bug: backwards-compatible include_table=False when returning

In sqlalchemy 2.0, it's:
```python
self._label_select_column(None, c, True, False, {}, include_table=False)
```

In older versions, it's
```python
self._label_select_column(None, c, True, False, {'include_table': False})
```

So instead, forward a flag to `vist_column` which can set this kwarg
safely itself.

Author: waltaskew

google/cloud/sqlalchemy_spanner/sqlalchemy_spanner.py

@@ -382,10 +382,11 @@ def limit_clause(self, select, **kw):
         return text
 
     def returning_clause(self, stmt, returning_cols, **kw):
-        # Set include_table=False because although table names are allowed in
-        # RETURNING clauses, schema names are not.
+        # Set the spanner_is_returning flag which is passed to visit_column.
         columns = [
-            self._label_select_column(None, c, True, False, {}, include_table=False)
+            self._label_select_column(
+                None, c, True, False, {"spanner_is_returning": True}
+            )
             for c in expression._select_iterables(returning_cols)
         ]
 
@@ -413,10 +414,6 @@ def visit_table(self, table, spanner_aliased=False, iscrud=False, **kwargs):
 
         And do similar for UPDATE and DELETE statements.
 
-        We don't need to correct INSERT statements, which is fortunate
-        because INSERT statements actually do not currently result in
-        calls to `visit_table`.
-
         This closely mirrors the mssql dialect which also avoids
         schema-qualified columns in SELECTs, although the behaviour is
         currently behind a deprecated 'legacy_schema_aliasing' flag.
@@ -437,7 +434,9 @@ def visit_alias(self, alias, **kw):
         kw["spanner_aliased"] = alias.element
         return super().visit_alias(alias, **kw)
 
-    def visit_column(self, column, add_to_result_map=None, **kw):
+    def visit_column(
+        self, column, add_to_result_map=None, spanner_is_returning=False, **kw
+    ):
         """Produces column expressions.
 
         In tandem with visit_table, replaces schema-qualified column
@@ -457,6 +456,21 @@ def visit_column(self, column, add_to_result_map=None, **kw):
                     )
 
                 return super().visit_column(converted, **kw)
+        if spanner_is_returning:
+            # Set include_table=False because although table names are
+            # allowed in RETURNING clauses, schema names are not.  We
+            # can't use the same aliasing trick above that we use with
+            # other statements, because INSERT statements don't result
+            # in visit_table calls and INSERT table names can't be
+            # aliased.  Statements like:
+            #
+            # INSERT INTO table (id, name)
+            # SELECT id, name FROM another_table
+            # THEN RETURN another_table.id
+            #
+            # aren't legal, so the columns remain unambiguous when not
+            # qualified by table name.
+            kw["include_table"] = False
 
         return super().visit_column(column, add_to_result_map=add_to_result_map, **kw)
 

test/mockserver_tests/test_auto_increment.py

@@ -125,9 +125,7 @@ def test_create_table_with_specific_sequence_kind(self):
     def test_insert_row(self):
         from test.mockserver_tests.auto_increment_model import Singer
 
-        self.add_insert_result(
-            "INSERT INTO singers (name) VALUES (@a0) THEN RETURN singers.id"
-        )
+        self.add_insert_result("INSERT INTO singers (name) VALUES (@a0) THEN RETURN id")
         engine = create_engine(
             "spanner:///projects/p/instances/i/databases/d",
             connect_args={"client": self.client, "pool": FixedSizePool(size=10)},

test/mockserver_tests/test_bit_reversed_sequence.py

@@ -110,7 +110,7 @@ def test_insert_row(self):
         add_result(
             "INSERT INTO singers (id, name) "
             "VALUES ( GET_NEXT_SEQUENCE_VALUE(SEQUENCE singer_id), @a0) "
-            "THEN RETURN singers.id",
+            "THEN RETURN id",
             result,
         )
         engine = create_engine(