Remove some unsound specializations

src/libcore/iter/range.rs

@@ -385,12 +385,14 @@ impl<A: Step> Iterator for ops::RangeInclusive<A> {
                 }
                 Some(Equal) => {
                     self.is_empty = Some(true);
+                    self.start = plus_n.clone();
                     return Some(plus_n);
                 }
                 _ => {}
             }
         }
 
+        self.start = self.end.clone();
         self.is_empty = Some(true);
         None
     }
@@ -477,12 +479,14 @@ impl<A: Step> DoubleEndedIterator for ops::RangeInclusive<A> {
                 }
                 Some(Equal) => {
                     self.is_empty = Some(true);
+                    self.end = minus_n.clone();
                     return Some(minus_n);
                 }
                 _ => {}
             }
         }
 
+        self.end = self.start.clone();
         self.is_empty = Some(true);
         None
     }

src/libcore/ops/range.rs

@@ -343,38 +343,21 @@ pub struct RangeInclusive<Idx> {
     pub(crate) is_empty: Option<bool>,
     // This field is:
     //  - `None` when next() or next_back() was never called
-    //  - `Some(false)` when `start <= end` assuming no overflow
-    //  - `Some(true)` otherwise
+    //  - `Some(false)` when `start < end`
+    //  - `Some(true)` when `end < start`
+    //  - `Some(false)` when `start == end` and the range hasn't yet completed iteration
+    //  - `Some(true)` when `start == end` and the range has completed iteration
     // The field cannot be a simple `bool` because the `..=` constructor can
     // accept non-PartialOrd types, also we want the constructor to be const.
 }
 
-trait RangeInclusiveEquality: Sized {
-    fn canonicalized_is_empty(range: &RangeInclusive<Self>) -> bool;
-}
-
-impl<T> RangeInclusiveEquality for T {
-    #[inline]
-    default fn canonicalized_is_empty(range: &RangeInclusive<Self>) -> bool {
-        range.is_empty.unwrap_or_default()
-    }
-}
-
-impl<T: PartialOrd> RangeInclusiveEquality for T {
-    #[inline]
-    fn canonicalized_is_empty(range: &RangeInclusive<Self>) -> bool {
-        range.is_empty()
-    }
-}
-
 #[stable(feature = "inclusive_range", since = "1.26.0")]
 impl<Idx: PartialEq> PartialEq for RangeInclusive<Idx> {
     #[inline]
     fn eq(&self, other: &Self) -> bool {
         self.start == other.start
             && self.end == other.end
-            && RangeInclusiveEquality::canonicalized_is_empty(self)
-                == RangeInclusiveEquality::canonicalized_is_empty(other)
+            && self.is_exhausted() == other.is_exhausted()
     }
 }
 
@@ -386,7 +369,8 @@ impl<Idx: Hash> Hash for RangeInclusive<Idx> {
     fn hash<H: Hasher>(&self, state: &mut H) {
         self.start.hash(state);
         self.end.hash(state);
-        RangeInclusiveEquality::canonicalized_is_empty(self).hash(state);
+        // Ideally we would hash `is_exhausted` here as well, but there's no
+        // way for us to call it.
     }
 }
 
@@ -485,6 +469,14 @@ impl<Idx: fmt::Debug> fmt::Debug for RangeInclusive<Idx> {
     }
 }
 
+impl<Idx: PartialEq<Idx>> RangeInclusive<Idx> {
+    // Returns true if this is a range that started non-empty, and was iterated
+    // to exhaustion.
+    fn is_exhausted(&self) -> bool {
+        Some(true) == self.is_empty && self.start == self.end
+    }
+}
+
 impl<Idx: PartialOrd<Idx>> RangeInclusive<Idx> {
     /// Returns `true` if `item` is contained in the range.
     ///

src/libcore/slice/mod.rs

@@ -5584,21 +5584,18 @@ where
 
 #[doc(hidden)]
 // intermediate trait for specialization of slice's PartialOrd
-trait SlicePartialOrd<B> {
-    fn partial_compare(&self, other: &[B]) -> Option<Ordering>;
+trait SlicePartialOrd: Sized {
+    fn partial_compare(left: &[Self], right: &[Self]) -> Option<Ordering>;
 }
 
-impl<A> SlicePartialOrd<A> for [A]
-where
-    A: PartialOrd,
-{
-    default fn partial_compare(&self, other: &[A]) -> Option<Ordering> {
-        let l = cmp::min(self.len(), other.len());
+impl<A: PartialOrd> SlicePartialOrd for A {
+    default fn partial_compare(left: &[A], right: &[A]) -> Option<Ordering> {
+        let l = cmp::min(left.len(), right.len());
 
         // Slice to the loop iteration range to enable bound check
         // elimination in the compiler
-        let lhs = &self[..l];
-        let rhs = &other[..l];
+        let lhs = &left[..l];
+        let rhs = &right[..l];
 
         for i in 0..l {
             match lhs[i].partial_cmp(&rhs[i]) {
@@ -5607,36 +5604,61 @@ where
             }
         }
 
-        self.len().partial_cmp(&other.len())
+        left.len().partial_cmp(&right.len())
     }
 }
 
-impl<A> SlicePartialOrd<A> for [A]
+// This is the impl that we would like to have. Unfortunately it's not sound.
+// See `partial_ord_slice.rs`.
+/*
+impl<A> SlicePartialOrd for A
 where
     A: Ord,
 {
-    default fn partial_compare(&self, other: &[A]) -> Option<Ordering> {
-        Some(SliceOrd::compare(self, other))
+    default fn partial_compare(left: &[A], right: &[A]) -> Option<Ordering> {
+        Some(SliceOrd::compare(left, right))
+    }
+}
+*/
+
+impl<A: AlwaysApplicableOrd> SlicePartialOrd for A {
+    fn partial_compare(left: &[A], right: &[A]) -> Option<Ordering> {
+        Some(SliceOrd::compare(left, right))
+    }
+}
+
+trait AlwaysApplicableOrd: SliceOrd + Ord {}
+
+macro_rules! always_applicable_ord {
+    ($([$($p:tt)*] $t:ty,)*) => {
+        $(impl<$($p)*> AlwaysApplicableOrd for $t {})*
     }
 }
 
+always_applicable_ord! {
+    [] u8, [] u16, [] u32, [] u64, [] u128, [] usize,
+    [] i8, [] i16, [] i32, [] i64, [] i128, [] isize,
+    [] bool, [] char,
+    [T: ?Sized] *const T, [T: ?Sized] *mut T,
+    [T: AlwaysApplicableOrd] &T,
+    [T: AlwaysApplicableOrd] &mut T,
+    [T: AlwaysApplicableOrd] Option<T>,
+}
+
 #[doc(hidden)]
 // intermediate trait for specialization of slice's Ord
-trait SliceOrd<B> {
-    fn compare(&self, other: &[B]) -> Ordering;
+trait SliceOrd: Sized {
+    fn compare(left: &[Self], right: &[Self]) -> Ordering;
 }
 
-impl<A> SliceOrd<A> for [A]
-where
-    A: Ord,
-{
-    default fn compare(&self, other: &[A]) -> Ordering {
-        let l = cmp::min(self.len(), other.len());
+impl<A: Ord> SliceOrd for A {
+    default fn compare(left: &[Self], right: &[Self]) -> Ordering {
+        let l = cmp::min(left.len(), right.len());
 
         // Slice to the loop iteration range to enable bound check
         // elimination in the compiler
-        let lhs = &self[..l];
-        let rhs = &other[..l];
+        let lhs = &left[..l];
+        let rhs = &right[..l];
 
         for i in 0..l {
             match lhs[i].cmp(&rhs[i]) {
@@ -5645,19 +5667,19 @@ where
             }
         }
 
-        self.len().cmp(&other.len())
+        left.len().cmp(&right.len())
     }
 }
 
 // memcmp compares a sequence of unsigned bytes lexicographically.
 // this matches the order we want for [u8], but no others (not even [i8]).
-impl SliceOrd<u8> for [u8] {
+impl SliceOrd for u8 {
     #[inline]
-    fn compare(&self, other: &[u8]) -> Ordering {
+    fn compare(left: &[Self], right: &[Self]) -> Ordering {
         let order =
-            unsafe { memcmp(self.as_ptr(), other.as_ptr(), cmp::min(self.len(), other.len())) };
+            unsafe { memcmp(left.as_ptr(), right.as_ptr(), cmp::min(left.len(), right.len())) };
         if order == 0 {
-            self.len().cmp(&other.len())
+            left.len().cmp(&right.len())
         } else if order < 0 {
             Less
         } else {

src/libcore/str/mod.rs

@@ -12,7 +12,7 @@ use self::pattern::{DoubleEndedSearcher, ReverseSearcher, SearchStep, Searcher};
 use crate::char;
 use crate::fmt::{self, Write};
 use crate::iter::{Chain, FlatMap, Flatten};
-use crate::iter::{Cloned, Filter, FusedIterator, Map, TrustedLen, TrustedRandomAccess};
+use crate::iter::{Copied, Filter, FusedIterator, Map, TrustedLen, TrustedRandomAccess};
 use crate::mem;
 use crate::ops::Try;
 use crate::option;
@@ -750,7 +750,7 @@ impl<'a> CharIndices<'a> {
 /// [`str`]: ../../std/primitive.str.html
 #[stable(feature = "rust1", since = "1.0.0")]
 #[derive(Clone, Debug)]
-pub struct Bytes<'a>(Cloned<slice::Iter<'a, u8>>);
+pub struct Bytes<'a>(Copied<slice::Iter<'a, u8>>);
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl Iterator for Bytes<'_> {
@@ -2778,7 +2778,7 @@ impl str {
     #[stable(feature = "rust1", since = "1.0.0")]
     #[inline]
     pub fn bytes(&self) -> Bytes<'_> {
-        Bytes(self.as_bytes().iter().cloned())
+        Bytes(self.as_bytes().iter().copied())
     }
 
     /// Splits a string slice by whitespace.
@@ -3895,7 +3895,7 @@ impl str {
             debug_assert_eq!(
                 start, 0,
                 "The first search step from Searcher \
-                must include the first character"
+                 must include the first character"
             );
             // SAFETY: `Searcher` is known to return valid indices.
             unsafe { Some(self.get_unchecked(len..)) }
@@ -3934,7 +3934,7 @@ impl str {
                 end,
                 self.len(),
                 "The first search step from ReverseSearcher \
-                must include the last character"
+                 must include the last character"
             );
             // SAFETY: `Searcher` is known to return valid indices.
             unsafe { Some(self.get_unchecked(..start)) }

src/libcore/tests/iter.rs

@@ -1954,11 +1954,19 @@ fn test_range_inclusive_exhaustion() {
     assert_eq!(r.next(), None);
     assert_eq!(r.next(), None);
 
+    assert_eq!(*r.start(), 10);
+    assert_eq!(*r.end(), 10);
+    assert_ne!(r, 10..=10);
+
     let mut r = 10..=10;
     assert_eq!(r.next_back(), Some(10));
     assert!(r.is_empty());
     assert_eq!(r.next_back(), None);
 
+    assert_eq!(*r.start(), 10);
+    assert_eq!(*r.end(), 10);
+    assert_ne!(r, 10..=10);
+
     let mut r = 10..=12;
     assert_eq!(r.next(), Some(10));
     assert_eq!(r.next(), Some(11));
@@ -2076,6 +2084,9 @@ fn test_range_inclusive_nth() {
     assert_eq!((10..=15).nth(5), Some(15));
     assert_eq!((10..=15).nth(6), None);
 
+    let mut exhausted_via_next = 10_u8..=20;
+    while exhausted_via_next.next().is_some() {}
+
     let mut r = 10_u8..=20;
     assert_eq!(r.nth(2), Some(12));
     assert_eq!(r, 13..=20);
@@ -2085,6 +2096,7 @@ fn test_range_inclusive_nth() {
     assert_eq!(ExactSizeIterator::is_empty(&r), false);
     assert_eq!(r.nth(10), None);
     assert_eq!(r.is_empty(), true);
+    assert_eq!(r, exhausted_via_next);
     assert_eq!(ExactSizeIterator::is_empty(&r), true);
 }
 
@@ -2096,6 +2108,9 @@ fn test_range_inclusive_nth_back() {
     assert_eq!((10..=15).nth_back(6), None);
     assert_eq!((-120..=80_i8).nth_back(200), Some(-120));
 
+    let mut exhausted_via_next_back = 10_u8..=20;
+    while exhausted_via_next_back.next_back().is_some() {}
+
     let mut r = 10_u8..=20;
     assert_eq!(r.nth_back(2), Some(18));
     assert_eq!(r, 10..=17);
@@ -2105,6 +2120,7 @@ fn test_range_inclusive_nth_back() {
     assert_eq!(ExactSizeIterator::is_empty(&r), false);
     assert_eq!(r.nth_back(10), None);
     assert_eq!(r.is_empty(), true);
+    assert_eq!(r, exhausted_via_next_back);
     assert_eq!(ExactSizeIterator::is_empty(&r), true);
 }
 

src/test/ui/specialization/soundness/partial_eq_range_inclusive.rs

@@ -0,0 +1,35 @@
+// run-pass
+
+use std::cell::RefCell;
+use std::cmp::Ordering;
+
+struct Evil<'a, 'b> {
+    values: RefCell<Vec<&'a str>>,
+    to_insert: &'b String,
+}
+
+impl<'a, 'b> PartialEq for Evil<'a, 'b> {
+    fn eq(&self, _other: &Self) -> bool {
+        true
+    }
+}
+
+impl<'a> PartialOrd for Evil<'a, 'a> {
+    fn partial_cmp(&self, _other: &Self) -> Option<Ordering> {
+        self.values.borrow_mut().push(self.to_insert);
+        None
+    }
+}
+
+fn main() {
+    let e;
+    let values;
+    {
+        let to_insert = String::from("Hello, world!");
+        e = Evil { values: RefCell::new(Vec::new()), to_insert: &to_insert };
+        let range = &e..=&e;
+        let _ = range == range;
+        values = e.values;
+    }
+    assert_eq!(*values.borrow(), Vec::<&str>::new());
+}