csv: fix quoting with projection

polars/polars-io/src/csv.rs

@@ -1262,4 +1262,32 @@ linenum,last_name,first_name
         assert_eq!(df.dtypes(), &[Utf8, Utf8, Utf8]);
         Ok(())
     }
+
+    fn test_projection_and_quoting() -> Result<()> {
+        let csv = "a,b,c,d
+A1,'B1',C1,1
+A2,\"B2\",C2,2
+A3,\"B3\",C3,3
+A3,\"B4_\"\"with_embedded_double_quotes\"\"\",C4,4";
+
+        let file = Cursor::new(csv);
+        let df = CsvReader::new(file).finish()?;
+        assert_eq!(df.shape(), (4, 4));
+
+        let file = Cursor::new(csv);
+        let df = CsvReader::new(file)
+            .with_n_threads(Some(1))
+            .with_projection(Some(vec![0, 2]))
+            .finish()?;
+        assert_eq!(df.shape(), (4, 2));
+
+        let file = Cursor::new(csv);
+        let df = CsvReader::new(file)
+            .with_n_threads(Some(1))
+            .with_projection(Some(vec![1]))
+            .finish()?;
+        assert_eq!(df.shape(), (4, 1));
+
+        Ok(())
+    }
 }

polars/polars-io/src/csv_core/parser.rs

@@ -503,13 +503,12 @@ pub(crate) fn parse_lines(
                                 next_projected = p
                             }
                             None => {
-                                let offset = read_sol - 1;
                                 if let Some(b'\n') = bytes.get(0) {
                                     bytes = &bytes[read_sol..];
                                     read += read_sol
                                 } else {
                                     let (bytes_rem, len) =
-                                        skip_this_line(&bytes[offset..], quote_char, offset);
+                                        skip_this_line(bytes, quote_char, offset);
                                     bytes = bytes_rem;
                                     read += len;
                                 }