perf(compilation): Directly construct Take and Chain

Moving `Take` and `Chain` from `std::io` into `core::io` required setting up constructors for use in
`std`. These constructors increased compilation time in `image` by 1.4% due to increased time spent
in LTO. Switching to unstable public fields for consturction instead.

Author: bushrat011899

library/core/src/io/mod.rs

@@ -15,6 +15,3 @@ pub use self::error::ErrorKind;
 pub use self::error::RawOsError;
 #[unstable(feature = "core_io", issue = "154046")]
 pub use self::util::{Chain, Empty, Repeat, Sink, Take, empty, repeat, sink};
-#[doc(hidden)]
-#[unstable(feature = "core_io_internals", reason = "exposed only for libstd", issue = "none")]
-pub use self::util::{chain, take};

library/core/src/io/util.rs

@@ -132,7 +132,6 @@ pub const fn sink() -> Sink {
 /// [`chain`]: ../../std/io/trait.Read.html#method.chain
 #[stable(feature = "rust1", since = "1.0.0")]
 #[derive(Debug)]
-#[non_exhaustive]
 pub struct Chain<T, U> {
     #[doc(hidden)]
     #[unstable(feature = "core_io_internals", reason = "exposed only for libstd", issue = "none")]
@@ -224,14 +223,6 @@ impl<T, U> Chain<T, U> {
     }
 }
 
-#[doc(hidden)]
-#[unstable(feature = "core_io_internals", reason = "exposed only for libstd", issue = "none")]
-#[must_use]
-#[inline]
-pub const fn chain<T, U>(first: T, second: U) -> Chain<T, U> {
-    Chain { first, second, done_first: false }
-}
-
 /// Reader adapter which limits the bytes read from an underlying reader.
 ///
 /// This struct is generally created by calling [`take`] on a reader.
@@ -240,7 +231,6 @@ pub const fn chain<T, U>(first: T, second: U) -> Chain<T, U> {
 /// [`take`]: ../../std/io/trait.Read.html#method.take
 #[stable(feature = "rust1", since = "1.0.0")]
 #[derive(Debug)]
-#[non_exhaustive]
 pub struct Take<T> {
     #[doc(hidden)]
     #[unstable(feature = "core_io_internals", reason = "exposed only for libstd", issue = "none")]
@@ -405,11 +395,3 @@ impl<T> Take<T> {
         &mut self.inner
     }
 }
-
-#[doc(hidden)]
-#[unstable(feature = "core_io_internals", reason = "exposed only for libstd", issue = "none")]
-#[must_use]
-#[inline]
-pub const fn take<T>(inner: T, limit: u64) -> Take<T> {
-    Take { inner, limit, len: limit }
-}

library/std/src/io/mod.rs

@@ -1184,7 +1184,7 @@ pub trait Read {
     where
         Self: Sized,
     {
-        core::io::chain(self, next)
+        Chain { first: self, second: next, done_first: false }
     }
 
     /// Creates an adapter which will read at most `limit` bytes from it.
@@ -1223,7 +1223,7 @@ pub trait Read {
     where
         Self: Sized,
     {
-        core::io::take(self, limit)
+        Take { inner: self, len: limit, limit }
     }
 
     /// Read and return a fixed array of bytes from this source.