rustc_type_ir/
lib.rs

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1// tidy-alphabetical-start
2#![allow(rustc::usage_of_ty_tykind)]
3#![allow(rustc::usage_of_type_ir_inherent)]
4#![cfg_attr(
5    feature = "nightly",
6    feature(associated_type_defaults, never_type, rustc_attrs, negative_impls)
7)]
8#![cfg_attr(feature = "nightly", allow(internal_features))]
9#![cfg_attr(not(bootstrap), allow(rustc::usage_of_type_ir_traits))]
10// tidy-alphabetical-end
11
12extern crate self as rustc_type_ir;
13
14use std::fmt;
15use std::hash::Hash;
16
17#[cfg(feature = "nightly")]
18use rustc_macros::{Decodable, Encodable, HashStable_NoContext};
19
20// These modules are `pub` since they are not glob-imported.
21pub mod data_structures;
22pub mod elaborate;
23pub mod error;
24pub mod fast_reject;
25#[cfg_attr(feature = "nightly", rustc_diagnostic_item = "type_ir_inherent")]
26pub mod inherent;
27pub mod ir_print;
28pub mod lang_items;
29pub mod lift;
30pub mod outlives;
31pub mod relate;
32pub mod search_graph;
33pub mod solve;
34
35// These modules are not `pub` since they are glob-imported.
36#[macro_use]
37mod macros;
38mod binder;
39mod canonical;
40mod const_kind;
41mod flags;
42mod fold;
43mod generic_arg;
44mod infer_ctxt;
45mod interner;
46mod opaque_ty;
47mod predicate;
48mod predicate_kind;
49mod region_kind;
50mod ty_info;
51mod ty_kind;
52mod upcast;
53mod visit;
54
55pub use AliasTyKind::*;
56pub use DynKind::*;
57pub use InferTy::*;
58pub use RegionKind::*;
59pub use TyKind::*;
60pub use Variance::*;
61pub use binder::*;
62pub use canonical::*;
63pub use const_kind::*;
64pub use flags::*;
65pub use fold::*;
66pub use generic_arg::*;
67pub use infer_ctxt::*;
68pub use interner::*;
69pub use opaque_ty::*;
70pub use predicate::*;
71pub use predicate_kind::*;
72pub use region_kind::*;
73pub use rustc_ast_ir::{Movability, Mutability, Pinnedness};
74pub use ty_info::*;
75pub use ty_kind::*;
76pub use upcast::*;
77pub use visit::*;
78
79rustc_index::newtype_index! {
80    /// A [De Bruijn index][dbi] is a standard means of representing
81    /// regions (and perhaps later types) in a higher-ranked setting. In
82    /// particular, imagine a type like this:
83    /// ```ignore (illustrative)
84    ///    for<'a> fn(for<'b> fn(&'b isize, &'a isize), &'a char)
85    /// // ^          ^            |          |           |
86    /// // |          |            |          |           |
87    /// // |          +------------+ 0        |           |
88    /// // |                                  |           |
89    /// // +----------------------------------+ 1         |
90    /// // |                                              |
91    /// // +----------------------------------------------+ 0
92    /// ```
93    /// In this type, there are two binders (the outer fn and the inner
94    /// fn). We need to be able to determine, for any given region, which
95    /// fn type it is bound by, the inner or the outer one. There are
96    /// various ways you can do this, but a De Bruijn index is one of the
97    /// more convenient and has some nice properties. The basic idea is to
98    /// count the number of binders, inside out. Some examples should help
99    /// clarify what I mean.
100    ///
101    /// Let's start with the reference type `&'b isize` that is the first
102    /// argument to the inner function. This region `'b` is assigned a De
103    /// Bruijn index of 0, meaning "the innermost binder" (in this case, a
104    /// fn). The region `'a` that appears in the second argument type (`&'a
105    /// isize`) would then be assigned a De Bruijn index of 1, meaning "the
106    /// second-innermost binder". (These indices are written on the arrows
107    /// in the diagram).
108    ///
109    /// What is interesting is that De Bruijn index attached to a particular
110    /// variable will vary depending on where it appears. For example,
111    /// the final type `&'a char` also refers to the region `'a` declared on
112    /// the outermost fn. But this time, this reference is not nested within
113    /// any other binders (i.e., it is not an argument to the inner fn, but
114    /// rather the outer one). Therefore, in this case, it is assigned a
115    /// De Bruijn index of 0, because the innermost binder in that location
116    /// is the outer fn.
117    ///
118    /// [dbi]: https://en.wikipedia.org/wiki/De_Bruijn_index
119    #[cfg_attr(feature = "nightly", derive(HashStable_NoContext))]
120    #[encodable]
121    #[orderable]
122    #[debug_format = "DebruijnIndex({})"]
123    #[gate_rustc_only]
124    pub struct DebruijnIndex {
125        const INNERMOST = 0;
126    }
127}
128
129impl DebruijnIndex {
130    /// Returns the resulting index when this value is moved into
131    /// `amount` number of new binders. So, e.g., if you had
132    ///
133    ///    for<'a> fn(&'a x)
134    ///
135    /// and you wanted to change it to
136    ///
137    ///    for<'a> fn(for<'b> fn(&'a x))
138    ///
139    /// you would need to shift the index for `'a` into a new binder.
140    #[inline]
141    #[must_use]
142    pub fn shifted_in(self, amount: u32) -> DebruijnIndex {
143        DebruijnIndex::from_u32(self.as_u32() + amount)
144    }
145
146    /// Update this index in place by shifting it "in" through
147    /// `amount` number of binders.
148    #[inline]
149    pub fn shift_in(&mut self, amount: u32) {
150        *self = self.shifted_in(amount);
151    }
152
153    /// Returns the resulting index when this value is moved out from
154    /// `amount` number of new binders.
155    #[inline]
156    #[must_use]
157    pub fn shifted_out(self, amount: u32) -> DebruijnIndex {
158        DebruijnIndex::from_u32(self.as_u32() - amount)
159    }
160
161    /// Update in place by shifting out from `amount` binders.
162    #[inline]
163    pub fn shift_out(&mut self, amount: u32) {
164        *self = self.shifted_out(amount);
165    }
166
167    /// Adjusts any De Bruijn indices so as to make `to_binder` the
168    /// innermost binder. That is, if we have something bound at `to_binder`,
169    /// it will now be bound at INNERMOST. This is an appropriate thing to do
170    /// when moving a region out from inside binders:
171    ///
172    /// ```ignore (illustrative)
173    ///             for<'a>   fn(for<'b>   for<'c>   fn(&'a u32), _)
174    /// // Binder:  D3           D2        D1            ^^
175    /// ```
176    ///
177    /// Here, the region `'a` would have the De Bruijn index D3,
178    /// because it is the bound 3 binders out. However, if we wanted
179    /// to refer to that region `'a` in the second argument (the `_`),
180    /// those two binders would not be in scope. In that case, we
181    /// might invoke `shift_out_to_binder(D3)`. This would adjust the
182    /// De Bruijn index of `'a` to D1 (the innermost binder).
183    ///
184    /// If we invoke `shift_out_to_binder` and the region is in fact
185    /// bound by one of the binders we are shifting out of, that is an
186    /// error (and should fail an assertion failure).
187    #[inline]
188    pub fn shifted_out_to_binder(self, to_binder: DebruijnIndex) -> Self {
189        self.shifted_out(to_binder.as_u32() - INNERMOST.as_u32())
190    }
191}
192
193pub fn debug_bound_var<T: std::fmt::Write>(
194    fmt: &mut T,
195    debruijn: DebruijnIndex,
196    var: impl std::fmt::Debug,
197) -> Result<(), std::fmt::Error> {
198    if debruijn == INNERMOST {
199        write!(fmt, "^{var:?}")
200    } else {
201        write!(fmt, "^{}_{:?}", debruijn.index(), var)
202    }
203}
204
205#[derive(Copy, Clone, PartialEq, Eq, Hash)]
206#[cfg_attr(feature = "nightly", derive(Decodable, Encodable, HashStable_NoContext))]
207#[cfg_attr(feature = "nightly", rustc_pass_by_value)]
208pub enum Variance {
209    Covariant,     // T<A> <: T<B> iff A <: B -- e.g., function return type
210    Invariant,     // T<A> <: T<B> iff B == A -- e.g., type of mutable cell
211    Contravariant, // T<A> <: T<B> iff B <: A -- e.g., function param type
212    Bivariant,     // T<A> <: T<B>            -- e.g., unused type parameter
213}
214
215impl Variance {
216    /// `a.xform(b)` combines the variance of a context with the
217    /// variance of a type with the following meaning. If we are in a
218    /// context with variance `a`, and we encounter a type argument in
219    /// a position with variance `b`, then `a.xform(b)` is the new
220    /// variance with which the argument appears.
221    ///
222    /// Example 1:
223    /// ```ignore (illustrative)
224    /// *mut Vec<i32>
225    /// ```
226    /// Here, the "ambient" variance starts as covariant. `*mut T` is
227    /// invariant with respect to `T`, so the variance in which the
228    /// `Vec<i32>` appears is `Covariant.xform(Invariant)`, which
229    /// yields `Invariant`. Now, the type `Vec<T>` is covariant with
230    /// respect to its type argument `T`, and hence the variance of
231    /// the `i32` here is `Invariant.xform(Covariant)`, which results
232    /// (again) in `Invariant`.
233    ///
234    /// Example 2:
235    /// ```ignore (illustrative)
236    /// fn(*const Vec<i32>, *mut Vec<i32)
237    /// ```
238    /// The ambient variance is covariant. A `fn` type is
239    /// contravariant with respect to its parameters, so the variance
240    /// within which both pointer types appear is
241    /// `Covariant.xform(Contravariant)`, or `Contravariant`. `*const
242    /// T` is covariant with respect to `T`, so the variance within
243    /// which the first `Vec<i32>` appears is
244    /// `Contravariant.xform(Covariant)` or `Contravariant`. The same
245    /// is true for its `i32` argument. In the `*mut T` case, the
246    /// variance of `Vec<i32>` is `Contravariant.xform(Invariant)`,
247    /// and hence the outermost type is `Invariant` with respect to
248    /// `Vec<i32>` (and its `i32` argument).
249    ///
250    /// Source: Figure 1 of "Taming the Wildcards:
251    /// Combining Definition- and Use-Site Variance" published in PLDI'11.
252    pub fn xform(self, v: Variance) -> Variance {
253        match (self, v) {
254            // Figure 1, column 1.
255            (Variance::Covariant, Variance::Covariant) => Variance::Covariant,
256            (Variance::Covariant, Variance::Contravariant) => Variance::Contravariant,
257            (Variance::Covariant, Variance::Invariant) => Variance::Invariant,
258            (Variance::Covariant, Variance::Bivariant) => Variance::Bivariant,
259
260            // Figure 1, column 2.
261            (Variance::Contravariant, Variance::Covariant) => Variance::Contravariant,
262            (Variance::Contravariant, Variance::Contravariant) => Variance::Covariant,
263            (Variance::Contravariant, Variance::Invariant) => Variance::Invariant,
264            (Variance::Contravariant, Variance::Bivariant) => Variance::Bivariant,
265
266            // Figure 1, column 3.
267            (Variance::Invariant, _) => Variance::Invariant,
268
269            // Figure 1, column 4.
270            (Variance::Bivariant, _) => Variance::Bivariant,
271        }
272    }
273}
274
275impl fmt::Debug for Variance {
276    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
277        f.write_str(match *self {
278            Variance::Covariant => "+",
279            Variance::Contravariant => "-",
280            Variance::Invariant => "o",
281            Variance::Bivariant => "*",
282        })
283    }
284}
285
286rustc_index::newtype_index! {
287    /// "Universes" are used during type- and trait-checking in the
288    /// presence of `for<..>` binders to control what sets of names are
289    /// visible. Universes are arranged into a tree: the root universe
290    /// contains names that are always visible. Each child then adds a new
291    /// set of names that are visible, in addition to those of its parent.
292    /// We say that the child universe "extends" the parent universe with
293    /// new names.
294    ///
295    /// To make this more concrete, consider this program:
296    ///
297    /// ```ignore (illustrative)
298    /// struct Foo { }
299    /// fn bar<T>(x: T) {
300    ///   let y: for<'a> fn(&'a u8, Foo) = ...;
301    /// }
302    /// ```
303    ///
304    /// The struct name `Foo` is in the root universe U0. But the type
305    /// parameter `T`, introduced on `bar`, is in an extended universe U1
306    /// -- i.e., within `bar`, we can name both `T` and `Foo`, but outside
307    /// of `bar`, we cannot name `T`. Then, within the type of `y`, the
308    /// region `'a` is in a universe U2 that extends U1, because we can
309    /// name it inside the fn type but not outside.
310    ///
311    /// Universes are used to do type- and trait-checking around these
312    /// "forall" binders (also called **universal quantification**). The
313    /// idea is that when, in the body of `bar`, we refer to `T` as a
314    /// type, we aren't referring to any type in particular, but rather a
315    /// kind of "fresh" type that is distinct from all other types we have
316    /// actually declared. This is called a **placeholder** type, and we
317    /// use universes to talk about this. In other words, a type name in
318    /// universe 0 always corresponds to some "ground" type that the user
319    /// declared, but a type name in a non-zero universe is a placeholder
320    /// type -- an idealized representative of "types in general" that we
321    /// use for checking generic functions.
322    #[cfg_attr(feature = "nightly", derive(HashStable_NoContext))]
323    #[encodable]
324    #[orderable]
325    #[debug_format = "U{}"]
326    #[gate_rustc_only]
327    pub struct UniverseIndex {}
328}
329
330impl UniverseIndex {
331    pub const ROOT: UniverseIndex = UniverseIndex::ZERO;
332
333    /// Returns the "next" universe index in order -- this new index
334    /// is considered to extend all previous universes. This
335    /// corresponds to entering a `forall` quantifier. So, for
336    /// example, suppose we have this type in universe `U`:
337    ///
338    /// ```ignore (illustrative)
339    /// for<'a> fn(&'a u32)
340    /// ```
341    ///
342    /// Once we "enter" into this `for<'a>` quantifier, we are in a
343    /// new universe that extends `U` -- in this new universe, we can
344    /// name the region `'a`, but that region was not nameable from
345    /// `U` because it was not in scope there.
346    pub fn next_universe(self) -> UniverseIndex {
347        UniverseIndex::from_u32(self.as_u32().checked_add(1).unwrap())
348    }
349
350    /// Returns `true` if `self` can name a name from `other` -- in other words,
351    /// if the set of names in `self` is a superset of those in
352    /// `other` (`self >= other`).
353    pub fn can_name(self, other: UniverseIndex) -> bool {
354        self >= other
355    }
356
357    /// Returns `true` if `self` cannot name some names from `other` -- in other
358    /// words, if the set of names in `self` is a strict subset of
359    /// those in `other` (`self < other`).
360    pub fn cannot_name(self, other: UniverseIndex) -> bool {
361        self < other
362    }
363
364    /// Returns `true` if `self` is the root universe, otherwise false.
365    pub fn is_root(self) -> bool {
366        self == Self::ROOT
367    }
368}
369
370impl Default for UniverseIndex {
371    fn default() -> Self {
372        Self::ROOT
373    }
374}
375
376rustc_index::newtype_index! {
377    #[cfg_attr(feature = "nightly", derive(HashStable_NoContext))]
378    #[encodable]
379    #[orderable]
380    #[debug_format = "{}"]
381    #[gate_rustc_only]
382    pub struct BoundVar {}
383}
384
385impl<I: Interner> inherent::BoundVarLike<I> for BoundVar {
386    fn var(self) -> BoundVar {
387        self
388    }
389
390    fn assert_eq(self, _var: I::BoundVarKind) {
391        unreachable!("FIXME: We really should have a separate `BoundConst` for consts")
392    }
393}
394
395/// Represents the various closure traits in the language. This
396/// will determine the type of the environment (`self`, in the
397/// desugaring) argument that the closure expects.
398///
399/// You can get the environment type of a closure using
400/// `tcx.closure_env_ty()`.
401#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
402#[cfg_attr(feature = "nightly", derive(Encodable, Decodable, HashStable_NoContext))]
403pub enum ClosureKind {
404    Fn,
405    FnMut,
406    FnOnce,
407}
408
409impl ClosureKind {
410    /// This is the initial value used when doing upvar inference.
411    pub const LATTICE_BOTTOM: ClosureKind = ClosureKind::Fn;
412
413    pub const fn as_str(self) -> &'static str {
414        match self {
415            ClosureKind::Fn => "Fn",
416            ClosureKind::FnMut => "FnMut",
417            ClosureKind::FnOnce => "FnOnce",
418        }
419    }
420
421    /// Returns `true` if a type that impls this closure kind
422    /// must also implement `other`.
423    #[rustfmt::skip]
424    pub fn extends(self, other: ClosureKind) -> bool {
425        use ClosureKind::*;
426        match (self, other) {
427              (Fn, Fn | FnMut | FnOnce)
428            | (FnMut,   FnMut | FnOnce)
429            | (FnOnce,          FnOnce) => true,
430            _ => false,
431        }
432    }
433}
434
435impl fmt::Display for ClosureKind {
436    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
437        self.as_str().fmt(f)
438    }
439}
rustc_type_ir/lib.rs

rustc_type_ir/
lib.rs
