1 // Copyright 2012-2015 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 pub use self::AutoAdjustment::*;
12 pub use self::AutoRef::*;
14 use middle::ty::{self, Ty, TypeAndMut, TypeFoldable};
15 use middle::ty::LvaluePreference::{NoPreference};
18 use syntax::codemap::Span;
22 #[derive(Copy, Clone)]
23 pub enum AutoAdjustment<'tcx> {
24 AdjustReifyFnPointer, // go from a fn-item type to a fn-pointer type
25 AdjustUnsafeFnPointer, // go from a safe fn pointer to an unsafe fn pointer
26 AdjustDerefRef(AutoDerefRef<'tcx>),
29 /// Represents coercing a pointer to a different kind of pointer - where 'kind'
30 /// here means either or both of raw vs borrowed vs unique and fat vs thin.
32 /// We transform pointers by following the following steps in order:
33 /// 1. Deref the pointer `self.autoderefs` times (may be 0).
34 /// 2. If `autoref` is `Some(_)`, then take the address and produce either a
35 /// `&` or `*` pointer.
36 /// 3. If `unsize` is `Some(_)`, then apply the unsize transformation,
37 /// which will do things like convert thin pointers to fat
38 /// pointers, or convert structs containing thin pointers to
39 /// structs containing fat pointers, or convert between fat
40 /// pointers. We don't store the details of how the transform is
41 /// done (in fact, we don't know that, because it might depend on
42 /// the precise type parameters). We just store the target
43 /// type. Trans figures out what has to be done at monomorphization
44 /// time based on the precise source/target type at hand.
46 /// To make that more concrete, here are some common scenarios:
48 /// 1. The simplest cases are where the pointer is not adjusted fat vs thin.
49 /// Here the pointer will be dereferenced N times (where a dereference can
50 /// happen to raw or borrowed pointers or any smart pointer which implements
51 /// Deref, including Box<_>). The number of dereferences is given by
52 /// `autoderefs`. It can then be auto-referenced zero or one times, indicated
53 /// by `autoref`, to either a raw or borrowed pointer. In these cases unsize is
56 /// 2. A thin-to-fat coercon involves unsizing the underlying data. We start
57 /// with a thin pointer, deref a number of times, unsize the underlying data,
58 /// then autoref. The 'unsize' phase may change a fixed length array to a
59 /// dynamically sized one, a concrete object to a trait object, or statically
60 /// sized struct to a dyncamically sized one. E.g., &[i32; 4] -> &[i32] is
65 /// autoderefs: 1, // &[i32; 4] -> [i32; 4]
66 /// autoref: Some(AutoPtr), // [i32] -> &[i32]
67 /// unsize: Some([i32]), // [i32; 4] -> [i32]
71 /// Note that for a struct, the 'deep' unsizing of the struct is not recorded.
72 /// E.g., `struct Foo<T> { x: T }` we can coerce &Foo<[i32; 4]> to &Foo<[i32]>
73 /// The autoderef and -ref are the same as in the above example, but the type
74 /// stored in `unsize` is `Foo<[i32]>`, we don't store any further detail about
75 /// the underlying conversions from `[i32; 4]` to `[i32]`.
77 /// 3. Coercing a `Box<T>` to `Box<Trait>` is an interesting special case. In
78 /// that case, we have the pointer we need coming in, so there are no
79 /// autoderefs, and no autoref. Instead we just do the `Unsize` transformation.
80 /// At some point, of course, `Box` should move out of the compiler, in which
81 /// case this is analogous to transformating a struct. E.g., Box<[i32; 4]> ->
82 /// Box<[i32]> is represented by:
88 /// unsize: Some(Box<[i32]>),
91 #[derive(Copy, Clone)]
92 pub struct AutoDerefRef<'tcx> {
93 /// Step 1. Apply a number of dereferences, producing an lvalue.
94 pub autoderefs: usize,
96 /// Step 2. Optionally produce a pointer/reference from the value.
97 pub autoref: Option<AutoRef<'tcx>>,
99 /// Step 3. Unsize a pointer/reference value, e.g. `&[T; n]` to
100 /// `&[T]`. The stored type is the target pointer type. Note that
101 /// the source could be a thin or fat pointer.
102 pub unsize: Option<Ty<'tcx>>,
105 impl<'tcx> AutoAdjustment<'tcx> {
106 pub fn is_identity(&self) -> bool {
108 AdjustReifyFnPointer |
109 AdjustUnsafeFnPointer => false,
110 AdjustDerefRef(ref r) => r.is_identity(),
114 impl<'tcx> AutoDerefRef<'tcx> {
115 pub fn is_identity(&self) -> bool {
116 self.autoderefs == 0 && self.unsize.is_none() && self.autoref.is_none()
121 #[derive(Copy, Clone, PartialEq, Debug)]
122 pub enum AutoRef<'tcx> {
123 /// Convert from T to &T.
124 AutoPtr(&'tcx ty::Region, hir::Mutability),
126 /// Convert from T to *T.
127 /// Value to thin pointer.
128 AutoUnsafe(hir::Mutability),
131 #[derive(Clone, Copy, RustcEncodable, RustcDecodable, Debug)]
132 pub enum CustomCoerceUnsized {
133 /// Records the index of the field being coerced.
137 impl<'tcx> ty::TyS<'tcx> {
138 /// See `expr_ty_adjusted`
139 pub fn adjust<F>(&'tcx self, cx: &ty::ctxt<'tcx>,
141 expr_id: ast::NodeId,
142 adjustment: Option<&AutoAdjustment<'tcx>>,
145 F: FnMut(ty::MethodCall) -> Option<Ty<'tcx>>,
147 if let ty::TyError = self.sty {
151 return match adjustment {
152 Some(adjustment) => {
154 AdjustReifyFnPointer => {
156 ty::TyBareFn(Some(_), b) => {
161 &format!("AdjustReifyFnPointer adjustment on non-fn-item: \
167 AdjustUnsafeFnPointer => {
169 ty::TyBareFn(None, b) => cx.safe_to_unsafe_fn_ty(b),
172 &format!("AdjustReifyFnPointer adjustment on non-fn-item: \
179 AdjustDerefRef(ref adj) => {
180 let mut adjusted_ty = self;
182 if !adjusted_ty.references_error() {
183 for i in 0..adj.autoderefs {
185 adjusted_ty.adjust_for_autoderef(cx,
193 if let Some(target) = adj.unsize {
196 adjusted_ty.adjust_for_autoref(cx, adj.autoref)
205 pub fn adjust_for_autoderef<F>(&'tcx self,
207 expr_id: ast::NodeId,
209 autoderef: u32, // how many autoderefs so far?
212 F: FnMut(ty::MethodCall) -> Option<Ty<'tcx>>,
214 let method_call = ty::MethodCall::autoderef(expr_id, autoderef);
215 let mut adjusted_ty = self;
216 if let Some(method_ty) = method_type(method_call) {
217 // Method calls always have all late-bound regions
218 // fully instantiated.
219 let fn_ret = cx.no_late_bound_regions(&method_ty.fn_ret()).unwrap();
220 adjusted_ty = fn_ret.unwrap();
222 match adjusted_ty.builtin_deref(true, NoPreference) {
227 &format!("the {}th autoderef failed: {}",
235 pub fn adjust_for_autoref(&'tcx self, cx: &ty::ctxt<'tcx>,
236 autoref: Option<AutoRef<'tcx>>)
240 Some(AutoPtr(r, m)) => {
241 cx.mk_ref(r, TypeAndMut { ty: self, mutbl: m })
243 Some(AutoUnsafe(m)) => {
244 cx.mk_ptr(TypeAndMut { ty: self, mutbl: m })