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Diffstat (limited to 'compiler/rustc_middle/src/ty/subst.rs')
| -rw-r--r-- | compiler/rustc_middle/src/ty/subst.rs | 687 |
1 files changed, 687 insertions, 0 deletions
diff --git a/compiler/rustc_middle/src/ty/subst.rs b/compiler/rustc_middle/src/ty/subst.rs new file mode 100644 index 00000000000..acd58ab7f96 --- /dev/null +++ b/compiler/rustc_middle/src/ty/subst.rs @@ -0,0 +1,687 @@ +// Type substitutions. + +use crate::infer::canonical::Canonical; +use crate::ty::codec::{TyDecoder, TyEncoder}; +use crate::ty::fold::{TypeFoldable, TypeFolder, TypeVisitor}; +use crate::ty::sty::{ClosureSubsts, GeneratorSubsts}; +use crate::ty::{self, Lift, List, ParamConst, Ty, TyCtxt}; + +use rustc_hir::def_id::DefId; +use rustc_macros::HashStable; +use rustc_serialize::{self, Decodable, Encodable}; +use rustc_span::{Span, DUMMY_SP}; +use smallvec::SmallVec; + +use core::intrinsics; +use std::cmp::Ordering; +use std::fmt; +use std::marker::PhantomData; +use std::mem; +use std::num::NonZeroUsize; + +/// An entity in the Rust type system, which can be one of +/// several kinds (types, lifetimes, and consts). +/// To reduce memory usage, a `GenericArg` is a interned pointer, +/// with the lowest 2 bits being reserved for a tag to +/// indicate the type (`Ty`, `Region`, or `Const`) it points to. +#[derive(Copy, Clone, PartialEq, Eq, Hash)] +pub struct GenericArg<'tcx> { + ptr: NonZeroUsize, + marker: PhantomData<(Ty<'tcx>, ty::Region<'tcx>, &'tcx ty::Const<'tcx>)>, +} + +const TAG_MASK: usize = 0b11; +const TYPE_TAG: usize = 0b00; +const REGION_TAG: usize = 0b01; +const CONST_TAG: usize = 0b10; + +#[derive(Debug, TyEncodable, TyDecodable, PartialEq, Eq, PartialOrd, Ord, HashStable)] +pub enum GenericArgKind<'tcx> { + Lifetime(ty::Region<'tcx>), + Type(Ty<'tcx>), + Const(&'tcx ty::Const<'tcx>), +} + +impl<'tcx> GenericArgKind<'tcx> { + fn pack(self) -> GenericArg<'tcx> { + let (tag, ptr) = match self { + GenericArgKind::Lifetime(lt) => { + // Ensure we can use the tag bits. + assert_eq!(mem::align_of_val(lt) & TAG_MASK, 0); + (REGION_TAG, lt as *const _ as usize) + } + GenericArgKind::Type(ty) => { + // Ensure we can use the tag bits. + assert_eq!(mem::align_of_val(ty) & TAG_MASK, 0); + (TYPE_TAG, ty as *const _ as usize) + } + GenericArgKind::Const(ct) => { + // Ensure we can use the tag bits. + assert_eq!(mem::align_of_val(ct) & TAG_MASK, 0); + (CONST_TAG, ct as *const _ as usize) + } + }; + + GenericArg { ptr: unsafe { NonZeroUsize::new_unchecked(ptr | tag) }, marker: PhantomData } + } +} + +impl fmt::Debug for GenericArg<'tcx> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + match self.unpack() { + GenericArgKind::Lifetime(lt) => lt.fmt(f), + GenericArgKind::Type(ty) => ty.fmt(f), + GenericArgKind::Const(ct) => ct.fmt(f), + } + } +} + +impl<'tcx> Ord for GenericArg<'tcx> { + fn cmp(&self, other: &GenericArg<'_>) -> Ordering { + self.unpack().cmp(&other.unpack()) + } +} + +impl<'tcx> PartialOrd for GenericArg<'tcx> { + fn partial_cmp(&self, other: &GenericArg<'_>) -> Option<Ordering> { + Some(self.cmp(&other)) + } +} + +impl<'tcx> From<ty::Region<'tcx>> for GenericArg<'tcx> { + fn from(r: ty::Region<'tcx>) -> GenericArg<'tcx> { + GenericArgKind::Lifetime(r).pack() + } +} + +impl<'tcx> From<Ty<'tcx>> for GenericArg<'tcx> { + fn from(ty: Ty<'tcx>) -> GenericArg<'tcx> { + GenericArgKind::Type(ty).pack() + } +} + +impl<'tcx> From<&'tcx ty::Const<'tcx>> for GenericArg<'tcx> { + fn from(c: &'tcx ty::Const<'tcx>) -> GenericArg<'tcx> { + GenericArgKind::Const(c).pack() + } +} + +impl<'tcx> GenericArg<'tcx> { + #[inline] + pub fn unpack(self) -> GenericArgKind<'tcx> { + let ptr = self.ptr.get(); + unsafe { + match ptr & TAG_MASK { + REGION_TAG => GenericArgKind::Lifetime(&*((ptr & !TAG_MASK) as *const _)), + TYPE_TAG => GenericArgKind::Type(&*((ptr & !TAG_MASK) as *const _)), + CONST_TAG => GenericArgKind::Const(&*((ptr & !TAG_MASK) as *const _)), + _ => intrinsics::unreachable(), + } + } + } + + /// Unpack the `GenericArg` as a type when it is known certainly to be a type. + /// This is true in cases where `Substs` is used in places where the kinds are known + /// to be limited (e.g. in tuples, where the only parameters are type parameters). + pub fn expect_ty(self) -> Ty<'tcx> { + match self.unpack() { + GenericArgKind::Type(ty) => ty, + _ => bug!("expected a type, but found another kind"), + } + } + + /// Unpack the `GenericArg` as a const when it is known certainly to be a const. + pub fn expect_const(self) -> &'tcx ty::Const<'tcx> { + match self.unpack() { + GenericArgKind::Const(c) => c, + _ => bug!("expected a const, but found another kind"), + } + } +} + +impl<'a, 'tcx> Lift<'tcx> for GenericArg<'a> { + type Lifted = GenericArg<'tcx>; + + fn lift_to_tcx(&self, tcx: TyCtxt<'tcx>) -> Option<Self::Lifted> { + match self.unpack() { + GenericArgKind::Lifetime(lt) => tcx.lift(<).map(|lt| lt.into()), + GenericArgKind::Type(ty) => tcx.lift(&ty).map(|ty| ty.into()), + GenericArgKind::Const(ct) => tcx.lift(&ct).map(|ct| ct.into()), + } + } +} + +impl<'tcx> TypeFoldable<'tcx> for GenericArg<'tcx> { + fn super_fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Self { + match self.unpack() { + GenericArgKind::Lifetime(lt) => lt.fold_with(folder).into(), + GenericArgKind::Type(ty) => ty.fold_with(folder).into(), + GenericArgKind::Const(ct) => ct.fold_with(folder).into(), + } + } + + fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool { + match self.unpack() { + GenericArgKind::Lifetime(lt) => lt.visit_with(visitor), + GenericArgKind::Type(ty) => ty.visit_with(visitor), + GenericArgKind::Const(ct) => ct.visit_with(visitor), + } + } +} + +impl<'tcx, E: TyEncoder<'tcx>> Encodable<E> for GenericArg<'tcx> { + fn encode(&self, e: &mut E) -> Result<(), E::Error> { + self.unpack().encode(e) + } +} + +impl<'tcx, D: TyDecoder<'tcx>> Decodable<D> for GenericArg<'tcx> { + fn decode(d: &mut D) -> Result<GenericArg<'tcx>, D::Error> { + Ok(GenericArgKind::decode(d)?.pack()) + } +} + +/// A substitution mapping generic parameters to new values. +pub type InternalSubsts<'tcx> = List<GenericArg<'tcx>>; + +pub type SubstsRef<'tcx> = &'tcx InternalSubsts<'tcx>; + +impl<'a, 'tcx> InternalSubsts<'tcx> { + /// Interpret these substitutions as the substitutions of a closure type. + /// Closure substitutions have a particular structure controlled by the + /// compiler that encodes information like the signature and closure kind; + /// see `ty::ClosureSubsts` struct for more comments. + pub fn as_closure(&'a self) -> ClosureSubsts<'a> { + ClosureSubsts { substs: self } + } + + /// Interpret these substitutions as the substitutions of a generator type. + /// Closure substitutions have a particular structure controlled by the + /// compiler that encodes information like the signature and generator kind; + /// see `ty::GeneratorSubsts` struct for more comments. + pub fn as_generator(&'tcx self) -> GeneratorSubsts<'tcx> { + GeneratorSubsts { substs: self } + } + + /// Creates a `InternalSubsts` that maps each generic parameter to itself. + pub fn identity_for_item(tcx: TyCtxt<'tcx>, def_id: DefId) -> SubstsRef<'tcx> { + Self::for_item(tcx, def_id, |param, _| tcx.mk_param_from_def(param)) + } + + /// Creates a `InternalSubsts` for generic parameter definitions, + /// by calling closures to obtain each kind. + /// The closures get to observe the `InternalSubsts` as they're + /// being built, which can be used to correctly + /// substitute defaults of generic parameters. + pub fn for_item<F>(tcx: TyCtxt<'tcx>, def_id: DefId, mut mk_kind: F) -> SubstsRef<'tcx> + where + F: FnMut(&ty::GenericParamDef, &[GenericArg<'tcx>]) -> GenericArg<'tcx>, + { + let defs = tcx.generics_of(def_id); + let count = defs.count(); + let mut substs = SmallVec::with_capacity(count); + Self::fill_item(&mut substs, tcx, defs, &mut mk_kind); + tcx.intern_substs(&substs) + } + + pub fn extend_to<F>(&self, tcx: TyCtxt<'tcx>, def_id: DefId, mut mk_kind: F) -> SubstsRef<'tcx> + where + F: FnMut(&ty::GenericParamDef, &[GenericArg<'tcx>]) -> GenericArg<'tcx>, + { + Self::for_item(tcx, def_id, |param, substs| { + self.get(param.index as usize).cloned().unwrap_or_else(|| mk_kind(param, substs)) + }) + } + + fn fill_item<F>( + substs: &mut SmallVec<[GenericArg<'tcx>; 8]>, + tcx: TyCtxt<'tcx>, + defs: &ty::Generics, + mk_kind: &mut F, + ) where + F: FnMut(&ty::GenericParamDef, &[GenericArg<'tcx>]) -> GenericArg<'tcx>, + { + if let Some(def_id) = defs.parent { + let parent_defs = tcx.generics_of(def_id); + Self::fill_item(substs, tcx, parent_defs, mk_kind); + } + Self::fill_single(substs, defs, mk_kind) + } + + fn fill_single<F>( + substs: &mut SmallVec<[GenericArg<'tcx>; 8]>, + defs: &ty::Generics, + mk_kind: &mut F, + ) where + F: FnMut(&ty::GenericParamDef, &[GenericArg<'tcx>]) -> GenericArg<'tcx>, + { + substs.reserve(defs.params.len()); + for param in &defs.params { + let kind = mk_kind(param, substs); + assert_eq!(param.index as usize, substs.len()); + substs.push(kind); + } + } + + pub fn is_noop(&self) -> bool { + self.is_empty() + } + + #[inline] + pub fn types(&'a self) -> impl DoubleEndedIterator<Item = Ty<'tcx>> + 'a { + self.iter() + .filter_map(|k| if let GenericArgKind::Type(ty) = k.unpack() { Some(ty) } else { None }) + } + + #[inline] + pub fn regions(&'a self) -> impl DoubleEndedIterator<Item = ty::Region<'tcx>> + 'a { + self.iter().filter_map(|k| { + if let GenericArgKind::Lifetime(lt) = k.unpack() { Some(lt) } else { None } + }) + } + + #[inline] + pub fn consts(&'a self) -> impl DoubleEndedIterator<Item = &'tcx ty::Const<'tcx>> + 'a { + self.iter().filter_map(|k| { + if let GenericArgKind::Const(ct) = k.unpack() { Some(ct) } else { None } + }) + } + + #[inline] + pub fn non_erasable_generics( + &'a self, + ) -> impl DoubleEndedIterator<Item = GenericArgKind<'tcx>> + 'a { + self.iter().filter_map(|k| match k.unpack() { + GenericArgKind::Lifetime(_) => None, + generic => Some(generic), + }) + } + + #[inline] + pub fn type_at(&self, i: usize) -> Ty<'tcx> { + if let GenericArgKind::Type(ty) = self[i].unpack() { + ty + } else { + bug!("expected type for param #{} in {:?}", i, self); + } + } + + #[inline] + pub fn region_at(&self, i: usize) -> ty::Region<'tcx> { + if let GenericArgKind::Lifetime(lt) = self[i].unpack() { + lt + } else { + bug!("expected region for param #{} in {:?}", i, self); + } + } + + #[inline] + pub fn const_at(&self, i: usize) -> &'tcx ty::Const<'tcx> { + if let GenericArgKind::Const(ct) = self[i].unpack() { + ct + } else { + bug!("expected const for param #{} in {:?}", i, self); + } + } + + #[inline] + pub fn type_for_def(&self, def: &ty::GenericParamDef) -> GenericArg<'tcx> { + self.type_at(def.index as usize).into() + } + + /// Transform from substitutions for a child of `source_ancestor` + /// (e.g., a trait or impl) to substitutions for the same child + /// in a different item, with `target_substs` as the base for + /// the target impl/trait, with the source child-specific + /// parameters (e.g., method parameters) on top of that base. + /// + /// For example given: + /// + /// ```no_run + /// trait X<S> { fn f<T>(); } + /// impl<U> X<U> for U { fn f<V>() {} } + /// ``` + /// + /// * If `self` is `[Self, S, T]`: the identity substs of `f` in the trait. + /// * If `source_ancestor` is the def_id of the trait. + /// * If `target_substs` is `[U]`, the substs for the impl. + /// * Then we will return `[U, T]`, the subst for `f` in the impl that + /// are needed for it to match the trait. + pub fn rebase_onto( + &self, + tcx: TyCtxt<'tcx>, + source_ancestor: DefId, + target_substs: SubstsRef<'tcx>, + ) -> SubstsRef<'tcx> { + let defs = tcx.generics_of(source_ancestor); + tcx.mk_substs(target_substs.iter().chain(self.iter().skip(defs.params.len()))) + } + + pub fn truncate_to(&self, tcx: TyCtxt<'tcx>, generics: &ty::Generics) -> SubstsRef<'tcx> { + tcx.mk_substs(self.iter().take(generics.count())) + } +} + +impl<'tcx> TypeFoldable<'tcx> for SubstsRef<'tcx> { + fn super_fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Self { + // This code is hot enough that it's worth specializing for the most + // common length lists, to avoid the overhead of `SmallVec` creation. + // The match arms are in order of frequency. The 1, 2, and 0 cases are + // typically hit in 90--99.99% of cases. When folding doesn't change + // the substs, it's faster to reuse the existing substs rather than + // calling `intern_substs`. + match self.len() { + 1 => { + let param0 = self[0].fold_with(folder); + if param0 == self[0] { self } else { folder.tcx().intern_substs(&[param0]) } + } + 2 => { + let param0 = self[0].fold_with(folder); + let param1 = self[1].fold_with(folder); + if param0 == self[0] && param1 == self[1] { + self + } else { + folder.tcx().intern_substs(&[param0, param1]) + } + } + 0 => self, + _ => { + let params: SmallVec<[_; 8]> = self.iter().map(|k| k.fold_with(folder)).collect(); + if params[..] == self[..] { self } else { folder.tcx().intern_substs(¶ms) } + } + } + } + + fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool { + self.iter().any(|t| t.visit_with(visitor)) + } +} + +/////////////////////////////////////////////////////////////////////////// +// Public trait `Subst` +// +// Just call `foo.subst(tcx, substs)` to perform a substitution across +// `foo`. Or use `foo.subst_spanned(tcx, substs, Some(span))` when +// there is more information available (for better errors). + +pub trait Subst<'tcx>: Sized { + fn subst(&self, tcx: TyCtxt<'tcx>, substs: &[GenericArg<'tcx>]) -> Self { + self.subst_spanned(tcx, substs, None) + } + + fn subst_spanned( + &self, + tcx: TyCtxt<'tcx>, + substs: &[GenericArg<'tcx>], + span: Option<Span>, + ) -> Self; +} + +impl<'tcx, T: TypeFoldable<'tcx>> Subst<'tcx> for T { + fn subst_spanned( + &self, + tcx: TyCtxt<'tcx>, + substs: &[GenericArg<'tcx>], + span: Option<Span>, + ) -> T { + let mut folder = SubstFolder { tcx, substs, span, binders_passed: 0 }; + (*self).fold_with(&mut folder) + } +} + +/////////////////////////////////////////////////////////////////////////// +// The actual substitution engine itself is a type folder. + +struct SubstFolder<'a, 'tcx> { + tcx: TyCtxt<'tcx>, + substs: &'a [GenericArg<'tcx>], + + /// The location for which the substitution is performed, if available. + span: Option<Span>, + + /// Number of region binders we have passed through while doing the substitution + binders_passed: u32, +} + +impl<'a, 'tcx> TypeFolder<'tcx> for SubstFolder<'a, 'tcx> { + fn tcx<'b>(&'b self) -> TyCtxt<'tcx> { + self.tcx + } + + fn fold_binder<T: TypeFoldable<'tcx>>(&mut self, t: &ty::Binder<T>) -> ty::Binder<T> { + self.binders_passed += 1; + let t = t.super_fold_with(self); + self.binders_passed -= 1; + t + } + + fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> { + // Note: This routine only handles regions that are bound on + // type declarations and other outer declarations, not those + // bound in *fn types*. Region substitution of the bound + // regions that appear in a function signature is done using + // the specialized routine `ty::replace_late_regions()`. + match *r { + ty::ReEarlyBound(data) => { + let rk = self.substs.get(data.index as usize).map(|k| k.unpack()); + match rk { + Some(GenericArgKind::Lifetime(lt)) => self.shift_region_through_binders(lt), + _ => { + let span = self.span.unwrap_or(DUMMY_SP); + let msg = format!( + "Region parameter out of range \ + when substituting in region {} (index={})", + data.name, data.index + ); + span_bug!(span, "{}", msg); + } + } + } + _ => r, + } + } + + fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> { + if !t.needs_subst() { + return t; + } + + match t.kind { + ty::Param(p) => self.ty_for_param(p, t), + _ => t.super_fold_with(self), + } + } + + fn fold_const(&mut self, c: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> { + if !c.needs_subst() { + return c; + } + + if let ty::ConstKind::Param(p) = c.val { + self.const_for_param(p, c) + } else { + c.super_fold_with(self) + } + } +} + +impl<'a, 'tcx> SubstFolder<'a, 'tcx> { + fn ty_for_param(&self, p: ty::ParamTy, source_ty: Ty<'tcx>) -> Ty<'tcx> { + // Look up the type in the substitutions. It really should be in there. + let opt_ty = self.substs.get(p.index as usize).map(|k| k.unpack()); + let ty = match opt_ty { + Some(GenericArgKind::Type(ty)) => ty, + Some(kind) => { + let span = self.span.unwrap_or(DUMMY_SP); + span_bug!( + span, + "expected type for `{:?}` ({:?}/{}) but found {:?} \ + when substituting, substs={:?}", + p, + source_ty, + p.index, + kind, + self.substs, + ); + } + None => { + let span = self.span.unwrap_or(DUMMY_SP); + span_bug!( + span, + "type parameter `{:?}` ({:?}/{}) out of range \ + when substituting, substs={:?}", + p, + source_ty, + p.index, + self.substs, + ); + } + }; + + self.shift_vars_through_binders(ty) + } + + fn const_for_param( + &self, + p: ParamConst, + source_ct: &'tcx ty::Const<'tcx>, + ) -> &'tcx ty::Const<'tcx> { + // Look up the const in the substitutions. It really should be in there. + let opt_ct = self.substs.get(p.index as usize).map(|k| k.unpack()); + let ct = match opt_ct { + Some(GenericArgKind::Const(ct)) => ct, + Some(kind) => { + let span = self.span.unwrap_or(DUMMY_SP); + span_bug!( + span, + "expected const for `{:?}` ({:?}/{}) but found {:?} \ + when substituting substs={:?}", + p, + source_ct, + p.index, + kind, + self.substs, + ); + } + None => { + let span = self.span.unwrap_or(DUMMY_SP); + span_bug!( + span, + "const parameter `{:?}` ({:?}/{}) out of range \ + when substituting substs={:?}", + p, + source_ct, + p.index, + self.substs, + ); + } + }; + + self.shift_vars_through_binders(ct) + } + + /// It is sometimes necessary to adjust the De Bruijn indices during substitution. This occurs + /// when we are substituting a type with escaping bound vars into a context where we have + /// passed through binders. That's quite a mouthful. Let's see an example: + /// + /// ``` + /// type Func<A> = fn(A); + /// type MetaFunc = for<'a> fn(Func<&'a i32>) + /// ``` + /// + /// The type `MetaFunc`, when fully expanded, will be + /// + /// for<'a> fn(fn(&'a i32)) + /// ^~ ^~ ^~~ + /// | | | + /// | | DebruijnIndex of 2 + /// Binders + /// + /// Here the `'a` lifetime is bound in the outer function, but appears as an argument of the + /// inner one. Therefore, that appearance will have a DebruijnIndex of 2, because we must skip + /// over the inner binder (remember that we count De Bruijn indices from 1). However, in the + /// definition of `MetaFunc`, the binder is not visible, so the type `&'a i32` will have a + /// De Bruijn index of 1. It's only during the substitution that we can see we must increase the + /// depth by 1 to account for the binder that we passed through. + /// + /// As a second example, consider this twist: + /// + /// ``` + /// type FuncTuple<A> = (A,fn(A)); + /// type MetaFuncTuple = for<'a> fn(FuncTuple<&'a i32>) + /// ``` + /// + /// Here the final type will be: + /// + /// for<'a> fn((&'a i32, fn(&'a i32))) + /// ^~~ ^~~ + /// | | + /// DebruijnIndex of 1 | + /// DebruijnIndex of 2 + /// + /// As indicated in the diagram, here the same type `&'a i32` is substituted once, but in the + /// first case we do not increase the De Bruijn index and in the second case we do. The reason + /// is that only in the second case have we passed through a fn binder. + fn shift_vars_through_binders<T: TypeFoldable<'tcx>>(&self, val: T) -> T { + debug!( + "shift_vars(val={:?}, binders_passed={:?}, has_escaping_bound_vars={:?})", + val, + self.binders_passed, + val.has_escaping_bound_vars() + ); + + if self.binders_passed == 0 || !val.has_escaping_bound_vars() { + return val; + } + + let result = ty::fold::shift_vars(self.tcx(), &val, self.binders_passed); + debug!("shift_vars: shifted result = {:?}", result); + + result + } + + fn shift_region_through_binders(&self, region: ty::Region<'tcx>) -> ty::Region<'tcx> { + if self.binders_passed == 0 || !region.has_escaping_bound_vars() { + return region; + } + ty::fold::shift_region(self.tcx, region, self.binders_passed) + } +} + +pub type CanonicalUserSubsts<'tcx> = Canonical<'tcx, UserSubsts<'tcx>>; + +/// Stores the user-given substs to reach some fully qualified path +/// (e.g., `<T>::Item` or `<T as Trait>::Item`). +#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, TyEncodable, TyDecodable)] +#[derive(HashStable, TypeFoldable, Lift)] +pub struct UserSubsts<'tcx> { + /// The substitutions for the item as given by the user. + pub substs: SubstsRef<'tcx>, + + /// The self type, in the case of a `<T>::Item` path (when applied + /// to an inherent impl). See `UserSelfTy` below. + pub user_self_ty: Option<UserSelfTy<'tcx>>, +} + +/// Specifies the user-given self type. In the case of a path that +/// refers to a member in an inherent impl, this self type is +/// sometimes needed to constrain the type parameters on the impl. For +/// example, in this code: +/// +/// ``` +/// struct Foo<T> { } +/// impl<A> Foo<A> { fn method() { } } +/// ``` +/// +/// when you then have a path like `<Foo<&'static u32>>::method`, +/// this struct would carry the `DefId` of the impl along with the +/// self type `Foo<u32>`. Then we can instantiate the parameters of +/// the impl (with the substs from `UserSubsts`) and apply those to +/// the self type, giving `Foo<?A>`. Finally, we unify that with +/// the self type here, which contains `?A` to be `&'static u32` +#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, TyEncodable, TyDecodable)] +#[derive(HashStable, TypeFoldable, Lift)] +pub struct UserSelfTy<'tcx> { + pub impl_def_id: DefId, + pub self_ty: Ty<'tcx>, +} |