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};
15 use middle::ty::HasTypeFlags;
16 use middle::ty::LvaluePreference::{NoPreference};
19 use syntax::codemap::Span;
23 #[derive(Copy, Clone)]
24 pub enum AutoAdjustment<'tcx> {
25 AdjustReifyFnPointer, // go from a fn-item type to a fn-pointer type
26 AdjustUnsafeFnPointer, // go from a safe fn pointer to an unsafe fn pointer
27 AdjustDerefRef(AutoDerefRef<'tcx>),
30 /// Represents coercing a pointer to a different kind of pointer - where 'kind'
31 /// here means either or both of raw vs borrowed vs unique and fat vs thin.
33 /// We transform pointers by following the following steps in order:
34 /// 1. Deref the pointer `self.autoderefs` times (may be 0).
35 /// 2. If `autoref` is `Some(_)`, then take the address and produce either a
36 /// `&` or `*` pointer.
37 /// 3. If `unsize` is `Some(_)`, then apply the unsize transformation,
38 /// which will do things like convert thin pointers to fat
39 /// pointers, or convert structs containing thin pointers to
40 /// structs containing fat pointers, or convert between fat
41 /// pointers. We don't store the details of how the transform is
42 /// done (in fact, we don't know that, because it might depend on
43 /// the precise type parameters). We just store the target
44 /// type. Trans figures out what has to be done at monomorphization
45 /// time based on the precise source/target type at hand.
47 /// To make that more concrete, here are some common scenarios:
49 /// 1. The simplest cases are where the pointer is not adjusted fat vs thin.
50 /// Here the pointer will be dereferenced N times (where a dereference can
51 /// happen to to raw or borrowed pointers or any smart pointer which implements
52 /// Deref, including Box<_>). The number of dereferences is given by
53 /// `autoderefs`. It can then be auto-referenced zero or one times, indicated
54 /// by `autoref`, to either a raw or borrowed pointer. In these cases unsize is
57 /// 2. A thin-to-fat coercon involves unsizing the underlying data. We start
58 /// with a thin pointer, deref a number of times, unsize the underlying data,
59 /// then autoref. The 'unsize' phase may change a fixed length array to a
60 /// dynamically sized one, a concrete object to a trait object, or statically
61 /// sized struct to a dyncamically sized one. E.g., &[i32; 4] -> &[i32] is
66 /// autoderefs: 1, // &[i32; 4] -> [i32; 4]
67 /// autoref: Some(AutoPtr), // [i32] -> &[i32]
68 /// unsize: Some([i32]), // [i32; 4] -> [i32]
72 /// Note that for a struct, the 'deep' unsizing of the struct is not recorded.
73 /// E.g., `struct Foo<T> { x: T }` we can coerce &Foo<[i32; 4]> to &Foo<[i32]>
74 /// The autoderef and -ref are the same as in the above example, but the type
75 /// stored in `unsize` is `Foo<[i32]>`, we don't store any further detail about
76 /// the underlying conversions from `[i32; 4]` to `[i32]`.
78 /// 3. Coercing a `Box<T>` to `Box<Trait>` is an interesting special case. In
79 /// that case, we have the pointer we need coming in, so there are no
80 /// autoderefs, and no autoref. Instead we just do the `Unsize` transformation.
81 /// At some point, of course, `Box` should move out of the compiler, in which
82 /// case this is analogous to transformating a struct. E.g., Box<[i32; 4]> ->
83 /// Box<[i32]> is represented by:
89 /// unsize: Some(Box<[i32]>),
92 #[derive(Copy, Clone)]
93 pub struct AutoDerefRef<'tcx> {
94 /// Step 1. Apply a number of dereferences, producing an lvalue.
95 pub autoderefs: usize,
97 /// Step 2. Optionally produce a pointer/reference from the value.
98 pub autoref: Option<AutoRef<'tcx>>,
100 /// Step 3. Unsize a pointer/reference value, e.g. `&[T; n]` to
101 /// `&[T]`. The stored type is the target pointer type. Note that
102 /// the source could be a thin or fat pointer.
103 pub unsize: Option<Ty<'tcx>>,
106 impl<'tcx> AutoAdjustment<'tcx> {
107 pub fn is_identity(&self) -> bool {
109 AdjustReifyFnPointer |
110 AdjustUnsafeFnPointer => false,
111 AdjustDerefRef(ref r) => r.is_identity(),
115 impl<'tcx> AutoDerefRef<'tcx> {
116 pub fn is_identity(&self) -> bool {
117 self.autoderefs == 0 && self.unsize.is_none() && self.autoref.is_none()
122 #[derive(Copy, Clone, PartialEq, Debug)]
123 pub enum AutoRef<'tcx> {
124 /// Convert from T to &T.
125 AutoPtr(&'tcx ty::Region, hir::Mutability),
127 /// Convert from T to *T.
128 /// Value to thin pointer.
129 AutoUnsafe(hir::Mutability),
132 #[derive(Clone, Copy, RustcEncodable, RustcDecodable, Debug)]
133 pub enum CustomCoerceUnsized {
134 /// Records the index of the field being coerced.
138 impl<'tcx> ty::TyS<'tcx> {
139 /// See `expr_ty_adjusted`
140 pub fn adjust<F>(&'tcx self, cx: &ty::ctxt<'tcx>,
142 expr_id: ast::NodeId,
143 adjustment: Option<&AutoAdjustment<'tcx>>,
146 F: FnMut(ty::MethodCall) -> Option<Ty<'tcx>>,
148 if let ty::TyError = self.sty {
152 return match adjustment {
153 Some(adjustment) => {
155 AdjustReifyFnPointer => {
157 ty::TyBareFn(Some(_), b) => {
162 &format!("AdjustReifyFnPointer adjustment on non-fn-item: \
168 AdjustUnsafeFnPointer => {
170 ty::TyBareFn(None, b) => cx.safe_to_unsafe_fn_ty(b),
173 &format!("AdjustReifyFnPointer adjustment on non-fn-item: \
180 AdjustDerefRef(ref adj) => {
181 let mut adjusted_ty = self;
183 if !adjusted_ty.references_error() {
184 for i in 0..adj.autoderefs {
186 adjusted_ty.adjust_for_autoderef(cx,
194 if let Some(target) = adj.unsize {
197 adjusted_ty.adjust_for_autoref(cx, adj.autoref)
206 pub fn adjust_for_autoderef<F>(&'tcx self,
208 expr_id: ast::NodeId,
210 autoderef: u32, // how many autoderefs so far?
213 F: FnMut(ty::MethodCall) -> Option<Ty<'tcx>>,
215 let method_call = ty::MethodCall::autoderef(expr_id, autoderef);
216 let mut adjusted_ty = self;
217 if let Some(method_ty) = method_type(method_call) {
218 // Method calls always have all late-bound regions
219 // fully instantiated.
220 let fn_ret = cx.no_late_bound_regions(&method_ty.fn_ret()).unwrap();
221 adjusted_ty = fn_ret.unwrap();
223 match adjusted_ty.builtin_deref(true, NoPreference) {
228 &format!("the {}th autoderef failed: {}",
236 pub fn adjust_for_autoref(&'tcx self, cx: &ty::ctxt<'tcx>,
237 autoref: Option<AutoRef<'tcx>>)
241 Some(AutoPtr(r, m)) => {
242 cx.mk_ref(r, TypeAndMut { ty: self, mutbl: m })
244 Some(AutoUnsafe(m)) => {
245 cx.mk_ptr(TypeAndMut { ty: self, mutbl: m })