compiler/rustc_middle/src/ty/structural_impls.rs

   1 //! This module contains implements of the `Lift` and `TypeFoldable`
   2 //! traits for various types in the Rust compiler. Most are written by
   3 //! hand, though we've recently added some macros and proc-macros to help with the tedium.
   4
   5 use crate::mir::interpret;
   6 use crate::mir::{Field, ProjectionKind};
   7 use crate::ty::fold::{FallibleTypeFolder, TypeFoldable, TypeSuperFoldable};
   8 use crate::ty::print::{with_no_trimmed_paths, FmtPrinter, Printer};
   9 use crate::ty::visit::{TypeSuperVisitable, TypeVisitable, TypeVisitor};
  10 use crate::ty::{self, AliasTy, InferConst, Lift, Term, TermKind, Ty, TyCtxt};
  11 use rustc_data_structures::functor::IdFunctor;
  12 use rustc_hir::def::Namespace;
  13 use rustc_index::vec::{Idx, IndexVec};
  14 use rustc_target::abi::TyAndLayout;
  15
  16 use std::fmt;
  17 use std::mem::ManuallyDrop;
  18 use std::ops::ControlFlow;
  19 use std::rc::Rc;
  20 use std::sync::Arc;
  21
  22 impl fmt::Debug for ty::TraitDef {
  23     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
  24         ty::tls::with(|tcx| {
  25             with_no_trimmed_paths!({
  26                 f.write_str(
  27                     &FmtPrinter::new(tcx, Namespace::TypeNS)
  28                         .print_def_path(self.def_id, &[])?
  29                         .into_buffer(),
  30                 )
  31             })
  32         })
  33     }
  34 }
  35
  36 impl<'tcx> fmt::Debug for ty::AdtDef<'tcx> {
  37     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
  38         ty::tls::with(|tcx| {
  39             with_no_trimmed_paths!({
  40                 f.write_str(
  41                     &FmtPrinter::new(tcx, Namespace::TypeNS)
  42                         .print_def_path(self.did(), &[])?
  43                         .into_buffer(),
  44                 )
  45             })
  46         })
  47     }
  48 }
  49
  50 impl fmt::Debug for ty::UpvarId {
  51     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
  52         let name = ty::tls::with(|tcx| tcx.hir().name(self.var_path.hir_id));
  53         write!(f, "UpvarId({:?};`{}`;{:?})", self.var_path.hir_id, name, self.closure_expr_id)
  54     }
  55 }
  56
  57 impl<'tcx> fmt::Debug for ty::ExistentialTraitRef<'tcx> {
  58     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
  59         with_no_trimmed_paths!(fmt::Display::fmt(self, f))
  60     }
  61 }
  62
  63 impl<'tcx> fmt::Debug for ty::adjustment::Adjustment<'tcx> {
  64     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
  65         write!(f, "{:?} -> {}", self.kind, self.target)
  66     }
  67 }
  68
  69 impl fmt::Debug for ty::BoundRegionKind {
  70     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
  71         match *self {
  72             ty::BrAnon(n, span) => write!(f, "BrAnon({n:?}, {span:?})"),
  73             ty::BrNamed(did, name) => {
  74                 if did.is_crate_root() {
  75                     write!(f, "BrNamed({})", name)
  76                 } else {
  77                     write!(f, "BrNamed({:?}, {})", did, name)
  78                 }
  79             }
  80             ty::BrEnv => write!(f, "BrEnv"),
  81         }
  82     }
  83 }
  84
  85 impl fmt::Debug for ty::FreeRegion {
  86     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
  87         write!(f, "ReFree({:?}, {:?})", self.scope, self.bound_region)
  88     }
  89 }
  90
  91 impl<'tcx> fmt::Debug for ty::FnSig<'tcx> {
  92     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
  93         write!(f, "({:?}; c_variadic: {})->{:?}", self.inputs(), self.c_variadic, self.output())
  94     }
  95 }
  96
  97 impl<'tcx> fmt::Debug for ty::ConstVid<'tcx> {
  98     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
  99         write!(f, "_#{}c", self.index)
 100     }
 101 }
 102
 103 impl<'tcx> fmt::Debug for ty::TraitRef<'tcx> {
 104     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 105         with_no_trimmed_paths!(fmt::Display::fmt(self, f))
 106     }
 107 }
 108
 109 impl<'tcx> fmt::Debug for Ty<'tcx> {
 110     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 111         with_no_trimmed_paths!(fmt::Display::fmt(self, f))
 112     }
 113 }
 114
 115 impl fmt::Debug for ty::ParamTy {
 116     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 117         write!(f, "{}/#{}", self.name, self.index)
 118     }
 119 }
 120
 121 impl fmt::Debug for ty::ParamConst {
 122     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 123         write!(f, "{}/#{}", self.name, self.index)
 124     }
 125 }
 126
 127 impl<'tcx> fmt::Debug for ty::TraitPredicate<'tcx> {
 128     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 129         if let ty::BoundConstness::ConstIfConst = self.constness {
 130             write!(f, "~const ")?;
 131         }
 132         write!(f, "TraitPredicate({:?}, polarity:{:?})", self.trait_ref, self.polarity)
 133     }
 134 }
 135
 136 impl<'tcx> fmt::Debug for ty::ProjectionPredicate<'tcx> {
 137     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 138         write!(f, "ProjectionPredicate({:?}, {:?})", self.projection_ty, self.term)
 139     }
 140 }
 141
 142 impl<'tcx> fmt::Debug for ty::Predicate<'tcx> {
 143     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 144         write!(f, "{:?}", self.kind())
 145     }
 146 }
 147
 148 impl<'tcx> fmt::Debug for ty::Clause<'tcx> {
 149     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 150         match *self {
 151             ty::Clause::Trait(ref a) => a.fmt(f),
 152             ty::Clause::RegionOutlives(ref pair) => pair.fmt(f),
 153             ty::Clause::TypeOutlives(ref pair) => pair.fmt(f),
 154             ty::Clause::Projection(ref pair) => pair.fmt(f),
 155         }
 156     }
 157 }
 158
 159 impl<'tcx> fmt::Debug for ty::PredicateKind<'tcx> {
 160     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 161         match *self {
 162             ty::PredicateKind::Clause(ref a) => a.fmt(f),
 163             ty::PredicateKind::Subtype(ref pair) => pair.fmt(f),
 164             ty::PredicateKind::Coerce(ref pair) => pair.fmt(f),
 165             ty::PredicateKind::WellFormed(data) => write!(f, "WellFormed({:?})", data),
 166             ty::PredicateKind::ObjectSafe(trait_def_id) => {
 167                 write!(f, "ObjectSafe({:?})", trait_def_id)
 168             }
 169             ty::PredicateKind::ClosureKind(closure_def_id, closure_substs, kind) => {
 170                 write!(f, "ClosureKind({:?}, {:?}, {:?})", closure_def_id, closure_substs, kind)
 171             }
 172             ty::PredicateKind::ConstEvaluatable(ct) => {
 173                 write!(f, "ConstEvaluatable({ct:?})")
 174             }
 175             ty::PredicateKind::ConstEquate(c1, c2) => write!(f, "ConstEquate({:?}, {:?})", c1, c2),
 176             ty::PredicateKind::TypeWellFormedFromEnv(ty) => {
 177                 write!(f, "TypeWellFormedFromEnv({:?})", ty)
 178             }
 179             ty::PredicateKind::Ambiguous => write!(f, "Ambiguous"),
 180         }
 181     }
 182 }
 183
 184 impl<'tcx> fmt::Debug for AliasTy<'tcx> {
 185     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 186         f.debug_struct("AliasTy")
 187             .field("substs", &self.substs)
 188             .field("def_id", &self.def_id)
 189             .finish()
 190     }
 191 }
 192
 193 ///////////////////////////////////////////////////////////////////////////
 194 // Atomic structs
 195 //
 196 // For things that don't carry any arena-allocated data (and are
 197 // copy...), just add them to this list.
 198
 199 TrivialTypeTraversalAndLiftImpls! {
 200     (),
 201     bool,
 202     usize,
 203     ::rustc_target::abi::VariantIdx,
 204     u32,
 205     u64,
 206     String,
 207     crate::middle::region::Scope,
 208     crate::ty::FloatTy,
 209     ::rustc_ast::InlineAsmOptions,
 210     ::rustc_ast::InlineAsmTemplatePiece,
 211     ::rustc_ast::NodeId,
 212     ::rustc_span::symbol::Symbol,
 213     ::rustc_hir::def::Res,
 214     ::rustc_hir::def_id::DefId,
 215     ::rustc_hir::def_id::LocalDefId,
 216     ::rustc_hir::HirId,
 217     ::rustc_hir::MatchSource,
 218     ::rustc_hir::Mutability,
 219     ::rustc_hir::Unsafety,
 220     ::rustc_target::asm::InlineAsmRegOrRegClass,
 221     ::rustc_target::spec::abi::Abi,
 222     crate::mir::coverage::ExpressionOperandId,
 223     crate::mir::coverage::CounterValueReference,
 224     crate::mir::coverage::InjectedExpressionId,
 225     crate::mir::coverage::InjectedExpressionIndex,
 226     crate::mir::coverage::MappedExpressionIndex,
 227     crate::mir::Local,
 228     crate::mir::Promoted,
 229     crate::traits::Reveal,
 230     crate::ty::adjustment::AutoBorrowMutability,
 231     crate::ty::AdtKind,
 232     crate::ty::BoundConstness,
 233     // Including `BoundRegionKind` is a *bit* dubious, but direct
 234     // references to bound region appear in `ty::Error`, and aren't
 235     // really meant to be folded. In general, we can only fold a fully
 236     // general `Region`.
 237     crate::ty::BoundRegionKind,
 238     crate::ty::AssocItem,
 239     crate::ty::AssocKind,
 240     crate::ty::AliasKind,
 241     crate::ty::Placeholder<crate::ty::BoundRegionKind>,
 242     crate::ty::ClosureKind,
 243     crate::ty::FreeRegion,
 244     crate::ty::InferTy,
 245     crate::ty::IntVarValue,
 246     crate::ty::ParamConst,
 247     crate::ty::ParamTy,
 248     crate::ty::adjustment::PointerCast,
 249     crate::ty::RegionVid,
 250     crate::ty::UniverseIndex,
 251     crate::ty::Variance,
 252     ::rustc_span::Span,
 253     ::rustc_errors::ErrorGuaranteed,
 254     Field,
 255     interpret::Scalar,
 256     rustc_target::abi::Size,
 257     rustc_type_ir::DebruijnIndex,
 258     ty::BoundVar,
 259     ty::Placeholder<ty::BoundVar>,
 260 }
 261
 262 TrivialTypeTraversalAndLiftImpls! {
 263     for<'tcx> {
 264         ty::ValTree<'tcx>,
 265     }
 266 }
 267
 268 ///////////////////////////////////////////////////////////////////////////
 269 // Lift implementations
 270
 271 impl<'tcx, A: Lift<'tcx>, B: Lift<'tcx>> Lift<'tcx> for (A, B) {
 272     type Lifted = (A::Lifted, B::Lifted);
 273     fn lift_to_tcx(self, tcx: TyCtxt<'tcx>) -> Option<Self::Lifted> {
 274         Some((tcx.lift(self.0)?, tcx.lift(self.1)?))
 275     }
 276 }
 277
 278 impl<'tcx, A: Lift<'tcx>, B: Lift<'tcx>, C: Lift<'tcx>> Lift<'tcx> for (A, B, C) {
 279     type Lifted = (A::Lifted, B::Lifted, C::Lifted);
 280     fn lift_to_tcx(self, tcx: TyCtxt<'tcx>) -> Option<Self::Lifted> {
 281         Some((tcx.lift(self.0)?, tcx.lift(self.1)?, tcx.lift(self.2)?))
 282     }
 283 }
 284
 285 impl<'tcx, T: Lift<'tcx>> Lift<'tcx> for Option<T> {
 286     type Lifted = Option<T::Lifted>;
 287     fn lift_to_tcx(self, tcx: TyCtxt<'tcx>) -> Option<Self::Lifted> {
 288         Some(match self {
 289             Some(x) => Some(tcx.lift(x)?),
 290             None => None,
 291         })
 292     }
 293 }
 294
 295 impl<'tcx, T: Lift<'tcx>, E: Lift<'tcx>> Lift<'tcx> for Result<T, E> {
 296     type Lifted = Result<T::Lifted, E::Lifted>;
 297     fn lift_to_tcx(self, tcx: TyCtxt<'tcx>) -> Option<Self::Lifted> {
 298         match self {
 299             Ok(x) => tcx.lift(x).map(Ok),
 300             Err(e) => tcx.lift(e).map(Err),
 301         }
 302     }
 303 }
 304
 305 impl<'tcx, T: Lift<'tcx>> Lift<'tcx> for Box<T> {
 306     type Lifted = Box<T::Lifted>;
 307     fn lift_to_tcx(self, tcx: TyCtxt<'tcx>) -> Option<Self::Lifted> {
 308         Some(Box::new(tcx.lift(*self)?))
 309     }
 310 }
 311
 312 impl<'tcx, T: Lift<'tcx> + Clone> Lift<'tcx> for Rc<T> {
 313     type Lifted = Rc<T::Lifted>;
 314     fn lift_to_tcx(self, tcx: TyCtxt<'tcx>) -> Option<Self::Lifted> {
 315         Some(Rc::new(tcx.lift(self.as_ref().clone())?))
 316     }
 317 }
 318
 319 impl<'tcx, T: Lift<'tcx> + Clone> Lift<'tcx> for Arc<T> {
 320     type Lifted = Arc<T::Lifted>;
 321     fn lift_to_tcx(self, tcx: TyCtxt<'tcx>) -> Option<Self::Lifted> {
 322         Some(Arc::new(tcx.lift(self.as_ref().clone())?))
 323     }
 324 }
 325 impl<'tcx, T: Lift<'tcx>> Lift<'tcx> for Vec<T> {
 326     type Lifted = Vec<T::Lifted>;
 327     fn lift_to_tcx(self, tcx: TyCtxt<'tcx>) -> Option<Self::Lifted> {
 328         self.into_iter().map(|v| tcx.lift(v)).collect()
 329     }
 330 }
 331
 332 impl<'tcx, I: Idx, T: Lift<'tcx>> Lift<'tcx> for IndexVec<I, T> {
 333     type Lifted = IndexVec<I, T::Lifted>;
 334     fn lift_to_tcx(self, tcx: TyCtxt<'tcx>) -> Option<Self::Lifted> {
 335         self.into_iter().map(|e| tcx.lift(e)).collect()
 336     }
 337 }
 338
 339 impl<'a, 'tcx> Lift<'tcx> for Term<'a> {
 340     type Lifted = ty::Term<'tcx>;
 341     fn lift_to_tcx(self, tcx: TyCtxt<'tcx>) -> Option<Self::Lifted> {
 342         Some(
 343             match self.unpack() {
 344                 TermKind::Ty(ty) => TermKind::Ty(tcx.lift(ty)?),
 345                 TermKind::Const(c) => TermKind::Const(tcx.lift(c)?),
 346             }
 347             .pack(),
 348         )
 349     }
 350 }
 351 impl<'a, 'tcx> Lift<'tcx> for ty::ParamEnv<'a> {
 352     type Lifted = ty::ParamEnv<'tcx>;
 353     fn lift_to_tcx(self, tcx: TyCtxt<'tcx>) -> Option<Self::Lifted> {
 354         tcx.lift(self.caller_bounds())
 355             .map(|caller_bounds| ty::ParamEnv::new(caller_bounds, self.reveal(), self.constness()))
 356     }
 357 }
 358
 359 ///////////////////////////////////////////////////////////////////////////
 360 // TypeFoldable implementations.
 361
 362 /// AdtDefs are basically the same as a DefId.
 363 impl<'tcx> TypeFoldable<'tcx> for ty::AdtDef<'tcx> {
 364     fn try_fold_with<F: FallibleTypeFolder<'tcx>>(self, _folder: &mut F) -> Result<Self, F::Error> {
 365         Ok(self)
 366     }
 367 }
 368
 369 impl<'tcx> TypeVisitable<'tcx> for ty::AdtDef<'tcx> {
 370     fn visit_with<V: TypeVisitor<'tcx>>(&self, _visitor: &mut V) -> ControlFlow<V::BreakTy> {
 371         ControlFlow::Continue(())
 372     }
 373 }
 374
 375 impl<'tcx, T: TypeFoldable<'tcx>, U: TypeFoldable<'tcx>> TypeFoldable<'tcx> for (T, U) {
 376     fn try_fold_with<F: FallibleTypeFolder<'tcx>>(
 377         self,
 378         folder: &mut F,
 379     ) -> Result<(T, U), F::Error> {
 380         Ok((self.0.try_fold_with(folder)?, self.1.try_fold_with(folder)?))
 381     }
 382 }
 383
 384 impl<'tcx, T: TypeVisitable<'tcx>, U: TypeVisitable<'tcx>> TypeVisitable<'tcx> for (T, U) {
 385     fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
 386         self.0.visit_with(visitor)?;
 387         self.1.visit_with(visitor)
 388     }
 389 }
 390
 391 impl<'tcx, A: TypeFoldable<'tcx>, B: TypeFoldable<'tcx>, C: TypeFoldable<'tcx>> TypeFoldable<'tcx>
 392     for (A, B, C)
 393 {
 394     fn try_fold_with<F: FallibleTypeFolder<'tcx>>(
 395         self,
 396         folder: &mut F,
 397     ) -> Result<(A, B, C), F::Error> {
 398         Ok((
 399             self.0.try_fold_with(folder)?,
 400             self.1.try_fold_with(folder)?,
 401             self.2.try_fold_with(folder)?,
 402         ))
 403     }
 404 }
 405
 406 impl<'tcx, A: TypeVisitable<'tcx>, B: TypeVisitable<'tcx>, C: TypeVisitable<'tcx>>
 407     TypeVisitable<'tcx> for (A, B, C)
 408 {
 409     fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
 410         self.0.visit_with(visitor)?;
 411         self.1.visit_with(visitor)?;
 412         self.2.visit_with(visitor)
 413     }
 414 }
 415
 416 EnumTypeTraversalImpl! {
 417     impl<'tcx, T> TypeFoldable<'tcx> for Option<T> {
 418         (Some)(a),
 419         (None),
 420     } where T: TypeFoldable<'tcx>
 421 }
 422 EnumTypeTraversalImpl! {
 423     impl<'tcx, T> TypeVisitable<'tcx> for Option<T> {
 424         (Some)(a),
 425         (None),
 426     } where T: TypeVisitable<'tcx>
 427 }
 428
 429 EnumTypeTraversalImpl! {
 430     impl<'tcx, T, E> TypeFoldable<'tcx> for Result<T, E> {
 431         (Ok)(a),
 432         (Err)(a),
 433     } where T: TypeFoldable<'tcx>, E: TypeFoldable<'tcx>,
 434 }
 435 EnumTypeTraversalImpl! {
 436     impl<'tcx, T, E> TypeVisitable<'tcx> for Result<T, E> {
 437         (Ok)(a),
 438         (Err)(a),
 439     } where T: TypeVisitable<'tcx>, E: TypeVisitable<'tcx>,
 440 }
 441
 442 impl<'tcx, T: TypeFoldable<'tcx>> TypeFoldable<'tcx> for Rc<T> {
 443     fn try_fold_with<F: FallibleTypeFolder<'tcx>>(
 444         mut self,
 445         folder: &mut F,
 446     ) -> Result<Self, F::Error> {
 447         // We merely want to replace the contained `T`, if at all possible,
 448         // so that we don't needlessly allocate a new `Rc` or indeed clone
 449         // the contained type.
 450         unsafe {
 451             // First step is to ensure that we have a unique reference to
 452             // the contained type, which `Rc::make_mut` will accomplish (by
 453             // allocating a new `Rc` and cloning the `T` only if required).
 454             // This is done *before* casting to `Rc<ManuallyDrop<T>>` so that
 455             // panicking during `make_mut` does not leak the `T`.
 456             Rc::make_mut(&mut self);
 457
 458             // Casting to `Rc<ManuallyDrop<T>>` is safe because `ManuallyDrop`
 459             // is `repr(transparent)`.
 460             let ptr = Rc::into_raw(self).cast::<ManuallyDrop<T>>();
 461             let mut unique = Rc::from_raw(ptr);
 462
 463             // Call to `Rc::make_mut` above guarantees that `unique` is the
 464             // sole reference to the contained value, so we can avoid doing
 465             // a checked `get_mut` here.
 466             let slot = Rc::get_mut_unchecked(&mut unique);
 467
 468             // Semantically move the contained type out from `unique`, fold
 469             // it, then move the folded value back into `unique`. Should
 470             // folding fail, `ManuallyDrop` ensures that the "moved-out"
 471             // value is not re-dropped.
 472             let owned = ManuallyDrop::take(slot);
 473             let folded = owned.try_fold_with(folder)?;
 474             *slot = ManuallyDrop::new(folded);
 475
 476             // Cast back to `Rc<T>`.
 477             Ok(Rc::from_raw(Rc::into_raw(unique).cast()))
 478         }
 479     }
 480 }
 481
 482 impl<'tcx, T: TypeVisitable<'tcx>> TypeVisitable<'tcx> for Rc<T> {
 483     fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
 484         (**self).visit_with(visitor)
 485     }
 486 }
 487
 488 impl<'tcx, T: TypeFoldable<'tcx>> TypeFoldable<'tcx> for Arc<T> {
 489     fn try_fold_with<F: FallibleTypeFolder<'tcx>>(
 490         mut self,
 491         folder: &mut F,
 492     ) -> Result<Self, F::Error> {
 493         // We merely want to replace the contained `T`, if at all possible,
 494         // so that we don't needlessly allocate a new `Arc` or indeed clone
 495         // the contained type.
 496         unsafe {
 497             // First step is to ensure that we have a unique reference to
 498             // the contained type, which `Arc::make_mut` will accomplish (by
 499             // allocating a new `Arc` and cloning the `T` only if required).
 500             // This is done *before* casting to `Arc<ManuallyDrop<T>>` so that
 501             // panicking during `make_mut` does not leak the `T`.
 502             Arc::make_mut(&mut self);
 503
 504             // Casting to `Arc<ManuallyDrop<T>>` is safe because `ManuallyDrop`
 505             // is `repr(transparent)`.
 506             let ptr = Arc::into_raw(self).cast::<ManuallyDrop<T>>();
 507             let mut unique = Arc::from_raw(ptr);
 508
 509             // Call to `Arc::make_mut` above guarantees that `unique` is the
 510             // sole reference to the contained value, so we can avoid doing
 511             // a checked `get_mut` here.
 512             let slot = Arc::get_mut_unchecked(&mut unique);
 513
 514             // Semantically move the contained type out from `unique`, fold
 515             // it, then move the folded value back into `unique`. Should
 516             // folding fail, `ManuallyDrop` ensures that the "moved-out"
 517             // value is not re-dropped.
 518             let owned = ManuallyDrop::take(slot);
 519             let folded = owned.try_fold_with(folder)?;
 520             *slot = ManuallyDrop::new(folded);
 521
 522             // Cast back to `Arc<T>`.
 523             Ok(Arc::from_raw(Arc::into_raw(unique).cast()))
 524         }
 525     }
 526 }
 527
 528 impl<'tcx, T: TypeVisitable<'tcx>> TypeVisitable<'tcx> for Arc<T> {
 529     fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
 530         (**self).visit_with(visitor)
 531     }
 532 }
 533
 534 impl<'tcx, T: TypeFoldable<'tcx>> TypeFoldable<'tcx> for Box<T> {
 535     fn try_fold_with<F: FallibleTypeFolder<'tcx>>(self, folder: &mut F) -> Result<Self, F::Error> {
 536         self.try_map_id(|value| value.try_fold_with(folder))
 537     }
 538 }
 539
 540 impl<'tcx, T: TypeVisitable<'tcx>> TypeVisitable<'tcx> for Box<T> {
 541     fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
 542         (**self).visit_with(visitor)
 543     }
 544 }
 545
 546 impl<'tcx, T: TypeFoldable<'tcx>> TypeFoldable<'tcx> for Vec<T> {
 547     fn try_fold_with<F: FallibleTypeFolder<'tcx>>(self, folder: &mut F) -> Result<Self, F::Error> {
 548         self.try_map_id(|t| t.try_fold_with(folder))
 549     }
 550 }
 551
 552 impl<'tcx, T: TypeVisitable<'tcx>> TypeVisitable<'tcx> for Vec<T> {
 553     fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
 554         self.iter().try_for_each(|t| t.visit_with(visitor))
 555     }
 556 }
 557
 558 impl<'tcx, T: TypeVisitable<'tcx>> TypeVisitable<'tcx> for &[T] {
 559     fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
 560         self.iter().try_for_each(|t| t.visit_with(visitor))
 561     }
 562 }
 563
 564 impl<'tcx, T: TypeFoldable<'tcx>> TypeFoldable<'tcx> for Box<[T]> {
 565     fn try_fold_with<F: FallibleTypeFolder<'tcx>>(self, folder: &mut F) -> Result<Self, F::Error> {
 566         self.try_map_id(|t| t.try_fold_with(folder))
 567     }
 568 }
 569
 570 impl<'tcx, T: TypeVisitable<'tcx>> TypeVisitable<'tcx> for Box<[T]> {
 571     fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
 572         self.iter().try_for_each(|t| t.visit_with(visitor))
 573     }
 574 }
 575
 576 impl<'tcx, T: TypeFoldable<'tcx>> TypeFoldable<'tcx> for ty::Binder<'tcx, T> {
 577     fn try_fold_with<F: FallibleTypeFolder<'tcx>>(self, folder: &mut F) -> Result<Self, F::Error> {
 578         folder.try_fold_binder(self)
 579     }
 580 }
 581
 582 impl<'tcx, T: TypeVisitable<'tcx>> TypeVisitable<'tcx> for ty::Binder<'tcx, T> {
 583     fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
 584         visitor.visit_binder(self)
 585     }
 586 }
 587
 588 impl<'tcx, T: TypeFoldable<'tcx>> TypeSuperFoldable<'tcx> for ty::Binder<'tcx, T> {
 589     fn try_super_fold_with<F: FallibleTypeFolder<'tcx>>(
 590         self,
 591         folder: &mut F,
 592     ) -> Result<Self, F::Error> {
 593         self.try_map_bound(|ty| ty.try_fold_with(folder))
 594     }
 595 }
 596
 597 impl<'tcx, T: TypeVisitable<'tcx>> TypeSuperVisitable<'tcx> for ty::Binder<'tcx, T> {
 598     fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
 599         self.as_ref().skip_binder().visit_with(visitor)
 600     }
 601 }
 602
 603 impl<'tcx> TypeFoldable<'tcx> for &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>> {
 604     fn try_fold_with<F: FallibleTypeFolder<'tcx>>(self, folder: &mut F) -> Result<Self, F::Error> {
 605         ty::util::fold_list(self, folder, |tcx, v| tcx.intern_poly_existential_predicates(v))
 606     }
 607 }
 608
 609 impl<'tcx> TypeFoldable<'tcx> for &'tcx ty::List<ty::Const<'tcx>> {
 610     fn try_fold_with<F: FallibleTypeFolder<'tcx>>(self, folder: &mut F) -> Result<Self, F::Error> {
 611         ty::util::fold_list(self, folder, |tcx, v| tcx.mk_const_list(v.iter()))
 612     }
 613 }
 614
 615 impl<'tcx> TypeFoldable<'tcx> for &'tcx ty::List<ProjectionKind> {
 616     fn try_fold_with<F: FallibleTypeFolder<'tcx>>(self, folder: &mut F) -> Result<Self, F::Error> {
 617         ty::util::fold_list(self, folder, |tcx, v| tcx.intern_projs(v))
 618     }
 619 }
 620
 621 impl<'tcx> TypeFoldable<'tcx> for Ty<'tcx> {
 622     fn try_fold_with<F: FallibleTypeFolder<'tcx>>(self, folder: &mut F) -> Result<Self, F::Error> {
 623         folder.try_fold_ty(self)
 624     }
 625 }
 626
 627 impl<'tcx> TypeVisitable<'tcx> for Ty<'tcx> {
 628     fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
 629         visitor.visit_ty(*self)
 630     }
 631 }
 632
 633 impl<'tcx> TypeSuperFoldable<'tcx> for Ty<'tcx> {
 634     fn try_super_fold_with<F: FallibleTypeFolder<'tcx>>(
 635         self,
 636         folder: &mut F,
 637     ) -> Result<Self, F::Error> {
 638         let kind = match *self.kind() {
 639             ty::RawPtr(tm) => ty::RawPtr(tm.try_fold_with(folder)?),
 640             ty::Array(typ, sz) => ty::Array(typ.try_fold_with(folder)?, sz.try_fold_with(folder)?),
 641             ty::Slice(typ) => ty::Slice(typ.try_fold_with(folder)?),
 642             ty::Adt(tid, substs) => ty::Adt(tid, substs.try_fold_with(folder)?),
 643             ty::Dynamic(trait_ty, region, representation) => ty::Dynamic(
 644                 trait_ty.try_fold_with(folder)?,
 645                 region.try_fold_with(folder)?,
 646                 representation,
 647             ),
 648             ty::Tuple(ts) => ty::Tuple(ts.try_fold_with(folder)?),
 649             ty::FnDef(def_id, substs) => ty::FnDef(def_id, substs.try_fold_with(folder)?),
 650             ty::FnPtr(f) => ty::FnPtr(f.try_fold_with(folder)?),
 651             ty::Ref(r, ty, mutbl) => {
 652                 ty::Ref(r.try_fold_with(folder)?, ty.try_fold_with(folder)?, mutbl)
 653             }
 654             ty::Generator(did, substs, movability) => {
 655                 ty::Generator(did, substs.try_fold_with(folder)?, movability)
 656             }
 657             ty::GeneratorWitness(types) => ty::GeneratorWitness(types.try_fold_with(folder)?),
 658             ty::Closure(did, substs) => ty::Closure(did, substs.try_fold_with(folder)?),
 659             ty::Alias(kind, data) => ty::Alias(kind, data.try_fold_with(folder)?),
 660
 661             ty::Bool
 662             | ty::Char
 663             | ty::Str
 664             | ty::Int(_)
 665             | ty::Uint(_)
 666             | ty::Float(_)
 667             | ty::Error(_)
 668             | ty::Infer(_)
 669             | ty::Param(..)
 670             | ty::Bound(..)
 671             | ty::Placeholder(..)
 672             | ty::Never
 673             | ty::Foreign(..) => return Ok(self),
 674         };
 675
 676         Ok(if *self.kind() == kind { self } else { folder.tcx().mk_ty(kind) })
 677     }
 678 }
 679
 680 impl<'tcx> TypeSuperVisitable<'tcx> for Ty<'tcx> {
 681     fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
 682         match self.kind() {
 683             ty::RawPtr(ref tm) => tm.visit_with(visitor),
 684             ty::Array(typ, sz) => {
 685                 typ.visit_with(visitor)?;
 686                 sz.visit_with(visitor)
 687             }
 688             ty::Slice(typ) => typ.visit_with(visitor),
 689             ty::Adt(_, substs) => substs.visit_with(visitor),
 690             ty::Dynamic(ref trait_ty, ref reg, _) => {
 691                 trait_ty.visit_with(visitor)?;
 692                 reg.visit_with(visitor)
 693             }
 694             ty::Tuple(ts) => ts.visit_with(visitor),
 695             ty::FnDef(_, substs) => substs.visit_with(visitor),
 696             ty::FnPtr(ref f) => f.visit_with(visitor),
 697             ty::Ref(r, ty, _) => {
 698                 r.visit_with(visitor)?;
 699                 ty.visit_with(visitor)
 700             }
 701             ty::Generator(_did, ref substs, _) => substs.visit_with(visitor),
 702             ty::GeneratorWitness(ref types) => types.visit_with(visitor),
 703             ty::Closure(_did, ref substs) => substs.visit_with(visitor),
 704             ty::Alias(_, ref data) => data.visit_with(visitor),
 705
 706             ty::Bool
 707             | ty::Char
 708             | ty::Str
 709             | ty::Int(_)
 710             | ty::Uint(_)
 711             | ty::Float(_)
 712             | ty::Error(_)
 713             | ty::Infer(_)
 714             | ty::Bound(..)
 715             | ty::Placeholder(..)
 716             | ty::Param(..)
 717             | ty::Never
 718             | ty::Foreign(..) => ControlFlow::Continue(()),
 719         }
 720     }
 721 }
 722
 723 impl<'tcx> TypeFoldable<'tcx> for ty::Region<'tcx> {
 724     fn try_fold_with<F: FallibleTypeFolder<'tcx>>(self, folder: &mut F) -> Result<Self, F::Error> {
 725         folder.try_fold_region(self)
 726     }
 727 }
 728
 729 impl<'tcx> TypeVisitable<'tcx> for ty::Region<'tcx> {
 730     fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
 731         visitor.visit_region(*self)
 732     }
 733 }
 734
 735 impl<'tcx> TypeSuperFoldable<'tcx> for ty::Region<'tcx> {
 736     fn try_super_fold_with<F: FallibleTypeFolder<'tcx>>(
 737         self,
 738         _folder: &mut F,
 739     ) -> Result<Self, F::Error> {
 740         Ok(self)
 741     }
 742 }
 743
 744 impl<'tcx> TypeSuperVisitable<'tcx> for ty::Region<'tcx> {
 745     fn super_visit_with<V: TypeVisitor<'tcx>>(&self, _visitor: &mut V) -> ControlFlow<V::BreakTy> {
 746         ControlFlow::Continue(())
 747     }
 748 }
 749
 750 impl<'tcx> TypeFoldable<'tcx> for ty::Predicate<'tcx> {
 751     fn try_fold_with<F: FallibleTypeFolder<'tcx>>(self, folder: &mut F) -> Result<Self, F::Error> {
 752         folder.try_fold_predicate(self)
 753     }
 754 }
 755
 756 impl<'tcx> TypeVisitable<'tcx> for ty::Predicate<'tcx> {
 757     fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
 758         visitor.visit_predicate(*self)
 759     }
 760
 761     #[inline]
 762     fn has_vars_bound_at_or_above(&self, binder: ty::DebruijnIndex) -> bool {
 763         self.outer_exclusive_binder() > binder
 764     }
 765
 766     #[inline]
 767     fn has_type_flags(&self, flags: ty::TypeFlags) -> bool {
 768         self.flags().intersects(flags)
 769     }
 770 }
 771
 772 impl<'tcx> TypeSuperFoldable<'tcx> for ty::Predicate<'tcx> {
 773     fn try_super_fold_with<F: FallibleTypeFolder<'tcx>>(
 774         self,
 775         folder: &mut F,
 776     ) -> Result<Self, F::Error> {
 777         let new = self.kind().try_fold_with(folder)?;
 778         Ok(folder.tcx().reuse_or_mk_predicate(self, new))
 779     }
 780 }
 781
 782 impl<'tcx> TypeSuperVisitable<'tcx> for ty::Predicate<'tcx> {
 783     fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
 784         self.kind().visit_with(visitor)
 785     }
 786 }
 787
 788 impl<'tcx> TypeFoldable<'tcx> for &'tcx ty::List<ty::Predicate<'tcx>> {
 789     fn try_fold_with<F: FallibleTypeFolder<'tcx>>(self, folder: &mut F) -> Result<Self, F::Error> {
 790         ty::util::fold_list(self, folder, |tcx, v| tcx.intern_predicates(v))
 791     }
 792 }
 793
 794 impl<'tcx, T: TypeFoldable<'tcx>, I: Idx> TypeFoldable<'tcx> for IndexVec<I, T> {
 795     fn try_fold_with<F: FallibleTypeFolder<'tcx>>(self, folder: &mut F) -> Result<Self, F::Error> {
 796         self.try_map_id(|x| x.try_fold_with(folder))
 797     }
 798 }
 799
 800 impl<'tcx, T: TypeVisitable<'tcx>, I: Idx> TypeVisitable<'tcx> for IndexVec<I, T> {
 801     fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
 802         self.iter().try_for_each(|t| t.visit_with(visitor))
 803     }
 804 }
 805
 806 impl<'tcx> TypeFoldable<'tcx> for ty::Const<'tcx> {
 807     fn try_fold_with<F: FallibleTypeFolder<'tcx>>(self, folder: &mut F) -> Result<Self, F::Error> {
 808         folder.try_fold_const(self)
 809     }
 810 }
 811
 812 impl<'tcx> TypeVisitable<'tcx> for ty::Const<'tcx> {
 813     fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
 814         visitor.visit_const(*self)
 815     }
 816 }
 817
 818 impl<'tcx> TypeSuperFoldable<'tcx> for ty::Const<'tcx> {
 819     fn try_super_fold_with<F: FallibleTypeFolder<'tcx>>(
 820         self,
 821         folder: &mut F,
 822     ) -> Result<Self, F::Error> {
 823         let ty = self.ty().try_fold_with(folder)?;
 824         let kind = self.kind().try_fold_with(folder)?;
 825         if ty != self.ty() || kind != self.kind() {
 826             Ok(folder.tcx().mk_const(kind, ty))
 827         } else {
 828             Ok(self)
 829         }
 830     }
 831 }
 832
 833 impl<'tcx> TypeSuperVisitable<'tcx> for ty::Const<'tcx> {
 834     fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
 835         self.ty().visit_with(visitor)?;
 836         self.kind().visit_with(visitor)
 837     }
 838 }
 839
 840 impl<'tcx> TypeFoldable<'tcx> for InferConst<'tcx> {
 841     fn try_fold_with<F: FallibleTypeFolder<'tcx>>(self, _folder: &mut F) -> Result<Self, F::Error> {
 842         Ok(self)
 843     }
 844 }
 845
 846 impl<'tcx> TypeVisitable<'tcx> for InferConst<'tcx> {
 847     fn visit_with<V: TypeVisitor<'tcx>>(&self, _visitor: &mut V) -> ControlFlow<V::BreakTy> {
 848         ControlFlow::Continue(())
 849     }
 850 }
 851
 852 impl<'tcx> TypeSuperVisitable<'tcx> for ty::UnevaluatedConst<'tcx> {
 853     fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
 854         self.substs.visit_with(visitor)
 855     }
 856 }
 857
 858 impl<'tcx> TypeVisitable<'tcx> for TyAndLayout<'tcx, Ty<'tcx>> {
 859     fn visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> ControlFlow<V::BreakTy> {
 860         visitor.visit_ty(self.ty)
 861     }
 862 }