1 files changed, 440 insertions, 0 deletions
diff --git a/compiler/rustc_hir/src/definitions.rs b/compiler/rustc_hir/src/definitions.rs
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+++ b/compiler/rustc_hir/src/definitions.rs
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+//! 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::symbol::{kw, sym, Symbol};
+
+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>,
+
+    /// 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) -> 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);
+
+        Definitions { table, next_disambiguator: Default::default(), stable_crate_id }
+    }
+
+    /// Adds a definition with a parent definition.
+    pub fn create_def(&mut self, parent: LocalDefId, data: DefPathData) -> 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 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.
+        LocalDefId { local_def_index: self.table.allocate(key, def_path_hash) }
+    }
+
+    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),
+        }
+    }
+}