compiler/rustc_hir/src/definitions.rs - third_party/github.com/rust-lang/rust - Git at Google

 //! For each definition, we track the following data. A definition
 //! here is defined somewhat circularly as "something with a `DefId`",
 //! but it generally corresponds to things like structs, enums, etc.
 //! There are also some rather random cases (like const initializer
 //! expressions) that are mostly just leftovers.

 use std::fmt::{self, Write};
 use std::hash::Hash;

 use rustc_data_structures::stable_hasher::StableHasher;
 use rustc_data_structures::unord::UnordMap;
 use rustc_hashes::Hash64;
 use rustc_index::IndexVec;
 use rustc_macros::{Decodable, Encodable};
 use rustc_span::{Symbol, kw, sym};
 use tracing::{debug, instrument};

 pub use crate::def_id::DefPathHash;
 use crate::def_id::{CRATE_DEF_INDEX, CrateNum, DefIndex, LOCAL_CRATE, LocalDefId, StableCrateId};
 use crate::def_path_hash_map::DefPathHashMap;

 /// The `DefPathTable` maps `DefIndex`es to `DefKey`s and vice versa.
 /// Internally the `DefPathTable` holds a tree of `DefKey`s, where each `DefKey`
 /// stores the `DefIndex` of its parent.
 /// There is one `DefPathTable` for each crate.
 #[derive(Debug)]
 pub struct DefPathTable {
     stable_crate_id: StableCrateId,
     index_to_key: IndexVec<DefIndex, DefKey>,
     // We do only store the local hash, as all the definitions are from the current crate.
     def_path_hashes: IndexVec<DefIndex, Hash64>,
     def_path_hash_to_index: DefPathHashMap,
 }

 impl DefPathTable {
     fn new(stable_crate_id: StableCrateId) -> DefPathTable {
         DefPathTable {
             stable_crate_id,
             index_to_key: Default::default(),
             def_path_hashes: Default::default(),
             def_path_hash_to_index: Default::default(),
         }
     }

     fn allocate(&mut self, key: DefKey, def_path_hash: DefPathHash) -> DefIndex {
         // Assert that all DefPathHashes correctly contain the local crate's StableCrateId.
         debug_assert_eq!(self.stable_crate_id, def_path_hash.stable_crate_id());
         let local_hash = def_path_hash.local_hash();

         let index = self.index_to_key.push(key);
         debug!("DefPathTable::insert() - {key:?} <-> {index:?}");

         self.def_path_hashes.push(local_hash);
         debug_assert!(self.def_path_hashes.len() == self.index_to_key.len());

         // Check for hash collisions of DefPathHashes. These should be
         // exceedingly rare.
         if let Some(existing) = self.def_path_hash_to_index.insert(&local_hash, &index) {
             let def_path1 = DefPath::make(LOCAL_CRATE, existing, |idx| self.def_key(idx));
             let def_path2 = DefPath::make(LOCAL_CRATE, index, |idx| self.def_key(idx));

             // Continuing with colliding DefPathHashes can lead to correctness
             // issues. We must abort compilation.
             //
             // The likelihood of such a collision is very small, so actually
             // running into one could be indicative of a poor hash function
             // being used.
             //
             // See the documentation for DefPathHash for more information.
             panic!(
                 "found DefPathHash collision between {def_path1:#?} and {def_path2:#?}. \
                     Compilation cannot continue."
             );
         }

         index
     }

     #[inline(always)]
     pub fn def_key(&self, index: DefIndex) -> DefKey {
         self.index_to_key[index]
     }

     #[instrument(level = "trace", skip(self), ret)]
     #[inline(always)]
     pub fn def_path_hash(&self, index: DefIndex) -> DefPathHash {
         let hash = self.def_path_hashes[index];
         DefPathHash::new(self.stable_crate_id, hash)
     }

     pub fn enumerated_keys_and_path_hashes(
         &self,
     ) -> impl Iterator<Item = (DefIndex, &DefKey, DefPathHash)> + ExactSizeIterator {
         self.index_to_key
             .iter_enumerated()
             .map(move |(index, key)| (index, key, self.def_path_hash(index)))
     }
 }

 #[derive(Debug)]
 pub struct DisambiguatorState {
     next: UnordMap<(LocalDefId, DefPathData), u32>,
 }

 impl DisambiguatorState {
     pub fn new() -> Self {
         Self { next: Default::default() }
     }

     /// Creates a `DisambiguatorState` where the next allocated `(LocalDefId, DefPathData)` pair
     /// will have `index` as the disambiguator.
     pub fn with(def_id: LocalDefId, data: DefPathData, index: u32) -> Self {
         let mut this = Self::new();
         this.next.insert((def_id, data), index);
         this
     }
 }

 /// The definition table containing node definitions.
 /// It holds the `DefPathTable` for `LocalDefId`s/`DefPath`s.
 /// It also stores mappings to convert `LocalDefId`s to/from `HirId`s.
 #[derive(Debug)]
 pub struct Definitions {
     table: DefPathTable,
 }

 /// A unique identifier that we can use to lookup a definition
 /// precisely. It combines the index of the definition's parent (if
 /// any) with a `DisambiguatedDefPathData`.
 #[derive(Copy, Clone, PartialEq, Debug, Encodable, Decodable)]
 pub struct DefKey {
     /// The parent path.
     pub parent: Option<DefIndex>,

     /// The identifier of this node.
     pub disambiguated_data: DisambiguatedDefPathData,
 }

 impl DefKey {
     pub(crate) fn compute_stable_hash(&self, parent: DefPathHash) -> DefPathHash {
         let mut hasher = StableHasher::new();

         // The new path is in the same crate as `parent`, and will contain the stable_crate_id.
         // Therefore, we only need to include information of the parent's local hash.
         parent.local_hash().hash(&mut hasher);

         let DisambiguatedDefPathData { ref data, disambiguator } = self.disambiguated_data;

         std::mem::discriminant(data).hash(&mut hasher);
         if let Some(name) = data.hashed_symbol() {
             // Get a stable hash by considering the symbol chars rather than
             // the symbol index.
             name.as_str().hash(&mut hasher);
         }

         disambiguator.hash(&mut hasher);

         let local_hash = hasher.finish();

         // Construct the new DefPathHash, making sure that the `crate_id`
         // portion of the hash is properly copied from the parent. This way the
         // `crate_id` part will be recursively propagated from the root to all
         // DefPathHashes in this DefPathTable.
         DefPathHash::new(parent.stable_crate_id(), local_hash)
     }

     #[inline]
     pub fn get_opt_name(&self) -> Option<Symbol> {
         self.disambiguated_data.data.get_opt_name()
     }
 }

 /// A pair of `DefPathData` and an integer disambiguator. The integer is
 /// normally `0`, but in the event that there are multiple defs with the
 /// same `parent` and `data`, we use this field to disambiguate
 /// between them. This introduces some artificial ordering dependency
 /// but means that if you have, e.g., two impls for the same type in
 /// the same module, they do get distinct `DefId`s.
 #[derive(Copy, Clone, PartialEq, Debug, Encodable, Decodable)]
 pub struct DisambiguatedDefPathData {
     pub data: DefPathData,
     pub disambiguator: u32,
 }

 impl DisambiguatedDefPathData {
     pub fn as_sym(&self, verbose: bool) -> Symbol {
         match self.data.name() {
             DefPathDataName::Named(name) => {
                 if verbose && self.disambiguator != 0 {
                     Symbol::intern(&format!("{}#{}", name, self.disambiguator))
                 } else {
                     name
                 }
             }
             DefPathDataName::Anon { namespace } => {
                 if let DefPathData::AnonAssocTy(method) = self.data {
                     Symbol::intern(&format!("{}::{{{}#{}}}", method, namespace, self.disambiguator))
                 } else {
                     Symbol::intern(&format!("{{{}#{}}}", namespace, self.disambiguator))
                 }
             }
         }
     }
 }

 #[derive(Clone, Debug, Encodable, Decodable)]
 pub struct DefPath {
     /// The path leading from the crate root to the item.
     pub data: Vec<DisambiguatedDefPathData>,

     /// The crate root this path is relative to.
     pub krate: CrateNum,
 }

 impl DefPath {
     pub fn make<FN>(krate: CrateNum, start_index: DefIndex, mut get_key: FN) -> DefPath
     where
         FN: FnMut(DefIndex) -> DefKey,
     {
         let mut data = vec![];
         let mut index = Some(start_index);
         loop {
             debug!("DefPath::make: krate={:?} index={:?}", krate, index);
             let p = index.unwrap();
             let key = get_key(p);
             debug!("DefPath::make: key={:?}", key);
             match key.disambiguated_data.data {
                 DefPathData::CrateRoot => {
                     assert!(key.parent.is_none());
                     break;
                 }
                 _ => {
                     data.push(key.disambiguated_data);
                     index = key.parent;
                 }
             }
         }
         data.reverse();
         DefPath { data, krate }
     }

     /// Returns a string representation of the `DefPath` without
     /// the crate-prefix. This method is useful if you don't have
     /// a `TyCtxt` available.
     pub fn to_string_no_crate_verbose(&self) -> String {
         let mut s = String::with_capacity(self.data.len() * 16);

         for component in &self.data {
             write!(s, "::{}", component.as_sym(true)).unwrap();
         }

         s
     }

     /// Returns a filename-friendly string of the `DefPath`, without
     /// the crate-prefix. This method is useful if you don't have
     /// a `TyCtxt` available.
     pub fn to_filename_friendly_no_crate(&self) -> String {
         let mut s = String::with_capacity(self.data.len() * 16);

         let mut opt_delimiter = None;
         for component in &self.data {
             s.extend(opt_delimiter);
             opt_delimiter = Some('-');
             write!(s, "{}", component.as_sym(true)).unwrap();
         }

         s
     }
 }

 /// New variants should only be added in synchronization with `enum DefKind`.
 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, Encodable, Decodable)]
 pub enum DefPathData {
     // Root: these should only be used for the root nodes, because
     // they are treated specially by the `def_path` function.
     /// The crate root (marker).
     CrateRoot,

     // Different kinds of items and item-like things:
     /// An impl.
     Impl,
     /// An `extern` block.
     ForeignMod,
     /// A `use` item.
     Use,
     /// A global asm item.
     GlobalAsm,
     /// Something in the type namespace.
     TypeNs(Symbol),
     /// Something in the value namespace.
     ValueNs(Symbol),
     /// Something in the macro namespace.
     MacroNs(Symbol),
     /// Something in the lifetime namespace.
     LifetimeNs(Symbol),
     /// A closure expression.
     Closure,

     // Subportions of items:
     /// Implicit constructor for a unit or tuple-like struct or enum variant.
     Ctor,
     /// A constant expression (see `{ast,hir}::AnonConst`).
     AnonConst,
     /// A constant expression created during AST->HIR lowering..
     LateAnonConst,
     /// A fresh anonymous lifetime created by desugaring elided lifetimes.
     DesugaredAnonymousLifetime,
     /// An existential `impl Trait` type node.
     /// Argument position `impl Trait` have a `TypeNs` with their pretty-printed name.
     OpaqueTy,
     /// Used for remapped captured lifetimes in an existential `impl Trait` type node.
     OpaqueLifetime(Symbol),
     /// An anonymous associated type from an RPITIT. The symbol refers to the name of the method
     /// that defined the type.
     AnonAssocTy(Symbol),
     /// A synthetic body for a coroutine's by-move body.
     SyntheticCoroutineBody,
     /// Additional static data referred to by a static.
     NestedStatic,
 }

 impl Definitions {
     pub fn def_path_table(&self) -> &DefPathTable {
         &self.table
     }

     /// Gets the number of definitions.
     pub fn def_index_count(&self) -> usize {
         self.table.index_to_key.len()
     }

     #[inline]
     pub fn def_key(&self, id: LocalDefId) -> DefKey {
         self.table.def_key(id.local_def_index)
     }

     #[inline(always)]
     pub fn def_path_hash(&self, id: LocalDefId) -> DefPathHash {
         self.table.def_path_hash(id.local_def_index)
     }

     /// Returns the path from the crate root to `index`. The root
     /// nodes are not included in the path (i.e., this will be an
     /// empty vector for the crate root). For an inlined item, this
     /// will be the path of the item in the external crate (but the
     /// path will begin with the path to the external crate).
     pub fn def_path(&self, id: LocalDefId) -> DefPath {
         DefPath::make(LOCAL_CRATE, id.local_def_index, |index| {
             self.def_key(LocalDefId { local_def_index: index })
         })
     }

     /// Adds a root definition (no parent) and a few other reserved definitions.
     pub fn new(stable_crate_id: StableCrateId) -> Definitions {
         let key = DefKey {
             parent: None,
             disambiguated_data: DisambiguatedDefPathData {
                 data: DefPathData::CrateRoot,
                 disambiguator: 0,
             },
         };

         // We want *both* halves of a DefPathHash to depend on the crate-id of the defining crate.
         // The crate-id can be more easily changed than the DefPath of an item, so, in the case of
         // a crate-local DefPathHash collision, the user can simply "roll the dice again" for all
         // DefPathHashes in the crate by changing the crate disambiguator (e.g. via bumping the
         // crate's version number).
         //
         // Children paths will only hash the local portion, and still inherit the change to the
         // root hash.
         let def_path_hash =
             DefPathHash::new(stable_crate_id, Hash64::new(stable_crate_id.as_u64()));

         // Create the root definition.
         let mut table = DefPathTable::new(stable_crate_id);
         let root = LocalDefId { local_def_index: table.allocate(key, def_path_hash) };
         assert_eq!(root.local_def_index, CRATE_DEF_INDEX);

         Definitions { table }
     }

     /// Creates a definition with a parent definition.
     /// If there are multiple definitions with the same DefPathData and the same parent, use
     /// `disambiguator` to differentiate them. Distinct `DisambiguatorState` instances are not
     /// guaranteed to generate unique disambiguators and should instead ensure that the `parent`
     /// and `data` pair is distinct from other instances.
     pub fn create_def(
         &mut self,
         parent: LocalDefId,
         data: DefPathData,
         disambiguator: &mut DisambiguatorState,
     ) -> LocalDefId {
         // We can't use `Debug` implementation for `LocalDefId` here, since it tries to acquire a
         // reference to `Definitions` and we're already holding a mutable reference.
         debug!(
             "create_def(parent={}, data={data:?})",
             self.def_path(parent).to_string_no_crate_verbose(),
         );

         // The root node must be created in `new()`.
         assert!(data != DefPathData::CrateRoot);

         // Find the next free disambiguator for this key.
         let disambiguator = {
             let next_disamb = disambiguator.next.entry((parent, data)).or_insert(0);
             let disambiguator = *next_disamb;
             *next_disamb = next_disamb.checked_add(1).expect("disambiguator overflow");
             disambiguator
         };
         let key = DefKey {
             parent: Some(parent.local_def_index),
             disambiguated_data: DisambiguatedDefPathData { data, disambiguator },
         };

         let parent_hash = self.table.def_path_hash(parent.local_def_index);
         let def_path_hash = key.compute_stable_hash(parent_hash);

         debug!("create_def: after disambiguation, key = {:?}", key);

         // Create the definition.
         LocalDefId { local_def_index: self.table.allocate(key, def_path_hash) }
     }

     #[inline(always)]
     /// Returns `None` if the `DefPathHash` does not correspond to a `LocalDefId`
     /// in the current compilation session. This can legitimately happen if the
     /// `DefPathHash` is from a `DefId` in an upstream crate or, during incr. comp.,
     /// if the `DefPathHash` is from a previous compilation session and
     /// the def-path does not exist anymore.
     pub fn local_def_path_hash_to_def_id(&self, hash: DefPathHash) -> Option<LocalDefId> {
         debug_assert!(hash.stable_crate_id() == self.table.stable_crate_id);
         self.table
             .def_path_hash_to_index
             .get(&hash.local_hash())
             .map(|local_def_index| LocalDefId { local_def_index })
     }

     pub fn def_path_hash_to_def_index_map(&self) -> &DefPathHashMap {
         &self.table.def_path_hash_to_index
     }

     pub fn num_definitions(&self) -> usize {
         self.table.def_path_hashes.len()
     }
 }

 #[derive(Copy, Clone, PartialEq, Debug)]
 pub enum DefPathDataName {
     Named(Symbol),
     Anon { namespace: Symbol },
 }

 impl DefPathData {
     pub fn get_opt_name(&self) -> Option<Symbol> {
         use self::DefPathData::*;
         match *self {
             TypeNs(name) | ValueNs(name) | MacroNs(name) | LifetimeNs(name)
             | OpaqueLifetime(name) => Some(name),

             DesugaredAnonymousLifetime => Some(kw::UnderscoreLifetime),

             Impl
             | ForeignMod
             | CrateRoot
             | Use
             | GlobalAsm
             | Closure
             | Ctor
             | AnonConst
             | LateAnonConst
             | OpaqueTy
             | AnonAssocTy(..)
             | SyntheticCoroutineBody
             | NestedStatic => None,
         }
     }

     fn hashed_symbol(&self) -> Option<Symbol> {
         use self::DefPathData::*;
         match *self {
             TypeNs(name) | ValueNs(name) | MacroNs(name) | LifetimeNs(name) | AnonAssocTy(name)
             | OpaqueLifetime(name) => Some(name),

             DesugaredAnonymousLifetime => Some(kw::UnderscoreLifetime),

             Impl
             | ForeignMod
             | CrateRoot
             | Use
             | GlobalAsm
             | Closure
             | Ctor
             | AnonConst
             | LateAnonConst
             | OpaqueTy
             | SyntheticCoroutineBody
             | NestedStatic => None,
         }
     }

     pub fn name(&self) -> DefPathDataName {
         use self::DefPathData::*;
         match *self {
             TypeNs(name) | ValueNs(name) | MacroNs(name) | LifetimeNs(name)
             | OpaqueLifetime(name) => DefPathDataName::Named(name),
             // Note that this does not show up in user print-outs.
             CrateRoot => DefPathDataName::Anon { namespace: kw::Crate },
             Impl => DefPathDataName::Anon { namespace: kw::Impl },
             ForeignMod => DefPathDataName::Anon { namespace: kw::Extern },
             Use => DefPathDataName::Anon { namespace: kw::Use },
             GlobalAsm => DefPathDataName::Anon { namespace: sym::global_asm },
             Closure => DefPathDataName::Anon { namespace: sym::closure },
             Ctor => DefPathDataName::Anon { namespace: sym::constructor },
             AnonConst | LateAnonConst => DefPathDataName::Anon { namespace: sym::constant },
             DesugaredAnonymousLifetime => DefPathDataName::Named(kw::UnderscoreLifetime),
             OpaqueTy => DefPathDataName::Anon { namespace: sym::opaque },
             AnonAssocTy(..) => DefPathDataName::Anon { namespace: sym::anon_assoc },
             SyntheticCoroutineBody => DefPathDataName::Anon { namespace: sym::synthetic },
             NestedStatic => DefPathDataName::Anon { namespace: sym::nested },
         }
     }
 }

 impl fmt::Display for DefPathData {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self.name() {
             DefPathDataName::Named(name) => f.write_str(name.as_str()),
             // FIXME(#70334): this will generate legacy {{closure}}, {{impl}}, etc
             DefPathDataName::Anon { namespace } => write!(f, "{{{{{namespace}}}}}"),
         }
     }
 }
	//! For each definition, we track the following data. A definition
	//! here is defined somewhat circularly as "something with a `DefId`",
	//! but it generally corresponds to things like structs, enums, etc.
	//! There are also some rather random cases (like const initializer
	//! expressions) that are mostly just leftovers.

	use std::fmt::{self, Write};
	use std::hash::Hash;

	use rustc_data_structures::stable_hasher::StableHasher;
	use rustc_data_structures::unord::UnordMap;
	use rustc_hashes::Hash64;
	use rustc_index::IndexVec;
	use rustc_macros::{Decodable, Encodable};
	use rustc_span::{Symbol, kw, sym};
	use tracing::{debug, instrument};

	pub use crate::def_id::DefPathHash;
	use crate::def_id::{CRATE_DEF_INDEX, CrateNum, DefIndex, LOCAL_CRATE, LocalDefId, StableCrateId};
	use crate::def_path_hash_map::DefPathHashMap;

	/// The `DefPathTable` maps `DefIndex`es to `DefKey`s and vice versa.
	/// Internally the `DefPathTable` holds a tree of `DefKey`s, where each `DefKey`
	/// stores the `DefIndex` of its parent.
	/// There is one `DefPathTable` for each crate.
	#[derive(Debug)]
	pub struct DefPathTable {
	stable_crate_id: StableCrateId,
	index_to_key: IndexVec<DefIndex, DefKey>,
	// We do only store the local hash, as all the definitions are from the current crate.
	def_path_hashes: IndexVec<DefIndex, Hash64>,
	def_path_hash_to_index: DefPathHashMap,
	}

	impl DefPathTable {
	fn new(stable_crate_id: StableCrateId) -> DefPathTable {
	DefPathTable {
	stable_crate_id,
	index_to_key: Default::default(),
	def_path_hashes: Default::default(),
	def_path_hash_to_index: Default::default(),
	}
	}

	fn allocate(&mut self, key: DefKey, def_path_hash: DefPathHash) -> DefIndex {
	// Assert that all DefPathHashes correctly contain the local crate's StableCrateId.
	debug_assert_eq!(self.stable_crate_id, def_path_hash.stable_crate_id());
	let local_hash = def_path_hash.local_hash();

	let index = self.index_to_key.push(key);
	debug!("DefPathTable::insert() - {key:?} <-> {index:?}");

	self.def_path_hashes.push(local_hash);
	debug_assert!(self.def_path_hashes.len() == self.index_to_key.len());

	// Check for hash collisions of DefPathHashes. These should be
	// exceedingly rare.
	if let Some(existing) = self.def_path_hash_to_index.insert(&local_hash, &index) {
	let def_path1 = DefPath::make(LOCAL_CRATE, existing, \|idx\| self.def_key(idx));
	let def_path2 = DefPath::make(LOCAL_CRATE, index, \|idx\| self.def_key(idx));

	// Continuing with colliding DefPathHashes can lead to correctness
	// issues. We must abort compilation.
	//
	// The likelihood of such a collision is very small, so actually
	// running into one could be indicative of a poor hash function
	// being used.
	//
	// See the documentation for DefPathHash for more information.
	panic!(
	"found DefPathHash collision between {def_path1:#?} and {def_path2:#?}. \
	Compilation cannot continue."
	);
	}

	index
	}

	#[inline(always)]
	pub fn def_key(&self, index: DefIndex) -> DefKey {
	self.index_to_key[index]
	}

	#[instrument(level = "trace", skip(self), ret)]
	#[inline(always)]
	pub fn def_path_hash(&self, index: DefIndex) -> DefPathHash {
	let hash = self.def_path_hashes[index];
	DefPathHash::new(self.stable_crate_id, hash)
	}

	pub fn enumerated_keys_and_path_hashes(
	&self,
	) -> impl Iterator<Item = (DefIndex, &DefKey, DefPathHash)> + ExactSizeIterator {
	self.index_to_key
	.iter_enumerated()
	.map(move \|(index, key)\| (index, key, self.def_path_hash(index)))
	}
	}

	#[derive(Debug)]
	pub struct DisambiguatorState {
	next: UnordMap<(LocalDefId, DefPathData), u32>,
	}

	impl DisambiguatorState {
	pub fn new() -> Self {
	Self { next: Default::default() }
	}

	/// Creates a `DisambiguatorState` where the next allocated `(LocalDefId, DefPathData)` pair
	/// will have `index` as the disambiguator.
	pub fn with(def_id: LocalDefId, data: DefPathData, index: u32) -> Self {
	let mut this = Self::new();
	this.next.insert((def_id, data), index);
	this
	}
	}

	/// The definition table containing node definitions.
	/// It holds the `DefPathTable` for `LocalDefId`s/`DefPath`s.
	/// It also stores mappings to convert `LocalDefId`s to/from `HirId`s.
	#[derive(Debug)]
	pub struct Definitions {
	table: DefPathTable,
	}

	/// A unique identifier that we can use to lookup a definition
	/// precisely. It combines the index of the definition's parent (if
	/// any) with a `DisambiguatedDefPathData`.
	#[derive(Copy, Clone, PartialEq, Debug, Encodable, Decodable)]
	pub struct DefKey {
	/// The parent path.
	pub parent: Option<DefIndex>,

	/// The identifier of this node.
	pub disambiguated_data: DisambiguatedDefPathData,
	}

	impl DefKey {
	pub(crate) fn compute_stable_hash(&self, parent: DefPathHash) -> DefPathHash {
	let mut hasher = StableHasher::new();

	// The new path is in the same crate as `parent`, and will contain the stable_crate_id.
	// Therefore, we only need to include information of the parent's local hash.
	parent.local_hash().hash(&mut hasher);

	let DisambiguatedDefPathData { ref data, disambiguator } = self.disambiguated_data;

	std::mem::discriminant(data).hash(&mut hasher);
	if let Some(name) = data.hashed_symbol() {
	// Get a stable hash by considering the symbol chars rather than
	// the symbol index.
	name.as_str().hash(&mut hasher);
	}

	disambiguator.hash(&mut hasher);

	let local_hash = hasher.finish();

	// Construct the new DefPathHash, making sure that the `crate_id`
	// portion of the hash is properly copied from the parent. This way the
	// `crate_id` part will be recursively propagated from the root to all
	// DefPathHashes in this DefPathTable.
	DefPathHash::new(parent.stable_crate_id(), local_hash)
	}

	#[inline]
	pub fn get_opt_name(&self) -> Option<Symbol> {
	self.disambiguated_data.data.get_opt_name()
	}
	}

	/// A pair of `DefPathData` and an integer disambiguator. The integer is
	/// normally `0`, but in the event that there are multiple defs with the
	/// same `parent` and `data`, we use this field to disambiguate
	/// between them. This introduces some artificial ordering dependency
	/// but means that if you have, e.g., two impls for the same type in
	/// the same module, they do get distinct `DefId`s.
	#[derive(Copy, Clone, PartialEq, Debug, Encodable, Decodable)]
	pub struct DisambiguatedDefPathData {
	pub data: DefPathData,
	pub disambiguator: u32,
	}

	impl DisambiguatedDefPathData {
	pub fn as_sym(&self, verbose: bool) -> Symbol {
	match self.data.name() {
	DefPathDataName::Named(name) => {
	if verbose && self.disambiguator != 0 {
	Symbol::intern(&format!("{}#{}", name, self.disambiguator))
	} else {
	name
	}
	}
	DefPathDataName::Anon { namespace } => {
	if let DefPathData::AnonAssocTy(method) = self.data {
	Symbol::intern(&format!("{}::{{{}#{}}}", method, namespace, self.disambiguator))
	} else {
	Symbol::intern(&format!("{{{}#{}}}", namespace, self.disambiguator))
	}
	}
	}
	}
	}

	#[derive(Clone, Debug, Encodable, Decodable)]
	pub struct DefPath {
	/// The path leading from the crate root to the item.
	pub data: Vec<DisambiguatedDefPathData>,

	/// The crate root this path is relative to.
	pub krate: CrateNum,
	}

	impl DefPath {
	pub fn make<FN>(krate: CrateNum, start_index: DefIndex, mut get_key: FN) -> DefPath
	where
	FN: FnMut(DefIndex) -> DefKey,
	{
	let mut data = vec![];
	let mut index = Some(start_index);
	loop {
	debug!("DefPath::make: krate={:?} index={:?}", krate, index);
	let p = index.unwrap();
	let key = get_key(p);
	debug!("DefPath::make: key={:?}", key);
	match key.disambiguated_data.data {
	DefPathData::CrateRoot => {
	assert!(key.parent.is_none());
	break;
	}
	_ => {
	data.push(key.disambiguated_data);
	index = key.parent;
	}
	}
	}
	data.reverse();
	DefPath { data, krate }
	}

	/// Returns a string representation of the `DefPath` without
	/// the crate-prefix. This method is useful if you don't have
	/// a `TyCtxt` available.
	pub fn to_string_no_crate_verbose(&self) -> String {
	let mut s = String::with_capacity(self.data.len() * 16);

	for component in &self.data {
	write!(s, "::{}", component.as_sym(true)).unwrap();
	}

	s
	}

	/// Returns a filename-friendly string of the `DefPath`, without
	/// the crate-prefix. This method is useful if you don't have
	/// a `TyCtxt` available.
	pub fn to_filename_friendly_no_crate(&self) -> String {
	let mut s = String::with_capacity(self.data.len() * 16);

	let mut opt_delimiter = None;
	for component in &self.data {
	s.extend(opt_delimiter);
	opt_delimiter = Some('-');
	write!(s, "{}", component.as_sym(true)).unwrap();
	}

	s
	}
	}

	/// New variants should only be added in synchronization with `enum DefKind`.
	#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, Encodable, Decodable)]
	pub enum DefPathData {
	// Root: these should only be used for the root nodes, because
	// they are treated specially by the `def_path` function.
	/// The crate root (marker).
	CrateRoot,

	// Different kinds of items and item-like things:
	/// An impl.
	Impl,
	/// An `extern` block.
	ForeignMod,
	/// A `use` item.
	Use,
	/// A global asm item.
	GlobalAsm,
	/// Something in the type namespace.
	TypeNs(Symbol),
	/// Something in the value namespace.
	ValueNs(Symbol),
	/// Something in the macro namespace.
	MacroNs(Symbol),
	/// Something in the lifetime namespace.
	LifetimeNs(Symbol),
	/// A closure expression.
	Closure,

	// Subportions of items:
	/// Implicit constructor for a unit or tuple-like struct or enum variant.
	Ctor,
	/// A constant expression (see `{ast,hir}::AnonConst`).
	AnonConst,
	/// A constant expression created during AST->HIR lowering..
	LateAnonConst,
	/// A fresh anonymous lifetime created by desugaring elided lifetimes.
	DesugaredAnonymousLifetime,
	/// An existential `impl Trait` type node.
	/// Argument position `impl Trait` have a `TypeNs` with their pretty-printed name.
	OpaqueTy,
	/// Used for remapped captured lifetimes in an existential `impl Trait` type node.
	OpaqueLifetime(Symbol),
	/// An anonymous associated type from an RPITIT. The symbol refers to the name of the method
	/// that defined the type.
	AnonAssocTy(Symbol),
	/// A synthetic body for a coroutine's by-move body.
	SyntheticCoroutineBody,
	/// Additional static data referred to by a static.
	NestedStatic,
	}

	impl Definitions {
	pub fn def_path_table(&self) -> &DefPathTable {
	&self.table
	}

	/// Gets the number of definitions.
	pub fn def_index_count(&self) -> usize {
	self.table.index_to_key.len()
	}

	#[inline]
	pub fn def_key(&self, id: LocalDefId) -> DefKey {
	self.table.def_key(id.local_def_index)
	}

	#[inline(always)]
	pub fn def_path_hash(&self, id: LocalDefId) -> DefPathHash {
	self.table.def_path_hash(id.local_def_index)
	}

	/// Returns the path from the crate root to `index`. The root
	/// nodes are not included in the path (i.e., this will be an
	/// empty vector for the crate root). For an inlined item, this
	/// will be the path of the item in the external crate (but the
	/// path will begin with the path to the external crate).
	pub fn def_path(&self, id: LocalDefId) -> DefPath {
	DefPath::make(LOCAL_CRATE, id.local_def_index, \|index\| {
	self.def_key(LocalDefId { local_def_index: index })
	})
	}

	/// Adds a root definition (no parent) and a few other reserved definitions.
	pub fn new(stable_crate_id: StableCrateId) -> Definitions {
	let key = DefKey {
	parent: None,
	disambiguated_data: DisambiguatedDefPathData {
	data: DefPathData::CrateRoot,
	disambiguator: 0,
	},
	};

	// We want both halves of a DefPathHash to depend on the crate-id of the defining crate.
	// The crate-id can be more easily changed than the DefPath of an item, so, in the case of
	// a crate-local DefPathHash collision, the user can simply "roll the dice again" for all
	// DefPathHashes in the crate by changing the crate disambiguator (e.g. via bumping the
	// crate's version number).
	//
	// Children paths will only hash the local portion, and still inherit the change to the
	// root hash.
	let def_path_hash =
	DefPathHash::new(stable_crate_id, Hash64::new(stable_crate_id.as_u64()));

	// Create the root definition.
	let mut table = DefPathTable::new(stable_crate_id);
	let root = LocalDefId { local_def_index: table.allocate(key, def_path_hash) };
	assert_eq!(root.local_def_index, CRATE_DEF_INDEX);

	Definitions { table }
	}

	/// Creates a definition with a parent definition.
	/// If there are multiple definitions with the same DefPathData and the same parent, use
	/// `disambiguator` to differentiate them. Distinct `DisambiguatorState` instances are not
	/// guaranteed to generate unique disambiguators and should instead ensure that the `parent`
	/// and `data` pair is distinct from other instances.
	pub fn create_def(
	&mut self,
	parent: LocalDefId,
	data: DefPathData,
	disambiguator: &mut DisambiguatorState,
	) -> LocalDefId {
	// We can't use `Debug` implementation for `LocalDefId` here, since it tries to acquire a
	// reference to `Definitions` and we're already holding a mutable reference.
	debug!(
	"create_def(parent={}, data={data:?})",
	self.def_path(parent).to_string_no_crate_verbose(),
	);

	// The root node must be created in `new()`.
	assert!(data != DefPathData::CrateRoot);

	// Find the next free disambiguator for this key.
	let disambiguator = {
	let next_disamb = disambiguator.next.entry((parent, data)).or_insert(0);
	let disambiguator = *next_disamb;
	*next_disamb = next_disamb.checked_add(1).expect("disambiguator overflow");
	disambiguator
	};
	let key = DefKey {
	parent: Some(parent.local_def_index),
	disambiguated_data: DisambiguatedDefPathData { data, disambiguator },
	};

	let parent_hash = self.table.def_path_hash(parent.local_def_index);
	let def_path_hash = key.compute_stable_hash(parent_hash);

	debug!("create_def: after disambiguation, key = {:?}", key);

	// Create the definition.
	LocalDefId { local_def_index: self.table.allocate(key, def_path_hash) }
	}

	#[inline(always)]
	/// Returns `None` if the `DefPathHash` does not correspond to a `LocalDefId`
	/// in the current compilation session. This can legitimately happen if the
	/// `DefPathHash` is from a `DefId` in an upstream crate or, during incr. comp.,
	/// if the `DefPathHash` is from a previous compilation session and
	/// the def-path does not exist anymore.
	pub fn local_def_path_hash_to_def_id(&self, hash: DefPathHash) -> Option<LocalDefId> {
	debug_assert!(hash.stable_crate_id() == self.table.stable_crate_id);
	self.table
	.def_path_hash_to_index
	.get(&hash.local_hash())
	.map(\|local_def_index\| LocalDefId { local_def_index })
	}

	pub fn def_path_hash_to_def_index_map(&self) -> &DefPathHashMap {
	&self.table.def_path_hash_to_index
	}

	pub fn num_definitions(&self) -> usize {
	self.table.def_path_hashes.len()
	}
	}

	#[derive(Copy, Clone, PartialEq, Debug)]
	pub enum DefPathDataName {
	Named(Symbol),
	Anon { namespace: Symbol },
	}

	impl DefPathData {
	pub fn get_opt_name(&self) -> Option<Symbol> {
	use self::DefPathData::*;
	match *self {
	TypeNs(name) \| ValueNs(name) \| MacroNs(name) \| LifetimeNs(name)
	\| OpaqueLifetime(name) => Some(name),

	DesugaredAnonymousLifetime => Some(kw::UnderscoreLifetime),

	Impl
	\| ForeignMod
	\| CrateRoot
	\| Use
	\| GlobalAsm
	\| Closure
	\| Ctor
	\| AnonConst
	\| LateAnonConst
	\| OpaqueTy
	\| AnonAssocTy(..)
	\| SyntheticCoroutineBody
	\| NestedStatic => None,
	}
	}

	fn hashed_symbol(&self) -> Option<Symbol> {
	use self::DefPathData::*;
	match *self {
	TypeNs(name) \| ValueNs(name) \| MacroNs(name) \| LifetimeNs(name) \| AnonAssocTy(name)
	\| OpaqueLifetime(name) => Some(name),

	DesugaredAnonymousLifetime => Some(kw::UnderscoreLifetime),

	Impl
	\| ForeignMod
	\| CrateRoot
	\| Use
	\| GlobalAsm
	\| Closure
	\| Ctor
	\| AnonConst
	\| LateAnonConst
	\| OpaqueTy
	\| SyntheticCoroutineBody
	\| NestedStatic => None,
	}
	}

	pub fn name(&self) -> DefPathDataName {
	use self::DefPathData::*;
	match *self {
	TypeNs(name) \| ValueNs(name) \| MacroNs(name) \| LifetimeNs(name)
	\| OpaqueLifetime(name) => DefPathDataName::Named(name),
	// Note that this does not show up in user print-outs.
	CrateRoot => DefPathDataName::Anon { namespace: kw::Crate },
	Impl => DefPathDataName::Anon { namespace: kw::Impl },
	ForeignMod => DefPathDataName::Anon { namespace: kw::Extern },
	Use => DefPathDataName::Anon { namespace: kw::Use },
	GlobalAsm => DefPathDataName::Anon { namespace: sym::global_asm },
	Closure => DefPathDataName::Anon { namespace: sym::closure },
	Ctor => DefPathDataName::Anon { namespace: sym::constructor },
	AnonConst \| LateAnonConst => DefPathDataName::Anon { namespace: sym::constant },
	DesugaredAnonymousLifetime => DefPathDataName::Named(kw::UnderscoreLifetime),
	OpaqueTy => DefPathDataName::Anon { namespace: sym::opaque },
	AnonAssocTy(..) => DefPathDataName::Anon { namespace: sym::anon_assoc },
	SyntheticCoroutineBody => DefPathDataName::Anon { namespace: sym::synthetic },
	NestedStatic => DefPathDataName::Anon { namespace: sym::nested },
	}
	}
	}

	impl fmt::Display for DefPathData {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
	match self.name() {
	DefPathDataName::Named(name) => f.write_str(name.as_str()),
	// FIXME(#70334): this will generate legacy {{closure}}, {{impl}}, etc
	DefPathDataName::Anon { namespace } => write!(f, "{{{{{namespace}}}}}"),
	}
	}
	}