pallet-contracts: Rent projection RPC (#4754)

* Initial approach

* Introduce the pallet-contracts-common crate

* Add rent::compute_rent_projection

* Wire everything together

* Fix build error.

* Rename EvictionDate → EvictionAt.

* Clean.

* Renaming and cleaning.

* Add documentation for rent_projection RPC.

* Add documentation for rent_projection runtime API.

* Refactor rent_budget.

Merge it with subsistence_treshold.

* Bump impl_version

* Constrain RPC impl with Block::Header::Number.

* Rename pallet-contracts-common into -primitives

* Add a comment for `compute_rent_projection` on the usage

* Small tidying

substrate/frame/contracts/common/Cargo.toml

@@ -0,0 +1,19 @@
+[package]
+name = "pallet-contracts-primitives"
+version = "2.0.0"
+authors = ["Parity Technologies <admin@parity.io>"]
+edition = "2018"
+
+[dependencies]
+# This crate should not rely on any of the frame primitives.
+codec = { package = "parity-scale-codec", version = "1.0.0", default-features = false, features = ["derive"] }
+sp-std = { version = "2.0.0", default-features = false, path = "../../../primitives/std" }
+sp-runtime = { version = "2.0.0", default-features = false, path = "../../../primitives/runtime" }
+
+[features]
+default = ["std"]
+std = [
+	"codec/std",
+	"sp-runtime/std",
+	"sp-std/std",
+]

substrate/frame/contracts/common/src/lib.rs

@@ -0,0 +1,47 @@
+// Copyright 2020 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Substrate is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Substrate. If not, see <http://www.gnu.org/licenses/>.
+
+//! A crate that hosts a common definitions that are relevent for the pallet-contracts.
+
+#![cfg_attr(not(feature = "std"), no_std)]
+
+use sp_std::prelude::*;
+
+/// A result type of a get storage call.
+pub type GetStorageResult = Result<Option<Vec<u8>>, ContractAccessError>;
+
+/// The possible errors that can happen querying the storage of a contract.
+#[derive(Eq, PartialEq, codec::Encode, codec::Decode, sp_runtime::RuntimeDebug)]
+pub enum ContractAccessError {
+	/// The given address doesn't point to a contract.
+	DoesntExist,
+	/// The specified contract is a tombstone and thus cannot have any storage.
+	IsTombstone,
+}
+
+/// A result type of a `rent_projection` call.
+pub type RentProjectionResult<BlockNumber> =
+	Result<RentProjection<BlockNumber>, ContractAccessError>;
+
+#[derive(Eq, PartialEq, codec::Encode, codec::Decode, sp_runtime::RuntimeDebug)]
+pub enum RentProjection<BlockNumber> {
+	/// Eviction is projected to happen at the specified block number.
+	EvictionAt(BlockNumber),
+	/// No eviction is scheduled.
+	///
+	/// E.g. because the contract accumulated enough funds to offset the rent storage costs.
+	NoEviction,
+}