lazycsv: Handle trailing empty cell gracefully

Author: simnalamburt

crates/lazycsv/src/lib.rs

@@ -328,10 +328,15 @@ impl<'a> Iterator for Csv<'a> {
             else {
                 self.state = IterState::Done;
                 return if start < self.buf.len() {
+                    // Return the last cell if there's remaining data.
                     Some(CsvIterItem::Cell(Cell {
                         buf: &self.buf[start..],
                     }))
+                } else if !self.buf.is_empty() && self.buf.ends_with(&[self.separator]) {
+                    // Handle trailing empty cell when no trailing newline is present.
+                    Some(CsvIterItem::Cell(Cell { buf: &[] }))
                 } else {
+                    // Gracefully reached EOF with no more data
                     None
                 };
             };

crates/lazycsv/tests/main.rs

@@ -59,51 +59,78 @@ fn basic() {
     assert_csv!(csv, EOF);
 }
 
+#[cfg(feature = "alloc")]
 #[test]
-fn no_trailing_newline() {
-    let mut csv = Csv::new(b"a,b,c\n1,2,3\n4,5,6");
+fn dequote() {
+    let cell = Cell {
+        buf: br#""Hi ""Quote"" yo""#,
+    };
+    assert_eq!(cell.try_as_str().unwrap(), r#"Hi "Quote" yo"#);
+}
 
+#[test]
+fn check_corner_cases() {
+    // No trailing newline
+    let mut csv = Csv::new(b"a,b,c\n1,2,3\n4,5,6");
+    assert_csv!(csv, position == 0);
     assert_csv!(csv, Cell(b"a"));
+    assert_csv!(csv, position == 2);
     assert_csv!(csv, Cell(b"b"));
+    assert_csv!(csv, position == 4);
     assert_csv!(csv, Cell(b"c"));
+    assert_csv!(csv, position == 5);
     assert_csv!(csv, LineEnd);
+    assert_csv!(csv, position == 6);
     assert_csv!(csv, Cell(b"1"));
+    assert_csv!(csv, position == 8);
     assert_csv!(csv, Cell(b"2"));
+    assert_csv!(csv, position == 10);
     assert_csv!(csv, Cell(b"3"));
+    assert_csv!(csv, position == 11);
     assert_csv!(csv, LineEnd);
+    assert_csv!(csv, position == 12);
     assert_csv!(csv, Cell(b"4"));
+    assert_csv!(csv, position == 14);
     assert_csv!(csv, Cell(b"5"));
+    assert_csv!(csv, position == 16);
     assert_csv!(csv, Cell(b"6"));
+    assert_csv!(csv, position == 17);
     assert_csv!(csv, EOF);
-}
-
-#[cfg(feature = "alloc")]
-#[test]
-fn dequote() {
-    let cell = Cell {
-        buf: br#""Hi ""Quote"" yo""#,
-    };
-    assert_eq!(cell.try_as_str().unwrap(), r#"Hi "Quote" yo"#);
-}
-
-#[test]
-fn position() {
-    let data = b"aaa,bbb\n100,200";
-    let mut csv = Csv::new(data);
+    assert_csv!(csv, position == 17);
 
+    // CRLF line endings
+    let mut csv = Csv::new(b"aaa,bbb\r\n100,200\r\n");
     assert_csv!(csv, position == 0); // Start position
     assert_csv!(csv, Cell(b"aaa")); // Yields Cell('aaa')
     assert_csv!(csv, position == 4); // Position after 'aaa,' (start of 'b')
     assert_csv!(csv, Cell(b"bbb")); // Yields Cell('bbb')
     assert_csv!(csv, position == 7); // Position after 'bbb' (start of '\r')
     assert_csv!(csv, LineEnd); // Yields LineEnd
-    assert_csv!(csv, position == 8); // Position after '\n' (start of '1')
+    assert_csv!(csv, position == 9); // Position after '\n' (start of '1')
     assert_csv!(csv, Cell(b"100")); // Yields Cell('100')
-    assert_csv!(csv, position == 12); // Position after '100,' (start of '2')
+    assert_csv!(csv, position == 13); // Position after '100,' (start of '2')
     assert_csv!(csv, Cell(b"200")); // Yields Cell('200')
-    assert_csv!(csv, position == 15); // Position after '200' (end of buffer)
+    assert_csv!(csv, position == 16); // Position after '200' (end of buffer)
+    assert_csv!(csv, LineEnd); // Yields LineEnd
+    assert_csv!(csv, position == 18); // Position after '\n' (end of buffer)
     assert_csv!(csv, EOF); // End of iteration
-    assert_csv!(csv, position == data.len()); // Position at the end
+    assert_csv!(csv, position == 18); // Position at the end
+
+    // empty cells at line end without trailing newline
+    let mut csv = Csv::new(b"aaa,\n100,");
+    assert_csv!(csv, position == 0);
+    assert_csv!(csv, Cell(b"aaa"));
+    assert_csv!(csv, position == 4);
+    assert_csv!(csv, Cell(b""));
+    assert_csv!(csv, position == 4);
+    assert_csv!(csv, LineEnd);
+    assert_csv!(csv, position == 5);
+    assert_csv!(csv, Cell(b"100"));
+    assert_csv!(csv, position == 9);
+    assert_csv!(csv, Cell(b""));
+    assert_csv!(csv, position == 9);
+    assert_csv!(csv, EOF);
+    assert_csv!(csv, position == 9);
 }
 
 #[test]