FRAME: Revamp Preimage pallet to use Consideration (#1363)

Make Preimage pallet use Consideration instead of handling deposits
directly.

Other half of paritytech/substrate#13666.
Depends/based on #1361.

Script for the lazy migration that should be run manually once:
[migrate-preimage-lazy.py](https://github.com/ggwpez/substrate-scripts/blob/master/migrate-preimage-lazy.py).

## TODO

- [x] Migration code.

---------

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
Co-authored-by: command-bot <>
Co-authored-by: Francisco Aguirre <franciscoaguirreperez@gmail.com>
Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

substrate/frame/support/src/dispatch.rs

@@ -138,6 +138,15 @@ impl From<Pays> for PostDispatchInfo {
 	}
 }
 
+impl From<bool> for Pays {
+	fn from(b: bool) -> Self {
+		match b {
+			true => Self::Yes,
+			false => Self::No,
+		}
+	}
+}
+
 /// A generalized group of dispatch types.
 ///
 /// NOTE whenever upgrading the enum make sure to also update

substrate/frame/support/src/traits.rs

@@ -90,8 +90,8 @@ pub use hooks::{
 pub mod schedule;
 mod storage;
 pub use storage::{
-	Consideration, Footprint, Incrementable, Instance, PartialStorageInfoTrait, StorageInfo,
-	StorageInfoTrait, StorageInstance, TrackedStorageKey, WhitelistedStorageKeys,
+	Consideration, Footprint, Incrementable, Instance, LinearStoragePrice, PartialStorageInfoTrait,
+	StorageInfo, StorageInfoTrait, StorageInstance, TrackedStorageKey, WhitelistedStorageKeys,
 };
 
 mod dispatch;

substrate/frame/support/src/traits/storage.rs

@@ -18,11 +18,13 @@
 //! Traits for encoding data related to pallet's storage items.
 
 use codec::{Encode, FullCodec, MaxEncodedLen};
+use core::marker::PhantomData;
 use impl_trait_for_tuples::impl_for_tuples;
 use scale_info::TypeInfo;
 pub use sp_core::storage::TrackedStorageKey;
+use sp_core::Get;
 use sp_runtime::{
-	traits::{Member, Saturating},
+	traits::{Convert, Member, Saturating},
 	DispatchError, RuntimeDebug,
 };
 use sp_std::{collections::btree_set::BTreeSet, prelude::*};
@@ -152,6 +154,20 @@ impl Footprint {
 	}
 }
 
+/// A storage price that increases linearly with the number of elements and their size.
+pub struct LinearStoragePrice<Base, Slope, Balance>(PhantomData<(Base, Slope, Balance)>);
+impl<Base, Slope, Balance> Convert<Footprint, Balance> for LinearStoragePrice<Base, Slope, Balance>
+where
+	Base: Get<Balance>,
+	Slope: Get<Balance>,
+	Balance: From<u64> + sp_runtime::Saturating,
+{
+	fn convert(a: Footprint) -> Balance {
+		let s: Balance = (a.count.saturating_mul(a.size)).into();
+		s.saturating_mul(Slope::get()).saturating_add(Base::get())
+	}
+}
+
 /// Some sort of cost taken from account temporarily in order to offset the cost to the chain of
 /// holding some data [`Footprint`] in state.
 ///
@@ -239,3 +255,25 @@ where
 }
 
 impl_incrementable!(u8, u16, u32, u64, u128, i8, i16, i32, i64, i128);
+
+#[cfg(test)]
+mod tests {
+	use super::*;
+	use sp_core::ConstU64;
+
+	#[test]
+	fn linear_storage_price_works() {
+		type Linear = LinearStoragePrice<ConstU64<7>, ConstU64<3>, u64>;
+		let p = |count, size| Linear::convert(Footprint { count, size });
+
+		assert_eq!(p(0, 0), 7);
+		assert_eq!(p(0, 1), 7);
+		assert_eq!(p(1, 0), 7);
+
+		assert_eq!(p(1, 1), 10);
+		assert_eq!(p(8, 1), 31);
+		assert_eq!(p(1, 8), 31);
+
+		assert_eq!(p(u64::MAX, u64::MAX), u64::MAX);
+	}
+}