rustc_metadata/rmeta/
mod.rs

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

rustc_metadata/rmeta/
mod.rs
