Allow top-level starred expression on match

CHANGES.md

@@ -8,7 +8,8 @@
   cell magics were tokenized, leading to possible indentation errors e.g. with
   `%%writefile`. (#2630)
 - Fixed Python 3.10 support on platforms without ProcessPoolExecutor (#2631)
-- Fixed `match` statements with open sequence subjects, like `match a, b:` (#2639)
+- Fixed `match` statements with open sequence subjects, like `match a, b:` or
+  `match a, *b:` (#2639 and #2659)
 - Fixed assignment to environment variables in Jupyter Notebooks (#2642)
 - Add `flake8-simplify` and `flake8-comprehensions` plugins (#2653)
 

src/blib2to3/Grammar.txt

@@ -238,7 +238,11 @@ yield_arg: 'from' test | testlist_star_expr
 # to reformat them.
 
 match_stmt: "match" subject_expr ':' NEWLINE INDENT case_block+ DEDENT
-subject_expr: namedexpr_test (',' namedexpr_test)* [',']
+
+# This is more permissive than the actual version. For example it
+# accepts `match *something:`, even though single-item starred expressions
+# are forbidden.
+subject_expr: (namedexpr_test|star_expr) (',' (namedexpr_test|star_expr))* [',']
 
 # cases
 case_block: "case" patterns [guard] ':' suite

tests/data/pattern_matching_extras.py

@@ -43,3 +43,10 @@ def func(match: case, case: match) -> case:
         pass
     case _:
         pass
+
+
+match a, *b, c:
+    case [*_]:
+        return "seq"
+    case {}:
+        return "map"