Double map and plain storage support, introduce macros

[dvc94ch]

Simplifies trait bounds.
Allows setting a custom client.
Adds support for plain and double-map storage items.

[ascjones]

Good stuff! Could you add a couple of tests for the double map and the plain storage?

[dvc94ch]

I added a proc-macro to generate client code for substrate modules. I'll look into generating test cases too which should fix your comment.

[dvc94ch]

Sorry, this PR has gotten a little out of hand. It still needs more field testing, and the substrate-subxt crate should probably be split into substrate-subxt-core and substrate-subxt, so the proc macros can be used for the default modules.

#[module]
pub trait Balances: System {
    type Balance: Parameter
        + Member
        + AtLeast32Bit
        + codec::Codec
        + Default
        + Copy
        + MaybeSerialize
        + Debug
        + From<<Self as System>::BlockNumber>;
}

#[derive(Clone, Decode, Default)]
pub struct AccountData<Balance> {
    pub free: Balance,
    pub reserved: Balance,
    pub misc_frozen: Balance,
    pub fee_frozen: Balance,
}

#[derive(Encode, Store)]
pub struct AccountStore<'a, T: Balances> {
    #[store(returns = AccountData<T::Balance>)]
    pub account_id: &'a <T as System>::AccountId,
}

#[derive(Call, Encode)]
pub struct TransferCall<'a, T: Balances> {
    pub to: &'a <T as System>::Address,
    #[codec(compact)]
    pub amount: T::Balance,
}

#[derive(Debug, Decode, Eq, Event, PartialEq)]
pub struct TransferEvent<T: Balances> {
    pub from: <T as System>::AccountId,
    pub to: <T as System>::AccountId,
    pub amount: T::Balance,
}

impl Balances for KusamaRuntime {
    type Balance = u128;
}

subxt_test!({
    name: transfer_test_case,
    runtime: KusamaRuntime,
    account: Alice,
    step: {
        state: {
            alice: AccountStore { account_id: &alice },
            bob: AccountStore { account_id: &bob },
        },
        call: TransferCall {
            to: &bob,
            amount: 10_000,
        },
        event: TransferEvent {
            from: alice.clone(),
            to: bob.clone(),
            amount: 10_000,
        },
        assert: {
            assert_eq!(pre.alice.free, post.alice.free - 10_000);
            assert_eq!(pre.bob.free, post.bob.free + 10_000);
        },
    },
});

[dvc94ch]

Mmh one problem is that the nonces are wrong when running multiple tests in parallel. Is it possible to disable nonce checking on dev chains?

[4meta5]

https://stackoverflow.com/questions/44947914/how-to-limit-the-number-of-test-threads-in-cargo-toml

Apparently, there was this rust-lang/rust#42684 which was resolved with the introduction of this https://crates.io/crates/serial_test

[dvc94ch]

Due to possible races it looks like it's the only way to do it. If we shared the client and set the account based on the thread id, arbitrary interleaving of tests will cause failures.

[ascjones]

Love the proc macros. Though still need a test case for double_map which is the ostensible purpose of this PR 😄

[dvc94ch]

Is it ok if I just add a test for plain? The system, balances and contracts modules don't contain any double_maps. I can follow up with splitting subxt into a core module and update system, balances and contracts to use the proc-macros. the generic-asset module contains some double_map's, I could add support for it.

[ascjones]

LGTM