compiler/rustc_span/src/def_id.rs - toolchain/rustc - Git at Google

 use crate::{HashStableContext, SpanDecoder, SpanEncoder, Symbol};
 use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_data_structures::stable_hasher::{
     Hash64, HashStable, StableHasher, StableOrd, ToStableHashKey,
 };
 use rustc_data_structures::unhash::Unhasher;
 use rustc_data_structures::AtomicRef;
 use rustc_index::Idx;
 use rustc_macros::HashStable_Generic;
 use rustc_serialize::{Decodable, Encodable};
 use std::fmt;
 use std::hash::{BuildHasherDefault, Hash, Hasher};

 pub type StableCrateIdMap =
     indexmap::IndexMap<StableCrateId, CrateNum, BuildHasherDefault<Unhasher>>;

 rustc_index::newtype_index! {
     #[orderable]
     #[debug_format = "crate{}"]
     pub struct CrateNum {}
 }

 /// Item definitions in the currently-compiled crate would have the `CrateNum`
 /// `LOCAL_CRATE` in their `DefId`.
 pub const LOCAL_CRATE: CrateNum = CrateNum::from_u32(0);

 impl CrateNum {
     #[inline]
     pub fn new(x: usize) -> CrateNum {
         CrateNum::from_usize(x)
     }

     // FIXME(typed_def_id): Replace this with `as_mod_def_id`.
     #[inline]
     pub fn as_def_id(self) -> DefId {
         DefId { krate: self, index: CRATE_DEF_INDEX }
     }

     #[inline]
     pub fn as_mod_def_id(self) -> ModDefId {
         ModDefId::new_unchecked(DefId { krate: self, index: CRATE_DEF_INDEX })
     }
 }

 impl fmt::Display for CrateNum {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         fmt::Display::fmt(&self.as_u32(), f)
     }
 }

 /// A `DefPathHash` is a fixed-size representation of a `DefPath` that is
 /// stable across crate and compilation session boundaries. It consists of two
 /// separate 64-bit hashes. The first uniquely identifies the crate this
 /// `DefPathHash` originates from (see [StableCrateId]), and the second
 /// uniquely identifies the corresponding `DefPath` within that crate. Together
 /// they form a unique identifier within an entire crate graph.
 ///
 /// There is a very small chance of hash collisions, which would mean that two
 /// different `DefPath`s map to the same `DefPathHash`. Proceeding compilation
 /// with such a hash collision would very probably lead to an ICE, and in the
 /// worst case lead to a silent mis-compilation. The compiler therefore actively
 /// and exhaustively checks for such hash collisions and aborts compilation if
 /// it finds one.
 ///
 /// `DefPathHash` uses 64-bit hashes for both the crate-id part and the
 /// crate-internal part, even though it is likely that there are many more
 /// `LocalDefId`s in a single crate than there are individual crates in a crate
 /// graph. Since we use the same number of bits in both cases, the collision
 /// probability for the crate-local part will be quite a bit higher (though
 /// still very small).
 ///
 /// This imbalance is not by accident: A hash collision in the
 /// crate-local part of a `DefPathHash` will be detected and reported while
 /// compiling the crate in question. Such a collision does not depend on
 /// outside factors and can be easily fixed by the crate maintainer (e.g. by
 /// renaming the item in question or by bumping the crate version in a harmless
 /// way).
 ///
 /// A collision between crate-id hashes on the other hand is harder to fix
 /// because it depends on the set of crates in the entire crate graph of a
 /// compilation session. Again, using the same crate with a different version
 /// number would fix the issue with a high probability -- but that might be
 /// easier said then done if the crates in questions are dependencies of
 /// third-party crates.
 ///
 /// That being said, given a high quality hash function, the collision
 /// probabilities in question are very small. For example, for a big crate like
 /// `rustc_middle` (with ~50000 `LocalDefId`s as of the time of writing) there
 /// is a probability of roughly 1 in 14,750,000,000 of a crate-internal
 /// collision occurring. For a big crate graph with 1000 crates in it, there is
 /// a probability of 1 in 36,890,000,000,000 of a `StableCrateId` collision.
 #[derive(Copy, Clone, Hash, PartialEq, Eq, PartialOrd, Ord, Debug)]
 #[derive(HashStable_Generic, Encodable, Decodable)]
 pub struct DefPathHash(pub Fingerprint);

 impl DefPathHash {
     /// Returns the [StableCrateId] identifying the crate this [DefPathHash]
     /// originates from.
     #[inline]
     pub fn stable_crate_id(&self) -> StableCrateId {
         StableCrateId(self.0.split().0)
     }

     /// Returns the crate-local part of the [DefPathHash].
     #[inline]
     pub fn local_hash(&self) -> Hash64 {
         self.0.split().1
     }

     /// Builds a new [DefPathHash] with the given [StableCrateId] and
     /// `local_hash`, where `local_hash` must be unique within its crate.
     pub fn new(stable_crate_id: StableCrateId, local_hash: Hash64) -> DefPathHash {
         DefPathHash(Fingerprint::new(stable_crate_id.0, local_hash))
     }
 }

 impl Default for DefPathHash {
     fn default() -> Self {
         DefPathHash(Fingerprint::ZERO)
     }
 }

 // Safety: `DefPathHash` sort order is not affected (de)serialization.
 unsafe impl StableOrd for DefPathHash {
     const CAN_USE_UNSTABLE_SORT: bool = true;
 }

 /// A [`StableCrateId`] is a 64-bit hash of a crate name, together with all
 /// `-Cmetadata` arguments, and some other data. It is to [`CrateNum`] what [`DefPathHash`] is to
 /// [`DefId`]. It is stable across compilation sessions.
 ///
 /// Since the ID is a hash value, there is a small chance that two crates
 /// end up with the same [`StableCrateId`]. The compiler will check for such
 /// collisions when loading crates and abort compilation in order to avoid
 /// further trouble.
 ///
 /// For more information on the possibility of hash collisions in rustc,
 /// see the discussion in [`DefId`].
 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Debug)]
 #[derive(Hash, HashStable_Generic, Encodable, Decodable)]
 pub struct StableCrateId(pub(crate) Hash64);

 impl StableCrateId {
     /// Computes the stable ID for a crate with the given name and
     /// `-Cmetadata` arguments.
     pub fn new(
         crate_name: Symbol,
         is_exe: bool,
         mut metadata: Vec<String>,
         cfg_version: &'static str,
     ) -> StableCrateId {
         let mut hasher = StableHasher::new();
         // We must hash the string text of the crate name, not the id, as the id is not stable
         // across builds.
         crate_name.as_str().hash(&mut hasher);

         // We don't want the stable crate ID to depend on the order of
         // -C metadata arguments, so sort them:
         metadata.sort();
         // Every distinct -C metadata value is only incorporated once:
         metadata.dedup();

         hasher.write(b"metadata");
         for s in &metadata {
             // Also incorporate the length of a metadata string, so that we generate
             // different values for `-Cmetadata=ab -Cmetadata=c` and
             // `-Cmetadata=a -Cmetadata=bc`
             hasher.write_usize(s.len());
             hasher.write(s.as_bytes());
         }

         // Also incorporate crate type, so that we don't get symbol conflicts when
         // linking against a library of the same name, if this is an executable.
         hasher.write(if is_exe { b"exe" } else { b"lib" });

         // Also incorporate the rustc version. Otherwise, with -Zsymbol-mangling-version=v0
         // and no -Cmetadata, symbols from the same crate compiled with different versions of
         // rustc are named the same.
         //
         // RUSTC_FORCE_RUSTC_VERSION is used to inject rustc version information
         // during testing.
         if let Some(val) = std::env::var_os("RUSTC_FORCE_RUSTC_VERSION") {
             hasher.write(val.to_string_lossy().into_owned().as_bytes())
         } else {
             hasher.write(cfg_version.as_bytes())
         }

         StableCrateId(hasher.finish())
     }

     #[inline]
     pub fn as_u64(self) -> u64 {
         self.0.as_u64()
     }
 }

 impl fmt::LowerHex for StableCrateId {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         fmt::LowerHex::fmt(&self.0, f)
     }
 }

 rustc_index::newtype_index! {
     /// A DefIndex is an index into the hir-map for a crate, identifying a
     /// particular definition. It should really be considered an interned
     /// shorthand for a particular DefPath.
     #[orderable]
     #[debug_format = "DefIndex({})"]
     pub struct DefIndex {
         /// The crate root is always assigned index 0 by the AST Map code,
         /// thanks to `NodeCollector::new`.
         const CRATE_DEF_INDEX = 0;
     }
 }

 /// A `DefId` identifies a particular *definition*, by combining a crate
 /// index and a def index.
 ///
 /// You can create a `DefId` from a `LocalDefId` using `local_def_id.to_def_id()`.
 #[derive(Clone, PartialEq, Eq, Copy)]
 // Don't derive order on 64-bit big-endian, so we can be consistent regardless of field order.
 #[cfg_attr(not(all(target_pointer_width = "64", target_endian = "big")), derive(PartialOrd, Ord))]
 // On below-64 bit systems we can simply use the derived `Hash` impl
 #[cfg_attr(not(target_pointer_width = "64"), derive(Hash))]
 #[repr(C)]
 #[rustc_pass_by_value]
 // We guarantee field order. Note that the order is essential here, see below why.
 pub struct DefId {
     // cfg-ing the order of fields so that the `DefIndex` which is high entropy always ends up in
     // the lower bits no matter the endianness. This allows the compiler to turn that `Hash` impl
     // into a direct call to `u64::hash(_)`.
     #[cfg(not(all(target_pointer_width = "64", target_endian = "big")))]
     pub index: DefIndex,
     pub krate: CrateNum,
     #[cfg(all(target_pointer_width = "64", target_endian = "big"))]
     pub index: DefIndex,
 }

 // On 64-bit systems, we can hash the whole `DefId` as one `u64` instead of two `u32`s. This
 // improves performance without impairing `FxHash` quality. So the below code gets compiled to a
 // noop on little endian systems because the memory layout of `DefId` is as follows:
 //
 // ```
 //     +-1--------------31-+-32-------------63-+
 //     ! index             ! krate             !
 //     +-------------------+-------------------+
 // ```
 //
 // The order here has direct impact on `FxHash` quality because we have far more `DefIndex` per
 // crate than we have `Crate`s within one compilation. Or in other words, this arrangement puts
 // more entropy in the low bits than the high bits. The reason this matters is that `FxHash`, which
 // is used throughout rustc, has problems distributing the entropy from the high bits, so reversing
 // the order would lead to a large number of collisions and thus far worse performance.
 //
 // On 64-bit big-endian systems, this compiles to a 64-bit rotation by 32 bits, which is still
 // faster than another `FxHash` round.
 #[cfg(target_pointer_width = "64")]
 impl Hash for DefId {
     fn hash<H: Hasher>(&self, h: &mut H) {
         (((self.krate.as_u32() as u64) << 32) | (self.index.as_u32() as u64)).hash(h)
     }
 }

 // Implement the same comparison as derived with the other field order.
 #[cfg(all(target_pointer_width = "64", target_endian = "big"))]
 impl Ord for DefId {
     #[inline]
     fn cmp(&self, other: &DefId) -> std::cmp::Ordering {
         Ord::cmp(&(self.index, self.krate), &(other.index, other.krate))
     }
 }
 #[cfg(all(target_pointer_width = "64", target_endian = "big"))]
 impl PartialOrd for DefId {
     #[inline]
     fn partial_cmp(&self, other: &DefId) -> Option<std::cmp::Ordering> {
         Some(self.cmp(other))
     }
 }

 impl DefId {
     /// Makes a local `DefId` from the given `DefIndex`.
     #[inline]
     pub fn local(index: DefIndex) -> DefId {
         DefId { krate: LOCAL_CRATE, index }
     }

     /// Returns whether the item is defined in the crate currently being compiled.
     #[inline]
     pub fn is_local(self) -> bool {
         self.krate == LOCAL_CRATE
     }

     #[inline]
     pub fn as_local(self) -> Option<LocalDefId> {
         self.is_local().then(|| LocalDefId { local_def_index: self.index })
     }

     #[inline]
     #[track_caller]
     pub fn expect_local(self) -> LocalDefId {
         // NOTE: `match` below is required to apply `#[track_caller]`,
         // i.e. don't use closures.
         match self.as_local() {
             Some(local_def_id) => local_def_id,
             None => panic!("DefId::expect_local: `{self:?}` isn't local"),
         }
     }

     #[inline]
     pub fn is_crate_root(self) -> bool {
         self.index == CRATE_DEF_INDEX
     }

     #[inline]
     pub fn as_crate_root(self) -> Option<CrateNum> {
         self.is_crate_root().then_some(self.krate)
     }

     #[inline]
     pub fn is_top_level_module(self) -> bool {
         self.is_local() && self.is_crate_root()
     }
 }

 impl From<LocalDefId> for DefId {
     fn from(local: LocalDefId) -> DefId {
         local.to_def_id()
     }
 }

 pub fn default_def_id_debug(def_id: DefId, f: &mut fmt::Formatter<'_>) -> fmt::Result {
     f.debug_struct("DefId").field("krate", &def_id.krate).field("index", &def_id.index).finish()
 }

 pub static DEF_ID_DEBUG: AtomicRef<fn(DefId, &mut fmt::Formatter<'_>) -> fmt::Result> =
     AtomicRef::new(&(default_def_id_debug as fn(_, &mut fmt::Formatter<'_>) -> _));

 impl fmt::Debug for DefId {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         (*DEF_ID_DEBUG)(*self, f)
     }
 }

 rustc_data_structures::define_id_collections!(DefIdMap, DefIdSet, DefIdMapEntry, DefId);

 /// A `LocalDefId` is equivalent to a `DefId` with `krate == LOCAL_CRATE`. Since
 /// we encode this information in the type, we can ensure at compile time that
 /// no `DefId`s from upstream crates get thrown into the mix. There are quite a
 /// few cases where we know that only `DefId`s from the local crate are expected;
 /// a `DefId` from a different crate would signify a bug somewhere. This
 /// is when `LocalDefId` comes in handy.
 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
 pub struct LocalDefId {
     pub local_def_index: DefIndex,
 }

 // To ensure correctness of incremental compilation,
 // `LocalDefId` must not implement `Ord` or `PartialOrd`.
 // See https://github.com/rust-lang/rust/issues/90317.
 impl !Ord for LocalDefId {}
 impl !PartialOrd for LocalDefId {}

 pub const CRATE_DEF_ID: LocalDefId = LocalDefId { local_def_index: CRATE_DEF_INDEX };

 impl Idx for LocalDefId {
     #[inline]
     fn new(idx: usize) -> Self {
         LocalDefId { local_def_index: Idx::new(idx) }
     }
     #[inline]
     fn index(self) -> usize {
         self.local_def_index.index()
     }
 }

 impl LocalDefId {
     #[inline]
     pub fn to_def_id(self) -> DefId {
         DefId { krate: LOCAL_CRATE, index: self.local_def_index }
     }

     #[inline]
     pub fn is_top_level_module(self) -> bool {
         self == CRATE_DEF_ID
     }
 }

 impl fmt::Debug for LocalDefId {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         self.to_def_id().fmt(f)
     }
 }

 impl<E: SpanEncoder> Encodable<E> for LocalDefId {
     fn encode(&self, s: &mut E) {
         self.to_def_id().encode(s);
     }
 }

 impl<D: SpanDecoder> Decodable<D> for LocalDefId {
     fn decode(d: &mut D) -> LocalDefId {
         DefId::decode(d).expect_local()
     }
 }

 rustc_data_structures::define_id_collections!(
     LocalDefIdMap,
     LocalDefIdSet,
     LocalDefIdMapEntry,
     LocalDefId
 );

 impl<CTX: HashStableContext> HashStable<CTX> for DefId {
     #[inline]
     fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
         self.to_stable_hash_key(hcx).hash_stable(hcx, hasher);
     }
 }

 impl<CTX: HashStableContext> HashStable<CTX> for LocalDefId {
     #[inline]
     fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
         self.to_stable_hash_key(hcx).hash_stable(hcx, hasher);
     }
 }

 impl<CTX: HashStableContext> HashStable<CTX> for CrateNum {
     #[inline]
     fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
         self.to_stable_hash_key(hcx).hash_stable(hcx, hasher);
     }
 }

 impl<CTX: HashStableContext> ToStableHashKey<CTX> for DefId {
     type KeyType = DefPathHash;

     #[inline]
     fn to_stable_hash_key(&self, hcx: &CTX) -> DefPathHash {
         hcx.def_path_hash(*self)
     }
 }

 impl<CTX: HashStableContext> ToStableHashKey<CTX> for LocalDefId {
     type KeyType = DefPathHash;

     #[inline]
     fn to_stable_hash_key(&self, hcx: &CTX) -> DefPathHash {
         hcx.def_path_hash(self.to_def_id())
     }
 }

 impl<CTX: HashStableContext> ToStableHashKey<CTX> for CrateNum {
     type KeyType = DefPathHash;

     #[inline]
     fn to_stable_hash_key(&self, hcx: &CTX) -> DefPathHash {
         self.as_def_id().to_stable_hash_key(hcx)
     }
 }

 impl<CTX: HashStableContext> ToStableHashKey<CTX> for DefPathHash {
     type KeyType = DefPathHash;

     #[inline]
     fn to_stable_hash_key(&self, _: &CTX) -> DefPathHash {
         *self
     }
 }

 macro_rules! typed_def_id {
     ($Name:ident, $LocalName:ident) => {
         #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Encodable, Decodable, HashStable_Generic)]
         pub struct $Name(DefId);

         impl $Name {
             pub const fn new_unchecked(def_id: DefId) -> Self {
                 Self(def_id)
             }

             pub fn to_def_id(self) -> DefId {
                 self.into()
             }

             pub fn is_local(self) -> bool {
                 self.0.is_local()
             }

             pub fn as_local(self) -> Option<$LocalName> {
                 self.0.as_local().map($LocalName::new_unchecked)
             }
         }

         impl From<$LocalName> for $Name {
             fn from(local: $LocalName) -> Self {
                 Self(local.0.to_def_id())
             }
         }

         impl From<$Name> for DefId {
             fn from(typed: $Name) -> Self {
                 typed.0
             }
         }

         #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Encodable, Decodable, HashStable_Generic)]
         pub struct $LocalName(LocalDefId);

         impl !Ord for $LocalName {}
         impl !PartialOrd for $LocalName {}

         impl $LocalName {
             pub const fn new_unchecked(def_id: LocalDefId) -> Self {
                 Self(def_id)
             }

             pub fn to_def_id(self) -> DefId {
                 self.0.into()
             }

             pub fn to_local_def_id(self) -> LocalDefId {
                 self.0
             }
         }

         impl From<$LocalName> for LocalDefId {
             fn from(typed: $LocalName) -> Self {
                 typed.0
             }
         }

         impl From<$LocalName> for DefId {
             fn from(typed: $LocalName) -> Self {
                 typed.0.into()
             }
         }
     };
 }

 // N.B.: when adding new typed `DefId`s update the corresponding trait impls in
 // `rustc_middle::dep_graph::def_node` for `DepNodeParams`.
 typed_def_id! { ModDefId, LocalModDefId }

 impl LocalModDefId {
     pub const CRATE_DEF_ID: Self = Self::new_unchecked(CRATE_DEF_ID);
 }

 impl ModDefId {
     pub fn is_top_level_module(self) -> bool {
         self.0.is_top_level_module()
     }
 }

 impl LocalModDefId {
     pub fn is_top_level_module(self) -> bool {
         self.0.is_top_level_module()
     }
 }
	use crate::{HashStableContext, SpanDecoder, SpanEncoder, Symbol};
	use rustc_data_structures::fingerprint::Fingerprint;
	use rustc_data_structures::stable_hasher::{
	Hash64, HashStable, StableHasher, StableOrd, ToStableHashKey,
	};
	use rustc_data_structures::unhash::Unhasher;
	use rustc_data_structures::AtomicRef;
	use rustc_index::Idx;
	use rustc_macros::HashStable_Generic;
	use rustc_serialize::{Decodable, Encodable};
	use std::fmt;
	use std::hash::{BuildHasherDefault, Hash, Hasher};

	pub type StableCrateIdMap =
	indexmap::IndexMap<StableCrateId, CrateNum, BuildHasherDefault<Unhasher>>;

	rustc_index::newtype_index! {
	#[orderable]
	#[debug_format = "crate{}"]
	pub struct CrateNum {}
	}

	/// Item definitions in the currently-compiled crate would have the `CrateNum`
	/// `LOCAL_CRATE` in their `DefId`.
	pub const LOCAL_CRATE: CrateNum = CrateNum::from_u32(0);

	impl CrateNum {
	#[inline]
	pub fn new(x: usize) -> CrateNum {
	CrateNum::from_usize(x)
	}

	// FIXME(typed_def_id): Replace this with `as_mod_def_id`.
	#[inline]
	pub fn as_def_id(self) -> DefId {
	DefId { krate: self, index: CRATE_DEF_INDEX }
	}

	#[inline]
	pub fn as_mod_def_id(self) -> ModDefId {
	ModDefId::new_unchecked(DefId { krate: self, index: CRATE_DEF_INDEX })
	}
	}

	impl fmt::Display for CrateNum {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
	fmt::Display::fmt(&self.as_u32(), f)
	}
	}

	/// A `DefPathHash` is a fixed-size representation of a `DefPath` that is
	/// stable across crate and compilation session boundaries. It consists of two
	/// separate 64-bit hashes. The first uniquely identifies the crate this
	/// `DefPathHash` originates from (see [StableCrateId]), and the second
	/// uniquely identifies the corresponding `DefPath` within that crate. Together
	/// they form a unique identifier within an entire crate graph.
	///
	/// There is a very small chance of hash collisions, which would mean that two
	/// different `DefPath`s map to the same `DefPathHash`. Proceeding compilation
	/// with such a hash collision would very probably lead to an ICE, and in the
	/// worst case lead to a silent mis-compilation. The compiler therefore actively
	/// and exhaustively checks for such hash collisions and aborts compilation if
	/// it finds one.
	///
	/// `DefPathHash` uses 64-bit hashes for both the crate-id part and the
	/// crate-internal part, even though it is likely that there are many more
	/// `LocalDefId`s in a single crate than there are individual crates in a crate
	/// graph. Since we use the same number of bits in both cases, the collision
	/// probability for the crate-local part will be quite a bit higher (though
	/// still very small).
	///
	/// This imbalance is not by accident: A hash collision in the
	/// crate-local part of a `DefPathHash` will be detected and reported while
	/// compiling the crate in question. Such a collision does not depend on
	/// outside factors and can be easily fixed by the crate maintainer (e.g. by
	/// renaming the item in question or by bumping the crate version in a harmless
	/// way).
	///
	/// A collision between crate-id hashes on the other hand is harder to fix
	/// because it depends on the set of crates in the entire crate graph of a
	/// compilation session. Again, using the same crate with a different version
	/// number would fix the issue with a high probability -- but that might be
	/// easier said then done if the crates in questions are dependencies of
	/// third-party crates.
	///
	/// That being said, given a high quality hash function, the collision
	/// probabilities in question are very small. For example, for a big crate like
	/// `rustc_middle` (with ~50000 `LocalDefId`s as of the time of writing) there
	/// is a probability of roughly 1 in 14,750,000,000 of a crate-internal
	/// collision occurring. For a big crate graph with 1000 crates in it, there is
	/// a probability of 1 in 36,890,000,000,000 of a `StableCrateId` collision.
	#[derive(Copy, Clone, Hash, PartialEq, Eq, PartialOrd, Ord, Debug)]
	#[derive(HashStable_Generic, Encodable, Decodable)]
	pub struct DefPathHash(pub Fingerprint);

	impl DefPathHash {
	/// Returns the [StableCrateId] identifying the crate this [DefPathHash]
	/// originates from.
	#[inline]
	pub fn stable_crate_id(&self) -> StableCrateId {
	StableCrateId(self.0.split().0)
	}

	/// Returns the crate-local part of the [DefPathHash].
	#[inline]
	pub fn local_hash(&self) -> Hash64 {
	self.0.split().1
	}

	/// Builds a new [DefPathHash] with the given [StableCrateId] and
	/// `local_hash`, where `local_hash` must be unique within its crate.
	pub fn new(stable_crate_id: StableCrateId, local_hash: Hash64) -> DefPathHash {
	DefPathHash(Fingerprint::new(stable_crate_id.0, local_hash))
	}
	}

	impl Default for DefPathHash {
	fn default() -> Self {
	DefPathHash(Fingerprint::ZERO)
	}
	}

	// Safety: `DefPathHash` sort order is not affected (de)serialization.
	unsafe impl StableOrd for DefPathHash {
	const CAN_USE_UNSTABLE_SORT: bool = true;
	}

	/// A [`StableCrateId`] is a 64-bit hash of a crate name, together with all
	/// `-Cmetadata` arguments, and some other data. It is to [`CrateNum`] what [`DefPathHash`] is to
	/// [`DefId`]. It is stable across compilation sessions.
	///
	/// Since the ID is a hash value, there is a small chance that two crates
	/// end up with the same [`StableCrateId`]. The compiler will check for such
	/// collisions when loading crates and abort compilation in order to avoid
	/// further trouble.
	///
	/// For more information on the possibility of hash collisions in rustc,
	/// see the discussion in [`DefId`].
	#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Debug)]
	#[derive(Hash, HashStable_Generic, Encodable, Decodable)]
	pub struct StableCrateId(pub(crate) Hash64);

	impl StableCrateId {
	/// Computes the stable ID for a crate with the given name and
	/// `-Cmetadata` arguments.
	pub fn new(
	crate_name: Symbol,
	is_exe: bool,
	mut metadata: Vec<String>,
	cfg_version: &'static str,
	) -> StableCrateId {
	let mut hasher = StableHasher::new();
	// We must hash the string text of the crate name, not the id, as the id is not stable
	// across builds.
	crate_name.as_str().hash(&mut hasher);

	// We don't want the stable crate ID to depend on the order of
	// -C metadata arguments, so sort them:
	metadata.sort();
	// Every distinct -C metadata value is only incorporated once:
	metadata.dedup();

	hasher.write(b"metadata");
	for s in &metadata {
	// Also incorporate the length of a metadata string, so that we generate
	// different values for `-Cmetadata=ab -Cmetadata=c` and
	// `-Cmetadata=a -Cmetadata=bc`
	hasher.write_usize(s.len());
	hasher.write(s.as_bytes());
	}

	// Also incorporate crate type, so that we don't get symbol conflicts when
	// linking against a library of the same name, if this is an executable.
	hasher.write(if is_exe { b"exe" } else { b"lib" });

	// Also incorporate the rustc version. Otherwise, with -Zsymbol-mangling-version=v0
	// and no -Cmetadata, symbols from the same crate compiled with different versions of
	// rustc are named the same.
	//
	// RUSTC_FORCE_RUSTC_VERSION is used to inject rustc version information
	// during testing.
	if let Some(val) = std::env::var_os("RUSTC_FORCE_RUSTC_VERSION") {
	hasher.write(val.to_string_lossy().into_owned().as_bytes())
	} else {
	hasher.write(cfg_version.as_bytes())
	}

	StableCrateId(hasher.finish())
	}

	#[inline]
	pub fn as_u64(self) -> u64 {
	self.0.as_u64()
	}
	}

	impl fmt::LowerHex for StableCrateId {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
	fmt::LowerHex::fmt(&self.0, f)
	}
	}

	rustc_index::newtype_index! {
	/// A DefIndex is an index into the hir-map for a crate, identifying a
	/// particular definition. It should really be considered an interned
	/// shorthand for a particular DefPath.
	#[orderable]
	#[debug_format = "DefIndex({})"]
	pub struct DefIndex {
	/// The crate root is always assigned index 0 by the AST Map code,
	/// thanks to `NodeCollector::new`.
	const CRATE_DEF_INDEX = 0;
	}
	}

	/// A `DefId` identifies a particular definition, by combining a crate
	/// index and a def index.
	///
	/// You can create a `DefId` from a `LocalDefId` using `local_def_id.to_def_id()`.
	#[derive(Clone, PartialEq, Eq, Copy)]
	// Don't derive order on 64-bit big-endian, so we can be consistent regardless of field order.
	#[cfg_attr(not(all(target_pointer_width = "64", target_endian = "big")), derive(PartialOrd, Ord))]
	// On below-64 bit systems we can simply use the derived `Hash` impl
	#[cfg_attr(not(target_pointer_width = "64"), derive(Hash))]
	#[repr(C)]
	#[rustc_pass_by_value]
	// We guarantee field order. Note that the order is essential here, see below why.
	pub struct DefId {
	// cfg-ing the order of fields so that the `DefIndex` which is high entropy always ends up in
	// the lower bits no matter the endianness. This allows the compiler to turn that `Hash` impl
	// into a direct call to `u64::hash(_)`.
	#[cfg(not(all(target_pointer_width = "64", target_endian = "big")))]
	pub index: DefIndex,
	pub krate: CrateNum,
	#[cfg(all(target_pointer_width = "64", target_endian = "big"))]
	pub index: DefIndex,
	}

	// On 64-bit systems, we can hash the whole `DefId` as one `u64` instead of two `u32`s. This
	// improves performance without impairing `FxHash` quality. So the below code gets compiled to a
	// noop on little endian systems because the memory layout of `DefId` is as follows:
	//
	// ```
	// +-1--------------31-+-32-------------63-+
	// ! index ! krate !
	// +-------------------+-------------------+
	// ```
	//
	// The order here has direct impact on `FxHash` quality because we have far more `DefIndex` per
	// crate than we have `Crate`s within one compilation. Or in other words, this arrangement puts
	// more entropy in the low bits than the high bits. The reason this matters is that `FxHash`, which
	// is used throughout rustc, has problems distributing the entropy from the high bits, so reversing
	// the order would lead to a large number of collisions and thus far worse performance.
	//
	// On 64-bit big-endian systems, this compiles to a 64-bit rotation by 32 bits, which is still
	// faster than another `FxHash` round.
	#[cfg(target_pointer_width = "64")]
	impl Hash for DefId {
	fn hash<H: Hasher>(&self, h: &mut H) {
	(((self.krate.as_u32() as u64) << 32) \| (self.index.as_u32() as u64)).hash(h)
	}
	}

	// Implement the same comparison as derived with the other field order.
	#[cfg(all(target_pointer_width = "64", target_endian = "big"))]
	impl Ord for DefId {
	#[inline]
	fn cmp(&self, other: &DefId) -> std::cmp::Ordering {
	Ord::cmp(&(self.index, self.krate), &(other.index, other.krate))
	}
	}
	#[cfg(all(target_pointer_width = "64", target_endian = "big"))]
	impl PartialOrd for DefId {
	#[inline]
	fn partial_cmp(&self, other: &DefId) -> Option<std::cmp::Ordering> {
	Some(self.cmp(other))
	}
	}

	impl DefId {
	/// Makes a local `DefId` from the given `DefIndex`.
	#[inline]
	pub fn local(index: DefIndex) -> DefId {
	DefId { krate: LOCAL_CRATE, index }
	}

	/// Returns whether the item is defined in the crate currently being compiled.
	#[inline]
	pub fn is_local(self) -> bool {
	self.krate == LOCAL_CRATE
	}

	#[inline]
	pub fn as_local(self) -> Option<LocalDefId> {
	self.is_local().then(\|\| LocalDefId { local_def_index: self.index })
	}

	#[inline]
	#[track_caller]
	pub fn expect_local(self) -> LocalDefId {
	// NOTE: `match` below is required to apply `#[track_caller]`,
	// i.e. don't use closures.
	match self.as_local() {
	Some(local_def_id) => local_def_id,
	None => panic!("DefId::expect_local: `{self:?}` isn't local"),
	}
	}

	#[inline]
	pub fn is_crate_root(self) -> bool {
	self.index == CRATE_DEF_INDEX
	}

	#[inline]
	pub fn as_crate_root(self) -> Option<CrateNum> {
	self.is_crate_root().then_some(self.krate)
	}

	#[inline]
	pub fn is_top_level_module(self) -> bool {
	self.is_local() && self.is_crate_root()
	}
	}

	impl From<LocalDefId> for DefId {
	fn from(local: LocalDefId) -> DefId {
	local.to_def_id()
	}
	}

	pub fn default_def_id_debug(def_id: DefId, f: &mut fmt::Formatter<'_>) -> fmt::Result {
	f.debug_struct("DefId").field("krate", &def_id.krate).field("index", &def_id.index).finish()
	}

	pub static DEF_ID_DEBUG: AtomicRef<fn(DefId, &mut fmt::Formatter<'_>) -> fmt::Result> =
	AtomicRef::new(&(default_def_id_debug as fn(_, &mut fmt::Formatter<'_>) -> _));

	impl fmt::Debug for DefId {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
	(DEF_ID_DEBUG)(self, f)
	}
	}

	rustc_data_structures::define_id_collections!(DefIdMap, DefIdSet, DefIdMapEntry, DefId);

	/// A `LocalDefId` is equivalent to a `DefId` with `krate == LOCAL_CRATE`. Since
	/// we encode this information in the type, we can ensure at compile time that
	/// no `DefId`s from upstream crates get thrown into the mix. There are quite a
	/// few cases where we know that only `DefId`s from the local crate are expected;
	/// a `DefId` from a different crate would signify a bug somewhere. This
	/// is when `LocalDefId` comes in handy.
	#[derive(Clone, Copy, PartialEq, Eq, Hash)]
	pub struct LocalDefId {
	pub local_def_index: DefIndex,
	}

	// To ensure correctness of incremental compilation,
	// `LocalDefId` must not implement `Ord` or `PartialOrd`.
	// See https://github.com/rust-lang/rust/issues/90317.
	impl !Ord for LocalDefId {}
	impl !PartialOrd for LocalDefId {}

	pub const CRATE_DEF_ID: LocalDefId = LocalDefId { local_def_index: CRATE_DEF_INDEX };

	impl Idx for LocalDefId {
	#[inline]
	fn new(idx: usize) -> Self {
	LocalDefId { local_def_index: Idx::new(idx) }
	}
	#[inline]
	fn index(self) -> usize {
	self.local_def_index.index()
	}
	}

	impl LocalDefId {
	#[inline]
	pub fn to_def_id(self) -> DefId {
	DefId { krate: LOCAL_CRATE, index: self.local_def_index }
	}

	#[inline]
	pub fn is_top_level_module(self) -> bool {
	self == CRATE_DEF_ID
	}
	}

	impl fmt::Debug for LocalDefId {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
	self.to_def_id().fmt(f)
	}
	}

	impl<E: SpanEncoder> Encodable<E> for LocalDefId {
	fn encode(&self, s: &mut E) {
	self.to_def_id().encode(s);
	}
	}

	impl<D: SpanDecoder> Decodable<D> for LocalDefId {
	fn decode(d: &mut D) -> LocalDefId {
	DefId::decode(d).expect_local()
	}
	}

	rustc_data_structures::define_id_collections!(
	LocalDefIdMap,
	LocalDefIdSet,
	LocalDefIdMapEntry,
	LocalDefId
	);

	impl<CTX: HashStableContext> HashStable<CTX> for DefId {
	#[inline]
	fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
	self.to_stable_hash_key(hcx).hash_stable(hcx, hasher);
	}
	}

	impl<CTX: HashStableContext> HashStable<CTX> for LocalDefId {
	#[inline]
	fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
	self.to_stable_hash_key(hcx).hash_stable(hcx, hasher);
	}
	}

	impl<CTX: HashStableContext> HashStable<CTX> for CrateNum {
	#[inline]
	fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
	self.to_stable_hash_key(hcx).hash_stable(hcx, hasher);
	}
	}

	impl<CTX: HashStableContext> ToStableHashKey<CTX> for DefId {
	type KeyType = DefPathHash;

	#[inline]
	fn to_stable_hash_key(&self, hcx: &CTX) -> DefPathHash {
	hcx.def_path_hash(*self)
	}
	}

	impl<CTX: HashStableContext> ToStableHashKey<CTX> for LocalDefId {
	type KeyType = DefPathHash;

	#[inline]
	fn to_stable_hash_key(&self, hcx: &CTX) -> DefPathHash {
	hcx.def_path_hash(self.to_def_id())
	}
	}

	impl<CTX: HashStableContext> ToStableHashKey<CTX> for CrateNum {
	type KeyType = DefPathHash;

	#[inline]
	fn to_stable_hash_key(&self, hcx: &CTX) -> DefPathHash {
	self.as_def_id().to_stable_hash_key(hcx)
	}
	}

	impl<CTX: HashStableContext> ToStableHashKey<CTX> for DefPathHash {
	type KeyType = DefPathHash;

	#[inline]
	fn to_stable_hash_key(&self, _: &CTX) -> DefPathHash {
	*self
	}
	}

	macro_rules! typed_def_id {
	($Name:ident, $LocalName:ident) => {
	#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Encodable, Decodable, HashStable_Generic)]
	pub struct $Name(DefId);

	impl $Name {
	pub const fn new_unchecked(def_id: DefId) -> Self {
	Self(def_id)
	}

	pub fn to_def_id(self) -> DefId {
	self.into()
	}

	pub fn is_local(self) -> bool {
	self.0.is_local()
	}

	pub fn as_local(self) -> Option<$LocalName> {
	self.0.as_local().map($LocalName::new_unchecked)
	}
	}

	impl From<$LocalName> for $Name {
	fn from(local: $LocalName) -> Self {
	Self(local.0.to_def_id())
	}
	}

	impl From<$Name> for DefId {
	fn from(typed: $Name) -> Self {
	typed.0
	}
	}

	#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, Encodable, Decodable, HashStable_Generic)]
	pub struct $LocalName(LocalDefId);

	impl !Ord for $LocalName {}
	impl !PartialOrd for $LocalName {}

	impl $LocalName {
	pub const fn new_unchecked(def_id: LocalDefId) -> Self {
	Self(def_id)
	}

	pub fn to_def_id(self) -> DefId {
	self.0.into()
	}

	pub fn to_local_def_id(self) -> LocalDefId {
	self.0
	}
	}

	impl From<$LocalName> for LocalDefId {
	fn from(typed: $LocalName) -> Self {
	typed.0
	}
	}

	impl From<$LocalName> for DefId {
	fn from(typed: $LocalName) -> Self {
	typed.0.into()
	}
	}
	};
	}

	// N.B.: when adding new typed `DefId`s update the corresponding trait impls in
	// `rustc_middle::dep_graph::def_node` for `DepNodeParams`.
	typed_def_id! { ModDefId, LocalModDefId }

	impl LocalModDefId {
	pub const CRATE_DEF_ID: Self = Self::new_unchecked(CRATE_DEF_ID);
	}

	impl ModDefId {
	pub fn is_top_level_module(self) -> bool {
	self.0.is_top_level_module()
	}
	}

	impl LocalModDefId {
	pub fn is_top_level_module(self) -> bool {
	self.0.is_top_level_module()
	}
	}