Rollup of 6 pull requests

.mailmap

@@ -70,6 +70,8 @@ David Manescu <[email protected]> <[email protected]>
 David Ross <[email protected]>
 Derek Chiang <[email protected]> Derek Chiang (Enchi Jiang) <[email protected]>
 Diggory Hardy <[email protected]> Diggory Hardy <[email protected]>
+Donough Liu <[email protected]> <[email protected]>
+Donough Liu <[email protected]> DingMing Liu <[email protected]>
 Dustin Bensing <[email protected]>
 Dylan Braithwaite <[email protected]> <[email protected]>
 Dzmitry Malyshau <[email protected]>

src/libcore/iter/adapters/mod.rs

@@ -1619,6 +1619,69 @@ impl<I: Iterator> Peekable<I> {
         let iter = &mut self.iter;
         self.peeked.get_or_insert_with(|| iter.next()).as_ref()
     }
+
+    /// Consume the next value of this iterator if a condition is true.
+    ///
+    /// If `func` returns `true` for the next value of this iterator, consume and return it.
+    /// Otherwise, return `None`.
+    ///
+    /// # Examples
+    /// Consume a number if it's equal to 0.
+    /// ```
+    /// #![feature(peekable_next_if)]
+    /// let mut iter = (0..5).peekable();
+    /// // The first item of the iterator is 0; consume it.
+    /// assert_eq!(iter.next_if(|&x| x == 0), Some(0));
+    /// // The next item returned is now 1, so `consume` will return `false`.
+    /// assert_eq!(iter.next_if(|&x| x == 0), None);
+    /// // `next_if` saves the value of the next item if it was not equal to `expected`.
+    /// assert_eq!(iter.next(), Some(1));
+    /// ```
+    ///
+    /// Consume any number less than 10.
+    /// ```
+    /// #![feature(peekable_next_if)]
+    /// let mut iter = (1..20).peekable();
+    /// // Consume all numbers less than 10
+    /// while iter.next_if(|&x| x < 10).is_some() {}
+    /// // The next value returned will be 10
+    /// assert_eq!(iter.next(), Some(10));
+    /// ```
+    #[unstable(feature = "peekable_next_if", issue = "72480")]
+    pub fn next_if(&mut self, func: impl FnOnce(&I::Item) -> bool) -> Option<I::Item> {
+        match self.next() {
+            Some(matched) if func(&matched) => Some(matched),
+            other => {
+                // Since we called `self.next()`, we consumed `self.peeked`.
+                assert!(self.peeked.is_none());
+                self.peeked = Some(other);
+                None
+            }
+        }
+    }
+
+    /// Consume the next item if it is equal to `expected`.
+    ///
+    /// # Example
+    /// Consume a number if it's equal to 0.
+    /// ```
+    /// #![feature(peekable_next_if)]
+    /// let mut iter = (0..5).peekable();
+    /// // The first item of the iterator is 0; consume it.
+    /// assert_eq!(iter.next_if_eq(&0), Some(0));
+    /// // The next item returned is now 1, so `consume` will return `false`.
+    /// assert_eq!(iter.next_if_eq(&0), None);
+    /// // `next_if_eq` saves the value of the next item if it was not equal to `expected`.
+    /// assert_eq!(iter.next(), Some(1));
+    /// ```
+    #[unstable(feature = "peekable_next_if", issue = "72480")]
+    pub fn next_if_eq<R>(&mut self, expected: &R) -> Option<I::Item>
+    where
+        R: ?Sized,
+        I::Item: PartialEq<R>,
+    {
+        self.next_if(|next| next == expected)
+    }
 }
 
 /// An iterator that rejects elements while `predicate` returns `true`.

src/libcore/num/f32.rs

@@ -810,4 +810,78 @@ impl f32 {
     pub fn from_ne_bytes(bytes: [u8; 4]) -> Self {
         Self::from_bits(u32::from_ne_bytes(bytes))
     }
+
+    /// Returns an ordering between self and other values.
+    /// Unlike the standard partial comparison between floating point numbers,
+    /// this comparison always produces an ordering in accordance to
+    /// the totalOrder predicate as defined in IEEE 754 (2008 revision)
+    /// floating point standard. The values are ordered in following order:
+    /// - Negative quiet NaN
+    /// - Negative signaling NaN
+    /// - Negative infinity
+    /// - Negative numbers
+    /// - Negative subnormal numbers
+    /// - Negative zero
+    /// - Positive zero
+    /// - Positive subnormal numbers
+    /// - Positive numbers
+    /// - Positive infinity
+    /// - Positive signaling NaN
+    /// - Positive quiet NaN
+    ///
+    /// # Example
+    /// ```
+    /// #![feature(total_cmp)]
+    /// struct GoodBoy {
+    ///     name: String,
+    ///     weight: f32,
+    /// }
+    ///
+    /// let mut bois = vec![
+    ///     GoodBoy { name: "Pucci".to_owned(), weight: 0.1 },
+    ///     GoodBoy { name: "Woofer".to_owned(), weight: 99.0 },
+    ///     GoodBoy { name: "Yapper".to_owned(), weight: 10.0 },
+    ///     GoodBoy { name: "Chonk".to_owned(), weight: f32::INFINITY },
+    ///     GoodBoy { name: "Abs. Unit".to_owned(), weight: f32::NAN },
+    ///     GoodBoy { name: "Floaty".to_owned(), weight: -5.0 },
+    /// ];
+    ///
+    /// bois.sort_by(|a, b| a.weight.total_cmp(&b.weight));
+    /// # assert!(bois.into_iter().map(|b| b.weight)
+    /// #     .zip([-5.0, 0.1, 10.0, 99.0, f32::INFINITY, f32::NAN].iter())
+    /// #     .all(|(a, b)| a.to_bits() == b.to_bits()))
+    /// ```
+    #[unstable(feature = "total_cmp", issue = "72599")]
+    #[inline]
+    pub fn total_cmp(&self, other: &Self) -> crate::cmp::Ordering {
+        let mut left = self.to_bits() as i32;
+        let mut right = other.to_bits() as i32;
+
+        // In case of negatives, flip all the bits except the sign
+        // to achieve a similar layout as two's complement integers
+        //
+        // Why does this work? IEEE 754 floats consist of three fields:
+        // Sign bit, exponent and mantissa. The set of exponent and mantissa
+        // fields as a whole have the property that their bitwise order is
+        // equal to the numeric magnitude where the magnitude is defined.
+        // The magnitude is not normally defined on NaN values, but
+        // IEEE 754 totalOrder defines the NaN values also to follow the
+        // bitwise order. This leads to order explained in the doc comment.
+        // However, the representation of magnitude is the same for negative
+        // and positive numbers – only the sign bit is different.
+        // To easily compare the floats as signed integers, we need to
+        // flip the exponent and mantissa bits in case of negative numbers.
+        // We effectively convert the numbers to "two's complement" form.
+        //
+        // To do the flipping, we construct a mask and XOR against it.
+        // We branchlessly calculate an "all-ones except for the sign bit"
+        // mask from negative-signed values: right shifting sign-extends
+        // the integer, so we "fill" the mask with sign bits, and then
+        // convert to unsigned to push one more zero bit.
+        // On positive values, the mask is all zeros, so it's a no-op.
+        left ^= (((left >> 31) as u32) >> 1) as i32;
+        right ^= (((right >> 31) as u32) >> 1) as i32;
+
+        left.cmp(&right)
+    }
 }

src/libcore/num/f64.rs

@@ -824,4 +824,78 @@ impl f64 {
     pub fn from_ne_bytes(bytes: [u8; 8]) -> Self {
         Self::from_bits(u64::from_ne_bytes(bytes))
     }
+
+    /// Returns an ordering between self and other values.
+    /// Unlike the standard partial comparison between floating point numbers,
+    /// this comparison always produces an ordering in accordance to
+    /// the totalOrder predicate as defined in IEEE 754 (2008 revision)
+    /// floating point standard. The values are ordered in following order:
+    /// - Negative quiet NaN
+    /// - Negative signaling NaN
+    /// - Negative infinity
+    /// - Negative numbers
+    /// - Negative subnormal numbers
+    /// - Negative zero
+    /// - Positive zero
+    /// - Positive subnormal numbers
+    /// - Positive numbers
+    /// - Positive infinity
+    /// - Positive signaling NaN
+    /// - Positive quiet NaN
+    ///
+    /// # Example
+    /// ```
+    /// #![feature(total_cmp)]
+    /// struct GoodBoy {
+    ///     name: String,
+    ///     weight: f64,
+    /// }
+    ///
+    /// let mut bois = vec![
+    ///     GoodBoy { name: "Pucci".to_owned(), weight: 0.1 },
+    ///     GoodBoy { name: "Woofer".to_owned(), weight: 99.0 },
+    ///     GoodBoy { name: "Yapper".to_owned(), weight: 10.0 },
+    ///     GoodBoy { name: "Chonk".to_owned(), weight: f64::INFINITY },
+    ///     GoodBoy { name: "Abs. Unit".to_owned(), weight: f64::NAN },
+    ///     GoodBoy { name: "Floaty".to_owned(), weight: -5.0 },
+    /// ];
+    ///
+    /// bois.sort_by(|a, b| a.weight.total_cmp(&b.weight));
+    /// # assert!(bois.into_iter().map(|b| b.weight)
+    /// #     .zip([-5.0, 0.1, 10.0, 99.0, f64::INFINITY, f64::NAN].iter())
+    /// #     .all(|(a, b)| a.to_bits() == b.to_bits()))
+    /// ```
+    #[unstable(feature = "total_cmp", issue = "72599")]
+    #[inline]
+    pub fn total_cmp(&self, other: &Self) -> crate::cmp::Ordering {
+        let mut left = self.to_bits() as i64;
+        let mut right = other.to_bits() as i64;
+
+        // In case of negatives, flip all the bits except the sign
+        // to achieve a similar layout as two's complement integers
+        //
+        // Why does this work? IEEE 754 floats consist of three fields:
+        // Sign bit, exponent and mantissa. The set of exponent and mantissa
+        // fields as a whole have the property that their bitwise order is
+        // equal to the numeric magnitude where the magnitude is defined.
+        // The magnitude is not normally defined on NaN values, but
+        // IEEE 754 totalOrder defines the NaN values also to follow the
+        // bitwise order. This leads to order explained in the doc comment.
+        // However, the representation of magnitude is the same for negative
+        // and positive numbers – only the sign bit is different.
+        // To easily compare the floats as signed integers, we need to
+        // flip the exponent and mantissa bits in case of negative numbers.
+        // We effectively convert the numbers to "two's complement" form.
+        //
+        // To do the flipping, we construct a mask and XOR against it.
+        // We branchlessly calculate an "all-ones except for the sign bit"
+        // mask from negative-signed values: right shifting sign-extends
+        // the integer, so we "fill" the mask with sign bits, and then
+        // convert to unsigned to push one more zero bit.
+        // On positive values, the mask is all zeros, so it's a no-op.
+        left ^= (((left >> 63) as u64) >> 1) as i64;
+        right ^= (((right >> 63) as u64) >> 1) as i64;
+
+        left.cmp(&right)
+    }
 }

src/libcore/tests/array.rs

@@ -241,3 +241,44 @@ fn iterator_drops() {
     }
     assert_eq!(i.get(), 5);
 }
+
+#[test]
+fn array_default_impl_avoids_leaks_on_panic() {
+    use core::sync::atomic::{AtomicUsize, Ordering::Relaxed};
+    static COUNTER: AtomicUsize = AtomicUsize::new(0);
+    #[derive(Debug)]
+    struct Bomb(usize);
+
+    impl Default for Bomb {
+        fn default() -> Bomb {
+            if COUNTER.load(Relaxed) == 3 {
+                panic!("bomb limit exceeded");
+            }
+
+            COUNTER.fetch_add(1, Relaxed);
+            Bomb(COUNTER.load(Relaxed))
+        }
+    }
+
+    impl Drop for Bomb {
+        fn drop(&mut self) {
+            COUNTER.fetch_sub(1, Relaxed);
+        }
+    }
+
+    let res = std::panic::catch_unwind(|| <[Bomb; 5]>::default());
+    let panic_msg = match res {
+        Ok(_) => unreachable!(),
+        Err(p) => p.downcast::<&'static str>().unwrap(),
+    };
+    assert_eq!(*panic_msg, "bomb limit exceeded");
+    // check that all bombs are successfully dropped
+    assert_eq!(COUNTER.load(Relaxed), 0);
+}
+
+#[test]
+fn empty_array_is_always_default() {
+    struct DoesNotImplDefault;
+
+    let _arr = <[DoesNotImplDefault; 0]>::default();
+}

src/libcore/tests/iter.rs

@@ -813,6 +813,30 @@ fn test_iterator_peekable_rfold() {
     assert_eq!(i, xs.len());
 }
 
+#[test]
+fn test_iterator_peekable_next_if_eq() {
+    // first, try on references
+    let xs = vec!["Heart", "of", "Gold"];
+    let mut it = xs.into_iter().peekable();
+    // try before `peek()`
+    assert_eq!(it.next_if_eq(&"trillian"), None);
+    assert_eq!(it.next_if_eq(&"Heart"), Some("Heart"));
+    // try after peek()
+    assert_eq!(it.peek(), Some(&"of"));
+    assert_eq!(it.next_if_eq(&"of"), Some("of"));
+    assert_eq!(it.next_if_eq(&"zaphod"), None);
+    // make sure `next()` still behaves
+    assert_eq!(it.next(), Some("Gold"));
+
+    // make sure comparison works for owned values
+    let xs = vec![String::from("Ludicrous"), "speed".into()];
+    let mut it = xs.into_iter().peekable();
+    // make sure basic functionality works
+    assert_eq!(it.next_if_eq("Ludicrous"), Some("Ludicrous".into()));
+    assert_eq!(it.next_if_eq("speed"), Some("speed".into()));
+    assert_eq!(it.next_if_eq(""), None);
+}
+
 /// This is an iterator that follows the Iterator contract,
 /// but it is not fused. After having returned None once, it will start
 /// producing elements if .next() is called again.

src/libcore/tests/lib.rs

@@ -43,6 +43,7 @@
 #![feature(leading_trailing_ones)]
 #![feature(const_forget)]
 #![feature(option_unwrap_none)]
+#![feature(peekable_next_if)]
 
 extern crate test;
 

src/librustc_trait_selection/traits/select.rs

@@ -1040,17 +1040,6 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         &mut self,
         stack: &TraitObligationStack<'o, 'tcx>,
     ) -> SelectionResult<'tcx, SelectionCandidate<'tcx>> {
-        if stack.obligation.predicate.references_error() {
-            // If we encounter a `Error`, we generally prefer the
-            // most "optimistic" result in response -- that is, the
-            // one least likely to report downstream errors. But
-            // because this routine is shared by coherence and by
-            // trait selection, there isn't an obvious "right" choice
-            // here in that respect, so we opt to just return
-            // ambiguity and let the upstream clients sort it out.
-            return Ok(None);
-        }
-
         if let Some(conflict) = self.is_knowable(stack) {
             debug!("coherence stage: not knowable");
             if self.intercrate_ambiguity_causes.is_some() {