refactor(frozen_dataclass): Enhance implementation for clarity and type safety

Author: tony

src/libtmux/_internal/frozen_dataclass.py

@@ -8,6 +8,7 @@
 from __future__ import annotations
 
 import dataclasses
+import functools
 import typing as t
 
 from typing_extensions import dataclass_transform
@@ -38,10 +39,15 @@ def frozen_dataclass(cls: type[_T]) -> type[_T]:
     # A. Convert to a dataclass with frozen=False
     cls = dataclasses.dataclass(cls)
 
+    # B. Explicitly annotate and initialize the `_frozen` attribute for static analysis
+    cls.__annotations__["_frozen"] = bool
+    setattr(cls, "_frozen", False)
+
     # Save the original __init__ to use in our hooks
     original_init = cls.__init__
 
     # C. Create a new __init__ that will call the original and then set _frozen flag
+    @functools.wraps(original_init)
     def __init__(self: t.Any, *args: t.Any, **kwargs: t.Any) -> None:
         # Call the original __init__
         original_init(self, *args, **kwargs)
@@ -52,6 +58,7 @@ def __init__(self: t.Any, *args: t.Any, **kwargs: t.Any) -> None:
     def __setattr__(self: t.Any, name: str, value: t.Any) -> None:
         # If _frozen is set and we're trying to set a field, block it
         if getattr(self, "_frozen", False) and not name.startswith("_"):
+            # Allow mutation of private (_-prefixed) attributes after initialization
             error_msg = f"{cls.__name__} is immutable: cannot modify field '{name}'"
             raise AttributeError(error_msg)
 
@@ -68,10 +75,9 @@ def __delattr__(self: t.Any, name: str) -> None:
         # Allow the deletion
         object.__delattr__(self, name)
 
-    # F. Inject into the class
-    # Add type ignore directives to silence mypy "Cannot assign to a method" errors
-    cls.__init__ = __init__  # type: ignore[method-assign]
-    cls.__setattr__ = __setattr__  # type: ignore[method-assign]
-    cls.__delattr__ = __delattr__  # type: ignore[method-assign]
+    # F. Inject into the class using setattr to avoid explicit mypy type ignores
+    setattr(cls, "__init__", __init__)
+    setattr(cls, "__setattr__", __setattr__)
+    setattr(cls, "__delattr__", __delattr__)
 
     return cls