Add internal flag to disable expression cache (#19569)

Author: ilevkivskyi

mypy/checkexpr.py

@@ -6030,8 +6030,10 @@ def accept(
             # We cannot use cache inside lambdas, because they skip immediate type
             # context, and use enclosing one, see infer_lambda_type_using_context().
             # TODO: consider using cache for more expression kinds.
-            elif isinstance(node, (CallExpr, ListExpr, TupleExpr, DictExpr, OpExpr)) and not (
-                self.in_lambda_expr or self.chk.current_node_deferred
+            elif (
+                isinstance(node, (CallExpr, ListExpr, TupleExpr, DictExpr, OpExpr))
+                and not (self.in_lambda_expr or self.chk.current_node_deferred)
+                and not self.chk.options.disable_expression_cache
             ):
                 if (node, type_context) in self.expr_cache:
                     binder_version, typ, messages, type_map = self.expr_cache[(node, type_context)]

mypy/main.py

@@ -1090,14 +1090,15 @@ def add_invertible_flag(
         help="Use a custom typing module",
     )
     internals_group.add_argument(
-        "--old-type-inference",
-        action="store_true",
-        help="Disable new experimental type inference algorithm",
+        "--old-type-inference", action="store_true", help=argparse.SUPPRESS
     )
     # Deprecated reverse variant of the above.
     internals_group.add_argument(
         "--new-type-inference", action="store_true", help=argparse.SUPPRESS
     )
+    internals_group.add_argument(
+        "--disable-expression-cache", action="store_true", help=argparse.SUPPRESS
+    )
     parser.add_argument(
         "--enable-incomplete-feature",
         action="append",

mypy/options.py

@@ -395,6 +395,8 @@ def __init__(self) -> None:
         self.old_type_inference = False
         # Deprecated reverse version of the above, do not use.
         self.new_type_inference = False
+        # Disable expression cache (for debugging).
+        self.disable_expression_cache = False
         # Export line-level, limited, fine-grained dependency information in cache data
         # (undocumented feature).
         self.export_ref_info = False