1 use crate::ty::subst::SubstsRef;
2 use crate::ty::{self, Ty, TyCtxt};
4 use rustc_hir::def_id::DefId;
5 use rustc_hir::lang_items::LangItem;
6 use rustc_macros::HashStable;
9 #[derive(Clone, Copy, Debug, PartialEq, Eq, TyEncodable, TyDecodable, Hash, HashStable)]
10 pub enum PointerCast {
11 /// Go from a fn-item type to a fn-pointer type.
14 /// Go from a safe fn pointer to an unsafe fn pointer.
17 /// Go from a non-capturing closure to an fn pointer or an unsafe fn pointer.
18 /// It cannot convert a closure that requires unsafe.
19 ClosureFnPointer(hir::Unsafety),
21 /// Go from a mut raw pointer to a const raw pointer.
24 /// Go from `*const [T; N]` to `*const T`
27 /// Unsize a pointer/reference value, e.g., `&[T; n]` to
28 /// `&[T]`. Note that the source could be a thin or fat pointer.
29 /// This will do things like convert thin pointers to fat
30 /// pointers, or convert structs containing thin pointers to
31 /// structs containing fat pointers, or convert between fat
32 /// pointers. We don't store the details of how the transform is
33 /// done (in fact, we don't know that, because it might depend on
34 /// the precise type parameters). We just store the target
35 /// type. Codegen backends and miri figure out what has to be done
36 /// based on the precise source/target type at hand.
40 /// Represents coercing a value to a different type of value.
42 /// We transform values by following a number of `Adjust` steps in order.
43 /// See the documentation on variants of `Adjust` for more details.
45 /// Here are some common scenarios:
47 /// 1. The simplest cases are where a pointer is not adjusted fat vs thin.
48 /// Here the pointer will be dereferenced N times (where a dereference can
49 /// happen to raw or borrowed pointers or any smart pointer which implements
50 /// `Deref`, including `Box<_>`). The types of dereferences is given by
51 /// `autoderefs`. It can then be auto-referenced zero or one times, indicated
52 /// by `autoref`, to either a raw or borrowed pointer. In these cases unsize is
55 /// 2. A thin-to-fat coercion involves unsizing the underlying data. We start
56 /// with a thin pointer, deref a number of times, unsize the underlying data,
57 /// then autoref. The 'unsize' phase may change a fixed length array to a
58 /// dynamically sized one, a concrete object to a trait object, or statically
59 /// sized struct to a dynamically sized one. E.g., `&[i32; 4]` -> `&[i32]` is
63 /// Deref(None) -> [i32; 4],
64 /// Borrow(AutoBorrow::Ref) -> &[i32; 4],
68 /// Note that for a struct, the 'deep' unsizing of the struct is not recorded.
69 /// E.g., `struct Foo<T> { x: T }` we can coerce `&Foo<[i32; 4]>` to `&Foo<[i32]>`
70 /// The autoderef and -ref are the same as in the above example, but the type
71 /// stored in `unsize` is `Foo<[i32]>`, we don't store any further detail about
72 /// the underlying conversions from `[i32; 4]` to `[i32]`.
74 /// 3. Coercing a `Box<T>` to `Box<dyn Trait>` is an interesting special case. In
75 /// that case, we have the pointer we need coming in, so there are no
76 /// autoderefs, and no autoref. Instead we just do the `Unsize` transformation.
77 /// At some point, of course, `Box` should move out of the compiler, in which
78 /// case this is analogous to transforming a struct. E.g., `Box<[i32; 4]>` ->
79 /// `Box<[i32]>` is an `Adjust::Unsize` with the target `Box<[i32]>`.
80 #[derive(Clone, TyEncodable, TyDecodable, HashStable, TypeFoldable)]
81 pub struct Adjustment<'tcx> {
82 pub kind: Adjust<'tcx>,
86 impl<'tcx> Adjustment<'tcx> {
87 pub fn is_region_borrow(&self) -> bool {
88 matches!(self.kind, Adjust::Borrow(AutoBorrow::Ref(..)))
92 #[derive(Clone, Debug, TyEncodable, TyDecodable, HashStable, TypeFoldable)]
93 pub enum Adjust<'tcx> {
94 /// Go from ! to any type.
97 /// Dereference once, producing a place.
98 Deref(Option<OverloadedDeref<'tcx>>),
100 /// Take the address and produce either a `&` or `*` pointer.
101 Borrow(AutoBorrow<'tcx>),
103 Pointer(PointerCast),
106 /// An overloaded autoderef step, representing a `Deref(Mut)::deref(_mut)`
107 /// call, with the signature `&'a T -> &'a U` or `&'a mut T -> &'a mut U`.
108 /// The target type is `U` in both cases, with the region and mutability
109 /// being those shared by both the receiver and the returned reference.
110 #[derive(Copy, Clone, PartialEq, Debug, TyEncodable, TyDecodable, HashStable, TypeFoldable)]
111 pub struct OverloadedDeref<'tcx> {
112 pub region: ty::Region<'tcx>,
113 pub mutbl: hir::Mutability,
114 /// The `Span` associated with the field access or method call
115 /// that triggered this overloaded deref.
119 impl<'tcx> OverloadedDeref<'tcx> {
120 pub fn method_call(&self, tcx: TyCtxt<'tcx>, source: Ty<'tcx>) -> (DefId, SubstsRef<'tcx>) {
121 let trait_def_id = match self.mutbl {
122 hir::Mutability::Not => tcx.require_lang_item(LangItem::Deref, None),
123 hir::Mutability::Mut => tcx.require_lang_item(LangItem::DerefMut, None),
125 let method_def_id = tcx
126 .associated_items(trait_def_id)
127 .in_definition_order()
128 .find(|m| m.kind == ty::AssocKind::Fn)
131 (method_def_id, tcx.mk_substs_trait(source, &[]))
135 /// At least for initial deployment, we want to limit two-phase borrows to
136 /// only a few specific cases. Right now, those are mostly "things that desugar"
137 /// into method calls:
138 /// - using `x.some_method()` syntax, where some_method takes `&mut self`,
139 /// - using `Foo::some_method(&mut x, ...)` syntax,
140 /// - binary assignment operators (`+=`, `-=`, `*=`, etc.).
141 /// Anything else should be rejected until generalized two-phase borrow support
142 /// is implemented. Right now, dataflow can't handle the general case where there
143 /// is more than one use of a mutable borrow, and we don't want to accept too much
144 /// new code via two-phase borrows, so we try to limit where we create two-phase
145 /// capable mutable borrows.
146 /// See #49434 for tracking.
147 #[derive(Copy, Clone, PartialEq, Debug, TyEncodable, TyDecodable, HashStable)]
148 pub enum AllowTwoPhase {
153 #[derive(Copy, Clone, PartialEq, Debug, TyEncodable, TyDecodable, HashStable)]
154 pub enum AutoBorrowMutability {
155 Mut { allow_two_phase_borrow: AllowTwoPhase },
159 impl From<AutoBorrowMutability> for hir::Mutability {
160 fn from(m: AutoBorrowMutability) -> Self {
162 AutoBorrowMutability::Mut { .. } => hir::Mutability::Mut,
163 AutoBorrowMutability::Not => hir::Mutability::Not,
168 #[derive(Copy, Clone, PartialEq, Debug, TyEncodable, TyDecodable, HashStable, TypeFoldable)]
169 pub enum AutoBorrow<'tcx> {
170 /// Converts from T to &T.
171 Ref(ty::Region<'tcx>, AutoBorrowMutability),
173 /// Converts from T to *T.
174 RawPtr(hir::Mutability),
177 /// Information for `CoerceUnsized` impls, storing information we
178 /// have computed about the coercion.
180 /// This struct can be obtained via the `coerce_impl_info` query.
181 /// Demanding this struct also has the side-effect of reporting errors
182 /// for inappropriate impls.
183 #[derive(Clone, Copy, TyEncodable, TyDecodable, Debug, HashStable)]
184 pub struct CoerceUnsizedInfo {
185 /// If this is a "custom coerce" impl, then what kind of custom
186 /// coercion is it? This applies to impls of `CoerceUnsized` for
187 /// structs, primarily, where we store a bit of info about which
188 /// fields need to be coerced.
189 pub custom_kind: Option<CustomCoerceUnsized>,
192 #[derive(Clone, Copy, TyEncodable, TyDecodable, Debug, HashStable)]
193 pub enum CustomCoerceUnsized {
194 /// Records the index of the field being coerced.