FIx off-by-one in char::steps_between

Author: CAD97

src/libcore/iter/range.rs

@@ -408,7 +408,7 @@ unsafe impl Step for char {
         let start = start as u32;
         let end = end as u32;
         if start <= end {
-            let count = end - start + 1;
+            let count = end - start;
             if start < 0xD800 && 0xE000 <= end {
                 usize::try_from(count - 0x800).ok()
             } else {

src/libcore/tests/iter.rs

@@ -1939,7 +1939,9 @@ fn test_char_range() {
     assert!(('\0'..=char::MAX).rev().eq((0..=char::MAX as u32).filter_map(char::from_u32).rev()));
 
     assert_eq!(('\u{D7FF}'..='\u{E000}').count(), 2);
+    assert_eq!(('\u{D7FF}'..='\u{E000}').size_hint(), (2, Some(2)));
     assert_eq!(('\u{D7FF}'..'\u{E000}').count(), 1);
+    assert_eq!(('\u{D7FF}'..'\u{E000}').size_hint(), (1, Some(1)));
 }
 
 #[test]