compiler/rustc_hir/src/definitions.rs - toolchain/rustc - 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.

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

 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::stable_hasher::StableHasher;
 use rustc_index::vec::IndexVec;
 use rustc_span::hygiene::ExpnId;
 use rustc_span::symbol::{kw, sym, Symbol};
 use rustc_span::Span;

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

 /// 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(Clone, Default, Debug)]
 pub struct DefPathTable {
     index_to_key: IndexVec<DefIndex, DefKey>,
     def_path_hashes: IndexVec<DefIndex, DefPathHash>,
     def_path_hash_to_index: DefPathHashMap,
 }

 impl DefPathTable {
     fn allocate(&mut self, key: DefKey, def_path_hash: DefPathHash) -> DefIndex {
         let index = {
             let index = DefIndex::from(self.index_to_key.len());
             debug!("DefPathTable::insert() - {:?} <-> {:?}", key, index);
             self.index_to_key.push(key);
             index
         };
         self.def_path_hashes.push(def_path_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(&def_path_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 {:?} and {:?}. \
                     Compilation cannot continue.",
                 def_path1, def_path2
             );
         }

         // Assert that all DefPathHashes correctly contain the local crate's
         // StableCrateId
         #[cfg(debug_assertions)]
         if let Some(root) = self.def_path_hashes.get(CRATE_DEF_INDEX) {
             assert!(def_path_hash.stable_crate_id() == root.stable_crate_id());
         }

         index
     }

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

     #[inline(always)]
     pub fn def_path_hash(&self, index: DefIndex) -> DefPathHash {
         let hash = self.def_path_hashes[index];
         debug!("def_path_hash({:?}) = {:?}", index, hash);
         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_hashes[index]))
     }
 }

 /// 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(Clone, Debug)]
 pub struct Definitions {
     table: DefPathTable,
     next_disambiguator: FxHashMap<(LocalDefId, DefPathData), u32>,

     /// Item with a given `LocalDefId` was defined during macro expansion with ID `ExpnId`.
     expansions_that_defined: FxHashMap<LocalDefId, ExpnId>,

     def_id_to_span: IndexVec<LocalDefId, Span>,

     /// The [StableCrateId] of the local crate.
     stable_crate_id: StableCrateId,
 }

 /// 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();

         parent.hash(&mut hasher);

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

         std::mem::discriminant(data).hash(&mut hasher);
         if let Some(name) = data.get_opt_name() {
             // 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: u64 = 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 fmt_maybe_verbose(&self, writer: &mut impl Write, verbose: bool) -> fmt::Result {
         match self.data.name() {
             DefPathDataName::Named(name) => {
                 if verbose && self.disambiguator != 0 {
                     write!(writer, "{}#{}", name, self.disambiguator)
                 } else {
                     writer.write_str(name.as_str())
                 }
             }
             DefPathDataName::Anon { namespace } => {
                 write!(writer, "{{{}#{}}}", namespace, self.disambiguator)
             }
         }
     }
 }

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

 #[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).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).unwrap();
         }

         s
     }
 }

 #[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.
     ClosureExpr,

     // Subportions of items:
     /// Implicit constructor for a unit or tuple-like struct or enum variant.
     Ctor,
     /// A constant expression (see `{ast,hir}::AnonConst`).
     AnonConst,
     /// An `impl Trait` type node.
     ImplTrait,
 }

 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, crate_span: Span) -> Definitions {
         let key = DefKey {
             parent: None,
             disambiguated_data: DisambiguatedDefPathData {
                 data: DefPathData::CrateRoot,
                 disambiguator: 0,
             },
         };

         let parent_hash = DefPathHash::new(stable_crate_id, 0);
         let def_path_hash = key.compute_stable_hash(parent_hash);

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

         let mut def_id_to_span = IndexVec::new();
         // A relative span's parent must be an absolute span.
         debug_assert_eq!(crate_span.data_untracked().parent, None);
         let _root = def_id_to_span.push(crate_span);
         debug_assert_eq!(_root, root);

         Definitions {
             table,
             next_disambiguator: Default::default(),
             expansions_that_defined: Default::default(),
             def_id_to_span,
             stable_crate_id,
         }
     }

     /// Adds a definition with a parent definition.
     pub fn create_def(
         &mut self,
         parent: LocalDefId,
         data: DefPathData,
         expn_id: ExpnId,
         span: Span,
     ) -> LocalDefId {
         debug!("create_def(parent={:?}, data={:?}, expn_id={:?})", parent, data, expn_id);

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

         // Find the next free disambiguator for this key.
         let disambiguator = {
             let next_disamb = self.next_disambiguator.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.
         let def_id = LocalDefId { local_def_index: self.table.allocate(key, def_path_hash) };

         if expn_id != ExpnId::root() {
             self.expansions_that_defined.insert(def_id, expn_id);
         }

         // A relative span's parent must be an absolute span.
         debug_assert_eq!(span.data_untracked().parent, None);
         let _id = self.def_id_to_span.push(span);
         debug_assert_eq!(_id, def_id);

         def_id
     }

     pub fn expansion_that_defined(&self, id: LocalDefId) -> ExpnId {
         self.expansions_that_defined.get(&id).copied().unwrap_or_else(ExpnId::root)
     }

     /// Retrieves the span of the given `DefId` if `DefId` is in the local crate.
     #[inline]
     pub fn def_span(&self, def_id: LocalDefId) -> Span {
         self.def_id_to_span[def_id]
     }

     pub fn iter_local_def_id(&self) -> impl Iterator<Item = LocalDefId> + '_ {
         self.table.def_path_hashes.indices().map(|local_def_index| LocalDefId { local_def_index })
     }

     #[inline(always)]
     pub fn local_def_path_hash_to_def_id(
         &self,
         hash: DefPathHash,
         err: &mut dyn FnMut() -> !,
     ) -> LocalDefId {
         debug_assert!(hash.stable_crate_id() == self.stable_crate_id);
         self.table
             .def_path_hash_to_index
             .get(&hash)
             .map(|local_def_index| LocalDefId { local_def_index })
             .unwrap_or_else(|| err())
     }

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

 #[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) => Some(name),

             Impl | ForeignMod | CrateRoot | Use | GlobalAsm | ClosureExpr | Ctor | AnonConst
             | ImplTrait => None,
         }
     }

     pub fn name(&self) -> DefPathDataName {
         use self::DefPathData::*;
         match *self {
             TypeNs(name) | ValueNs(name) | MacroNs(name) | LifetimeNs(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 },
             ClosureExpr => DefPathDataName::Anon { namespace: sym::closure },
             Ctor => DefPathDataName::Anon { namespace: sym::constructor },
             AnonConst => DefPathDataName::Anon { namespace: sym::constant },
             ImplTrait => DefPathDataName::Anon { namespace: sym::opaque },
         }
     }
 }

 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.

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

	use rustc_data_structures::fx::FxHashMap;
	use rustc_data_structures::stable_hasher::StableHasher;
	use rustc_index::vec::IndexVec;
	use rustc_span::hygiene::ExpnId;
	use rustc_span::symbol::{kw, sym, Symbol};
	use rustc_span::Span;

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

	/// 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(Clone, Default, Debug)]
	pub struct DefPathTable {
	index_to_key: IndexVec<DefIndex, DefKey>,
	def_path_hashes: IndexVec<DefIndex, DefPathHash>,
	def_path_hash_to_index: DefPathHashMap,
	}

	impl DefPathTable {
	fn allocate(&mut self, key: DefKey, def_path_hash: DefPathHash) -> DefIndex {
	let index = {
	let index = DefIndex::from(self.index_to_key.len());
	debug!("DefPathTable::insert() - {:?} <-> {:?}", key, index);
	self.index_to_key.push(key);
	index
	};
	self.def_path_hashes.push(def_path_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(&def_path_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 {:?} and {:?}. \
	Compilation cannot continue.",
	def_path1, def_path2
	);
	}

	// Assert that all DefPathHashes correctly contain the local crate's
	// StableCrateId
	#[cfg(debug_assertions)]
	if let Some(root) = self.def_path_hashes.get(CRATE_DEF_INDEX) {
	assert!(def_path_hash.stable_crate_id() == root.stable_crate_id());
	}

	index
	}

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

	#[inline(always)]
	pub fn def_path_hash(&self, index: DefIndex) -> DefPathHash {
	let hash = self.def_path_hashes[index];
	debug!("def_path_hash({:?}) = {:?}", index, hash);
	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_hashes[index]))
	}
	}

	/// 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(Clone, Debug)]
	pub struct Definitions {
	table: DefPathTable,
	next_disambiguator: FxHashMap<(LocalDefId, DefPathData), u32>,

	/// Item with a given `LocalDefId` was defined during macro expansion with ID `ExpnId`.
	expansions_that_defined: FxHashMap<LocalDefId, ExpnId>,

	def_id_to_span: IndexVec<LocalDefId, Span>,

	/// The [StableCrateId] of the local crate.
	stable_crate_id: StableCrateId,
	}

	/// 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();

	parent.hash(&mut hasher);

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

	std::mem::discriminant(data).hash(&mut hasher);
	if let Some(name) = data.get_opt_name() {
	// 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: u64 = 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 fmt_maybe_verbose(&self, writer: &mut impl Write, verbose: bool) -> fmt::Result {
	match self.data.name() {
	DefPathDataName::Named(name) => {
	if verbose && self.disambiguator != 0 {
	write!(writer, "{}#{}", name, self.disambiguator)
	} else {
	writer.write_str(name.as_str())
	}
	}
	DefPathDataName::Anon { namespace } => {
	write!(writer, "{{{}#{}}}", namespace, self.disambiguator)
	}
	}
	}
	}

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

	#[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).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).unwrap();
	}

	s
	}
	}

	#[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.
	ClosureExpr,

	// Subportions of items:
	/// Implicit constructor for a unit or tuple-like struct or enum variant.
	Ctor,
	/// A constant expression (see `{ast,hir}::AnonConst`).
	AnonConst,
	/// An `impl Trait` type node.
	ImplTrait,
	}

	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, crate_span: Span) -> Definitions {
	let key = DefKey {
	parent: None,
	disambiguated_data: DisambiguatedDefPathData {
	data: DefPathData::CrateRoot,
	disambiguator: 0,
	},
	};

	let parent_hash = DefPathHash::new(stable_crate_id, 0);
	let def_path_hash = key.compute_stable_hash(parent_hash);

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

	let mut def_id_to_span = IndexVec::new();
	// A relative span's parent must be an absolute span.
	debug_assert_eq!(crate_span.data_untracked().parent, None);
	let _root = def_id_to_span.push(crate_span);
	debug_assert_eq!(_root, root);

	Definitions {
	table,
	next_disambiguator: Default::default(),
	expansions_that_defined: Default::default(),
	def_id_to_span,
	stable_crate_id,
	}
	}

	/// Adds a definition with a parent definition.
	pub fn create_def(
	&mut self,
	parent: LocalDefId,
	data: DefPathData,
	expn_id: ExpnId,
	span: Span,
	) -> LocalDefId {
	debug!("create_def(parent={:?}, data={:?}, expn_id={:?})", parent, data, expn_id);

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

	// Find the next free disambiguator for this key.
	let disambiguator = {
	let next_disamb = self.next_disambiguator.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.
	let def_id = LocalDefId { local_def_index: self.table.allocate(key, def_path_hash) };

	if expn_id != ExpnId::root() {
	self.expansions_that_defined.insert(def_id, expn_id);
	}

	// A relative span's parent must be an absolute span.
	debug_assert_eq!(span.data_untracked().parent, None);
	let _id = self.def_id_to_span.push(span);
	debug_assert_eq!(_id, def_id);

	def_id
	}

	pub fn expansion_that_defined(&self, id: LocalDefId) -> ExpnId {
	self.expansions_that_defined.get(&id).copied().unwrap_or_else(ExpnId::root)
	}

	/// Retrieves the span of the given `DefId` if `DefId` is in the local crate.
	#[inline]
	pub fn def_span(&self, def_id: LocalDefId) -> Span {
	self.def_id_to_span[def_id]
	}

	pub fn iter_local_def_id(&self) -> impl Iterator<Item = LocalDefId> + '_ {
	self.table.def_path_hashes.indices().map(\|local_def_index\| LocalDefId { local_def_index })
	}

	#[inline(always)]
	pub fn local_def_path_hash_to_def_id(
	&self,
	hash: DefPathHash,
	err: &mut dyn FnMut() -> !,
	) -> LocalDefId {
	debug_assert!(hash.stable_crate_id() == self.stable_crate_id);
	self.table
	.def_path_hash_to_index
	.get(&hash)
	.map(\|local_def_index\| LocalDefId { local_def_index })
	.unwrap_or_else(\|\| err())
	}

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

	#[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) => Some(name),

	Impl \| ForeignMod \| CrateRoot \| Use \| GlobalAsm \| ClosureExpr \| Ctor \| AnonConst
	\| ImplTrait => None,
	}
	}

	pub fn name(&self) -> DefPathDataName {
	use self::DefPathData::*;
	match *self {
	TypeNs(name) \| ValueNs(name) \| MacroNs(name) \| LifetimeNs(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 },
	ClosureExpr => DefPathDataName::Anon { namespace: sym::closure },
	Ctor => DefPathDataName::Anon { namespace: sym::constructor },
	AnonConst => DefPathDataName::Anon { namespace: sym::constant },
	ImplTrait => DefPathDataName::Anon { namespace: sym::opaque },
	}
	}
	}

	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),
	}
	}
	}