Fix special case for #284 when statement starts with orphaned AS.

2 files changed, 8 insertions, 5 deletions

diff --git a/sqlparse/engine/grouping.py b/sqlparse/engine/grouping.py
index 5fa3909..3c49201 100644
--- a/sqlparse/engine/grouping.py
+++ b/sqlparse/engine/grouping.py
@@ -380,7 +380,7 @@ def _group(tlist, cls, match,
 
         if match(token):
             nidx, next_ = tlist.token_next(tidx)
-            if valid_prev(prev_) and valid_next(next_):
+            if prev_ and valid_prev(prev_) and valid_next(next_):
                 from_idx, to_idx = post(tlist, pidx, tidx, nidx)
                 grp = tlist.group_tokens(cls, from_idx, to_idx, extend=extend)
 
diff --git a/tests/test_regressions.py b/tests/test_regressions.py
index ba908d3..d646325 100644
--- a/tests/test_regressions.py
+++ b/tests/test_regressions.py
@@ -316,7 +316,10 @@ def test_token_next_doesnt_ignore_skip_cm():
     assert tok.value == 'select'
 
 
-def test_issue284_as_grouping():
-    sql = 'SELECT x AS'
-    p = sqlparse.parse(sql)[0]
-    assert sql == str(p)
+@pytest.mark.parametrize('s', [
+    'SELECT x AS',
+    'AS'
+])
+def test_issue284_as_grouping(s):
+    p = sqlparse.parse(s)[0]
+    assert s == str(p)