compiler/rustc_metadata/src/rmeta/mod.rs

use decoder::Metadata;
use def_path_hash_map::DefPathHashMapRef;
use table::{Table, TableBuilder};

use rustc_ast as ast;
use rustc_attr as attr;
use rustc_data_structures::svh::Svh;
use rustc_data_structures::sync::MetadataRef;
use rustc_hir as hir;
use rustc_hir::def::{CtorKind, DefKind};
use rustc_hir::def_id::{DefId, DefIndex, DefPathHash, StableCrateId};
use rustc_hir::definitions::DefKey;
use rustc_hir::lang_items;
use rustc_index::{bit_set::FiniteBitSet, vec::IndexVec};
use rustc_middle::metadata::ModChild;
use rustc_middle::middle::exported_symbols::{ExportedSymbol, SymbolExportLevel};
use rustc_middle::mir;
use rustc_middle::thir;
use rustc_middle::ty::fast_reject::SimplifiedType;
use rustc_middle::ty::query::Providers;
use rustc_middle::ty::{self, ReprOptions, Ty};
use rustc_serialize::opaque::Encoder;
use rustc_session::config::SymbolManglingVersion;
use rustc_session::cstore::{CrateDepKind, ForeignModule, LinkagePreference, NativeLib};
use rustc_span::edition::Edition;
use rustc_span::hygiene::{ExpnIndex, MacroKind};
use rustc_span::symbol::{Ident, Symbol};
use rustc_span::{self, ExpnData, ExpnHash, ExpnId, Span};
use rustc_target::spec::{PanicStrategy, TargetTriple};

use std::marker::PhantomData;
use std::num::NonZeroUsize;

pub use decoder::provide_extern;
use decoder::DecodeContext;
crate use decoder::{CrateMetadata, CrateNumMap, MetadataBlob};
use encoder::EncodeContext;
pub use encoder::{encode_metadata, EncodedMetadata};
use rustc_span::hygiene::SyntaxContextData;

mod decoder;
mod def_path_hash_map;
mod encoder;
mod table;

crate fn rustc_version() -> String {
    format!("rustc {}", option_env!("CFG_VERSION").unwrap_or("unknown version"))
}

/// Metadata encoding version.
/// N.B., increment this if you change the format of metadata such that
/// the rustc version can't be found to compare with `rustc_version()`.
const METADATA_VERSION: u8 = 6;

/// Metadata header which includes `METADATA_VERSION`.
///
/// This header is followed by the position of the `CrateRoot`,
/// which is encoded as a 32-bit big-endian unsigned integer,
/// and further followed by the rustc version string.
pub const METADATA_HEADER: &[u8] = &[b'r', b'u', b's', b't', 0, 0, 0, METADATA_VERSION];

/// Additional metadata for a `Lazy<T>` where `T` may not be `Sized`,
/// e.g. for `Lazy<[T]>`, this is the length (count of `T` values).
trait LazyMeta {
    type Meta: Copy + 'static;
}

impl<T> LazyMeta for T {
    type Meta = ();
}

impl<T> LazyMeta for [T] {
    type Meta = usize;
}

/// A value of type T referred to by its absolute position
/// in the metadata, and which can be decoded lazily.
///
/// Metadata is effective a tree, encoded in post-order,
/// and with the root's position written next to the header.
/// That means every single `Lazy` points to some previous
/// location in the metadata and is part of a larger node.
///
/// The first `Lazy` in a node is encoded as the backwards
/// distance from the position where the containing node
/// starts and where the `Lazy` points to, while the rest
/// use the forward distance from the previous `Lazy`.
/// Distances start at 1, as 0-byte nodes are invalid.
/// Also invalid are nodes being referred in a different
/// order than they were encoded in.
///
/// # Sequences (`Lazy<[T]>`)
///
/// Unlike `Lazy<Vec<T>>`, the length is encoded next to the
/// position, not at the position, which means that the length
/// doesn't need to be known before encoding all the elements.
///
/// If the length is 0, no position is encoded, but otherwise,
/// the encoding is that of `Lazy`, with the distinction that
/// the minimal distance the length of the sequence, i.e.
/// it's assumed there's no 0-byte element in the sequence.
#[must_use]
// FIXME(#59875) the `Meta` parameter only exists to dodge
// invariance wrt `T` (coming from the `meta: T::Meta` field).
struct Lazy<T, Meta = <T as LazyMeta>::Meta>
where
    T: ?Sized + LazyMeta<Meta = Meta>,
    Meta: 'static + Copy,
{
    position: NonZeroUsize,
    meta: Meta,
    _marker: PhantomData<T>,
}

impl<T: ?Sized + LazyMeta> Lazy<T> {
    fn from_position_and_meta(position: NonZeroUsize, meta: T::Meta) -> Lazy<T> {
        Lazy { position, meta, _marker: PhantomData }
    }
}

impl<T> Lazy<T> {
    fn from_position(position: NonZeroUsize) -> Lazy<T> {
        Lazy::from_position_and_meta(position, ())
    }
}

impl<T> Lazy<[T]> {
    fn empty() -> Lazy<[T]> {
        Lazy::from_position_and_meta(NonZeroUsize::new(1).unwrap(), 0)
    }
}

impl<T: ?Sized + LazyMeta> Copy for Lazy<T> {}
impl<T: ?Sized + LazyMeta> Clone for Lazy<T> {
    fn clone(&self) -> Self {
        *self
    }
}

/// Encoding / decoding state for `Lazy`.
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
enum LazyState {
    /// Outside of a metadata node.
    NoNode,

    /// Inside a metadata node, and before any `Lazy`.
    /// The position is that of the node itself.
    NodeStart(NonZeroUsize),

    /// Inside a metadata node, with a previous `Lazy`.
    /// The position is where that previous `Lazy` would start.
    Previous(NonZeroUsize),
}

// FIXME(#59875) `Lazy!(T)` replaces `Lazy<T>`, passing the `Meta` parameter
// manually, instead of relying on the default, to get the correct variance.
// Only needed when `T` itself contains a parameter (e.g. `'tcx`).
macro_rules! Lazy {
    (Table<$I:ty, $T:ty>) => {Lazy<Table<$I, $T>, usize>};
    ([$T:ty]) => {Lazy<[$T], usize>};
    ($T:ty) => {Lazy<$T, ()>};
}

type SyntaxContextTable = Lazy<Table<u32, Lazy<SyntaxContextData>>>;
type ExpnDataTable = Lazy<Table<ExpnIndex, Lazy<ExpnData>>>;
type ExpnHashTable = Lazy<Table<ExpnIndex, Lazy<ExpnHash>>>;

#[derive(MetadataEncodable, MetadataDecodable)]
crate struct ProcMacroData {
    proc_macro_decls_static: DefIndex,
    stability: Option<attr::Stability>,
    macros: Lazy<[DefIndex]>,
}

/// Serialized metadata for a crate.
/// When compiling a proc-macro crate, we encode many of
/// the `Lazy<[T]>` fields as `Lazy::empty()`. This serves two purposes:
///
/// 1. We avoid performing unnecessary work. Proc-macro crates can only
/// export proc-macros functions, which are compiled into a shared library.
/// As a result, a large amount of the information we normally store
/// (e.g. optimized MIR) is unneeded by downstream crates.
/// 2. We avoid serializing invalid `CrateNum`s. When we deserialize
/// a proc-macro crate, we don't load any of its dependencies (since we
/// just need to invoke a native function from the shared library).
/// This means that any foreign `CrateNum`s that we serialize cannot be
/// deserialized, since we will not know how to map them into the current
/// compilation session. If we were to serialize a proc-macro crate like
/// a normal crate, much of what we serialized would be unusable in addition
/// to being unused.
#[derive(MetadataEncodable, MetadataDecodable)]
crate struct CrateRoot<'tcx> {
    name: Symbol,
    triple: TargetTriple,
    extra_filename: String,
    hash: Svh,
    stable_crate_id: StableCrateId,
    panic_strategy: PanicStrategy,
    panic_in_drop_strategy: PanicStrategy,
    edition: Edition,
    has_global_allocator: bool,
    has_panic_handler: bool,
    has_default_lib_allocator: bool,

    crate_deps: Lazy<[CrateDep]>,
    dylib_dependency_formats: Lazy<[Option<LinkagePreference>]>,
    lib_features: Lazy<[(Symbol, Option<Symbol>)]>,
    lang_items: Lazy<[(DefIndex, usize)]>,
    lang_items_missing: Lazy<[lang_items::LangItem]>,
    diagnostic_items: Lazy<[(Symbol, DefIndex)]>,
    native_libraries: Lazy<[NativeLib]>,
    foreign_modules: Lazy<[ForeignModule]>,
    traits: Lazy<[DefIndex]>,
    impls: Lazy<[TraitImpls]>,
    incoherent_impls: Lazy<[IncoherentImpls]>,
    interpret_alloc_index: Lazy<[u32]>,
    proc_macro_data: Option<ProcMacroData>,

    tables: LazyTables<'tcx>,

    exported_symbols: Lazy!([(ExportedSymbol<'tcx>, SymbolExportLevel)]),

    syntax_contexts: SyntaxContextTable,
    expn_data: ExpnDataTable,
    expn_hashes: ExpnHashTable,

    def_path_hash_map: Lazy<DefPathHashMapRef<'tcx>>,

    source_map: Lazy<[rustc_span::SourceFile]>,

    compiler_builtins: bool,
    needs_allocator: bool,
    needs_panic_runtime: bool,
    no_builtins: bool,
    panic_runtime: bool,
    profiler_runtime: bool,
    symbol_mangling_version: SymbolManglingVersion,
}

#[derive(Encodable, Decodable)]
crate struct CrateDep {
    pub name: Symbol,
    pub hash: Svh,
    pub host_hash: Option<Svh>,
    pub kind: CrateDepKind,
    pub extra_filename: String,
}

#[derive(MetadataEncodable, MetadataDecodable)]
crate struct TraitImpls {
    trait_id: (u32, DefIndex),
    impls: Lazy<[(DefIndex, Option<SimplifiedType>)]>,
}

#[derive(MetadataEncodable, MetadataDecodable)]
crate struct IncoherentImpls {
    self_ty: SimplifiedType,
    impls: Lazy<[DefIndex]>,
}

/// Define `LazyTables` and `TableBuilders` at the same time.
macro_rules! define_tables {
    ($($name:ident: Table<$IDX:ty, $T:ty>),+ $(,)?) => {
        #[derive(MetadataEncodable, MetadataDecodable)]
        crate struct LazyTables<'tcx> {
            $($name: Lazy!(Table<$IDX, $T>)),+
        }

        #[derive(Default)]
        struct TableBuilders<'tcx> {
            $($name: TableBuilder<$IDX, $T>),+
        }

        impl<'tcx> TableBuilders<'tcx> {
            fn encode(&self, buf: &mut Encoder) -> LazyTables<'tcx> {
                LazyTables {
                    $($name: self.$name.encode(buf)),+
                }
            }
        }
    }
}

define_tables! {
    kind: Table<DefIndex, Lazy<EntryKind>>,
    attributes: Table<DefIndex, Lazy<[ast::Attribute]>>,
    children: Table<DefIndex, Lazy<[DefIndex]>>,

    opt_def_kind: Table<DefIndex, Lazy<DefKind>>,
    visibility: Table<DefIndex, Lazy<ty::Visibility>>,
    def_span: Table<DefIndex, Lazy<Span>>,
    def_ident_span: Table<DefIndex, Lazy<Span>>,
    lookup_stability: Table<DefIndex, Lazy<attr::Stability>>,
    lookup_const_stability: Table<DefIndex, Lazy<attr::ConstStability>>,
    lookup_deprecation_entry: Table<DefIndex, Lazy<attr::Deprecation>>,
    // As an optimization, a missing entry indicates an empty `&[]`.
    explicit_item_bounds: Table<DefIndex, Lazy!([(ty::Predicate<'tcx>, Span)])>,
    explicit_predicates_of: Table<DefIndex, Lazy!(ty::GenericPredicates<'tcx>)>,
    generics_of: Table<DefIndex, Lazy<ty::Generics>>,
    // As an optimization, a missing entry indicates an empty `&[]`.
    inferred_outlives_of: Table<DefIndex, Lazy!([(ty::Predicate<'tcx>, Span)])>,
    super_predicates_of: Table<DefIndex, Lazy!(ty::GenericPredicates<'tcx>)>,
    type_of: Table<DefIndex, Lazy!(Ty<'tcx>)>,
    variances_of: Table<DefIndex, Lazy<[ty::Variance]>>,
    fn_sig: Table<DefIndex, Lazy!(ty::PolyFnSig<'tcx>)>,
    impl_trait_ref: Table<DefIndex, Lazy!(ty::TraitRef<'tcx>)>,
    const_param_default: Table<DefIndex, Lazy<rustc_middle::ty::Const<'tcx>>>,
    optimized_mir: Table<DefIndex, Lazy!(mir::Body<'tcx>)>,
    mir_for_ctfe: Table<DefIndex, Lazy!(mir::Body<'tcx>)>,
    promoted_mir: Table<DefIndex, Lazy!(IndexVec<mir::Promoted, mir::Body<'tcx>>)>,
    thir_abstract_const: Table<DefIndex, Lazy!(&'tcx [thir::abstract_const::Node<'tcx>])>,
    impl_parent: Table<DefIndex, Lazy!(DefId)>,
    impl_polarity: Table<DefIndex, Lazy!(ty::ImplPolarity)>,
    impl_constness: Table<DefIndex, Lazy!(hir::Constness)>,
    impl_defaultness: Table<DefIndex, Lazy!(hir::Defaultness)>,
    // FIXME(eddyb) perhaps compute this on the fly if cheap enough?
    coerce_unsized_info: Table<DefIndex, Lazy!(ty::adjustment::CoerceUnsizedInfo)>,
    mir_const_qualif: Table<DefIndex, Lazy!(mir::ConstQualifs)>,
    rendered_const: Table<DefIndex, Lazy!(String)>,
    asyncness: Table<DefIndex, Lazy!(hir::IsAsync)>,
    fn_arg_names: Table<DefIndex, Lazy!([Ident])>,
    generator_kind: Table<DefIndex, Lazy!(hir::GeneratorKind)>,

    trait_item_def_id: Table<DefIndex, Lazy<DefId>>,
    inherent_impls: Table<DefIndex, Lazy<[DefIndex]>>,
    expn_that_defined: Table<DefIndex, Lazy<ExpnId>>,
    unused_generic_params: Table<DefIndex, Lazy<FiniteBitSet<u32>>>,
    repr_options: Table<DefIndex, Lazy<ReprOptions>>,
    // `def_keys` and `def_path_hashes` represent a lazy version of a
    // `DefPathTable`. This allows us to avoid deserializing an entire
    // `DefPathTable` up front, since we may only ever use a few
    // definitions from any given crate.
    def_keys: Table<DefIndex, Lazy<DefKey>>,
    def_path_hashes: Table<DefIndex, Lazy<DefPathHash>>,
    proc_macro_quoted_spans: Table<usize, Lazy<Span>>,
}

#[derive(Copy, Clone, MetadataEncodable, MetadataDecodable)]
enum EntryKind {
    AnonConst,
    Const,
    Static,
    ForeignStatic,
    ForeignMod,
    ForeignType,
    GlobalAsm,
    Type,
    TypeParam,
    ConstParam,
    OpaqueTy,
    Enum,
    Field,
    Variant(Lazy<VariantData>),
    Struct(Lazy<VariantData>),
    Union(Lazy<VariantData>),
    Fn(Lazy<FnData>),
    ForeignFn(Lazy<FnData>),
    Mod(Lazy<[ModChild]>),
    MacroDef(Lazy<ast::MacArgs>, /*macro_rules*/ bool),
    ProcMacro(MacroKind),
    Closure,
    Generator,
    Trait(Lazy<TraitData>),
    Impl,
    AssocFn(Lazy<AssocFnData>),
    AssocType(AssocContainer),
    AssocConst(AssocContainer),
    TraitAlias,
}

#[derive(MetadataEncodable, MetadataDecodable)]
struct FnData {
    constness: hir::Constness,
}

#[derive(TyEncodable, TyDecodable)]
struct VariantData {
    ctor_kind: CtorKind,
    discr: ty::VariantDiscr,
    /// If this is unit or tuple-variant/struct, then this is the index of the ctor id.
    ctor: Option<DefIndex>,
    is_non_exhaustive: bool,
}

#[derive(TyEncodable, TyDecodable)]
struct TraitData {
    unsafety: hir::Unsafety,
    paren_sugar: bool,
    has_auto_impl: bool,
    is_marker: bool,
    skip_array_during_method_dispatch: bool,
    specialization_kind: ty::trait_def::TraitSpecializationKind,
    must_implement_one_of: Option<Box<[Ident]>>,
}

/// Describes whether the container of an associated item
/// is a trait or an impl and whether, in a trait, it has
/// a default, or an in impl, whether it's marked "default".
#[derive(Copy, Clone, TyEncodable, TyDecodable)]
enum AssocContainer {
    TraitRequired,
    TraitWithDefault,
    ImplDefault,
    ImplFinal,
}

impl AssocContainer {
    fn with_def_id(&self, def_id: DefId) -> ty::AssocItemContainer {
        match *self {
            AssocContainer::TraitRequired | AssocContainer::TraitWithDefault => {
                ty::TraitContainer(def_id)
            }

            AssocContainer::ImplDefault | AssocContainer::ImplFinal => ty::ImplContainer(def_id),
        }
    }

    fn defaultness(&self) -> hir::Defaultness {
        match *self {
            AssocContainer::TraitRequired => hir::Defaultness::Default { has_value: false },

            AssocContainer::TraitWithDefault | AssocContainer::ImplDefault => {
                hir::Defaultness::Default { has_value: true }
            }

            AssocContainer::ImplFinal => hir::Defaultness::Final,
        }
    }
}

#[derive(MetadataEncodable, MetadataDecodable)]
struct AssocFnData {
    fn_data: FnData,
    container: AssocContainer,
    has_self: bool,
}

#[derive(TyEncodable, TyDecodable)]
struct GeneratorData<'tcx> {
    layout: mir::GeneratorLayout<'tcx>,
}

// Tags used for encoding Spans:
const TAG_VALID_SPAN_LOCAL: u8 = 0;
const TAG_VALID_SPAN_FOREIGN: u8 = 1;
const TAG_PARTIAL_SPAN: u8 = 2;

pub fn provide(providers: &mut Providers) {
    encoder::provide(providers);
    decoder::provide(providers);
}