Switch libcore array implementations to const generics.

src/libcore/array_stage0.rs

@@ -0,0 +1,295 @@
+//! Implementations of things like `Eq` for fixed-length arrays
+//! up to a certain length. Eventually we should able to generalize
+//! to all lengths.
+//!
+//! *[See also the array primitive type](../../std/primitive.array.html).*
+
+#![stable(feature = "core_array", since = "1.36.0")]
+
+use crate::borrow::{Borrow, BorrowMut};
+use crate::cmp::Ordering;
+use crate::convert::{Infallible, TryFrom};
+use crate::fmt;
+use crate::hash::{Hash, self};
+use crate::marker::Unsize;
+use crate::slice::{Iter, IterMut};
+
+/// Utility trait implemented only on arrays of fixed size
+///
+/// This trait can be used to implement other traits on fixed-size arrays
+/// without causing much metadata bloat.
+///
+/// The trait is marked unsafe in order to restrict implementors to fixed-size
+/// arrays. User of this trait can assume that implementors have the exact
+/// layout in memory of a fixed size array (for example, for unsafe
+/// initialization).
+///
+/// Note that the traits AsRef and AsMut provide similar methods for types that
+/// may not be fixed-size arrays. Implementors should prefer those traits
+/// instead.
+#[unstable(feature = "fixed_size_array", issue = "27778")]
+pub unsafe trait FixedSizeArray<T> {
+    /// Converts the array to immutable slice
+    #[unstable(feature = "fixed_size_array", issue = "27778")]
+    fn as_slice(&self) -> &[T];
+    /// Converts the array to mutable slice
+    #[unstable(feature = "fixed_size_array", issue = "27778")]
+    fn as_mut_slice(&mut self) -> &mut [T];
+}
+
+#[unstable(feature = "fixed_size_array", issue = "27778")]
+unsafe impl<T, A: Unsize<[T]>> FixedSizeArray<T> for A {
+    #[inline]
+    fn as_slice(&self) -> &[T] {
+        self
+    }
+    #[inline]
+    fn as_mut_slice(&mut self) -> &mut [T] {
+        self
+    }
+}
+
+/// The error type returned when a conversion from a slice to an array fails.
+#[stable(feature = "try_from", since = "1.34.0")]
+#[derive(Debug, Copy, Clone)]
+pub struct TryFromSliceError(());
+
+#[stable(feature = "core_array", since = "1.36.0")]
+impl fmt::Display for TryFromSliceError {
+    #[inline]
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(self.__description(), f)
+    }
+}
+
+impl TryFromSliceError {
+    #[unstable(feature = "array_error_internals",
+           reason = "available through Error trait and this method should not \
+                     be exposed publicly",
+           issue = "0")]
+    #[inline]
+    #[doc(hidden)]
+    pub fn __description(&self) -> &str {
+        "could not convert slice to array"
+    }
+}
+
+#[stable(feature = "try_from_slice_error", since = "1.36.0")]
+impl From<Infallible> for TryFromSliceError {
+    fn from(x: Infallible) -> TryFromSliceError {
+        match x {}
+    }
+}
+
+macro_rules! __impl_slice_eq1 {
+    ($Lhs: ty, $Rhs: ty) => {
+        __impl_slice_eq1! { $Lhs, $Rhs, Sized }
+    };
+    ($Lhs: ty, $Rhs: ty, $Bound: ident) => {
+        #[stable(feature = "rust1", since = "1.0.0")]
+        impl<'a, 'b, A: $Bound, B> PartialEq<$Rhs> for $Lhs where A: PartialEq<B> {
+            #[inline]
+            fn eq(&self, other: &$Rhs) -> bool { self[..] == other[..] }
+            #[inline]
+            fn ne(&self, other: &$Rhs) -> bool { self[..] != other[..] }
+        }
+    }
+}
+
+macro_rules! __impl_slice_eq2 {
+    ($Lhs: ty, $Rhs: ty) => {
+        __impl_slice_eq2! { $Lhs, $Rhs, Sized }
+    };
+    ($Lhs: ty, $Rhs: ty, $Bound: ident) => {
+        __impl_slice_eq1!($Lhs, $Rhs, $Bound);
+
+        #[stable(feature = "rust1", since = "1.0.0")]
+        impl<'a, 'b, A: $Bound, B> PartialEq<$Lhs> for $Rhs where B: PartialEq<A> {
+            #[inline]
+            fn eq(&self, other: &$Lhs) -> bool { self[..] == other[..] }
+            #[inline]
+            fn ne(&self, other: &$Lhs) -> bool { self[..] != other[..] }
+        }
+    }
+}
+
+// macro for implementing n-element array functions and operations
+macro_rules! array_impls {
+    ($($N:expr)+) => {
+        $(
+            #[stable(feature = "rust1", since = "1.0.0")]
+            impl<T> AsRef<[T]> for [T; $N] {
+                #[inline]
+                fn as_ref(&self) -> &[T] {
+                    &self[..]
+                }
+            }
+
+            #[stable(feature = "rust1", since = "1.0.0")]
+            impl<T> AsMut<[T]> for [T; $N] {
+                #[inline]
+                fn as_mut(&mut self) -> &mut [T] {
+                    &mut self[..]
+                }
+            }
+
+            #[stable(feature = "array_borrow", since = "1.4.0")]
+            impl<T> Borrow<[T]> for [T; $N] {
+                fn borrow(&self) -> &[T] {
+                    self
+                }
+            }
+
+            #[stable(feature = "array_borrow", since = "1.4.0")]
+            impl<T> BorrowMut<[T]> for [T; $N] {
+                fn borrow_mut(&mut self) -> &mut [T] {
+                    self
+                }
+            }
+
+            #[stable(feature = "try_from", since = "1.34.0")]
+            impl<T> TryFrom<&[T]> for [T; $N] where T: Copy {
+                type Error = TryFromSliceError;
+
+                fn try_from(slice: &[T]) -> Result<[T; $N], TryFromSliceError> {
+                    <&Self>::try_from(slice).map(|r| *r)
+                }
+            }
+
+            #[stable(feature = "try_from", since = "1.34.0")]
+            impl<'a, T> TryFrom<&'a [T]> for &'a [T; $N] {
+                type Error = TryFromSliceError;
+
+                fn try_from(slice: &[T]) -> Result<&[T; $N], TryFromSliceError> {
+                    if slice.len() == $N {
+                        let ptr = slice.as_ptr() as *const [T; $N];
+                        unsafe { Ok(&*ptr) }
+                    } else {
+                        Err(TryFromSliceError(()))
+                    }
+                }
+            }
+
+            #[stable(feature = "try_from", since = "1.34.0")]
+            impl<'a, T> TryFrom<&'a mut [T]> for &'a mut [T; $N] {
+                type Error = TryFromSliceError;
+
+                fn try_from(slice: &mut [T]) -> Result<&mut [T; $N], TryFromSliceError> {
+                    if slice.len() == $N {
+                        let ptr = slice.as_mut_ptr() as *mut [T; $N];
+                        unsafe { Ok(&mut *ptr) }
+                    } else {
+                        Err(TryFromSliceError(()))
+                    }
+                }
+            }
+
+            #[stable(feature = "rust1", since = "1.0.0")]
+            impl<T: Hash> Hash for [T; $N] {
+                fn hash<H: hash::Hasher>(&self, state: &mut H) {
+                    Hash::hash(&self[..], state)
+                }
+            }
+
+            #[stable(feature = "rust1", since = "1.0.0")]
+            impl<T: fmt::Debug> fmt::Debug for [T; $N] {
+                fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+                    fmt::Debug::fmt(&&self[..], f)
+                }
+            }
+
+            #[stable(feature = "rust1", since = "1.0.0")]
+            impl<'a, T> IntoIterator for &'a [T; $N] {
+                type Item = &'a T;
+                type IntoIter = Iter<'a, T>;
+
+                fn into_iter(self) -> Iter<'a, T> {
+                    self.iter()
+                }
+            }
+
+            #[stable(feature = "rust1", since = "1.0.0")]
+            impl<'a, T> IntoIterator for &'a mut [T; $N] {
+                type Item = &'a mut T;
+                type IntoIter = IterMut<'a, T>;
+
+                fn into_iter(self) -> IterMut<'a, T> {
+                    self.iter_mut()
+                }
+            }
+
+            // NOTE: some less important impls are omitted to reduce code bloat
+            __impl_slice_eq1! { [A; $N], [B; $N] }
+            __impl_slice_eq2! { [A; $N], [B] }
+            __impl_slice_eq2! { [A; $N], &'b [B] }
+            __impl_slice_eq2! { [A; $N], &'b mut [B] }
+            // __impl_slice_eq2! { [A; $N], &'b [B; $N] }
+            // __impl_slice_eq2! { [A; $N], &'b mut [B; $N] }
+
+            #[stable(feature = "rust1", since = "1.0.0")]
+            impl<T:Eq> Eq for [T; $N] { }
+
+            #[stable(feature = "rust1", since = "1.0.0")]
+            impl<T:PartialOrd> PartialOrd for [T; $N] {
+                #[inline]
+                fn partial_cmp(&self, other: &[T; $N]) -> Option<Ordering> {
+                    PartialOrd::partial_cmp(&&self[..], &&other[..])
+                }
+                #[inline]
+                fn lt(&self, other: &[T; $N]) -> bool {
+                    PartialOrd::lt(&&self[..], &&other[..])
+                }
+                #[inline]
+                fn le(&self, other: &[T; $N]) -> bool {
+                    PartialOrd::le(&&self[..], &&other[..])
+                }
+                #[inline]
+                fn ge(&self, other: &[T; $N]) -> bool {
+                    PartialOrd::ge(&&self[..], &&other[..])
+                }
+                #[inline]
+                fn gt(&self, other: &[T; $N]) -> bool {
+                    PartialOrd::gt(&&self[..], &&other[..])
+                }
+            }
+
+            #[stable(feature = "rust1", since = "1.0.0")]
+            impl<T:Ord> Ord for [T; $N] {
+                #[inline]
+                fn cmp(&self, other: &[T; $N]) -> Ordering {
+                    Ord::cmp(&&self[..], &&other[..])
+                }
+            }
+        )+
+    }
+}
+
+array_impls! {
+     0  1  2  3  4  5  6  7  8  9
+    10 11 12 13 14 15 16 17 18 19
+    20 21 22 23 24 25 26 27 28 29
+    30 31 32
+}
+
+// The Default impls cannot be generated using the array_impls! macro because
+// they require array literals.
+
+macro_rules! array_impl_default {
+    {$n:expr, $t:ident $($ts:ident)*} => {
+        #[stable(since = "1.4.0", feature = "array_default")]
+        impl<T> Default for [T; $n] where T: Default {
+            fn default() -> [T; $n] {
+                [$t::default(), $($ts::default()),*]
+            }
+        }
+        array_impl_default!{($n - 1), $($ts)*}
+    };
+    {$n:expr,} => {
+        #[stable(since = "1.4.0", feature = "array_default")]
+        impl<T> Default for [T; $n] {
+            fn default() -> [T; $n] { [] }
+        }
+    };
+}
+
+array_impl_default!{32, T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T T}

src/libcore/lib.rs

@@ -75,6 +75,7 @@
 #![feature(concat_idents)]
 #![feature(const_fn)]
 #![feature(const_fn_union)]
+#![feature(const_generics)]
 #![feature(doc_cfg)]
 #![feature(doc_spotlight)]
 #![feature(extern_types)]
@@ -189,6 +190,7 @@ pub mod borrow;
 /* Core types and methods on primitives */
 
 pub mod any;
+#[cfg_attr(stage0, path = "array_stage0.rs")]
 pub mod array;
 pub mod ascii;
 pub mod sync;

src/test/ui/const-generics/broken-mir-2.rs

@@ -1,9 +1,11 @@
+// run-pass
+
 #![feature(const_generics)]
 //~^ WARN the feature `const_generics` is incomplete and may cause the compiler to crash
 
 use std::fmt::Debug;
 
 #[derive(Debug)]
-struct S<T: Debug, const N: usize>([T; N]); //~ ERROR `[T; _]` doesn't implement `std::fmt::Debug`
+struct S<T: Debug, const N: usize>([T; N]);
 
 fn main() {}

src/test/ui/const-generics/broken-mir-2.stderr

@@ -1,19 +1,6 @@
 warning: the feature `const_generics` is incomplete and may cause the compiler to crash
-  --> $DIR/broken-mir-2.rs:1:12
+  --> $DIR/broken-mir-2.rs:3:12
    |
 LL | #![feature(const_generics)]
    |            ^^^^^^^^^^^^^^
 
-error[E0277]: `[T; _]` doesn't implement `std::fmt::Debug`
-  --> $DIR/broken-mir-2.rs:7:36
-   |
-LL | struct S<T: Debug, const N: usize>([T; N]);
-   |                                    ^^^^^^ `[T; _]` cannot be formatted using `{:?}` because it doesn't implement `std::fmt::Debug`
-   |
-   = help: the trait `std::fmt::Debug` is not implemented for `[T; _]`
-   = note: required because of the requirements on the impl of `std::fmt::Debug` for `&[T; _]`
-   = note: required for the cast to the object type `dyn std::fmt::Debug`
-
-error: aborting due to previous error
-
-For more information about this error, try `rustc --explain E0277`.