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use crate::ty::subst::SubstsRef;
use crate::ty::{self, Ty, TyCtxt};
use rustc_hir as hir;
use rustc_hir::def_id::DefId;
use rustc_hir::lang_items::LangItem;
use rustc_macros::HashStable;
use rustc_span::Span;
#[derive(Clone, Copy, Debug, PartialEq, Eq, TyEncodable, TyDecodable, Hash, HashStable)]
pub enum PointerCast {
/// Go from a fn-item type to a fn-pointer type.
ReifyFnPointer,
/// Go from a safe fn pointer to an unsafe fn pointer.
UnsafeFnPointer,
/// Go from a non-capturing closure to an fn pointer or an unsafe fn pointer.
/// It cannot convert a closure that requires unsafe.
ClosureFnPointer(hir::Unsafety),
/// Go from a mut raw pointer to a const raw pointer.
MutToConstPointer,
/// Go from `*const [T; N]` to `*const T`
ArrayToPointer,
/// Unsize a pointer/reference value, e.g., `&[T; n]` to
/// `&[T]`. Note that the source could be a thin or fat pointer.
/// This will do things like convert thin pointers to fat
/// pointers, or convert structs containing thin pointers to
/// structs containing fat pointers, or convert between fat
/// pointers. We don't store the details of how the transform is
/// done (in fact, we don't know that, because it might depend on
/// the precise type parameters). We just store the target
/// type. Codegen backends and miri figure out what has to be done
/// based on the precise source/target type at hand.
Unsize,
}
/// Represents coercing a value to a different type of value.
///
/// We transform values by following a number of `Adjust` steps in order.
/// See the documentation on variants of `Adjust` for more details.
///
/// Here are some common scenarios:
///
/// 1. The simplest cases are where a pointer is not adjusted fat vs thin.
/// Here the pointer will be dereferenced N times (where a dereference can
/// happen to raw or borrowed pointers or any smart pointer which implements
/// `Deref`, including `Box<_>`). The types of dereferences is given by
/// `autoderefs`. It can then be auto-referenced zero or one times, indicated
/// by `autoref`, to either a raw or borrowed pointer. In these cases unsize is
/// `false`.
///
/// 2. A thin-to-fat coercion involves unsizing the underlying data. We start
/// with a thin pointer, deref a number of times, unsize the underlying data,
/// then autoref. The 'unsize' phase may change a fixed length array to a
/// dynamically sized one, a concrete object to a trait object, or statically
/// sized struct to a dynamically sized one. E.g., `&[i32; 4]` -> `&[i32]` is
/// represented by:
///
/// ```ignore (illustrative)
/// Deref(None) -> [i32; 4],
/// Borrow(AutoBorrow::Ref) -> &[i32; 4],
/// Unsize -> &[i32],
/// ```
///
/// Note that for a struct, the 'deep' unsizing of the struct is not recorded.
/// E.g., `struct Foo<T> { x: T }` we can coerce `&Foo<[i32; 4]>` to `&Foo<[i32]>`
/// The autoderef and -ref are the same as in the above example, but the type
/// stored in `unsize` is `Foo<[i32]>`, we don't store any further detail about
/// the underlying conversions from `[i32; 4]` to `[i32]`.
///
/// 3. Coercing a `Box<T>` to `Box<dyn Trait>` is an interesting special case. In
/// that case, we have the pointer we need coming in, so there are no
/// autoderefs, and no autoref. Instead we just do the `Unsize` transformation.
/// At some point, of course, `Box` should move out of the compiler, in which
/// case this is analogous to transforming a struct. E.g., `Box<[i32; 4]>` ->
/// `Box<[i32]>` is an `Adjust::Unsize` with the target `Box<[i32]>`.
#[derive(Clone, TyEncodable, TyDecodable, HashStable, TypeFoldable, TypeVisitable)]
pub struct Adjustment<'tcx> {
pub kind: Adjust<'tcx>,
pub target: Ty<'tcx>,
}
impl<'tcx> Adjustment<'tcx> {
pub fn is_region_borrow(&self) -> bool {
matches!(self.kind, Adjust::Borrow(AutoBorrow::Ref(..)))
}
}
#[derive(Clone, Debug, TyEncodable, TyDecodable, HashStable, TypeFoldable, TypeVisitable)]
pub enum Adjust<'tcx> {
/// Go from ! to any type.
NeverToAny,
/// Dereference once, producing a place.
Deref(Option<OverloadedDeref<'tcx>>),
/// Take the address and produce either a `&` or `*` pointer.
Borrow(AutoBorrow<'tcx>),
Pointer(PointerCast),
}
/// An overloaded autoderef step, representing a `Deref(Mut)::deref(_mut)`
/// call, with the signature `&'a T -> &'a U` or `&'a mut T -> &'a mut U`.
/// The target type is `U` in both cases, with the region and mutability
/// being those shared by both the receiver and the returned reference.
#[derive(Copy, Clone, PartialEq, Debug, TyEncodable, TyDecodable, HashStable)]
#[derive(TypeFoldable, TypeVisitable)]
pub struct OverloadedDeref<'tcx> {
pub region: ty::Region<'tcx>,
pub mutbl: hir::Mutability,
/// The `Span` associated with the field access or method call
/// that triggered this overloaded deref.
pub span: Span,
}
impl<'tcx> OverloadedDeref<'tcx> {
pub fn method_call(&self, tcx: TyCtxt<'tcx>, source: Ty<'tcx>) -> (DefId, SubstsRef<'tcx>) {
let trait_def_id = match self.mutbl {
hir::Mutability::Not => tcx.require_lang_item(LangItem::Deref, None),
hir::Mutability::Mut => tcx.require_lang_item(LangItem::DerefMut, None),
};
let method_def_id = tcx
.associated_items(trait_def_id)
.in_definition_order()
.find(|m| m.kind == ty::AssocKind::Fn)
.unwrap()
.def_id;
(method_def_id, tcx.mk_substs_trait(source, &[]))
}
}
/// At least for initial deployment, we want to limit two-phase borrows to
/// only a few specific cases. Right now, those are mostly "things that desugar"
/// into method calls:
/// - using `x.some_method()` syntax, where some_method takes `&mut self`,
/// - using `Foo::some_method(&mut x, ...)` syntax,
/// - binary assignment operators (`+=`, `-=`, `*=`, etc.).
/// Anything else should be rejected until generalized two-phase borrow support
/// is implemented. Right now, dataflow can't handle the general case where there
/// is more than one use of a mutable borrow, and we don't want to accept too much
/// new code via two-phase borrows, so we try to limit where we create two-phase
/// capable mutable borrows.
/// See #49434 for tracking.
#[derive(Copy, Clone, PartialEq, Debug, TyEncodable, TyDecodable, HashStable)]
pub enum AllowTwoPhase {
Yes,
No,
}
#[derive(Copy, Clone, PartialEq, Debug, TyEncodable, TyDecodable, HashStable)]
pub enum AutoBorrowMutability {
Mut { allow_two_phase_borrow: AllowTwoPhase },
Not,
}
impl From<AutoBorrowMutability> for hir::Mutability {
fn from(m: AutoBorrowMutability) -> Self {
match m {
AutoBorrowMutability::Mut { .. } => hir::Mutability::Mut,
AutoBorrowMutability::Not => hir::Mutability::Not,
}
}
}
#[derive(Copy, Clone, PartialEq, Debug, TyEncodable, TyDecodable, HashStable)]
#[derive(TypeFoldable, TypeVisitable)]
pub enum AutoBorrow<'tcx> {
/// Converts from T to &T.
Ref(ty::Region<'tcx>, AutoBorrowMutability),
/// Converts from T to *T.
RawPtr(hir::Mutability),
}
/// Information for `CoerceUnsized` impls, storing information we
/// have computed about the coercion.
///
/// This struct can be obtained via the `coerce_impl_info` query.
/// Demanding this struct also has the side-effect of reporting errors
/// for inappropriate impls.
#[derive(Clone, Copy, TyEncodable, TyDecodable, Debug, HashStable)]
pub struct CoerceUnsizedInfo {
/// If this is a "custom coerce" impl, then what kind of custom
/// coercion is it? This applies to impls of `CoerceUnsized` for
/// structs, primarily, where we store a bit of info about which
/// fields need to be coerced.
pub custom_kind: Option<CustomCoerceUnsized>,
}
#[derive(Clone, Copy, TyEncodable, TyDecodable, Debug, HashStable)]
pub enum CustomCoerceUnsized {
/// Records the index of the field being coerced.
Struct(usize),
}
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