//! The type system. We currently use this to infer types for completion, hover //! information and various assists. macro_rules! impl_froms { ($e:ident: $($v:ident $(($($sv:ident),*))?),*) => { $( impl From<$v> for $e { fn from(it: $v) -> $e { $e::$v(it) } } $($( impl From<$sv> for $e { fn from(it: $sv) -> $e { $e::$v($v::$sv(it)) } } )*)? )* } } mod autoderef; pub mod primitive; pub mod traits; pub mod method_resolution; mod op; mod lower; mod infer; pub mod display; pub(crate) mod utils; pub mod db; pub mod diagnostics; pub mod expr; #[cfg(test)] mod tests; #[cfg(test)] mod test_db; mod marks; use std::ops::Deref; use std::sync::Arc; use std::{iter, mem}; use hir_def::{ expr::ExprId, type_ref::Mutability, AdtId, AssocContainerId, DefWithBodyId, GenericDefId, HasModule, Lookup, TraitId, TypeAliasId, TypeParamId, }; use ra_db::{impl_intern_key, salsa, CrateId}; use crate::{ db::HirDatabase, primitive::{FloatTy, IntTy, Uncertain}, utils::{generics, make_mut_slice, Generics}, }; use display::HirDisplay; pub use autoderef::autoderef; pub use infer::{do_infer_query, InferTy, InferenceResult}; pub use lower::CallableDef; pub use lower::{ callable_item_sig, ImplTraitLoweringMode, TyDefId, TyLoweringContext, ValueTyDefId, }; pub use traits::{InEnvironment, Obligation, ProjectionPredicate, TraitEnvironment}; /// A type constructor or type name: this might be something like the primitive /// type `bool`, a struct like `Vec`, or things like function pointers or /// tuples. #[derive(Copy, Clone, PartialEq, Eq, Debug, Hash)] pub enum TypeCtor { /// The primitive boolean type. Written as `bool`. Bool, /// The primitive character type; holds a Unicode scalar value /// (a non-surrogate code point). Written as `char`. Char, /// A primitive integer type. For example, `i32`. Int(Uncertain<IntTy>), /// A primitive floating-point type. For example, `f64`. Float(Uncertain<FloatTy>), /// Structures, enumerations and unions. Adt(AdtId), /// The pointee of a string slice. Written as `str`. Str, /// The pointee of an array slice. Written as `[T]`. Slice, /// An array with the given length. Written as `[T; n]`. Array, /// A raw pointer. Written as `*mut T` or `*const T` RawPtr(Mutability), /// A reference; a pointer with an associated lifetime. Written as /// `&'a mut T` or `&'a T`. Ref(Mutability), /// The anonymous type of a function declaration/definition. Each /// function has a unique type, which is output (for a function /// named `foo` returning an `i32`) as `fn() -> i32 {foo}`. /// /// This includes tuple struct / enum variant constructors as well. /// /// For example the type of `bar` here: /// /// ``` /// fn foo() -> i32 { 1 } /// let bar = foo; // bar: fn() -> i32 {foo} /// ``` FnDef(CallableDef), /// A pointer to a function. Written as `fn() -> i32`. /// /// For example the type of `bar` here: /// /// ``` /// fn foo() -> i32 { 1 } /// let bar: fn() -> i32 = foo; /// ``` FnPtr { num_args: u16 }, /// The never type `!`. Never, /// A tuple type. For example, `(i32, bool)`. Tuple { cardinality: u16 }, /// Represents an associated item like `Iterator::Item`. This is used /// when we have tried to normalize a projection like `T::Item` but /// couldn't find a better representation. In that case, we generate /// an **application type** like `(Iterator::Item)<T>`. AssociatedType(TypeAliasId), /// The type of a specific closure. /// /// The closure signature is stored in a `FnPtr` type in the first type /// parameter. Closure { def: DefWithBodyId, expr: ExprId }, } /// This exists just for Chalk, because Chalk just has a single `StructId` where /// we have different kinds of ADTs, primitive types and special type /// constructors like tuples and function pointers. #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)] pub struct TypeCtorId(salsa::InternId); impl_intern_key!(TypeCtorId); impl TypeCtor { pub fn num_ty_params(self, db: &impl HirDatabase) -> usize { match self { TypeCtor::Bool | TypeCtor::Char | TypeCtor::Int(_) | TypeCtor::Float(_) | TypeCtor::Str | TypeCtor::Never => 0, TypeCtor::Slice | TypeCtor::Array | TypeCtor::RawPtr(_) | TypeCtor::Ref(_) | TypeCtor::Closure { .. } // 1 param representing the signature of the closure => 1, TypeCtor::Adt(adt) => { let generic_params = generics(db, adt.into()); generic_params.len() } TypeCtor::FnDef(callable) => { let generic_params = generics(db, callable.into()); generic_params.len() } TypeCtor::AssociatedType(type_alias) => { let generic_params = generics(db, type_alias.into()); generic_params.len() } TypeCtor::FnPtr { num_args } => num_args as usize + 1, TypeCtor::Tuple { cardinality } => cardinality as usize, } } pub fn krate(self, db: &impl HirDatabase) -> Option<CrateId> { match self { TypeCtor::Bool | TypeCtor::Char | TypeCtor::Int(_) | TypeCtor::Float(_) | TypeCtor::Str | TypeCtor::Never | TypeCtor::Slice | TypeCtor::Array | TypeCtor::RawPtr(_) | TypeCtor::Ref(_) | TypeCtor::FnPtr { .. } | TypeCtor::Tuple { .. } => None, // Closure's krate is irrelevant for coherence I would think? TypeCtor::Closure { .. } => None, TypeCtor::Adt(adt) => Some(adt.module(db).krate), TypeCtor::FnDef(callable) => Some(callable.krate(db)), TypeCtor::AssociatedType(type_alias) => Some(type_alias.lookup(db).module(db).krate), } } pub fn as_generic_def(self) -> Option<GenericDefId> { match self { TypeCtor::Bool | TypeCtor::Char | TypeCtor::Int(_) | TypeCtor::Float(_) | TypeCtor::Str | TypeCtor::Never | TypeCtor::Slice | TypeCtor::Array | TypeCtor::RawPtr(_) | TypeCtor::Ref(_) | TypeCtor::FnPtr { .. } | TypeCtor::Tuple { .. } | TypeCtor::Closure { .. } => None, TypeCtor::Adt(adt) => Some(adt.into()), TypeCtor::FnDef(callable) => Some(callable.into()), TypeCtor::AssociatedType(type_alias) => Some(type_alias.into()), } } } /// A nominal type with (maybe 0) type parameters. This might be a primitive /// type like `bool`, a struct, tuple, function pointer, reference or /// several other things. #[derive(Clone, PartialEq, Eq, Debug, Hash)] pub struct ApplicationTy { pub ctor: TypeCtor, pub parameters: Substs, } /// A "projection" type corresponds to an (unnormalized) /// projection like `<P0 as Trait<P1..Pn>>::Foo`. Note that the /// trait and all its parameters are fully known. #[derive(Clone, PartialEq, Eq, Debug, Hash)] pub struct ProjectionTy { pub associated_ty: TypeAliasId, pub parameters: Substs, } impl ProjectionTy { pub fn trait_ref(&self, db: &impl HirDatabase) -> TraitRef { TraitRef { trait_: self.trait_(db), substs: self.parameters.clone() } } fn trait_(&self, db: &impl HirDatabase) -> TraitId { match self.associated_ty.lookup(db).container { AssocContainerId::TraitId(it) => it, _ => panic!("projection ty without parent trait"), } } } impl TypeWalk for ProjectionTy { fn walk(&self, f: &mut impl FnMut(&Ty)) { self.parameters.walk(f); } fn walk_mut_binders(&mut self, f: &mut impl FnMut(&mut Ty, usize), binders: usize) { self.parameters.walk_mut_binders(f, binders); } } /// A type. /// /// See also the `TyKind` enum in rustc (librustc/ty/sty.rs), which represents /// the same thing (but in a different way). /// /// This should be cheap to clone. #[derive(Clone, PartialEq, Eq, Debug, Hash)] pub enum Ty { /// A nominal type with (maybe 0) type parameters. This might be a primitive /// type like `bool`, a struct, tuple, function pointer, reference or /// several other things. Apply(ApplicationTy), /// A "projection" type corresponds to an (unnormalized) /// projection like `<P0 as Trait<P1..Pn>>::Foo`. Note that the /// trait and all its parameters are fully known. Projection(ProjectionTy), /// A placeholder for a type parameter; for example, `T` in `fn f<T>(x: T) /// {}` when we're type-checking the body of that function. In this /// situation, we know this stands for *some* type, but don't know the exact /// type. Placeholder(TypeParamId), /// A bound type variable. This is used in various places: when representing /// some polymorphic type like the type of function `fn f<T>`, the type /// parameters get turned into variables; during trait resolution, inference /// variables get turned into bound variables and back; and in `Dyn` the /// `Self` type is represented with a bound variable as well. Bound(u32), /// A type variable used during type checking. Infer(InferTy), /// A trait object (`dyn Trait` or bare `Trait` in pre-2018 Rust). /// /// The predicates are quantified over the `Self` type, i.e. `Ty::Bound(0)` /// represents the `Self` type inside the bounds. This is currently /// implicit; Chalk has the `Binders` struct to make it explicit, but it /// didn't seem worth the overhead yet. Dyn(Arc<[GenericPredicate]>), /// An opaque type (`impl Trait`). /// /// The predicates are quantified over the `Self` type; see `Ty::Dyn` for /// more. Opaque(Arc<[GenericPredicate]>), /// A placeholder for a type which could not be computed; this is propagated /// to avoid useless error messages. Doubles as a placeholder where type /// variables are inserted before type checking, since we want to try to /// infer a better type here anyway -- for the IDE use case, we want to try /// to infer as much as possible even in the presence of type errors. Unknown, } /// A list of substitutions for generic parameters. #[derive(Clone, PartialEq, Eq, Debug, Hash)] pub struct Substs(Arc<[Ty]>); impl TypeWalk for Substs { fn walk(&self, f: &mut impl FnMut(&Ty)) { for t in self.0.iter() { t.walk(f); } } fn walk_mut_binders(&mut self, f: &mut impl FnMut(&mut Ty, usize), binders: usize) { for t in make_mut_slice(&mut self.0) { t.walk_mut_binders(f, binders); } } } impl Substs { pub fn empty() -> Substs { Substs(Arc::new([])) } pub fn single(ty: Ty) -> Substs { Substs(Arc::new([ty])) } pub fn prefix(&self, n: usize) -> Substs { Substs(self.0[..std::cmp::min(self.0.len(), n)].into()) } pub fn as_single(&self) -> &Ty { if self.0.len() != 1 { panic!("expected substs of len 1, got {:?}", self); } &self.0[0] } /// Return Substs that replace each parameter by itself (i.e. `Ty::Param`). pub(crate) fn type_params_for_generics(generic_params: &Generics) -> Substs { Substs(generic_params.iter().map(|(id, _)| Ty::Placeholder(id)).collect()) } /// Return Substs that replace each parameter by itself (i.e. `Ty::Param`). pub fn type_params(db: &impl HirDatabase, def: impl Into<GenericDefId>) -> Substs { let params = generics(db, def.into()); Substs::type_params_for_generics(¶ms) } /// Return Substs that replace each parameter by a bound variable. pub(crate) fn bound_vars(generic_params: &Generics) -> Substs { Substs(generic_params.iter().enumerate().map(|(idx, _)| Ty::Bound(idx as u32)).collect()) } pub fn build_for_def(db: &impl HirDatabase, def: impl Into<GenericDefId>) -> SubstsBuilder { let def = def.into(); let params = generics(db, def); let param_count = params.len(); Substs::builder(param_count) } pub(crate) fn build_for_generics(generic_params: &Generics) -> SubstsBuilder { Substs::builder(generic_params.len()) } pub fn build_for_type_ctor(db: &impl HirDatabase, type_ctor: TypeCtor) -> SubstsBuilder { Substs::builder(type_ctor.num_ty_params(db)) } fn builder(param_count: usize) -> SubstsBuilder { SubstsBuilder { vec: Vec::with_capacity(param_count), param_count } } } #[derive(Debug, Clone)] pub struct SubstsBuilder { vec: Vec<Ty>, param_count: usize, } impl SubstsBuilder { pub fn build(self) -> Substs { assert_eq!(self.vec.len(), self.param_count); Substs(self.vec.into()) } pub fn push(mut self, ty: Ty) -> Self { self.vec.push(ty); self } fn remaining(&self) -> usize { self.param_count - self.vec.len() } pub fn fill_with_bound_vars(self, starting_from: u32) -> Self { self.fill((starting_from..).map(Ty::Bound)) } pub fn fill_with_unknown(self) -> Self { self.fill(iter::repeat(Ty::Unknown)) } pub fn fill(mut self, filler: impl Iterator<Item = Ty>) -> Self { self.vec.extend(filler.take(self.remaining())); assert_eq!(self.remaining(), 0); self } pub fn use_parent_substs(mut self, parent_substs: &Substs) -> Self { assert!(self.vec.is_empty()); assert!(parent_substs.len() <= self.param_count); self.vec.extend(parent_substs.iter().cloned()); self } } impl Deref for Substs { type Target = [Ty]; fn deref(&self) -> &[Ty] { &self.0 } } #[derive(Copy, Clone, PartialEq, Eq, Debug)] pub struct Binders<T> { pub num_binders: usize, pub value: T, } impl<T> Binders<T> { pub fn new(num_binders: usize, value: T) -> Self { Self { num_binders, value } } } impl<T: Clone> Binders<&T> { pub fn cloned(&self) -> Binders<T> { Binders { num_binders: self.num_binders, value: self.value.clone() } } } impl<T: TypeWalk> Binders<T> { /// Substitutes all variables. pub fn subst(self, subst: &Substs) -> T { assert_eq!(subst.len(), self.num_binders); self.value.subst_bound_vars(subst) } /// Substitutes just a prefix of the variables (shifting the rest). pub fn subst_prefix(self, subst: &Substs) -> Binders<T> { assert!(subst.len() < self.num_binders); Binders::new(self.num_binders - subst.len(), self.value.subst_bound_vars(subst)) } } /// A trait with type parameters. This includes the `Self`, so this represents a concrete type implementing the trait. /// Name to be bikeshedded: TraitBound? TraitImplements? #[derive(Clone, PartialEq, Eq, Debug, Hash)] pub struct TraitRef { /// FIXME name? pub trait_: TraitId, pub substs: Substs, } impl TraitRef { pub fn self_ty(&self) -> &Ty { &self.substs[0] } } impl TypeWalk for TraitRef { fn walk(&self, f: &mut impl FnMut(&Ty)) { self.substs.walk(f); } fn walk_mut_binders(&mut self, f: &mut impl FnMut(&mut Ty, usize), binders: usize) { self.substs.walk_mut_binders(f, binders); } } /// Like `generics::WherePredicate`, but with resolved types: A condition on the /// parameters of a generic item. #[derive(Debug, Clone, PartialEq, Eq, Hash)] pub enum GenericPredicate { /// The given trait needs to be implemented for its type parameters. Implemented(TraitRef), /// An associated type bindings like in `Iterator<Item = T>`. Projection(ProjectionPredicate), /// We couldn't resolve the trait reference. (If some type parameters can't /// be resolved, they will just be Unknown). Error, } impl GenericPredicate { pub fn is_error(&self) -> bool { match self { GenericPredicate::Error => true, _ => false, } } pub fn is_implemented(&self) -> bool { match self { GenericPredicate::Implemented(_) => true, _ => false, } } pub fn trait_ref(&self, db: &impl HirDatabase) -> Option<TraitRef> { match self { GenericPredicate::Implemented(tr) => Some(tr.clone()), GenericPredicate::Projection(proj) => Some(proj.projection_ty.trait_ref(db)), GenericPredicate::Error => None, } } } impl TypeWalk for GenericPredicate { fn walk(&self, f: &mut impl FnMut(&Ty)) { match self { GenericPredicate::Implemented(trait_ref) => trait_ref.walk(f), GenericPredicate::Projection(projection_pred) => projection_pred.walk(f), GenericPredicate::Error => {} } } fn walk_mut_binders(&mut self, f: &mut impl FnMut(&mut Ty, usize), binders: usize) { match self { GenericPredicate::Implemented(trait_ref) => trait_ref.walk_mut_binders(f, binders), GenericPredicate::Projection(projection_pred) => { projection_pred.walk_mut_binders(f, binders) } GenericPredicate::Error => {} } } } /// Basically a claim (currently not validated / checked) that the contained /// type / trait ref contains no inference variables; any inference variables it /// contained have been replaced by bound variables, and `num_vars` tells us how /// many there are. This is used to erase irrelevant differences between types /// before using them in queries. #[derive(Debug, Clone, PartialEq, Eq, Hash)] pub struct Canonical<T> { pub value: T, pub num_vars: usize, } /// A function signature as seen by type inference: Several parameter types and /// one return type. #[derive(Clone, PartialEq, Eq, Debug)] pub struct FnSig { params_and_return: Arc<[Ty]>, } /// A polymorphic function signature. pub type PolyFnSig = Binders<FnSig>; impl FnSig { pub fn from_params_and_return(mut params: Vec<Ty>, ret: Ty) -> FnSig { params.push(ret); FnSig { params_and_return: params.into() } } pub fn from_fn_ptr_substs(substs: &Substs) -> FnSig { FnSig { params_and_return: Arc::clone(&substs.0) } } pub fn params(&self) -> &[Ty] { &self.params_and_return[0..self.params_and_return.len() - 1] } pub fn ret(&self) -> &Ty { &self.params_and_return[self.params_and_return.len() - 1] } } impl TypeWalk for FnSig { fn walk(&self, f: &mut impl FnMut(&Ty)) { for t in self.params_and_return.iter() { t.walk(f); } } fn walk_mut_binders(&mut self, f: &mut impl FnMut(&mut Ty, usize), binders: usize) { for t in make_mut_slice(&mut self.params_and_return) { t.walk_mut_binders(f, binders); } } } impl Ty { pub fn simple(ctor: TypeCtor) -> Ty { Ty::Apply(ApplicationTy { ctor, parameters: Substs::empty() }) } pub fn apply_one(ctor: TypeCtor, param: Ty) -> Ty { Ty::Apply(ApplicationTy { ctor, parameters: Substs::single(param) }) } pub fn apply(ctor: TypeCtor, parameters: Substs) -> Ty { Ty::Apply(ApplicationTy { ctor, parameters }) } pub fn unit() -> Self { Ty::apply(TypeCtor::Tuple { cardinality: 0 }, Substs::empty()) } pub fn as_reference(&self) -> Option<(&Ty, Mutability)> { match self { Ty::Apply(ApplicationTy { ctor: TypeCtor::Ref(mutability), parameters }) => { Some((parameters.as_single(), *mutability)) } _ => None, } } pub fn as_adt(&self) -> Option<(AdtId, &Substs)> { match self { Ty::Apply(ApplicationTy { ctor: TypeCtor::Adt(adt_def), parameters }) => { Some((*adt_def, parameters)) } _ => None, } } pub fn as_tuple(&self) -> Option<&Substs> { match self { Ty::Apply(ApplicationTy { ctor: TypeCtor::Tuple { .. }, parameters }) => { Some(parameters) } _ => None, } } pub fn as_callable(&self) -> Option<(CallableDef, &Substs)> { match self { Ty::Apply(ApplicationTy { ctor: TypeCtor::FnDef(callable_def), parameters }) => { Some((*callable_def, parameters)) } _ => None, } } /// If this is a `dyn Trait` type, this returns the `Trait` part. pub fn dyn_trait_ref(&self) -> Option<&TraitRef> { match self { Ty::Dyn(bounds) => bounds.get(0).and_then(|b| match b { GenericPredicate::Implemented(trait_ref) => Some(trait_ref), _ => None, }), _ => None, } } fn builtin_deref(&self) -> Option<Ty> { match self { Ty::Apply(a_ty) => match a_ty.ctor { TypeCtor::Ref(..) => Some(Ty::clone(a_ty.parameters.as_single())), TypeCtor::RawPtr(..) => Some(Ty::clone(a_ty.parameters.as_single())), _ => None, }, _ => None, } } fn callable_sig(&self, db: &impl HirDatabase) -> Option<FnSig> { match self { Ty::Apply(a_ty) => match a_ty.ctor { TypeCtor::FnPtr { .. } => Some(FnSig::from_fn_ptr_substs(&a_ty.parameters)), TypeCtor::FnDef(def) => { let sig = db.callable_item_signature(def); Some(sig.subst(&a_ty.parameters)) } TypeCtor::Closure { .. } => { let sig_param = &a_ty.parameters[0]; sig_param.callable_sig(db) } _ => None, }, _ => None, } } /// If this is a type with type parameters (an ADT or function), replaces /// the `Substs` for these type parameters with the given ones. (So e.g. if /// `self` is `Option<_>` and the substs contain `u32`, we'll have /// `Option<u32>` afterwards.) pub fn apply_substs(self, substs: Substs) -> Ty { match self { Ty::Apply(ApplicationTy { ctor, parameters: previous_substs }) => { assert_eq!(previous_substs.len(), substs.len()); Ty::Apply(ApplicationTy { ctor, parameters: substs }) } _ => self, } } /// Returns the type parameters of this type if it has some (i.e. is an ADT /// or function); so if `self` is `Option<u32>`, this returns the `u32`. pub fn substs(&self) -> Option<Substs> { match self { Ty::Apply(ApplicationTy { parameters, .. }) => Some(parameters.clone()), _ => None, } } /// If this is an `impl Trait` or `dyn Trait`, returns that trait. pub fn inherent_trait(&self) -> Option<TraitId> { match self { Ty::Dyn(predicates) | Ty::Opaque(predicates) => { predicates.iter().find_map(|pred| match pred { GenericPredicate::Implemented(tr) => Some(tr.trait_), _ => None, }) } _ => None, } } } /// This allows walking structures that contain types to do something with those /// types, similar to Chalk's `Fold` trait. pub trait TypeWalk { fn walk(&self, f: &mut impl FnMut(&Ty)); fn walk_mut(&mut self, f: &mut impl FnMut(&mut Ty)) { self.walk_mut_binders(&mut |ty, _binders| f(ty), 0); } /// Walk the type, counting entered binders. /// /// `Ty::Bound` variables use DeBruijn indexing, which means that 0 refers /// to the innermost binder, 1 to the next, etc.. So when we want to /// substitute a certain bound variable, we can't just walk the whole type /// and blindly replace each instance of a certain index; when we 'enter' /// things that introduce new bound variables, we have to keep track of /// that. Currently, the only thing that introduces bound variables on our /// side are `Ty::Dyn` and `Ty::Opaque`, which each introduce a bound /// variable for the self type. fn walk_mut_binders(&mut self, f: &mut impl FnMut(&mut Ty, usize), binders: usize); fn fold_binders(mut self, f: &mut impl FnMut(Ty, usize) -> Ty, binders: usize) -> Self where Self: Sized, { self.walk_mut_binders( &mut |ty_mut, binders| { let ty = mem::replace(ty_mut, Ty::Unknown); *ty_mut = f(ty, binders); }, binders, ); self } fn fold(mut self, f: &mut impl FnMut(Ty) -> Ty) -> Self where Self: Sized, { self.walk_mut(&mut |ty_mut| { let ty = mem::replace(ty_mut, Ty::Unknown); *ty_mut = f(ty); }); self } /// Substitutes `Ty::Bound` vars with the given substitution. fn subst_bound_vars(mut self, substs: &Substs) -> Self where Self: Sized, { self.walk_mut_binders( &mut |ty, binders| { if let &mut Ty::Bound(idx) = ty { if idx as usize >= binders && (idx as usize - binders) < substs.len() { *ty = substs.0[idx as usize - binders].clone(); } else if idx as usize >= binders + substs.len() { // shift free binders *ty = Ty::Bound(idx - substs.len() as u32); } } }, 0, ); self } /// Shifts up `Ty::Bound` vars by `n`. fn shift_bound_vars(self, n: i32) -> Self where Self: Sized, { self.fold_binders( &mut |ty, binders| match ty { Ty::Bound(idx) if idx as usize >= binders => { assert!(idx as i32 >= -n); Ty::Bound((idx as i32 + n) as u32) } ty => ty, }, 0, ) } } impl TypeWalk for Ty { fn walk(&self, f: &mut impl FnMut(&Ty)) { match self { Ty::Apply(a_ty) => { for t in a_ty.parameters.iter() { t.walk(f); } } Ty::Projection(p_ty) => { for t in p_ty.parameters.iter() { t.walk(f); } } Ty::Dyn(predicates) | Ty::Opaque(predicates) => { for p in predicates.iter() { p.walk(f); } } Ty::Placeholder { .. } | Ty::Bound(_) | Ty::Infer(_) | Ty::Unknown => {} } f(self); } fn walk_mut_binders(&mut self, f: &mut impl FnMut(&mut Ty, usize), binders: usize) { match self { Ty::Apply(a_ty) => { a_ty.parameters.walk_mut_binders(f, binders); } Ty::Projection(p_ty) => { p_ty.parameters.walk_mut_binders(f, binders); } Ty::Dyn(predicates) | Ty::Opaque(predicates) => { for p in make_mut_slice(predicates) { p.walk_mut_binders(f, binders + 1); } } Ty::Placeholder { .. } | Ty::Bound(_) | Ty::Infer(_) | Ty::Unknown => {} } f(self, binders); } }