contracts: Run start function (#1367)

Fixes #116 

Start function wasn't allowed in a contract. Now it is allowed and is
being run.

It was disallowed because it is not used by Rust and supporting it made
the code more complex. However, not running the start function violates
the wasm standard. This makes life harder for some languages (see linked
ticket).

substrate/frame/contracts/src/exec.rs

@@ -21,7 +21,7 @@ use crate::{
 	storage::{self, meter::Diff, WriteOutcome},
 	BalanceOf, CodeHash, CodeInfo, CodeInfoOf, Config, ContractInfo, ContractInfoOf,
 	DebugBufferVec, Determinism, Error, Event, Nonce, Origin, Pallet as Contracts, Schedule,
-	WasmBlob, LOG_TARGET,
+	LOG_TARGET,
 };
 use frame_support::{
 	crypto::ecdsa::ECDSAExt,
@@ -318,6 +318,22 @@ pub trait Ext: sealing::Sealed {
 	/// Returns a nonce that is incremented for every instantiated contract.
 	fn nonce(&mut self) -> u64;
 
+	/// Increment the reference count of a of a stored code by one.
+	///
+	/// # Errors
+	///
+	/// [`Error::CodeNotFound`] is returned if no stored code found having the specified
+	/// `code_hash`.
+	fn increment_refcount(code_hash: CodeHash<Self::T>) -> Result<(), DispatchError>;
+
+	/// Decrement the reference count of a stored code by one.
+	///
+	/// # Note
+	///
+	/// A contract whose reference count dropped to zero isn't automatically removed. A
+	/// `remove_code` transaction must be submitted by the original uploader to do so.
+	fn decrement_refcount(code_hash: CodeHash<Self::T>);
+
 	/// Adds a delegate dependency to [`ContractInfo`]'s `delegate_dependencies` field.
 	///
 	/// This ensures that the delegated contract is not removed while it is still in use. It
@@ -381,22 +397,6 @@ pub trait Executable<T: Config>: Sized {
 		gas_meter: &mut GasMeter<T>,
 	) -> Result<Self, DispatchError>;
 
-	/// Increment the reference count of a of a stored code by one.
-	///
-	/// # Errors
-	///
-	/// [`Error::CodeNotFound`] is returned if no stored code found having the specified
-	/// `code_hash`.
-	fn increment_refcount(code_hash: CodeHash<T>) -> Result<(), DispatchError>;
-
-	/// Decrement the reference count of a stored code by one.
-	///
-	/// # Note
-	///
-	/// A contract whose reference count dropped to zero isn't automatically removed. A
-	/// `remove_code` transaction must be submitted by the original uploader to do so.
-	fn decrement_refcount(code_hash: CodeHash<T>);
-
 	/// Execute the specified exported function and return the result.
 	///
 	/// When the specified function is `Constructor` the executable is stored and its
@@ -1285,10 +1285,10 @@ where
 
 		info.queue_trie_for_deletion();
 		ContractInfoOf::<T>::remove(&frame.account_id);
-		E::decrement_refcount(info.code_hash);
+		Self::decrement_refcount(info.code_hash);
 
 		for (code_hash, deposit) in info.delegate_dependencies() {
-			E::decrement_refcount(*code_hash);
+			Self::decrement_refcount(*code_hash);
 			frame
 				.nested_storage
 				.charge_deposit(frame.account_id.clone(), StorageDeposit::Refund(*deposit));
@@ -1491,8 +1491,8 @@ where
 
 		frame.nested_storage.charge_deposit(frame.account_id.clone(), deposit);
 
-		E::increment_refcount(hash)?;
-		E::decrement_refcount(prev_hash);
+		Self::increment_refcount(hash)?;
+		Self::decrement_refcount(prev_hash);
 		Contracts::<Self::T>::deposit_event(
 			vec![T::Hashing::hash_of(&frame.account_id), hash, prev_hash],
 			Event::ContractCodeUpdated {
@@ -1525,6 +1525,25 @@ where
 		}
 	}
 
+	fn increment_refcount(code_hash: CodeHash<Self::T>) -> Result<(), DispatchError> {
+		<CodeInfoOf<Self::T>>::mutate(code_hash, |existing| -> Result<(), DispatchError> {
+			if let Some(info) = existing {
+				*info.refcount_mut() = info.refcount().saturating_add(1);
+				Ok(())
+			} else {
+				Err(Error::<T>::CodeNotFound.into())
+			}
+		})
+	}
+
+	fn decrement_refcount(code_hash: CodeHash<T>) {
+		<CodeInfoOf<T>>::mutate(code_hash, |existing| {
+			if let Some(info) = existing {
+				*info.refcount_mut() = info.refcount().saturating_sub(1);
+			}
+		});
+	}
+
 	fn add_delegate_dependency(
 		&mut self,
 		code_hash: CodeHash<Self::T>,
@@ -1537,7 +1556,7 @@ where
 		let deposit = T::CodeHashLockupDepositPercent::get().mul_ceil(code_info.deposit());
 
 		info.add_delegate_dependency(code_hash, deposit)?;
-		<WasmBlob<T>>::increment_refcount(code_hash)?;
+		Self::increment_refcount(code_hash)?;
 		frame
 			.nested_storage
 			.charge_deposit(frame.account_id.clone(), StorageDeposit::Charge(deposit));
@@ -1552,8 +1571,7 @@ where
 		let info = frame.contract_info.get(&frame.account_id);
 
 		let deposit = info.remove_delegate_dependency(code_hash)?;
-		<WasmBlob<T>>::decrement_refcount(*code_hash);
-
+		Self::decrement_refcount(*code_hash);
 		frame
 			.nested_storage
 			.charge_deposit(frame.account_id.clone(), StorageDeposit::Refund(deposit));
@@ -1600,11 +1618,7 @@ mod tests {
 	use pallet_contracts_primitives::ReturnFlags;
 	use pretty_assertions::assert_eq;
 	use sp_runtime::{traits::Hash, DispatchError};
-	use std::{
-		cell::RefCell,
-		collections::hash_map::{Entry, HashMap},
-		rc::Rc,
-	};
+	use std::{cell::RefCell, collections::hash_map::HashMap, rc::Rc};
 
 	type System = frame_system::Pallet<Test>;
 
@@ -1635,7 +1649,6 @@ mod tests {
 		func_type: ExportedFunction,
 		code_hash: CodeHash<Test>,
 		code_info: CodeInfo<Test>,
-		refcount: u64,
 	}
 
 	#[derive(Default, Clone)]
@@ -1664,37 +1677,11 @@ mod tests {
 						func_type,
 						code_hash: hash,
 						code_info: CodeInfo::<Test>::new(ALICE),
-						refcount: 1,
 					},
 				);
 				hash
 			})
 		}
-
-		fn increment_refcount(code_hash: CodeHash<Test>) -> Result<(), DispatchError> {
-			Loader::mutate(|loader| {
-				match loader.map.entry(code_hash) {
-					Entry::Vacant(_) => Err(<Error<Test>>::CodeNotFound)?,
-					Entry::Occupied(mut entry) => entry.get_mut().refcount += 1,
-				}
-				Ok(())
-			})
-		}
-
-		fn decrement_refcount(code_hash: CodeHash<Test>) {
-			use std::collections::hash_map::Entry::Occupied;
-			Loader::mutate(|loader| {
-				let mut entry = match loader.map.entry(code_hash) {
-					Occupied(e) => e,
-					_ => panic!("code_hash does not exist"),
-				};
-				let refcount = &mut entry.get_mut().refcount;
-				*refcount -= 1;
-				if *refcount == 0 {
-					entry.remove();
-				}
-			});
-		}
 	}
 
 	impl Executable<Test> for MockExecutable {
@@ -1707,14 +1694,6 @@ mod tests {
 			})
 		}
 
-		fn increment_refcount(code_hash: CodeHash<Test>) -> Result<(), DispatchError> {
-			MockLoader::increment_refcount(code_hash)
-		}
-
-		fn decrement_refcount(code_hash: CodeHash<Test>) {
-			MockLoader::decrement_refcount(code_hash);
-		}
-
 		fn execute<E: Ext<T = Test>>(
 			self,
 			ext: &mut E,
@@ -1722,7 +1701,7 @@ mod tests {
 			input_data: Vec<u8>,
 		) -> ExecResult {
 			if let &Constructor = function {
-				Self::increment_refcount(self.code_hash).unwrap();
+				E::increment_refcount(self.code_hash).unwrap();
 			}
 			// # Safety
 			//
@@ -1733,7 +1712,7 @@ mod tests {
 			// The transmute is necessary because `execute` has to be generic over all
 			// `E: Ext`. However, `MockExecutable` can't be generic over `E` as it would
 			// constitute a cycle.
-			let ext = unsafe { std::mem::transmute(ext) };
+			let ext = unsafe { mem::transmute(ext) };
 			if function == &self.func_type {
 				(self.func)(MockCtx { ext, input_data }, &self)
 			} else {