Delegate to inner `vec::IntoIter` from `env::ArgsOs`

Delegate from `std::env::ArgsOs` to the methods of the inner
platform-specific iterators, when it would be more efficient than just
using the default methods of its own impl. Most platforms use
`vec::IntoIter` as the inner type, so prioritize delegating to the
methods it provides.

`std::env::Args` is implemented atop `std::env::ArgsOs` and performs
UTF-8 validation with a panic for invalid data. This is a visible effect
which users certainly rely on, so we can't skip any arguments. Any
further iterator methods would skip some elements, so no change is
needed for that type.

Add `#[inline]` for any methods which simply wrap the inner iterator.

3 files changed, 132 insertions, 20 deletions

diff --git a/library/std/src/sys/args/common.rs b/library/std/src/sys/args/common.rs
index 43ac5e95923..303b373ccf9 100644
--- a/library/std/src/sys/args/common.rs
+++ b/library/std/src/sys/args/common.rs
@@ -1,5 +1,7 @@
 use crate::ffi::OsString;
-use crate::{fmt, vec};
+use crate::num::NonZero;
+use crate::ops::Try;
+use crate::{array, fmt, vec};
 
 pub struct Args {
     iter: vec::IntoIter<OsString>,
@@ -9,6 +11,7 @@ impl !Send for Args {}
 impl !Sync for Args {}
 
 impl Args {
+    #[inline]
     pub(super) fn new(args: Vec<OsString>) -> Self {
         Args { iter: args.into_iter() }
     }
@@ -22,22 +25,77 @@ impl fmt::Debug for Args {
 
 impl Iterator for Args {
     type Item = OsString;
+
+    #[inline]
     fn next(&mut self) -> Option<OsString> {
         self.iter.next()
     }
+
+    #[inline]
+    fn next_chunk<const N: usize>(
+        &mut self,
+    ) -> Result<[OsString; N], array::IntoIter<OsString, N>> {
+        self.iter.next_chunk()
+    }
+
+    #[inline]
     fn size_hint(&self) -> (usize, Option<usize>) {
         self.iter.size_hint()
     }
-}
 
-impl ExactSizeIterator for Args {
-    fn len(&self) -> usize {
+    #[inline]
+    fn count(self) -> usize {
         self.iter.len()
     }
+
+    #[inline]
+    fn last(mut self) -> Option<OsString> {
+        self.iter.next_back()
+    }
+
+    #[inline]
+    fn advance_by(&mut self, n: usize) -> Result<(), NonZero<usize>> {
+        self.iter.advance_by(n)
+    }
+
+    #[inline]
+    fn try_fold<B, F, R>(&mut self, init: B, f: F) -> R
+    where
+        F: FnMut(B, Self::Item) -> R,
+        R: Try<Output = B>,
+    {
+        self.iter.try_fold(init, f)
+    }
+
+    #[inline]
+    fn fold<B, F>(self, init: B, f: F) -> B
+    where
+        F: FnMut(B, Self::Item) -> B,
+    {
+        self.iter.fold(init, f)
+    }
 }
 
 impl DoubleEndedIterator for Args {
+    #[inline]
     fn next_back(&mut self) -> Option<OsString> {
         self.iter.next_back()
     }
+
+    #[inline]
+    fn advance_back_by(&mut self, n: usize) -> Result<(), NonZero<usize>> {
+        self.iter.advance_back_by(n)
+    }
+}
+
+impl ExactSizeIterator for Args {
+    #[inline]
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+
+    #[inline]
+    fn is_empty(&self) -> bool {
+        self.iter.is_empty()
+    }
 }
diff --git a/library/std/src/sys/args/sgx.rs b/library/std/src/sys/args/sgx.rs
index 2a4bc76aefb..f800500c22a 100644
--- a/library/std/src/sys/args/sgx.rs
+++ b/library/std/src/sys/args/sgx.rs
@@ -1,6 +1,8 @@
 #![allow(fuzzy_provenance_casts)] // FIXME: this module systematically confuses pointers and integers
 
 use crate::ffi::OsString;
+use crate::num::NonZero;
+use crate::ops::Try;
 use crate::sync::atomic::{Atomic, AtomicUsize, Ordering};
 use crate::sys::os_str::Buf;
 use crate::sys::pal::abi::usercalls::alloc;
@@ -28,35 +30,81 @@ pub unsafe fn init(argc: isize, argv: *const *const u8) {
 
 pub fn args() -> Args {
     let args = unsafe { (ARGS.load(Ordering::Relaxed) as *const ArgsStore).as_ref() };
-    if let Some(args) = args { Args(args.iter()) } else { Args([].iter()) }
+    let slice = args.map(|args| args.as_slice()).unwrap_or(&[]);
+    Args { iter: slice.iter() }
 }
 
-pub struct Args(slice::Iter<'static, OsString>);
+pub struct Args {
+    iter: slice::Iter<'static, OsString>,
+}
 
 impl fmt::Debug for Args {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        self.0.as_slice().fmt(f)
+        self.iter.as_slice().fmt(f)
     }
 }
 
 impl Iterator for Args {
     type Item = OsString;
+
     fn next(&mut self) -> Option<OsString> {
-        self.0.next().cloned()
+        self.iter.next().cloned()
     }
+
+    #[inline]
     fn size_hint(&self) -> (usize, Option<usize>) {
-        self.0.size_hint()
+        self.iter.size_hint()
     }
-}
 
-impl ExactSizeIterator for Args {
-    fn len(&self) -> usize {
-        self.0.len()
+    #[inline]
+    fn count(self) -> usize {
+        self.iter.len()
+    }
+
+    fn last(self) -> Option<OsString> {
+        self.iter.last().cloned()
+    }
+
+    #[inline]
+    fn advance_by(&mut self, n: usize) -> Result<(), NonZero<usize>> {
+        self.iter.advance_by(n)
+    }
+
+    fn try_fold<B, F, R>(&mut self, init: B, f: F) -> R
+    where
+        F: FnMut(B, Self::Item) -> R,
+        R: Try<Output = B>,
+    {
+        self.iter.by_ref().cloned().try_fold(init, f)
+    }
+
+    fn fold<B, F>(self, init: B, f: F) -> B
+    where
+        F: FnMut(B, Self::Item) -> B,
+    {
+        self.iter.cloned().fold(init, f)
     }
 }
 
 impl DoubleEndedIterator for Args {
     fn next_back(&mut self) -> Option<OsString> {
-        self.0.next_back().cloned()
+        self.iter.next_back().cloned()
+    }
+
+    #[inline]
+    fn advance_back_by(&mut self, n: usize) -> Result<(), NonZero<usize>> {
+        self.iter.advance_back_by(n)
+    }
+}
+
+impl ExactSizeIterator for Args {
+    #[inline]
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+
+    #[inline]
+    fn is_empty(&self) -> bool {
+        self.iter.is_empty()
     }
 }
diff --git a/library/std/src/sys/args/unsupported.rs b/library/std/src/sys/args/unsupported.rs
index a2d75a61976..ecffc6d2641 100644
--- a/library/std/src/sys/args/unsupported.rs
+++ b/library/std/src/sys/args/unsupported.rs
@@ -15,22 +15,28 @@ impl fmt::Debug for Args {
 
 impl Iterator for Args {
     type Item = OsString;
+
+    #[inline]
     fn next(&mut self) -> Option<OsString> {
         None
     }
+
+    #[inline]
     fn size_hint(&self) -> (usize, Option<usize>) {
         (0, Some(0))
     }
 }
 
-impl ExactSizeIterator for Args {
-    fn len(&self) -> usize {
-        0
-    }
-}
-
 impl DoubleEndedIterator for Args {
+    #[inline]
     fn next_back(&mut self) -> Option<OsString> {
         None
     }
 }
+
+impl ExactSizeIterator for Args {
+    #[inline]
+    fn len(&self) -> usize {
+        0
+    }
+}