1 use crate::HashStableContext;
2 use rustc_data_structures::fingerprint::Fingerprint;
3 use rustc_data_structures::stable_hasher::{HashStable, StableHasher, ToStableHashKey};
4 use rustc_data_structures::AtomicRef;
5 use rustc_index::vec::Idx;
6 use rustc_macros::HashStable_Generic;
7 use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
8 use std::borrow::Borrow;
10 use std::hash::{Hash, Hasher};
12 rustc_index::newtype_index! {
15 DEBUG_FORMAT = "crate{}"
19 /// Item definitions in the currently-compiled crate would have the `CrateNum`
20 /// `LOCAL_CRATE` in their `DefId`.
21 pub const LOCAL_CRATE: CrateNum = CrateNum::from_u32(0);
25 pub fn new(x: usize) -> CrateNum {
26 CrateNum::from_usize(x)
30 pub fn as_def_id(&self) -> DefId {
31 DefId { krate: *self, index: CRATE_DEF_INDEX }
35 impl fmt::Display for CrateNum {
36 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
37 fmt::Display::fmt(&self.private, f)
41 /// As a local identifier, a `CrateNum` is only meaningful within its context, e.g. within a tcx.
42 /// Therefore, make sure to include the context when encode a `CrateNum`.
43 impl<E: Encoder> Encodable<E> for CrateNum {
44 default fn encode(&self, s: &mut E) -> Result<(), E::Error> {
45 s.emit_u32(self.as_u32())
49 impl<D: Decoder> Decodable<D> for CrateNum {
50 default fn decode(d: &mut D) -> CrateNum {
51 CrateNum::from_u32(d.read_u32())
55 /// A `DefPathHash` is a fixed-size representation of a `DefPath` that is
56 /// stable across crate and compilation session boundaries. It consists of two
57 /// separate 64-bit hashes. The first uniquely identifies the crate this
58 /// `DefPathHash` originates from (see [StableCrateId]), and the second
59 /// uniquely identifies the corresponding `DefPath` within that crate. Together
60 /// they form a unique identifier within an entire crate graph.
62 /// There is a very small chance of hash collisions, which would mean that two
63 /// different `DefPath`s map to the same `DefPathHash`. Proceeding compilation
64 /// with such a hash collision would very probably lead to an ICE, and in the
65 /// worst case lead to a silent mis-compilation. The compiler therefore actively
66 /// and exhaustively checks for such hash collisions and aborts compilation if
69 /// `DefPathHash` uses 64-bit hashes for both the crate-id part and the
70 /// crate-internal part, even though it is likely that there are many more
71 /// `LocalDefId`s in a single crate than there are individual crates in a crate
72 /// graph. Since we use the same number of bits in both cases, the collision
73 /// probability for the crate-local part will be quite a bit higher (though
74 /// still very small).
76 /// This imbalance is not by accident: A hash collision in the
77 /// crate-local part of a `DefPathHash` will be detected and reported while
78 /// compiling the crate in question. Such a collision does not depend on
79 /// outside factors and can be easily fixed by the crate maintainer (e.g. by
80 /// renaming the item in question or by bumping the crate version in a harmless
83 /// A collision between crate-id hashes on the other hand is harder to fix
84 /// because it depends on the set of crates in the entire crate graph of a
85 /// compilation session. Again, using the same crate with a different version
86 /// number would fix the issue with a high probability -- but that might be
87 /// easier said then done if the crates in questions are dependencies of
88 /// third-party crates.
90 /// That being said, given a high quality hash function, the collision
91 /// probabilities in question are very small. For example, for a big crate like
92 /// `rustc_middle` (with ~50000 `LocalDefId`s as of the time of writing) there
93 /// is a probability of roughly 1 in 14,750,000,000 of a crate-internal
94 /// collision occurring. For a big crate graph with 1000 crates in it, there is
95 /// a probability of 1 in 36,890,000,000,000 of a `StableCrateId` collision.
96 #[derive(Copy, Clone, Hash, PartialEq, Eq, PartialOrd, Ord, Debug)]
97 #[derive(HashStable_Generic, Encodable, Decodable)]
98 pub struct DefPathHash(pub Fingerprint);
101 /// Returns the [StableCrateId] identifying the crate this [DefPathHash]
104 pub fn stable_crate_id(&self) -> StableCrateId {
105 StableCrateId(self.0.as_value().0)
108 /// Returns the crate-local part of the [DefPathHash].
112 pub fn local_hash(&self) -> u64 {
116 /// Builds a new [DefPathHash] with the given [StableCrateId] and
117 /// `local_hash`, where `local_hash` must be unique within its crate.
118 pub fn new(stable_crate_id: StableCrateId, local_hash: u64) -> DefPathHash {
119 DefPathHash(Fingerprint::new(stable_crate_id.0, local_hash))
123 impl Borrow<Fingerprint> for DefPathHash {
125 fn borrow(&self) -> &Fingerprint {
130 /// A [`StableCrateId`] is a 64-bit hash of a crate name, together with all
131 /// `-Cmetadata` arguments, and some other data. It is to [`CrateNum`] what [`DefPathHash`] is to
132 /// [`DefId`]. It is stable across compilation sessions.
134 /// Since the ID is a hash value, there is a small chance that two crates
135 /// end up with the same [`StableCrateId`]. The compiler will check for such
136 /// collisions when loading crates and abort compilation in order to avoid
139 /// For more information on the possibility of hash collisions in rustc,
140 /// see the discussion in [`DefId`].
141 #[derive(Copy, Clone, Hash, PartialEq, Eq, PartialOrd, Ord, Debug)]
142 #[derive(HashStable_Generic, Encodable, Decodable)]
143 pub struct StableCrateId(pub(crate) u64);
146 pub fn to_u64(self) -> u64 {
150 /// Computes the stable ID for a crate with the given name and
151 /// `-Cmetadata` arguments.
152 pub fn new(crate_name: &str, is_exe: bool, mut metadata: Vec<String>) -> StableCrateId {
153 let mut hasher = StableHasher::new();
154 crate_name.hash(&mut hasher);
156 // We don't want the stable crate ID to depend on the order of
157 // -C metadata arguments, so sort them:
159 // Every distinct -C metadata value is only incorporated once:
162 hasher.write(b"metadata");
164 // Also incorporate the length of a metadata string, so that we generate
165 // different values for `-Cmetadata=ab -Cmetadata=c` and
166 // `-Cmetadata=a -Cmetadata=bc`
167 hasher.write_usize(s.len());
168 hasher.write(s.as_bytes());
171 // Also incorporate crate type, so that we don't get symbol conflicts when
172 // linking against a library of the same name, if this is an executable.
173 hasher.write(if is_exe { b"exe" } else { b"lib" });
175 // Also incorporate the rustc version. Otherwise, with -Zsymbol-mangling-version=v0
176 // and no -Cmetadata, symbols from the same crate compiled with different versions of
177 // rustc are named the same.
179 // RUSTC_FORCE_RUSTC_VERSION is used to inject rustc version information
181 if let Some(val) = std::env::var_os("RUSTC_FORCE_RUSTC_VERSION") {
182 hasher.write(val.to_string_lossy().into_owned().as_bytes())
184 hasher.write(option_env!("CFG_VERSION").unwrap_or("unknown version").as_bytes());
187 StableCrateId(hasher.finish())
191 rustc_index::newtype_index! {
192 /// A DefIndex is an index into the hir-map for a crate, identifying a
193 /// particular definition. It should really be considered an interned
194 /// shorthand for a particular DefPath.
195 pub struct DefIndex {
196 ENCODABLE = custom // (only encodable in metadata)
198 DEBUG_FORMAT = "DefIndex({})",
199 /// The crate root is always assigned index 0 by the AST Map code,
200 /// thanks to `NodeCollector::new`.
201 const CRATE_DEF_INDEX = 0,
205 impl<E: Encoder> Encodable<E> for DefIndex {
206 default fn encode(&self, _: &mut E) -> Result<(), E::Error> {
207 panic!("cannot encode `DefIndex` with `{}`", std::any::type_name::<E>());
211 impl<D: Decoder> Decodable<D> for DefIndex {
212 default fn decode(_: &mut D) -> DefIndex {
213 panic!("cannot decode `DefIndex` with `{}`", std::any::type_name::<D>());
217 /// A `DefId` identifies a particular *definition*, by combining a crate
218 /// index and a def index.
220 /// You can create a `DefId` from a `LocalDefId` using `local_def_id.to_def_id()`.
221 #[derive(Clone, PartialEq, Eq, PartialOrd, Ord, Copy)]
222 // On below-64 bit systems we can simply use the derived `Hash` impl
223 #[cfg_attr(not(target_pointer_width = "64"), derive(Hash))]
225 // We guarantee field order. Note that the order is essential here, see below why.
227 // cfg-ing the order of fields so that the `DefIndex` which is high entropy always ends up in
228 // the lower bits no matter the endianness. This allows the compiler to turn that `Hash` impl
229 // into a direct call to 'u64::hash(_)`.
230 #[cfg(not(all(target_pointer_width = "64", target_endian = "big")))]
233 #[cfg(all(target_pointer_width = "64", target_endian = "big"))]
237 // On 64-bit systems, we can hash the whole `DefId` as one `u64` instead of two `u32`s. This
238 // improves performance without impairing `FxHash` quality. So the below code gets compiled to a
239 // noop on little endian systems because the memory layout of `DefId` is as follows:
242 // +-1--------------31-+-32-------------63-+
244 // +-------------------+-------------------+
247 // The order here has direct impact on `FxHash` quality because we have far more `DefIndex` per
248 // crate than we have `Crate`s within one compilation. Or in other words, this arrangement puts
249 // more entropy in the low bits than the high bits. The reason this matters is that `FxHash`, which
250 // is used throughout rustc, has problems distributing the entropy from the high bits, so reversing
251 // the order would lead to a large number of collisions and thus far worse performance.
253 // On 64-bit big-endian systems, this compiles to a 64-bit rotation by 32 bits, which is still
254 // faster than another `FxHash` round.
255 #[cfg(target_pointer_width = "64")]
256 impl Hash for DefId {
257 fn hash<H: Hasher>(&self, h: &mut H) {
258 (((self.krate.as_u32() as u64) << 32) | (self.index.as_u32() as u64)).hash(h)
263 /// Makes a local `DefId` from the given `DefIndex`.
265 pub fn local(index: DefIndex) -> DefId {
266 DefId { krate: LOCAL_CRATE, index }
269 /// Returns whether the item is defined in the crate currently being compiled.
271 pub fn is_local(self) -> bool {
272 self.krate == LOCAL_CRATE
276 pub fn as_local(self) -> Option<LocalDefId> {
277 if self.is_local() { Some(LocalDefId { local_def_index: self.index }) } else { None }
281 pub fn expect_local(self) -> LocalDefId {
282 self.as_local().unwrap_or_else(|| panic!("DefId::expect_local: `{:?}` isn't local", self))
285 pub fn is_top_level_module(self) -> bool {
286 self.is_local() && self.index == CRATE_DEF_INDEX
290 impl<E: Encoder> Encodable<E> for DefId {
291 default fn encode(&self, s: &mut E) -> Result<(), E::Error> {
292 s.emit_struct(false, |s| {
293 s.emit_struct_field("krate", true, |s| self.krate.encode(s))?;
295 s.emit_struct_field("index", false, |s| self.index.encode(s))
300 impl<D: Decoder> Decodable<D> for DefId {
301 default fn decode(d: &mut D) -> DefId {
302 DefId { krate: Decodable::decode(d), index: Decodable::decode(d) }
306 pub fn default_def_id_debug(def_id: DefId, f: &mut fmt::Formatter<'_>) -> fmt::Result {
307 f.debug_struct("DefId").field("krate", &def_id.krate).field("index", &def_id.index).finish()
310 pub static DEF_ID_DEBUG: AtomicRef<fn(DefId, &mut fmt::Formatter<'_>) -> fmt::Result> =
311 AtomicRef::new(&(default_def_id_debug as fn(_, &mut fmt::Formatter<'_>) -> _));
313 impl fmt::Debug for DefId {
314 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
315 (*DEF_ID_DEBUG)(*self, f)
319 rustc_data_structures::define_id_collections!(DefIdMap, DefIdSet, DefId);
321 /// A `LocalDefId` is equivalent to a `DefId` with `krate == LOCAL_CRATE`. Since
322 /// we encode this information in the type, we can ensure at compile time that
323 /// no `DefId`s from upstream crates get thrown into the mix. There are quite a
324 /// few cases where we know that only `DefId`s from the local crate are expected;
325 /// a `DefId` from a different crate would signify a bug somewhere. This
326 /// is when `LocalDefId` comes in handy.
327 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
328 pub struct LocalDefId {
329 pub local_def_index: DefIndex,
332 // To ensure correctness of incremental compilation,
333 // `LocalDefId` must not implement `Ord` or `PartialOrd`.
334 // See https://github.com/rust-lang/rust/issues/90317.
335 impl !Ord for LocalDefId {}
336 impl !PartialOrd for LocalDefId {}
338 pub const CRATE_DEF_ID: LocalDefId = LocalDefId { local_def_index: CRATE_DEF_INDEX };
340 impl Idx for LocalDefId {
342 fn new(idx: usize) -> Self {
343 LocalDefId { local_def_index: Idx::new(idx) }
346 fn index(self) -> usize {
347 self.local_def_index.index()
353 pub fn to_def_id(self) -> DefId {
354 DefId { krate: LOCAL_CRATE, index: self.local_def_index }
358 pub fn is_top_level_module(self) -> bool {
359 self.local_def_index == CRATE_DEF_INDEX
363 impl fmt::Debug for LocalDefId {
364 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
365 self.to_def_id().fmt(f)
369 impl<E: Encoder> Encodable<E> for LocalDefId {
370 fn encode(&self, s: &mut E) -> Result<(), E::Error> {
371 self.to_def_id().encode(s)
375 impl<D: Decoder> Decodable<D> for LocalDefId {
376 fn decode(d: &mut D) -> LocalDefId {
377 DefId::decode(d).expect_local()
381 rustc_data_structures::define_id_collections!(LocalDefIdMap, LocalDefIdSet, LocalDefId);
383 impl<CTX: HashStableContext> HashStable<CTX> for DefId {
385 fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
386 self.to_stable_hash_key(hcx).hash_stable(hcx, hasher);
390 impl<CTX: HashStableContext> HashStable<CTX> for LocalDefId {
392 fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
393 self.to_stable_hash_key(hcx).hash_stable(hcx, hasher);
397 impl<CTX: HashStableContext> HashStable<CTX> for CrateNum {
399 fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
400 self.to_stable_hash_key(hcx).hash_stable(hcx, hasher);
404 impl<CTX: HashStableContext> ToStableHashKey<CTX> for DefId {
405 type KeyType = DefPathHash;
408 fn to_stable_hash_key(&self, hcx: &CTX) -> DefPathHash {
409 hcx.def_path_hash(*self)
413 impl<CTX: HashStableContext> ToStableHashKey<CTX> for LocalDefId {
414 type KeyType = DefPathHash;
417 fn to_stable_hash_key(&self, hcx: &CTX) -> DefPathHash {
418 hcx.def_path_hash(self.to_def_id())
422 impl<CTX: HashStableContext> ToStableHashKey<CTX> for CrateNum {
423 type KeyType = DefPathHash;
426 fn to_stable_hash_key(&self, hcx: &CTX) -> DefPathHash {
427 self.as_def_id().to_stable_hash_key(hcx)