#[pallet::storage] can not use independently

[yanganto]

Is there an existing issue?

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• This is not a support question.

Description of bug

Base on the documentation to migration list as following,

• storage-migrations
• Upgrades
  • the example in Upgrades page

A legacy data structure should be stored in another module as following, such that the migration can be performed.

mod migration {
    use super::*;
    #[frame_support::pallet] 
    pub mod v1 {
       #[pallet::storage]
       pub type Number<T> = StorageValue<_, u64>;
    }
}

However, the #[pallet::config] or possible more things are asked while compiling.
This is a bug to keep both version of data structure at the same time. Also this will be an issue for data migration with the storage described with#[pallet::storage].

Steps to reproduce

No response

[kianenigma]

This is the macro that you are supposed to use to maintain the old storage formats around for migration:

#11387