Fix utf-8 bom positions.

test/test_prefix.py

@@ -59,3 +59,16 @@ def test_prefix_splitting_types(string, types):
     assert leaf.type == 'endmarker'
     parsed_tokens = list(leaf._split_prefix())
     assert [t.type for t in parsed_tokens] == types
+
+
+def test_utf8_bom():
+    tree = parso.parse(unicode_bom + 'a = 1')
+    expr_stmt = tree.children[0]
+    assert expr_stmt.start_pos == (1, 0)
+
+    tree = parso.parse(unicode_bom + '\n')
+    endmarker = tree.children[0]
+    parts = list(endmarker._split_prefix())
+    assert [p.type for p in parts] == ['bom', 'newline', 'spacing']
+    assert [p.start_pos for p in parts] == [(1, 0), (1, 0), (2, 0)]
+    assert [p.end_pos for p in parts] == [(1, 0), (2, 0), (2, 0)]