[Beta] Backports (#7945)

* ECIP 1041 - Remove Difficulty Bomb (#7905)

Enable difficulty bomb defusion at block:
 - 5900000 on Ethereum Classic mainnet,
 - 2300000 on morden testnet.

Reference:
https://github.com/ethereumproject/ECIPs/blob/master/ECIPs/ECIP-1041.md

* spec: Validate required divisor fields are not 0 (#7933)

* Add validate_non_zero function

It's used to validate that a Spec's uint field used as a divisor is not zero.

* Add deserialize_with to gas_limit_bound_divisor

Prevents panics due to divide-by-zero on the gas_limit_bound_divisor
field.

* Add deserialize_with to difficulty_bound_divisor

Prevents panics due to divide-by-zero on the difficulty_bound_divisor
field.

* Add validate_optional_non_zero function

Used to validate Option<Uint> divisor fields.

* Use deserialize_with on optional divisor fields.

* Add #[serde(default)] attribute to divisor fields

When using `#[serde(deserialize_with)]`, `#[serde(default)]` must be specified so that missing
fields can be deserialized with the deserializer for `None`.

* Kovan WASM fork code (#7849)

* kovan fork code

* introduce ethcore level vm_factory and let it fail

* fix json tests

* wasmcosts as option

* review changes

* wasm costs in parser

* fix evm tests

* review fixes

* fix test

* remove redundant json field

ethcore/vm/src/lib.rs

@@ -38,7 +38,7 @@ pub mod tests;
 pub use action_params::{ActionParams, ActionValue, ParamsType};
 pub use call_type::CallType;
 pub use env_info::{EnvInfo, LastHashes};
-pub use schedule::{Schedule, CleanDustMode};
+pub use schedule::{Schedule, CleanDustMode, WasmCosts};
 pub use ext::{Ext, MessageCallResult, ContractCreateResult, CreateContractAddress};
 pub use return_data::{ReturnData, GasLeft};
 pub use error::{Error, Result};

ethcore/vm/src/schedule.rs

@@ -113,8 +113,8 @@ pub struct Schedule {
 	pub kill_dust: CleanDustMode,
 	/// Enable EIP-86 rules
 	pub eip86: bool,
-	/// Wasm extra schedule settings
-	pub wasm: WasmCosts,
+	/// Wasm extra schedule settings, if wasm activated
+	pub wasm: Option<WasmCosts>,
 }
 
 /// Wasm cost table
@@ -231,7 +231,7 @@ impl Schedule {
 			have_static_call: false,
 			kill_dust: CleanDustMode::Off,
 			eip86: false,
-			wasm: Default::default(),
+			wasm: None,
 		}
 	}
 
@@ -294,9 +294,17 @@ impl Schedule {
 			have_static_call: false,
 			kill_dust: CleanDustMode::Off,
 			eip86: false,
-			wasm: Default::default(),
+			wasm: None,
 		}
 	}
+
+	/// Returns wasm schedule
+	///
+	/// May panic if there is no wasm schedule
+	pub fn wasm(&self) -> &WasmCosts {
+		// *** Prefer PANIC here instead of silently breaking consensus! ***
+		self.wasm.as_ref().expect("Wasm schedule expected to exist while checking wasm contract. Misconfigured client?")
+	}
 }
 
 impl Default for Schedule {

ethcore/vm/src/tests.rs

@@ -78,15 +78,23 @@ pub fn test_finalize(res: Result<GasLeft>) -> Result<U256> {
 }
 
 impl FakeExt {
+	/// New fake externalities
 	pub fn new() -> Self {
 		FakeExt::default()
 	}
 
+	/// New fake externalities with byzantium schedule rules
 	pub fn new_byzantium() -> Self {
 		let mut ext = FakeExt::default();
 		ext.schedule = Schedule::new_byzantium();
 		ext
 	}
+
+	/// Alter fake externalities to allow wasm
+	pub fn with_wasm(mut self) -> Self {
+		self.schedule.wasm = Some(Default::default());
+		self
+	}
 }
 
 impl Ext for FakeExt {