rustc_type_ir/ty_info.rs
1use std::cmp::Ordering;
2use std::hash::{Hash, Hasher};
3use std::ops::Deref;
4
5#[cfg(feature = "nightly")]
6use rustc_data_structures::fingerprint::Fingerprint;
7#[cfg(feature = "nightly")]
8use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
9
10use crate::{DebruijnIndex, TypeFlags};
11
12/// A helper type that you can wrap round your own type in order to automatically
13/// cache the stable hash, type flags and debruijn index on creation and
14/// not recompute it whenever the information is needed.
15/// This is only done in incremental mode. You can also opt out of caching by using
16/// StableHash::ZERO for the hash, in which case the hash gets computed each time.
17/// This is useful if you have values that you intern but never (can?) use for stable
18/// hashing.
19#[derive(Copy, Clone)]
20pub struct WithCachedTypeInfo<T> {
21 pub internee: T,
22
23 #[cfg(feature = "nightly")]
24 pub stable_hash: Fingerprint,
25
26 /// This field provides fast access to information that is also contained
27 /// in `kind`.
28 ///
29 /// This field shouldn't be used directly and may be removed in the future.
30 /// Use `Ty::flags()` instead.
31 pub flags: TypeFlags,
32
33 /// This field provides fast access to information that is also contained
34 /// in `kind`.
35 ///
36 /// This is a kind of confusing thing: it stores the smallest
37 /// binder such that
38 ///
39 /// (a) the binder itself captures nothing but
40 /// (b) all the late-bound things within the type are captured
41 /// by some sub-binder.
42 ///
43 /// So, for a type without any late-bound things, like `u32`, this
44 /// will be *innermost*, because that is the innermost binder that
45 /// captures nothing. But for a type `&'D u32`, where `'D` is a
46 /// late-bound region with De Bruijn index `D`, this would be `D + 1`
47 /// -- the binder itself does not capture `D`, but `D` is captured
48 /// by an inner binder.
49 ///
50 /// We call this concept an "exclusive" binder `D` because all
51 /// De Bruijn indices within the type are contained within `0..D`
52 /// (exclusive).
53 pub outer_exclusive_binder: DebruijnIndex,
54}
55
56impl<T: PartialEq> PartialEq for WithCachedTypeInfo<T> {
57 #[inline]
58 fn eq(&self, other: &Self) -> bool {
59 self.internee.eq(&other.internee)
60 }
61}
62
63impl<T: Eq> Eq for WithCachedTypeInfo<T> {}
64
65impl<T: Ord> PartialOrd for WithCachedTypeInfo<T> {
66 fn partial_cmp(&self, other: &WithCachedTypeInfo<T>) -> Option<Ordering> {
67 Some(self.internee.cmp(&other.internee))
68 }
69}
70
71impl<T: Ord> Ord for WithCachedTypeInfo<T> {
72 fn cmp(&self, other: &WithCachedTypeInfo<T>) -> Ordering {
73 self.internee.cmp(&other.internee)
74 }
75}
76
77impl<T> Deref for WithCachedTypeInfo<T> {
78 type Target = T;
79
80 #[inline]
81 fn deref(&self) -> &T {
82 &self.internee
83 }
84}
85
86impl<T: Hash> Hash for WithCachedTypeInfo<T> {
87 #[inline]
88 fn hash<H: Hasher>(&self, s: &mut H) {
89 #[cfg(feature = "nightly")]
90 if self.stable_hash != Fingerprint::ZERO {
91 return self.stable_hash.hash(s);
92 }
93
94 self.internee.hash(s)
95 }
96}
97
98#[cfg(feature = "nightly")]
99impl<T: HashStable<CTX>, CTX> HashStable<CTX> for WithCachedTypeInfo<T> {
100 fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
101 if self.stable_hash == Fingerprint::ZERO || cfg!(debug_assertions) {
102 // No cached hash available. This can only mean that incremental is disabled.
103 // We don't cache stable hashes in non-incremental mode, because they are used
104 // so rarely that the performance actually suffers.
105
106 // We need to build the hash as if we cached it and then hash that hash, as
107 // otherwise the hashes will differ between cached and non-cached mode.
108 let stable_hash: Fingerprint = {
109 let mut hasher = StableHasher::new();
110 self.internee.hash_stable(hcx, &mut hasher);
111 hasher.finish()
112 };
113 if cfg!(debug_assertions) && self.stable_hash != Fingerprint::ZERO {
114 assert_eq!(
115 stable_hash, self.stable_hash,
116 "cached stable hash does not match freshly computed stable hash"
117 );
118 }
119 stable_hash.hash_stable(hcx, hasher);
120 } else {
121 self.stable_hash.hash_stable(hcx, hasher);
122 }
123 }
124}