vendor/rustc-ap-rustc_ast/src/ptr.rs

   1 //! The AST pointer.
   2 //!
   3 //! Provides `P<T>`, a frozen owned smart pointer.
   4 //!
   5 //! # Motivations and benefits
   6 //!
   7 //! * **Identity**: sharing AST nodes is problematic for the various analysis
   8 //!   passes (e.g., one may be able to bypass the borrow checker with a shared
   9 //!   `ExprKind::AddrOf` node taking a mutable borrow).
  10 //!
  11 //! * **Immutability**: `P<T>` disallows mutating its inner `T`, unlike `Box<T>`
  12 //!   (unless it contains an `Unsafe` interior, but that may be denied later).
  13 //!   This mainly prevents mistakes, but can also enforces a kind of "purity".
  14 //!
  15 //! * **Efficiency**: folding can reuse allocation space for `P<T>` and `Vec<T>`,
  16 //!   the latter even when the input and output types differ (as it would be the
  17 //!   case with arenas or a GADT AST using type parameters to toggle features).
  18 //!
  19 //! * **Maintainability**: `P<T>` provides a fixed interface - `Deref`,
  20 //!   `and_then` and `map` - which can remain fully functional even if the
  21 //!   implementation changes (using a special thread-local heap, for example).
  22 //!   Moreover, a switch to, e.g., `P<'a, T>` would be easy and mostly automated.
  23
  24 use std::fmt::{self, Debug, Display};
  25 use std::iter::FromIterator;
  26 use std::ops::{Deref, DerefMut};
  27 use std::{slice, vec};
  28
  29 use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
  30
  31 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
  32 /// An owned smart pointer.
  33 pub struct P<T: ?Sized> {
  34     ptr: Box<T>,
  35 }
  36
  37 /// Construct a `P<T>` from a `T` value.
  38 #[allow(non_snake_case)]
  39 pub fn P<T: 'static>(value: T) -> P<T> {
  40     P { ptr: box value }
  41 }
  42
  43 impl<T: 'static> P<T> {
  44     /// Move out of the pointer.
  45     /// Intended for chaining transformations not covered by `map`.
  46     pub fn and_then<U, F>(self, f: F) -> U
  47     where
  48         F: FnOnce(T) -> U,
  49     {
  50         f(*self.ptr)
  51     }
  52
  53     /// Equivalent to `and_then(|x| x)`.
  54     pub fn into_inner(self) -> T {
  55         *self.ptr
  56     }
  57
  58     /// Produce a new `P<T>` from `self` without reallocating.
  59     pub fn map<F>(mut self, f: F) -> P<T>
  60     where
  61         F: FnOnce(T) -> T,
  62     {
  63         let x = f(*self.ptr);
  64         *self.ptr = x;
  65
  66         self
  67     }
  68
  69     /// Optionally produce a new `P<T>` from `self` without reallocating.
  70     pub fn filter_map<F>(mut self, f: F) -> Option<P<T>>
  71     where
  72         F: FnOnce(T) -> Option<T>,
  73     {
  74         *self.ptr = f(*self.ptr)?;
  75         Some(self)
  76     }
  77 }
  78
  79 impl<T: ?Sized> Deref for P<T> {
  80     type Target = T;
  81
  82     fn deref(&self) -> &T {
  83         &self.ptr
  84     }
  85 }
  86
  87 impl<T: ?Sized> DerefMut for P<T> {
  88     fn deref_mut(&mut self) -> &mut T {
  89         &mut self.ptr
  90     }
  91 }
  92
  93 impl<T: 'static + Clone> Clone for P<T> {
  94     fn clone(&self) -> P<T> {
  95         P((**self).clone())
  96     }
  97 }
  98
  99 impl<T: ?Sized + Debug> Debug for P<T> {
 100     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 101         Debug::fmt(&self.ptr, f)
 102     }
 103 }
 104
 105 impl<T: Display> Display for P<T> {
 106     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 107         Display::fmt(&**self, f)
 108     }
 109 }
 110
 111 impl<T> fmt::Pointer for P<T> {
 112     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 113         fmt::Pointer::fmt(&self.ptr, f)
 114     }
 115 }
 116
 117 impl<D: Decoder, T: 'static + Decodable<D>> Decodable<D> for P<T> {
 118     fn decode(d: &mut D) -> Result<P<T>, D::Error> {
 119         Decodable::decode(d).map(P)
 120     }
 121 }
 122
 123 impl<S: Encoder, T: Encodable<S>> Encodable<S> for P<T> {
 124     fn encode(&self, s: &mut S) -> Result<(), S::Error> {
 125         (**self).encode(s)
 126     }
 127 }
 128
 129 impl<T> P<[T]> {
 130     pub const fn new() -> P<[T]> {
 131         // HACK(eddyb) bypass the lack of a `const fn` to create an empty `Box<[T]>`
 132         // (as trait methods, `default` in this case, can't be `const fn` yet).
 133         P {
 134             ptr: unsafe {
 135                 use std::ptr::NonNull;
 136                 std::mem::transmute(NonNull::<[T; 0]>::dangling() as NonNull<[T]>)
 137             },
 138         }
 139     }
 140
 141     #[inline(never)]
 142     pub fn from_vec(v: Vec<T>) -> P<[T]> {
 143         P { ptr: v.into_boxed_slice() }
 144     }
 145
 146     #[inline(never)]
 147     pub fn into_vec(self) -> Vec<T> {
 148         self.ptr.into_vec()
 149     }
 150 }
 151
 152 impl<T> Default for P<[T]> {
 153     /// Creates an empty `P<[T]>`.
 154     fn default() -> P<[T]> {
 155         P::new()
 156     }
 157 }
 158
 159 impl<T: Clone> Clone for P<[T]> {
 160     fn clone(&self) -> P<[T]> {
 161         P::from_vec(self.to_vec())
 162     }
 163 }
 164
 165 impl<T> From<Vec<T>> for P<[T]> {
 166     fn from(v: Vec<T>) -> Self {
 167         P::from_vec(v)
 168     }
 169 }
 170
 171 impl<T> Into<Vec<T>> for P<[T]> {
 172     fn into(self) -> Vec<T> {
 173         self.into_vec()
 174     }
 175 }
 176
 177 impl<T> FromIterator<T> for P<[T]> {
 178     fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> P<[T]> {
 179         P::from_vec(iter.into_iter().collect())
 180     }
 181 }
 182
 183 impl<T> IntoIterator for P<[T]> {
 184     type Item = T;
 185     type IntoIter = vec::IntoIter<T>;
 186
 187     fn into_iter(self) -> Self::IntoIter {
 188         self.into_vec().into_iter()
 189     }
 190 }
 191
 192 impl<'a, T> IntoIterator for &'a P<[T]> {
 193     type Item = &'a T;
 194     type IntoIter = slice::Iter<'a, T>;
 195     fn into_iter(self) -> Self::IntoIter {
 196         self.ptr.into_iter()
 197     }
 198 }
 199
 200 impl<S: Encoder, T: Encodable<S>> Encodable<S> for P<[T]> {
 201     fn encode(&self, s: &mut S) -> Result<(), S::Error> {
 202         Encodable::encode(&**self, s)
 203     }
 204 }
 205
 206 impl<D: Decoder, T: Decodable<D>> Decodable<D> for P<[T]> {
 207     fn decode(d: &mut D) -> Result<P<[T]>, D::Error> {
 208         Ok(P::from_vec(Decodable::decode(d)?))
 209     }
 210 }
 211
 212 impl<CTX, T> HashStable<CTX> for P<T>
 213 where
 214     T: ?Sized + HashStable<CTX>,
 215 {
 216     fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
 217         (**self).hash_stable(hcx, hasher);
 218     }
 219 }