rustc_middle/query/
erase.rs

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

rustc_middle/query/
erase.rs
