Cookbook: Handling Rails validation error types

[skryukov]

I believe this should address #177

We could try to upstream the ability to set the errors type to the JS core, enabling something like:

const form = useForm<UserType, string[]>(...)

However, this approach is verbose, and I would still lean towards using global types 😅.

[pricci1]

Considering that the code examples in the documentation and the generators pass the errors as arrays, maybe the global re-export should be part of the setup guide or even the inertia:install generator.

And also, maybe make the type be a string or a string array, though that would force everyone to check the runtime type

-    errors: Partial<Record<keyof TForm, string>>;
+    errors: Partial<Record<keyof TForm, string | string[]>>;

[skryukov]

@pricci1 yeah, adding them to the generator makes sense. We can also include a link to the cookbook in the generated file so it’s easily understandable.

[BrandonShar]

I like this strategy of updating docs before trying a more brittle solution!