rustc_hir/
definitions.rs

1//! For each definition, we track the following data. A definition
2//! here is defined somewhat circularly as "something with a `DefId`",
3//! but it generally corresponds to things like structs, enums, etc.
4//! There are also some rather random cases (like const initializer
5//! expressions) that are mostly just leftovers.
6
7use std::fmt::{self, Write};
8use std::hash::Hash;
9
10use rustc_data_structures::stable_hasher::StableHasher;
11use rustc_data_structures::unord::UnordMap;
12use rustc_hashes::Hash64;
13use rustc_index::IndexVec;
14use rustc_macros::{Decodable, Encodable};
15use rustc_span::{Symbol, kw, sym};
16use tracing::{debug, instrument};
17
18pub use crate::def_id::DefPathHash;
19use crate::def_id::{CRATE_DEF_INDEX, CrateNum, DefIndex, LOCAL_CRATE, LocalDefId, StableCrateId};
20use crate::def_path_hash_map::DefPathHashMap;
21
22/// The `DefPathTable` maps `DefIndex`es to `DefKey`s and vice versa.
23/// Internally the `DefPathTable` holds a tree of `DefKey`s, where each `DefKey`
24/// stores the `DefIndex` of its parent.
25/// There is one `DefPathTable` for each crate.
26#[derive(Debug)]
27pub struct DefPathTable {
28    stable_crate_id: StableCrateId,
29    index_to_key: IndexVec<DefIndex, DefKey>,
30    // We do only store the local hash, as all the definitions are from the current crate.
31    def_path_hashes: IndexVec<DefIndex, Hash64>,
32    def_path_hash_to_index: DefPathHashMap,
33}
34
35impl DefPathTable {
36    fn new(stable_crate_id: StableCrateId) -> DefPathTable {
37        DefPathTable {
38            stable_crate_id,
39            index_to_key: Default::default(),
40            def_path_hashes: Default::default(),
41            def_path_hash_to_index: Default::default(),
42        }
43    }
44
45    fn allocate(&mut self, key: DefKey, def_path_hash: DefPathHash) -> DefIndex {
46        // Assert that all DefPathHashes correctly contain the local crate's StableCrateId.
47        debug_assert_eq!(self.stable_crate_id, def_path_hash.stable_crate_id());
48        let local_hash = def_path_hash.local_hash();
49
50        let index = self.index_to_key.push(key);
51        debug!("DefPathTable::insert() - {key:?} <-> {index:?}");
52
53        self.def_path_hashes.push(local_hash);
54        debug_assert!(self.def_path_hashes.len() == self.index_to_key.len());
55
56        // Check for hash collisions of DefPathHashes. These should be
57        // exceedingly rare.
58        if let Some(existing) = self.def_path_hash_to_index.insert(&local_hash, &index) {
59            let def_path1 = DefPath::make(LOCAL_CRATE, existing, |idx| self.def_key(idx));
60            let def_path2 = DefPath::make(LOCAL_CRATE, index, |idx| self.def_key(idx));
61
62            // Continuing with colliding DefPathHashes can lead to correctness
63            // issues. We must abort compilation.
64            //
65            // The likelihood of such a collision is very small, so actually
66            // running into one could be indicative of a poor hash function
67            // being used.
68            //
69            // See the documentation for DefPathHash for more information.
70            panic!(
71                "found DefPathHash collision between {def_path1:#?} and {def_path2:#?}. \
72                    Compilation cannot continue."
73            );
74        }
75
76        index
77    }
78
79    #[inline(always)]
80    pub fn def_key(&self, index: DefIndex) -> DefKey {
81        self.index_to_key[index]
82    }
83
84    #[instrument(level = "trace", skip(self), ret)]
85    #[inline(always)]
86    pub fn def_path_hash(&self, index: DefIndex) -> DefPathHash {
87        let hash = self.def_path_hashes[index];
88        DefPathHash::new(self.stable_crate_id, hash)
89    }
90
91    pub fn enumerated_keys_and_path_hashes(
92        &self,
93    ) -> impl Iterator<Item = (DefIndex, &DefKey, DefPathHash)> + ExactSizeIterator {
94        self.index_to_key
95            .iter_enumerated()
96            .map(move |(index, key)| (index, key, self.def_path_hash(index)))
97    }
98}
99
100#[derive(Debug)]
101pub struct DisambiguatorState {
102    next: UnordMap<(LocalDefId, DefPathData), u32>,
103}
104
105impl DisambiguatorState {
106    pub fn new() -> Self {
107        Self { next: Default::default() }
108    }
109
110    /// Creates a `DisambiguatorState` where the next allocated `(LocalDefId, DefPathData)` pair
111    /// will have `index` as the disambiguator.
112    pub fn with(def_id: LocalDefId, data: DefPathData, index: u32) -> Self {
113        let mut this = Self::new();
114        this.next.insert((def_id, data), index);
115        this
116    }
117}
118
119/// The definition table containing node definitions.
120/// It holds the `DefPathTable` for `LocalDefId`s/`DefPath`s.
121/// It also stores mappings to convert `LocalDefId`s to/from `HirId`s.
122#[derive(Debug)]
123pub struct Definitions {
124    table: DefPathTable,
125}
126
127/// A unique identifier that we can use to lookup a definition
128/// precisely. It combines the index of the definition's parent (if
129/// any) with a `DisambiguatedDefPathData`.
130#[derive(Copy, Clone, PartialEq, Debug, Encodable, Decodable)]
131pub struct DefKey {
132    /// The parent path.
133    pub parent: Option<DefIndex>,
134
135    /// The identifier of this node.
136    pub disambiguated_data: DisambiguatedDefPathData,
137}
138
139impl DefKey {
140    pub(crate) fn compute_stable_hash(&self, parent: DefPathHash) -> DefPathHash {
141        let mut hasher = StableHasher::new();
142
143        // The new path is in the same crate as `parent`, and will contain the stable_crate_id.
144        // Therefore, we only need to include information of the parent's local hash.
145        parent.local_hash().hash(&mut hasher);
146
147        let DisambiguatedDefPathData { ref data, disambiguator } = self.disambiguated_data;
148
149        std::mem::discriminant(data).hash(&mut hasher);
150        if let Some(name) = data.hashed_symbol() {
151            // Get a stable hash by considering the symbol chars rather than
152            // the symbol index.
153            name.as_str().hash(&mut hasher);
154        }
155
156        disambiguator.hash(&mut hasher);
157
158        let local_hash = hasher.finish();
159
160        // Construct the new DefPathHash, making sure that the `crate_id`
161        // portion of the hash is properly copied from the parent. This way the
162        // `crate_id` part will be recursively propagated from the root to all
163        // DefPathHashes in this DefPathTable.
164        DefPathHash::new(parent.stable_crate_id(), local_hash)
165    }
166
167    #[inline]
168    pub fn get_opt_name(&self) -> Option<Symbol> {
169        self.disambiguated_data.data.get_opt_name()
170    }
171}
172
173/// A pair of `DefPathData` and an integer disambiguator. The integer is
174/// normally `0`, but in the event that there are multiple defs with the
175/// same `parent` and `data`, we use this field to disambiguate
176/// between them. This introduces some artificial ordering dependency
177/// but means that if you have, e.g., two impls for the same type in
178/// the same module, they do get distinct `DefId`s.
179#[derive(Copy, Clone, PartialEq, Debug, Encodable, Decodable)]
180pub struct DisambiguatedDefPathData {
181    pub data: DefPathData,
182    pub disambiguator: u32,
183}
184
185impl DisambiguatedDefPathData {
186    pub fn as_sym(&self, verbose: bool) -> Symbol {
187        match self.data.name() {
188            DefPathDataName::Named(name) => {
189                if verbose && self.disambiguator != 0 {
190                    Symbol::intern(&format!("{}#{}", name, self.disambiguator))
191                } else {
192                    name
193                }
194            }
195            DefPathDataName::Anon { namespace } => {
196                if let DefPathData::AnonAssocTy(method) = self.data {
197                    Symbol::intern(&format!("{}::{{{}#{}}}", method, namespace, self.disambiguator))
198                } else {
199                    Symbol::intern(&format!("{{{}#{}}}", namespace, self.disambiguator))
200                }
201            }
202        }
203    }
204}
205
206#[derive(Clone, Debug, Encodable, Decodable)]
207pub struct DefPath {
208    /// The path leading from the crate root to the item.
209    pub data: Vec<DisambiguatedDefPathData>,
210
211    /// The crate root this path is relative to.
212    pub krate: CrateNum,
213}
214
215impl DefPath {
216    pub fn make<FN>(krate: CrateNum, start_index: DefIndex, mut get_key: FN) -> DefPath
217    where
218        FN: FnMut(DefIndex) -> DefKey,
219    {
220        let mut data = vec![];
221        let mut index = Some(start_index);
222        loop {
223            debug!("DefPath::make: krate={:?} index={:?}", krate, index);
224            let p = index.unwrap();
225            let key = get_key(p);
226            debug!("DefPath::make: key={:?}", key);
227            match key.disambiguated_data.data {
228                DefPathData::CrateRoot => {
229                    assert!(key.parent.is_none());
230                    break;
231                }
232                _ => {
233                    data.push(key.disambiguated_data);
234                    index = key.parent;
235                }
236            }
237        }
238        data.reverse();
239        DefPath { data, krate }
240    }
241
242    /// Returns a string representation of the `DefPath` without
243    /// the crate-prefix. This method is useful if you don't have
244    /// a `TyCtxt` available.
245    pub fn to_string_no_crate_verbose(&self) -> String {
246        let mut s = String::with_capacity(self.data.len() * 16);
247
248        for component in &self.data {
249            write!(s, "::{}", component.as_sym(true)).unwrap();
250        }
251
252        s
253    }
254
255    /// Returns a filename-friendly string of the `DefPath`, without
256    /// the crate-prefix. This method is useful if you don't have
257    /// a `TyCtxt` available.
258    pub fn to_filename_friendly_no_crate(&self) -> String {
259        let mut s = String::with_capacity(self.data.len() * 16);
260
261        let mut opt_delimiter = None;
262        for component in &self.data {
263            s.extend(opt_delimiter);
264            opt_delimiter = Some('-');
265            write!(s, "{}", component.as_sym(true)).unwrap();
266        }
267
268        s
269    }
270}
271
272/// New variants should only be added in synchronization with `enum DefKind`.
273#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, Encodable, Decodable)]
274pub enum DefPathData {
275    // Root: these should only be used for the root nodes, because
276    // they are treated specially by the `def_path` function.
277    /// The crate root (marker).
278    CrateRoot,
279
280    // Different kinds of items and item-like things:
281    /// An impl.
282    Impl,
283    /// An `extern` block.
284    ForeignMod,
285    /// A `use` item.
286    Use,
287    /// A global asm item.
288    GlobalAsm,
289    /// Something in the type namespace.
290    TypeNs(Symbol),
291    /// Something in the value namespace.
292    ValueNs(Symbol),
293    /// Something in the macro namespace.
294    MacroNs(Symbol),
295    /// Something in the lifetime namespace.
296    LifetimeNs(Symbol),
297    /// A closure expression.
298    Closure,
299
300    // Subportions of items:
301    /// Implicit constructor for a unit or tuple-like struct or enum variant.
302    Ctor,
303    /// A constant expression (see `{ast,hir}::AnonConst`).
304    AnonConst,
305    /// An existential `impl Trait` type node.
306    /// Argument position `impl Trait` have a `TypeNs` with their pretty-printed name.
307    OpaqueTy,
308    /// Used for remapped captured lifetimes in an existential `impl Trait` type node.
309    OpaqueLifetime(Symbol),
310    /// An anonymous associated type from an RPITIT. The symbol refers to the name of the method
311    /// that defined the type.
312    AnonAssocTy(Symbol),
313    /// A synthetic body for a coroutine's by-move body.
314    SyntheticCoroutineBody,
315    /// Additional static data referred to by a static.
316    NestedStatic,
317}
318
319impl Definitions {
320    pub fn def_path_table(&self) -> &DefPathTable {
321        &self.table
322    }
323
324    /// Gets the number of definitions.
325    pub fn def_index_count(&self) -> usize {
326        self.table.index_to_key.len()
327    }
328
329    #[inline]
330    pub fn def_key(&self, id: LocalDefId) -> DefKey {
331        self.table.def_key(id.local_def_index)
332    }
333
334    #[inline(always)]
335    pub fn def_path_hash(&self, id: LocalDefId) -> DefPathHash {
336        self.table.def_path_hash(id.local_def_index)
337    }
338
339    /// Returns the path from the crate root to `index`. The root
340    /// nodes are not included in the path (i.e., this will be an
341    /// empty vector for the crate root). For an inlined item, this
342    /// will be the path of the item in the external crate (but the
343    /// path will begin with the path to the external crate).
344    pub fn def_path(&self, id: LocalDefId) -> DefPath {
345        DefPath::make(LOCAL_CRATE, id.local_def_index, |index| {
346            self.def_key(LocalDefId { local_def_index: index })
347        })
348    }
349
350    /// Adds a root definition (no parent) and a few other reserved definitions.
351    pub fn new(stable_crate_id: StableCrateId) -> Definitions {
352        let key = DefKey {
353            parent: None,
354            disambiguated_data: DisambiguatedDefPathData {
355                data: DefPathData::CrateRoot,
356                disambiguator: 0,
357            },
358        };
359
360        // We want *both* halves of a DefPathHash to depend on the crate-id of the defining crate.
361        // The crate-id can be more easily changed than the DefPath of an item, so, in the case of
362        // a crate-local DefPathHash collision, the user can simply "roll the dice again" for all
363        // DefPathHashes in the crate by changing the crate disambiguator (e.g. via bumping the
364        // crate's version number).
365        //
366        // Children paths will only hash the local portion, and still inherit the change to the
367        // root hash.
368        let def_path_hash =
369            DefPathHash::new(stable_crate_id, Hash64::new(stable_crate_id.as_u64()));
370
371        // Create the root definition.
372        let mut table = DefPathTable::new(stable_crate_id);
373        let root = LocalDefId { local_def_index: table.allocate(key, def_path_hash) };
374        assert_eq!(root.local_def_index, CRATE_DEF_INDEX);
375
376        Definitions { table }
377    }
378
379    /// Creates a definition with a parent definition.
380    /// If there are multiple definitions with the same DefPathData and the same parent, use
381    /// `disambiguator` to differentiate them. Distinct `DisambiguatorState` instances are not
382    /// guaranteed to generate unique disambiguators and should instead ensure that the `parent`
383    /// and `data` pair is distinct from other instances.
384    pub fn create_def(
385        &mut self,
386        parent: LocalDefId,
387        data: DefPathData,
388        disambiguator: &mut DisambiguatorState,
389    ) -> LocalDefId {
390        // We can't use `Debug` implementation for `LocalDefId` here, since it tries to acquire a
391        // reference to `Definitions` and we're already holding a mutable reference.
392        debug!(
393            "create_def(parent={}, data={data:?})",
394            self.def_path(parent).to_string_no_crate_verbose(),
395        );
396
397        // The root node must be created in `new()`.
398        assert!(data != DefPathData::CrateRoot);
399
400        // Find the next free disambiguator for this key.
401        let disambiguator = {
402            let next_disamb = disambiguator.next.entry((parent, data)).or_insert(0);
403            let disambiguator = *next_disamb;
404            *next_disamb = next_disamb.checked_add(1).expect("disambiguator overflow");
405            disambiguator
406        };
407        let key = DefKey {
408            parent: Some(parent.local_def_index),
409            disambiguated_data: DisambiguatedDefPathData { data, disambiguator },
410        };
411
412        let parent_hash = self.table.def_path_hash(parent.local_def_index);
413        let def_path_hash = key.compute_stable_hash(parent_hash);
414
415        debug!("create_def: after disambiguation, key = {:?}", key);
416
417        // Create the definition.
418        LocalDefId { local_def_index: self.table.allocate(key, def_path_hash) }
419    }
420
421    #[inline(always)]
422    /// Returns `None` if the `DefPathHash` does not correspond to a `LocalDefId`
423    /// in the current compilation session. This can legitimately happen if the
424    /// `DefPathHash` is from a `DefId` in an upstream crate or, during incr. comp.,
425    /// if the `DefPathHash` is from a previous compilation session and
426    /// the def-path does not exist anymore.
427    pub fn local_def_path_hash_to_def_id(&self, hash: DefPathHash) -> Option<LocalDefId> {
428        debug_assert!(hash.stable_crate_id() == self.table.stable_crate_id);
429        self.table
430            .def_path_hash_to_index
431            .get(&hash.local_hash())
432            .map(|local_def_index| LocalDefId { local_def_index })
433    }
434
435    pub fn def_path_hash_to_def_index_map(&self) -> &DefPathHashMap {
436        &self.table.def_path_hash_to_index
437    }
438
439    pub fn num_definitions(&self) -> usize {
440        self.table.def_path_hashes.len()
441    }
442}
443
444#[derive(Copy, Clone, PartialEq, Debug)]
445pub enum DefPathDataName {
446    Named(Symbol),
447    Anon { namespace: Symbol },
448}
449
450impl DefPathData {
451    pub fn get_opt_name(&self) -> Option<Symbol> {
452        use self::DefPathData::*;
453        match *self {
454            TypeNs(name) | ValueNs(name) | MacroNs(name) | LifetimeNs(name)
455            | OpaqueLifetime(name) => Some(name),
456
457            Impl
458            | ForeignMod
459            | CrateRoot
460            | Use
461            | GlobalAsm
462            | Closure
463            | Ctor
464            | AnonConst
465            | OpaqueTy
466            | AnonAssocTy(..)
467            | SyntheticCoroutineBody
468            | NestedStatic => None,
469        }
470    }
471
472    fn hashed_symbol(&self) -> Option<Symbol> {
473        use self::DefPathData::*;
474        match *self {
475            TypeNs(name) | ValueNs(name) | MacroNs(name) | LifetimeNs(name) | AnonAssocTy(name)
476            | OpaqueLifetime(name) => Some(name),
477
478            Impl
479            | ForeignMod
480            | CrateRoot
481            | Use
482            | GlobalAsm
483            | Closure
484            | Ctor
485            | AnonConst
486            | OpaqueTy
487            | SyntheticCoroutineBody
488            | NestedStatic => None,
489        }
490    }
491
492    pub fn name(&self) -> DefPathDataName {
493        use self::DefPathData::*;
494        match *self {
495            TypeNs(name) | ValueNs(name) | MacroNs(name) | LifetimeNs(name)
496            | OpaqueLifetime(name) => DefPathDataName::Named(name),
497            // Note that this does not show up in user print-outs.
498            CrateRoot => DefPathDataName::Anon { namespace: kw::Crate },
499            Impl => DefPathDataName::Anon { namespace: kw::Impl },
500            ForeignMod => DefPathDataName::Anon { namespace: kw::Extern },
501            Use => DefPathDataName::Anon { namespace: kw::Use },
502            GlobalAsm => DefPathDataName::Anon { namespace: sym::global_asm },
503            Closure => DefPathDataName::Anon { namespace: sym::closure },
504            Ctor => DefPathDataName::Anon { namespace: sym::constructor },
505            AnonConst => DefPathDataName::Anon { namespace: sym::constant },
506            OpaqueTy => DefPathDataName::Anon { namespace: sym::opaque },
507            AnonAssocTy(..) => DefPathDataName::Anon { namespace: sym::anon_assoc },
508            SyntheticCoroutineBody => DefPathDataName::Anon { namespace: sym::synthetic },
509            NestedStatic => DefPathDataName::Anon { namespace: sym::nested },
510        }
511    }
512}
513
514impl fmt::Display for DefPathData {
515    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
516        match self.name() {
517            DefPathDataName::Named(name) => f.write_str(name.as_str()),
518            // FIXME(#70334): this will generate legacy {{closure}}, {{impl}}, etc
519            DefPathDataName::Anon { namespace } => write!(f, "{{{{{namespace}}}}}"),
520        }
521    }
522}
rustc_hir/definitions.rs

rustc_hir/
definitions.rs
