Fix crash in match statement when subject expression have unpacked tuple

mypy/checker.py

@@ -6124,6 +6124,12 @@ def _get_recursive_sub_patterns_map(
         sub_patterns_map: dict[Expression, Type] = {}
         typ_ = get_proper_type(typ)
         if isinstance(expr, TupleExpr) and isinstance(typ_, TupleType):
+            if any(isinstance(item, StarExpr) for item in expr.items):
+                # For a starred item (e.g. `*bar`), there's no one-to-one correspondence
+                # between expr.items and typ_.items, we are returning early to avoid an
+                # assertion crash. See: https://github.com/python/mypy/issues/21468.
+                return sub_patterns_map
+
             # When matching a tuple expression with a sequence pattern, narrow individual tuple items
             assert len(expr.items) == len(typ_.items)
             for item_expr, item_typ in zip(expr.items, typ_.items):

test-data/unit/check-python310.test

@@ -509,6 +509,20 @@ match m, (n, o):
         pass  # E: Statement is unreachable
 [builtins fixtures/tuple.pyi]
 
+[case testMatchUnpackedTupleSubjectExpressionNoCrash]
+# flags: --strict-equality --warn-unreachable
+# See: https://github.com/python/mypy/issues/21468
+
+foo: int = 1
+bar: tuple[int, int] = 1, 2
+
+match foo, *bar:
+    case x, y, z:
+        reveal_type(x) # N: Revealed type is "builtins.int"
+        reveal_type(y) # N: Revealed type is "builtins.int"
+        reveal_type(z) # N: Revealed type is "builtins.int"
+[builtins fixtures/tuple.pyi]
+
 -- Mapping Pattern --
 
 [case testMatchMappingPatternCaptures]