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
) {
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
) {
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, Copy)]
222 // Don't derive order on 64-bit big-endian, so we can be consistent regardless of field order.
223 #[cfg_attr(not(all(target_pointer_width = "64", target_endian = "big")), derive(PartialOrd, Ord))]
224 // On below-64 bit systems we can simply use the derived `Hash` impl
225 #[cfg_attr(not(target_pointer_width = "64"), derive(Hash))]
227 #[rustc_pass_by_value]
228 // We guarantee field order. Note that the order is essential here, see below why.
230 // cfg-ing the order of fields so that the `DefIndex` which is high entropy always ends up in
231 // the lower bits no matter the endianness. This allows the compiler to turn that `Hash` impl
232 // into a direct call to 'u64::hash(_)`.
233 #[cfg(not(all(target_pointer_width = "64", target_endian = "big")))]
236 #[cfg(all(target_pointer_width = "64", target_endian = "big"))]
240 // On 64-bit systems, we can hash the whole `DefId` as one `u64` instead of two `u32`s. This
241 // improves performance without impairing `FxHash` quality. So the below code gets compiled to a
242 // noop on little endian systems because the memory layout of `DefId` is as follows:
245 // +-1--------------31-+-32-------------63-+
247 // +-------------------+-------------------+
250 // The order here has direct impact on `FxHash` quality because we have far more `DefIndex` per
251 // crate than we have `Crate`s within one compilation. Or in other words, this arrangement puts
252 // more entropy in the low bits than the high bits. The reason this matters is that `FxHash`, which
253 // is used throughout rustc, has problems distributing the entropy from the high bits, so reversing
254 // the order would lead to a large number of collisions and thus far worse performance.
256 // On 64-bit big-endian systems, this compiles to a 64-bit rotation by 32 bits, which is still
257 // faster than another `FxHash` round.
258 #[cfg(target_pointer_width = "64")]
259 impl Hash
for DefId
{
260 fn hash
<H
: Hasher
>(&self, h
: &mut H
) {
261 (((self.krate
.as_u32() as u64) << 32) | (self.index
.as_u32() as u64)).hash(h
)
265 // Implement the same comparison as derived with the other field order.
266 #[cfg(all(target_pointer_width = "64", target_endian = "big"))]
269 fn cmp(&self, other
: &DefId
) -> std
::cmp
::Ordering
{
270 Ord
::cmp(&(self.index
, self.krate
), &(other
.index
, other
.krate
))
273 #[cfg(all(target_pointer_width = "64", target_endian = "big"))]
274 impl PartialOrd
for DefId
{
276 fn partial_cmp(&self, other
: &DefId
) -> Option
<std
::cmp
::Ordering
> {
277 Some(Ord
::cmp(self, other
))
282 /// Makes a local `DefId` from the given `DefIndex`.
284 pub fn local(index
: DefIndex
) -> DefId
{
285 DefId { krate: LOCAL_CRATE, index }
288 /// Returns whether the item is defined in the crate currently being compiled.
290 pub fn is_local(self) -> bool
{
291 self.krate
== LOCAL_CRATE
295 pub fn as_local(self) -> Option
<LocalDefId
> {
296 if self.is_local() { Some(LocalDefId { local_def_index: self.index }
) } else { None }
301 pub fn expect_local(self) -> LocalDefId
{
302 // NOTE: `match` below is required to apply `#[track_caller]`,
303 // i.e. don't use closures.
304 match self.as_local() {
305 Some(local_def_id
) => local_def_id
,
306 None
=> panic
!("DefId::expect_local: `{:?}` isn't local", self),
311 pub fn is_crate_root(self) -> bool
{
312 self.index
== CRATE_DEF_INDEX
316 pub fn as_crate_root(self) -> Option
<CrateNum
> {
317 if self.is_crate_root() { Some(self.krate) }
else { None }
321 pub fn is_top_level_module(self) -> bool
{
322 self.is_local() && self.is_crate_root()
326 impl From
<LocalDefId
> for DefId
{
327 fn from(local
: LocalDefId
) -> DefId
{
332 impl<E
: Encoder
> Encodable
<E
> for DefId
{
333 default fn encode(&self, s
: &mut E
) {
334 self.krate
.encode(s
);
335 self.index
.encode(s
);
339 impl<D
: Decoder
> Decodable
<D
> for DefId
{
340 default fn decode(d
: &mut D
) -> DefId
{
341 DefId { krate: Decodable::decode(d), index: Decodable::decode(d) }
345 pub fn default_def_id_debug(def_id
: DefId
, f
: &mut fmt
::Formatter
<'_
>) -> fmt
::Result
{
346 f
.debug_struct("DefId").field("krate", &def_id
.krate
).field("index", &def_id
.index
).finish()
349 pub static DEF_ID_DEBUG
: AtomicRef
<fn(DefId
, &mut fmt
::Formatter
<'_
>) -> fmt
::Result
> =
350 AtomicRef
::new(&(default_def_id_debug
as fn(_
, &mut fmt
::Formatter
<'_
>) -> _
));
352 impl fmt
::Debug
for DefId
{
353 fn fmt(&self, f
: &mut fmt
::Formatter
<'_
>) -> fmt
::Result
{
354 (*DEF_ID_DEBUG
)(*self, f
)
358 rustc_data_structures
::define_id_collections
!(DefIdMap
, DefIdSet
, DefIdMapEntry
, DefId
);
360 /// A `LocalDefId` is equivalent to a `DefId` with `krate == LOCAL_CRATE`. Since
361 /// we encode this information in the type, we can ensure at compile time that
362 /// no `DefId`s from upstream crates get thrown into the mix. There are quite a
363 /// few cases where we know that only `DefId`s from the local crate are expected;
364 /// a `DefId` from a different crate would signify a bug somewhere. This
365 /// is when `LocalDefId` comes in handy.
366 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
367 pub struct LocalDefId
{
368 pub local_def_index
: DefIndex
,
371 // To ensure correctness of incremental compilation,
372 // `LocalDefId` must not implement `Ord` or `PartialOrd`.
373 // See https://github.com/rust-lang/rust/issues/90317.
374 impl !Ord
for LocalDefId {}
375 impl !PartialOrd
for LocalDefId {}
377 pub const CRATE_DEF_ID
: LocalDefId
= LocalDefId { local_def_index: CRATE_DEF_INDEX }
;
379 impl Idx
for LocalDefId
{
381 fn new(idx
: usize) -> Self {
382 LocalDefId { local_def_index: Idx::new(idx) }
385 fn index(self) -> usize {
386 self.local_def_index
.index()
392 pub fn to_def_id(self) -> DefId
{
393 DefId { krate: LOCAL_CRATE, index: self.local_def_index }
397 pub fn is_top_level_module(self) -> bool
{
402 impl fmt
::Debug
for LocalDefId
{
403 fn fmt(&self, f
: &mut fmt
::Formatter
<'_
>) -> fmt
::Result
{
404 self.to_def_id().fmt(f
)
408 impl<E
: Encoder
> Encodable
<E
> for LocalDefId
{
409 fn encode(&self, s
: &mut E
) {
410 self.to_def_id().encode(s
);
414 impl<D
: Decoder
> Decodable
<D
> for LocalDefId
{
415 fn decode(d
: &mut D
) -> LocalDefId
{
416 DefId
::decode(d
).expect_local()
420 rustc_data_structures
::define_id_collections
!(
427 impl<CTX
: HashStableContext
> HashStable
<CTX
> for DefId
{
429 fn hash_stable(&self, hcx
: &mut CTX
, hasher
: &mut StableHasher
) {
430 self.to_stable_hash_key(hcx
).hash_stable(hcx
, hasher
);
434 impl<CTX
: HashStableContext
> HashStable
<CTX
> for LocalDefId
{
436 fn hash_stable(&self, hcx
: &mut CTX
, hasher
: &mut StableHasher
) {
437 self.to_stable_hash_key(hcx
).hash_stable(hcx
, hasher
);
441 impl<CTX
: HashStableContext
> HashStable
<CTX
> for CrateNum
{
443 fn hash_stable(&self, hcx
: &mut CTX
, hasher
: &mut StableHasher
) {
444 self.to_stable_hash_key(hcx
).hash_stable(hcx
, hasher
);
448 impl<CTX
: HashStableContext
> ToStableHashKey
<CTX
> for DefId
{
449 type KeyType
= DefPathHash
;
452 fn to_stable_hash_key(&self, hcx
: &CTX
) -> DefPathHash
{
453 hcx
.def_path_hash(*self)
457 impl<CTX
: HashStableContext
> ToStableHashKey
<CTX
> for LocalDefId
{
458 type KeyType
= DefPathHash
;
461 fn to_stable_hash_key(&self, hcx
: &CTX
) -> DefPathHash
{
462 hcx
.def_path_hash(self.to_def_id())
466 impl<CTX
: HashStableContext
> ToStableHashKey
<CTX
> for CrateNum
{
467 type KeyType
= DefPathHash
;
470 fn to_stable_hash_key(&self, hcx
: &CTX
) -> DefPathHash
{
471 self.as_def_id().to_stable_hash_key(hcx
)