rustc_metadata/rmeta/
mod.rs

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1use std::marker::PhantomData;
2use std::num::NonZero;
3
4pub(crate) use decoder::{CrateMetadata, CrateNumMap, MetadataBlob, TargetModifiers};
5use decoder::{DecodeContext, Metadata};
6use def_path_hash_map::DefPathHashMapRef;
7use encoder::EncodeContext;
8pub use encoder::{EncodedMetadata, encode_metadata, rendered_const};
9use rustc_abi::{FieldIdx, ReprOptions, VariantIdx};
10use rustc_ast::expand::StrippedCfgItem;
11use rustc_data_structures::fx::FxHashMap;
12use rustc_data_structures::svh::Svh;
13use rustc_hir::PreciseCapturingArgKind;
14use rustc_hir::def::{CtorKind, DefKind, DocLinkResMap};
15use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, DefIndex, DefPathHash, StableCrateId};
16use rustc_hir::definitions::DefKey;
17use rustc_hir::lang_items::LangItem;
18use rustc_index::IndexVec;
19use rustc_index::bit_set::DenseBitSet;
20use rustc_macros::{
21    Decodable, Encodable, MetadataDecodable, MetadataEncodable, TyDecodable, TyEncodable,
22};
23use rustc_middle::metadata::ModChild;
24use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrs;
25use rustc_middle::middle::debugger_visualizer::DebuggerVisualizerFile;
26use rustc_middle::middle::exported_symbols::{ExportedSymbol, SymbolExportInfo};
27use rustc_middle::middle::lib_features::FeatureStability;
28use rustc_middle::middle::resolve_bound_vars::ObjectLifetimeDefault;
29use rustc_middle::ty::fast_reject::SimplifiedType;
30use rustc_middle::ty::{
31    self, DeducedParamAttrs, ParameterizedOverTcx, Ty, TyCtxt, UnusedGenericParams,
32};
33use rustc_middle::util::Providers;
34use rustc_middle::{mir, trivially_parameterized_over_tcx};
35use rustc_serialize::opaque::FileEncoder;
36use rustc_session::config::{SymbolManglingVersion, TargetModifier};
37use rustc_session::cstore::{CrateDepKind, ForeignModule, LinkagePreference, NativeLib};
38use rustc_span::edition::Edition;
39use rustc_span::hygiene::{ExpnIndex, MacroKind, SyntaxContextData};
40use rustc_span::{self, ExpnData, ExpnHash, ExpnId, Ident, Span, Symbol};
41use rustc_target::spec::{PanicStrategy, TargetTuple};
42use table::TableBuilder;
43use {rustc_ast as ast, rustc_attr_parsing as attr, rustc_hir as hir};
44
45use crate::creader::CrateMetadataRef;
46
47mod decoder;
48mod def_path_hash_map;
49mod encoder;
50mod table;
51
52pub(crate) fn rustc_version(cfg_version: &'static str) -> String {
53    format!("rustc {cfg_version}")
54}
55
56/// Metadata encoding version.
57/// N.B., increment this if you change the format of metadata such that
58/// the rustc version can't be found to compare with `rustc_version()`.
59const METADATA_VERSION: u8 = 9;
60
61/// Metadata header which includes `METADATA_VERSION`.
62///
63/// This header is followed by the length of the compressed data, then
64/// the position of the `CrateRoot`, which is encoded as a 64-bit little-endian
65/// unsigned integer, and further followed by the rustc version string.
66pub const METADATA_HEADER: &[u8] = &[b'r', b'u', b's', b't', 0, 0, 0, METADATA_VERSION];
67
68/// A value of type T referred to by its absolute position
69/// in the metadata, and which can be decoded lazily.
70///
71/// Metadata is effective a tree, encoded in post-order,
72/// and with the root's position written next to the header.
73/// That means every single `LazyValue` points to some previous
74/// location in the metadata and is part of a larger node.
75///
76/// The first `LazyValue` in a node is encoded as the backwards
77/// distance from the position where the containing node
78/// starts and where the `LazyValue` points to, while the rest
79/// use the forward distance from the previous `LazyValue`.
80/// Distances start at 1, as 0-byte nodes are invalid.
81/// Also invalid are nodes being referred in a different
82/// order than they were encoded in.
83#[must_use]
84struct LazyValue<T> {
85    position: NonZero<usize>,
86    _marker: PhantomData<fn() -> T>,
87}
88
89impl<T: ParameterizedOverTcx> ParameterizedOverTcx for LazyValue<T> {
90    type Value<'tcx> = LazyValue<T::Value<'tcx>>;
91}
92
93impl<T> LazyValue<T> {
94    fn from_position(position: NonZero<usize>) -> LazyValue<T> {
95        LazyValue { position, _marker: PhantomData }
96    }
97}
98
99/// A list of lazily-decoded values.
100///
101/// Unlike `LazyValue<Vec<T>>`, the length is encoded next to the
102/// position, not at the position, which means that the length
103/// doesn't need to be known before encoding all the elements.
104///
105/// If the length is 0, no position is encoded, but otherwise,
106/// the encoding is that of `LazyArray`, with the distinction that
107/// the minimal distance the length of the sequence, i.e.
108/// it's assumed there's no 0-byte element in the sequence.
109struct LazyArray<T> {
110    position: NonZero<usize>,
111    num_elems: usize,
112    _marker: PhantomData<fn() -> T>,
113}
114
115impl<T: ParameterizedOverTcx> ParameterizedOverTcx for LazyArray<T> {
116    type Value<'tcx> = LazyArray<T::Value<'tcx>>;
117}
118
119impl<T> Default for LazyArray<T> {
120    fn default() -> LazyArray<T> {
121        LazyArray::from_position_and_num_elems(NonZero::new(1).unwrap(), 0)
122    }
123}
124
125impl<T> LazyArray<T> {
126    fn from_position_and_num_elems(position: NonZero<usize>, num_elems: usize) -> LazyArray<T> {
127        LazyArray { position, num_elems, _marker: PhantomData }
128    }
129}
130
131/// A list of lazily-decoded values, with the added capability of random access.
132///
133/// Random-access table (i.e. offering constant-time `get`/`set`), similar to
134/// `LazyArray<T>`, but without requiring encoding or decoding all the values
135/// eagerly and in-order.
136struct LazyTable<I, T> {
137    position: NonZero<usize>,
138    /// The encoded size of the elements of a table is selected at runtime to drop
139    /// trailing zeroes. This is the number of bytes used for each table element.
140    width: usize,
141    /// How many elements are in the table.
142    len: usize,
143    _marker: PhantomData<fn(I) -> T>,
144}
145
146impl<I: 'static, T: ParameterizedOverTcx> ParameterizedOverTcx for LazyTable<I, T> {
147    type Value<'tcx> = LazyTable<I, T::Value<'tcx>>;
148}
149
150impl<I, T> LazyTable<I, T> {
151    fn from_position_and_encoded_size(
152        position: NonZero<usize>,
153        width: usize,
154        len: usize,
155    ) -> LazyTable<I, T> {
156        LazyTable { position, width, len, _marker: PhantomData }
157    }
158}
159
160impl<T> Copy for LazyValue<T> {}
161impl<T> Clone for LazyValue<T> {
162    fn clone(&self) -> Self {
163        *self
164    }
165}
166
167impl<T> Copy for LazyArray<T> {}
168impl<T> Clone for LazyArray<T> {
169    fn clone(&self) -> Self {
170        *self
171    }
172}
173
174impl<I, T> Copy for LazyTable<I, T> {}
175impl<I, T> Clone for LazyTable<I, T> {
176    fn clone(&self) -> Self {
177        *self
178    }
179}
180
181/// Encoding / decoding state for `Lazy`s (`LazyValue`, `LazyArray`, and `LazyTable`).
182#[derive(Copy, Clone, PartialEq, Eq, Debug)]
183enum LazyState {
184    /// Outside of a metadata node.
185    NoNode,
186
187    /// Inside a metadata node, and before any `Lazy`s.
188    /// The position is that of the node itself.
189    NodeStart(NonZero<usize>),
190
191    /// Inside a metadata node, with a previous `Lazy`s.
192    /// The position is where that previous `Lazy` would start.
193    Previous(NonZero<usize>),
194}
195
196type SyntaxContextTable = LazyTable<u32, Option<LazyValue<SyntaxContextData>>>;
197type ExpnDataTable = LazyTable<ExpnIndex, Option<LazyValue<ExpnData>>>;
198type ExpnHashTable = LazyTable<ExpnIndex, Option<LazyValue<ExpnHash>>>;
199
200#[derive(MetadataEncodable, MetadataDecodable)]
201pub(crate) struct ProcMacroData {
202    proc_macro_decls_static: DefIndex,
203    stability: Option<attr::Stability>,
204    macros: LazyArray<DefIndex>,
205}
206
207/// Serialized crate metadata.
208///
209/// This contains just enough information to determine if we should load the `CrateRoot` or not.
210/// Prefer [`CrateRoot`] whenever possible to avoid ICEs when using `omit-git-hash` locally.
211/// See #76720 for more details.
212///
213/// If you do modify this struct, also bump the [`METADATA_VERSION`] constant.
214#[derive(MetadataEncodable, MetadataDecodable)]
215pub(crate) struct CrateHeader {
216    pub(crate) triple: TargetTuple,
217    pub(crate) hash: Svh,
218    pub(crate) name: Symbol,
219    /// Whether this is the header for a proc-macro crate.
220    ///
221    /// This is separate from [`ProcMacroData`] to avoid having to update [`METADATA_VERSION`] every
222    /// time ProcMacroData changes.
223    pub(crate) is_proc_macro_crate: bool,
224}
225
226/// Serialized `.rmeta` data for a crate.
227///
228/// When compiling a proc-macro crate, we encode many of
229/// the `LazyArray<T>` fields as `Lazy::empty()`. This serves two purposes:
230///
231/// 1. We avoid performing unnecessary work. Proc-macro crates can only
232/// export proc-macros functions, which are compiled into a shared library.
233/// As a result, a large amount of the information we normally store
234/// (e.g. optimized MIR) is unneeded by downstream crates.
235/// 2. We avoid serializing invalid `CrateNum`s. When we deserialize
236/// a proc-macro crate, we don't load any of its dependencies (since we
237/// just need to invoke a native function from the shared library).
238/// This means that any foreign `CrateNum`s that we serialize cannot be
239/// deserialized, since we will not know how to map them into the current
240/// compilation session. If we were to serialize a proc-macro crate like
241/// a normal crate, much of what we serialized would be unusable in addition
242/// to being unused.
243#[derive(MetadataEncodable, MetadataDecodable)]
244pub(crate) struct CrateRoot {
245    /// A header used to detect if this is the right crate to load.
246    header: CrateHeader,
247
248    extra_filename: String,
249    stable_crate_id: StableCrateId,
250    required_panic_strategy: Option<PanicStrategy>,
251    panic_in_drop_strategy: PanicStrategy,
252    edition: Edition,
253    has_global_allocator: bool,
254    has_alloc_error_handler: bool,
255    has_panic_handler: bool,
256    has_default_lib_allocator: bool,
257
258    crate_deps: LazyArray<CrateDep>,
259    dylib_dependency_formats: LazyArray<Option<LinkagePreference>>,
260    lib_features: LazyArray<(Symbol, FeatureStability)>,
261    stability_implications: LazyArray<(Symbol, Symbol)>,
262    lang_items: LazyArray<(DefIndex, LangItem)>,
263    lang_items_missing: LazyArray<LangItem>,
264    stripped_cfg_items: LazyArray<StrippedCfgItem<DefIndex>>,
265    diagnostic_items: LazyArray<(Symbol, DefIndex)>,
266    native_libraries: LazyArray<NativeLib>,
267    foreign_modules: LazyArray<ForeignModule>,
268    traits: LazyArray<DefIndex>,
269    impls: LazyArray<TraitImpls>,
270    incoherent_impls: LazyArray<IncoherentImpls>,
271    interpret_alloc_index: LazyArray<u64>,
272    proc_macro_data: Option<ProcMacroData>,
273
274    tables: LazyTables,
275    debugger_visualizers: LazyArray<DebuggerVisualizerFile>,
276
277    exported_symbols: LazyArray<(ExportedSymbol<'static>, SymbolExportInfo)>,
278
279    syntax_contexts: SyntaxContextTable,
280    expn_data: ExpnDataTable,
281    expn_hashes: ExpnHashTable,
282
283    def_path_hash_map: LazyValue<DefPathHashMapRef<'static>>,
284
285    source_map: LazyTable<u32, Option<LazyValue<rustc_span::SourceFile>>>,
286    target_modifiers: LazyArray<TargetModifier>,
287
288    compiler_builtins: bool,
289    needs_allocator: bool,
290    needs_panic_runtime: bool,
291    no_builtins: bool,
292    panic_runtime: bool,
293    profiler_runtime: bool,
294    symbol_mangling_version: SymbolManglingVersion,
295
296    specialization_enabled_in: bool,
297}
298
299/// On-disk representation of `DefId`.
300/// This creates a type-safe way to enforce that we remap the CrateNum between the on-disk
301/// representation and the compilation session.
302#[derive(Copy, Clone)]
303pub(crate) struct RawDefId {
304    krate: u32,
305    index: u32,
306}
307
308impl From<DefId> for RawDefId {
309    fn from(val: DefId) -> Self {
310        RawDefId { krate: val.krate.as_u32(), index: val.index.as_u32() }
311    }
312}
313
314impl RawDefId {
315    /// This exists so that `provide_one!` is happy
316    fn decode(self, meta: (CrateMetadataRef<'_>, TyCtxt<'_>)) -> DefId {
317        self.decode_from_cdata(meta.0)
318    }
319
320    fn decode_from_cdata(self, cdata: CrateMetadataRef<'_>) -> DefId {
321        let krate = CrateNum::from_u32(self.krate);
322        let krate = cdata.map_encoded_cnum_to_current(krate);
323        DefId { krate, index: DefIndex::from_u32(self.index) }
324    }
325}
326
327#[derive(Encodable, Decodable)]
328pub(crate) struct CrateDep {
329    pub name: Symbol,
330    pub hash: Svh,
331    pub host_hash: Option<Svh>,
332    pub kind: CrateDepKind,
333    pub extra_filename: String,
334    pub is_private: bool,
335}
336
337#[derive(MetadataEncodable, MetadataDecodable)]
338pub(crate) struct TraitImpls {
339    trait_id: (u32, DefIndex),
340    impls: LazyArray<(DefIndex, Option<SimplifiedType>)>,
341}
342
343#[derive(MetadataEncodable, MetadataDecodable)]
344pub(crate) struct IncoherentImpls {
345    self_ty: SimplifiedType,
346    impls: LazyArray<DefIndex>,
347}
348
349/// Define `LazyTables` and `TableBuilders` at the same time.
350macro_rules! define_tables {
351    (
352        - defaulted: $($name1:ident: Table<$IDX1:ty, $T1:ty>,)+
353        - optional: $($name2:ident: Table<$IDX2:ty, $T2:ty>,)+
354    ) => {
355        #[derive(MetadataEncodable, MetadataDecodable)]
356        pub(crate) struct LazyTables {
357            $($name1: LazyTable<$IDX1, $T1>,)+
358            $($name2: LazyTable<$IDX2, Option<$T2>>,)+
359        }
360
361        #[derive(Default)]
362        struct TableBuilders {
363            $($name1: TableBuilder<$IDX1, $T1>,)+
364            $($name2: TableBuilder<$IDX2, Option<$T2>>,)+
365        }
366
367        impl TableBuilders {
368            fn encode(&self, buf: &mut FileEncoder) -> LazyTables {
369                LazyTables {
370                    $($name1: self.$name1.encode(buf),)+
371                    $($name2: self.$name2.encode(buf),)+
372                }
373            }
374        }
375    }
376}
377
378define_tables! {
379- defaulted:
380    intrinsic: Table<DefIndex, Option<LazyValue<ty::IntrinsicDef>>>,
381    is_macro_rules: Table<DefIndex, bool>,
382    type_alias_is_lazy: Table<DefIndex, bool>,
383    attr_flags: Table<DefIndex, AttrFlags>,
384    // The u64 is the crate-local part of the DefPathHash. All hashes in this crate have the same
385    // StableCrateId, so we omit encoding those into the table.
386    //
387    // Note also that this table is fully populated (no gaps) as every DefIndex should have a
388    // corresponding DefPathHash.
389    def_path_hashes: Table<DefIndex, u64>,
390    explicit_item_bounds: Table<DefIndex, LazyArray<(ty::Clause<'static>, Span)>>,
391    explicit_item_self_bounds: Table<DefIndex, LazyArray<(ty::Clause<'static>, Span)>>,
392    inferred_outlives_of: Table<DefIndex, LazyArray<(ty::Clause<'static>, Span)>>,
393    explicit_super_predicates_of: Table<DefIndex, LazyArray<(ty::Clause<'static>, Span)>>,
394    explicit_implied_predicates_of: Table<DefIndex, LazyArray<(ty::Clause<'static>, Span)>>,
395    explicit_implied_const_bounds: Table<DefIndex, LazyArray<(ty::PolyTraitRef<'static>, Span)>>,
396    inherent_impls: Table<DefIndex, LazyArray<DefIndex>>,
397    associated_types_for_impl_traits_in_associated_fn: Table<DefIndex, LazyArray<DefId>>,
398    opt_rpitit_info: Table<DefIndex, Option<LazyValue<ty::ImplTraitInTraitData>>>,
399    // Reexported names are not associated with individual `DefId`s,
400    // e.g. a glob import can introduce a lot of names, all with the same `DefId`.
401    // That's why the encoded list needs to contain `ModChild` structures describing all the names
402    // individually instead of `DefId`s.
403    module_children_reexports: Table<DefIndex, LazyArray<ModChild>>,
404    cross_crate_inlinable: Table<DefIndex, bool>,
405
406- optional:
407    attributes: Table<DefIndex, LazyArray<hir::Attribute>>,
408    // For non-reexported names in a module every name is associated with a separate `DefId`,
409    // so we can take their names, visibilities etc from other encoded tables.
410    module_children_non_reexports: Table<DefIndex, LazyArray<DefIndex>>,
411    associated_item_or_field_def_ids: Table<DefIndex, LazyArray<DefIndex>>,
412    def_kind: Table<DefIndex, DefKind>,
413    visibility: Table<DefIndex, LazyValue<ty::Visibility<DefIndex>>>,
414    safety: Table<DefIndex, hir::Safety>,
415    def_span: Table<DefIndex, LazyValue<Span>>,
416    def_ident_span: Table<DefIndex, LazyValue<Span>>,
417    lookup_stability: Table<DefIndex, LazyValue<attr::Stability>>,
418    lookup_const_stability: Table<DefIndex, LazyValue<attr::ConstStability>>,
419    lookup_default_body_stability: Table<DefIndex, LazyValue<attr::DefaultBodyStability>>,
420    lookup_deprecation_entry: Table<DefIndex, LazyValue<attr::Deprecation>>,
421    explicit_predicates_of: Table<DefIndex, LazyValue<ty::GenericPredicates<'static>>>,
422    generics_of: Table<DefIndex, LazyValue<ty::Generics>>,
423    type_of: Table<DefIndex, LazyValue<ty::EarlyBinder<'static, Ty<'static>>>>,
424    variances_of: Table<DefIndex, LazyArray<ty::Variance>>,
425    fn_sig: Table<DefIndex, LazyValue<ty::EarlyBinder<'static, ty::PolyFnSig<'static>>>>,
426    codegen_fn_attrs: Table<DefIndex, LazyValue<CodegenFnAttrs>>,
427    impl_trait_header: Table<DefIndex, LazyValue<ty::ImplTraitHeader<'static>>>,
428    const_param_default: Table<DefIndex, LazyValue<ty::EarlyBinder<'static, rustc_middle::ty::Const<'static>>>>,
429    object_lifetime_default: Table<DefIndex, LazyValue<ObjectLifetimeDefault>>,
430    optimized_mir: Table<DefIndex, LazyValue<mir::Body<'static>>>,
431    mir_for_ctfe: Table<DefIndex, LazyValue<mir::Body<'static>>>,
432    closure_saved_names_of_captured_variables: Table<DefIndex, LazyValue<IndexVec<FieldIdx, Symbol>>>,
433    mir_coroutine_witnesses: Table<DefIndex, LazyValue<mir::CoroutineLayout<'static>>>,
434    promoted_mir: Table<DefIndex, LazyValue<IndexVec<mir::Promoted, mir::Body<'static>>>>,
435    thir_abstract_const: Table<DefIndex, LazyValue<ty::EarlyBinder<'static, ty::Const<'static>>>>,
436    impl_parent: Table<DefIndex, RawDefId>,
437    constness: Table<DefIndex, hir::Constness>,
438    const_conditions: Table<DefIndex, LazyValue<ty::ConstConditions<'static>>>,
439    defaultness: Table<DefIndex, hir::Defaultness>,
440    // FIXME(eddyb) perhaps compute this on the fly if cheap enough?
441    coerce_unsized_info: Table<DefIndex, LazyValue<ty::adjustment::CoerceUnsizedInfo>>,
442    mir_const_qualif: Table<DefIndex, LazyValue<mir::ConstQualifs>>,
443    rendered_const: Table<DefIndex, LazyValue<String>>,
444    rendered_precise_capturing_args: Table<DefIndex, LazyArray<PreciseCapturingArgKind<Symbol, Symbol>>>,
445    asyncness: Table<DefIndex, ty::Asyncness>,
446    fn_arg_names: Table<DefIndex, LazyArray<Option<Ident>>>,
447    coroutine_kind: Table<DefIndex, hir::CoroutineKind>,
448    coroutine_for_closure: Table<DefIndex, RawDefId>,
449    coroutine_by_move_body_def_id: Table<DefIndex, RawDefId>,
450    eval_static_initializer: Table<DefIndex, LazyValue<mir::interpret::ConstAllocation<'static>>>,
451    trait_def: Table<DefIndex, LazyValue<ty::TraitDef>>,
452    trait_item_def_id: Table<DefIndex, RawDefId>,
453    expn_that_defined: Table<DefIndex, LazyValue<ExpnId>>,
454    default_fields: Table<DefIndex, LazyValue<DefId>>,
455    params_in_repr: Table<DefIndex, LazyValue<DenseBitSet<u32>>>,
456    repr_options: Table<DefIndex, LazyValue<ReprOptions>>,
457    // `def_keys` and `def_path_hashes` represent a lazy version of a
458    // `DefPathTable`. This allows us to avoid deserializing an entire
459    // `DefPathTable` up front, since we may only ever use a few
460    // definitions from any given crate.
461    def_keys: Table<DefIndex, LazyValue<DefKey>>,
462    proc_macro_quoted_spans: Table<usize, LazyValue<Span>>,
463    variant_data: Table<DefIndex, LazyValue<VariantData>>,
464    assoc_container: Table<DefIndex, ty::AssocItemContainer>,
465    macro_definition: Table<DefIndex, LazyValue<ast::DelimArgs>>,
466    proc_macro: Table<DefIndex, MacroKind>,
467    deduced_param_attrs: Table<DefIndex, LazyArray<DeducedParamAttrs>>,
468    trait_impl_trait_tys: Table<DefIndex, LazyValue<DefIdMap<ty::EarlyBinder<'static, Ty<'static>>>>>,
469    doc_link_resolutions: Table<DefIndex, LazyValue<DocLinkResMap>>,
470    doc_link_traits_in_scope: Table<DefIndex, LazyArray<DefId>>,
471    assumed_wf_types_for_rpitit: Table<DefIndex, LazyArray<(Ty<'static>, Span)>>,
472    opaque_ty_origin: Table<DefIndex, LazyValue<hir::OpaqueTyOrigin<DefId>>>,
473}
474
475#[derive(TyEncodable, TyDecodable)]
476struct VariantData {
477    idx: VariantIdx,
478    discr: ty::VariantDiscr,
479    /// If this is unit or tuple-variant/struct, then this is the index of the ctor id.
480    ctor: Option<(CtorKind, DefIndex)>,
481    is_non_exhaustive: bool,
482}
483
484bitflags::bitflags! {
485    #[derive(Default)]
486    pub struct AttrFlags: u8 {
487        const IS_DOC_HIDDEN = 1 << 0;
488    }
489}
490
491/// A span tag byte encodes a bunch of data, so that we can cut out a few extra bytes from span
492/// encodings (which are very common, for example, libcore has ~650,000 unique spans and over 1.1
493/// million references to prior-written spans).
494///
495/// The byte format is split into several parts:
496///
497/// [ a a a a a c d d ]
498///
499/// `a` bits represent the span length. We have 5 bits, so we can store lengths up to 30 inline, with
500/// an all-1s pattern representing that the length is stored separately.
501///
502/// `c` represents whether the span context is zero (and then it is not stored as a separate varint)
503/// for direct span encodings, and whether the offset is absolute or relative otherwise (zero for
504/// absolute).
505///
506/// d bits represent the kind of span we are storing (local, foreign, partial, indirect).
507#[derive(Encodable, Decodable, Copy, Clone)]
508struct SpanTag(u8);
509
510#[derive(Debug, Copy, Clone, PartialEq, Eq)]
511enum SpanKind {
512    Local = 0b00,
513    Foreign = 0b01,
514    Partial = 0b10,
515    // Indicates the actual span contents are elsewhere.
516    // If this is the kind, then the span context bit represents whether it is a relative or
517    // absolute offset.
518    Indirect = 0b11,
519}
520
521impl SpanTag {
522    fn new(kind: SpanKind, context: rustc_span::SyntaxContext, length: usize) -> SpanTag {
523        let mut data = 0u8;
524        data |= kind as u8;
525        if context.is_root() {
526            data |= 0b100;
527        }
528        let all_1s_len = (0xffu8 << 3) >> 3;
529        // strictly less than - all 1s pattern is a sentinel for storage being out of band.
530        if length < all_1s_len as usize {
531            data |= (length as u8) << 3;
532        } else {
533            data |= all_1s_len << 3;
534        }
535
536        SpanTag(data)
537    }
538
539    fn indirect(relative: bool, length_bytes: u8) -> SpanTag {
540        let mut tag = SpanTag(SpanKind::Indirect as u8);
541        if relative {
542            tag.0 |= 0b100;
543        }
544        assert!(length_bytes <= 8);
545        tag.0 |= length_bytes << 3;
546        tag
547    }
548
549    fn kind(self) -> SpanKind {
550        let masked = self.0 & 0b11;
551        match masked {
552            0b00 => SpanKind::Local,
553            0b01 => SpanKind::Foreign,
554            0b10 => SpanKind::Partial,
555            0b11 => SpanKind::Indirect,
556            _ => unreachable!(),
557        }
558    }
559
560    fn is_relative_offset(self) -> bool {
561        debug_assert_eq!(self.kind(), SpanKind::Indirect);
562        self.0 & 0b100 != 0
563    }
564
565    fn context(self) -> Option<rustc_span::SyntaxContext> {
566        if self.0 & 0b100 != 0 { Some(rustc_span::SyntaxContext::root()) } else { None }
567    }
568
569    fn length(self) -> Option<rustc_span::BytePos> {
570        let all_1s_len = (0xffu8 << 3) >> 3;
571        let len = self.0 >> 3;
572        if len != all_1s_len { Some(rustc_span::BytePos(u32::from(len))) } else { None }
573    }
574}
575
576// Tags for encoding Symbol's
577const SYMBOL_STR: u8 = 0;
578const SYMBOL_OFFSET: u8 = 1;
579const SYMBOL_PREINTERNED: u8 = 2;
580
581pub fn provide(providers: &mut Providers) {
582    encoder::provide(providers);
583    decoder::provide(providers);
584}
585
586trivially_parameterized_over_tcx! {
587    VariantData,
588    RawDefId,
589    TraitImpls,
590    IncoherentImpls,
591    CrateHeader,
592    CrateRoot,
593    CrateDep,
594    AttrFlags,
595}
rustc_metadata/rmeta/mod.rs

rustc_metadata/rmeta/
mod.rs
