1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183
// Copyright 2012-2015 The Rust Project Developers. See the COPYRIGHT // file at the top-level directory of this distribution and at // http://rust-lang.org/COPYRIGHT. // // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your // option. This file may not be copied, modified, or distributed // except according to those terms. use hir; use hir::def_id::DefId; use ty::{self, Ty, TyCtxt}; use ty::subst::Substs; /// 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: /// /// ``` /// 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<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, RustcEncodable, RustcDecodable)] pub struct Adjustment<'tcx> { pub kind: Adjust<'tcx>, pub target: Ty<'tcx>, } #[derive(Clone, Debug, RustcEncodable, RustcDecodable)] pub enum Adjust<'tcx> { /// Go from ! to any type. NeverToAny, /// 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. ClosureFnPointer, /// Go from a mut raw pointer to a const raw pointer. MutToConstPointer, /// Dereference once, producing a place. Deref(Option<OverloadedDeref<'tcx>>), /// Take the address and produce either a `&` or `*` pointer. Borrow(AutoBorrow<'tcx>), /// 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, } /// 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, RustcEncodable, RustcDecodable)] pub struct OverloadedDeref<'tcx> { pub region: ty::Region<'tcx>, pub mutbl: hir::Mutability, } impl<'a, 'gcx, 'tcx> OverloadedDeref<'tcx> { pub fn method_call(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>, source: Ty<'tcx>) -> (DefId, &'tcx Substs<'tcx>) { let trait_def_id = match self.mutbl { hir::MutImmutable => tcx.lang_items().deref_trait(), hir::MutMutable => tcx.lang_items().deref_mut_trait() }; let method_def_id = tcx.associated_items(trait_def_id.unwrap()) .find(|m| m.kind == ty::AssociatedKind::Method).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 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, RustcEncodable, RustcDecodable)] pub enum AllowTwoPhase { Yes, No } #[derive(Copy, Clone, PartialEq, Debug, RustcEncodable, RustcDecodable)] pub enum AutoBorrowMutability { Mutable { allow_two_phase_borrow: AllowTwoPhase }, Immutable, } impl From<AutoBorrowMutability> for hir::Mutability { fn from(m: AutoBorrowMutability) -> Self { match m { AutoBorrowMutability::Mutable { .. } => hir::MutMutable, AutoBorrowMutability::Immutable => hir::MutImmutable, } } } #[derive(Copy, Clone, PartialEq, Debug, RustcEncodable, RustcDecodable)] pub enum AutoBorrow<'tcx> { /// Convert from T to &T. Ref(ty::Region<'tcx>, AutoBorrowMutability), /// Convert 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, RustcEncodable, RustcDecodable, Debug)] 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, RustcEncodable, RustcDecodable, Debug)] pub enum CustomCoerceUnsized { /// Records the index of the field being coerced. Struct(usize) }