rustc_middle/query/
erase.rs

1use std::ffi::OsStr;
2use std::intrinsics::transmute_unchecked;
3use std::mem::MaybeUninit;
4
5use rustc_span::ErrorGuaranteed;
6
7use crate::mir::interpret::EvalToValTreeResult;
8use crate::query::CyclePlaceholder;
9use crate::ty::adjustment::CoerceUnsizedInfo;
10use crate::ty::{self, Ty, TyCtxt};
11use crate::{mir, traits};
12
13#[derive(Copy, Clone)]
14pub struct Erased<T: Copy> {
15    // We use `MaybeUninit` here so we can store any value
16    // in `data` since we aren't actually storing a `T`.
17    data: MaybeUninit<T>,
18}
19
20pub trait EraseType: Copy {
21    type Result: Copy;
22}
23
24// Allow `type_alias_bounds` since compilation will fail without `EraseType`.
25#[allow(type_alias_bounds)]
26pub type Erase<T: EraseType> = Erased<impl Copy>;
27
28#[inline(always)]
29#[define_opaque(Erase)]
30pub fn erase<T: EraseType>(src: T) -> Erase<T> {
31    // Ensure the sizes match
32    const {
33        if size_of::<T>() != size_of::<T::Result>() {
34            panic!("size of T must match erased type T::Result")
35        }
36    };
37
38    Erased::<<T as EraseType>::Result> {
39        // `transmute_unchecked` is needed here because it does not have `transmute`'s size check
40        // (and thus allows to transmute between `T` and `MaybeUninit<T::Result>`) (we do the size
41        // check ourselves in the `const` block above).
42        //
43        // `transmute_copy` is also commonly used for this (and it would work here since
44        // `EraseType: Copy`), but `transmute_unchecked` better explains the intent.
45        //
46        // SAFETY: It is safe to transmute to MaybeUninit for types with the same sizes.
47        data: unsafe { transmute_unchecked::<T, MaybeUninit<T::Result>>(src) },
48    }
49}
50
51/// Restores an erased value.
52#[inline(always)]
53#[define_opaque(Erase)]
54pub fn restore<T: EraseType>(value: Erase<T>) -> T {
55    let value: Erased<<T as EraseType>::Result> = value;
56    // See comment in `erase` for why we use `transmute_unchecked`.
57    //
58    // SAFETY: Due to the use of impl Trait in `Erase` the only way to safely create an instance
59    // of `Erase` is to call `erase`, so we know that `value.data` is a valid instance of `T` of
60    // the right size.
61    unsafe { transmute_unchecked::<MaybeUninit<T::Result>, T>(value.data) }
62}
63
64impl<T> EraseType for &'_ T {
65    type Result = [u8; size_of::<&'static ()>()];
66}
67
68impl<T> EraseType for &'_ [T] {
69    type Result = [u8; size_of::<&'static [()]>()];
70}
71
72impl EraseType for &'_ OsStr {
73    type Result = [u8; size_of::<&'static OsStr>()];
74}
75
76impl<T> EraseType for &'_ ty::List<T> {
77    type Result = [u8; size_of::<&'static ty::List<()>>()];
78}
79
80impl<T> EraseType for &'_ ty::ListWithCachedTypeInfo<T> {
81    type Result = [u8; size_of::<&'static ty::ListWithCachedTypeInfo<()>>()];
82}
83
84impl<I: rustc_index::Idx, T> EraseType for &'_ rustc_index::IndexSlice<I, T> {
85    type Result = [u8; size_of::<&'static rustc_index::IndexSlice<u32, ()>>()];
86}
87
88impl<T> EraseType for Result<&'_ T, traits::query::NoSolution> {
89    type Result = [u8; size_of::<Result<&'static (), traits::query::NoSolution>>()];
90}
91
92impl<T> EraseType for Result<&'_ [T], traits::query::NoSolution> {
93    type Result = [u8; size_of::<Result<&'static [()], traits::query::NoSolution>>()];
94}
95
96impl<T> EraseType for Result<&'_ T, rustc_errors::ErrorGuaranteed> {
97    type Result = [u8; size_of::<Result<&'static (), rustc_errors::ErrorGuaranteed>>()];
98}
99
100impl<T> EraseType for Result<&'_ [T], rustc_errors::ErrorGuaranteed> {
101    type Result = [u8; size_of::<Result<&'static [()], rustc_errors::ErrorGuaranteed>>()];
102}
103
104impl<T> EraseType for Result<&'_ T, traits::CodegenObligationError> {
105    type Result = [u8; size_of::<Result<&'static (), traits::CodegenObligationError>>()];
106}
107
108impl<T> EraseType for Result<&'_ T, &'_ ty::layout::FnAbiError<'_>> {
109    type Result = [u8; size_of::<Result<&'static (), &'static ty::layout::FnAbiError<'static>>>()];
110}
111
112impl<T> EraseType for Result<(&'_ T, crate::thir::ExprId), rustc_errors::ErrorGuaranteed> {
113    type Result = [u8; size_of::<
114        Result<(&'static (), crate::thir::ExprId), rustc_errors::ErrorGuaranteed>,
115    >()];
116}
117
118impl EraseType for Result<Option<ty::Instance<'_>>, rustc_errors::ErrorGuaranteed> {
119    type Result =
120        [u8; size_of::<Result<Option<ty::Instance<'static>>, rustc_errors::ErrorGuaranteed>>()];
121}
122
123impl EraseType for Result<CoerceUnsizedInfo, rustc_errors::ErrorGuaranteed> {
124    type Result = [u8; size_of::<Result<CoerceUnsizedInfo, rustc_errors::ErrorGuaranteed>>()];
125}
126
127impl EraseType
128    for Result<Option<ty::EarlyBinder<'_, ty::Const<'_>>>, rustc_errors::ErrorGuaranteed>
129{
130    type Result = [u8; size_of::<
131        Result<Option<ty::EarlyBinder<'static, ty::Const<'static>>>, rustc_errors::ErrorGuaranteed>,
132    >()];
133}
134
135impl EraseType for Result<ty::GenericArg<'_>, traits::query::NoSolution> {
136    type Result = [u8; size_of::<Result<ty::GenericArg<'static>, traits::query::NoSolution>>()];
137}
138
139impl EraseType for Result<bool, &ty::layout::LayoutError<'_>> {
140    type Result = [u8; size_of::<Result<bool, &'static ty::layout::LayoutError<'static>>>()];
141}
142
143impl EraseType for Result<rustc_abi::TyAndLayout<'_, Ty<'_>>, &ty::layout::LayoutError<'_>> {
144    type Result = [u8; size_of::<
145        Result<
146            rustc_abi::TyAndLayout<'static, Ty<'static>>,
147            &'static ty::layout::LayoutError<'static>,
148        >,
149    >()];
150}
151
152impl EraseType for Result<mir::ConstAlloc<'_>, mir::interpret::ErrorHandled> {
153    type Result = [u8; size_of::<Result<mir::ConstAlloc<'static>, mir::interpret::ErrorHandled>>()];
154}
155
156impl EraseType for Result<mir::ConstValue<'_>, mir::interpret::ErrorHandled> {
157    type Result = [u8; size_of::<Result<mir::ConstValue<'static>, mir::interpret::ErrorHandled>>()];
158}
159
160impl EraseType for EvalToValTreeResult<'_> {
161    type Result = [u8; size_of::<EvalToValTreeResult<'static>>()];
162}
163
164impl EraseType for Result<&'_ ty::List<Ty<'_>>, ty::util::AlwaysRequiresDrop> {
165    type Result =
166        [u8; size_of::<Result<&'static ty::List<Ty<'static>>, ty::util::AlwaysRequiresDrop>>()];
167}
168
169impl EraseType for Result<ty::EarlyBinder<'_, Ty<'_>>, CyclePlaceholder> {
170    type Result = [u8; size_of::<Result<ty::EarlyBinder<'static, Ty<'_>>, CyclePlaceholder>>()];
171}
172
173impl<T> EraseType for Option<&'_ T> {
174    type Result = [u8; size_of::<Option<&'static ()>>()];
175}
176
177impl<T> EraseType for Option<&'_ [T]> {
178    type Result = [u8; size_of::<Option<&'static [()]>>()];
179}
180
181impl EraseType for Option<&'_ OsStr> {
182    type Result = [u8; size_of::<Option<&'static OsStr>>()];
183}
184
185impl EraseType for Option<mir::DestructuredConstant<'_>> {
186    type Result = [u8; size_of::<Option<mir::DestructuredConstant<'static>>>()];
187}
188
189impl EraseType for Option<ty::ImplTraitHeader<'_>> {
190    type Result = [u8; size_of::<Option<ty::ImplTraitHeader<'static>>>()];
191}
192
193impl EraseType for Option<ty::EarlyBinder<'_, Ty<'_>>> {
194    type Result = [u8; size_of::<Option<ty::EarlyBinder<'static, Ty<'static>>>>()];
195}
196
197impl EraseType for rustc_hir::MaybeOwner<'_> {
198    type Result = [u8; size_of::<rustc_hir::MaybeOwner<'static>>()];
199}
200
201impl<T: EraseType> EraseType for ty::EarlyBinder<'_, T> {
202    type Result = T::Result;
203}
204
205impl EraseType for ty::Binder<'_, ty::FnSig<'_>> {
206    type Result = [u8; size_of::<ty::Binder<'static, ty::FnSig<'static>>>()];
207}
208
209impl EraseType for ty::Binder<'_, ty::CoroutineWitnessTypes<TyCtxt<'_>>> {
210    type Result =
211        [u8; size_of::<ty::Binder<'static, ty::CoroutineWitnessTypes<TyCtxt<'static>>>>()];
212}
213
214impl EraseType for ty::Binder<'_, &'_ ty::List<Ty<'_>>> {
215    type Result = [u8; size_of::<ty::Binder<'static, &'static ty::List<Ty<'static>>>>()];
216}
217
218impl<T0, T1> EraseType for (&'_ T0, &'_ T1) {
219    type Result = [u8; size_of::<(&'static (), &'static ())>()];
220}
221
222impl<T0, T1> EraseType for (&'_ T0, &'_ [T1]) {
223    type Result = [u8; size_of::<(&'static (), &'static [()])>()];
224}
225
226impl<T0, T1> EraseType for (&'_ [T0], &'_ [T1]) {
227    type Result = [u8; size_of::<(&'static [()], &'static [()])>()];
228}
229
230impl<T0> EraseType for (&'_ T0, Result<(), ErrorGuaranteed>) {
231    type Result = [u8; size_of::<(&'static (), Result<(), ErrorGuaranteed>)>()];
232}
233
234macro_rules! trivial {
235    ($($ty:ty),+ $(,)?) => {
236        $(
237            impl EraseType for $ty {
238                type Result = [u8; size_of::<$ty>()];
239            }
240        )*
241    }
242}
243
244trivial! {
245    (),
246    bool,
247    Option<(rustc_span::def_id::DefId, rustc_session::config::EntryFnType)>,
248    Option<rustc_ast::expand::allocator::AllocatorKind>,
249    Option<rustc_attr_data_structures::ConstStability>,
250    Option<rustc_attr_data_structures::DefaultBodyStability>,
251    Option<rustc_attr_data_structures::Stability>,
252    Option<rustc_data_structures::svh::Svh>,
253    Option<rustc_hir::def::DefKind>,
254    Option<rustc_hir::CoroutineKind>,
255    Option<rustc_hir::HirId>,
256    Option<rustc_middle::middle::stability::DeprecationEntry>,
257    Option<rustc_middle::ty::AsyncDestructor>,
258    Option<rustc_middle::ty::Destructor>,
259    Option<rustc_middle::ty::ImplTraitInTraitData>,
260    Option<rustc_middle::ty::ScalarInt>,
261    Option<rustc_span::def_id::CrateNum>,
262    Option<rustc_span::def_id::DefId>,
263    Option<rustc_span::def_id::LocalDefId>,
264    Option<rustc_span::Span>,
265    Option<rustc_abi::FieldIdx>,
266    Option<rustc_target::spec::PanicStrategy>,
267    Option<usize>,
268    Option<rustc_middle::ty::IntrinsicDef>,
269    Option<rustc_abi::Align>,
270    Result<(), rustc_errors::ErrorGuaranteed>,
271    Result<(), rustc_middle::traits::query::NoSolution>,
272    Result<rustc_middle::traits::EvaluationResult, rustc_middle::traits::OverflowError>,
273    rustc_abi::ReprOptions,
274    rustc_ast::expand::allocator::AllocatorKind,
275    rustc_attr_data_structures::ConstStability,
276    rustc_attr_data_structures::DefaultBodyStability,
277    rustc_attr_data_structures::Deprecation,
278    rustc_attr_data_structures::Stability,
279    rustc_data_structures::svh::Svh,
280    rustc_errors::ErrorGuaranteed,
281    rustc_hir::Constness,
282    rustc_hir::def_id::DefId,
283    rustc_hir::def_id::DefIndex,
284    rustc_hir::def_id::LocalDefId,
285    rustc_hir::def_id::LocalModDefId,
286    rustc_hir::def::DefKind,
287    rustc_hir::Defaultness,
288    rustc_hir::definitions::DefKey,
289    rustc_hir::CoroutineKind,
290    rustc_hir::HirId,
291    rustc_hir::IsAsync,
292    rustc_hir::ItemLocalId,
293    rustc_hir::LangItem,
294    rustc_hir::OpaqueTyOrigin<rustc_hir::def_id::DefId>,
295    rustc_hir::OwnerId,
296    rustc_hir::Upvar,
297    rustc_index::bit_set::FiniteBitSet<u32>,
298    rustc_middle::middle::dependency_format::Linkage,
299    rustc_middle::middle::exported_symbols::SymbolExportInfo,
300    rustc_middle::middle::resolve_bound_vars::ObjectLifetimeDefault,
301    rustc_middle::middle::resolve_bound_vars::ResolvedArg,
302    rustc_middle::middle::stability::DeprecationEntry,
303    rustc_middle::mir::ConstQualifs,
304    rustc_middle::mir::interpret::AllocId,
305    rustc_middle::mir::interpret::CtfeProvenance,
306    rustc_middle::mir::interpret::ErrorHandled,
307    rustc_middle::thir::ExprId,
308    rustc_middle::traits::CodegenObligationError,
309    rustc_middle::traits::EvaluationResult,
310    rustc_middle::traits::OverflowError,
311    rustc_middle::traits::query::NoSolution,
312    rustc_middle::traits::WellFormedLoc,
313    rustc_middle::ty::adjustment::CoerceUnsizedInfo,
314    rustc_middle::ty::AssocItem,
315    rustc_middle::ty::AssocItemContainer,
316    rustc_middle::ty::Asyncness,
317    rustc_middle::ty::AsyncDestructor,
318    rustc_middle::ty::BoundVariableKind,
319    rustc_middle::ty::AnonConstKind,
320    rustc_middle::ty::DeducedParamAttrs,
321    rustc_middle::ty::Destructor,
322    rustc_middle::ty::fast_reject::SimplifiedType,
323    rustc_middle::ty::ImplPolarity,
324    rustc_middle::ty::Representability,
325    rustc_middle::ty::UnusedGenericParams,
326    rustc_middle::ty::util::AlwaysRequiresDrop,
327    rustc_middle::ty::Visibility<rustc_span::def_id::DefId>,
328    rustc_session::config::CrateType,
329    rustc_session::config::EntryFnType,
330    rustc_session::config::OptLevel,
331    rustc_session::config::SymbolManglingVersion,
332    rustc_session::cstore::CrateDepKind,
333    rustc_session::cstore::ExternCrate,
334    rustc_session::cstore::LinkagePreference,
335    rustc_session::Limits,
336    rustc_session::lint::LintExpectationId,
337    rustc_span::def_id::CrateNum,
338    rustc_span::def_id::DefPathHash,
339    rustc_span::ExpnHash,
340    rustc_span::ExpnId,
341    rustc_span::Span,
342    rustc_span::Symbol,
343    rustc_span::Ident,
344    rustc_target::spec::PanicStrategy,
345    rustc_type_ir::Variance,
346    u32,
347    usize,
348}
349
350macro_rules! tcx_lifetime {
351    ($($($fake_path:ident)::+),+ $(,)?) => {
352        $(
353            impl<'tcx> EraseType for $($fake_path)::+<'tcx> {
354                type Result = [u8; size_of::<$($fake_path)::+<'static>>()];
355            }
356        )*
357    }
358}
359
360tcx_lifetime! {
361    rustc_middle::middle::exported_symbols::ExportedSymbol,
362    rustc_middle::mir::Const,
363    rustc_middle::mir::DestructuredConstant,
364    rustc_middle::mir::ConstAlloc,
365    rustc_middle::mir::ConstValue,
366    rustc_middle::mir::interpret::GlobalId,
367    rustc_middle::mir::interpret::LitToConstInput,
368    rustc_middle::mir::interpret::EvalStaticInitializerRawResult,
369    rustc_middle::mir::mono::MonoItemPartitions,
370    rustc_middle::traits::query::MethodAutoderefStepsResult,
371    rustc_middle::traits::query::type_op::AscribeUserType,
372    rustc_middle::traits::query::type_op::Eq,
373    rustc_middle::traits::query::type_op::ProvePredicate,
374    rustc_middle::traits::query::type_op::Subtype,
375    rustc_middle::ty::AdtDef,
376    rustc_middle::ty::AliasTy,
377    rustc_middle::ty::ClauseKind,
378    rustc_middle::ty::ClosureTypeInfo,
379    rustc_middle::ty::Const,
380    rustc_middle::ty::DestructuredConst,
381    rustc_middle::ty::ExistentialTraitRef,
382    rustc_middle::ty::FnSig,
383    rustc_middle::ty::GenericArg,
384    rustc_middle::ty::GenericPredicates,
385    rustc_middle::ty::ConstConditions,
386    rustc_middle::ty::inhabitedness::InhabitedPredicate,
387    rustc_middle::ty::Instance,
388    rustc_middle::ty::InstanceKind,
389    rustc_middle::ty::layout::FnAbiError,
390    rustc_middle::ty::layout::LayoutError,
391    rustc_middle::ty::ParamEnv,
392    rustc_middle::ty::TypingEnv,
393    rustc_middle::ty::Predicate,
394    rustc_middle::ty::SymbolName,
395    rustc_middle::ty::TraitRef,
396    rustc_middle::ty::Ty,
397    rustc_middle::ty::UnevaluatedConst,
398    rustc_middle::ty::ValTree,
399    rustc_middle::ty::VtblEntry,
400}
rustc_middle/query/erase.rs

rustc_middle/query/
erase.rs
