Prevent final reassignment in match case

Author: omerhadari

mypy/checker.py

@@ -5577,6 +5577,8 @@ def infer_variable_types_from_type_maps(
                 previous_type, _, _ = self.check_lvalue(expr)
                 if previous_type is not None:
                     already_exists = True
+                    if isinstance(expr.node, Var) and expr.node.is_final:
+                        self.msg.cant_assign_to_final(expr.name, False, expr)
                     if self.check_subtype(
                         typ,
                         previous_type,

test-data/unit/check-python310.test

@@ -2839,3 +2839,16 @@ match value_type:
     case _:
         assert_never(value_type)
 [builtins fixtures/tuple.pyi]
+
+
+[case testAssignmentToFinalInMatchCaseNotAllowed]
+# flags: --python-version 3.10
+from typing import Final
+
+def scope() -> None:
+    FOO: Final = 8
+
+val = 8
+match val:
+    case FOO:  # E: Cannot assign to final name "FOO"
+        pass