vec<ReturnTypeImplTrait>>,
64 impl<'a> TyLoweringContext<'a> {
65 pub fn new(db: &'a dyn HirDatabase, resolver: &'a Resolver) -> Self {
66 let impl_trait_counter = std::cell::Cell::new(0);
67 let impl_trait_mode = ImplTraitLoweringMode::Disallowed;
68 let type_param_mode = TypeParamLoweringMode::Placeholder;
69 let in_binders = DebruijnIndex::INNERMOST;
70 let opaque_type_data = std::cell::RefCell::new(Vec::new());
82 pub fn with_debruijn<T>(
84 debruijn: DebruijnIndex,
85 f: impl FnOnce(&TyLoweringContext) -> T,
87 let opaque_ty_data_vec = self.opaque_type_data.replace(Vec::new());
90 impl_trait_counter: std::cell::Cell::new(self.impl_trait_counter.get()),
91 opaque_type_data: std::cell::RefCell::new(opaque_ty_data_vec),
94 let result = f(&new_ctx);
95 self.impl_trait_counter.set(new_ctx.impl_trait_counter.get());
96 self.opaque_type_data.replace(new_ctx.opaque_type_data.into_inner());
100 pub fn with_shifted_in<T>(
102 debruijn: DebruijnIndex,
103 f: impl FnOnce(&TyLoweringContext) -> T,
105 self.with_debruijn(self.in_binders.shifted_in_from(debruijn), f)
108 pub fn with_impl_trait_mode(self, impl_trait_mode: ImplTraitLoweringMode) -> Self {
109 Self { impl_trait_mode, ..self }
112 pub fn with_type_param_mode(self, type_param_mode: TypeParamLoweringMode) -> Self {
113 Self { type_param_mode, ..self }
117 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
118 pub enum ImplTraitLoweringMode {
119 /// `impl Trait` gets lowered into an opaque type that doesn't unify with
120 /// anything except itself. This is used in places where values flow 'out',
121 /// i.e. for arguments of the function we're currently checking, and return
122 /// types of functions we're calling.
124 /// `impl Trait` gets lowered into a type variable. Used for argument
125 /// position impl Trait when inside the respective function, since it allows
126 /// us to support that without Chalk.
128 /// `impl Trait` gets lowered into a variable that can unify with some
129 /// type. This is used in places where values flow 'in', i.e. for arguments
130 /// of functions we're calling, and the return type of the function we're
131 /// currently checking.
133 /// `impl Trait` is disallowed and will be an error.
137 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
138 pub enum TypeParamLoweringMode {
143 impl<'a> TyLoweringContext<'a> {
144 pub fn lower_ty(&self, type_ref: &TypeRef) -> Ty {
145 self.lower_ty_ext(type_ref).0
148 pub fn lower_ty_ext(&self, type_ref: &TypeRef) -> (Ty, Option<TypeNs>) {
150 let ty = match type_ref {
151 TypeRef::Never => TyKind::Never.intern(&Interner),
152 TypeRef::Tuple(inner) => {
153 let inner_tys = inner.iter().map(|tr| self.lower_ty(tr));
154 TyKind::Tuple(inner_tys.len(), Substitution::from_iter(&Interner, inner_tys))
157 TypeRef::Path(path) => {
158 let (ty, res_) = self.lower_path(path);
162 TypeRef::RawPtr(inner, mutability) => {
163 let inner_ty = self.lower_ty(inner);
164 TyKind::Raw(lower_to_chalk_mutability(*mutability), inner_ty).intern(&Interner)
166 TypeRef::Array(inner) => {
167 let inner_ty = self.lower_ty(inner);
168 TyKind::Array(inner_ty, dummy_usize_const()).intern(&Interner)
170 TypeRef::Slice(inner) => {
171 let inner_ty = self.lower_ty(inner);
172 TyKind::Slice(inner_ty).intern(&Interner)
174 TypeRef::Reference(inner, _, mutability) => {
175 let inner_ty = self.lower_ty(inner);
176 let lifetime = static_lifetime();
177 TyKind::Ref(lower_to_chalk_mutability(*mutability), lifetime, inner_ty)
180 TypeRef::Placeholder => TyKind::Error.intern(&Interner),
181 TypeRef::Fn(params, is_varargs) => {
182 let substs = self.with_shifted_in(DebruijnIndex::ONE, |ctx| {
183 Substitution::from_iter(&Interner, params.iter().map(|tr| ctx.lower_ty(tr)))
185 TyKind::Function(FnPointer {
186 num_binders: 0, // FIXME lower `for<'a> fn()` correctly
187 sig: FnSig { abi: (), safety: Safety::Safe, variadic: *is_varargs },
188 substitution: FnSubst(substs),
192 TypeRef::DynTrait(bounds) => {
194 TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, 0)).intern(&Interner);
195 let bounds = self.with_shifted_in(DebruijnIndex::ONE, |ctx| {
196 QuantifiedWhereClauses::from_iter(
198 bounds.iter().flat_map(|b| ctx.lower_type_bound(b, self_ty.clone(), false)),
201 let bounds = crate::make_only_type_binders(1, bounds);
202 TyKind::Dyn(DynTy { bounds, lifetime: static_lifetime() }).intern(&Interner)
204 TypeRef::ImplTrait(bounds) => {
205 match self.impl_trait_mode {
206 ImplTraitLoweringMode::Opaque => {
207 let idx = self.impl_trait_counter.get();
208 self.impl_trait_counter.set(idx + 1);
210 assert!(idx as usize == self.opaque_type_data.borrow().len());
211 // this dance is to make sure the data is in the right
212 // place even if we encounter more opaque types while
213 // lowering the bounds
214 self.opaque_type_data.borrow_mut().push(ReturnTypeImplTrait {
215 bounds: crate::make_only_type_binders(1, Vec::new()),
217 // We don't want to lower the bounds inside the binders
218 // we're currently in, because they don't end up inside
219 // those binders. E.g. when we have `impl Trait<impl
220 // OtherTrait<T>>`, the `impl OtherTrait<T>` can't refer
221 // to the self parameter from `impl Trait`, and the
222 // bounds aren't actually stored nested within each
223 // other, but separately. So if the `T` refers to a type
224 // parameter of the outer function, it's just one binder
225 // away instead of two.
226 let actual_opaque_type_data = self
227 .with_debruijn(DebruijnIndex::INNERMOST, |ctx| {
228 ctx.lower_impl_trait(&bounds)
230 self.opaque_type_data.borrow_mut()[idx as usize] = actual_opaque_type_data;
232 let func = match self.resolver.generic_def() {
233 Some(GenericDefId::FunctionId(f)) => f,
234 _ => panic!("opaque impl trait lowering in non-function"),
236 let impl_trait_id = ImplTraitId::ReturnTypeImplTrait(func, idx);
237 let opaque_ty_id = self.db.intern_impl_trait_id(impl_trait_id).into();
238 let generics = generics(self.db.upcast(), func.into());
239 let parameters = generics.bound_vars_subst(self.in_binders);
240 TyKind::Alias(AliasTy::Opaque(OpaqueTy {
242 substitution: parameters,
246 ImplTraitLoweringMode::Param => {
247 let idx = self.impl_trait_counter.get();
248 // FIXME we're probably doing something wrong here
249 self.impl_trait_counter.set(idx + count_impl_traits(type_ref) as u16);
250 if let Some(def) = self.resolver.generic_def() {
251 let generics = generics(self.db.upcast(), def);
254 .filter(|(_, data)| {
255 data.provenance == TypeParamProvenance::ArgumentImplTrait
258 .map_or(TyKind::Error, |(id, _)| {
259 TyKind::Placeholder(to_placeholder_idx(self.db, id))
261 param.intern(&Interner)
263 TyKind::Error.intern(&Interner)
266 ImplTraitLoweringMode::Variable => {
267 let idx = self.impl_trait_counter.get();
268 // FIXME we're probably doing something wrong here
269 self.impl_trait_counter.set(idx + count_impl_traits(type_ref) as u16);
270 let (parent_params, self_params, list_params, _impl_trait_params) =
271 if let Some(def) = self.resolver.generic_def() {
272 let generics = generics(self.db.upcast(), def);
273 generics.provenance_split()
277 TyKind::BoundVar(BoundVar::new(
279 idx as usize + parent_params + self_params + list_params,
283 ImplTraitLoweringMode::Disallowed => {
284 // FIXME: report error
285 TyKind::Error.intern(&Interner)
289 TypeRef::Error => TyKind::Error.intern(&Interner),
294 /// This is only for `generic_predicates_for_param`, where we can't just
295 /// lower the self types of the predicates since that could lead to cycles.
296 /// So we just check here if the `type_ref` resolves to a generic param, and which.
297 fn lower_ty_only_param(&self, type_ref: &TypeRef) -> Option<TypeParamId> {
298 let path = match type_ref {
299 TypeRef::Path(path) => path,
302 if path.type_anchor().is_some() {
305 if path.segments().len() > 1 {
309 match self.resolver.resolve_path_in_type_ns(self.db.upcast(), path.mod_path()) {
310 Some((it, None)) => it,
313 if let TypeNs::GenericParam(param_id) = resolution {
320 pub(crate) fn lower_ty_relative_path(
323 // We need the original resolution to lower `Self::AssocTy` correctly
325 remaining_segments: PathSegments<'_>,
326 ) -> (Ty, Option<TypeNs>) {
327 if remaining_segments.len() == 1 {
328 // resolve unselected assoc types
329 let segment = remaining_segments.first().unwrap();
330 (self.select_associated_type(res, segment), None)
331 } else if remaining_segments.len() > 1 {
332 // FIXME report error (ambiguous associated type)
333 (TyKind::Error.intern(&Interner), None)
339 pub(crate) fn lower_partly_resolved_path(
342 resolved_segment: PathSegment<'_>,
343 remaining_segments: PathSegments<'_>,
345 ) -> (Ty, Option<TypeNs>) {
346 let ty = match resolution {
347 TypeNs::TraitId(trait_) => {
348 // if this is a bare dyn Trait, we'll directly put the required ^0 for the self type in there
349 let self_ty = if remaining_segments.len() == 0 {
351 TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, 0))
358 self.lower_trait_ref_from_resolved_path(trait_, resolved_segment, self_ty);
359 let ty = if remaining_segments.len() == 1 {
360 let segment = remaining_segments.first().unwrap();
361 let found = associated_type_by_name_including_super_traits(
367 Some((super_trait_ref, associated_ty)) => {
368 // FIXME handle type parameters on the segment
369 TyKind::Alias(AliasTy::Projection(ProjectionTy {
370 associated_ty_id: to_assoc_type_id(associated_ty),
371 substitution: super_trait_ref.substitution,
376 // FIXME: report error (associated type not found)
377 TyKind::Error.intern(&Interner)
380 } else if remaining_segments.len() > 1 {
381 // FIXME report error (ambiguous associated type)
382 TyKind::Error.intern(&Interner)
385 bounds: crate::make_only_type_binders(
387 QuantifiedWhereClauses::from_iter(
389 Some(crate::wrap_empty_binders(WhereClause::Implemented(
394 lifetime: static_lifetime(),
396 TyKind::Dyn(dyn_ty).intern(&Interner)
400 TypeNs::GenericParam(param_id) => {
401 let generics = generics(
403 self.resolver.generic_def().expect("generics in scope"),
405 match self.type_param_mode {
406 TypeParamLoweringMode::Placeholder => {
407 TyKind::Placeholder(to_placeholder_idx(self.db, param_id))
409 TypeParamLoweringMode::Variable => {
410 let idx = generics.param_idx(param_id).expect("matching generics");
411 TyKind::BoundVar(BoundVar::new(self.in_binders, idx))
416 TypeNs::SelfType(impl_id) => {
417 let generics = generics(self.db.upcast(), impl_id.into());
418 let substs = match self.type_param_mode {
419 TypeParamLoweringMode::Placeholder => generics.type_params_subst(self.db),
420 TypeParamLoweringMode::Variable => generics.bound_vars_subst(self.in_binders),
422 self.db.impl_self_ty(impl_id).substitute(&Interner, &substs)
424 TypeNs::AdtSelfType(adt) => {
425 let generics = generics(self.db.upcast(), adt.into());
426 let substs = match self.type_param_mode {
427 TypeParamLoweringMode::Placeholder => generics.type_params_subst(self.db),
428 TypeParamLoweringMode::Variable => generics.bound_vars_subst(self.in_binders),
430 self.db.ty(adt.into()).substitute(&Interner, &substs)
433 TypeNs::AdtId(it) => self.lower_path_inner(resolved_segment, it.into(), infer_args),
434 TypeNs::BuiltinType(it) => {
435 self.lower_path_inner(resolved_segment, it.into(), infer_args)
437 TypeNs::TypeAliasId(it) => {
438 self.lower_path_inner(resolved_segment, it.into(), infer_args)
440 // FIXME: report error
441 TypeNs::EnumVariantId(_) => return (TyKind::Error.intern(&Interner), None),
443 self.lower_ty_relative_path(ty, Some(resolution), remaining_segments)
446 pub(crate) fn lower_path(&self, path: &Path) -> (Ty, Option<TypeNs>) {
447 // Resolve the path (in type namespace)
448 if let Some(type_ref) = path.type_anchor() {
449 let (ty, res) = self.lower_ty_ext(&type_ref);
450 return self.lower_ty_relative_path(ty, res, path.segments());
452 let (resolution, remaining_index) =
453 match self.resolver.resolve_path_in_type_ns(self.db.upcast(), path.mod_path()) {
455 None => return (TyKind::Error.intern(&Interner), None),
457 let (resolved_segment, remaining_segments) = match remaining_index {
459 path.segments().last().expect("resolved path has at least one element"),
462 Some(i) => (path.segments().get(i - 1).unwrap(), path.segments().skip(i)),
464 self.lower_partly_resolved_path(resolution, resolved_segment, remaining_segments, false)
467 fn select_associated_type(&self, res: Option<TypeNs>, segment: PathSegment<'_>) -> Ty {
468 if let Some(res) = res {
469 let ty = associated_type_shorthand_candidates(
472 move |name, t, associated_ty| {
473 if name == segment.name {
474 let substs = match self.type_param_mode {
475 TypeParamLoweringMode::Placeholder => {
476 // if we're lowering to placeholders, we have to put
478 let generics = generics(
480 self.resolver.generic_def().expect(
481 "there should be generics if there's a generic param",
484 let s = generics.type_params_subst(self.db);
485 s.apply(t.substitution.clone(), &Interner)
487 TypeParamLoweringMode::Variable => t.substitution.clone(),
489 // We need to shift in the bound vars, since
490 // associated_type_shorthand_candidates does not do that
491 let substs = substs.shifted_in_from(self.in_binders);
492 // FIXME handle type parameters on the segment
494 TyKind::Alias(AliasTy::Projection(ProjectionTy {
495 associated_ty_id: to_assoc_type_id(associated_ty),
496 substitution: substs,
506 ty.unwrap_or(TyKind::Error.intern(&Interner))
508 TyKind::Error.intern(&Interner)
514 segment: PathSegment<'_>,
518 let generic_def = match typeable {
519 TyDefId::BuiltinType(_) => None,
520 TyDefId::AdtId(it) => Some(it.into()),
521 TyDefId::TypeAliasId(it) => Some(it.into()),
523 let substs = self.substs_from_path_segment(segment, generic_def, infer_args, None);
524 self.db.ty(typeable).substitute(&Interner, &substs)
527 /// Collect generic arguments from a path into a `Substs`. See also
528 /// `create_substs_for_ast_path` and `def_to_ty` in rustc.
529 pub(super) fn substs_from_path(
532 // Note that we don't call `db.value_type(resolved)` here,
533 // `ValueTyDefId` is just a convenient way to pass generics and
534 // special-case enum variants
535 resolved: ValueTyDefId,
538 let last = path.segments().last().expect("path should have at least one segment");
539 let (segment, generic_def) = match resolved {
540 ValueTyDefId::FunctionId(it) => (last, Some(it.into())),
541 ValueTyDefId::StructId(it) => (last, Some(it.into())),
542 ValueTyDefId::UnionId(it) => (last, Some(it.into())),
543 ValueTyDefId::ConstId(it) => (last, Some(it.into())),
544 ValueTyDefId::StaticId(_) => (last, None),
545 ValueTyDefId::EnumVariantId(var) => {
546 // the generic args for an enum variant may be either specified
547 // on the segment referring to the enum, or on the segment
548 // referring to the variant. So `Option::<T>::None` and
549 // `Option::None::<T>` are both allowed (though the former is
550 // preferred). See also `def_ids_for_path_segments` in rustc.
551 let len = path.segments().len();
552 let penultimate = if len >= 2 { path.segments().get(len - 2) } else { None };
553 let segment = match penultimate {
554 Some(segment) if segment.args_and_bindings.is_some() => segment,
557 (segment, Some(var.parent.into()))
560 self.substs_from_path_segment(segment, generic_def, infer_args, None)
563 fn substs_from_path_segment(
565 segment: PathSegment<'_>,
566 def_generic: Option<GenericDefId>,
568 explicit_self_ty: Option<Ty>,
570 let mut substs = Vec::new();
571 let def_generics = def_generic.map(|def| generics(self.db.upcast(), def));
573 let (parent_params, self_params, type_params, impl_trait_params) =
574 def_generics.map_or((0, 0, 0, 0), |g| g.provenance_split());
575 let total_len = parent_params + self_params + type_params + impl_trait_params;
577 substs.extend(iter::repeat(TyKind::Error.intern(&Interner)).take(parent_params));
579 let fill_self_params = || {
583 .chain(iter::repeat(TyKind::Error.intern(&Interner)))
587 let mut had_explicit_type_args = false;
589 if let Some(generic_args) = &segment.args_and_bindings {
590 if !generic_args.has_self_type {
594 if generic_args.has_self_type { self_params + type_params } else { type_params };
595 let skip = if generic_args.has_self_type && self_params == 0 { 1 } else { 0 };
596 // if args are provided, it should be all of them, but we can't rely on that
597 for arg in generic_args
600 .filter(|arg| matches!(arg, GenericArg::Type(_)))
605 GenericArg::Type(type_ref) => {
606 had_explicit_type_args = true;
607 let ty = self.lower_ty(type_ref);
610 GenericArg::Lifetime(_) => {}
617 // handle defaults. In expression or pattern path segments without
618 // explicitly specified type arguments, missing type arguments are inferred
619 // (i.e. defaults aren't used).
620 if !infer_args || had_explicit_type_args {
621 if let Some(def_generic) = def_generic {
622 let defaults = self.db.generic_defaults(def_generic);
623 assert_eq!(total_len, defaults.len());
625 for default_ty in defaults.iter().skip(substs.len()) {
626 // each default can depend on the previous parameters
627 let substs_so_far = Substitution::from_iter(&Interner, substs.clone());
628 substs.push(default_ty.clone().substitute(&Interner, &substs_so_far));
633 // add placeholders for args that were not provided
634 // FIXME: emit diagnostics in contexts where this is not allowed
635 for _ in substs.len()..total_len {
636 substs.push(TyKind::Error.intern(&Interner));
638 assert_eq!(substs.len(), total_len);
640 Substitution::from_iter(&Interner, substs)
643 fn lower_trait_ref_from_path(
646 explicit_self_ty: Option<Ty>,
647 ) -> Option<TraitRef> {
649 match self.resolver.resolve_path_in_type_ns_fully(self.db.upcast(), path.mod_path())? {
650 TypeNs::TraitId(tr) => tr,
653 let segment = path.segments().last().expect("path should have at least one segment");
654 Some(self.lower_trait_ref_from_resolved_path(resolved, segment, explicit_self_ty))
657 pub(crate) fn lower_trait_ref_from_resolved_path(
660 segment: PathSegment<'_>,
661 explicit_self_ty: Option<Ty>,
663 let substs = self.trait_ref_substs_from_path(segment, resolved, explicit_self_ty);
664 TraitRef { trait_id: to_chalk_trait_id(resolved), substitution: substs }
669 trait_ref: &HirTraitRef,
670 explicit_self_ty: Option<Ty>,
671 ) -> Option<TraitRef> {
672 self.lower_trait_ref_from_path(&trait_ref.path, explicit_self_ty)
675 fn trait_ref_substs_from_path(
677 segment: PathSegment<'_>,
679 explicit_self_ty: Option<Ty>,
681 self.substs_from_path_segment(segment, Some(resolved.into()), false, explicit_self_ty)
684 pub(crate) fn lower_where_predicate(
686 where_predicate: &'a WherePredicate,
687 ignore_bindings: bool,
688 ) -> impl Iterator<Item = QuantifiedWhereClause> + 'a {
689 match where_predicate {
690 WherePredicate::ForLifetime { target, bound, .. }
691 | WherePredicate::TypeBound { target, bound } => {
692 let self_ty = match target {
693 WherePredicateTypeTarget::TypeRef(type_ref) => self.lower_ty(type_ref),
694 WherePredicateTypeTarget::TypeParam(param_id) => {
695 let generic_def = self.resolver.generic_def().expect("generics in scope");
696 let generics = generics(self.db.upcast(), generic_def);
698 hir_def::TypeParamId { parent: generic_def, local_id: *param_id };
699 let placeholder = to_placeholder_idx(self.db, param_id);
700 match self.type_param_mode {
701 TypeParamLoweringMode::Placeholder => TyKind::Placeholder(placeholder),
702 TypeParamLoweringMode::Variable => {
703 let idx = generics.param_idx(param_id).expect("matching generics");
704 TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, idx))
710 self.lower_type_bound(bound, self_ty, ignore_bindings)
714 WherePredicate::Lifetime { .. } => vec![].into_iter(),
718 pub(crate) fn lower_type_bound(
720 bound: &'a TypeBound,
722 ignore_bindings: bool,
723 ) -> impl Iterator<Item = QuantifiedWhereClause> + 'a {
724 let mut bindings = None;
725 let trait_ref = match bound {
726 TypeBound::Path(path) => {
727 bindings = self.lower_trait_ref_from_path(path, Some(self_ty));
728 bindings.clone().map(WhereClause::Implemented).map(|b| crate::wrap_empty_binders(b))
730 TypeBound::Lifetime(_) => None,
731 TypeBound::Error => None,
733 trait_ref.into_iter().chain(
736 .filter(move |_| !ignore_bindings)
737 .flat_map(move |tr| self.assoc_type_bindings_from_type_bound(bound, tr)),
741 fn assoc_type_bindings_from_type_bound(
743 bound: &'a TypeBound,
745 ) -> impl Iterator<Item = QuantifiedWhereClause> + 'a {
746 let last_segment = match bound {
747 TypeBound::Path(path) => path.segments().last(),
748 TypeBound::Error | TypeBound::Lifetime(_) => None,
752 .flat_map(|segment| segment.args_and_bindings.into_iter())
753 .flat_map(|args_and_bindings| args_and_bindings.bindings.iter())
754 .flat_map(move |binding| {
755 let found = associated_type_by_name_including_super_traits(
760 let (super_trait_ref, associated_ty) = match found {
761 None => return SmallVec::<[QuantifiedWhereClause; 1]>::new(),
764 let projection_ty = ProjectionTy {
765 associated_ty_id: to_assoc_type_id(associated_ty),
766 substitution: super_trait_ref.substitution,
768 let mut preds = SmallVec::with_capacity(
769 binding.type_ref.as_ref().map_or(0, |_| 1) + binding.bounds.len(),
771 if let Some(type_ref) = &binding.type_ref {
772 let ty = self.lower_ty(type_ref);
774 AliasEq { alias: AliasTy::Projection(projection_ty.clone()), ty };
775 preds.push(crate::wrap_empty_binders(WhereClause::AliasEq(alias_eq)));
777 for bound in &binding.bounds {
778 preds.extend(self.lower_type_bound(
780 TyKind::Alias(AliasTy::Projection(projection_ty.clone())).intern(&Interner),
788 fn lower_impl_trait(&self, bounds: &[TypeBound]) -> ReturnTypeImplTrait {
789 cov_mark::hit!(lower_rpit);
791 TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, 0)).intern(&Interner);
792 let predicates = self.with_shifted_in(DebruijnIndex::ONE, |ctx| {
793 bounds.iter().flat_map(|b| ctx.lower_type_bound(b, self_ty.clone(), false)).collect()
795 ReturnTypeImplTrait { bounds: crate::make_only_type_binders(1, predicates) }
799 fn count_impl_traits(type_ref: &TypeRef) -> usize {
801 type_ref.walk(&mut |type_ref| {
802 if matches!(type_ref, TypeRef::ImplTrait(_)) {
809 /// Build the signature of a callable item (function, struct or enum variant).
810 pub fn callable_item_sig(db: &dyn HirDatabase, def: CallableDefId) -> PolyFnSig {
812 CallableDefId::FunctionId(f) => fn_sig_for_fn(db, f),
813 CallableDefId::StructId(s) => fn_sig_for_struct_constructor(db, s),
814 CallableDefId::EnumVariantId(e) => fn_sig_for_enum_variant_constructor(db, e),
818 pub fn associated_type_shorthand_candidates<R>(
819 db: &dyn HirDatabase,
821 mut cb: impl FnMut(&Name, &TraitRef, TypeAliasId) -> Option<R>,
823 let mut search = |t| {
824 for t in all_super_trait_refs(db, t) {
825 let data = db.trait_data(t.hir_trait_id());
827 for (name, assoc_id) in &data.items {
828 if let AssocItemId::TypeAliasId(alias) = assoc_id {
829 if let Some(result) = cb(name, &t, *alias) {
839 TypeNs::SelfType(impl_id) => search(
840 // we're _in_ the impl -- the binders get added back later. Correct,
841 // but it would be nice to make this more explicit
842 db.impl_trait(impl_id)?.into_value_and_skipped_binders().0,
844 TypeNs::GenericParam(param_id) => {
845 let predicates = db.generic_predicates_for_param(param_id);
846 let res = predicates.iter().find_map(|pred| match pred.skip_binders().skip_binders() {
847 // FIXME: how to correctly handle higher-ranked bounds here?
848 WhereClause::Implemented(tr) => search(
850 .shifted_out_to(DebruijnIndex::ONE)
851 .expect("FIXME unexpected higher-ranked trait bound"),
855 if let res @ Some(_) = res {
858 // Handle `Self::Type` referring to own associated type in trait definitions
859 if let GenericDefId::TraitId(trait_id) = param_id.parent {
860 let generics = generics(db.upcast(), trait_id.into());
861 if generics.params.types[param_id.local_id].provenance
862 == TypeParamProvenance::TraitSelf
864 let trait_ref = TyBuilder::trait_ref(db, trait_id)
865 .fill_with_bound_vars(DebruijnIndex::INNERMOST, 0)
867 return search(trait_ref);
876 /// Build the type of all specific fields of a struct or enum variant.
877 pub(crate) fn field_types_query(
878 db: &dyn HirDatabase,
879 variant_id: VariantId,
880 ) -> Arc<ArenaMap<LocalFieldId, Binders<Ty>>> {
881 let var_data = variant_id.variant_data(db.upcast());
882 let (resolver, def): (_, GenericDefId) = match variant_id {
883 VariantId::StructId(it) => (it.resolver(db.upcast()), it.into()),
884 VariantId::UnionId(it) => (it.resolver(db.upcast()), it.into()),
885 VariantId::EnumVariantId(it) => (it.parent.resolver(db.upcast()), it.parent.into()),
887 let generics = generics(db.upcast(), def);
888 let mut res = ArenaMap::default();
890 TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
891 for (field_id, field_data) in var_data.fields().iter() {
892 res.insert(field_id, make_binders(&generics, ctx.lower_ty(&field_data.type_ref)))
897 /// This query exists only to be used when resolving short-hand associated types
900 /// See the analogous query in rustc and its comment:
901 /// https://github.com/rust-lang/rust/blob/9150f844e2624eb013ec78ca08c1d416e6644026/src/librustc_typeck/astconv.rs#L46
902 /// This is a query mostly to handle cycles somewhat gracefully; e.g. the
903 /// following bounds are disallowed: `T: Foo<U::Item>, U: Foo<T::Item>`, but
904 /// these are fine: `T: Foo<U::Item>, U: Foo<()>`.
905 pub(crate) fn generic_predicates_for_param_query(
906 db: &dyn HirDatabase,
907 param_id: TypeParamId,
908 ) -> Arc<[Binders<QuantifiedWhereClause>]> {
909 let resolver = param_id.parent.resolver(db.upcast());
911 TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
912 let generics = generics(db.upcast(), param_id.parent);
914 .where_predicates_in_scope()
915 // we have to filter out all other predicates *first*, before attempting to lower them
916 .filter(|pred| match pred {
917 WherePredicate::ForLifetime { target, .. }
918 | WherePredicate::TypeBound { target, .. } => match target {
919 WherePredicateTypeTarget::TypeRef(type_ref) => {
920 ctx.lower_ty_only_param(type_ref) == Some(param_id)
922 WherePredicateTypeTarget::TypeParam(local_id) => *local_id == param_id.local_id,
924 WherePredicate::Lifetime { .. } => false,
926 .flat_map(|pred| ctx.lower_where_predicate(pred, true).map(|p| make_binders(&generics, p)))
930 pub(crate) fn generic_predicates_for_param_recover(
931 _db: &dyn HirDatabase,
933 _param_id: &TypeParamId,
934 ) -> Arc<[Binders<QuantifiedWhereClause>]> {
938 pub(crate) fn trait_environment_query(
939 db: &dyn HirDatabase,
941 ) -> Arc<TraitEnvironment> {
942 let resolver = def.resolver(db.upcast());
943 let ctx = TyLoweringContext::new(db, &resolver)
944 .with_type_param_mode(TypeParamLoweringMode::Placeholder);
945 let mut traits_in_scope = Vec::new();
946 let mut clauses = Vec::new();
947 for pred in resolver.where_predicates_in_scope() {
948 for pred in ctx.lower_where_predicate(pred, false) {
949 if let WhereClause::Implemented(tr) = &pred.skip_binders() {
951 .push((tr.self_type_parameter(&Interner).clone(), tr.hir_trait_id()));
953 let program_clause: chalk_ir::ProgramClause<Interner> =
954 pred.clone().to_chalk(db).cast(&Interner);
955 clauses.push(program_clause.into_from_env_clause(&Interner));
959 let container: Option<AssocContainerId> = match def {
960 // FIXME: is there a function for this?
961 GenericDefId::FunctionId(f) => Some(f.lookup(db.upcast()).container),
962 GenericDefId::AdtId(_) => None,
963 GenericDefId::TraitId(_) => None,
964 GenericDefId::TypeAliasId(t) => Some(t.lookup(db.upcast()).container),
965 GenericDefId::ImplId(_) => None,
966 GenericDefId::EnumVariantId(_) => None,
967 GenericDefId::ConstId(c) => Some(c.lookup(db.upcast()).container),
969 if let Some(AssocContainerId::TraitId(trait_id)) = container {
970 // add `Self: Trait<T1, T2, ...>` to the environment in trait
971 // function default implementations (and hypothetical code
972 // inside consts or type aliases)
973 cov_mark::hit!(trait_self_implements_self);
974 let substs = TyBuilder::type_params_subst(db, trait_id);
975 let trait_ref = TraitRef { trait_id: to_chalk_trait_id(trait_id), substitution: substs };
976 let pred = WhereClause::Implemented(trait_ref);
977 let program_clause: chalk_ir::ProgramClause<Interner> = pred.to_chalk(db).cast(&Interner);
978 clauses.push(program_clause.into_from_env_clause(&Interner));
981 let env = chalk_ir::Environment::new(&Interner).add_clauses(&Interner, clauses);
983 Arc::new(TraitEnvironment { traits_from_clauses: traits_in_scope, env })
986 /// Resolve the where clause(s) of an item with generics.
987 pub(crate) fn generic_predicates_query(
988 db: &dyn HirDatabase,
990 ) -> Arc<[Binders<QuantifiedWhereClause>]> {
991 let resolver = def.resolver(db.upcast());
993 TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
994 let generics = generics(db.upcast(), def);
996 .where_predicates_in_scope()
997 .flat_map(|pred| ctx.lower_where_predicate(pred, false).map(|p| make_binders(&generics, p)))
1001 /// Resolve the default type params from generics
1002 pub(crate) fn generic_defaults_query(
1003 db: &dyn HirDatabase,
1005 ) -> Arc<[Binders<Ty>]> {
1006 let resolver = def.resolver(db.upcast());
1008 TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1009 let generic_params = generics(db.upcast(), def);
1011 let defaults = generic_params
1014 .map(|(idx, (_, p))| {
1016 p.default.as_ref().map_or(TyKind::Error.intern(&Interner), |t| ctx.lower_ty(t));
1018 // Each default can only refer to previous parameters.
1019 ty = ty.fold_binders(
1020 &mut |ty, binders| match ty.kind(&Interner) {
1021 TyKind::BoundVar(BoundVar { debruijn, index }) if *debruijn == binders => {
1023 // type variable default referring to parameter coming
1024 // after it. This is forbidden (FIXME: report
1026 TyKind::Error.intern(&Interner)
1033 DebruijnIndex::INNERMOST,
1036 crate::make_only_type_binders(idx, ty)
1043 fn fn_sig_for_fn(db: &dyn HirDatabase, def: FunctionId) -> PolyFnSig {
1044 let data = db.function_data(def);
1045 let resolver = def.resolver(db.upcast());
1046 let ctx_params = TyLoweringContext::new(db, &resolver)
1047 .with_impl_trait_mode(ImplTraitLoweringMode::Variable)
1048 .with_type_param_mode(TypeParamLoweringMode::Variable);
1049 let params = data.params.iter().map(|tr| ctx_params.lower_ty(tr)).collect::<Vec<_>>();
1050 let ctx_ret = TyLoweringContext::new(db, &resolver)
1051 .with_impl_trait_mode(ImplTraitLoweringMode::Opaque)
1052 .with_type_param_mode(TypeParamLoweringMode::Variable);
1053 let ret = ctx_ret.lower_ty(&data.ret_type);
1054 let generics = generics(db.upcast(), def.into());
1055 make_binders(&generics, CallableSig::from_params_and_return(params, ret, data.is_varargs()))
1058 /// Build the declared type of a function. This should not need to look at the
1060 fn type_for_fn(db: &dyn HirDatabase, def: FunctionId) -> Binders<Ty> {
1061 let generics = generics(db.upcast(), def.into());
1062 let substs = generics.bound_vars_subst(DebruijnIndex::INNERMOST);
1065 TyKind::FnDef(CallableDefId::FunctionId(def).to_chalk(db), substs).intern(&Interner),
1069 /// Build the declared type of a const.
1070 fn type_for_const(db: &dyn HirDatabase, def: ConstId) -> Binders<Ty> {
1071 let data = db.const_data(def);
1072 let generics = generics(db.upcast(), def.into());
1073 let resolver = def.resolver(db.upcast());
1075 TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1077 make_binders(&generics, ctx.lower_ty(&data.type_ref))
1080 /// Build the declared type of a static.
1081 fn type_for_static(db: &dyn HirDatabase, def: StaticId) -> Binders<Ty> {
1082 let data = db.static_data(def);
1083 let resolver = def.resolver(db.upcast());
1084 let ctx = TyLoweringContext::new(db, &resolver);
1086 Binders::empty(&Interner, ctx.lower_ty(&data.type_ref))
1089 fn fn_sig_for_struct_constructor(db: &dyn HirDatabase, def: StructId) -> PolyFnSig {
1090 let struct_data = db.struct_data(def);
1091 let fields = struct_data.variant_data.fields();
1092 let resolver = def.resolver(db.upcast());
1094 TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1095 let params = fields.iter().map(|(_, field)| ctx.lower_ty(&field.type_ref)).collect::<Vec<_>>();
1096 let (ret, binders) = type_for_adt(db, def.into()).into_value_and_skipped_binders();
1097 Binders::new(binders, CallableSig::from_params_and_return(params, ret, false))
1100 /// Build the type of a tuple struct constructor.
1101 fn type_for_struct_constructor(db: &dyn HirDatabase, def: StructId) -> Binders<Ty> {
1102 let struct_data = db.struct_data(def);
1103 if let StructKind::Unit = struct_data.variant_data.kind() {
1104 return type_for_adt(db, def.into());
1106 let generics = generics(db.upcast(), def.into());
1107 let substs = generics.bound_vars_subst(DebruijnIndex::INNERMOST);
1110 TyKind::FnDef(CallableDefId::StructId(def).to_chalk(db), substs).intern(&Interner),
1114 fn fn_sig_for_enum_variant_constructor(db: &dyn HirDatabase, def: EnumVariantId) -> PolyFnSig {
1115 let enum_data = db.enum_data(def.parent);
1116 let var_data = &enum_data.variants[def.local_id];
1117 let fields = var_data.variant_data.fields();
1118 let resolver = def.parent.resolver(db.upcast());
1120 TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1121 let params = fields.iter().map(|(_, field)| ctx.lower_ty(&field.type_ref)).collect::<Vec<_>>();
1122 let (ret, binders) = type_for_adt(db, def.parent.into()).into_value_and_skipped_binders();
1123 Binders::new(binders, CallableSig::from_params_and_return(params, ret, false))
1126 /// Build the type of a tuple enum variant constructor.
1127 fn type_for_enum_variant_constructor(db: &dyn HirDatabase, def: EnumVariantId) -> Binders<Ty> {
1128 let enum_data = db.enum_data(def.parent);
1129 let var_data = &enum_data.variants[def.local_id].variant_data;
1130 if let StructKind::Unit = var_data.kind() {
1131 return type_for_adt(db, def.parent.into());
1133 let generics = generics(db.upcast(), def.parent.into());
1134 let substs = generics.bound_vars_subst(DebruijnIndex::INNERMOST);
1137 TyKind::FnDef(CallableDefId::EnumVariantId(def).to_chalk(db), substs).intern(&Interner),
1141 fn type_for_adt(db: &dyn HirDatabase, adt: AdtId) -> Binders<Ty> {
1142 let generics = generics(db.upcast(), adt.into());
1143 let b = TyBuilder::adt(db, adt);
1144 let ty = b.fill_with_bound_vars(DebruijnIndex::INNERMOST, 0).build();
1145 make_binders(&generics, ty)
1148 fn type_for_type_alias(db: &dyn HirDatabase, t: TypeAliasId) -> Binders<Ty> {
1149 let generics = generics(db.upcast(), t.into());
1150 let resolver = t.resolver(db.upcast());
1152 TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1153 if db.type_alias_data(t).is_extern {
1154 Binders::empty(&Interner, TyKind::Foreign(crate::to_foreign_def_id(t)).intern(&Interner))
1156 let type_ref = &db.type_alias_data(t).type_ref;
1157 let inner = ctx.lower_ty(type_ref.as_deref().unwrap_or(&TypeRef::Error));
1158 make_binders(&generics, inner)
1162 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
1163 pub enum CallableDefId {
1164 FunctionId(FunctionId),
1166 EnumVariantId(EnumVariantId),
1168 impl_from!(FunctionId, StructId, EnumVariantId for CallableDefId);
1170 impl CallableDefId {
1171 pub fn krate(self, db: &dyn HirDatabase) -> CrateId {
1172 let db = db.upcast();
1174 CallableDefId::FunctionId(f) => f.lookup(db).module(db),
1175 CallableDefId::StructId(s) => s.lookup(db).container,
1176 CallableDefId::EnumVariantId(e) => e.parent.lookup(db).container,
1182 impl From<CallableDefId> for GenericDefId {
1183 fn from(def: CallableDefId) -> GenericDefId {
1185 CallableDefId::FunctionId(f) => f.into(),
1186 CallableDefId::StructId(s) => s.into(),
1187 CallableDefId::EnumVariantId(e) => e.into(),
1192 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
1194 BuiltinType(BuiltinType),
1196 TypeAliasId(TypeAliasId),
1198 impl_from!(BuiltinType, AdtId(StructId, EnumId, UnionId), TypeAliasId for TyDefId);
1200 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
1201 pub enum ValueTyDefId {
1202 FunctionId(FunctionId),
1205 EnumVariantId(EnumVariantId),
1209 impl_from!(FunctionId, StructId, UnionId, EnumVariantId, ConstId, StaticId for ValueTyDefId);
1211 /// Build the declared type of an item. This depends on the namespace; e.g. for
1212 /// `struct Foo(usize)`, we have two types: The type of the struct itself, and
1213 /// the constructor function `(usize) -> Foo` which lives in the values
1215 pub(crate) fn ty_query(db: &dyn HirDatabase, def: TyDefId) -> Binders<Ty> {
1217 TyDefId::BuiltinType(it) => Binders::empty(&Interner, TyBuilder::builtin(it)),
1218 TyDefId::AdtId(it) => type_for_adt(db, it),
1219 TyDefId::TypeAliasId(it) => type_for_type_alias(db, it),
1223 pub(crate) fn ty_recover(db: &dyn HirDatabase, _cycle: &[String], def: &TyDefId) -> Binders<Ty> {
1224 let generics = match *def {
1225 TyDefId::BuiltinType(_) => {
1226 return Binders::empty(&Interner, TyKind::Error.intern(&Interner))
1228 TyDefId::AdtId(it) => generics(db.upcast(), it.into()),
1229 TyDefId::TypeAliasId(it) => generics(db.upcast(), it.into()),
1231 make_binders(&generics, TyKind::Error.intern(&Interner))
1234 pub(crate) fn value_ty_query(db: &dyn HirDatabase, def: ValueTyDefId) -> Binders<Ty> {
1236 ValueTyDefId::FunctionId(it) => type_for_fn(db, it),
1237 ValueTyDefId::StructId(it) => type_for_struct_constructor(db, it),
1238 ValueTyDefId::UnionId(it) => type_for_adt(db, it.into()),
1239 ValueTyDefId::EnumVariantId(it) => type_for_enum_variant_constructor(db, it),
1240 ValueTyDefId::ConstId(it) => type_for_const(db, it),
1241 ValueTyDefId::StaticId(it) => type_for_static(db, it),
1245 pub(crate) fn impl_self_ty_query(db: &dyn HirDatabase, impl_id: ImplId) -> Binders<Ty> {
1246 let impl_data = db.impl_data(impl_id);
1247 let resolver = impl_id.resolver(db.upcast());
1248 let generics = generics(db.upcast(), impl_id.into());
1250 TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1251 make_binders(&generics, ctx.lower_ty(&impl_data.self_ty))
1254 pub(crate) fn const_param_ty_query(db: &dyn HirDatabase, def: ConstParamId) -> Ty {
1255 let parent_data = db.generic_params(def.parent);
1256 let data = &parent_data.consts[def.local_id];
1257 let resolver = def.parent.resolver(db.upcast());
1258 let ctx = TyLoweringContext::new(db, &resolver);
1260 ctx.lower_ty(&data.ty)
1263 pub(crate) fn impl_self_ty_recover(
1264 db: &dyn HirDatabase,
1268 let generics = generics(db.upcast(), (*impl_id).into());
1269 make_binders(&generics, TyKind::Error.intern(&Interner))
1272 pub(crate) fn impl_trait_query(db: &dyn HirDatabase, impl_id: ImplId) -> Option<Binders<TraitRef>> {
1273 let impl_data = db.impl_data(impl_id);
1274 let resolver = impl_id.resolver(db.upcast());
1276 TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
1277 let (self_ty, binders) = db.impl_self_ty(impl_id).into_value_and_skipped_binders();
1278 let target_trait = impl_data.target_trait.as_ref()?;
1279 Some(Binders::new(binders, ctx.lower_trait_ref(target_trait, Some(self_ty))?))
1282 pub(crate) fn return_type_impl_traits(
1283 db: &dyn HirDatabase,
1284 def: hir_def::FunctionId,
1285 ) -> Option<Arc<Binders<ReturnTypeImplTraits>>> {
1286 // FIXME unify with fn_sig_for_fn instead of doing lowering twice, maybe
1287 let data = db.function_data(def);
1288 let resolver = def.resolver(db.upcast());
1289 let ctx_ret = TyLoweringContext::new(db, &resolver)
1290 .with_impl_trait_mode(ImplTraitLoweringMode::Opaque)
1291 .with_type_param_mode(TypeParamLoweringMode::Variable);
1292 let _ret = (&ctx_ret).lower_ty(&data.ret_type);
1293 let generics = generics(db.upcast(), def.into());
1294 let return_type_impl_traits =
1295 ReturnTypeImplTraits { impl_traits: ctx_ret.opaque_type_data.into_inner() };
1296 if return_type_impl_traits.impl_traits.is_empty() {
1299 Some(Arc::new(make_binders(&generics, return_type_impl_traits)))
1303 pub(crate) fn lower_to_chalk_mutability(m: hir_def::type_ref::Mutability) -> Mutability {
1305 hir_def::type_ref::Mutability::Shared => Mutability::Not,
1306 hir_def::type_ref::Mutability::Mut => Mutability::Mut,
1310 fn make_binders<T>(generics: &Generics, value: T) -> Binders<T> {
1311 crate::make_only_type_binders(generics.len(), value)