A str-annotated field whose default_factory produces browser storage is never treated as browser storage #7498

Severity: LOW, pre-existing on main (0.10 dev). Found while addressing review on #7495.

What happens

A field whose default_factory produces a browser storage value, with a plain annotation, is never treated as browser storage:

class State(rx.State):
    theme: str = rx.field(default_factory=lambda: rx.LocalStorage("light", name="theme"))

State._is_client_storage("theme") is False, the var is not compiled into the client storage section, and it is never synced with the browser. Each instance just holds a LocalStorage instance as an ordinary str value. Nothing warns.

The same declaration with the storage annotation (theme: rx.LocalStorage = rx.field(default_factory=...)) is detected through the annotation (but see the separate hydration error issue filed with this one).

Why

BaseState._is_client_storage (reflex/state.py) only looks at field.default and at the annotation. A factory only reveals what it produces when called, and nothing calls it at class creation. After #7495 a plain assignment through the class (State.theme = "dark") calls the factory once and turns the field into browser storage, so the var is detected from then on; without such an assignment it is not. Note also that _is_client_storage is cached per class, so a class assignment made after the first lookup would not be seen until the cache is cleared.

Options

• Evaluate a declared default_factory once at class creation when the annotation is not a storage type, and classify the field by the result (cost: one factory call per such field per class).
• Or reject / warn about a factory-produced storage default and document that browser storage must be declared as a default value or with a storage annotation.

Generated by Claude Code