Auto merge of #76391 - danii:master, r=cuviper

Split up core/test/iter.rs into multiple files

This PR removes the `// ignore-tidy-filelength` at the top of [iter.rs](https://github.com/rust-lang/rust/blob/04f44fb9232dc960d213d0df4a203c387215a5ff/library/core/tests/iter.rs) by splitting it into several sub files. I have split the file per test, based on what I felt the test was really trying to test.
Addresses issue #60302.
- [associated_util.rs](https://github.com/rust-lang/rust/blob/d29180a8ed2752c5dfa2bca1d28ca05dc9bf6bf1/library/core/tests/iter/associated_util.rs) - For testing the module level functions. (Maybe should be renamed?)
- [collection.rs](https://github.com/rust-lang/rust/blob/d29180a8ed2752c5dfa2bca1d28ca05dc9bf6bf1/library/core/tests/iter/collection.rs) - For testing methods that use the values of all the items in an iterator, and creates one value from them, whether it be a Vec of all the values, or a number that represents the sum.
- [mod.rs](https://github.com/rust-lang/rust/blob/d29180a8ed2752c5dfa2bca1d28ca05dc9bf6bf1/library/core/tests/iter/mod.rs) - For utility structs used in all tests, and other tests I didn't know where to place.
- [range.rs](https://github.com/rust-lang/rust/blob/d29180a8ed2752c5dfa2bca1d28ca05dc9bf6bf1/library/core/tests/iter/range.rs) - For testing ranges.
- [transformation.rs](https://github.com/rust-lang/rust/blob/d29180a8ed2752c5dfa2bca1d28ca05dc9bf6bf1/library/core/tests/iter/transformation.rs) - For testing methods that transform all the values in an iterator.
- [util.rs](https://github.com/rust-lang/rust/blob/d29180a8ed2752c5dfa2bca1d28ca05dc9bf6bf1/library/core/tests/iter/util.rs) - For testing methods that provide utility in more specific use cases.

"Programatically"
-----------------------
You may have noticed I "Programatically" split up the file. [This is how](https://gist.github.com/danii/a58b3bcafa9faf1c3e4b01ad7495baf4) I managed to do that. 😛 Hope that's fine.

Author: bors

library/core/tests/iter.rs

@@ -0,0 +1,272 @@
+use super::*;
+use core::iter::*;
+
+#[test]
+fn test_iterator_chain() {
+    let xs = [0, 1, 2, 3, 4, 5];
+    let ys = [30, 40, 50, 60];
+    let expected = [0, 1, 2, 3, 4, 5, 30, 40, 50, 60];
+    let it = xs.iter().chain(&ys);
+    let mut i = 0;
+    for &x in it {
+        assert_eq!(x, expected[i]);
+        i += 1;
+    }
+    assert_eq!(i, expected.len());
+
+    let ys = (30..).step_by(10).take(4);
+    let it = xs.iter().cloned().chain(ys);
+    let mut i = 0;
+    for x in it {
+        assert_eq!(x, expected[i]);
+        i += 1;
+    }
+    assert_eq!(i, expected.len());
+}
+
+#[test]
+fn test_iterator_chain_advance_by() {
+    fn test_chain(xs: &[i32], ys: &[i32]) {
+        let len = xs.len() + ys.len();
+
+        for i in 0..xs.len() {
+            let mut iter = Unfuse::new(xs).chain(Unfuse::new(ys));
+            iter.advance_by(i).unwrap();
+            assert_eq!(iter.next(), Some(&xs[i]));
+            assert_eq!(iter.advance_by(100), Err(len - i - 1));
+        }
+
+        for i in 0..ys.len() {
+            let mut iter = Unfuse::new(xs).chain(Unfuse::new(ys));
+            iter.advance_by(xs.len() + i).unwrap();
+            assert_eq!(iter.next(), Some(&ys[i]));
+            assert_eq!(iter.advance_by(100), Err(ys.len() - i - 1));
+        }
+
+        let mut iter = xs.iter().chain(ys);
+        iter.advance_by(len).unwrap();
+        assert_eq!(iter.next(), None);
+
+        let mut iter = xs.iter().chain(ys);
+        assert_eq!(iter.advance_by(len + 1), Err(len));
+    }
+
+    test_chain(&[], &[]);
+    test_chain(&[], &[0, 1, 2, 3, 4, 5]);
+    test_chain(&[0, 1, 2, 3, 4, 5], &[]);
+    test_chain(&[0, 1, 2, 3, 4, 5], &[30, 40, 50, 60]);
+}
+
+#[test]
+fn test_iterator_chain_advance_back_by() {
+    fn test_chain(xs: &[i32], ys: &[i32]) {
+        let len = xs.len() + ys.len();
+
+        for i in 0..ys.len() {
+            let mut iter = Unfuse::new(xs).chain(Unfuse::new(ys));
+            iter.advance_back_by(i).unwrap();
+            assert_eq!(iter.next_back(), Some(&ys[ys.len() - i - 1]));
+            assert_eq!(iter.advance_back_by(100), Err(len - i - 1));
+        }
+
+        for i in 0..xs.len() {
+            let mut iter = Unfuse::new(xs).chain(Unfuse::new(ys));
+            iter.advance_back_by(ys.len() + i).unwrap();
+            assert_eq!(iter.next_back(), Some(&xs[xs.len() - i - 1]));
+            assert_eq!(iter.advance_back_by(100), Err(xs.len() - i - 1));
+        }
+
+        let mut iter = xs.iter().chain(ys);
+        iter.advance_back_by(len).unwrap();
+        assert_eq!(iter.next_back(), None);
+
+        let mut iter = xs.iter().chain(ys);
+        assert_eq!(iter.advance_back_by(len + 1), Err(len));
+    }
+
+    test_chain(&[], &[]);
+    test_chain(&[], &[0, 1, 2, 3, 4, 5]);
+    test_chain(&[0, 1, 2, 3, 4, 5], &[]);
+    test_chain(&[0, 1, 2, 3, 4, 5], &[30, 40, 50, 60]);
+}
+
+#[test]
+fn test_iterator_chain_nth() {
+    let xs = [0, 1, 2, 3, 4, 5];
+    let ys = [30, 40, 50, 60];
+    let zs = [];
+    let expected = [0, 1, 2, 3, 4, 5, 30, 40, 50, 60];
+    for (i, x) in expected.iter().enumerate() {
+        assert_eq!(Some(x), xs.iter().chain(&ys).nth(i));
+    }
+    assert_eq!(zs.iter().chain(&xs).nth(0), Some(&0));
+
+    let mut it = xs.iter().chain(&zs);
+    assert_eq!(it.nth(5), Some(&5));
+    assert_eq!(it.next(), None);
+}
+
+#[test]
+fn test_iterator_chain_nth_back() {
+    let xs = [0, 1, 2, 3, 4, 5];
+    let ys = [30, 40, 50, 60];
+    let zs = [];
+    let expected = [0, 1, 2, 3, 4, 5, 30, 40, 50, 60];
+    for (i, x) in expected.iter().rev().enumerate() {
+        assert_eq!(Some(x), xs.iter().chain(&ys).nth_back(i));
+    }
+    assert_eq!(zs.iter().chain(&xs).nth_back(0), Some(&5));
+
+    let mut it = xs.iter().chain(&zs);
+    assert_eq!(it.nth_back(5), Some(&0));
+    assert_eq!(it.next(), None);
+}
+
+#[test]
+fn test_iterator_chain_last() {
+    let xs = [0, 1, 2, 3, 4, 5];
+    let ys = [30, 40, 50, 60];
+    let zs = [];
+    assert_eq!(xs.iter().chain(&ys).last(), Some(&60));
+    assert_eq!(zs.iter().chain(&ys).last(), Some(&60));
+    assert_eq!(ys.iter().chain(&zs).last(), Some(&60));
+    assert_eq!(zs.iter().chain(&zs).last(), None);
+}
+
+#[test]
+fn test_iterator_chain_count() {
+    let xs = [0, 1, 2, 3, 4, 5];
+    let ys = [30, 40, 50, 60];
+    let zs = [];
+    assert_eq!(xs.iter().chain(&ys).count(), 10);
+    assert_eq!(zs.iter().chain(&ys).count(), 4);
+}
+
+#[test]
+fn test_iterator_chain_find() {
+    let xs = [0, 1, 2, 3, 4, 5];
+    let ys = [30, 40, 50, 60];
+    let mut iter = xs.iter().chain(&ys);
+    assert_eq!(iter.find(|&&i| i == 4), Some(&4));
+    assert_eq!(iter.next(), Some(&5));
+    assert_eq!(iter.find(|&&i| i == 40), Some(&40));
+    assert_eq!(iter.next(), Some(&50));
+    assert_eq!(iter.find(|&&i| i == 100), None);
+    assert_eq!(iter.next(), None);
+}
+
+#[test]
+fn test_iterator_chain_size_hint() {
+    // this chains an iterator of length 0 with an iterator of length 1,
+    // so after calling `.next()` once, the iterator is empty and the
+    // state is `ChainState::Back`. `.size_hint()` should now disregard
+    // the size hint of the left iterator
+    let mut iter = Toggle { is_empty: true }.chain(once(()));
+    assert_eq!(iter.next(), Some(()));
+    assert_eq!(iter.size_hint(), (0, Some(0)));
+
+    let mut iter = once(()).chain(Toggle { is_empty: true });
+    assert_eq!(iter.next_back(), Some(()));
+    assert_eq!(iter.size_hint(), (0, Some(0)));
+}
+
+#[test]
+fn test_iterator_chain_unfused() {
+    // Chain shouldn't be fused in its second iterator, depending on direction
+    let mut iter = NonFused::new(empty()).chain(Toggle { is_empty: true });
+    iter.next().unwrap_none();
+    iter.next().unwrap();
+    iter.next().unwrap_none();
+
+    let mut iter = Toggle { is_empty: true }.chain(NonFused::new(empty()));
+    iter.next_back().unwrap_none();
+    iter.next_back().unwrap();
+    iter.next_back().unwrap_none();
+}
+
+#[test]
+fn test_chain_fold() {
+    let xs = [1, 2, 3];
+    let ys = [1, 2, 0];
+
+    let mut iter = xs.iter().chain(&ys);
+    iter.next();
+    let mut result = Vec::new();
+    iter.fold((), |(), &elt| result.push(elt));
+    assert_eq!(&[2, 3, 1, 2, 0], &result[..]);
+}
+
+#[test]
+fn test_chain_try_folds() {
+    let c = || (0..10).chain(10..20);
+
+    let f = &|acc, x| i32::checked_add(2 * acc, x);
+    assert_eq!(c().try_fold(7, f), (0..20).try_fold(7, f));
+    assert_eq!(c().try_rfold(7, f), (0..20).rev().try_fold(7, f));
+
+    let mut iter = c();
+    assert_eq!(iter.position(|x| x == 5), Some(5));
+    assert_eq!(iter.next(), Some(6), "stopped in front, state Both");
+    assert_eq!(iter.position(|x| x == 13), Some(6));
+    assert_eq!(iter.next(), Some(14), "stopped in back, state Back");
+    assert_eq!(iter.try_fold(0, |acc, x| Some(acc + x)), Some((15..20).sum()));
+
+    let mut iter = c().rev(); // use rev to access try_rfold
+    assert_eq!(iter.position(|x| x == 15), Some(4));
+    assert_eq!(iter.next(), Some(14), "stopped in back, state Both");
+    assert_eq!(iter.position(|x| x == 5), Some(8));
+    assert_eq!(iter.next(), Some(4), "stopped in front, state Front");
+    assert_eq!(iter.try_fold(0, |acc, x| Some(acc + x)), Some((0..4).sum()));
+
+    let mut iter = c();
+    iter.by_ref().rev().nth(14); // skip the last 15, ending in state Front
+    assert_eq!(iter.try_fold(7, f), (0..5).try_fold(7, f));
+
+    let mut iter = c();
+    iter.nth(14); // skip the first 15, ending in state Back
+    assert_eq!(iter.try_rfold(7, f), (15..20).try_rfold(7, f));
+}
+
+#[test]
+fn test_double_ended_chain() {
+    let xs = [1, 2, 3, 4, 5];
+    let ys = [7, 9, 11];
+    let mut it = xs.iter().chain(&ys).rev();
+    assert_eq!(it.next().unwrap(), &11);
+    assert_eq!(it.next().unwrap(), &9);
+    assert_eq!(it.next_back().unwrap(), &1);
+    assert_eq!(it.next_back().unwrap(), &2);
+    assert_eq!(it.next_back().unwrap(), &3);
+    assert_eq!(it.next_back().unwrap(), &4);
+    assert_eq!(it.next_back().unwrap(), &5);
+    assert_eq!(it.next_back().unwrap(), &7);
+    assert_eq!(it.next_back(), None);
+
+    // test that .chain() is well behaved with an unfused iterator
+    struct CrazyIterator(bool);
+    impl CrazyIterator {
+        fn new() -> CrazyIterator {
+            CrazyIterator(false)
+        }
+    }
+    impl Iterator for CrazyIterator {
+        type Item = i32;
+        fn next(&mut self) -> Option<i32> {
+            if self.0 {
+                Some(99)
+            } else {
+                self.0 = true;
+                None
+            }
+        }
+    }
+
+    impl DoubleEndedIterator for CrazyIterator {
+        fn next_back(&mut self) -> Option<i32> {
+            self.next()
+        }
+    }
+
+    assert_eq!(CrazyIterator::new().chain(0..10).rev().last(), Some(0));
+    assert!((0..10).chain(CrazyIterator::new()).rev().any(|i| i == 0));
+}

library/core/tests/iter/adapters/chain.rs

@@ -0,0 +1,52 @@
+use core::iter::*;
+
+#[test]
+fn test_cloned() {
+    let xs = [2, 4, 6, 8];
+
+    let mut it = xs.iter().cloned();
+    assert_eq!(it.len(), 4);
+    assert_eq!(it.next(), Some(2));
+    assert_eq!(it.len(), 3);
+    assert_eq!(it.next(), Some(4));
+    assert_eq!(it.len(), 2);
+    assert_eq!(it.next_back(), Some(8));
+    assert_eq!(it.len(), 1);
+    assert_eq!(it.next_back(), Some(6));
+    assert_eq!(it.len(), 0);
+    assert_eq!(it.next_back(), None);
+}
+
+#[test]
+fn test_cloned_side_effects() {
+    let mut count = 0;
+    {
+        let iter = [1, 2, 3]
+            .iter()
+            .map(|x| {
+                count += 1;
+                x
+            })
+            .cloned()
+            .zip(&[1]);
+        for _ in iter {}
+    }
+    assert_eq!(count, 2);
+}
+
+#[test]
+fn test_cloned_try_folds() {
+    let a = [1, 2, 3, 4, 5, 6, 7, 8, 9];
+    let f = &|acc, x| i32::checked_add(2 * acc, x);
+    let f_ref = &|acc, &x| i32::checked_add(2 * acc, x);
+    assert_eq!(a.iter().cloned().try_fold(7, f), a.iter().try_fold(7, f_ref));
+    assert_eq!(a.iter().cloned().try_rfold(7, f), a.iter().try_rfold(7, f_ref));
+
+    let a = [10, 20, 30, 40, 100, 60, 70, 80, 90];
+    let mut iter = a.iter().cloned();
+    assert_eq!(iter.try_fold(0_i8, |acc, x| acc.checked_add(x)), None);
+    assert_eq!(iter.next(), Some(60));
+    let mut iter = a.iter().cloned();
+    assert_eq!(iter.try_rfold(0_i8, |acc, x| acc.checked_add(x)), None);
+    assert_eq!(iter.next_back(), Some(70));
+}

library/core/tests/iter/adapters/cloned.rs

@@ -0,0 +1,18 @@
+use core::iter::*;
+
+#[test]
+fn test_copied() {
+    let xs = [2, 4, 6, 8];
+
+    let mut it = xs.iter().copied();
+    assert_eq!(it.len(), 4);
+    assert_eq!(it.next(), Some(2));
+    assert_eq!(it.len(), 3);
+    assert_eq!(it.next(), Some(4));
+    assert_eq!(it.len(), 2);
+    assert_eq!(it.next_back(), Some(8));
+    assert_eq!(it.len(), 1);
+    assert_eq!(it.next_back(), Some(6));
+    assert_eq!(it.len(), 0);
+    assert_eq!(it.next_back(), None);
+}

library/core/tests/iter/adapters/copied.rs

@@ -0,0 +1,31 @@
+use core::iter::*;
+
+#[test]
+fn test_cycle() {
+    let cycle_len = 3;
+    let it = (0..).step_by(1).take(cycle_len).cycle();
+    assert_eq!(it.size_hint(), (usize::MAX, None));
+    for (i, x) in it.take(100).enumerate() {
+        assert_eq!(i % cycle_len, x);
+    }
+
+    let mut it = (0..).step_by(1).take(0).cycle();
+    assert_eq!(it.size_hint(), (0, Some(0)));
+    assert_eq!(it.next(), None);
+
+    assert_eq!(empty::<i32>().cycle().fold(0, |acc, x| acc + x), 0);
+
+    assert_eq!(once(1).cycle().skip(1).take(4).fold(0, |acc, x| acc + x), 4);
+
+    assert_eq!((0..10).cycle().take(5).sum::<i32>(), 10);
+    assert_eq!((0..10).cycle().take(15).sum::<i32>(), 55);
+    assert_eq!((0..10).cycle().take(25).sum::<i32>(), 100);
+
+    let mut iter = (0..10).cycle();
+    iter.nth(14);
+    assert_eq!(iter.take(8).sum::<i32>(), 38);
+
+    let mut iter = (0..10).cycle();
+    iter.nth(9);
+    assert_eq!(iter.take(3).sum::<i32>(), 3);
+}