fix: Fix error with self-merge operations

bigframes/core/blocks.py

@@ -2166,7 +2166,7 @@ def merge(
  result_columns.append(get_column_left[col_id])
  for col_id in other.value_columns:
  if col_id in right_join_ids:
- if other.col_id_to_label[matching_right_id] in matching_join_labels:
+ if other.col_id_to_label[col_id] in matching_join_labels:
  pass
  else:
  result_columns.append(get_column_right[col_id])

tests/system/small/test_dataframe.py

@@ -1635,6 +1635,29 @@ def test_merge_left_on_right_on(scalars_dfs, merge_how):
  )
 
 
+def test_self_merge_self_w_on_args():
+ data = {
+ "A": pd.Series([1, 2, 3], dtype="Int64"),
+ "B": pd.Series([1, 2, 3], dtype="Int64"),
+ "C": pd.Series([100, 200, 300], dtype="Int64"),
+ "D": pd.Series(["alpha", "beta", "gamma"], dtype="string[pyarrow]"),
+ }
+ df = pd.DataFrame(data)
+
+ df1 = df[["A", "C"]]
+ df2 = df[["B", "C", "D"]]
+ pd_result = df1.merge(df2, left_on=["A", "C"], right_on=["B", "C"], how="inner")
+
+ bf_df = bpd.DataFrame(data)
+
+ bf_df1 = bf_df[["A", "C"]]
+ bf_df2 = bf_df[["B", "C", "D"]]
+ bf_result = bf_df1.merge(
+ bf_df2, left_on=["A", "C"], right_on=["B", "C"], how="inner"
+ ).to_pandas()
+ pd.testing.assert_frame_equal(bf_result, pd_result, check_index_type=False)
+
+
 @pytest.mark.parametrize(
  ("decimals",),
  [