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-rw-r--r--compiler/rustc_middle/src/ty/subst.rs785
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diff --git a/compiler/rustc_middle/src/ty/subst.rs b/compiler/rustc_middle/src/ty/subst.rs
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+// 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>,
+}
generated by cgit v1.2.3 (git 2.39.1) at 2024-06-02 19:41:50 +0000