Implement the account storage API

[greenhat]

As discussed in #333
And later on the call with @bobbinth, @bitwalker @igamigo @phklive

For the first iteration, use functions consistent with transaction kernel's:

• set_storage_item / get_storage_item for getting/setting value slots.
• set_storage_map_item / get_storage_map_item for reading, updating storage maps.

Also, if we could encapsulate them in a module, that may be slightly better ergonomics. For example, storage::get_item, storage::set_item, storage::get_map_item, storage::set_map_item.

For the second iteration, we go with macros:

#[component]
struct MyComponent {

    #[storage_slot(0)]  
    foo: StorageMap,

    #[storage_slot(1)]  
    pub_key: Value,

    #[storage_slot(2)]  
    misc: StorageMap,
}

Where the Value and StorageMap implement a trait similar to Mapping from https://github.com/r55-eth/r55/blob/main/eth-riscv-runtime/src/types.rs, so that the storage access will look like self.pub_key.read() and self.pub_key.write(value).

The storage metadata in the toml format is described in 0xPolygonMiden/miden-base#1015 needs to be generated and stored in the Miden package compiled artifact. The attribute macros can generate the metadata, and we can "smuggle" it past the rustc via the custom link_section (as wit-bindgen smuggles WIT binary, see generated bindings.rs) into the compiler.

[greenhat]

@bobbinth @bitwalker @igamigo @phklive
I updated the description with the design we discussed on today's call.

[bobbinth]

For the first iteration, we implement the generic set_storage_value(slot: usize, value: Word) and get_storage_value(slot: usize) -> Word functions and their map and vec variants.

I would probably use naming a bit more consistent with transaction kernel's.

• set_storage_item / get_storage_item for getting/setting value slots.
• set_storage_map_item / get_storage_map_item for reading updating storage maps.

Also, if we could encapsulate them in a module, that may be slightly better ergonomics. For example, storage::get_item, storage::set_item, storage::get_map_item, storage::set_map_item.

#[account_storage]
struct MyAccountStorage {

    #[storage_slot(0)]  
    foo: Mapping<Word>,

    #[storage_slot(1)]  
    pub_key: Mapping<StorageVec>,

    #[storage_slot(2)]  
    misc: Mapping<Word>,
}

I would make some small corrections to the above:

#[component]
struct MyComponent {

    #[storage_slot(0)]  
    foo: StorageMap,

    #[storage_slot(1)]  
    pub_key: Value,

    #[storage_slot(2)]  
    misc: StorageMap,
}

[greenhat]

@bobbinth Thank you! I updated the description.