fix(rust, python): fix is_sorted for structs

polars/polars-ops/src/series/ops/various.rs

@@ -70,9 +70,26 @@ pub trait SeriesMethods: SeriesSealed {
         // Compare adjacent elements with no-copy slices that don't include any nulls
         let offset = !options.nulls_last as i64 * nc as i64;
         let (s1, s2) = (s.slice(offset, slen), s.slice(offset + 1, slen));
-        match options.descending {
-            true => Ok(Series::gt_eq(&s1, &s2)?.all()),
-            false => Ok(Series::lt_eq(&s1, &s2)?.all()),
+        let cmp_op = match options.descending {
+            true => Series::gt_eq,
+            false => Series::lt_eq,
+        };
+        match s.dtype() {
+            // For structs compare per-field. We don't have to check any types or field names though
+            // since we're just comparing two offset slices of the same Series. The loop is to both
+            // short-circuit on false and propagate errors. Maybe there's a way with iterators?
+            #[cfg(feature = "dtype-struct")]
+            DataType::Struct(_) => {
+                let mut struct_cmp = true;
+                for (l, r) in s1.struct_()?.fields().iter().zip(s2.struct_()?.fields()) {
+                    struct_cmp &= cmp_op(l, r)?.all();
+                    if !struct_cmp {
+                        break;
+                    }
+                }
+                Ok(struct_cmp)
+            }
+            _ => Ok(cmp_op(&s1, &s2)?.all()),
         }
     }
 }