Move support macros to attribute procedural macros

[gui1117]

This issue is about moving decl_* to one simple module with attribute macro, inspired by ink macros.
goal is readability, understandability and IDE support, I test with rust-analyzer on vscode.

the idea is to have something like

#[frame_support::pallet(Example)]
pub mod pallet {
	#[pallet::trait_]
	pub trait Trait: frame_system::Trait {
		#[pallet::const_]
		type MyGetParam: Get<u32>;
	}

	#[pallet::module]
	pub struct Module<T, I>(core::marker::PhantomData<T, I>);

.....
}

Precise design should now be discussed in the PR #6877

[gui1117]

Good point from @bkchr IDE support is quite poor for rust macro for the moment and proper handling of proc-macro expansion from IDE could come.

I conclude myself that instead of optimizing syntax for having function information for storages, maybe better to optimize readibility/understandability and remove as much boilerplate as possible.

[bkchr]

goal is readability, understandability and IDE support, I test with rust-analyzer on vscode.

IDE support should be not the goal here. If the compiler accepts it, it is valid code. This means the IDE needs to improve and I don't want that we write code that makes rust-analyzer happy. If they finished their proc-macro support and something does not work, we should open an upstream issue.

(Too slow)

[bkchr]

Regarding storage, we could switch either to something like this:

#[storage]
struct Storage {
    my_item: Map,
    my_other_item: Value,
}

Which gives you access to the stuff by doing:

Storage::my_value().get();

Storage::my_other_value().set("hey");

We would return some fake instances that still write data directly to the storage as it is done currently.

Or if we want to split up the storage items, as you proposed, I would do the following:

#[storage(map)]
struct TotalBalance<T>(T::Balance);

Regarding putting everything into a module, I'm not a real fan of it. I understand that there is currently no other way, but I don't really like it :D

[kianenigma]

Pretty old but might still be related: https://hackmd.io/n_tTUbpMQiKiG7F2dURb6g?view

[gui1117]

could relate #5678

[kianenigma]

@thiolliere you probably made a mistake here? you are referencing the same issue 😄

could relate #5678

[gui1117]

@thiolliere you probably made a mistake here? you are referencing the same issue smile

could relate #5678

aah :-/ it was this one #5040

Also I have a WIP branch https://github.com/paritytech/substrate/compare/gui-macro-attribute?expand=1

I still have to figure out how we want to do storage declararion (and try to reuse current proc_macro implementation) and add some tests.

[gui1117]

EDIT: see message below