sort: treat "NaN" as string in numeric sort

src/sort/sort.rs

@@ -382,8 +382,10 @@ fn permissive_f64_parse(a: &str) -> f64 {
     // On the flip side, this will give NEG_INFINITY for "1,234", which might be OK
     // because there's no way to handle both CSV and thousands separators without a new flag.
     // GNU sort treats "1,234" as "1" in numeric, so maybe it's fine.
+    // GNU sort treats "NaN" as non-number in numeric, so it needs special care.
     let sa: &str = a.split_whitespace().next().unwrap();
     match sa.parse::<f64>() {
+        Ok(a) if a.is_nan() => std::f64::NEG_INFINITY,
         Ok(a) => a,
         Err(_) => std::f64::NEG_INFINITY,
     }

tests/fixtures/sort/numeric_floats_with_nan.expected

@@ -0,0 +1,3 @@
+NaN
+.02
+.03

tests/fixtures/sort/numeric_floats_with_nan.txt

@@ -0,0 +1,3 @@
+.03
+.02
+NaN

tests/test_sort.rs

@@ -12,6 +12,11 @@ fn test_numeric_floats() {
     test_helper("numeric_floats", "-n");
 }
 
+#[test]
+fn test_numeric_floats_with_nan() {
+    test_helper("numeric_floats_with_nan", "-n");
+}
+
 #[test]
 fn test_numeric_unfixed_floats() {
     test_helper("numeric_unfixed_floats", "-n");