Allow pallet to declare its default parts and make construct_runtime automatically use them by default

[gui1117]

Instead of having to declare:

construct_runtime!(
...
Example: example::{Module, Storage, Call},
);

we could be able to do:

construct_runtime!(
...
Example: example all_parts_except::{Call},
// which would result in using `Module, Storage` in this example
);

(syntax must be improved)

a stale PR exist #6494 but doesn't implement the except_part logic.

[KiChjang]

Are there any cases where a pallet part is included in a pallet, but the user doesn't want to declare it to be used? If not, then we could automatically declare the existence of a pallet part simply via the inclusion of its corresponding attribute, i.e. this pallet:

#[frame_support::pallet]
pub mod pallet {
    #[pallet::pallet]
    pub struct Pallet<T>(_);

    #[pallet::config]
    pub trait Config: frame_system::Config {}

    #[pallet::call]
    impl<T: Config> Pallet<T> {}
}

would automatically declare Pallet, Call and nothing else -- the #[pallet::*] attribute macros would automatically declare those parts. We can then remove the need for the user to explicitly declare pallet parts via the decl_construct_runtime_args! macro as implemented in #6494.

Then if a user tries to use a non-existent pallet part during runtime construction, we could then generate a more helpful error message saying something like "Pallet does not contain #[pallet::genesis_config], declare one in order to include Config for the pallet in the runtime".

[gui1117]

indeed I think decl_construct_runtime_args! of #6494 should be automatically generated by the pallet macro.

Then if a user tries to use a non-existent pallet part during runtime construction, we could then generate a more helpful error message saying something like "Pallet does not contain #[pallet::genesis_config], declare one in order to include Config for the pallet in the runtime".

I also agree and on that, but that would be not possible to support in old decl_* macros, so as long as it is not deprecated I'm not sure how it can be implemented.

But in general yes I think pallet macro declares pallet items, those items are to be aggregated in construct_runtime.
I think forcing construct_runtime to read exclusively items declared by pallet macro, allows better error message and more consistent code.

Also I don't think we need to support declaration of parts for decl_* macros. no need to enhance decl_* macros, but we shouldn't break them IMHO

[stale]

Hey, is anyone still working on this? Due to the inactivity this issue has been automatically marked as stale. It will be closed if no further activity occurs. Thank you for your contributions.

[gui1117]

still relevant