fix: guard short parenthesis groups in StripWhitespaceFilter

sqlparse/filters/others.py

@@ -112,13 +112,15 @@ def _stripws_identifierlist(self, tlist):
         return self._stripws_default(tlist)
 
     def _stripws_parenthesis(self, tlist):
-        while tlist.tokens[1].is_whitespace:
+        # Short groups (e.g. "(::)") lack open/body/close slots for inner ws pops.
+        while len(tlist.tokens) > 2 and tlist.tokens[1].is_whitespace:
             tlist.tokens.pop(1)
-        while tlist.tokens[-2].is_whitespace:
+        while len(tlist.tokens) > 2 and tlist.tokens[-2].is_whitespace:
             tlist.tokens.pop(-2)
-        if tlist.tokens[-2].is_group:
+        if len(tlist.tokens) > 2 and tlist.tokens[-2].is_group:
             # save to remove the last whitespace
-            while tlist.tokens[-2].tokens[-1].is_whitespace:
+            while (tlist.tokens[-2].tokens
+                   and tlist.tokens[-2].tokens[-1].is_whitespace):
                 tlist.tokens[-2].tokens.pop(-1)
         self._stripws_default(tlist)
 

tests/test_format.py

@@ -432,6 +432,9 @@ def test_parenthesis(self):
         assert f("select f(\n\n\n1\n\n\n)") == 'select f(1)'
         assert f("select f(\n\n\n 1 \n\n\n)") == 'select f(1)'
         assert f("select f(\n\n\n  1  \n\n\n)") == 'select f(1)'
+        # Cast-like "(::)" is one Identifier inside Parenthesis; must not IndexError
+        assert f('(::)') == '(::)'
+        assert f('()') == '()'
 
     def test_where(self):
         f = lambda sql: sqlparse.format(sql, reindent=True)