Support multiple top-level as-expressions on case statements (#2716)

CHANGES.md

@@ -10,6 +10,8 @@
   underlying SyntaxError (#2693)
 - Fix mapping cases that contain as-expressions, like `case {"key": 1 | 2 as password}`
   (#2686)
+- Fix cases that contain multiple top-level as-expressions, like `case 1 as a, 2 as b`
+  (#2716)
 - No longer color diff headers white as it's unreadable in light themed terminals
   (#2691)
 - Tuple unpacking on `return` and `yield` constructs now implies 3.8+ (#2700)

src/blib2to3/Grammar.txt

@@ -247,5 +247,5 @@ subject_expr: (namedexpr_test|star_expr) (',' (namedexpr_test|star_expr))* [',']
 # cases
 case_block: "case" patterns [guard] ':' suite
 guard: 'if' namedexpr_test
-patterns: pattern ['as' pattern]
-pattern: (expr|star_expr) (',' (expr|star_expr))* [',']
+patterns: pattern (',' pattern)* [',']
+pattern: (expr|star_expr) ['as' expr]

tests/data/pattern_matching_extras.py

@@ -92,3 +92,14 @@ def func(match: case, case: match) -> case:
         pass
     case {"maybe": something(complicated as this) as that}:
         pass
+
+
+match something:
+    case 1 as a:
+        pass
+
+    case 2 as b, 3 as c:
+        pass
+
+    case 4 as d, (5 as e), (6 | 7 as g), *h:
+        pass