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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-17 12:02:58 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-17 12:02:58 +0000 |
commit | 698f8c2f01ea549d77d7dc3338a12e04c11057b9 (patch) | |
tree | 173a775858bd501c378080a10dca74132f05bc50 /compiler/rustc_middle/src/ty/subst.rs | |
parent | Initial commit. (diff) | |
download | rustc-698f8c2f01ea549d77d7dc3338a12e04c11057b9.tar.xz rustc-698f8c2f01ea549d77d7dc3338a12e04c11057b9.zip |
Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'compiler/rustc_middle/src/ty/subst.rs')
-rw-r--r-- | compiler/rustc_middle/src/ty/subst.rs | 785 |
1 files changed, 785 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 000000000..6262aa180 --- /dev/null +++ b/compiler/rustc_middle/src/ty/subst.rs @@ -0,0 +1,785 @@ +// Type substitutions. + +use crate::mir; +use crate::ty::codec::{TyDecoder, TyEncoder}; +use crate::ty::fold::{FallibleTypeFolder, TypeFoldable, TypeFolder, TypeSuperFoldable}; +use crate::ty::sty::{ClosureSubsts, GeneratorSubsts, InlineConstSubsts}; +use crate::ty::visit::{TypeVisitable, TypeVisitor}; +use crate::ty::{self, Lift, List, ParamConst, Ty, TyCtxt}; + +use rustc_data_structures::intern::{Interned, WithStableHash}; +use rustc_hir::def_id::DefId; +use rustc_macros::HashStable; +use rustc_serialize::{self, Decodable, Encodable}; +use smallvec::SmallVec; + +use core::intrinsics; +use std::cmp::Ordering; +use std::fmt; +use std::marker::PhantomData; +use std::mem; +use std::num::NonZeroUsize; +use std::ops::ControlFlow; +use std::slice; + +/// 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 an interned pointer, +/// with the lowest 2 bits being reserved for a tag to +/// indicate the type (`Ty`, `Region`, or `Const`) it points to. +/// +/// Note: the `PartialEq`, `Eq` and `Hash` derives are only valid because `Ty`, +/// `Region` and `Const` are all interned. +#[derive(Copy, Clone, PartialEq, Eq, Hash)] +pub struct GenericArg<'tcx> { + ptr: NonZeroUsize, + marker: PhantomData<(Ty<'tcx>, ty::Region<'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)] +pub enum GenericArgKind<'tcx> { + Lifetime(ty::Region<'tcx>), + Type(Ty<'tcx>), + Const(ty::Const<'tcx>), +} + +/// This function goes from `&'a [Ty<'tcx>]` to `&'a [GenericArg<'tcx>]` +/// +/// This is sound as, for types, `GenericArg` is just +/// `NonZeroUsize::new_unchecked(ty as *const _ as usize)` as +/// long as we use `0` for the `TYPE_TAG`. +pub fn ty_slice_as_generic_args<'a, 'tcx>(ts: &'a [Ty<'tcx>]) -> &'a [GenericArg<'tcx>] { + assert_eq!(TYPE_TAG, 0); + // SAFETY: the whole slice is valid and immutable. + // `Ty` and `GenericArg` is explained above. + unsafe { slice::from_raw_parts(ts.as_ptr().cast(), ts.len()) } +} + +impl<'tcx> List<Ty<'tcx>> { + /// Allows to freely switch between `List<Ty<'tcx>>` and `List<GenericArg<'tcx>>`. + /// + /// As lists are interned, `List<Ty<'tcx>>` and `List<GenericArg<'tcx>>` have + /// be interned together, see `intern_type_list` for more details. + #[inline] + pub fn as_substs(&'tcx self) -> SubstsRef<'tcx> { + assert_eq!(TYPE_TAG, 0); + // SAFETY: `List<T>` is `#[repr(C)]`. `Ty` and `GenericArg` is explained above. + unsafe { &*(self as *const List<Ty<'tcx>> as *const List<GenericArg<'tcx>>) } + } +} + +impl<'tcx> GenericArgKind<'tcx> { + #[inline] + 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.0.0) & TAG_MASK, 0); + (REGION_TAG, lt.0.0 as *const ty::RegionKind<'tcx> as usize) + } + GenericArgKind::Type(ty) => { + // Ensure we can use the tag bits. + assert_eq!(mem::align_of_val(&*ty.0.0) & TAG_MASK, 0); + (TYPE_TAG, ty.0.0 as *const WithStableHash<ty::TyS<'tcx>> as usize) + } + GenericArgKind::Const(ct) => { + // Ensure we can use the tag bits. + assert_eq!(mem::align_of_val(&*ct.0.0) & TAG_MASK, 0); + (CONST_TAG, ct.0.0 as *const ty::ConstS<'tcx> as usize) + } + }; + + GenericArg { ptr: unsafe { NonZeroUsize::new_unchecked(ptr | tag) }, marker: PhantomData } + } +} + +impl<'tcx> 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<'tcx>) -> Ordering { + self.unpack().cmp(&other.unpack()) + } +} + +impl<'tcx> PartialOrd for GenericArg<'tcx> { + fn partial_cmp(&self, other: &GenericArg<'tcx>) -> Option<Ordering> { + Some(self.cmp(&other)) + } +} + +impl<'tcx> From<ty::Region<'tcx>> for GenericArg<'tcx> { + #[inline] + fn from(r: ty::Region<'tcx>) -> GenericArg<'tcx> { + GenericArgKind::Lifetime(r).pack() + } +} + +impl<'tcx> From<Ty<'tcx>> for GenericArg<'tcx> { + #[inline] + fn from(ty: Ty<'tcx>) -> GenericArg<'tcx> { + GenericArgKind::Type(ty).pack() + } +} + +impl<'tcx> From<ty::Const<'tcx>> for GenericArg<'tcx> { + #[inline] + fn from(c: 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(); + // SAFETY: use of `Interned::new_unchecked` here is ok because these + // pointers were originally created from `Interned` types in `pack()`, + // and this is just going in the other direction. + unsafe { + match ptr & TAG_MASK { + REGION_TAG => GenericArgKind::Lifetime(ty::Region(Interned::new_unchecked( + &*((ptr & !TAG_MASK) as *const ty::RegionKind<'tcx>), + ))), + TYPE_TAG => GenericArgKind::Type(Ty(Interned::new_unchecked( + &*((ptr & !TAG_MASK) as *const WithStableHash<ty::TyS<'tcx>>), + ))), + CONST_TAG => GenericArgKind::Const(ty::Const(Interned::new_unchecked( + &*((ptr & !TAG_MASK) as *const ty::ConstS<'tcx>), + ))), + _ => intrinsics::unreachable(), + } + } + } + + /// Unpack the `GenericArg` as a region when it is known certainly to be a region. + pub fn expect_region(self) -> ty::Region<'tcx> { + match self.unpack() { + GenericArgKind::Lifetime(lt) => lt, + _ => bug!("expected a region, but found another kind"), + } + } + + /// 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) -> 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(lt).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 try_fold_with<F: FallibleTypeFolder<'tcx>>(self, folder: &mut F) -> Result<Self, F::Error> { + match self.unpack() { + GenericArgKind::Lifetime(lt) => lt.try_fold_with(folder).map(Into::into), + GenericArgKind::Type(ty) => ty.try_fold_with(folder).map(Into::into), + GenericArgKind::Const(ct) => ct.try_fold_with(folder).map(Into::into), + } + } +} + +impl<'tcx> TypeVisitable<'tcx> for GenericArg<'tcx> { + fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> { + 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<I = TyCtxt<'tcx>>> Encodable<E> for GenericArg<'tcx> { + fn encode(&self, e: &mut E) { + self.unpack().encode(e) + } +} + +impl<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> Decodable<D> for GenericArg<'tcx> { + fn decode(d: &mut D) -> GenericArg<'tcx> { + 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<'tcx> InternalSubsts<'tcx> { + /// Checks whether all elements of this list are types, if so, transmute. + pub fn try_as_type_list(&'tcx self) -> Option<&'tcx List<Ty<'tcx>>> { + if self.iter().all(|arg| matches!(arg.unpack(), GenericArgKind::Type(_))) { + assert_eq!(TYPE_TAG, 0); + // SAFETY: All elements are types, see `List<Ty<'tcx>>::as_substs`. + Some(unsafe { &*(self as *const List<GenericArg<'tcx>> as *const List<Ty<'tcx>>) }) + } else { + None + } + } + + /// 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(&'tcx self) -> ClosureSubsts<'tcx> { + ClosureSubsts { substs: self } + } + + /// Interpret these substitutions as the substitutions of a generator type. + /// Generator 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 } + } + + /// Interpret these substitutions as the substitutions of an inline const. + /// Inline const substitutions have a particular structure controlled by the + /// compiler that encodes information like the inferred type; + /// see `ty::InlineConstSubsts` struct for more comments. + pub fn as_inline_const(&'tcx self) -> InlineConstSubsts<'tcx> { + InlineConstSubsts { substs: self } + } + + /// Creates an `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 an `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)) + }) + } + + pub 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) + } + + pub 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); + } + } + + #[inline] + pub fn types(&'tcx self) -> impl DoubleEndedIterator<Item = Ty<'tcx>> + 'tcx { + self.iter() + .filter_map(|k| if let GenericArgKind::Type(ty) = k.unpack() { Some(ty) } else { None }) + } + + #[inline] + pub fn regions(&'tcx self) -> impl DoubleEndedIterator<Item = ty::Region<'tcx>> + 'tcx { + self.iter().filter_map(|k| { + if let GenericArgKind::Lifetime(lt) = k.unpack() { Some(lt) } else { None } + }) + } + + #[inline] + pub fn consts(&'tcx self) -> impl DoubleEndedIterator<Item = ty::Const<'tcx>> + 'tcx { + self.iter().filter_map(|k| { + if let GenericArgKind::Const(ct) = k.unpack() { Some(ct) } else { None } + }) + } + + #[inline] + pub fn non_erasable_generics( + &'tcx self, + ) -> impl DoubleEndedIterator<Item = GenericArgKind<'tcx>> + 'tcx { + 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) -> 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 try_fold_with<F: FallibleTypeFolder<'tcx>>(self, folder: &mut F) -> Result<Self, F::Error> { + // 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].try_fold_with(folder)?; + if param0 == self[0] { Ok(self) } else { Ok(folder.tcx().intern_substs(&[param0])) } + } + 2 => { + let param0 = self[0].try_fold_with(folder)?; + let param1 = self[1].try_fold_with(folder)?; + if param0 == self[0] && param1 == self[1] { + Ok(self) + } else { + Ok(folder.tcx().intern_substs(&[param0, param1])) + } + } + 0 => Ok(self), + _ => ty::util::fold_list(self, folder, |tcx, v| tcx.intern_substs(v)), + } + } +} + +impl<'tcx> TypeVisitable<'tcx> for SubstsRef<'tcx> { + fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> { + self.iter().try_for_each(|t| t.visit_with(visitor)) + } +} + +impl<'tcx> TypeFoldable<'tcx> for &'tcx ty::List<Ty<'tcx>> { + fn try_fold_with<F: FallibleTypeFolder<'tcx>>(self, folder: &mut F) -> Result<Self, F::Error> { + // This code is fairly hot, though not as hot as `SubstsRef`. + // + // When compiling stage 2, I get the following results: + // + // len | total | % + // --- | --------- | ----- + // 2 | 15083590 | 48.1 + // 3 | 7540067 | 24.0 + // 1 | 5300377 | 16.9 + // 4 | 1351897 | 4.3 + // 0 | 1256849 | 4.0 + // + // I've tried it with some private repositories and got + // close to the same result, with 4 and 0 swapping places + // sometimes. + match self.len() { + 2 => { + let param0 = self[0].try_fold_with(folder)?; + let param1 = self[1].try_fold_with(folder)?; + if param0 == self[0] && param1 == self[1] { + Ok(self) + } else { + Ok(folder.tcx().intern_type_list(&[param0, param1])) + } + } + _ => ty::util::fold_list(self, folder, |tcx, v| tcx.intern_type_list(v)), + } + } +} + +impl<'tcx> TypeVisitable<'tcx> for &'tcx ty::List<Ty<'tcx>> { + fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> { + self.iter().try_for_each(|t| t.visit_with(visitor)) + } +} + +// Just call `foo.subst(tcx, substs)` to perform a substitution across `foo`. +#[rustc_on_unimplemented(message = "Calling `subst` must now be done through an `EarlyBinder`")] +pub trait Subst<'tcx>: Sized { + type Inner; + + fn subst(self, tcx: TyCtxt<'tcx>, substs: &[GenericArg<'tcx>]) -> Self::Inner; +} + +impl<'tcx, T: TypeFoldable<'tcx>> Subst<'tcx> for ty::EarlyBinder<T> { + type Inner = T; + + fn subst(self, tcx: TyCtxt<'tcx>, substs: &[GenericArg<'tcx>]) -> Self::Inner { + let mut folder = SubstFolder { tcx, substs, binders_passed: 0 }; + self.0.fold_with(&mut folder) + } +} + +/////////////////////////////////////////////////////////////////////////// +// The actual substitution engine itself is a type folder. + +struct SubstFolder<'a, 'tcx> { + tcx: TyCtxt<'tcx>, + substs: &'a [GenericArg<'tcx>], + + /// Number of region binders we have passed through while doing the substitution + binders_passed: u32, +} + +impl<'a, 'tcx> TypeFolder<'tcx> for SubstFolder<'a, 'tcx> { + #[inline] + fn tcx<'b>(&'b self) -> TyCtxt<'tcx> { + self.tcx + } + + fn fold_binder<T: TypeFoldable<'tcx>>( + &mut self, + t: ty::Binder<'tcx, T>, + ) -> ty::Binder<'tcx, 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> { + #[cold] + #[inline(never)] + fn region_param_out_of_range(data: ty::EarlyBoundRegion) -> ! { + bug!( + "Region parameter out of range when substituting in region {} (index={})", + data.name, + data.index + ) + } + + // 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), + _ => region_param_out_of_range(data), + } + } + _ => 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: ty::Const<'tcx>) -> ty::Const<'tcx> { + if let ty::ConstKind::Param(p) = c.kind() { + self.const_for_param(p, c) + } else { + c.super_fold_with(self) + } + } + + #[inline] + fn fold_mir_const(&mut self, c: mir::ConstantKind<'tcx>) -> mir::ConstantKind<'tcx> { + 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) => self.type_param_expected(p, source_ty, kind), + None => self.type_param_out_of_range(p, source_ty), + }; + + self.shift_vars_through_binders(ty) + } + + #[cold] + #[inline(never)] + fn type_param_expected(&self, p: ty::ParamTy, ty: Ty<'tcx>, kind: GenericArgKind<'tcx>) -> ! { + bug!( + "expected type for `{:?}` ({:?}/{}) but found {:?} when substituting, substs={:?}", + p, + ty, + p.index, + kind, + self.substs, + ) + } + + #[cold] + #[inline(never)] + fn type_param_out_of_range(&self, p: ty::ParamTy, ty: Ty<'tcx>) -> ! { + bug!( + "type parameter `{:?}` ({:?}/{}) out of range when substituting, substs={:?}", + p, + ty, + p.index, + self.substs, + ) + } + + fn const_for_param(&self, p: ParamConst, source_ct: ty::Const<'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) => self.const_param_expected(p, source_ct, kind), + None => self.const_param_out_of_range(p, source_ct), + }; + + self.shift_vars_through_binders(ct) + } + + #[cold] + #[inline(never)] + fn const_param_expected( + &self, + p: ty::ParamConst, + ct: ty::Const<'tcx>, + kind: GenericArgKind<'tcx>, + ) -> ! { + bug!( + "expected const for `{:?}` ({:?}/{}) but found {:?} when substituting substs={:?}", + p, + ct, + p.index, + kind, + self.substs, + ) + } + + #[cold] + #[inline(never)] + fn const_param_out_of_range(&self, p: ty::ParamConst, ct: ty::Const<'tcx>) -> ! { + bug!( + "const parameter `{:?}` ({:?}/{}) out of range when substituting substs={:?}", + p, + ct, + p.index, + self.substs, + ) + } + + /// 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 + /// ```ignore (illustrative) + /// 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: + /// ```ignore (illustrative) + /// 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(TypeFolder::tcx(self), 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) + } +} + +/// 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, TypeVisitable, 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: +/// +/// ```ignore (illustrative) +/// 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, TypeVisitable, Lift)] +pub struct UserSelfTy<'tcx> { + pub impl_def_id: DefId, + pub self_ty: Ty<'tcx>, +} |