also use polars count with util::count_rows() helper if polars featur…

…es is enabled

src/cmd/count.rs

@@ -155,7 +155,7 @@ fn count_input(
 }
 
 #[cfg(feature = "polars")]
-fn polars_count_input(
+pub fn polars_count_input(
     conf: &Config,
     low_memory: bool,
 ) -> Result<(u64, usize), crate::clitypes::CliError> {

src/util.rs

@@ -21,6 +21,8 @@ use serde::de::DeserializeOwned;
 use serde::de::{Deserialize, Deserializer, Error};
 use sysinfo::System;
 
+#[cfg(feature = "polars")]
+use crate::cmd::count::polars_count_input;
 use crate::{
     config,
     config::{Config, Delimiter, DEFAULT_WTR_BUFFER_CAPACITY},
@@ -293,10 +295,32 @@ pub fn count_rows(conf: &Config) -> Result<u64, CliError> {
         Ok(idx.count())
     } else {
         // index does not exist or is stale,
-        // count records by iterating through records
+        // count records by using polars mem-mapped reader if available
+        // otherwise, count records by iterating through records
         // Do this only once per invocation and cache the result in ROW_COUNT,
         // so we don't have to re-count rows every time we need to know the
         // rowcount for CSVs that don't have an index.
+        #[cfg(feature = "polars")]
+        let count_opt = ROW_COUNT.get_or_init(|| {
+            if let Ok((count, _)) = polars_count_input(conf, false) {
+                Some(count)
+            } else {
+                // if polars_count_input fails, fall back to regular CSV reader
+                if let Ok(mut rdr) = conf.reader() {
+                    let mut count = 0_u64;
+                    let mut _record = csv::ByteRecord::new();
+                    #[allow(clippy::used_underscore_binding)]
+                    while rdr.read_byte_record(&mut _record).unwrap_or_default() {
+                        count += 1;
+                    }
+                    Some(count)
+                } else {
+                    None
+                }
+            }
+        });
+
+        #[cfg(not(feature = "polars"))]
         let count_opt = ROW_COUNT.get_or_init(|| {
             if let Ok(mut rdr) = conf.reader() {
                 let mut count = 0_u64;