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::exported_symbols::{ExportedSymbol, SymbolExportInfo};
28use rustc_middle::middle::lib_features::FeatureStability;
29use rustc_middle::middle::resolve_bound_vars::ObjectLifetimeDefault;
30use rustc_middle::mir;
31use rustc_middle::ty::fast_reject::SimplifiedType;
32use rustc_middle::ty::{self, DeducedParamAttrs, Ty, TyCtxt, UnusedGenericParams};
33use rustc_middle::util::Providers;
34use rustc_serialize::opaque::FileEncoder;
35use rustc_session::config::{SymbolManglingVersion, TargetModifier};
36use rustc_session::cstore::{CrateDepKind, ForeignModule, LinkagePreference, NativeLib};
37use rustc_span::edition::Edition;
38use rustc_span::hygiene::{ExpnIndex, MacroKind, SyntaxContextKey};
39use rustc_span::{self, ExpnData, ExpnHash, ExpnId, Ident, Span, Symbol};
40use rustc_target::spec::{PanicStrategy, TargetTuple};
41use table::TableBuilder;
42use {rustc_ast as ast, rustc_hir as hir};
43
44use crate::creader::CrateMetadataRef;
45
46mod decoder;
47mod def_path_hash_map;
48mod encoder;
49mod parameterized;
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 = 10;
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> LazyValue<T> {
90    fn from_position(position: NonZero<usize>) -> LazyValue<T> {
91        LazyValue { position, _marker: PhantomData }
92    }
93}
94
95/// A list of lazily-decoded values.
96///
97/// Unlike `LazyValue<Vec<T>>`, the length is encoded next to the
98/// position, not at the position, which means that the length
99/// doesn't need to be known before encoding all the elements.
100///
101/// If the length is 0, no position is encoded, but otherwise,
102/// the encoding is that of `LazyArray`, with the distinction that
103/// the minimal distance the length of the sequence, i.e.
104/// it's assumed there's no 0-byte element in the sequence.
105struct LazyArray<T> {
106    position: NonZero<usize>,
107    num_elems: usize,
108    _marker: PhantomData<fn() -> T>,
109}
110
111impl<T> Default for LazyArray<T> {
112    fn default() -> LazyArray<T> {
113        LazyArray::from_position_and_num_elems(NonZero::new(1).unwrap(), 0)
114    }
115}
116
117impl<T> LazyArray<T> {
118    fn from_position_and_num_elems(position: NonZero<usize>, num_elems: usize) -> LazyArray<T> {
119        LazyArray { position, num_elems, _marker: PhantomData }
120    }
121}
122
123/// A list of lazily-decoded values, with the added capability of random access.
124///
125/// Random-access table (i.e. offering constant-time `get`/`set`), similar to
126/// `LazyArray<T>`, but without requiring encoding or decoding all the values
127/// eagerly and in-order.
128struct LazyTable<I, T> {
129    position: NonZero<usize>,
130    /// The encoded size of the elements of a table is selected at runtime to drop
131    /// trailing zeroes. This is the number of bytes used for each table element.
132    width: usize,
133    /// How many elements are in the table.
134    len: usize,
135    _marker: PhantomData<fn(I) -> T>,
136}
137
138impl<I, T> LazyTable<I, T> {
139    fn from_position_and_encoded_size(
140        position: NonZero<usize>,
141        width: usize,
142        len: usize,
143    ) -> LazyTable<I, T> {
144        LazyTable { position, width, len, _marker: PhantomData }
145    }
146}
147
148impl<T> Copy for LazyValue<T> {}
149impl<T> Clone for LazyValue<T> {
150    fn clone(&self) -> Self {
151        *self
152    }
153}
154
155impl<T> Copy for LazyArray<T> {}
156impl<T> Clone for LazyArray<T> {
157    fn clone(&self) -> Self {
158        *self
159    }
160}
161
162impl<I, T> Copy for LazyTable<I, T> {}
163impl<I, T> Clone for LazyTable<I, T> {
164    fn clone(&self) -> Self {
165        *self
166    }
167}
168
169/// Encoding / decoding state for `Lazy`s (`LazyValue`, `LazyArray`, and `LazyTable`).
170#[derive(Copy, Clone, PartialEq, Eq, Debug)]
171enum LazyState {
172    /// Outside of a metadata node.
173    NoNode,
174
175    /// Inside a metadata node, and before any `Lazy`s.
176    /// The position is that of the node itself.
177    NodeStart(NonZero<usize>),
178
179    /// Inside a metadata node, with a previous `Lazy`s.
180    /// The position is where that previous `Lazy` would start.
181    Previous(NonZero<usize>),
182}
183
184type SyntaxContextTable = LazyTable<u32, Option<LazyValue<SyntaxContextKey>>>;
185type ExpnDataTable = LazyTable<ExpnIndex, Option<LazyValue<ExpnData>>>;
186type ExpnHashTable = LazyTable<ExpnIndex, Option<LazyValue<ExpnHash>>>;
187
188#[derive(MetadataEncodable, MetadataDecodable)]
189pub(crate) struct ProcMacroData {
190    proc_macro_decls_static: DefIndex,
191    stability: Option<hir::Stability>,
192    macros: LazyArray<DefIndex>,
193}
194
195/// Serialized crate metadata.
196///
197/// This contains just enough information to determine if we should load the `CrateRoot` or not.
198/// Prefer [`CrateRoot`] whenever possible to avoid ICEs when using `omit-git-hash` locally.
199/// See #76720 for more details.
200///
201/// If you do modify this struct, also bump the [`METADATA_VERSION`] constant.
202#[derive(MetadataEncodable, MetadataDecodable)]
203pub(crate) struct CrateHeader {
204    pub(crate) triple: TargetTuple,
205    pub(crate) hash: Svh,
206    pub(crate) name: Symbol,
207    /// Whether this is the header for a proc-macro crate.
208    ///
209    /// This is separate from [`ProcMacroData`] to avoid having to update [`METADATA_VERSION`] every
210    /// time ProcMacroData changes.
211    pub(crate) is_proc_macro_crate: bool,
212    /// Whether this crate metadata section is just a stub.
213    /// Stubs do not contain the full metadata (it will be typically stored
214    /// in a separate rmeta file).
215    ///
216    /// This is used inside rlibs and dylibs when using `-Zembed-metadata=no`.
217    pub(crate) is_stub: bool,
218}
219
220/// Serialized `.rmeta` data for a crate.
221///
222/// When compiling a proc-macro crate, we encode many of
223/// the `LazyArray<T>` fields as `Lazy::empty()`. This serves two purposes:
224///
225/// 1. We avoid performing unnecessary work. Proc-macro crates can only
226/// export proc-macros functions, which are compiled into a shared library.
227/// As a result, a large amount of the information we normally store
228/// (e.g. optimized MIR) is unneeded by downstream crates.
229/// 2. We avoid serializing invalid `CrateNum`s. When we deserialize
230/// a proc-macro crate, we don't load any of its dependencies (since we
231/// just need to invoke a native function from the shared library).
232/// This means that any foreign `CrateNum`s that we serialize cannot be
233/// deserialized, since we will not know how to map them into the current
234/// compilation session. If we were to serialize a proc-macro crate like
235/// a normal crate, much of what we serialized would be unusable in addition
236/// to being unused.
237#[derive(MetadataEncodable, MetadataDecodable)]
238pub(crate) struct CrateRoot {
239    /// A header used to detect if this is the right crate to load.
240    header: CrateHeader,
241
242    extra_filename: String,
243    stable_crate_id: StableCrateId,
244    required_panic_strategy: Option<PanicStrategy>,
245    panic_in_drop_strategy: PanicStrategy,
246    edition: Edition,
247    has_global_allocator: bool,
248    has_alloc_error_handler: bool,
249    has_panic_handler: bool,
250    has_default_lib_allocator: bool,
251
252    crate_deps: LazyArray<CrateDep>,
253    dylib_dependency_formats: LazyArray<Option<LinkagePreference>>,
254    lib_features: LazyArray<(Symbol, FeatureStability)>,
255    stability_implications: LazyArray<(Symbol, Symbol)>,
256    lang_items: LazyArray<(DefIndex, LangItem)>,
257    lang_items_missing: LazyArray<LangItem>,
258    stripped_cfg_items: LazyArray<StrippedCfgItem<DefIndex>>,
259    diagnostic_items: LazyArray<(Symbol, DefIndex)>,
260    native_libraries: LazyArray<NativeLib>,
261    foreign_modules: LazyArray<ForeignModule>,
262    traits: LazyArray<DefIndex>,
263    impls: LazyArray<TraitImpls>,
264    incoherent_impls: LazyArray<IncoherentImpls>,
265    interpret_alloc_index: LazyArray<u64>,
266    proc_macro_data: Option<ProcMacroData>,
267
268    tables: LazyTables,
269    debugger_visualizers: LazyArray<DebuggerVisualizerFile>,
270
271    exportable_items: LazyArray<DefIndex>,
272    stable_order_of_exportable_impls: LazyArray<(DefIndex, usize)>,
273    exported_non_generic_symbols: LazyArray<(ExportedSymbol<'static>, SymbolExportInfo)>,
274    exported_generic_symbols: LazyArray<(ExportedSymbol<'static>, SymbolExportInfo)>,
275
276    syntax_contexts: SyntaxContextTable,
277    expn_data: ExpnDataTable,
278    expn_hashes: ExpnHashTable,
279
280    def_path_hash_map: LazyValue<DefPathHashMapRef<'static>>,
281
282    source_map: LazyTable<u32, Option<LazyValue<rustc_span::SourceFile>>>,
283    target_modifiers: LazyArray<TargetModifier>,
284
285    compiler_builtins: bool,
286    needs_allocator: bool,
287    needs_panic_runtime: bool,
288    no_builtins: bool,
289    panic_runtime: bool,
290    profiler_runtime: bool,
291    symbol_mangling_version: SymbolManglingVersion,
292
293    specialization_enabled_in: bool,
294}
295
296/// On-disk representation of `DefId`.
297/// This creates a type-safe way to enforce that we remap the CrateNum between the on-disk
298/// representation and the compilation session.
299#[derive(Copy, Clone)]
300pub(crate) struct RawDefId {
301    krate: u32,
302    index: u32,
303}
304
305impl From<DefId> for RawDefId {
306    fn from(val: DefId) -> Self {
307        RawDefId { krate: val.krate.as_u32(), index: val.index.as_u32() }
308    }
309}
310
311impl RawDefId {
312    /// This exists so that `provide_one!` is happy
313    fn decode(self, meta: (CrateMetadataRef<'_>, TyCtxt<'_>)) -> DefId {
314        self.decode_from_cdata(meta.0)
315    }
316
317    fn decode_from_cdata(self, cdata: CrateMetadataRef<'_>) -> DefId {
318        let krate = CrateNum::from_u32(self.krate);
319        let krate = cdata.map_encoded_cnum_to_current(krate);
320        DefId { krate, index: DefIndex::from_u32(self.index) }
321    }
322}
323
324#[derive(Encodable, Decodable)]
325pub(crate) struct CrateDep {
326    pub name: Symbol,
327    pub hash: Svh,
328    pub host_hash: Option<Svh>,
329    pub kind: CrateDepKind,
330    pub extra_filename: String,
331    pub is_private: bool,
332}
333
334#[derive(MetadataEncodable, MetadataDecodable)]
335pub(crate) struct TraitImpls {
336    trait_id: (u32, DefIndex),
337    impls: LazyArray<(DefIndex, Option<SimplifiedType>)>,
338}
339
340#[derive(MetadataEncodable, MetadataDecodable)]
341pub(crate) struct IncoherentImpls {
342    self_ty: SimplifiedType,
343    impls: LazyArray<DefIndex>,
344}
345
346/// Define `LazyTables` and `TableBuilders` at the same time.
347macro_rules! define_tables {
348    (
349        - defaulted: $($name1:ident: Table<$IDX1:ty, $T1:ty>,)+
350        - optional: $($name2:ident: Table<$IDX2:ty, $T2:ty>,)+
351    ) => {
352        #[derive(MetadataEncodable, MetadataDecodable)]
353        pub(crate) struct LazyTables {
354            $($name1: LazyTable<$IDX1, $T1>,)+
355            $($name2: LazyTable<$IDX2, Option<$T2>>,)+
356        }
357
358        #[derive(Default)]
359        struct TableBuilders {
360            $($name1: TableBuilder<$IDX1, $T1>,)+
361            $($name2: TableBuilder<$IDX2, Option<$T2>>,)+
362        }
363
364        impl TableBuilders {
365            fn encode(&self, buf: &mut FileEncoder) -> LazyTables {
366                LazyTables {
367                    $($name1: self.$name1.encode(buf),)+
368                    $($name2: self.$name2.encode(buf),)+
369                }
370            }
371        }
372    }
373}
374
375define_tables! {
376- defaulted:
377    intrinsic: Table<DefIndex, Option<LazyValue<ty::IntrinsicDef>>>,
378    is_macro_rules: Table<DefIndex, bool>,
379    type_alias_is_lazy: Table<DefIndex, bool>,
380    attr_flags: Table<DefIndex, AttrFlags>,
381    // The u64 is the crate-local part of the DefPathHash. All hashes in this crate have the same
382    // StableCrateId, so we omit encoding those into the table.
383    //
384    // Note also that this table is fully populated (no gaps) as every DefIndex should have a
385    // corresponding DefPathHash.
386    def_path_hashes: Table<DefIndex, u64>,
387    explicit_item_bounds: Table<DefIndex, LazyArray<(ty::Clause<'static>, Span)>>,
388    explicit_item_self_bounds: Table<DefIndex, LazyArray<(ty::Clause<'static>, Span)>>,
389    inferred_outlives_of: Table<DefIndex, LazyArray<(ty::Clause<'static>, Span)>>,
390    explicit_super_predicates_of: Table<DefIndex, LazyArray<(ty::Clause<'static>, Span)>>,
391    explicit_implied_predicates_of: Table<DefIndex, LazyArray<(ty::Clause<'static>, Span)>>,
392    explicit_implied_const_bounds: Table<DefIndex, LazyArray<(ty::PolyTraitRef<'static>, Span)>>,
393    inherent_impls: Table<DefIndex, LazyArray<DefIndex>>,
394    opt_rpitit_info: Table<DefIndex, Option<LazyValue<ty::ImplTraitInTraitData>>>,
395    // Reexported names are not associated with individual `DefId`s,
396    // e.g. a glob import can introduce a lot of names, all with the same `DefId`.
397    // That's why the encoded list needs to contain `ModChild` structures describing all the names
398    // individually instead of `DefId`s.
399    module_children_reexports: Table<DefIndex, LazyArray<ModChild>>,
400    cross_crate_inlinable: Table<DefIndex, bool>,
401
402- optional:
403    attributes: Table<DefIndex, LazyArray<hir::Attribute>>,
404    // For non-reexported names in a module every name is associated with a separate `DefId`,
405    // so we can take their names, visibilities etc from other encoded tables.
406    module_children_non_reexports: Table<DefIndex, LazyArray<DefIndex>>,
407    associated_item_or_field_def_ids: Table<DefIndex, LazyArray<DefIndex>>,
408    def_kind: Table<DefIndex, DefKind>,
409    visibility: Table<DefIndex, LazyValue<ty::Visibility<DefIndex>>>,
410    safety: Table<DefIndex, hir::Safety>,
411    def_span: Table<DefIndex, LazyValue<Span>>,
412    def_ident_span: Table<DefIndex, LazyValue<Span>>,
413    lookup_stability: Table<DefIndex, LazyValue<hir::Stability>>,
414    lookup_const_stability: Table<DefIndex, LazyValue<hir::ConstStability>>,
415    lookup_default_body_stability: Table<DefIndex, LazyValue<hir::DefaultBodyStability>>,
416    lookup_deprecation_entry: Table<DefIndex, LazyValue<attrs::Deprecation>>,
417    explicit_predicates_of: Table<DefIndex, LazyValue<ty::GenericPredicates<'static>>>,
418    generics_of: Table<DefIndex, LazyValue<ty::Generics>>,
419    type_of: Table<DefIndex, LazyValue<ty::EarlyBinder<'static, Ty<'static>>>>,
420    variances_of: Table<DefIndex, LazyArray<ty::Variance>>,
421    fn_sig: Table<DefIndex, LazyValue<ty::EarlyBinder<'static, ty::PolyFnSig<'static>>>>,
422    codegen_fn_attrs: Table<DefIndex, LazyValue<CodegenFnAttrs>>,
423    impl_trait_header: Table<DefIndex, LazyValue<ty::ImplTraitHeader<'static>>>,
424    const_param_default: Table<DefIndex, LazyValue<ty::EarlyBinder<'static, rustc_middle::ty::Const<'static>>>>,
425    object_lifetime_default: Table<DefIndex, LazyValue<ObjectLifetimeDefault>>,
426    optimized_mir: Table<DefIndex, LazyValue<mir::Body<'static>>>,
427    mir_for_ctfe: Table<DefIndex, LazyValue<mir::Body<'static>>>,
428    closure_saved_names_of_captured_variables: Table<DefIndex, LazyValue<IndexVec<FieldIdx, Symbol>>>,
429    mir_coroutine_witnesses: Table<DefIndex, LazyValue<mir::CoroutineLayout<'static>>>,
430    promoted_mir: Table<DefIndex, LazyValue<IndexVec<mir::Promoted, mir::Body<'static>>>>,
431    thir_abstract_const: Table<DefIndex, LazyValue<ty::EarlyBinder<'static, ty::Const<'static>>>>,
432    impl_parent: Table<DefIndex, RawDefId>,
433    constness: Table<DefIndex, hir::Constness>,
434    const_conditions: Table<DefIndex, LazyValue<ty::ConstConditions<'static>>>,
435    defaultness: Table<DefIndex, hir::Defaultness>,
436    // FIXME(eddyb) perhaps compute this on the fly if cheap enough?
437    coerce_unsized_info: Table<DefIndex, LazyValue<ty::adjustment::CoerceUnsizedInfo>>,
438    mir_const_qualif: Table<DefIndex, LazyValue<mir::ConstQualifs>>,
439    rendered_const: Table<DefIndex, LazyValue<String>>,
440    rendered_precise_capturing_args: Table<DefIndex, LazyArray<PreciseCapturingArgKind<Symbol, Symbol>>>,
441    asyncness: Table<DefIndex, ty::Asyncness>,
442    fn_arg_idents: Table<DefIndex, LazyArray<Option<Ident>>>,
443    coroutine_kind: Table<DefIndex, hir::CoroutineKind>,
444    coroutine_for_closure: Table<DefIndex, RawDefId>,
445    adt_destructor: Table<DefIndex, LazyValue<ty::Destructor>>,
446    adt_async_destructor: Table<DefIndex, LazyValue<ty::AsyncDestructor>>,
447    coroutine_by_move_body_def_id: Table<DefIndex, RawDefId>,
448    eval_static_initializer: Table<DefIndex, LazyValue<mir::interpret::ConstAllocation<'static>>>,
449    trait_def: Table<DefIndex, LazyValue<ty::TraitDef>>,
450    trait_item_def_id: Table<DefIndex, RawDefId>,
451    expn_that_defined: Table<DefIndex, LazyValue<ExpnId>>,
452    default_fields: Table<DefIndex, LazyValue<DefId>>,
453    params_in_repr: Table<DefIndex, LazyValue<DenseBitSet<u32>>>,
454    repr_options: Table<DefIndex, LazyValue<ReprOptions>>,
455    // `def_keys` and `def_path_hashes` represent a lazy version of a
456    // `DefPathTable`. This allows us to avoid deserializing an entire
457    // `DefPathTable` up front, since we may only ever use a few
458    // definitions from any given crate.
459    def_keys: Table<DefIndex, LazyValue<DefKey>>,
460    proc_macro_quoted_spans: Table<usize, LazyValue<Span>>,
461    variant_data: Table<DefIndex, LazyValue<VariantData>>,
462    assoc_container: Table<DefIndex, ty::AssocItemContainer>,
463    macro_definition: Table<DefIndex, LazyValue<ast::DelimArgs>>,
464    proc_macro: Table<DefIndex, MacroKind>,
465    deduced_param_attrs: Table<DefIndex, LazyArray<DeducedParamAttrs>>,
466    trait_impl_trait_tys: Table<DefIndex, LazyValue<DefIdMap<ty::EarlyBinder<'static, Ty<'static>>>>>,
467    doc_link_resolutions: Table<DefIndex, LazyValue<DocLinkResMap>>,
468    doc_link_traits_in_scope: Table<DefIndex, LazyArray<DefId>>,
469    assumed_wf_types_for_rpitit: Table<DefIndex, LazyArray<(Ty<'static>, Span)>>,
470    opaque_ty_origin: Table<DefIndex, LazyValue<hir::OpaqueTyOrigin<DefId>>>,
471    anon_const_kind: Table<DefIndex, LazyValue<ty::AnonConstKind>>,
472    associated_types_for_impl_traits_in_trait_or_impl: Table<DefIndex, LazyValue<DefIdMap<Vec<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_PREDEFINED: u8 = 2;
580
581pub fn provide(providers: &mut Providers) {
582    encoder::provide(providers);
583    decoder::provide(providers);
584}
rustc_metadata/rmeta/mod.rs

rustc_metadata/rmeta/
mod.rs
