Export utf8_char_width() publicly in core::std behind the "str_internals" feature gate and use it in sys::windows::stdio instead of reimplementing it there.

Author: Count-Count

library/core/src/str/mod.rs

@@ -71,6 +71,9 @@ pub use iter::SplitInclusive;
 #[unstable(feature = "str_internals", issue = "none")]
 pub use validations::next_code_point;
 
+#[unstable(feature = "str_internals", issue = "none")]
+pub use validations::utf8_char_width;
+
 use iter::MatchIndicesInternal;
 use iter::SplitInternal;
 use iter::{MatchesInternal, SplitNInternal};

library/std/src/sys/windows/stdio.rs

@@ -8,6 +8,7 @@ use crate::str;
 use crate::sys::c;
 use crate::sys::cvt;
 use crate::sys::handle::Handle;
+use core::str::utf8_char_width;
 
 // Don't cache handles but get them fresh for every read/write. This allows us to track changes to
 // the value over time (such as if a process calls `SetStdHandle` while it's running). See #40490.
@@ -60,18 +61,6 @@ fn is_console(handle: c::HANDLE) -> bool {
     unsafe { c::GetConsoleMode(handle, &mut mode) != 0 }
 }
 
-// Simple reimplementation of std::str::utf8_char_width() which is feature-gated
-fn utf8_char_width(b: u8) -> usize {
-    match b {
-        0x00..=0x7F => 1,
-        0x80..=0xC1 => 0,
-        0xC2..=0xDF => 2,
-        0xE0..=0xEF => 3,
-        0xF0..=0xF4 => 4,
-        0xF5..=0xFF => 0,
-    }
-}
-
 fn write(
     handle_id: c::DWORD,
     data: &[u8],