count: empty CSVs count as zero also for polars

fixes #1741

src/cmd/count.rs

@@ -211,11 +211,19 @@ pub fn polars_count_input(
  };
 
  // read the file into a Polars LazyFrame
- let lazy_df = LazyCsvReader::new(filepath.clone())
+ let lazy_df = match LazyCsvReader::new(filepath.clone())
  .with_separator(conf.get_delimiter())
  .with_comment_prefix(comment_prefix)
  .low_memory(low_memory)
- .finish()?;
+ .finish()
+ {
+ Ok(lazy_df) => lazy_df,
+ Err(e) => {
+ log::warn!("polars error: {}", e);
+ let (count_regular, _) = count_input(conf, false)?;
+ return Ok((count_regular, 0));
+ },
+ };
 
  // and leverage the magic of Polars SQL with its lazy evaluation, to count the records
  // in an optimized manner with its blazing fast multithreaded, mem-mapped CSV reader!

tests/test_count.rs

@@ -20,6 +20,18 @@ fn count_simple() {
  assert_eq!(got, expected.to_string());
 }
 
+#[test]
+fn count_empty() {
+ let wrk = Workdir::new("count_empty");
+ wrk.create_from_string("empty.csv", "");
+ let mut cmd = wrk.command("count");
+ cmd.arg("empty.csv");
+
+ let got: String = wrk.stdout(&mut cmd);
+ let expected = "0";
+ assert_eq!(got, expected.to_string());
+}
+
 #[test]
 fn count_simple_tsv() {
  let wrk = Workdir::new("count_simple_tsv");