fix: keep RENAME TABLE clauses as separate identifiers (issue779)

RENAME TABLE a TO b, c TO d grouped the target of the first clause and
the source of the second into a single IdentifierList, because the comma
between the two clauses was treated as an identifier-list separator.

Detect the rename layout by the TO keywords flanking both sides of the
comma and leave such a comma ungrouped, so each renamed table stays a
separate Identifier. Genuine target lists such as GRANT ... TO a, b are
left untouched.

tests/test_regressions.py

@@ -414,6 +414,30 @@ def test_issue562_tzcasts():
            'SELECT f(HOUR\n         from bar AT TIME ZONE \'UTC\')\nfrom foo'
 
 
+def test_issue779_rename_table_pairs():
+    # The comma in ``RENAME TABLE a TO b, c TO d`` separates independent
+    # rename clauses. The target of one clause and the source of the next
+    # must stay separate Identifiers and not be merged into an IdentifierList.
+    p = sqlparse.parse('RENAME TABLE a TO b, c TO d')[0]
+    idents = [t for t in p.tokens if isinstance(t, sql.Identifier)]
+    assert [t.value for t in idents] == ['a', 'b', 'c', 'd']
+    assert not [t for t in p.tokens if isinstance(t, sql.IdentifierList)]
+    comma = p.token_next_by(m=(T.Punctuation, ','))[1]
+    assert comma is not None and comma.parent is p
+
+    # Backtick-quoted identifiers from the original report behave the same.
+    p = sqlparse.parse(
+        'rename table `db`.`test1` to test2, `db`.`test3` to test4')[0]
+    idents = [t for t in p.tokens if isinstance(t, sql.Identifier)]
+    assert [t.value for t in idents] == [
+        '`db`.`test1`', 'test2', '`db`.`test3`', 'test4']
+    assert not [t for t in p.tokens if isinstance(t, sql.IdentifierList)]
+
+    # A genuine ``TO`` target list (e.g. GRANT ... TO a, b) must still group.
+    p = sqlparse.parse('GRANT SELECT ON t TO a, b')[0]
+    assert p.token_next_by(i=sql.IdentifierList)[1] is not None
+
+
 def test_as_in_parentheses_indents():
     # did raise NoneType has no attribute is_group in _process_parentheses
     formatted = sqlparse.format('(as foo)', reindent=True)