feat: Field expansion renaming

crates/polars-plan/src/logical_plan/conversion/expr_expansion.rs

@@ -407,10 +407,19 @@ fn expand_struct_fields(
         polars_ensure!(name.as_ref() != "*", InvalidOperation: "cannot combine wildcards and column names");
 
         if !exclude.contains(name) {
-            result.push(replace_struct_multiple_fields_with_field(
-                full_expr.clone(),
-                name,
-            ))
+            let mut new_expr = replace_struct_multiple_fields_with_field(full_expr.clone(), name);
+            match new_expr {
+                Expr::KeepName(expr) => {
+                    new_expr = Expr::Alias(expr, name.clone());
+                },
+                Expr::RenameAlias { expr, function } => {
+                    let name = function.call(&name)?;
+                    new_expr = Expr::Alias(expr, ColumnName::from(name));
+                },
+                _ => {},
+            }
+
+            result.push(new_expr)
         }
     }
     Ok(())

py-polars/tests/unit/test_expansion.py

@@ -131,3 +131,10 @@ def test_struct_field_expand_star() -> None:
     )
     struct_df = df.select(pl.struct(["aaa", "bbb", "ccc", "ddd"]).alias("struct_col"))
     assert_frame_equal(struct_df.select(pl.col("struct_col").struct.field("*")), df)
+
+
+def test_struct_field_expand_rewrite() -> None:
+    df = pl.DataFrame({"A": [1], "B": [2]})
+    assert df.select(
+        pl.struct(["A", "B"]).struct.field("*").name.prefix("foo_")
+    ).to_dict(as_series=False) == {"foo_A": [1], "foo_B": [2]}