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 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191
// 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 ty::{self, Ty, TyCtxt, TypeAndMut}; use ty::LvaluePreference::{NoPreference}; use syntax::ast; use syntax_pos::Span; use hir; #[derive(Copy, Clone, RustcEncodable, RustcDecodable)] pub struct Adjustment<'tcx> { pub kind: Adjust<'tcx>, pub target: Ty<'tcx> } #[derive(Copy, 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, /// Represents coercing a pointer to a different kind of pointer - where 'kind' /// here means either or both of raw vs borrowed vs unique and fat vs thin. /// /// We transform pointers by following the following steps in order: /// 1. Deref the pointer `self.autoderefs` times (may be 0). /// 2. If `autoref` is `Some(_)`, then take the address and produce either a /// `&` or `*` pointer. /// 3. If `unsize` is `Some(_)`, then apply the unsize transformation, /// which 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. Trans figures out what has to be done at monomorphization /// time based on the precise source/target type at hand. /// /// To make that more concrete, here are some common scenarios: /// /// 1. The simplest cases are where the 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 number 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 /// None. /// /// 2. A thin-to-fat coercon 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 dyncamically sized one. E.g., &[i32; 4] -> &[i32] is /// represented by: /// /// ``` /// Adjust::DerefRef { /// autoderefs: 1, // &[i32; 4] -> [i32; 4] /// autoref: Some(AutoBorrow::Ref), // [i32] -> &[i32] /// unsize: Some([i32]), // [i32; 4] -> [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 transformating a struct. E.g., Box<[i32; 4]> -> /// Box<[i32]> is represented by: /// /// ``` /// Adjust::DerefRef { /// autoderefs: 0, /// autoref: None, /// unsize: Some(Box<[i32]>), /// } /// ``` DerefRef { /// Step 1. Apply a number of dereferences, producing an lvalue. autoderefs: usize, /// Step 2. Optionally produce a pointer/reference from the value. autoref: Option<AutoBorrow<'tcx>>, /// Step 3. Unsize a pointer/reference value, e.g. `&[T; n]` to /// `&[T]`. Note that the source could be a thin or fat pointer. unsize: bool, } } impl<'tcx> Adjustment<'tcx> { pub fn is_identity(&self) -> bool { match self.kind { Adjust::NeverToAny => self.target.is_never(), Adjust::DerefRef { autoderefs: 0, autoref: None, unsize: false } => true, Adjust::ReifyFnPointer | Adjust::UnsafeFnPointer | Adjust::ClosureFnPointer | Adjust::MutToConstPointer | Adjust::DerefRef {..} => false, } } } #[derive(Copy, Clone, PartialEq, Debug, RustcEncodable, RustcDecodable)] pub enum AutoBorrow<'tcx> { /// Convert from T to &T. Ref(&'tcx ty::Region, hir::Mutability), /// Convert from T to *T. RawPtr(hir::Mutability), } #[derive(Clone, Copy, RustcEncodable, RustcDecodable, Debug)] pub enum CustomCoerceUnsized { /// Records the index of the field being coerced. Struct(usize) } impl<'a, 'gcx, 'tcx> ty::TyS<'tcx> { pub fn adjust_for_autoderef<F>(&'tcx self, tcx: TyCtxt<'a, 'gcx, 'tcx>, expr_id: ast::NodeId, expr_span: Span, autoderef: u32, // how many autoderefs so far? mut method_type: F) -> Ty<'tcx> where F: FnMut(ty::MethodCall) -> Option<Ty<'tcx>>, { let method_call = ty::MethodCall::autoderef(expr_id, autoderef); let mut adjusted_ty = self; if let Some(method_ty) = method_type(method_call) { // Method calls always have all late-bound regions // fully instantiated. adjusted_ty = tcx.no_late_bound_regions(&method_ty.fn_ret()).unwrap(); } match adjusted_ty.builtin_deref(true, NoPreference) { Some(mt) => mt.ty, None => { span_bug!( expr_span, "the {}th autoderef for {} failed: {}", autoderef, expr_id, adjusted_ty); } } } pub fn adjust_for_autoref(&'tcx self, tcx: TyCtxt<'a, 'gcx, 'tcx>, autoref: Option<AutoBorrow<'tcx>>) -> Ty<'tcx> { match autoref { None => self, Some(AutoBorrow::Ref(r, m)) => { tcx.mk_ref(r, TypeAndMut { ty: self, mutbl: m }) } Some(AutoBorrow::RawPtr(m)) => { tcx.mk_ptr(TypeAndMut { ty: self, mutbl: m }) } } } }