Warn when layout base is near the end of storage

Author: matheusaaguiar

libsolidity/analysis/PostTypeContractLevelChecker.cpp

@@ -144,4 +144,47 @@ void PostTypeContractLevelChecker::checkStorageLayoutSpecifier(ContractDefinitio
 			baseSlotExpression.location(),
 			"Contract extends past the end of storage when this base slot value is specified."
 		);
+
+	warnStorageLayoutBaseNearStorageEnd(_contract);
 }
+
+void PostTypeContractLevelChecker::warnStorageLayoutBaseNearStorageEnd(ContractDefinition const& _contract)
+{
+	if (Error::containsErrors(m_errorReporter.errors()))
+		return;
+
+	auto storageSize = u256(contractStorageSizeUpperBound(_contract, VariableDeclaration::Location::Unspecified));
+	auto baseSlot = layoutBaseForInheritanceHierarchy(_contract, DataLocation::Storage);
+	if (
+		u256 slotsLeft = std::numeric_limits<u256>::max() - baseSlot - storageSize;
+		!Error::containsErrors(m_errorReporter.errors()) &&
+		slotsLeft <= u256(1) << 64
+	)
+	{
+		auto const& location = _contract.storageLayoutSpecifier() ?
+			_contract.storageLayoutSpecifier()->location() :
+			_contract.location()
+		;
+
+		auto errorID = 3495_error;
+		std::string errorMsg = "This contract is very close to the end of storage. This limits its future upgradability.";
+		if (_contract.stateVariables().size() > 0)
+			m_errorReporter.warning(
+				errorID,
+				location,
+				errorMsg,
+				SecondarySourceLocation{}.append(
+					fmt::format(
+						"There are {} slots between this state variable and the end of the storage.",
+						formatNumberReadable(slotsLeft)
+					),
+					_contract.stateVariables().back()->location()
+			));
+		else
+			m_errorReporter.warning(
+				errorID,
+				location,
+				errorMsg
+			);
+	}
+}

libsolidity/analysis/PostTypeContractLevelChecker.h

@@ -52,6 +52,8 @@ class PostTypeContractLevelChecker
 
 	void checkStorageLayoutSpecifier(ContractDefinition const& _contract);
 
+	void warnStorageLayoutBaseNearStorageEnd(ContractDefinition const& _contract);
+
 	langutil::ErrorReporter& m_errorReporter;
 };