Fix use of byte count instead of char count.

parser/src/scanner.rs

@@ -1775,8 +1775,9 @@ impl<T: Input> Scanner<T> {
             }
 
             // We need to manually update our position; we haven't called a `skip` function.
-            self.mark.col += line_buffer.len();
-            self.mark.index += line_buffer.len();
+            let n_chars = line_buffer.chars().count();
+            self.mark.col += n_chars;
+            self.mark.index += n_chars;
 
             // We can now append our bytes to our `string`.
             string.reserve(line_buffer.as_bytes().len());

parser/tests/fuzz.rs

@@ -74,3 +74,14 @@ fn fuzz_2() {
     let s = str::from_utf8(raw_input).unwrap();
     let _ = run_parser(s);
 }
+
+#[test]
+fn fuzz_3() {
+    // Span mismatch when parsing with `StrInput` and `BufferedInput`.
+    // In block scalars, there was a section in which we took the byte count rather than the char
+    // count to update the index. The issue didn't happen with `StrInput` as the buffer was always
+    // full and the offending code was never executed.
+    let raw_input: &[u8] = &[124, 13, 32, 210, 180, 65];
+    let s = str::from_utf8(raw_input).unwrap();
+    let _ = run_parser(s);
+}