# rustc_type_ir/lib.rs

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```
// tidy-alphabetical-start
#![allow(rustc::usage_of_ty_tykind)]
#![cfg_attr(
feature = "nightly",
feature(associated_type_defaults, never_type, rustc_attrs, negative_impls)
)]
#![cfg_attr(feature = "nightly", allow(internal_features))]
#![cfg_attr(not(bootstrap), allow(rustc::usage_of_type_ir_inherent))]
#![warn(unreachable_pub)]
// tidy-alphabetical-end
extern crate self as rustc_type_ir;
use std::fmt;
use std::hash::Hash;
#[cfg(feature = "nightly")]
use rustc_macros::{Decodable, Encodable, HashStable_NoContext};
// These modules are `pub` since they are not glob-imported.
#[macro_use]
pub mod visit;
#[cfg(feature = "nightly")]
pub mod codec;
pub mod data_structures;
pub mod elaborate;
pub mod error;
pub mod fast_reject;
pub mod fold;
#[cfg_attr(feature = "nightly", rustc_diagnostic_item = "type_ir_inherent")]
pub mod inherent;
pub mod ir_print;
pub mod lang_items;
pub mod lift;
pub mod outlives;
pub mod relate;
pub mod search_graph;
pub mod solve;
// These modules are not `pub` since they are glob-imported.
#[macro_use]
mod macros;
mod binder;
mod canonical;
mod const_kind;
mod effects;
mod flags;
mod generic_arg;
mod infer_ctxt;
mod interner;
mod opaque_ty;
mod predicate;
mod predicate_kind;
mod region_kind;
mod ty_info;
mod ty_kind;
mod upcast;
pub use AliasTyKind::*;
pub use DynKind::*;
pub use InferTy::*;
pub use RegionKind::*;
pub use TyKind::*;
pub use Variance::*;
pub use binder::*;
pub use canonical::*;
#[cfg(feature = "nightly")]
pub use codec::*;
pub use const_kind::*;
pub use effects::*;
pub use flags::*;
pub use generic_arg::*;
pub use infer_ctxt::*;
pub use interner::*;
pub use opaque_ty::*;
pub use predicate::*;
pub use predicate_kind::*;
pub use region_kind::*;
pub use ty_info::*;
pub use ty_kind::*;
pub use upcast::*;
rustc_index::newtype_index! {
/// A [De Bruijn index][dbi] is a standard means of representing
/// regions (and perhaps later types) in a higher-ranked setting. In
/// particular, imagine a type like this:
/// ```ignore (illustrative)
/// for<'a> fn(for<'b> fn(&'b isize, &'a isize), &'a char)
/// // ^ ^ | | |
/// // | | | | |
/// // | +------------+ 0 | |
/// // | | |
/// // +----------------------------------+ 1 |
/// // | |
/// // +----------------------------------------------+ 0
/// ```
/// In this type, there are two binders (the outer fn and the inner
/// fn). We need to be able to determine, for any given region, which
/// fn type it is bound by, the inner or the outer one. There are
/// various ways you can do this, but a De Bruijn index is one of the
/// more convenient and has some nice properties. The basic idea is to
/// count the number of binders, inside out. Some examples should help
/// clarify what I mean.
///
/// Let's start with the reference type `&'b isize` that is the first
/// argument to the inner function. This region `'b` is assigned a De
/// Bruijn index of 0, meaning "the innermost binder" (in this case, a
/// fn). The region `'a` that appears in the second argument type (`&'a
/// isize`) would then be assigned a De Bruijn index of 1, meaning "the
/// second-innermost binder". (These indices are written on the arrows
/// in the diagram).
///
/// What is interesting is that De Bruijn index attached to a particular
/// variable will vary depending on where it appears. For example,
/// the final type `&'a char` also refers to the region `'a` declared on
/// the outermost fn. But this time, this reference is not nested within
/// any other binders (i.e., it is not an argument to the inner fn, but
/// rather the outer one). Therefore, in this case, it is assigned a
/// De Bruijn index of 0, because the innermost binder in that location
/// is the outer fn.
///
/// [dbi]: https://en.wikipedia.org/wiki/De_Bruijn_index
#[cfg_attr(feature = "nightly", derive(HashStable_NoContext))]
#[encodable]
#[orderable]
#[debug_format = "DebruijnIndex({})"]
#[gate_rustc_only]
pub struct DebruijnIndex {
const INNERMOST = 0;
}
}
impl DebruijnIndex {
/// Returns the resulting index when this value is moved into
/// `amount` number of new binders. So, e.g., if you had
///
/// for<'a> fn(&'a x)
///
/// and you wanted to change it to
///
/// for<'a> fn(for<'b> fn(&'a x))
///
/// you would need to shift the index for `'a` into a new binder.
#[inline]
#[must_use]
pub fn shifted_in(self, amount: u32) -> DebruijnIndex {
DebruijnIndex::from_u32(self.as_u32() + amount)
}
/// Update this index in place by shifting it "in" through
/// `amount` number of binders.
#[inline]
pub fn shift_in(&mut self, amount: u32) {
*self = self.shifted_in(amount);
}
/// Returns the resulting index when this value is moved out from
/// `amount` number of new binders.
#[inline]
#[must_use]
pub fn shifted_out(self, amount: u32) -> DebruijnIndex {
DebruijnIndex::from_u32(self.as_u32() - amount)
}
/// Update in place by shifting out from `amount` binders.
#[inline]
pub fn shift_out(&mut self, amount: u32) {
*self = self.shifted_out(amount);
}
/// Adjusts any De Bruijn indices so as to make `to_binder` the
/// innermost binder. That is, if we have something bound at `to_binder`,
/// it will now be bound at INNERMOST. This is an appropriate thing to do
/// when moving a region out from inside binders:
///
/// ```ignore (illustrative)
/// for<'a> fn(for<'b> for<'c> fn(&'a u32), _)
/// // Binder: D3 D2 D1 ^^
/// ```
///
/// Here, the region `'a` would have the De Bruijn index D3,
/// because it is the bound 3 binders out. However, if we wanted
/// to refer to that region `'a` in the second argument (the `_`),
/// those two binders would not be in scope. In that case, we
/// might invoke `shift_out_to_binder(D3)`. This would adjust the
/// De Bruijn index of `'a` to D1 (the innermost binder).
///
/// If we invoke `shift_out_to_binder` and the region is in fact
/// bound by one of the binders we are shifting out of, that is an
/// error (and should fail an assertion failure).
#[inline]
pub fn shifted_out_to_binder(self, to_binder: DebruijnIndex) -> Self {
self.shifted_out(to_binder.as_u32() - INNERMOST.as_u32())
}
}
pub fn debug_bound_var<T: std::fmt::Write>(
fmt: &mut T,
debruijn: DebruijnIndex,
var: impl std::fmt::Debug,
) -> Result<(), std::fmt::Error> {
if debruijn == INNERMOST {
write!(fmt, "^{var:?}")
} else {
write!(fmt, "^{}_{:?}", debruijn.index(), var)
}
}
#[derive(Copy, Clone, PartialEq, Eq, Hash)]
#[cfg_attr(feature = "nightly", derive(Decodable, Encodable, HashStable_NoContext))]
#[cfg_attr(feature = "nightly", rustc_pass_by_value)]
pub enum Variance {
Covariant, // T<A> <: T<B> iff A <: B -- e.g., function return type
Invariant, // T<A> <: T<B> iff B == A -- e.g., type of mutable cell
Contravariant, // T<A> <: T<B> iff B <: A -- e.g., function param type
Bivariant, // T<A> <: T<B> -- e.g., unused type parameter
}
impl Variance {
/// `a.xform(b)` combines the variance of a context with the
/// variance of a type with the following meaning. If we are in a
/// context with variance `a`, and we encounter a type argument in
/// a position with variance `b`, then `a.xform(b)` is the new
/// variance with which the argument appears.
///
/// Example 1:
/// ```ignore (illustrative)
/// *mut Vec<i32>
/// ```
/// Here, the "ambient" variance starts as covariant. `*mut T` is
/// invariant with respect to `T`, so the variance in which the
/// `Vec<i32>` appears is `Covariant.xform(Invariant)`, which
/// yields `Invariant`. Now, the type `Vec<T>` is covariant with
/// respect to its type argument `T`, and hence the variance of
/// the `i32` here is `Invariant.xform(Covariant)`, which results
/// (again) in `Invariant`.
///
/// Example 2:
/// ```ignore (illustrative)
/// fn(*const Vec<i32>, *mut Vec<i32)
/// ```
/// The ambient variance is covariant. A `fn` type is
/// contravariant with respect to its parameters, so the variance
/// within which both pointer types appear is
/// `Covariant.xform(Contravariant)`, or `Contravariant`. `*const
/// T` is covariant with respect to `T`, so the variance within
/// which the first `Vec<i32>` appears is
/// `Contravariant.xform(Covariant)` or `Contravariant`. The same
/// is true for its `i32` argument. In the `*mut T` case, the
/// variance of `Vec<i32>` is `Contravariant.xform(Invariant)`,
/// and hence the outermost type is `Invariant` with respect to
/// `Vec<i32>` (and its `i32` argument).
///
/// Source: Figure 1 of "Taming the Wildcards:
/// Combining Definition- and Use-Site Variance" published in PLDI'11.
pub fn xform(self, v: Variance) -> Variance {
match (self, v) {
// Figure 1, column 1.
(Variance::Covariant, Variance::Covariant) => Variance::Covariant,
(Variance::Covariant, Variance::Contravariant) => Variance::Contravariant,
(Variance::Covariant, Variance::Invariant) => Variance::Invariant,
(Variance::Covariant, Variance::Bivariant) => Variance::Bivariant,
// Figure 1, column 2.
(Variance::Contravariant, Variance::Covariant) => Variance::Contravariant,
(Variance::Contravariant, Variance::Contravariant) => Variance::Covariant,
(Variance::Contravariant, Variance::Invariant) => Variance::Invariant,
(Variance::Contravariant, Variance::Bivariant) => Variance::Bivariant,
// Figure 1, column 3.
(Variance::Invariant, _) => Variance::Invariant,
// Figure 1, column 4.
(Variance::Bivariant, _) => Variance::Bivariant,
}
}
}
impl fmt::Debug for Variance {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.write_str(match *self {
Variance::Covariant => "+",
Variance::Contravariant => "-",
Variance::Invariant => "o",
Variance::Bivariant => "*",
})
}
}
rustc_index::newtype_index! {
/// "Universes" are used during type- and trait-checking in the
/// presence of `for<..>` binders to control what sets of names are
/// visible. Universes are arranged into a tree: the root universe
/// contains names that are always visible. Each child then adds a new
/// set of names that are visible, in addition to those of its parent.
/// We say that the child universe "extends" the parent universe with
/// new names.
///
/// To make this more concrete, consider this program:
///
/// ```ignore (illustrative)
/// struct Foo { }
/// fn bar<T>(x: T) {
/// let y: for<'a> fn(&'a u8, Foo) = ...;
/// }
/// ```
///
/// The struct name `Foo` is in the root universe U0. But the type
/// parameter `T`, introduced on `bar`, is in an extended universe U1
/// -- i.e., within `bar`, we can name both `T` and `Foo`, but outside
/// of `bar`, we cannot name `T`. Then, within the type of `y`, the
/// region `'a` is in a universe U2 that extends U1, because we can
/// name it inside the fn type but not outside.
///
/// Universes are used to do type- and trait-checking around these
/// "forall" binders (also called **universal quantification**). The
/// idea is that when, in the body of `bar`, we refer to `T` as a
/// type, we aren't referring to any type in particular, but rather a
/// kind of "fresh" type that is distinct from all other types we have
/// actually declared. This is called a **placeholder** type, and we
/// use universes to talk about this. In other words, a type name in
/// universe 0 always corresponds to some "ground" type that the user
/// declared, but a type name in a non-zero universe is a placeholder
/// type -- an idealized representative of "types in general" that we
/// use for checking generic functions.
#[cfg_attr(feature = "nightly", derive(HashStable_NoContext))]
#[encodable]
#[orderable]
#[debug_format = "U{}"]
#[gate_rustc_only]
pub struct UniverseIndex {}
}
impl UniverseIndex {
pub const ROOT: UniverseIndex = UniverseIndex::ZERO;
/// Returns the "next" universe index in order -- this new index
/// is considered to extend all previous universes. This
/// corresponds to entering a `forall` quantifier. So, for
/// example, suppose we have this type in universe `U`:
///
/// ```ignore (illustrative)
/// for<'a> fn(&'a u32)
/// ```
///
/// Once we "enter" into this `for<'a>` quantifier, we are in a
/// new universe that extends `U` -- in this new universe, we can
/// name the region `'a`, but that region was not nameable from
/// `U` because it was not in scope there.
pub fn next_universe(self) -> UniverseIndex {
UniverseIndex::from_u32(self.as_u32().checked_add(1).unwrap())
}
/// Returns `true` if `self` can name a name from `other` -- in other words,
/// if the set of names in `self` is a superset of those in
/// `other` (`self >= other`).
pub fn can_name(self, other: UniverseIndex) -> bool {
self >= other
}
/// Returns `true` if `self` cannot name some names from `other` -- in other
/// words, if the set of names in `self` is a strict subset of
/// those in `other` (`self < other`).
pub fn cannot_name(self, other: UniverseIndex) -> bool {
self < other
}
/// Returns `true` if `self` is the root universe, otherwise false.
pub fn is_root(self) -> bool {
self == Self::ROOT
}
}
impl Default for UniverseIndex {
fn default() -> Self {
Self::ROOT
}
}
rustc_index::newtype_index! {
#[cfg_attr(feature = "nightly", derive(HashStable_NoContext))]
#[encodable]
#[orderable]
#[debug_format = "{}"]
#[gate_rustc_only]
pub struct BoundVar {}
}
impl<I: Interner> inherent::BoundVarLike<I> for BoundVar {
fn var(self) -> BoundVar {
self
}
fn assert_eq(self, _var: I::BoundVarKind) {
unreachable!("FIXME: We really should have a separate `BoundConst` for consts")
}
}
/// Represents the various closure traits in the language. This
/// will determine the type of the environment (`self`, in the
/// desugaring) argument that the closure expects.
///
/// You can get the environment type of a closure using
/// `tcx.closure_env_ty()`.
#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
#[cfg_attr(feature = "nightly", derive(Encodable, Decodable, HashStable_NoContext))]
pub enum ClosureKind {
Fn,
FnMut,
FnOnce,
}
impl ClosureKind {
/// This is the initial value used when doing upvar inference.
pub const LATTICE_BOTTOM: ClosureKind = ClosureKind::Fn;
pub const fn as_str(self) -> &'static str {
match self {
ClosureKind::Fn => "Fn",
ClosureKind::FnMut => "FnMut",
ClosureKind::FnOnce => "FnOnce",
}
}
/// Returns `true` if a type that impls this closure kind
/// must also implement `other`.
#[rustfmt::skip]
pub fn extends(self, other: ClosureKind) -> bool {
use ClosureKind::*;
match (self, other) {
(Fn, Fn | FnMut | FnOnce)
| (FnMut, FnMut | FnOnce)
| (FnOnce, FnOnce) => true,
_ => false,
}
}
}
impl fmt::Display for ClosureKind {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
self.as_str().fmt(f)
}
}
```