Fix an issue with negative indexes causing IndexError in some cases.

andialbrecht · andialbrecht · commit 10231d89d76c · 2020-09-30T15:15:56.000+02:00
diff --git a/sqlparse/engine/grouping.py b/sqlparse/engine/grouping.py
@@ -432,6 +432,8 @@ def _group(tlist, cls, match,
     pidx, prev_ = None, None
     for idx, token in enumerate(list(tlist)):
         tidx = idx - tidx_offset
+        if tidx < 0:  # tidx shouldn't get negative
+            continue
 
         if token.is_whitespace:
             continue
