update function's doc comment

Author: 2bndy5

Diff for: cpp-linter/src/common_fs/mod.rs

@@ -219,18 +219,15 @@ impl FileObj {
     }
 }
 
-/// Gets the line and column number from a given `offset` (of bytes) for given
-/// `file_path`.
+/// Gets the line number for a given `offset` (of bytes) from the given
+/// buffer `contents`.
 ///
-/// This computes the line and column numbers from a buffer of bytes read from the
-/// `file_path`. In non-UTF-8 encoded files, this does not guarantee that a word
-/// boundary exists at the returned column number. However, the `offset` given to this
-/// function is expected to originate from diagnostic information provided by
-/// clang-format or clang-tidy.
+/// The `offset` given to this function is expected to originate from
+/// diagnostic information provided by clang-format. Any `offset` out of
+/// bounds is clamped to the given `contents` buffer's length.
 pub fn get_line_count_from_offset(contents: &[u8], offset: u32) -> u32 {
     let offset = (offset as usize).min(contents.len());
     let lines = contents[0..offset].split(|byte| byte == &b'\n');
-
     lines.count() as u32
 }
 
@@ -316,6 +313,20 @@ mod test {
         assert_eq!(lines, 13);
     }
 
+    #[test]
+    fn get_line_count_edge_cases() {
+        // Empty content
+        assert_eq!(get_line_count_from_offset(&[], 0), 1);
+
+        // No newlines
+        assert_eq!(get_line_count_from_offset(b"abc", 3), 1);
+
+        // Consecutive newlines
+        assert_eq!(get_line_count_from_offset(b"a\n\nb", 3), 3);
+
+        // Offset beyond content length
+        assert_eq!(get_line_count_from_offset(b"a\nb\n", 10), 3);
+    }
     // *********************** tests for FileObj::get_ranges()
 
     #[test]