Auto merge of #92070 - rukai:replace_vec_into_iter_with_array_into_iter, r=Mark-Simulacrum

Replace usages of vec![].into_iter with [].into_iter

`[].into_iter` is idiomatic over `vec![].into_iter` because its simpler and faster (unless the vec is optimized away in which case it would be the same)

So we should change all the implementation, documentation and tests to use it.

I skipped:
* `src/tools` - Those are copied in from upstream
* `src/test/ui` - Hard to tell if `vec![].into_iter` was used intentionally or not here and not much benefit to changing it.
*  any case where `vec![].into_iter` was used because we specifically needed a `Vec::IntoIter<T>`
*  any case where it looked like we were intentionally using `vec![].into_iter` to test it.

Author: bors

alloc/src/collections/btree/map/tests.rs

@@ -728,7 +728,7 @@ fn test_range_large() {
 #[test]
 fn test_range_inclusive_max_value() {
     let max = usize::MAX;
-    let map: BTreeMap<_, _> = vec![(max, 0)].into_iter().collect();
+    let map: BTreeMap<_, _> = [(max, 0)].into_iter().collect();
 
     assert_eq!(map.range(max..=max).collect::<Vec<_>>(), &[(&max, &0)]);
 }
@@ -2128,7 +2128,7 @@ fn test_into_iter_drop_leak_height_1() {
 
 #[test]
 fn test_into_keys() {
-    let vec = vec![(1, 'a'), (2, 'b'), (3, 'c')];
+    let vec = [(1, 'a'), (2, 'b'), (3, 'c')];
     let map: BTreeMap<_, _> = vec.into_iter().collect();
     let keys: Vec<_> = map.into_keys().collect();
 

alloc/src/collections/vec_deque/mod.rs

@@ -669,7 +669,7 @@ impl<T, A: Allocator> VecDeque<T, A> {
     /// ```
     /// use std::collections::VecDeque;
     ///
-    /// let mut buf: VecDeque<i32> = vec![1].into_iter().collect();
+    /// let mut buf: VecDeque<i32> = [1].into_iter().collect();
     /// buf.reserve_exact(10);
     /// assert!(buf.capacity() >= 11);
     /// ```
@@ -692,7 +692,7 @@ impl<T, A: Allocator> VecDeque<T, A> {
     /// ```
     /// use std::collections::VecDeque;
     ///
-    /// let mut buf: VecDeque<i32> = vec![1].into_iter().collect();
+    /// let mut buf: VecDeque<i32> = [1].into_iter().collect();
     /// buf.reserve(10);
     /// assert!(buf.capacity() >= 11);
     /// ```
@@ -1153,7 +1153,7 @@ impl<T, A: Allocator> VecDeque<T, A> {
     /// ```
     /// use std::collections::VecDeque;
     ///
-    /// let v: VecDeque<_> = vec![1, 2, 3].into_iter().collect();
+    /// let v: VecDeque<_> = [1, 2, 3].into_iter().collect();
     /// let range = v.range(2..).copied().collect::<VecDeque<_>>();
     /// assert_eq!(range, [3]);
     ///
@@ -1188,7 +1188,7 @@ impl<T, A: Allocator> VecDeque<T, A> {
     /// ```
     /// use std::collections::VecDeque;
     ///
-    /// let mut v: VecDeque<_> = vec![1, 2, 3].into_iter().collect();
+    /// let mut v: VecDeque<_> = [1, 2, 3].into_iter().collect();
     /// for v in v.range_mut(2..) {
     ///   *v *= 2;
     /// }
@@ -1235,7 +1235,7 @@ impl<T, A: Allocator> VecDeque<T, A> {
     /// ```
     /// use std::collections::VecDeque;
     ///
-    /// let mut v: VecDeque<_> = vec![1, 2, 3].into_iter().collect();
+    /// let mut v: VecDeque<_> = [1, 2, 3].into_iter().collect();
     /// let drained = v.drain(2..).collect::<VecDeque<_>>();
     /// assert_eq!(drained, [3]);
     /// assert_eq!(v, [1, 2]);
@@ -2025,7 +2025,7 @@ impl<T, A: Allocator> VecDeque<T, A> {
     /// ```
     /// use std::collections::VecDeque;
     ///
-    /// let mut buf: VecDeque<_> = vec![1, 2, 3].into_iter().collect();
+    /// let mut buf: VecDeque<_> = [1, 2, 3].into_iter().collect();
     /// let buf2 = buf.split_off(1);
     /// assert_eq!(buf, [1]);
     /// assert_eq!(buf2, [2, 3]);
@@ -2091,8 +2091,8 @@ impl<T, A: Allocator> VecDeque<T, A> {
     /// ```
     /// use std::collections::VecDeque;
     ///
-    /// let mut buf: VecDeque<_> = vec![1, 2].into_iter().collect();
-    /// let mut buf2: VecDeque<_> = vec![3, 4].into_iter().collect();
+    /// let mut buf: VecDeque<_> = [1, 2].into_iter().collect();
+    /// let mut buf2: VecDeque<_> = [3, 4].into_iter().collect();
     /// buf.append(&mut buf2);
     /// assert_eq!(buf, [1, 2, 3, 4]);
     /// assert_eq!(buf2, []);

alloc/tests/linked_list.rs

@@ -304,7 +304,7 @@ fn test_show() {
     let list: LinkedList<_> = (0..10).collect();
     assert_eq!(format!("{:?}", list), "[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]");
 
-    let list: LinkedList<_> = vec!["just", "one", "test", "more"].iter().cloned().collect();
+    let list: LinkedList<_> = ["just", "one", "test", "more"].into_iter().collect();
     assert_eq!(format!("{:?}", list), "[\"just\", \"one\", \"test\", \"more\"]");
 }
 
@@ -336,7 +336,7 @@ fn test_extend() {
     assert_eq!(a.len(), 4);
     assert!(a.iter().eq(&[1, 2, 3, 4]));
 
-    let b: LinkedList<_> = vec![5, 6, 7].into_iter().collect();
+    let b: LinkedList<_> = [5, 6, 7].into_iter().collect();
     a.extend(b); // specializes to `append`
 
     assert_eq!(a.len(), 7);
@@ -375,7 +375,7 @@ fn drain_filter_empty() {
 
 #[test]
 fn drain_filter_zst() {
-    let mut list: LinkedList<_> = vec![(), (), (), (), ()].into_iter().collect();
+    let mut list: LinkedList<_> = [(), (), (), (), ()].into_iter().collect();
     let initial_len = list.len();
     let mut count = 0;
 
@@ -398,7 +398,7 @@ fn drain_filter_zst() {
 
 #[test]
 fn drain_filter_false() {
-    let mut list: LinkedList<_> = vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10].into_iter().collect();
+    let mut list: LinkedList<_> = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10].into_iter().collect();
 
     let initial_len = list.len();
     let mut count = 0;
@@ -421,7 +421,7 @@ fn drain_filter_false() {
 
 #[test]
 fn drain_filter_true() {
-    let mut list: LinkedList<_> = vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10].into_iter().collect();
+    let mut list: LinkedList<_> = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10].into_iter().collect();
 
     let initial_len = list.len();
     let mut count = 0;
@@ -447,7 +447,7 @@ fn drain_filter_true() {
 fn drain_filter_complex() {
     {
         //                [+xxx++++++xxxxx++++x+x++]
-        let mut list = vec![
+        let mut list = [
             1, 2, 4, 6, 7, 9, 11, 13, 15, 17, 18, 20, 22, 24, 26, 27, 29, 31, 33, 34, 35, 36, 37,
             39,
         ]
@@ -467,11 +467,10 @@ fn drain_filter_complex() {
 
     {
         // [xxx++++++xxxxx++++x+x++]
-        let mut list = vec![
-            2, 4, 6, 7, 9, 11, 13, 15, 17, 18, 20, 22, 24, 26, 27, 29, 31, 33, 34, 35, 36, 37, 39,
-        ]
-        .into_iter()
-        .collect::<LinkedList<_>>();
+        let mut list =
+            [2, 4, 6, 7, 9, 11, 13, 15, 17, 18, 20, 22, 24, 26, 27, 29, 31, 33, 34, 35, 36, 37, 39]
+                .into_iter()
+                .collect::<LinkedList<_>>();
 
         let removed = list.drain_filter(|x| *x % 2 == 0).collect::<Vec<_>>();
         assert_eq!(removed.len(), 10);
@@ -487,7 +486,7 @@ fn drain_filter_complex() {
     {
         // [xxx++++++xxxxx++++x+x]
         let mut list =
-            vec![2, 4, 6, 7, 9, 11, 13, 15, 17, 18, 20, 22, 24, 26, 27, 29, 31, 33, 34, 35, 36]
+            [2, 4, 6, 7, 9, 11, 13, 15, 17, 18, 20, 22, 24, 26, 27, 29, 31, 33, 34, 35, 36]
                 .into_iter()
                 .collect::<LinkedList<_>>();
 
@@ -504,7 +503,7 @@ fn drain_filter_complex() {
 
     {
         // [xxxxxxxxxx+++++++++++]
-        let mut list = vec![2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19]
+        let mut list = [2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19]
             .into_iter()
             .collect::<LinkedList<_>>();
 
@@ -518,7 +517,7 @@ fn drain_filter_complex() {
 
     {
         // [+++++++++++xxxxxxxxxx]
-        let mut list = vec![1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20]
+        let mut list = [1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20]
             .into_iter()
             .collect::<LinkedList<_>>();
 

alloc/tests/string.rs

@@ -489,7 +489,7 @@ fn test_from_iterator() {
     b.extend(u.chars());
     assert_eq!(s, b);
 
-    let c: String = vec![t, u].into_iter().collect();
+    let c: String = [t, u].into_iter().collect();
     assert_eq!(s, c);
 
     let mut d = t.to_string();

alloc/tests/vec.rs

@@ -449,10 +449,10 @@ fn zero_sized_values() {
 
 #[test]
 fn test_partition() {
-    assert_eq!(vec![].into_iter().partition(|x: &i32| *x < 3), (vec![], vec![]));
-    assert_eq!(vec![1, 2, 3].into_iter().partition(|x| *x < 4), (vec![1, 2, 3], vec![]));
-    assert_eq!(vec![1, 2, 3].into_iter().partition(|x| *x < 2), (vec![1], vec![2, 3]));
-    assert_eq!(vec![1, 2, 3].into_iter().partition(|x| *x < 0), (vec![], vec![1, 2, 3]));
+    assert_eq!([].into_iter().partition(|x: &i32| *x < 3), (vec![], vec![]));
+    assert_eq!([1, 2, 3].into_iter().partition(|x| *x < 4), (vec![1, 2, 3], vec![]));
+    assert_eq!([1, 2, 3].into_iter().partition(|x| *x < 2), (vec![1], vec![2, 3]));
+    assert_eq!([1, 2, 3].into_iter().partition(|x| *x < 0), (vec![], vec![1, 2, 3]));
 }
 
 #[test]
@@ -924,7 +924,7 @@ fn test_into_iter_debug() {
 
 #[test]
 fn test_into_iter_count() {
-    assert_eq!(vec![1, 2, 3].into_iter().count(), 3);
+    assert_eq!([1, 2, 3].into_iter().count(), 3);
 }
 
 #[test]
@@ -933,7 +933,7 @@ fn test_into_iter_clone() {
         let v: Vec<i32> = it.collect();
         assert_eq!(&v[..], slice);
     }
-    let mut it = vec![1, 2, 3].into_iter();
+    let mut it = [1, 2, 3].into_iter();
     iter_equal(it.clone(), &[1, 2, 3]);
     assert_eq!(it.next(), Some(1));
     let mut it = it.rev();
@@ -972,7 +972,7 @@ fn test_into_iter_leak() {
 
 #[test]
 fn test_into_iter_advance_by() {
-    let mut i = vec![1, 2, 3, 4, 5].into_iter();
+    let mut i = [1, 2, 3, 4, 5].into_iter();
     i.advance_by(0).unwrap();
     i.advance_back_by(0).unwrap();
     assert_eq!(i.as_slice(), [1, 2, 3, 4, 5]);
@@ -1799,7 +1799,7 @@ fn test_stable_pointers() {
     assert_eq!(*v0, 13);
     next_then_drop(v.splice(5..8, vec![1])); // replacement is smaller than original range
     assert_eq!(*v0, 13);
-    next_then_drop(v.splice(5..6, vec![1; 10].into_iter().filter(|_| true))); // lower bound not exact
+    next_then_drop(v.splice(5..6, [1; 10].into_iter().filter(|_| true))); // lower bound not exact
     assert_eq!(*v0, 13);
 
     // spare_capacity_mut

alloc/tests/vec_deque.rs

@@ -927,8 +927,8 @@ fn test_as_mut_slices() {
 
 #[test]
 fn test_append() {
-    let mut a: VecDeque<_> = vec![1, 2, 3].into_iter().collect();
-    let mut b: VecDeque<_> = vec![4, 5, 6].into_iter().collect();
+    let mut a: VecDeque<_> = [1, 2, 3].into_iter().collect();
+    let mut b: VecDeque<_> = [4, 5, 6].into_iter().collect();
 
     // normal append
     a.append(&mut b);
@@ -1209,7 +1209,7 @@ fn test_try_reserve() {
 
     {
         // Same basic idea, but with non-zero len
-        let mut ten_bytes: VecDeque<u8> = vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10].into_iter().collect();
+        let mut ten_bytes: VecDeque<u8> = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10].into_iter().collect();
 
         if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_CAP - 10).map_err(|e| e.kind()) {
             panic!("isize::MAX shouldn't trigger an overflow!");
@@ -1240,7 +1240,7 @@ fn test_try_reserve() {
 
     {
         // Same basic idea, but with interesting type size
-        let mut ten_u32s: VecDeque<u32> = vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10].into_iter().collect();
+        let mut ten_u32s: VecDeque<u32> = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10].into_iter().collect();
 
         if let Err(CapacityOverflow) = ten_u32s.try_reserve(MAX_CAP / 4 - 10).map_err(|e| e.kind())
         {
@@ -1322,7 +1322,7 @@ fn test_try_reserve_exact() {
     }
 
     {
-        let mut ten_bytes: VecDeque<u8> = vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10].into_iter().collect();
+        let mut ten_bytes: VecDeque<u8> = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10].into_iter().collect();
 
         if let Err(CapacityOverflow) =
             ten_bytes.try_reserve_exact(MAX_CAP - 10).map_err(|e| e.kind())
@@ -1355,7 +1355,7 @@ fn test_try_reserve_exact() {
     }
 
     {
-        let mut ten_u32s: VecDeque<u32> = vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10].into_iter().collect();
+        let mut ten_u32s: VecDeque<u32> = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10].into_iter().collect();
 
         if let Err(CapacityOverflow) =
             ten_u32s.try_reserve_exact(MAX_CAP / 4 - 10).map_err(|e| e.kind())

core/src/convert/mod.rs

@@ -91,7 +91,7 @@ pub use num::FloatToInt;
 /// ```rust
 /// use std::convert::identity;
 ///
-/// let iter = vec![Some(1), None, Some(3)].into_iter();
+/// let iter = [Some(1), None, Some(3)].into_iter();
 /// let filtered = iter.filter_map(identity).collect::<Vec<_>>();
 /// assert_eq!(vec![1, 3], filtered);
 /// ```

core/src/iter/adapters/map.rs

@@ -19,7 +19,7 @@ use crate::ops::Try;
 /// you can also [`map`] backwards:
 ///
 /// ```rust
-/// let v: Vec<i32> = vec![1, 2, 3].into_iter().map(|x| x + 1).rev().collect();
+/// let v: Vec<i32> = [1, 2, 3].into_iter().map(|x| x + 1).rev().collect();
 ///
 /// assert_eq!(v, [4, 3, 2]);
 /// ```
@@ -32,7 +32,7 @@ use crate::ops::Try;
 /// ```rust
 /// let mut c = 0;
 ///
-/// for pair in vec!['a', 'b', 'c'].into_iter()
+/// for pair in ['a', 'b', 'c'].into_iter()
 ///                                .map(|letter| { c += 1; (letter, c) }) {
 ///     println!("{:?}", pair);
 /// }
@@ -49,7 +49,7 @@ use crate::ops::Try;
 /// ```rust
 /// let mut c = 0;
 ///
-/// for pair in vec!['a', 'b', 'c'].into_iter()
+/// for pair in ['a', 'b', 'c'].into_iter()
 ///                                .map(|letter| { c += 1; (letter, c) })
 ///                                .rev() {
 ///     println!("{:?}", pair);

core/src/iter/traits/collect.rs

@@ -124,7 +124,7 @@ pub trait FromIterator<A>: Sized {
 /// Basic usage:
 ///
 /// ```
-/// let v = vec![1, 2, 3];
+/// let v = [1, 2, 3];
 /// let mut iter = v.into_iter();
 ///
 /// assert_eq!(Some(1), iter.next());
@@ -215,7 +215,7 @@ pub trait IntoIterator {
     /// Basic usage:
     ///
     /// ```
-    /// let v = vec![1, 2, 3];
+    /// let v = [1, 2, 3];
     /// let mut iter = v.into_iter();
     ///
     /// assert_eq!(Some(1), iter.next());

core/src/iter/traits/iterator.rs

@@ -590,7 +590,7 @@ pub trait Iterator {
     /// #[derive(PartialEq, Debug)]
     /// struct NotClone(usize);
     ///
-    /// let v = vec![NotClone(0), NotClone(1), NotClone(2)];
+    /// let v = [NotClone(0), NotClone(1), NotClone(2)];
     /// let mut it = v.into_iter().intersperse_with(|| NotClone(99));
     ///
     /// assert_eq!(it.next(), Some(NotClone(0)));  // The first element from `v`.
@@ -1270,7 +1270,7 @@ pub trait Iterator {
     /// `take` will limit itself to the size of the underlying iterator:
     ///
     /// ```
-    /// let v = vec![1, 2];
+    /// let v = [1, 2];
     /// let mut iter = v.into_iter().take(5);
     /// assert_eq!(iter.next(), Some(1));
     /// assert_eq!(iter.next(), Some(2));
@@ -1604,7 +1604,7 @@ pub trait Iterator {
     /// Basic usage:
     ///
     /// ```
-    /// let mut words = vec!["hello", "world", "of", "Rust"].into_iter();
+    /// let mut words = ["hello", "world", "of", "Rust"].into_iter();
     ///
     /// // Take the first two words.
     /// let hello_world: Vec<_> = words.by_ref().take(2).collect();
@@ -2700,7 +2700,7 @@ pub trait Iterator {
     /// incomparable. You can work around this by using [`Iterator::reduce`]:
     /// ```
     /// assert_eq!(
-    ///     vec![2.4, f32::NAN, 1.3]
+    ///     [2.4, f32::NAN, 1.3]
     ///         .into_iter()
     ///         .reduce(f32::max)
     ///         .unwrap(),
@@ -2738,7 +2738,7 @@ pub trait Iterator {
     /// incomparable. You can work around this by using [`Iterator::reduce`]:
     /// ```
     /// assert_eq!(
-    ///     vec![2.4, f32::NAN, 1.3]
+    ///     [2.4, f32::NAN, 1.3]
     ///         .into_iter()
     ///         .reduce(f32::min)
     ///         .unwrap(),