Rollup merge of rust-lang#82917 - cuviper:iter-zip, r=m-ou-se

Add function core::iter::zip

This makes it a little easier to `zip` iterators:

```rust
for (x, y) in zip(xs, ys) {}
// vs.
for (x, y) in xs.into_iter().zip(ys) {}
```

You can `zip(&mut xs, &ys)` for the conventional `iter_mut()` and
`iter()`, respectively. This can also support arbitrary nesting, where
it's easier to see the item layout than with arbitrary `zip` chains:

```rust
for ((x, y), z) in zip(zip(xs, ys), zs) {}
for (x, (y, z)) in zip(xs, zip(ys, zs)) {}
// vs.
for ((x, y), z) in xs.into_iter().zip(ys).zip(xz) {}
for (x, (y, z)) in xs.into_iter().zip((ys.into_iter().zip(xz)) {}
```

It may also format more nicely, especially when the first iterator is a
longer chain of methods -- for example:

```rust
    iter::zip(
        trait_ref.substs.types().skip(1),
        impl_trait_ref.substs.types().skip(1),
    )
    // vs.
    trait_ref
        .substs
        .types()
        .skip(1)
        .zip(impl_trait_ref.substs.types().skip(1))
```

This replaces the tuple-pair `IntoIterator` in rust-lang#78204.
There is prior art for the utility of this in [`itertools::zip`].

[`itertools::zip`]: https://docs.rs/itertools/0.10.0/itertools/fn.zip.html

Author: Dylan-DPC

alloc/src/lib.rs

@@ -108,6 +108,7 @@
 // that the feature-gate isn't enabled. Ideally, it wouldn't check for the feature gate for docs
 // from other crates, but since this can only appear for lang items, it doesn't seem worth fixing.
 #![feature(intra_doc_pointers)]
+#![feature(iter_zip)]
 #![feature(lang_items)]
 #![feature(layout_for_ptr)]
 #![feature(maybe_uninit_ref)]

alloc/src/vec/mod.rs

@@ -58,7 +58,7 @@ use core::convert::TryFrom;
 use core::fmt;
 use core::hash::{Hash, Hasher};
 use core::intrinsics::{arith_offset, assume};
-use core::iter::FromIterator;
+use core::iter::{self, FromIterator};
 use core::marker::PhantomData;
 use core::mem::{self, ManuallyDrop, MaybeUninit};
 use core::ops::{self, Index, IndexMut, Range, RangeBounds};
@@ -2268,11 +2268,8 @@ impl<T: Clone, A: Allocator> ExtendFromWithinSpec for Vec<T, A> {
         // - caller guaratees that src is a valid index
         let to_clone = unsafe { this.get_unchecked(src) };
 
-        to_clone
-            .iter()
-            .cloned()
-            .zip(spare.iter_mut())
-            .map(|(src, dst)| dst.write(src))
+        iter::zip(to_clone, spare)
+            .map(|(src, dst)| dst.write(src.clone()))
             // Note:
             // - Element was just initialized with `MaybeUninit::write`, so it's ok to increace len
             // - len is increased after each element to prevent leaks (see issue #82533)

core/src/array/iter.rs

@@ -2,7 +2,7 @@
 
 use crate::{
     fmt,
-    iter::{ExactSizeIterator, FusedIterator, TrustedLen, TrustedRandomAccess},
+    iter::{self, ExactSizeIterator, FusedIterator, TrustedLen, TrustedRandomAccess},
     mem::{self, MaybeUninit},
     ops::Range,
     ptr,
@@ -215,7 +215,7 @@ impl<T: Clone, const N: usize> Clone for IntoIter<T, N> {
         let mut new = Self { data: MaybeUninit::uninit_array(), alive: 0..0 };
 
         // Clone all alive elements.
-        for (src, dst) in self.as_slice().iter().zip(&mut new.data) {
+        for (src, dst) in iter::zip(self.as_slice(), &mut new.data) {
             // Write a clone into the new array, then update its alive range.
             // If cloning panics, we'll correctly drop the previous items.
             dst.write(src.clone());

core/src/fmt/mod.rs

@@ -4,6 +4,7 @@
 
 use crate::cell::{Cell, Ref, RefCell, RefMut, UnsafeCell};
 use crate::char::EscapeDebugExtArgs;
+use crate::iter;
 use crate::marker::PhantomData;
 use crate::mem;
 use crate::num::flt2dec;
@@ -1088,7 +1089,7 @@ pub fn write(output: &mut dyn Write, args: Arguments<'_>) -> Result {
     match args.fmt {
         None => {
             // We can use default formatting parameters for all arguments.
-            for (arg, piece) in args.args.iter().zip(args.pieces.iter()) {
+            for (arg, piece) in iter::zip(args.args, args.pieces) {
                 formatter.buf.write_str(*piece)?;
                 (arg.formatter)(arg.value, &mut formatter)?;
                 idx += 1;
@@ -1097,7 +1098,7 @@ pub fn write(output: &mut dyn Write, args: Arguments<'_>) -> Result {
         Some(fmt) => {
             // Every spec has a corresponding argument that is preceded by
             // a string piece.
-            for (arg, piece) in fmt.iter().zip(args.pieces.iter()) {
+            for (arg, piece) in iter::zip(fmt, args.pieces) {
                 formatter.buf.write_str(*piece)?;
                 // SAFETY: arg and args.args come from the same Arguments,
                 // which guarantees the indexes are always within bounds.

core/src/iter/adapters/mod.rs

@@ -51,6 +51,9 @@ pub use self::map_while::MapWhile;
 #[unstable(feature = "trusted_random_access", issue = "none")]
 pub use self::zip::TrustedRandomAccess;
 
+#[unstable(feature = "iter_zip", issue = "83574")]
+pub use self::zip::zip;
+
 /// This trait provides transitive access to source-stage in an interator-adapter pipeline
 /// under the conditions that
 /// * the iterator source `S` itself implements `SourceIter<Source = S>`

core/src/iter/adapters/zip.rs

@@ -5,8 +5,8 @@ use crate::iter::{InPlaceIterable, SourceIter, TrustedLen};
 
 /// An iterator that iterates two other iterators simultaneously.
 ///
-/// This `struct` is created by [`Iterator::zip`]. See its documentation
-/// for more.
+/// This `struct` is created by [`zip`] or [`Iterator::zip`].
+/// See their documentation for more.
 #[derive(Clone)]
 #[must_use = "iterators are lazy and do nothing unless consumed"]
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -33,6 +33,37 @@ impl<A: Iterator, B: Iterator> Zip<A, B> {
     }
 }
 
+/// Converts the arguments to iterators and zips them.
+///
+/// See the documentation of [`Iterator::zip`] for more.
+///
+/// # Examples
+///
+/// ```
+/// #![feature(iter_zip)]
+/// use std::iter::zip;
+///
+/// let xs = [1, 2, 3];
+/// let ys = [4, 5, 6];
+/// for (x, y) in zip(&xs, &ys) {
+///     println!("x:{}, y:{}", x, y);
+/// }
+///
+/// // Nested zips are also possible:
+/// let zs = [7, 8, 9];
+/// for ((x, y), z) in zip(zip(&xs, &ys), &zs) {
+///     println!("x:{}, y:{}, z:{}", x, y, z);
+/// }
+/// ```
+#[unstable(feature = "iter_zip", issue = "83574")]
+pub fn zip<A, B>(a: A, b: B) -> Zip<A::IntoIter, B::IntoIter>
+where
+    A: IntoIterator,
+    B: IntoIterator,
+{
+    ZipImpl::new(a.into_iter(), b.into_iter())
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<A, B> Iterator for Zip<A, B>
 where

core/src/iter/mod.rs

@@ -389,6 +389,8 @@ pub use self::traits::{
     DoubleEndedIterator, ExactSizeIterator, Extend, FromIterator, IntoIterator, Product, Sum,
 };
 
+#[unstable(feature = "iter_zip", issue = "83574")]
+pub use self::adapters::zip;
 #[stable(feature = "iter_cloned", since = "1.1.0")]
 pub use self::adapters::Cloned;
 #[stable(feature = "iter_copied", since = "1.36.0")]

core/src/num/bignum.rs

@@ -181,11 +181,12 @@ macro_rules! define_bignum {
             /// Adds `other` to itself and returns its own mutable reference.
             pub fn add<'a>(&'a mut self, other: &$name) -> &'a mut $name {
                 use crate::cmp;
+                use crate::iter;
                 use crate::num::bignum::FullOps;
 
                 let mut sz = cmp::max(self.size, other.size);
                 let mut carry = false;
-                for (a, b) in self.base[..sz].iter_mut().zip(&other.base[..sz]) {
+                for (a, b) in iter::zip(&mut self.base[..sz], &other.base[..sz]) {
                     let (c, v) = (*a).full_add(*b, carry);
                     *a = v;
                     carry = c;
@@ -219,11 +220,12 @@ macro_rules! define_bignum {
             /// Subtracts `other` from itself and returns its own mutable reference.
             pub fn sub<'a>(&'a mut self, other: &$name) -> &'a mut $name {
                 use crate::cmp;
+                use crate::iter;
                 use crate::num::bignum::FullOps;
 
                 let sz = cmp::max(self.size, other.size);
                 let mut noborrow = true;
-                for (a, b) in self.base[..sz].iter_mut().zip(&other.base[..sz]) {
+                for (a, b) in iter::zip(&mut self.base[..sz], &other.base[..sz]) {
                     let (c, v) = (*a).full_add(!*b, noborrow);
                     *a = v;
                     noborrow = c;

core/src/slice/ascii.rs

@@ -1,5 +1,6 @@
 //! Operations on ASCII `[u8]`.
 
+use crate::iter;
 use crate::mem;
 
 #[lang = "slice_u8"]
@@ -19,7 +20,7 @@ impl [u8] {
     #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
     #[inline]
     pub fn eq_ignore_ascii_case(&self, other: &[u8]) -> bool {
-        self.len() == other.len() && self.iter().zip(other).all(|(a, b)| a.eq_ignore_ascii_case(b))
+        self.len() == other.len() && iter::zip(self, other).all(|(a, b)| a.eq_ignore_ascii_case(b))
     }
 
     /// Converts this slice to its ASCII upper case equivalent in-place.

std/src/lib.rs

@@ -278,6 +278,7 @@
 #![feature(integer_atomics)]
 #![feature(into_future)]
 #![feature(intra_doc_pointers)]
+#![feature(iter_zip)]
 #![feature(lang_items)]
 #![feature(link_args)]
 #![feature(linkage)]