compiler/rustc_middle/src/query/erase.rs

   1 use crate::mir;
   2 use crate::traits;
   3 use crate::ty::{self, Ty};
   4 use std::mem::{size_of, transmute_copy, MaybeUninit};
   5
   6 #[derive(Copy, Clone)]
   7 pub struct Erased<T: Copy> {
   8     // We use `MaybeUninit` here so we can store any value
   9     // in `data` since we aren't actually storing a `T`.
  10     data: MaybeUninit<T>,
  11 }
  12
  13 pub trait EraseType: Copy {
  14     type Result: Copy;
  15 }
  16
  17 // Allow `type_alias_bounds` since compilation will fail without `EraseType`.
  18 #[allow(type_alias_bounds)]
  19 pub type Erase<T: EraseType> = Erased<impl Copy>;
  20
  21 #[inline(always)]
  22 pub fn erase<T: EraseType>(src: T) -> Erase<T> {
  23     // Ensure the sizes match
  24     const {
  25         if std::mem::size_of::<T>() != std::mem::size_of::<T::Result>() {
  26             panic!("size of T must match erased type T::Result")
  27         }
  28     };
  29
  30     Erased::<<T as EraseType>::Result> {
  31         // SAFETY: It is safe to transmute to MaybeUninit for types with the same sizes.
  32         data: unsafe { transmute_copy(&src) },
  33     }
  34 }
  35
  36 /// Restores an erased value.
  37 #[inline(always)]
  38 pub fn restore<T: EraseType>(value: Erase<T>) -> T {
  39     let value: Erased<<T as EraseType>::Result> = value;
  40     // SAFETY: Due to the use of impl Trait in `Erase` the only way to safely create an instance
  41     // of `Erase` is to call `erase`, so we know that `value.data` is a valid instance of `T` of
  42     // the right size.
  43     unsafe { transmute_copy(&value.data) }
  44 }
  45
  46 impl<T> EraseType for &'_ T {
  47     type Result = [u8; size_of::<*const ()>()];
  48 }
  49
  50 impl<T> EraseType for &'_ [T] {
  51     type Result = [u8; size_of::<*const [()]>()];
  52 }
  53
  54 impl<T> EraseType for &'_ ty::List<T> {
  55     type Result = [u8; size_of::<*const ()>()];
  56 }
  57
  58 impl<I: rustc_index::Idx, T> EraseType for &'_ rustc_index::IndexSlice<I, T> {
  59     type Result = [u8; size_of::<&'static rustc_index::IndexSlice<u32, ()>>()];
  60 }
  61
  62 impl<T> EraseType for Result<&'_ T, traits::query::NoSolution> {
  63     type Result = [u8; size_of::<Result<&'static (), traits::query::NoSolution>>()];
  64 }
  65
  66 impl<T> EraseType for Result<&'_ T, rustc_errors::ErrorGuaranteed> {
  67     type Result = [u8; size_of::<Result<&'static (), rustc_errors::ErrorGuaranteed>>()];
  68 }
  69
  70 impl<T> EraseType for Result<&'_ T, traits::CodegenObligationError> {
  71     type Result = [u8; size_of::<Result<&'static (), traits::CodegenObligationError>>()];
  72 }
  73
  74 impl<T> EraseType for Result<&'_ T, &'_ ty::layout::FnAbiError<'_>> {
  75     type Result = [u8; size_of::<Result<&'static (), &'static ty::layout::FnAbiError<'static>>>()];
  76 }
  77
  78 impl<T> EraseType for Result<(&'_ T, rustc_middle::thir::ExprId), rustc_errors::ErrorGuaranteed> {
  79     type Result = [u8; size_of::<
  80         Result<(&'static (), rustc_middle::thir::ExprId), rustc_errors::ErrorGuaranteed>,
  81     >()];
  82 }
  83
  84 impl EraseType for Result<Option<ty::Instance<'_>>, rustc_errors::ErrorGuaranteed> {
  85     type Result =
  86         [u8; size_of::<Result<Option<ty::Instance<'static>>, rustc_errors::ErrorGuaranteed>>()];
  87 }
  88
  89 impl EraseType for Result<Option<ty::EarlyBinder<ty::Const<'_>>>, rustc_errors::ErrorGuaranteed> {
  90     type Result = [u8; size_of::<
  91         Result<Option<ty::EarlyBinder<ty::Const<'static>>>, rustc_errors::ErrorGuaranteed>,
  92     >()];
  93 }
  94
  95 impl EraseType for Result<ty::GenericArg<'_>, traits::query::NoSolution> {
  96     type Result = [u8; size_of::<Result<ty::GenericArg<'static>, traits::query::NoSolution>>()];
  97 }
  98
  99 impl EraseType for Result<bool, &ty::layout::LayoutError<'_>> {
 100     type Result = [u8; size_of::<Result<bool, &'static ty::layout::LayoutError<'static>>>()];
 101 }
 102
 103 impl EraseType
 104     for Result<rustc_target::abi::TyAndLayout<'_, Ty<'_>>, &ty::layout::LayoutError<'_>>
 105 {
 106     type Result = [u8; size_of::<
 107         Result<
 108             rustc_target::abi::TyAndLayout<'static, Ty<'static>>,
 109             &'static ty::layout::LayoutError<'static>,
 110         >,
 111     >()];
 112 }
 113
 114 impl EraseType for Result<ty::Const<'_>, mir::interpret::LitToConstError> {
 115     type Result = [u8; size_of::<Result<ty::Const<'static>, mir::interpret::LitToConstError>>()];
 116 }
 117
 118 impl EraseType for Result<mir::ConstantKind<'_>, mir::interpret::LitToConstError> {
 119     type Result =
 120         [u8; size_of::<Result<mir::ConstantKind<'static>, mir::interpret::LitToConstError>>()];
 121 }
 122
 123 impl EraseType for Result<mir::interpret::ConstAlloc<'_>, mir::interpret::ErrorHandled> {
 124     type Result = [u8; size_of::<
 125         Result<mir::interpret::ConstAlloc<'static>, mir::interpret::ErrorHandled>,
 126     >()];
 127 }
 128
 129 impl EraseType for Result<mir::interpret::ConstValue<'_>, mir::interpret::ErrorHandled> {
 130     type Result = [u8; size_of::<
 131         Result<mir::interpret::ConstValue<'static>, mir::interpret::ErrorHandled>,
 132     >()];
 133 }
 134
 135 impl EraseType for Result<Option<ty::ValTree<'_>>, mir::interpret::ErrorHandled> {
 136     type Result =
 137         [u8; size_of::<Result<Option<ty::ValTree<'static>>, mir::interpret::ErrorHandled>>()];
 138 }
 139
 140 impl EraseType for Result<&'_ ty::List<Ty<'_>>, ty::util::AlwaysRequiresDrop> {
 141     type Result =
 142         [u8; size_of::<Result<&'static ty::List<Ty<'static>>, ty::util::AlwaysRequiresDrop>>()];
 143 }
 144
 145 impl<T> EraseType for Option<&'_ T> {
 146     type Result = [u8; size_of::<Option<&'static ()>>()];
 147 }
 148
 149 impl<T> EraseType for Option<&'_ [T]> {
 150     type Result = [u8; size_of::<Option<&'static [()]>>()];
 151 }
 152
 153 impl EraseType for Option<rustc_middle::hir::Owner<'_>> {
 154     type Result = [u8; size_of::<Option<rustc_middle::hir::Owner<'static>>>()];
 155 }
 156
 157 impl EraseType for Option<mir::DestructuredConstant<'_>> {
 158     type Result = [u8; size_of::<Option<mir::DestructuredConstant<'static>>>()];
 159 }
 160
 161 impl EraseType for Option<ty::EarlyBinder<ty::TraitRef<'_>>> {
 162     type Result = [u8; size_of::<Option<ty::EarlyBinder<ty::TraitRef<'static>>>>()];
 163 }
 164
 165 impl EraseType for Option<ty::EarlyBinder<Ty<'_>>> {
 166     type Result = [u8; size_of::<Option<ty::EarlyBinder<Ty<'static>>>>()];
 167 }
 168
 169 impl<T> EraseType for rustc_hir::MaybeOwner<&'_ T> {
 170     type Result = [u8; size_of::<rustc_hir::MaybeOwner<&'static ()>>()];
 171 }
 172
 173 impl<T: EraseType> EraseType for ty::EarlyBinder<T> {
 174     type Result = T::Result;
 175 }
 176
 177 impl EraseType for ty::Binder<'_, ty::FnSig<'_>> {
 178     type Result = [u8; size_of::<ty::Binder<'static, ty::FnSig<'static>>>()];
 179 }
 180
 181 impl EraseType for ty::Binder<'_, &'_ ty::List<Ty<'_>>> {
 182     type Result = [u8; size_of::<ty::Binder<'static, &'static ty::List<Ty<'static>>>>()];
 183 }
 184
 185 impl<T0, T1> EraseType for (&'_ T0, &'_ T1) {
 186     type Result = [u8; size_of::<(&'static (), &'static ())>()];
 187 }
 188
 189 impl<T0, T1> EraseType for (&'_ T0, &'_ [T1]) {
 190     type Result = [u8; size_of::<(&'static (), &'static [()])>()];
 191 }
 192
 193 macro_rules! trivial {
 194     ($($ty:ty),+ $(,)?) => {
 195         $(
 196             impl EraseType for $ty {
 197                 type Result = [u8; size_of::<$ty>()];
 198             }
 199         )*
 200     }
 201 }
 202
 203 trivial! {
 204     (),
 205     bool,
 206     Option<(rustc_span::def_id::DefId, rustc_session::config::EntryFnType)>,
 207     Option<rustc_ast::expand::allocator::AllocatorKind>,
 208     Option<rustc_attr::ConstStability>,
 209     Option<rustc_attr::DefaultBodyStability>,
 210     Option<rustc_attr::Stability>,
 211     Option<rustc_data_structures::svh::Svh>,
 212     Option<rustc_hir::def::DefKind>,
 213     Option<rustc_hir::GeneratorKind>,
 214     Option<rustc_hir::HirId>,
 215     Option<rustc_middle::middle::stability::DeprecationEntry>,
 216     Option<rustc_middle::ty::Destructor>,
 217     Option<rustc_middle::ty::ImplTraitInTraitData>,
 218     Option<rustc_span::def_id::CrateNum>,
 219     Option<rustc_span::def_id::DefId>,
 220     Option<rustc_span::def_id::LocalDefId>,
 221     Option<rustc_span::Span>,
 222     Option<rustc_target::spec::PanicStrategy>,
 223     Option<usize>,
 224     Result<(), rustc_errors::ErrorGuaranteed>,
 225     Result<(), rustc_middle::traits::query::NoSolution>,
 226     Result<rustc_middle::traits::EvaluationResult, rustc_middle::traits::OverflowError>,
 227     rustc_ast::expand::allocator::AllocatorKind,
 228     rustc_attr::ConstStability,
 229     rustc_attr::DefaultBodyStability,
 230     rustc_attr::Deprecation,
 231     rustc_attr::Stability,
 232     rustc_data_structures::svh::Svh,
 233     rustc_errors::ErrorGuaranteed,
 234     rustc_hir::Constness,
 235     rustc_hir::def_id::DefId,
 236     rustc_hir::def_id::DefIndex,
 237     rustc_hir::def_id::LocalDefId,
 238     rustc_hir::def_id::LocalModDefId,
 239     rustc_hir::def::DefKind,
 240     rustc_hir::Defaultness,
 241     rustc_hir::definitions::DefKey,
 242     rustc_hir::GeneratorKind,
 243     rustc_hir::HirId,
 244     rustc_hir::IsAsync,
 245     rustc_hir::ItemLocalId,
 246     rustc_hir::LangItem,
 247     rustc_hir::OwnerId,
 248     rustc_hir::Upvar,
 249     rustc_index::bit_set::FiniteBitSet<u32>,
 250     rustc_middle::middle::dependency_format::Linkage,
 251     rustc_middle::middle::exported_symbols::SymbolExportInfo,
 252     rustc_middle::middle::resolve_bound_vars::ObjectLifetimeDefault,
 253     rustc_middle::middle::resolve_bound_vars::ResolvedArg,
 254     rustc_middle::middle::stability::DeprecationEntry,
 255     rustc_middle::mir::ConstQualifs,
 256     rustc_middle::mir::interpret::AllocId,
 257     rustc_middle::mir::interpret::ErrorHandled,
 258     rustc_middle::mir::interpret::LitToConstError,
 259     rustc_middle::thir::ExprId,
 260     rustc_middle::traits::CodegenObligationError,
 261     rustc_middle::traits::EvaluationResult,
 262     rustc_middle::traits::OverflowError,
 263     rustc_middle::traits::query::NoSolution,
 264     rustc_middle::traits::WellFormedLoc,
 265     rustc_middle::ty::adjustment::CoerceUnsizedInfo,
 266     rustc_middle::ty::AssocItem,
 267     rustc_middle::ty::AssocItemContainer,
 268     rustc_middle::ty::BoundVariableKind,
 269     rustc_middle::ty::DeducedParamAttrs,
 270     rustc_middle::ty::Destructor,
 271     rustc_middle::ty::fast_reject::SimplifiedType,
 272     rustc_middle::ty::ImplPolarity,
 273     rustc_middle::ty::Representability,
 274     rustc_middle::ty::ReprOptions,
 275     rustc_middle::ty::UnusedGenericParams,
 276     rustc_middle::ty::util::AlwaysRequiresDrop,
 277     rustc_middle::ty::Visibility<rustc_span::def_id::DefId>,
 278     rustc_session::config::CrateType,
 279     rustc_session::config::EntryFnType,
 280     rustc_session::config::OptLevel,
 281     rustc_session::config::SymbolManglingVersion,
 282     rustc_session::cstore::CrateDepKind,
 283     rustc_session::cstore::ExternCrate,
 284     rustc_session::cstore::LinkagePreference,
 285     rustc_session::Limits,
 286     rustc_session::lint::LintExpectationId,
 287     rustc_span::def_id::CrateNum,
 288     rustc_span::def_id::DefPathHash,
 289     rustc_span::ExpnHash,
 290     rustc_span::ExpnId,
 291     rustc_span::Span,
 292     rustc_span::Symbol,
 293     rustc_span::symbol::Ident,
 294     rustc_target::spec::PanicStrategy,
 295     rustc_type_ir::Variance,
 296     u32,
 297     usize,
 298 }
 299
 300 macro_rules! tcx_lifetime {
 301     ($($($fake_path:ident)::+),+ $(,)?) => {
 302         $(
 303             impl<'tcx> EraseType for $($fake_path)::+<'tcx> {
 304                 type Result = [u8; size_of::<$($fake_path)::+<'static>>()];
 305             }
 306         )*
 307     }
 308 }
 309
 310 tcx_lifetime! {
 311     rustc_middle::hir::Owner,
 312     rustc_middle::middle::exported_symbols::ExportedSymbol,
 313     rustc_middle::mir::ConstantKind,
 314     rustc_middle::mir::DestructuredConstant,
 315     rustc_middle::mir::interpret::ConstAlloc,
 316     rustc_middle::mir::interpret::ConstValue,
 317     rustc_middle::mir::interpret::GlobalId,
 318     rustc_middle::mir::interpret::LitToConstInput,
 319     rustc_middle::traits::query::MethodAutoderefStepsResult,
 320     rustc_middle::traits::query::type_op::AscribeUserType,
 321     rustc_middle::traits::query::type_op::Eq,
 322     rustc_middle::traits::query::type_op::ProvePredicate,
 323     rustc_middle::traits::query::type_op::Subtype,
 324     rustc_middle::ty::AdtDef,
 325     rustc_middle::ty::AliasTy,
 326     rustc_middle::ty::ClauseKind,
 327     rustc_middle::ty::ClosureTypeInfo,
 328     rustc_middle::ty::Const,
 329     rustc_middle::ty::DestructuredConst,
 330     rustc_middle::ty::ExistentialTraitRef,
 331     rustc_middle::ty::FnSig,
 332     rustc_middle::ty::GenericArg,
 333     rustc_middle::ty::GenericPredicates,
 334     rustc_middle::ty::inhabitedness::InhabitedPredicate,
 335     rustc_middle::ty::Instance,
 336     rustc_middle::ty::InstanceDef,
 337     rustc_middle::ty::layout::FnAbiError,
 338     rustc_middle::ty::layout::LayoutError,
 339     rustc_middle::ty::ParamEnv,
 340     rustc_middle::ty::Predicate,
 341     rustc_middle::ty::SymbolName,
 342     rustc_middle::ty::TraitRef,
 343     rustc_middle::ty::Ty,
 344     rustc_middle::ty::UnevaluatedConst,
 345     rustc_middle::ty::ValTree,
 346     rustc_middle::ty::VtblEntry,
 347 }