Auto merge of rust-lang#104629 - JohnTitor:rollup-vp3m98i, r=JohnTitor

Rollup of 6 pull requests

Successful merges:

 - rust-lang#103901 (Add tracking issue for `const_arguments_as_str`)
 - rust-lang#104112 (rustdoc: Add copy to the description of repeat)
 - rust-lang#104435 (`VecDeque::resize` should re-use the buffer in the passed-in element)
 - rust-lang#104467 (Fix substraction with overflow in `wrong_number_of_generic_args.rs`)
 - rust-lang#104608 (Cleanup macro matching recovery)
 - rust-lang#104626 (Fix doctest errors related to rustc_middle)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

Author: bors

Diff for: compiler/rustc_expand/src/mbe/macro_rules.rs

@@ -495,7 +495,6 @@ fn try_match_macro<'matcher, T: Tracker<'matcher>>(
     // hacky, but speeds up the `html5ever` benchmark significantly. (Issue
     // 68836 suggests a more comprehensive but more complex change to deal with
     // this situation.)
-    // FIXME(Nilstrieb): Stop recovery from happening on this parser and retry later with recovery if the macro failed to match.
     let parser = parser_from_cx(sess, arg.clone(), T::recovery());
     // Try each arm's matchers.
     let mut tt_parser = TtParser::new(name);

Diff for: compiler/rustc_hir_analysis/src/structured_errors/wrong_number_of_generic_args.rs

@@ -728,7 +728,8 @@ impl<'a, 'tcx> WrongNumberOfGenericArgs<'a, 'tcx> {
         && let Some(trait_path_segment) = path.segments.get(0) {
             let num_generic_args_supplied_to_trait = trait_path_segment.args().num_generic_params();
 
-            if num_assoc_fn_excess_args == num_trait_generics_except_self - num_generic_args_supplied_to_trait {
+            if num_generic_args_supplied_to_trait + num_assoc_fn_excess_args == num_trait_generics_except_self
+            {
                 if let Some(span) = self.gen_args.span_ext()
                 && let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(span) {
                     let sugg = vec![

Diff for: compiler/rustc_middle/Cargo.toml

@@ -4,7 +4,6 @@ version = "0.0.0"
 edition = "2021"
 
 [lib]
-doctest = false
 
 [dependencies]
 bitflags = "1.2.1"

Diff for: compiler/rustc_middle/src/query/mod.rs

@@ -1648,6 +1648,8 @@ rustc_queries! {
     /// a generic type parameter will panic if you call this method on it:
     ///
     /// ```
+    /// use std::fmt::Debug;
+    ///
     /// pub trait Foo<T: Debug> {}
     /// ```
     ///

Diff for: compiler/rustc_middle/src/ty/inhabitedness/mod.rs

@@ -5,7 +5,7 @@
 //!
 //! # Example
 //! ```rust
-//! enum Void {}
+//! #![feature(never_type)]
 //! mod a {
 //!     pub mod b {
 //!         pub struct SecretlyUninhabited {
@@ -15,6 +15,7 @@
 //! }
 //!
 //! mod c {
+//!     enum Void {}
 //!     pub struct AlsoSecretlyUninhabited {
 //!         _priv: Void,
 //!     }
@@ -35,7 +36,7 @@
 //! `Foo`.
 //!
 //! # Example
-//! ```rust
+//! ```ignore(illustrative)
 //! let foo_result: Result<T, Foo> = ... ;
 //! let Ok(t) = foo_result;
 //! ```

Diff for: compiler/rustc_parse/src/parser/expr.rs

@@ -2078,12 +2078,7 @@ impl<'a> Parser<'a> {
 
         if self.token.kind == TokenKind::Semi
             && matches!(self.token_cursor.frame.delim_sp, Some((Delimiter::Parenthesis, _)))
-            // HACK: This is needed so we can detect whether we're inside a macro,
-            // where regular assumptions about what tokens can follow other tokens
-            // don't necessarily apply.
             && self.may_recover()
-            // FIXME(Nilstrieb): Remove this check once `may_recover` actually stops recovery
-            && self.subparser_name.is_none()
         {
             // It is likely that the closure body is a block but where the
             // braces have been removed. We will recover and eat the next

Diff for: library/alloc/src/collections/vec_deque/mod.rs

@@ -10,7 +10,7 @@
 use core::cmp::{self, Ordering};
 use core::fmt;
 use core::hash::{Hash, Hasher};
-use core::iter::{repeat_with, FromIterator};
+use core::iter::{repeat_n, repeat_with, FromIterator};
 use core::marker::PhantomData;
 use core::mem::{ManuallyDrop, MaybeUninit, SizedTypeProperties};
 use core::ops::{Index, IndexMut, Range, RangeBounds};
@@ -2833,7 +2833,12 @@ impl<T: Clone, A: Allocator> VecDeque<T, A> {
     /// ```
     #[stable(feature = "deque_extras", since = "1.16.0")]
     pub fn resize(&mut self, new_len: usize, value: T) {
-        self.resize_with(new_len, || value.clone());
+        if new_len > self.len() {
+            let extra = new_len - self.len();
+            self.extend(repeat_n(value, extra))
+        } else {
+            self.truncate(new_len);
+        }
     }
 }
 

Diff for: library/alloc/src/lib.rs

@@ -124,6 +124,7 @@
 #![feature(inplace_iteration)]
 #![feature(iter_advance_by)]
 #![feature(iter_next_chunk)]
+#![feature(iter_repeat_n)]
 #![feature(layout_for_ptr)]
 #![feature(maybe_uninit_slice)]
 #![feature(maybe_uninit_uninit_array)]

Diff for: library/alloc/src/slice.rs

@@ -458,7 +458,7 @@ impl<T> [T] {
         hack::into_vec(self)
     }
 
-    /// Creates a vector by repeating a slice `n` times.
+    /// Creates a vector by copying a slice `n` times.
     ///
     /// # Panics
     ///

Diff for: library/alloc/tests/vec_deque.rs

@@ -1727,3 +1727,11 @@ fn test_from_zero_sized_vec() {
     let queue = VecDeque::from(v);
     assert_eq!(queue.len(), 100);
 }
+
+#[test]
+fn test_resize_keeps_reserved_space_from_item() {
+    let v = Vec::<i32>::with_capacity(1234);
+    let mut d = VecDeque::new();
+    d.resize(1, v);
+    assert_eq!(d[0].capacity(), 1234);
+}

Diff for: library/core/src/fmt/mod.rs

@@ -510,7 +510,7 @@ impl<'a> Arguments<'a> {
     /// assert_eq!(format_args!("{}", 1).as_str(), None);
     /// ```
     #[stable(feature = "fmt_as_str", since = "1.52.0")]
-    #[rustc_const_unstable(feature = "const_arguments_as_str", issue = "none")]
+    #[rustc_const_unstable(feature = "const_arguments_as_str", issue = "103900")]
     #[must_use]
     #[inline]
     pub const fn as_str(&self) -> Option<&'static str> {

Diff for: library/core/src/iter/mod.rs

@@ -401,6 +401,8 @@ pub use self::sources::{once, Once};
 pub use self::sources::{once_with, OnceWith};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use self::sources::{repeat, Repeat};
+#[unstable(feature = "iter_repeat_n", issue = "104434")]
+pub use self::sources::{repeat_n, RepeatN};
 #[stable(feature = "iterator_repeat_with", since = "1.28.0")]
 pub use self::sources::{repeat_with, RepeatWith};
 #[stable(feature = "iter_successors", since = "1.34.0")]

Diff for: library/core/src/iter/sources.rs

@@ -4,6 +4,7 @@ mod from_generator;
 mod once;
 mod once_with;
 mod repeat;
+mod repeat_n;
 mod repeat_with;
 mod successors;
 
@@ -16,6 +17,9 @@ pub use self::empty::{empty, Empty};
 #[stable(feature = "iter_once", since = "1.2.0")]
 pub use self::once::{once, Once};
 
+#[unstable(feature = "iter_repeat_n", issue = "104434")]
+pub use self::repeat_n::{repeat_n, RepeatN};
+
 #[stable(feature = "iterator_repeat_with", since = "1.28.0")]
 pub use self::repeat_with::{repeat_with, RepeatWith};
 

Diff for: library/core/src/iter/sources/repeat_n.rs

@@ -0,0 +1,195 @@
+use crate::iter::{FusedIterator, TrustedLen};
+use crate::mem::ManuallyDrop;
+
+/// Creates a new iterator that repeats a single element a given number of times.
+///
+/// The `repeat_n()` function repeats a single value exactly `n` times.
+///
+/// This is very similar to using [`repeat()`] with [`Iterator::take()`],
+/// but there are two differences:
+/// - `repeat_n()` can return the original value, rather than always cloning.
+/// - `repeat_n()` produces an [`ExactSizeIterator`].
+///
+/// [`repeat()`]: crate::iter::repeat
+///
+/// # Examples
+///
+/// Basic usage:
+///
+/// ```
+/// #![feature(iter_repeat_n)]
+/// use std::iter;
+///
+/// // four of the the number four:
+/// let mut four_fours = iter::repeat_n(4, 4);
+///
+/// assert_eq!(Some(4), four_fours.next());
+/// assert_eq!(Some(4), four_fours.next());
+/// assert_eq!(Some(4), four_fours.next());
+/// assert_eq!(Some(4), four_fours.next());
+///
+/// // no more fours
+/// assert_eq!(None, four_fours.next());
+/// ```
+///
+/// For non-`Copy` types,
+///
+/// ```
+/// #![feature(iter_repeat_n)]
+/// use std::iter;
+///
+/// let v: Vec<i32> = Vec::with_capacity(123);
+/// let mut it = iter::repeat_n(v, 5);
+///
+/// for i in 0..4 {
+///     // It starts by cloning things
+///     let cloned = it.next().unwrap();
+///     assert_eq!(cloned.len(), 0);
+///     assert_eq!(cloned.capacity(), 0);
+/// }
+///
+/// // ... but the last item is the original one
+/// let last = it.next().unwrap();
+/// assert_eq!(last.len(), 0);
+/// assert_eq!(last.capacity(), 123);
+///
+/// // ... and now we're done
+/// assert_eq!(None, it.next());
+/// ```
+#[inline]
+#[unstable(feature = "iter_repeat_n", issue = "104434")]
+#[doc(hidden)] // waiting on ACP#120 to decide whether to expose publicly
+pub fn repeat_n<T: Clone>(element: T, count: usize) -> RepeatN<T> {
+    let mut element = ManuallyDrop::new(element);
+
+    if count == 0 {
+        // SAFETY: we definitely haven't dropped it yet, since we only just got
+        // passed it in, and because the count is zero the instance we're about
+        // to create won't drop it, so to avoid leaking we need to now.
+        unsafe { ManuallyDrop::drop(&mut element) };
+    }
+
+    RepeatN { element, count }
+}
+
+/// An iterator that repeats an element an exact number of times.
+///
+/// This `struct` is created by the [`repeat_n()`] function.
+/// See its documentation for more.
+#[derive(Clone, Debug)]
+#[unstable(feature = "iter_repeat_n", issue = "104434")]
+#[doc(hidden)] // waiting on ACP#120 to decide whether to expose publicly
+pub struct RepeatN<A> {
+    count: usize,
+    // Invariant: has been dropped iff count == 0.
+    element: ManuallyDrop<A>,
+}
+
+impl<A> RepeatN<A> {
+    /// If we haven't already dropped the element, return it in an option.
+    ///
+    /// Clears the count so it won't be dropped again later.
+    #[inline]
+    fn take_element(&mut self) -> Option<A> {
+        if self.count > 0 {
+            self.count = 0;
+            // SAFETY: We just set count to zero so it won't be dropped again,
+            // and it used to be non-zero so it hasn't already been dropped.
+            unsafe { Some(ManuallyDrop::take(&mut self.element)) }
+        } else {
+            None
+        }
+    }
+}
+
+#[unstable(feature = "iter_repeat_n", issue = "104434")]
+impl<A> Drop for RepeatN<A> {
+    fn drop(&mut self) {
+        self.take_element();
+    }
+}
+
+#[unstable(feature = "iter_repeat_n", issue = "104434")]
+impl<A: Clone> Iterator for RepeatN<A> {
+    type Item = A;
+
+    #[inline]
+    fn next(&mut self) -> Option<A> {
+        if self.count == 0 {
+            return None;
+        }
+
+        self.count -= 1;
+        Some(if self.count == 0 {
+            // SAFETY: the check above ensured that the count used to be non-zero,
+            // so element hasn't been dropped yet, and we just lowered the count to
+            // zero so it won't be dropped later, and thus it's okay to take it here.
+            unsafe { ManuallyDrop::take(&mut self.element) }
+        } else {
+            A::clone(&mut self.element)
+        })
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let len = self.len();
+        (len, Some(len))
+    }
+
+    #[inline]
+    fn advance_by(&mut self, skip: usize) -> Result<(), usize> {
+        let len = self.count;
+
+        if skip >= len {
+            self.take_element();
+        }
+
+        if skip > len {
+            Err(len)
+        } else {
+            self.count = len - skip;
+            Ok(())
+        }
+    }
+
+    #[inline]
+    fn last(mut self) -> Option<A> {
+        self.take_element()
+    }
+
+    #[inline]
+    fn count(self) -> usize {
+        self.len()
+    }
+}
+
+#[unstable(feature = "iter_repeat_n", issue = "104434")]
+impl<A: Clone> ExactSizeIterator for RepeatN<A> {
+    fn len(&self) -> usize {
+        self.count
+    }
+}
+
+#[unstable(feature = "iter_repeat_n", issue = "104434")]
+impl<A: Clone> DoubleEndedIterator for RepeatN<A> {
+    #[inline]
+    fn next_back(&mut self) -> Option<A> {
+        self.next()
+    }
+
+    #[inline]
+    fn advance_back_by(&mut self, n: usize) -> Result<(), usize> {
+        self.advance_by(n)
+    }
+
+    #[inline]
+    fn nth_back(&mut self, n: usize) -> Option<A> {
+        self.nth(n)
+    }
+}
+
+#[unstable(feature = "iter_repeat_n", issue = "104434")]
+impl<A: Clone> FusedIterator for RepeatN<A> {}
+
+#[unstable(feature = "trusted_len", issue = "37572")]
+unsafe impl<A: Clone> TrustedLen for RepeatN<A> {}