solidity/libsolidity/analysis/TypeChecker.cpp

/*
	This file is part of solidity.

	solidity 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.

	solidity 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 solidity.  If not, see <http://www.gnu.org/licenses/>.
*/
// SPDX-License-Identifier: GPL-3.0
/**
 * @author Christian <c@ethdev.com>
 * @date 2015
 * Type analyzer and checker.
 */

#include <libsolidity/analysis/TypeChecker.h>
#include <libsolidity/ast/AST.h>
#include <libsolidity/ast/ASTUtils.h>
#include <libsolidity/ast/TypeProvider.h>

#include <libyul/AsmAnalysis.h>
#include <libyul/AsmAnalysisInfo.h>
#include <libyul/AsmData.h>

#include <liblangutil/ErrorReporter.h>

#include <libsolutil/Algorithms.h>
#include <libsolutil/StringUtils.h>

#include <boost/algorithm/string/join.hpp>
#include <boost/algorithm/string/predicate.hpp>
#include <boost/range/adaptor/reversed.hpp>

#include <memory>
#include <vector>

using namespace std;
using namespace solidity;
using namespace solidity::util;
using namespace solidity::langutil;
using namespace solidity::frontend;

bool TypeChecker::typeSupportedByOldABIEncoder(Type const& _type, bool _isLibraryCall)
{
	if (_isLibraryCall && _type.dataStoredIn(DataLocation::Storage))
		return true;
	if (_type.category() == Type::Category::Struct)
		return false;
	if (_type.category() == Type::Category::Array)
	{
		auto const& arrayType = dynamic_cast<ArrayType const&>(_type);
		auto base = arrayType.baseType();
		if (!typeSupportedByOldABIEncoder(*base, _isLibraryCall) || (base->category() == Type::Category::Array && base->isDynamicallySized()))
			return false;
	}
	return true;
}

bool TypeChecker::checkTypeRequirements(SourceUnit const& _source)
{
	m_currentSourceUnit = &_source;
	_source.accept(*this);
	m_currentSourceUnit = nullptr;
	return Error::containsOnlyWarnings(m_errorReporter.errors());
}

TypePointer const& TypeChecker::type(Expression const& _expression) const
{
	solAssert(!!_expression.annotation().type, "Type requested but not present.");
	return _expression.annotation().type;
}

TypePointer const& TypeChecker::type(VariableDeclaration const& _variable) const
{
	solAssert(!!_variable.annotation().type, "Type requested but not present.");
	return _variable.annotation().type;
}

bool TypeChecker::visit(ContractDefinition const& _contract)
{
	m_currentContract = &_contract;

	ASTNode::listAccept(_contract.baseContracts(), *this);

	for (auto const& n: _contract.subNodes())
		n->accept(*this);

	m_currentContract = nullptr;

	return false;
}

void TypeChecker::checkDoubleStorageAssignment(Assignment const& _assignment)
{
	TupleType const& lhs = dynamic_cast<TupleType const&>(*type(_assignment.leftHandSide()));
	TupleType const& rhs = dynamic_cast<TupleType const&>(*type(_assignment.rightHandSide()));

	if (lhs.components().size() != rhs.components().size())
	{
		solAssert(m_errorReporter.hasErrors(), "");
		return;
	}

	size_t storageToStorageCopies = 0;
	size_t toStorageCopies = 0;
	for (size_t i = 0; i < lhs.components().size(); ++i)
	{
		ReferenceType const* ref = dynamic_cast<ReferenceType const*>(lhs.components()[i]);
		if (!ref || !ref->dataStoredIn(DataLocation::Storage) || ref->isPointer())
			continue;
		toStorageCopies++;
		if (rhs.components()[i]->dataStoredIn(DataLocation::Storage))
			storageToStorageCopies++;
	}
	if (storageToStorageCopies >= 1 && toStorageCopies >= 2)
		m_errorReporter.warning(
			7238_error,
			_assignment.location(),
			"This assignment performs two copies to storage. Since storage copies do not first "
			"copy to a temporary location, one of them might be overwritten before the second "
			"is executed and thus may have unexpected effects. It is safer to perform the copies "
			"separately or assign to storage pointers first."
		);
}

TypePointers TypeChecker::typeCheckABIDecodeAndRetrieveReturnType(FunctionCall const& _functionCall, bool _abiEncoderV2)
{
	vector<ASTPointer<Expression const>> arguments = _functionCall.arguments();
	if (arguments.size() != 2)
		m_errorReporter.typeError(
			5782_error,
			_functionCall.location(),
			"This function takes two arguments, but " +
			toString(arguments.size()) +
			" were provided."
		);

	if (arguments.size() >= 1)
		if (
			!type(*arguments.front())->isImplicitlyConvertibleTo(*TypeProvider::bytesMemory()) &&
			!type(*arguments.front())->isImplicitlyConvertibleTo(*TypeProvider::bytesCalldata())
		)
			m_errorReporter.typeError(
				1956_error,
				arguments.front()->location(),
				"The first argument to \"abi.decode\" must be implicitly convertible to "
				"bytes memory or bytes calldata, but is of type " +
				type(*arguments.front())->toString() +
				"."
			);

	if (arguments.size() < 2)
		return {};

	// The following is a rather syntactic restriction, but we check it here anyway:
	// The second argument has to be a tuple expression containing type names.
	TupleExpression const* tupleExpression = dynamic_cast<TupleExpression const*>(arguments[1].get());
	if (!tupleExpression)
	{
		m_errorReporter.typeError(
			6444_error,
			arguments[1]->location(),
			"The second argument to \"abi.decode\" has to be a tuple of types."
		);
		return {};
	}

	TypePointers components;
	for (auto const& typeArgument: tupleExpression->components())
	{
		solAssert(typeArgument, "");
		if (TypeType const* argTypeType = dynamic_cast<TypeType const*>(type(*typeArgument)))
		{
			TypePointer actualType = argTypeType->actualType();
			solAssert(actualType, "");
			// We force memory because the parser currently cannot handle
			// data locations. Furthermore, storage can be a little dangerous and
			// calldata is not really implemented anyway.
			actualType = TypeProvider::withLocationIfReference(DataLocation::Memory, actualType);
			// We force address payable for address types.
			if (actualType->category() == Type::Category::Address)
				actualType = TypeProvider::payableAddress();
			solAssert(
				!actualType->dataStoredIn(DataLocation::CallData) &&
				!actualType->dataStoredIn(DataLocation::Storage),
				""
			);
			if (!actualType->fullEncodingType(false, _abiEncoderV2, false))
				m_errorReporter.typeError(
					9611_error,
					typeArgument->location(),
					"Decoding type " + actualType->toString(false) + " not supported."
				);

			if (auto referenceType = dynamic_cast<ReferenceType const*>(actualType))
			{
				auto result = referenceType->validForLocation(referenceType->location());
				if (!result)
					m_errorReporter.typeError(
						6118_error,
						typeArgument->location(),
						result.message()
					);
			}

			components.push_back(actualType);
		}
		else
		{
			m_errorReporter.typeError(1039_error, typeArgument->location(), "Argument has to be a type name.");
			components.push_back(TypeProvider::emptyTuple());
		}
	}
	return components;
}

TypePointers TypeChecker::typeCheckMetaTypeFunctionAndRetrieveReturnType(FunctionCall const& _functionCall)
{
	vector<ASTPointer<Expression const>> arguments = _functionCall.arguments();
	if (arguments.size() != 1)
	{
		m_errorReporter.typeError(
			8885_error,
			_functionCall.location(),
			"This function takes one argument, but " +
			toString(arguments.size()) +
			" were provided."
		);
		return {};
	}
	TypePointer firstArgType = type(*arguments.front());

	bool wrongType = false;
	if (firstArgType->category() == Type::Category::TypeType)
	{
		TypeType const* typeTypePtr = dynamic_cast<TypeType const*>(firstArgType);
		Type::Category typeCategory = typeTypePtr->actualType()->category();
		if (
			typeCategory != Type::Category::Contract &&
			typeCategory != Type::Category::Integer
		)
			wrongType = true;
	}
	else
		wrongType = true;

	if (wrongType)
	{
		m_errorReporter.typeError(
			4259_error,
			arguments.front()->location(),
			"Invalid type for argument in the function call. "
			"A contract type or an integer type is required, but " +
			type(*arguments.front())->toString(true) + " provided."
		);
		return {};
	}

	return {TypeProvider::meta(dynamic_cast<TypeType const&>(*firstArgType).actualType())};
}

void TypeChecker::endVisit(InheritanceSpecifier const& _inheritance)
{
	auto base = dynamic_cast<ContractDefinition const*>(&dereference(_inheritance.name()));
	solAssert(base, "Base contract not available.");
	solAssert(m_currentContract, "");

	if (m_currentContract->isInterface() && !base->isInterface())
		m_errorReporter.typeError(6536_error, _inheritance.location(), "Interfaces can only inherit from other interfaces.");

	auto const& arguments = _inheritance.arguments();
	TypePointers parameterTypes;
	if (!base->isInterface())
		// Interfaces do not have constructors, so there are zero parameters.
		parameterTypes = ContractType(*base).newExpressionType()->parameterTypes();

	if (arguments)
	{
		if (parameterTypes.size() != arguments->size())
		{
			m_errorReporter.typeError(
				7927_error,
				_inheritance.location(),
				"Wrong argument count for constructor call: " +
				toString(arguments->size()) +
				" arguments given but expected " +
				toString(parameterTypes.size()) +
				". Remove parentheses if you do not want to provide arguments here."
			);
		}
		for (size_t i = 0; i < std::min(arguments->size(), parameterTypes.size()); ++i)
		{
			BoolResult result = type(*(*arguments)[i])->isImplicitlyConvertibleTo(*parameterTypes[i]);
			if (!result)
				m_errorReporter.typeErrorConcatenateDescriptions(
					9827_error,
					(*arguments)[i]->location(),
					"Invalid type for argument in constructor call. "
					"Invalid implicit conversion from " +
					type(*(*arguments)[i])->toString() +
					" to " +
					parameterTypes[i]->toString() +
					" requested.",
					result.message()
				);
		}
	}
}

void TypeChecker::endVisit(ModifierDefinition const& _modifier)
{
	if (_modifier.virtualSemantics())
		if (auto const* contractDef = dynamic_cast<ContractDefinition const*>(_modifier.scope()))
			if (contractDef->isLibrary())
				m_errorReporter.typeError(
					3275_error,
					_modifier.location(),
					"Modifiers in a library cannot be virtual."
				);

	if (!_modifier.isImplemented() && !_modifier.virtualSemantics())
		m_errorReporter.typeError(8063_error, _modifier.location(), "Modifiers without implementation must be marked virtual.");
}

bool TypeChecker::visit(FunctionDefinition const& _function)
{
	if (_function.markedVirtual())
	{
		if (_function.isFree())
			m_errorReporter.syntaxError(4493_error, _function.location(), "Free functions cannot be virtual.");
		else if (_function.isConstructor())
			m_errorReporter.typeError(7001_error, _function.location(), "Constructors cannot be virtual.");
		else if (_function.annotation().contract->isInterface())
			m_errorReporter.warning(5815_error, _function.location(), "Interface functions are implicitly \"virtual\"");
		else if (_function.visibility() == Visibility::Private)
			m_errorReporter.typeError(3942_error, _function.location(), "\"virtual\" and \"private\" cannot be used together.");
		else if (_function.libraryFunction())
			m_errorReporter.typeError(7801_error, _function.location(), "Library functions cannot be \"virtual\".");
	}
	if (_function.overrides() && _function.isFree())
		m_errorReporter.syntaxError(1750_error, _function.location(), "Free functions cannot override.");

	if (_function.isPayable())
	{
		if (_function.libraryFunction())
			m_errorReporter.typeError(7708_error, _function.location(), "Library functions cannot be payable.");
		else if (_function.isFree())
			m_errorReporter.typeError(9559_error, _function.location(), "Free functions cannot be payable.");
		else if (_function.isOrdinary() && !_function.isPartOfExternalInterface())
			m_errorReporter.typeError(5587_error, _function.location(), "\"internal\" and \"private\" functions cannot be payable.");
	}

	vector<VariableDeclaration const*> internalParametersInConstructor;

	auto checkArgumentAndReturnParameter = [&](VariableDeclaration const& _var) {
		if (type(_var)->containsNestedMapping())
			if (_var.referenceLocation() == VariableDeclaration::Location::Storage)
				solAssert(
					_function.libraryFunction() || _function.isConstructor() || !_function.isPublic(),
					"Mapping types for parameters or return variables "
					"can only be used in internal or library functions."
				);
		bool functionIsExternallyVisible =
			(!_function.isConstructor() && _function.isPublic()) ||
			(_function.isConstructor() && !m_currentContract->abstract());
		if (
			_function.isConstructor() &&
			_var.referenceLocation() == VariableDeclaration::Location::Storage &&
			!m_currentContract->abstract()
		)
			m_errorReporter.typeError(
				3644_error,
				_var.location(),
				"This parameter has a type that can only be used internally. "
				"You can make the contract abstract to avoid this problem."
			);
		else if (functionIsExternallyVisible)
		{
			auto iType = type(_var)->interfaceType(_function.libraryFunction());

			if (!iType)
			{
				string message = iType.message();
				solAssert(!message.empty(), "Expected detailed error message!");
				if (_function.isConstructor())
					message += " You can make the contract abstract to avoid this problem.";
				m_errorReporter.typeError(4103_error, _var.location(), message);
			}
			else if (
				!useABICoderV2() &&
				!typeSupportedByOldABIEncoder(*type(_var), _function.libraryFunction())
			)
			{
				string message =
					"This type is only supported in ABI coder v2. "
					"Use \"pragma abicoder v2;\" to enable the feature.";
				if (_function.isConstructor())
					message +=
						" Alternatively, make the contract abstract and supply the "
						"constructor arguments from a derived contract.";
				m_errorReporter.typeError(
					4957_error,
					_var.location(),
					message
				);
			}
		}
	};
	for (ASTPointer<VariableDeclaration> const& var: _function.parameters())
	{
		checkArgumentAndReturnParameter(*var);
		var->accept(*this);
	}
	for (ASTPointer<VariableDeclaration> const& var: _function.returnParameters())
	{
		checkArgumentAndReturnParameter(*var);
		var->accept(*this);
	}

	set<Declaration const*> modifiers;
	for (ASTPointer<ModifierInvocation> const& modifier: _function.modifiers())
	{
		vector<ContractDefinition const*> baseContracts;
		if (auto contract = dynamic_cast<ContractDefinition const*>(_function.scope()))
		{
			baseContracts = contract->annotation().linearizedBaseContracts;
			// Delete first base which is just the main contract itself
			baseContracts.erase(baseContracts.begin());
		}

		visitManually(
			*modifier,
			_function.isConstructor() ? baseContracts : vector<ContractDefinition const*>()
		);
		Declaration const* decl = &dereference(*modifier->name());
		if (modifiers.count(decl))
		{
			if (dynamic_cast<ContractDefinition const*>(decl))
				m_errorReporter.declarationError(1697_error, modifier->location(), "Base constructor already provided.");
		}
		else
			modifiers.insert(decl);
	}

	solAssert(_function.isFree() == !m_currentContract, "");
	if (!m_currentContract)
	{
		solAssert(!_function.isConstructor(), "");
		solAssert(!_function.isFallback(), "");
		solAssert(!_function.isReceive(), "");
	}
	else if (m_currentContract->isInterface())
	{
		if (_function.isImplemented())
			m_errorReporter.typeError(4726_error, _function.location(), "Functions in interfaces cannot have an implementation.");

		if (_function.isConstructor())
			m_errorReporter.typeError(6482_error, _function.location(), "Constructor cannot be defined in interfaces.");
		else if (_function.visibility() != Visibility::External)
			m_errorReporter.typeError(1560_error, _function.location(), "Functions in interfaces must be declared external.");
	}
	else if (m_currentContract->contractKind() == ContractKind::Library)
		if (_function.isConstructor())
			m_errorReporter.typeError(7634_error, _function.location(), "Constructor cannot be defined in libraries.");

	if (_function.isImplemented())
		_function.body().accept(*this);
	else if (_function.isConstructor())
		m_errorReporter.typeError(5700_error, _function.location(), "Constructor must be implemented if declared.");
	else if (_function.libraryFunction())
		m_errorReporter.typeError(9231_error, _function.location(), "Library functions must be implemented if declared.");
	else if (!_function.virtualSemantics())
	{
		if (_function.isFree())
			solAssert(m_errorReporter.hasErrors(), "");
		else
			m_errorReporter.typeError(5424_error, _function.location(), "Functions without implementation must be marked virtual.");
	}


	if (_function.isFallback())
		typeCheckFallbackFunction(_function);
	else if (_function.isReceive())
		typeCheckReceiveFunction(_function);
	else if (_function.isConstructor())
		typeCheckConstructor(_function);

	return false;
}

bool TypeChecker::visit(VariableDeclaration const& _variable)
{
	_variable.typeName().accept(*this);

	// type is filled either by ReferencesResolver directly from the type name or by
	// TypeChecker at the VariableDeclarationStatement level.
	TypePointer varType = _variable.annotation().type;
	solAssert(!!varType, "Variable type not provided.");

	if (_variable.value())
	{
		if (_variable.isStateVariable() && varType->containsNestedMapping())
		{
			m_errorReporter.typeError(
				6280_error,
				_variable.location(),
				"Types in storage containing (nested) mappings cannot be assigned to."
			);
			_variable.value()->accept(*this);
		}
		else
			expectType(*_variable.value(), *varType);
	}
	if (_variable.isConstant())
	{
		if (!_variable.type()->isValueType())
		{
			bool allowed = false;
			if (auto arrayType = dynamic_cast<ArrayType const*>(_variable.type()))
				allowed = arrayType->isByteArray();
			if (!allowed)
				m_errorReporter.typeError(9259_error, _variable.location(), "Constants of non-value type not yet implemented.");
		}

		if (!_variable.value())
			m_errorReporter.typeError(4266_error, _variable.location(), "Uninitialized \"constant\" variable.");
		else if (!*_variable.value()->annotation().isPure)
			m_errorReporter.typeError(
				8349_error,
				_variable.value()->location(),
				"Initial value for constant variable has to be compile-time constant."
			);
	}
	else if (_variable.immutable())
	{
		if (!_variable.type()->isValueType())
			m_errorReporter.typeError(6377_error, _variable.location(), "Immutable variables cannot have a non-value type.");
		if (
			auto const* functionType = dynamic_cast<FunctionType const*>(_variable.type());
			functionType && functionType->kind() == FunctionType::Kind::External
		)
			m_errorReporter.typeError(3366_error, _variable.location(), "Immutable variables of external function type are not yet supported.");
		solAssert(_variable.type()->sizeOnStack() == 1 || m_errorReporter.hasErrors(), "");
	}

	if (!_variable.isStateVariable())
	{
		if (
			_variable.referenceLocation() == VariableDeclaration::Location::CallData ||
			_variable.referenceLocation() == VariableDeclaration::Location::Memory
		)
			if (varType->containsNestedMapping())
				m_errorReporter.fatalTypeError(
					4061_error,
					_variable.location(),
					"Type " + varType->toString(true) + " is only valid in storage because it contains a (nested) mapping."
				);
	}
	else if (_variable.visibility() >= Visibility::Public)
	{
		FunctionType getter(_variable);
		if (!useABICoderV2())
		{
			vector<string> unsupportedTypes;
			for (auto const& param: getter.parameterTypes() + getter.returnParameterTypes())
				if (!typeSupportedByOldABIEncoder(*param, false /* isLibrary */))
					unsupportedTypes.emplace_back(param->toString());
			if (!unsupportedTypes.empty())
				m_errorReporter.typeError(
					2763_error,
					_variable.location(),
					"The following types are only supported for getters in ABI coder v2: " +
					joinHumanReadable(unsupportedTypes) +
					". Either remove \"public\" or use \"pragma abicoder v2;\" to enable the feature."
				);
		}
		if (!getter.interfaceFunctionType())
			m_errorReporter.typeError(6744_error, _variable.location(), "Internal or recursive type is not allowed for public state variables.");
	}

	bool isStructMemberDeclaration = dynamic_cast<StructDefinition const*>(_variable.scope()) != nullptr;
	if (isStructMemberDeclaration)
		return false;

	if (auto referenceType = dynamic_cast<ReferenceType const*>(varType))
	{
		auto result = referenceType->validForLocation(referenceType->location());
		if (result)
		{
			bool isLibraryStorageParameter = (_variable.isLibraryFunctionParameter() && referenceType->location() == DataLocation::Storage);
			bool callDataCheckRequired = ((_variable.isConstructorParameter() || _variable.isPublicCallableParameter()) && !isLibraryStorageParameter);
			if (callDataCheckRequired)
				result = referenceType->validForLocation(DataLocation::CallData);
		}
		if (!result)
		{
			solAssert(!result.message().empty(), "Expected detailed error message");
			m_errorReporter.typeError(1534_error, _variable.location(), result.message());
			return false;
		}
	}

	return false;
}

void TypeChecker::visitManually(
	ModifierInvocation const& _modifier,
	vector<ContractDefinition const*> const& _bases
)
{
	std::vector<ASTPointer<Expression>> const& arguments =
		_modifier.arguments() ? *_modifier.arguments() : std::vector<ASTPointer<Expression>>();
	for (ASTPointer<Expression> const& argument: arguments)
		argument->accept(*this);

	_modifier.name()->accept(*this);

	auto const* declaration = &dereference(*_modifier.name());
	vector<ASTPointer<VariableDeclaration>> emptyParameterList;
	vector<ASTPointer<VariableDeclaration>> const* parameters = nullptr;
	if (auto modifierDecl = dynamic_cast<ModifierDefinition const*>(declaration))
		parameters = &modifierDecl->parameters();
	else
		// check parameters for Base constructors
		for (ContractDefinition const* base: _bases)
			if (declaration == base)
			{
				if (auto referencedConstructor = base->constructor())
					parameters = &referencedConstructor->parameters();
				else
					parameters = &emptyParameterList;
				break;
			}
	if (!parameters)
	{
		m_errorReporter.typeError(4659_error, _modifier.location(), "Referenced declaration is neither modifier nor base class.");
		return;
	}
	if (parameters->size() != arguments.size())
	{
		m_errorReporter.typeError(
			2973_error,
			_modifier.location(),
			"Wrong argument count for modifier invocation: " +
			toString(arguments.size()) +
			" arguments given but expected " +
			toString(parameters->size()) +
			"."
		);
		return;
	}
	for (size_t i = 0; i < arguments.size(); ++i)
	{
		BoolResult result = type(*arguments[i])->isImplicitlyConvertibleTo(*type(*(*parameters)[i]));
		if (!result)
			m_errorReporter.typeErrorConcatenateDescriptions(
				4649_error,
				arguments[i]->location(),
				"Invalid type for argument in modifier invocation. "
				"Invalid implicit conversion from " +
				type(*arguments[i])->toString() +
				" to " +
				type(*(*parameters)[i])->toString() +
				" requested.",
				result.message()
			);
	}
}

bool TypeChecker::visit(EventDefinition const& _eventDef)
{
	solAssert(_eventDef.visibility() > Visibility::Internal, "");
	unsigned numIndexed = 0;
	for (ASTPointer<VariableDeclaration> const& var: _eventDef.parameters())
	{
		if (var->isIndexed())
			numIndexed++;
		if (type(*var)->containsNestedMapping())
			m_errorReporter.typeError(
				3448_error,
				var->location(),
				"Type containing a (nested) mapping is not allowed as event parameter type."
			);
		if (!type(*var)->interfaceType(false))
			m_errorReporter.typeError(3417_error, var->location(), "Internal or recursive type is not allowed as event parameter type.");
		if (
			!useABICoderV2() &&
			!typeSupportedByOldABIEncoder(*type(*var), false /* isLibrary */)
		)
			m_errorReporter.typeError(
				3061_error,
				var->location(),
				"This type is only supported in ABI coder v2. "
				"Use \"pragma abicoder v2;\" to enable the feature."
			);
	}
	if (_eventDef.isAnonymous() && numIndexed > 4)
		m_errorReporter.typeError(8598_error, _eventDef.location(), "More than 4 indexed arguments for anonymous event.");
	else if (!_eventDef.isAnonymous() && numIndexed > 3)
		m_errorReporter.typeError(7249_error, _eventDef.location(), "More than 3 indexed arguments for event.");
	return true;
}

void TypeChecker::endVisit(FunctionTypeName const& _funType)
{
	FunctionType const& fun = dynamic_cast<FunctionType const&>(*_funType.annotation().type);
	if (fun.kind() == FunctionType::Kind::External)
	{
		for (auto const& t: _funType.parameterTypes() + _funType.returnParameterTypes())
		{
			solAssert(t->annotation().type, "Type not set for parameter.");
			if (!t->annotation().type->interfaceType(false).get())
				m_errorReporter.typeError(2582_error, t->location(), "Internal type cannot be used for external function type.");
		}
		solAssert(fun.interfaceType(false), "External function type uses internal types.");
	}
}

bool TypeChecker::visit(InlineAssembly const& _inlineAssembly)
{
	// External references have already been resolved in a prior stage and stored in the annotation.
	// We run the resolve step again regardless.
	yul::ExternalIdentifierAccess::Resolver identifierAccess = [&](
		yul::Identifier const& _identifier,
		yul::IdentifierContext _context,
		bool
	)
	{
		auto ref = _inlineAssembly.annotation().externalReferences.find(&_identifier);
		if (ref == _inlineAssembly.annotation().externalReferences.end())
			return false;
		InlineAssemblyAnnotation::ExternalIdentifierInfo& identifierInfo = ref->second;
		Declaration const* declaration = identifierInfo.declaration;
		solAssert(!!declaration, "");
		bool requiresStorage = identifierInfo.isSlot || identifierInfo.isOffset;
		if (auto var = dynamic_cast<VariableDeclaration const*>(declaration))
		{
			solAssert(var->type(), "Expected variable type!");
			if (var->immutable())
			{
				m_errorReporter.typeError(3773_error, _identifier.location, "Assembly access to immutable variables is not supported.");
				return false;
			}
			if (var->isConstant())
			{
				var = rootConstVariableDeclaration(*var);

				if (var && !var->value())
				{
					m_errorReporter.typeError(3224_error, _identifier.location, "Constant has no value.");
					return false;
				}
				else if (_context == yul::IdentifierContext::LValue)
				{
					m_errorReporter.typeError(6252_error, _identifier.location, "Constant variables cannot be assigned to.");
					return false;
				}
				else if (requiresStorage)
				{
					m_errorReporter.typeError(6617_error, _identifier.location, "The suffixes .offset and .slot can only be used on non-constant storage variables.");
					return false;
				}
				else if (var && var->value() && !var->value()->annotation().type && !dynamic_cast<Literal const*>(var->value().get()))
				{
					m_errorReporter.typeError(
						2249_error,
						_identifier.location,
						"Constant variables with non-literal values cannot be forward referenced from inline assembly."
					);
					return false;
				}
				else if (!var || !type(*var)->isValueType() || (
					!dynamic_cast<Literal const*>(var->value().get()) &&
					type(*var->value())->category() != Type::Category::RationalNumber
				))
				{
					m_errorReporter.typeError(7615_error, _identifier.location, "Only direct number constants and references to such constants are supported by inline assembly.");
					return false;
				}
			}

			solAssert(!dynamic_cast<FixedPointType const*>(var->type()), "FixedPointType not implemented.");

			if (requiresStorage)
			{
				if (!var->isStateVariable() && !var->type()->dataStoredIn(DataLocation::Storage))
				{
					m_errorReporter.typeError(3622_error, _identifier.location, "The suffixes .offset and .slot can only be used on storage variables.");
					return false;
				}
				else if (_context == yul::IdentifierContext::LValue)
				{
					if (var->isStateVariable())
					{
						m_errorReporter.typeError(4713_error, _identifier.location, "State variables cannot be assigned to - you have to use \"sstore()\".");
						return false;
					}
					else if (identifierInfo.isOffset)
					{
						m_errorReporter.typeError(9739_error, _identifier.location, "Only .slot can be assigned to.");
						return false;
					}
					else
						solAssert(identifierInfo.isSlot, "");
				}
			}
			else if (!var->isConstant() && var->isStateVariable())
			{
				m_errorReporter.typeError(1408_error, _identifier.location, "Only local variables are supported. To access storage variables, use the .slot and .offset suffixes.");
				return false;
			}
			else if (var->type()->dataStoredIn(DataLocation::Storage))
			{
				m_errorReporter.typeError(9068_error, _identifier.location, "You have to use the .slot or .offset suffix to access storage reference variables.");
				return false;
			}
			else if (var->type()->sizeOnStack() != 1)
			{
				if (var->type()->dataStoredIn(DataLocation::CallData))
					m_errorReporter.typeError(2370_error, _identifier.location, "Call data elements cannot be accessed directly. Copy to a local variable first or use \"calldataload\" or \"calldatacopy\" with manually determined offsets and sizes.");
				else
					m_errorReporter.typeError(9857_error, _identifier.location, "Only types that use one stack slot are supported.");
				return false;
			}
		}
		else if (requiresStorage)
		{
			m_errorReporter.typeError(7944_error, _identifier.location, "The suffixes .offset and .slot can only be used on storage variables.");
			return false;
		}
		else if (_context == yul::IdentifierContext::LValue)
		{
			if (dynamic_cast<MagicVariableDeclaration const*>(declaration))
				return false;

			m_errorReporter.typeError(1990_error, _identifier.location, "Only local variables can be assigned to in inline assembly.");
			return false;
		}

		if (_context == yul::IdentifierContext::RValue)
		{
			solAssert(!!declaration->type(), "Type of declaration required but not yet determined.");
			if (dynamic_cast<FunctionDefinition const*>(declaration))
			{
				m_errorReporter.declarationError(2025_error, _identifier.location, "Access to functions is not allowed in inline assembly.");
				return false;
			}
			else if (dynamic_cast<VariableDeclaration const*>(declaration))
			{
			}
			else if (auto contract = dynamic_cast<ContractDefinition const*>(declaration))
			{
				if (!contract->isLibrary())
				{
					m_errorReporter.typeError(4977_error, _identifier.location, "Expected a library.");
					return false;
				}
			}
			else
				return false;
		}
		identifierInfo.valueSize = 1;
		return true;
	};
	solAssert(!_inlineAssembly.annotation().analysisInfo, "");
	_inlineAssembly.annotation().analysisInfo = make_shared<yul::AsmAnalysisInfo>();
	yul::AsmAnalyzer analyzer(
		*_inlineAssembly.annotation().analysisInfo,
		m_errorReporter,
		_inlineAssembly.dialect(),
		identifierAccess
	);
	if (!analyzer.analyze(_inlineAssembly.operations()))
		return false;
	return true;
}

bool TypeChecker::visit(IfStatement const& _ifStatement)
{
	expectType(_ifStatement.condition(), *TypeProvider::boolean());
	_ifStatement.trueStatement().accept(*this);
	if (_ifStatement.falseStatement())
		_ifStatement.falseStatement()->accept(*this);
	return false;
}

void TypeChecker::endVisit(TryStatement const& _tryStatement)
{
	FunctionCall const* externalCall = dynamic_cast<FunctionCall const*>(&_tryStatement.externalCall());
	if (!externalCall || *externalCall->annotation().kind != FunctionCallKind::FunctionCall)
	{
		m_errorReporter.typeError(
			5347_error,
			_tryStatement.externalCall().location(),
			"Try can only be used with external function calls and contract creation calls."
		);
		return;
	}

	FunctionType const& functionType = dynamic_cast<FunctionType const&>(*externalCall->expression().annotation().type);
	if (
		functionType.kind() != FunctionType::Kind::External &&
		functionType.kind() != FunctionType::Kind::Creation &&
		functionType.kind() != FunctionType::Kind::DelegateCall
	)
	{
		m_errorReporter.typeError(
			2536_error,
			_tryStatement.externalCall().location(),
			"Try can only be used with external function calls and contract creation calls."
		);
		return;
	}

	externalCall->annotation().tryCall = true;

	solAssert(_tryStatement.clauses().size() >= 2, "");
	solAssert(_tryStatement.clauses().front(), "");

	TryCatchClause const& successClause = *_tryStatement.clauses().front();
	if (successClause.parameters())
	{
		TypePointers returnTypes =
			m_evmVersion.supportsReturndata() ?
			functionType.returnParameterTypes() :
			functionType.returnParameterTypesWithoutDynamicTypes();
		std::vector<ASTPointer<VariableDeclaration>> const& parameters =
			successClause.parameters()->parameters();
		if (returnTypes.size() != parameters.size())
			m_errorReporter.typeError(
				2800_error,
				successClause.location(),
				"Function returns " +
				to_string(functionType.returnParameterTypes().size()) +
				" values, but returns clause has " +
				to_string(parameters.size()) +
				" variables."
			);
		size_t len = min(returnTypes.size(), parameters.size());
		for (size_t i = 0; i < len; ++i)
		{
			solAssert(returnTypes[i], "");
			if (parameters[i] && *parameters[i]->annotation().type != *returnTypes[i])
				m_errorReporter.typeError(
					6509_error,
					parameters[i]->location(),
					"Invalid type, expected " +
					returnTypes[i]->toString(false) +
					" but got " +
					parameters[i]->annotation().type->toString() +
					"."
				);
		}
	}

	TryCatchClause const* errorClause = nullptr;
	TryCatchClause const* lowLevelClause = nullptr;
	for (size_t i = 1; i < _tryStatement.clauses().size(); ++i)
	{
		TryCatchClause const& clause = *_tryStatement.clauses()[i];
		if (clause.errorName() == "")
		{
			if (lowLevelClause)
				m_errorReporter.typeError(
					5320_error,
					clause.location(),
					SecondarySourceLocation{}.append("The first clause is here:", lowLevelClause->location()),
					"This try statement already has a low-level catch clause."
				);
			lowLevelClause = &clause;
			if (clause.parameters() && !clause.parameters()->parameters().empty())
			{
				if (
					clause.parameters()->parameters().size() != 1 ||
					*clause.parameters()->parameters().front()->type() != *TypeProvider::bytesMemory()
				)
					m_errorReporter.typeError(6231_error, clause.location(), "Expected `catch (bytes memory ...) { ... }` or `catch { ... }`.");
				if (!m_evmVersion.supportsReturndata())
					m_errorReporter.typeError(
						9908_error,
						clause.location(),
						"This catch clause type cannot be used on the selected EVM version (" +
						m_evmVersion.name() +
						"). You need at least a Byzantium-compatible EVM or use `catch { ... }`."
					);
			}
		}
		else if (clause.errorName() == "Error")
		{
			if (!m_evmVersion.supportsReturndata())
				m_errorReporter.typeError(
					1812_error,
					clause.location(),
					"This catch clause type cannot be used on the selected EVM version (" +
					m_evmVersion.name() +
					"). You need at least a Byzantium-compatible EVM or use `catch { ... }`."
				);

			if (errorClause)
				m_errorReporter.typeError(
					1036_error,
					clause.location(),
					SecondarySourceLocation{}.append("The first clause is here:", errorClause->location()),
					"This try statement already has an \"Error\" catch clause."
				);
			errorClause = &clause;
			if (
				!clause.parameters() ||
				clause.parameters()->parameters().size() != 1 ||
				*clause.parameters()->parameters().front()->type() != *TypeProvider::stringMemory()
			)
				m_errorReporter.typeError(2943_error, clause.location(), "Expected `catch Error(string memory ...) { ... }`.");
		}
		else
			m_errorReporter.typeError(
				3542_error,
				clause.location(),
				"Invalid catch clause name. Expected either `catch (...)` or `catch Error(...)`."
			);
	}
}

bool TypeChecker::visit(WhileStatement const& _whileStatement)
{
	expectType(_whileStatement.condition(), *TypeProvider::boolean());
	_whileStatement.body().accept(*this);
	return false;
}

bool TypeChecker::visit(ForStatement const& _forStatement)
{
	if (_forStatement.initializationExpression())
		_forStatement.initializationExpression()->accept(*this);
	if (_forStatement.condition())
		expectType(*_forStatement.condition(), *TypeProvider::boolean());
	if (_forStatement.loopExpression())
		_forStatement.loopExpression()->accept(*this);
	_forStatement.body().accept(*this);
	return false;
}

void TypeChecker::endVisit(Return const& _return)
{
	ParameterList const* params = _return.annotation().functionReturnParameters;
	if (!_return.expression())
	{
		if (params && !params->parameters().empty())
			m_errorReporter.typeError(6777_error, _return.location(), "Return arguments required.");
		return;
	}
	if (!params)
	{
		m_errorReporter.typeError(7552_error, _return.location(), "Return arguments not allowed.");
		return;
	}
	TypePointers returnTypes;
	for (auto const& var: params->parameters())
		returnTypes.push_back(type(*var));
	if (auto tupleType = dynamic_cast<TupleType const*>(type(*_return.expression())))
	{
		if (tupleType->components().size() != params->parameters().size())
			m_errorReporter.typeError(5132_error, _return.location(), "Different number of arguments in return statement than in returns declaration.");
		else
		{
			BoolResult result = tupleType->isImplicitlyConvertibleTo(TupleType(returnTypes));
			if (!result)
				m_errorReporter.typeErrorConcatenateDescriptions(
					5992_error,
					_return.expression()->location(),
					"Return argument type " +
					type(*_return.expression())->toString() +
					" is not implicitly convertible to expected type " +
					TupleType(returnTypes).toString(false) + ".",
					result.message()
				);
		}
	}
	else if (params->parameters().size() != 1)
		m_errorReporter.typeError(8863_error, _return.location(), "Different number of arguments in return statement than in returns declaration.");
	else
	{
		TypePointer const& expected = type(*params->parameters().front());
		BoolResult result = type(*_return.expression())->isImplicitlyConvertibleTo(*expected);
		if (!result)
			m_errorReporter.typeErrorConcatenateDescriptions(
				6359_error,
				_return.expression()->location(),
				"Return argument type " +
				type(*_return.expression())->toString() +
				" is not implicitly convertible to expected type (type of first return variable) " +
				expected->toString() + ".",
				result.message()
			);
	}
}

void TypeChecker::endVisit(EmitStatement const& _emit)
{
	if (
		*_emit.eventCall().annotation().kind != FunctionCallKind::FunctionCall ||
		type(_emit.eventCall().expression())->category() != Type::Category::Function ||
		dynamic_cast<FunctionType const&>(*type(_emit.eventCall().expression())).kind() != FunctionType::Kind::Event
	)
		m_errorReporter.typeError(9292_error, _emit.eventCall().expression().location(), "Expression has to be an event invocation.");
}

bool TypeChecker::visit(VariableDeclarationStatement const& _statement)
{
	if (!_statement.initialValue())
	{
		// No initial value is only permitted for single variables with specified type.
		// This usually already results in a parser error.
		if (_statement.declarations().size() != 1 || !_statement.declarations().front())
		{
			solAssert(m_errorReporter.hasErrors(), "");

			// It is okay to return here, as there are no named components on the
			// left-hand-side that could cause any damage later.
			return false;
		}

		VariableDeclaration const& varDecl = *_statement.declarations().front();
		solAssert(varDecl.annotation().type, "");

		if (dynamic_cast<MappingType const*>(type(varDecl)))
			m_errorReporter.typeError(
				4182_error,
				varDecl.location(),
				"Uninitialized mapping. Mappings cannot be created dynamically, you have to assign them from a state variable."
			);
		varDecl.accept(*this);
		return false;
	}

	// Here we have an initial value and might have to derive some types before we can visit
	// the variable declaration(s).

	_statement.initialValue()->accept(*this);
	TypePointers valueTypes;
	if (auto tupleType = dynamic_cast<TupleType const*>(type(*_statement.initialValue())))
		valueTypes = tupleType->components();
	else
		valueTypes = TypePointers{type(*_statement.initialValue())};

	vector<ASTPointer<VariableDeclaration>> const& variables = _statement.declarations();
	if (variables.empty())
		// We already have an error for this in the SyntaxChecker.
		solAssert(m_errorReporter.hasErrors(), "");
	else if (valueTypes.size() != variables.size())
		m_errorReporter.typeError(
			7364_error,
			_statement.location(),
			"Different number of components on the left hand side (" +
			toString(variables.size()) +
			") than on the right hand side (" +
			toString(valueTypes.size()) +
			")."
		);

	for (size_t i = 0; i < min(variables.size(), valueTypes.size()); ++i)
	{
		if (!variables[i])
			continue;
		VariableDeclaration const& var = *variables[i];
		solAssert(!var.value(), "Value has to be tied to statement.");
		TypePointer const& valueComponentType = valueTypes[i];
		solAssert(!!valueComponentType, "");
		solAssert(var.annotation().type, "");

		var.accept(*this);
		BoolResult result = valueComponentType->isImplicitlyConvertibleTo(*var.annotation().type);
		if (!result)
		{
			auto errorMsg = "Type " +
				valueComponentType->toString() +
				" is not implicitly convertible to expected type " +
				var.annotation().type->toString();
			if (
				valueComponentType->category() == Type::Category::RationalNumber &&
				dynamic_cast<RationalNumberType const&>(*valueComponentType).isFractional() &&
				valueComponentType->mobileType()
			)
			{
				if (var.annotation().type->operator==(*valueComponentType->mobileType()))
					m_errorReporter.typeError(
						5107_error,
						_statement.location(),
						errorMsg + ", but it can be explicitly converted."
					);
				else
					m_errorReporter.typeError(
						4486_error,
						_statement.location(),
						errorMsg +
						". Try converting to type " +
						valueComponentType->mobileType()->toString() +
						" or use an explicit conversion."
					);
			}
			else
				m_errorReporter.typeErrorConcatenateDescriptions(
					9574_error,
					_statement.location(),
					errorMsg + ".",
					result.message()
				);
		}
	}

	if (valueTypes.size() != variables.size())
	{
		solAssert(m_errorReporter.hasErrors(), "Should have errors!");
		for (auto const& var: variables)
			if (var && !var->annotation().type)
				BOOST_THROW_EXCEPTION(FatalError());
	}

	return false;
}

void TypeChecker::endVisit(ExpressionStatement const& _statement)
{
	if (type(_statement.expression())->category() == Type::Category::RationalNumber)
		if (!dynamic_cast<RationalNumberType const&>(*type(_statement.expression())).mobileType())
			m_errorReporter.typeError(3757_error, _statement.expression().location(), "Invalid rational number.");

	if (auto call = dynamic_cast<FunctionCall const*>(&_statement.expression()))
	{
		if (auto callType = dynamic_cast<FunctionType const*>(type(call->expression())))
		{
			auto kind = callType->kind();
			if (
				kind == FunctionType::Kind::BareCall ||
				kind == FunctionType::Kind::BareCallCode ||
				kind == FunctionType::Kind::BareDelegateCall ||
				kind == FunctionType::Kind::BareStaticCall
			)
				m_errorReporter.warning(9302_error, _statement.location(), "Return value of low-level calls not used.");
			else if (kind == FunctionType::Kind::Send)
				m_errorReporter.warning(5878_error, _statement.location(), "Failure condition of 'send' ignored. Consider using 'transfer' instead.");
		}
	}
}

bool TypeChecker::visit(Conditional const& _conditional)
{
	expectType(_conditional.condition(), *TypeProvider::boolean());

	_conditional.trueExpression().accept(*this);
	_conditional.falseExpression().accept(*this);

	TypePointer trueType = type(_conditional.trueExpression())->mobileType();
	TypePointer falseType = type(_conditional.falseExpression())->mobileType();

	TypePointer commonType = nullptr;

	if (!trueType)
		m_errorReporter.typeError(9717_error, _conditional.trueExpression().location(), "Invalid mobile type in true expression.");
	else
		commonType = trueType;

	if (!falseType)
		m_errorReporter.typeError(3703_error, _conditional.falseExpression().location(), "Invalid mobile type in false expression.");
	else
		commonType = falseType;

	if (!trueType && !falseType)
		BOOST_THROW_EXCEPTION(FatalError());
	else if (trueType && falseType)
	{
		commonType = Type::commonType(trueType, falseType);

		if (!commonType)
		{
			m_errorReporter.typeError(
					1080_error,
					_conditional.location(),
					"True expression's type " +
					trueType->toString() +
					" does not match false expression's type " +
					falseType->toString() +
					"."
					);
			// even we can't find a common type, we have to set a type here,
			// otherwise the upper statement will not be able to check the type.
			commonType = trueType;
		}
	}

	_conditional.annotation().isConstant = false;
	_conditional.annotation().type = commonType;
	_conditional.annotation().isPure =
		*_conditional.condition().annotation().isPure &&
		*_conditional.trueExpression().annotation().isPure &&
		*_conditional.falseExpression().annotation().isPure;

	_conditional.annotation().isLValue = false;

	if (_conditional.annotation().willBeWrittenTo)
		m_errorReporter.typeError(
			2212_error,
			_conditional.location(),
			"Conditional expression as left value is not supported yet."
		);

	return false;
}

void TypeChecker::checkExpressionAssignment(Type const& _type, Expression const& _expression)
{
	if (auto const* tupleExpression = dynamic_cast<TupleExpression const*>(&_expression))
	{
		if (tupleExpression->components().empty())
			m_errorReporter.typeError(5547_error, _expression.location(), "Empty tuple on the left hand side.");

		auto const* tupleType = dynamic_cast<TupleType const*>(&_type);
		auto const& types = tupleType && tupleExpression->components().size() != 1 ? tupleType->components() : vector<TypePointer> { &_type };

		solAssert(
			tupleExpression->components().size() == types.size() || m_errorReporter.hasErrors(),
			"Array sizes don't match and no errors generated."
		);

		for (size_t i = 0; i < min(tupleExpression->components().size(), types.size()); i++)
			if (types[i])
			{
				solAssert(!!tupleExpression->components()[i], "");
				checkExpressionAssignment(*types[i], *tupleExpression->components()[i]);
			}
	}
	else if (_type.nameable() && _type.containsNestedMapping())
	{
		bool isLocalOrReturn = false;
		if (auto const* identifier = dynamic_cast<Identifier const*>(&_expression))
			if (auto const *variableDeclaration = dynamic_cast<VariableDeclaration const*>(identifier->annotation().referencedDeclaration))
				if (variableDeclaration->isLocalOrReturn())
					isLocalOrReturn = true;
		if (!isLocalOrReturn)
			m_errorReporter.typeError(9214_error, _expression.location(), "Types in storage containing (nested) mappings cannot be assigned to.");
	}
}

bool TypeChecker::visit(Assignment const& _assignment)
{
	requireLValue(
		_assignment.leftHandSide(),
		_assignment.assignmentOperator() == Token::Assign
	);
	TypePointer t = type(_assignment.leftHandSide());
	_assignment.annotation().type = t;
	_assignment.annotation().isPure = false;
	_assignment.annotation().isLValue = false;
	_assignment.annotation().isConstant = false;

	checkExpressionAssignment(*t, _assignment.leftHandSide());

	if (TupleType const* tupleType = dynamic_cast<TupleType const*>(t))
	{
		if (_assignment.assignmentOperator() != Token::Assign)
			m_errorReporter.typeError(
				4289_error,
				_assignment.location(),
				"Compound assignment is not allowed for tuple types."
			);
		// Sequenced assignments of tuples is not valid, make the result a "void" type.
		_assignment.annotation().type = TypeProvider::emptyTuple();

		expectType(_assignment.rightHandSide(), *tupleType);

		// expectType does not cause fatal errors, so we have to check again here.
		if (dynamic_cast<TupleType const*>(type(_assignment.rightHandSide())))
			checkDoubleStorageAssignment(_assignment);
	}
	else if (_assignment.assignmentOperator() == Token::Assign)
		expectType(_assignment.rightHandSide(), *t);
	else
	{
		// compound assignment
		_assignment.rightHandSide().accept(*this);
		TypePointer resultType = t->binaryOperatorResult(
			TokenTraits::AssignmentToBinaryOp(_assignment.assignmentOperator()),
			type(_assignment.rightHandSide())
		);
		if (!resultType || *resultType != *t)
			m_errorReporter.typeError(
				7366_error,
				_assignment.location(),
				"Operator " +
				string(TokenTraits::toString(_assignment.assignmentOperator())) +
				" not compatible with types " +
				t->toString() +
				" and " +
				type(_assignment.rightHandSide())->toString()
			);
	}
	return false;
}

bool TypeChecker::visit(TupleExpression const& _tuple)
{
	_tuple.annotation().isConstant = false;
	vector<ASTPointer<Expression>> const& components = _tuple.components();
	TypePointers types;

	if (_tuple.annotation().willBeWrittenTo)
	{
		if (_tuple.isInlineArray())
			m_errorReporter.fatalTypeError(3025_error, _tuple.location(), "Inline array type cannot be declared as LValue.");
		for (auto const& component: components)
			if (component)
			{
				requireLValue(
					*component,
					_tuple.annotation().lValueOfOrdinaryAssignment
				);
				types.push_back(type(*component));
			}
			else
				types.push_back(TypePointer());
		if (components.size() == 1)
			_tuple.annotation().type = type(*components[0]);
		else
			_tuple.annotation().type = TypeProvider::tuple(move(types));
		// If some of the components are not LValues, the error is reported above.
		_tuple.annotation().isLValue = true;
		_tuple.annotation().isPure = false;
	}
	else
	{
		bool isPure = true;
		TypePointer inlineArrayType = nullptr;

		for (size_t i = 0; i < components.size(); ++i)
		{
			if (!components[i])
				m_errorReporter.fatalTypeError(8381_error, _tuple.location(), "Tuple component cannot be empty.");

			components[i]->accept(*this);
			types.push_back(type(*components[i]));

			if (types[i]->category() == Type::Category::Tuple)
				if (dynamic_cast<TupleType const&>(*types[i]).components().empty())
				{
					if (_tuple.isInlineArray())
						m_errorReporter.fatalTypeError(5604_error, components[i]->location(), "Array component cannot be empty.");
					m_errorReporter.typeError(6473_error, components[i]->location(), "Tuple component cannot be empty.");
				}

			// Note: code generation will visit each of the expression even if they are not assigned from.
			if (types[i]->category() == Type::Category::RationalNumber && components.size() > 1)
				if (!dynamic_cast<RationalNumberType const&>(*types[i]).mobileType())
					m_errorReporter.fatalTypeError(3390_error, components[i]->location(), "Invalid rational number.");

			if (_tuple.isInlineArray())
			{
				solAssert(!!types[i], "Inline array cannot have empty components");

				if ((i == 0 || inlineArrayType) && !types[i]->mobileType())
					m_errorReporter.fatalTypeError(9563_error, components[i]->location(), "Invalid mobile type.");

				if (i == 0)
					inlineArrayType = types[i]->mobileType();
				else if (inlineArrayType)
					inlineArrayType = Type::commonType(inlineArrayType, types[i]);
			}
			if (!*components[i]->annotation().isPure)
				isPure = false;
		}
		_tuple.annotation().isPure = isPure;
		if (_tuple.isInlineArray())
		{
			if (!inlineArrayType)
				m_errorReporter.fatalTypeError(6378_error, _tuple.location(), "Unable to deduce common type for array elements.");
			else if (!inlineArrayType->nameable())
				m_errorReporter.fatalTypeError(
					9656_error,
					_tuple.location(),
					"Unable to deduce nameable type for array elements. Try adding explicit type conversion for the first element."
				);
			else if (inlineArrayType->containsNestedMapping())
				m_errorReporter.fatalTypeError(
					1545_error,
					_tuple.location(),
					"Type " + inlineArrayType->toString(true) + " is only valid in storage."
				);

			_tuple.annotation().type = TypeProvider::array(DataLocation::Memory, inlineArrayType, types.size());
		}
		else
		{
			if (components.size() == 1)
				_tuple.annotation().type = type(*components[0]);
			else
				_tuple.annotation().type = TypeProvider::tuple(move(types));
		}

		_tuple.annotation().isLValue = false;
	}
	return false;
}

bool TypeChecker::visit(UnaryOperation const& _operation)
{
	// Inc, Dec, Add, Sub, Not, BitNot, Delete
	Token op = _operation.getOperator();
	bool const modifying = (op == Token::Inc || op == Token::Dec || op == Token::Delete);
	if (modifying)
		requireLValue(_operation.subExpression(), false);
	else
		_operation.subExpression().accept(*this);
	TypePointer const& subExprType = type(_operation.subExpression());
	TypePointer t = type(_operation.subExpression())->unaryOperatorResult(op);
	if (!t)
	{
		string description = "Unary operator " + string(TokenTraits::toString(op)) + " cannot be applied to type " + subExprType->toString();
		if (modifying)
			// Cannot just report the error, ignore the unary operator, and continue,
			// because the sub-expression was already processed with requireLValue()
			m_errorReporter.fatalTypeError(9767_error, _operation.location(), description);
		else
			m_errorReporter.typeError(4907_error, _operation.location(), description);
		t = subExprType;
	}
	_operation.annotation().type = t;
	_operation.annotation().isConstant = false;
	_operation.annotation().isPure = !modifying && *_operation.subExpression().annotation().isPure;
	_operation.annotation().isLValue = false;

	return false;
}

void TypeChecker::endVisit(BinaryOperation const& _operation)
{
	TypePointer const& leftType = type(_operation.leftExpression());
	TypePointer const& rightType = type(_operation.rightExpression());
	TypeResult result = leftType->binaryOperatorResult(_operation.getOperator(), rightType);
	TypePointer commonType = result.get();
	if (!commonType)
	{
		m_errorReporter.typeError(
			2271_error,
			_operation.location(),
			"Operator " +
			string(TokenTraits::toString(_operation.getOperator())) +
			" not compatible with types " +
			leftType->toString() +
			" and " +
			rightType->toString() +
			(!result.message().empty() ? ". " + result.message() : "")
		);
		commonType = leftType;
	}
	_operation.annotation().commonType = commonType;
	_operation.annotation().type =
		TokenTraits::isCompareOp(_operation.getOperator()) ?
		TypeProvider::boolean() :
		commonType;
	_operation.annotation().isPure =
		*_operation.leftExpression().annotation().isPure &&
		*_operation.rightExpression().annotation().isPure;
	_operation.annotation().isLValue = false;
	_operation.annotation().isConstant = false;

	if (_operation.getOperator() == Token::Exp || _operation.getOperator() == Token::SHL)
	{
		string operation = _operation.getOperator() == Token::Exp ? "exponentiation" : "shift";
		if (
			leftType->category() == Type::Category::RationalNumber &&
			rightType->category() != Type::Category::RationalNumber
		)
			if ((
				commonType->category() == Type::Category::Integer &&
				dynamic_cast<IntegerType const&>(*commonType).numBits() != 256
			) || (
				commonType->category() == Type::Category::FixedPoint &&
				dynamic_cast<FixedPointType const&>(*commonType).numBits() != 256
			))
				m_errorReporter.warning(
					9085_error,
					_operation.location(),
					"Result of " + operation + " has type " + commonType->toString() + " and thus "
					"might overflow. Silence this warning by converting the literal to the "
					"expected type."
				);
		if (
			commonType->category() == Type::Category::Integer &&
			rightType->category() == Type::Category::Integer &&
			dynamic_cast<IntegerType const&>(*commonType).numBits() <
			dynamic_cast<IntegerType const&>(*rightType).numBits()
		)
			m_errorReporter.warning(
				3149_error,
				_operation.location(),
				"The result type of the " +
				operation +
				" operation is equal to the type of the first operand (" +
				commonType->toString() +
				") ignoring the (larger) type of the second operand (" +
				rightType->toString() +
				") which might be unexpected. Silence this warning by either converting "
				"the first or the second operand to the type of the other."
			);
	}
}

TypePointer TypeChecker::typeCheckTypeConversionAndRetrieveReturnType(
	FunctionCall const& _functionCall
)
{
	solAssert(*_functionCall.annotation().kind == FunctionCallKind::TypeConversion, "");
	TypePointer const& expressionType = type(_functionCall.expression());

	vector<ASTPointer<Expression const>> const& arguments = _functionCall.arguments();
	bool const isPositionalCall = _functionCall.names().empty();

	TypePointer resultType = dynamic_cast<TypeType const&>(*expressionType).actualType();
	if (arguments.size() != 1)
		m_errorReporter.typeError(
			2558_error,
			_functionCall.location(),
			"Exactly one argument expected for explicit type conversion."
		);
	else if (!isPositionalCall)
		m_errorReporter.typeError(
			5153_error,
			_functionCall.location(),
			"Type conversion cannot allow named arguments."
		);
	else
	{
		Type const* argType = type(*arguments.front());
		// Resulting data location is memory unless we are converting from a reference
		// type with a different data location.
		// (data location cannot yet be specified for type conversions)
		DataLocation dataLoc = DataLocation::Memory;
		if (auto argRefType = dynamic_cast<ReferenceType const*>(argType))
			dataLoc = argRefType->location();
		if (auto type = dynamic_cast<ReferenceType const*>(resultType))
			resultType = TypeProvider::withLocation(type, dataLoc, type->isPointer());
		BoolResult result = argType->isExplicitlyConvertibleTo(*resultType);
		if (result)
		{
			if (auto argArrayType = dynamic_cast<ArrayType const*>(argType))
			{
				auto resultArrayType = dynamic_cast<ArrayType const*>(resultType);
				solAssert(!!resultArrayType, "");
				solAssert(
					argArrayType->location() != DataLocation::Storage ||
					(
						(
							resultArrayType->isPointer() ||
							(argArrayType->isByteArray() && resultArrayType->isByteArray())
						) &&
						resultArrayType->location() == DataLocation::Storage
					),
					"Invalid explicit conversion to storage type."
				);
			}
		}
		else
		{
			if (
				resultType->category() == Type::Category::Contract &&
				argType->category() == Type::Category::Address
			)
			{
				solAssert(dynamic_cast<ContractType const*>(resultType)->isPayable(), "");
				solAssert(
					dynamic_cast<AddressType const*>(argType)->stateMutability() <
						StateMutability::Payable,
					""
				);
				SecondarySourceLocation ssl;
				if (
					auto const* identifier = dynamic_cast<Identifier const*>(arguments.front().get())
				)
					if (
						auto const* variableDeclaration = dynamic_cast<VariableDeclaration const*>(
							identifier->annotation().referencedDeclaration
						)
					)
						ssl.append(
							"Did you mean to declare this variable as \"address payable\"?",
							variableDeclaration->location()
						);
				m_errorReporter.typeError(
					7398_error,
					_functionCall.location(),
					ssl,
					"Explicit type conversion not allowed from non-payable \"address\" to \"" +
					resultType->toString() +
					"\", which has a payable fallback function."
				);
			}
			else if (
				auto const* functionType = dynamic_cast<FunctionType const*>(argType);
				functionType &&
				functionType->kind() == FunctionType::Kind::External &&
				resultType->category() == Type::Category::Address
			)
				m_errorReporter.typeError(
					5030_error,
					_functionCall.location(),
					"Explicit type conversion not allowed from \"" +
					argType->toString() +
					"\" to \"" +
					resultType->toString() +
					"\". To obtain the address of the contract of the function, " +
					"you can use the .address member of the function."
				);
			else
				m_errorReporter.typeErrorConcatenateDescriptions(
					9640_error,
					_functionCall.location(),
					"Explicit type conversion not allowed from \"" +
					argType->toString() +
					"\" to \"" +
					resultType->toString() +
					"\".",
					result.message()
				);
		}
		if (auto addressType = dynamic_cast<AddressType const*>(resultType))
			if (addressType->stateMutability() != StateMutability::Payable)
			{
				bool payable = false;
				if (argType->category() != Type::Category::Address)
					payable = argType->isExplicitlyConvertibleTo(*TypeProvider::payableAddress());
				resultType = payable ? TypeProvider::payableAddress() : TypeProvider::address();
			}
	}
	return resultType;
}

void TypeChecker::typeCheckFunctionCall(
	FunctionCall const& _functionCall,
	FunctionTypePointer _functionType
)
{
	// Actual function call or struct constructor call.

	solAssert(!!_functionType, "");
	solAssert(_functionType->kind() != FunctionType::Kind::ABIDecode, "");

	if (_functionType->kind() == FunctionType::Kind::Declaration)
	{
		solAssert(_functionType->declaration().annotation().contract, "");
		if (
			m_currentContract &&
			m_currentContract->derivesFrom(*_functionType->declaration().annotation().contract) &&
			!dynamic_cast<FunctionDefinition const&>(_functionType->declaration()).isImplemented()
		)
			m_errorReporter.typeError(
				7501_error,
				_functionCall.location(),
				"Cannot call unimplemented base function."
			);
		else
			m_errorReporter.typeError(
				3419_error,
				_functionCall.location(),
				"Cannot call function via contract type name."
			);
		return;
	}

	// Check for unsupported use of bare static call
	if (
		_functionType->kind() == FunctionType::Kind::BareStaticCall &&
		!m_evmVersion.hasStaticCall()
	)
		m_errorReporter.typeError(
			5052_error,
			_functionCall.location(),
			"\"staticcall\" is not supported by the VM version."
		);

	// Perform standard function call type checking
	typeCheckFunctionGeneralChecks(_functionCall, _functionType);
}

void TypeChecker::typeCheckFallbackFunction(FunctionDefinition const& _function)
{
	solAssert(_function.isFallback(), "");

	if (_function.libraryFunction())
		m_errorReporter.typeError(5982_error, _function.location(), "Libraries cannot have fallback functions.");
	if (_function.stateMutability() != StateMutability::NonPayable && _function.stateMutability() != StateMutability::Payable)
		m_errorReporter.typeError(
			4575_error,
			_function.location(),
			"Fallback function must be payable or non-payable, but is \"" +
			stateMutabilityToString(_function.stateMutability()) +
			"\"."
		);
	if (_function.visibility() != Visibility::External)
		m_errorReporter.typeError(1159_error, _function.location(), "Fallback function must be defined as \"external\".");
	if (!_function.returnParameters().empty())
	{
		if (_function.returnParameters().size() > 1 || *type(*_function.returnParameters().front()) != *TypeProvider::bytesMemory())
			m_errorReporter.typeError(5570_error, _function.returnParameterList()->location(), "Fallback function can only have a single \"bytes memory\" return value.");
		else
			m_errorReporter.typeError(6151_error, _function.returnParameterList()->location(), "Return values for fallback functions are not yet implemented.");
	}
	if (!_function.parameters().empty())
		m_errorReporter.typeError(3978_error, _function.parameterList().location(), "Fallback function cannot take parameters.");
}

void TypeChecker::typeCheckReceiveFunction(FunctionDefinition const& _function)
{
	solAssert(_function.isReceive(), "");

	if (_function.libraryFunction())
		m_errorReporter.typeError(4549_error, _function.location(), "Libraries cannot have receive ether functions.");

	if (_function.stateMutability() != StateMutability::Payable)
		m_errorReporter.typeError(
			7793_error,
			_function.location(),
			"Receive ether function must be payable, but is \"" +
			stateMutabilityToString(_function.stateMutability()) +
			"\"."
		);
	if (_function.visibility() != Visibility::External)
		m_errorReporter.typeError(4095_error, _function.location(), "Receive ether function must be defined as \"external\".");
	if (!_function.returnParameters().empty())
		m_errorReporter.typeError(6899_error, _function.returnParameterList()->location(), "Receive ether function cannot return values.");
	if (!_function.parameters().empty())
		m_errorReporter.typeError(6857_error, _function.parameterList().location(), "Receive ether function cannot take parameters.");
}


void TypeChecker::typeCheckConstructor(FunctionDefinition const& _function)
{
	solAssert(_function.isConstructor(), "");
	if (_function.overrides())
		m_errorReporter.typeError(1209_error, _function.location(), "Constructors cannot override.");
	if (!_function.returnParameters().empty())
		m_errorReporter.typeError(9712_error, _function.returnParameterList()->location(), "Non-empty \"returns\" directive for constructor.");
	if (_function.stateMutability() != StateMutability::NonPayable && _function.stateMutability() != StateMutability::Payable)
		m_errorReporter.typeError(
			1558_error,
			_function.location(),
			"Constructor must be payable or non-payable, but is \"" +
			stateMutabilityToString(_function.stateMutability()) +
			"\"."
		);
	if (!_function.noVisibilitySpecified())
	{
		auto const& contract = dynamic_cast<ContractDefinition const&>(*_function.scope());
		if (_function.visibility() != Visibility::Public && _function.visibility() != Visibility::Internal)
			m_errorReporter.typeError(9239_error, _function.location(), "Constructor cannot have visibility.");
		else if (_function.isPublic() && contract.abstract())
			m_errorReporter.declarationError(
				8295_error,
				_function.location(),
				"Abstract contracts cannot have public constructors. Remove the \"public\" keyword to fix this."
			);
		else if (!_function.isPublic() && !contract.abstract())
			m_errorReporter.declarationError(
				1845_error,
				_function.location(),
				"Non-abstract contracts cannot have internal constructors. Remove the \"internal\" keyword and make the contract abstract to fix this."
			);
		else
			m_errorReporter.warning(
				2462_error,
				_function.location(),
				"Visibility for constructor is ignored. If you want the contract to be non-deployable, making it \"abstract\" is sufficient."
			);
	}
}

void TypeChecker::typeCheckABIEncodeFunctions(
	FunctionCall const& _functionCall,
	FunctionTypePointer _functionType
)
{
	solAssert(!!_functionType, "");
	solAssert(
		_functionType->kind() == FunctionType::Kind::ABIEncode ||
		_functionType->kind() == FunctionType::Kind::ABIEncodePacked ||
		_functionType->kind() == FunctionType::Kind::ABIEncodeWithSelector ||
		_functionType->kind() == FunctionType::Kind::ABIEncodeWithSignature,
		"ABI function has unexpected FunctionType::Kind."
	);
	solAssert(_functionType->takesArbitraryParameters(), "ABI functions should be variadic.");

	bool const isPacked = _functionType->kind() == FunctionType::Kind::ABIEncodePacked;
	solAssert(_functionType->padArguments() != isPacked, "ABI function with unexpected padding");

	bool const abiEncoderV2 = useABICoderV2();

	// Check for named arguments
	if (!_functionCall.names().empty())
	{
		m_errorReporter.typeError(
			2627_error,
			_functionCall.location(),
			"Named arguments cannot be used for functions that take arbitrary parameters."
		);
		return;
	}

	// Perform standard function call type checking
	typeCheckFunctionGeneralChecks(_functionCall, _functionType);

	// Check additional arguments for variadic functions
	vector<ASTPointer<Expression const>> const& arguments = _functionCall.arguments();
	for (size_t i = 0; i < arguments.size(); ++i)
	{
		auto const& argType = type(*arguments[i]);

		if (argType->category() == Type::Category::RationalNumber)
		{
			auto const& rationalType = dynamic_cast<RationalNumberType const&>(*argType);
			if (rationalType.isFractional())
			{
				m_errorReporter.typeError(
					6090_error,
					arguments[i]->location(),
					"Fractional numbers cannot yet be encoded."
				);
				continue;
			}
			else if (!argType->mobileType())
			{
				m_errorReporter.typeError(
					8009_error,
					arguments[i]->location(),
					"Invalid rational number (too large or division by zero)."
				);
				continue;
			}
			else if (isPacked)
			{
				m_errorReporter.typeError(
					7279_error,
					arguments[i]->location(),
					"Cannot perform packed encoding for a literal."
					" Please convert it to an explicit type first."
				);
				continue;
			}
		}

		if (isPacked && !typeSupportedByOldABIEncoder(*argType, false /* isLibrary */))
		{
			m_errorReporter.typeError(
				9578_error,
				arguments[i]->location(),
				"Type not supported in packed mode."
			);
			continue;
		}

		if (!argType->fullEncodingType(false, abiEncoderV2, !_functionType->padArguments()))
			m_errorReporter.typeError(
				2056_error,
				arguments[i]->location(),
				"This type cannot be encoded."
			);
	}
}

void TypeChecker::typeCheckFunctionGeneralChecks(
	FunctionCall const& _functionCall,
	FunctionTypePointer _functionType
)
{
	// Actual function call or struct constructor call.

	solAssert(!!_functionType, "");
	solAssert(_functionType->kind() != FunctionType::Kind::ABIDecode, "");

	bool const isPositionalCall = _functionCall.names().empty();
	bool const isVariadic = _functionType->takesArbitraryParameters();

	auto functionCallKind = *_functionCall.annotation().kind;

	solAssert(
		!isVariadic || functionCallKind == FunctionCallKind::FunctionCall,
		"Struct constructor calls cannot be variadic."
	);

	TypePointers const& parameterTypes = _functionType->parameterTypes();
	vector<ASTPointer<Expression const>> const& arguments = _functionCall.arguments();
	vector<ASTPointer<ASTString>> const& argumentNames = _functionCall.names();

	// Check number of passed in arguments
	if (
		arguments.size() < parameterTypes.size() ||
		(!isVariadic && arguments.size() > parameterTypes.size())
	)
	{
		bool const isStructConstructorCall =
			functionCallKind == FunctionCallKind::StructConstructorCall;

		auto [errorId, description] = [&]() -> tuple<ErrorId, string> {
			string msg = isVariadic ?
				"Need at least " +
				toString(parameterTypes.size()) +
				" arguments for " +
				string(isStructConstructorCall ? "struct constructor" : "function call") +
				", but provided only " +
				toString(arguments.size()) +
				"."
				:
				"Wrong argument count for " +
				string(isStructConstructorCall ? "struct constructor" : "function call") +
				": " +
				toString(arguments.size()) +
				" arguments given but " +
				string(isVariadic ? "need at least " : "expected ") +
				toString(parameterTypes.size()) +
				".";

			if (isStructConstructorCall)
				return { isVariadic ? 1123_error : 9755_error, msg };
			else if (
				_functionType->kind() == FunctionType::Kind::BareCall ||
				_functionType->kind() == FunctionType::Kind::BareCallCode ||
				_functionType->kind() == FunctionType::Kind::BareDelegateCall ||
				_functionType->kind() == FunctionType::Kind::BareStaticCall
			)
			{
				if (arguments.empty())
					return {
						isVariadic ? 7653_error : 6138_error,
						msg +
						" This function requires a single bytes argument."
						" Use \"\" as argument to provide empty calldata."
					};
				else
					return {
						isVariadic ? 9390_error : 8922_error,
						msg +
						" This function requires a single bytes argument."
						" If all your arguments are value types, you can use"
						" abi.encode(...) to properly generate it."
					};
			}
			else if (
				_functionType->kind() == FunctionType::Kind::KECCAK256 ||
				_functionType->kind() == FunctionType::Kind::SHA256 ||
				_functionType->kind() == FunctionType::Kind::RIPEMD160
			)
				return {
					isVariadic ? 1220_error : 4323_error,
					msg +
					" This function requires a single bytes argument."
					" Use abi.encodePacked(...) to obtain the pre-0.5.0"
					" behaviour or abi.encode(...) to use ABI encoding."
				};
			else
				return { isVariadic ? 9308_error : 6160_error, msg };
		}();

		m_errorReporter.typeError(errorId, _functionCall.location(), description);
		return;
	}

	// Parameter to argument map
	std::vector<Expression const*> paramArgMap(parameterTypes.size());

	// Map parameters to arguments - trivially for positional calls, less so for named calls
	if (isPositionalCall)
		for (size_t i = 0; i < paramArgMap.size(); ++i)
			paramArgMap[i] = arguments[i].get();
	else
	{
		auto const& parameterNames = _functionType->parameterNames();

		solAssert(
			parameterNames.size() == argumentNames.size(),
			"Unexpected parameter length mismatch!"
		);

		// Check for duplicate argument names
		{
			bool duplication = false;
			for (size_t i = 0; i < argumentNames.size(); i++)
				for (size_t j = i + 1; j < argumentNames.size(); j++)
					if (*argumentNames[i] == *argumentNames[j])
					{
						duplication = true;
						m_errorReporter.typeError(
							6995_error,
							arguments[i]->location(),
							"Duplicate named argument \"" + *argumentNames[i] + "\"."
						);
					}
			if (duplication)
				return;
		}

		// map parameter names to argument names
		{
			bool not_all_mapped = false;

			for (size_t i = 0; i < argumentNames.size(); i++)
			{
				size_t j;
				for (j = 0; j < parameterNames.size(); j++)
					if (parameterNames[j] == *argumentNames[i])
						break;

				if (j < parameterNames.size())
					paramArgMap[j] = arguments[i].get();
				else
				{
					not_all_mapped = true;
					m_errorReporter.typeError(
						4974_error,
						_functionCall.location(),
						"Named argument \"" +
						*argumentNames[i] +
						"\" does not match function declaration."
					);
				}
			}

			if (not_all_mapped)
				return;
		}
	}

	// Check for compatible types between arguments and parameters
	for (size_t i = 0; i < paramArgMap.size(); ++i)
	{
		solAssert(!!paramArgMap[i], "unmapped parameter");
		if (!type(*paramArgMap[i])->isImplicitlyConvertibleTo(*parameterTypes[i]))
		{
			auto [errorId, description] = [&]() -> tuple<ErrorId, string> {
				string msg =
					"Invalid type for argument in function call. "
					"Invalid implicit conversion from " +
					type(*paramArgMap[i])->toString() +
					" to " +
					parameterTypes[i]->toString() +
					" requested.";
				if (
					_functionType->kind() == FunctionType::Kind::BareCall ||
					_functionType->kind() == FunctionType::Kind::BareCallCode ||
					_functionType->kind() == FunctionType::Kind::BareDelegateCall ||
					_functionType->kind() == FunctionType::Kind::BareStaticCall
				)
					return {
						8051_error,
						msg +
						" This function requires a single bytes argument."
						" If all your arguments are value types, you can"
						" use abi.encode(...) to properly generate it."
					};
				else if (
					_functionType->kind() == FunctionType::Kind::KECCAK256 ||
					_functionType->kind() == FunctionType::Kind::SHA256 ||
					_functionType->kind() == FunctionType::Kind::RIPEMD160
				)
					return {
						7556_error,
						msg +
						" This function requires a single bytes argument."
						" Use abi.encodePacked(...) to obtain the pre-0.5.0"
						" behaviour or abi.encode(...) to use ABI encoding."
					};
				else
					return { 9553_error, msg };
			}();
			m_errorReporter.typeError(errorId, paramArgMap[i]->location(), description);
		}
	}

	TypePointers const& returnParameterTypes = _functionType->returnParameterTypes();
	bool isLibraryCall = (_functionType->kind() == FunctionType::Kind::DelegateCall);
	bool callRequiresABIEncoding =
		// ABIEncode/ABIDecode calls not included because they should have been already validated
		// at this point and they have variadic arguments so they need special handling.
		_functionType->kind() == FunctionType::Kind::DelegateCall ||
		_functionType->kind() == FunctionType::Kind::External ||
		_functionType->kind() == FunctionType::Kind::Creation ||
		_functionType->kind() == FunctionType::Kind::Event;

	if (callRequiresABIEncoding && !useABICoderV2())
	{
		solAssert(!isVariadic, "");
		solAssert(parameterTypes.size() == arguments.size(), "");
		solAssert(!_functionType->isBareCall(), "");
		solAssert(*_functionCall.annotation().kind == FunctionCallKind::FunctionCall, "");

		for (size_t i = 0; i < parameterTypes.size(); ++i)
		{
			solAssert(parameterTypes[i], "");

			if (!typeSupportedByOldABIEncoder(*parameterTypes[i], isLibraryCall))
				m_errorReporter.typeError(
					2443_error,
					paramArgMap[i]->location(),
					"The type of this parameter, " + parameterTypes[i]->toString(true) + ", "
					"is only supported in ABI coder v2. "
					"Use \"pragma abicoder v2;\" to enable the feature."
				);
		}

		for (size_t i = 0; i < returnParameterTypes.size(); ++i)
		{
			solAssert(returnParameterTypes[i], "");

			if (!typeSupportedByOldABIEncoder(*returnParameterTypes[i], isLibraryCall))
				m_errorReporter.typeError(
					2428_error,
					_functionCall.location(),
					"The type of return parameter " + toString(i + 1) + ", " + returnParameterTypes[i]->toString(true) + ", "
					"is only supported in ABI coder v2. "
					"Use \"pragma abicoder v2;\" to enable the feature."
				);
		}
	}
}

bool TypeChecker::visit(FunctionCall const& _functionCall)
{
	vector<ASTPointer<Expression const>> const& arguments = _functionCall.arguments();
	bool argumentsArePure = true;

	// We need to check arguments' type first as they will be needed for overload resolution.
	for (ASTPointer<Expression const> const& argument: arguments)
	{
		argument->accept(*this);
		if (!*argument->annotation().isPure)
			argumentsArePure = false;
	}

	// Store argument types - and names if given - for overload resolution
	{
		FuncCallArguments funcCallArgs;

		funcCallArgs.names = _functionCall.names();

		for (ASTPointer<Expression const> const& argument: arguments)
			funcCallArgs.types.push_back(type(*argument));

		_functionCall.expression().annotation().arguments = std::move(funcCallArgs);
	}

	_functionCall.expression().accept(*this);

	Type const* expressionType = type(_functionCall.expression());

	// Determine function call kind and function type for this FunctionCall node
	FunctionCallAnnotation& funcCallAnno = _functionCall.annotation();
	FunctionTypePointer functionType = nullptr;
	funcCallAnno.isConstant = false;

	bool isLValue = false;

	// Determine and assign function call kind, lvalue, purity and function type for this FunctionCall node
	switch (expressionType->category())
	{
	case Type::Category::Function:
		functionType = dynamic_cast<FunctionType const*>(expressionType);
		funcCallAnno.kind = FunctionCallKind::FunctionCall;

		// Purity for function calls also depends upon the callee and its FunctionType
		funcCallAnno.isPure =
			argumentsArePure &&
			*_functionCall.expression().annotation().isPure &&
			functionType &&
			functionType->isPure();

		if (
			functionType->kind() == FunctionType::Kind::ArrayPush ||
			functionType->kind() == FunctionType::Kind::ByteArrayPush
		)
			isLValue = functionType->parameterTypes().empty();

		break;

	case Type::Category::TypeType:
	{
		// Determine type for type conversion or struct construction expressions
		TypePointer const& actualType = dynamic_cast<TypeType const&>(*expressionType).actualType();
		solAssert(!!actualType, "");

		if (actualType->category() == Type::Category::Struct)
		{
			if (actualType->containsNestedMapping())
				m_errorReporter.fatalTypeError(
					9515_error,
					_functionCall.location(),
					"Struct containing a (nested) mapping cannot be constructed."
				);
			functionType = dynamic_cast<StructType const&>(*actualType).constructorType();
			funcCallAnno.kind = FunctionCallKind::StructConstructorCall;
		}
		else
			funcCallAnno.kind = FunctionCallKind::TypeConversion;

		funcCallAnno.isPure = argumentsArePure;

		break;
	}

	default:
		m_errorReporter.fatalTypeError(5704_error, _functionCall.location(), "Type is not callable");
		// Unreachable, because fatalTypeError throws. We don't set kind, but that's okay because the switch below
		// is never reached. And, even if it was, SetOnce would trigger an assertion violation and not UB.
		funcCallAnno.isPure = argumentsArePure;
		break;
	}

	funcCallAnno.isLValue = isLValue;

	// Determine return types
	switch (*funcCallAnno.kind)
	{
	case FunctionCallKind::TypeConversion:
		funcCallAnno.type = typeCheckTypeConversionAndRetrieveReturnType(_functionCall);
		break;

	case FunctionCallKind::StructConstructorCall: // fall-through
	case FunctionCallKind::FunctionCall:
	{
		TypePointers returnTypes;

		switch (functionType->kind())
		{
		case FunctionType::Kind::ABIDecode:
		{
			returnTypes = typeCheckABIDecodeAndRetrieveReturnType(
				_functionCall,
				useABICoderV2()
			);
			break;
		}
		case FunctionType::Kind::ABIEncode:
		case FunctionType::Kind::ABIEncodePacked:
		case FunctionType::Kind::ABIEncodeWithSelector:
		case FunctionType::Kind::ABIEncodeWithSignature:
		{
			typeCheckABIEncodeFunctions(_functionCall, functionType);
			returnTypes = functionType->returnParameterTypes();
			break;
		}
		case FunctionType::Kind::MetaType:
			returnTypes = typeCheckMetaTypeFunctionAndRetrieveReturnType(_functionCall);
			break;
		default:
		{
			typeCheckFunctionCall(_functionCall, functionType);
			returnTypes = m_evmVersion.supportsReturndata() ?
				functionType->returnParameterTypes() :
				functionType->returnParameterTypesWithoutDynamicTypes();
			break;
		}
		}

		funcCallAnno.type = returnTypes.size() == 1 ?
			move(returnTypes.front()) :
			TypeProvider::tuple(move(returnTypes));

		break;
	}

	default:
		// for non-callables, ensure error reported and annotate node to void function
		solAssert(m_errorReporter.hasErrors(), "");
		funcCallAnno.kind = FunctionCallKind::FunctionCall;
		funcCallAnno.type = TypeProvider::emptyTuple();
		break;
	}

	return false;
}

bool TypeChecker::visit(FunctionCallOptions const& _functionCallOptions)
{
	solAssert(_functionCallOptions.options().size() == _functionCallOptions.names().size(), "Lengths of name & value arrays differ!");

	_functionCallOptions.expression().annotation().arguments = _functionCallOptions.annotation().arguments;

	_functionCallOptions.expression().accept(*this);

	_functionCallOptions.annotation().isPure = false;
	_functionCallOptions.annotation().isConstant = false;
	_functionCallOptions.annotation().isLValue = false;

	auto expressionFunctionType = dynamic_cast<FunctionType const*>(type(_functionCallOptions.expression()));
	if (!expressionFunctionType)
	{
		m_errorReporter.fatalTypeError(2622_error, _functionCallOptions.location(), "Expected callable expression before call options.");
		return false;
	}

	bool setSalt = false;
	bool setValue = false;
	bool setGas = false;

	FunctionType::Kind kind = expressionFunctionType->kind();
	if (
		kind != FunctionType::Kind::Creation &&
		kind != FunctionType::Kind::External &&
		kind != FunctionType::Kind::BareCall &&
		kind != FunctionType::Kind::BareCallCode &&
		kind != FunctionType::Kind::BareDelegateCall &&
		kind != FunctionType::Kind::BareStaticCall
	)
	{
		m_errorReporter.fatalTypeError(
			2193_error,
			_functionCallOptions.location(),
			"Function call options can only be set on external function calls or contract creations."
		);
		return false;
	}

	auto setCheckOption = [&](bool& _option, string const&& _name, bool _alreadySet = false)
	{
		if (_option || _alreadySet)
			m_errorReporter.typeError(
				9886_error,
				_functionCallOptions.location(),
				_alreadySet ?
				"Option \"" + std::move(_name) + "\" has already been set." :
				"Duplicate option \"" + std::move(_name) + "\"."
			);

		_option = true;
	};

	for (size_t i = 0; i < _functionCallOptions.names().size(); ++i)
	{
		string const& name = *(_functionCallOptions.names()[i]);
		if (name == "salt")
		{
			if (kind == FunctionType::Kind::Creation)
			{
				setCheckOption(setSalt, "salt", expressionFunctionType->saltSet());
				expectType(*_functionCallOptions.options()[i], *TypeProvider::fixedBytes(32));
			}
			else
				m_errorReporter.typeError(
					2721_error,
					_functionCallOptions.location(),
					"Function call option \"salt\" can only be used with \"new\"."
				);
		}
		else if (name == "value")
		{
			if (kind == FunctionType::Kind::BareDelegateCall)
				m_errorReporter.typeError(
					6189_error,
					_functionCallOptions.location(),
					"Cannot set option \"value\" for delegatecall."
				);
			else if (kind == FunctionType::Kind::BareStaticCall)
				m_errorReporter.typeError(
					2842_error,
					_functionCallOptions.location(),
					"Cannot set option \"value\" for staticcall."
				);
			else if (!expressionFunctionType->isPayable())
				m_errorReporter.typeError(
					7006_error,
					_functionCallOptions.location(),
					kind == FunctionType::Kind::Creation ?
						"Cannot set option \"value\", since the constructor of " +
						expressionFunctionType->returnParameterTypes().front()->toString() +
						" is not payable." :
						"Cannot set option \"value\" on a non-payable function type."
				);
			else
			{
				expectType(*_functionCallOptions.options()[i], *TypeProvider::uint256());

				setCheckOption(setValue, "value", expressionFunctionType->valueSet());
			}
		}
		else if (name == "gas")
		{
			if (kind == FunctionType::Kind::Creation)
				m_errorReporter.typeError(
					9903_error,
					_functionCallOptions.location(),
					"Function call option \"gas\" cannot be used with \"new\"."
				);
			else
			{
				expectType(*_functionCallOptions.options()[i], *TypeProvider::uint256());

				setCheckOption(setGas, "gas", expressionFunctionType->gasSet());
			}
		}
		else
			m_errorReporter.typeError(
				9318_error,
				_functionCallOptions.location(),
				"Unknown call option \"" + name + "\". Valid options are \"salt\", \"value\" and \"gas\"."
			);
	}

	if (setSalt && !m_evmVersion.hasCreate2())
		m_errorReporter.typeError(
			5189_error,
			_functionCallOptions.location(),
			"Unsupported call option \"salt\" (requires Constantinople-compatible VMs)."
		);

	_functionCallOptions.annotation().type = expressionFunctionType->copyAndSetCallOptions(setGas, setValue, setSalt);
	return false;
}

void TypeChecker::endVisit(NewExpression const& _newExpression)
{
	TypePointer type = _newExpression.typeName().annotation().type;
	solAssert(!!type, "Type name not resolved.");

	_newExpression.annotation().isConstant = false;
	_newExpression.annotation().isLValue = false;

	if (auto contractName = dynamic_cast<UserDefinedTypeName const*>(&_newExpression.typeName()))
	{
		auto contract = dynamic_cast<ContractDefinition const*>(&dereference(*contractName));

		if (!contract)
			m_errorReporter.fatalTypeError(5540_error, _newExpression.location(), "Identifier is not a contract.");
		if (contract->isInterface())
			m_errorReporter.fatalTypeError(2971_error, _newExpression.location(), "Cannot instantiate an interface.");
		if (contract->abstract())
			m_errorReporter.typeError(4614_error, _newExpression.location(), "Cannot instantiate an abstract contract.");

		if (m_currentContract)
		{
			// TODO this is not properly detecting creation-cycles if they go through
			// internal library functions or free functions. It will be caught at
			// code generation time, but it would of course be better to catch it here.
			m_currentContract->annotation().contractDependencies.insert(contract);
			solAssert(
				!contract->annotation().linearizedBaseContracts.empty(),
				"Linearized base contracts not yet available."
			);
			if (contractDependenciesAreCyclic(*m_currentContract))
				m_errorReporter.typeError(
					4579_error,
					_newExpression.location(),
					"Circular reference for contract creation (cannot create instance of derived or same contract)."
				);
		}

		_newExpression.annotation().type = FunctionType::newExpressionType(*contract);
		_newExpression.annotation().isPure = false;
	}
	else if (type->category() == Type::Category::Array)
	{
		if (type->containsNestedMapping())
			m_errorReporter.fatalTypeError(
				1164_error,
				_newExpression.typeName().location(),
				"Array containing a (nested) mapping cannot be constructed in memory."
			);
		if (!type->isDynamicallySized())
			m_errorReporter.typeError(
				3904_error,
				_newExpression.typeName().location(),
				"Length has to be placed in parentheses after the array type for new expression."
			);
		type = TypeProvider::withLocationIfReference(DataLocation::Memory, type);
		_newExpression.annotation().type = TypeProvider::function(
			TypePointers{TypeProvider::uint256()},
			TypePointers{type},
			strings(1, ""),
			strings(1, ""),
			FunctionType::Kind::ObjectCreation,
			false,
			StateMutability::Pure
		);
		_newExpression.annotation().isPure = true;
	}
	else
	{
		_newExpression.annotation().isPure = false;
		m_errorReporter.fatalTypeError(8807_error, _newExpression.location(), "Contract or array type expected.");
	}
}

bool TypeChecker::visit(MemberAccess const& _memberAccess)
{
	_memberAccess.expression().accept(*this);
	TypePointer exprType = type(_memberAccess.expression());
	ASTString const& memberName = _memberAccess.memberName();

	auto& annotation = _memberAccess.annotation();

	// Retrieve the types of the arguments if this is used to call a function.
	auto const& arguments = annotation.arguments;
	MemberList::MemberMap possibleMembers = exprType->members(currentDefinitionScope()).membersByName(memberName);
	size_t const initialMemberCount = possibleMembers.size();
	if (initialMemberCount > 1 && arguments)
	{
		// do overload resolution
		for (auto it = possibleMembers.begin(); it != possibleMembers.end();)
			if (
				it->type->category() == Type::Category::Function &&
				!dynamic_cast<FunctionType const&>(*it->type).canTakeArguments(*arguments, exprType)
			)
				it = possibleMembers.erase(it);
			else
				++it;
	}

	annotation.isConstant = false;

	if (possibleMembers.empty())
	{
		if (initialMemberCount == 0 && !dynamic_cast<ArraySliceType const*>(exprType))
		{
			// Try to see if the member was removed because it is only available for storage types.
			auto storageType = TypeProvider::withLocationIfReference(
				DataLocation::Storage,
				exprType
			);
			if (!storageType->members(currentDefinitionScope()).membersByName(memberName).empty())
				m_errorReporter.fatalTypeError(
					4994_error,
					_memberAccess.location(),
					"Member \"" + memberName + "\" is not available in " +
					exprType->toString() +
					" outside of storage."
				);
		}

		auto [errorId, description] = [&]() -> tuple<ErrorId, string> {
			string errorMsg = "Member \"" + memberName + "\" not found or not visible "
				"after argument-dependent lookup in " + exprType->toString() + ".";

			if (auto const* funType = dynamic_cast<FunctionType const*>(exprType))
			{
				TypePointers const& t = funType->returnParameterTypes();

				if (memberName == "value")
				{
					if (funType->kind() == FunctionType::Kind::Creation)
						return {
							8827_error,
							"Constructor for " + t.front()->toString() + " must be payable for member \"value\" to be available."
						};
					else if (
						funType->kind() == FunctionType::Kind::DelegateCall ||
						funType->kind() == FunctionType::Kind::BareDelegateCall
					)
						return { 8477_error, "Member \"value\" is not allowed in delegated calls due to \"msg.value\" persisting." };
					else
						return { 8820_error, "Member \"value\" is only available for payable functions." };
				}
				else if (
					t.size() == 1 && (
						t.front()->category() == Type::Category::Struct ||
						t.front()->category() == Type::Category::Contract
					)
				)
					return { 6005_error, errorMsg + " Did you intend to call the function?" };
			}
			else if (exprType->category() == Type::Category::Contract)
			{
				for (MemberList::Member const& addressMember: TypeProvider::payableAddress()->nativeMembers(nullptr))
					if (addressMember.name == memberName)
					{
						auto const* var = dynamic_cast<Identifier const*>(&_memberAccess.expression());
						string varName = var ? var->name() : "...";
						errorMsg += " Use \"address(" + varName + ")." + memberName + "\" to access this address member.";
						return { 3125_error, errorMsg };
					}
			}
			else if (auto const* addressType = dynamic_cast<AddressType const*>(exprType))
			{
				// Trigger error when using send or transfer with a non-payable fallback function.
				if (memberName == "send" || memberName == "transfer")
				{
					solAssert(
						addressType->stateMutability() != StateMutability::Payable,
						"Expected address not-payable as members were not found"
					);

					return { 9862_error, "\"send\" and \"transfer\" are only available for objects of type \"address payable\", not \"" + exprType->toString() + "\"." };
				}
			}

			return { 9582_error, errorMsg };
		}();

		m_errorReporter.fatalTypeError(
			errorId,
			_memberAccess.location(),
			description
		);
	}
	else if (possibleMembers.size() > 1)
		m_errorReporter.fatalTypeError(
			6675_error,
			_memberAccess.location(),
			"Member \"" + memberName + "\" not unique "
			"after argument-dependent lookup in " + exprType->toString() +
			(memberName == "value" ? " - did you forget the \"payable\" modifier?" : ".")
		);

	annotation.referencedDeclaration = possibleMembers.front().declaration;
	annotation.type = possibleMembers.front().type;

	VirtualLookup requiredLookup = VirtualLookup::Static;

	if (auto funType = dynamic_cast<FunctionType const*>(annotation.type))
	{
		solAssert(
			!funType->bound() || exprType->isImplicitlyConvertibleTo(*funType->selfType()),
			"Function \"" + memberName + "\" cannot be called on an object of type " +
			exprType->toString() + " (expected " + funType->selfType()->toString() + ")."
		);

		if (
			dynamic_cast<FunctionType const*>(exprType) &&
			!annotation.referencedDeclaration &&
			(memberName == "value" || memberName == "gas")
		)
			m_errorReporter.typeError(
				1621_error,
				_memberAccess.location(),
				"Using \"." + memberName + "(...)\" is deprecated. Use \"{" + memberName + ": ...}\" instead."
			);

		if (
			funType->kind() == FunctionType::Kind::ArrayPush &&
			arguments.value().numArguments() != 0 &&
			exprType->containsNestedMapping()
		)
			m_errorReporter.typeError(
				8871_error,
				_memberAccess.location(),
				"Storage arrays with nested mappings do not support .push(<arg>)."
			);

		if (!funType->bound())
			if (auto contractType = dynamic_cast<ContractType const*>(exprType))
				if (contractType->isSuper())
					requiredLookup = VirtualLookup::Super;
	}

	annotation.requiredLookup = requiredLookup;

	if (auto const* structType = dynamic_cast<StructType const*>(exprType))
		annotation.isLValue = !structType->dataStoredIn(DataLocation::CallData);
	else if (exprType->category() == Type::Category::Array)
		annotation.isLValue = false;
	else if (exprType->category() == Type::Category::FixedBytes)
		annotation.isLValue = false;
	else if (TypeType const* typeType = dynamic_cast<decltype(typeType)>(exprType))
	{
		if (ContractType const* contractType = dynamic_cast<decltype(contractType)>(typeType->actualType()))
		{
			annotation.isLValue = annotation.referencedDeclaration->isLValue();
			if (
				auto const* functionType = dynamic_cast<FunctionType const*>(annotation.type);
				functionType &&
				functionType->kind() == FunctionType::Kind::Declaration
			)
				annotation.isPure = *_memberAccess.expression().annotation().isPure;
		}
		else
			annotation.isLValue = false;
	}
	else if (exprType->category() == Type::Category::Module)
	{
		annotation.isPure = *_memberAccess.expression().annotation().isPure;
		annotation.isLValue = false;
	}
	else
		annotation.isLValue = false;

	// TODO some members might be pure, but for example `address(0x123).balance` is not pure
	// although every subexpression is, so leaving this limited for now.
	if (auto tt = dynamic_cast<TypeType const*>(exprType))
		if (tt->actualType()->category() == Type::Category::Enum)
			annotation.isPure = true;
	if (
		auto const* functionType = dynamic_cast<FunctionType const*>(exprType);
		functionType &&
		functionType->hasDeclaration() &&
		dynamic_cast<FunctionDefinition const*>(&functionType->declaration()) &&
		memberName == "selector"
	)
		if (auto const* parentAccess = dynamic_cast<MemberAccess const*>(&_memberAccess.expression()))
		{
			bool isPure = *parentAccess->expression().annotation().isPure;
			if (auto const* exprInt = dynamic_cast<Identifier const*>(&parentAccess->expression()))
				if (exprInt->name() == "this" || exprInt->name() == "super")
					isPure = true;

			annotation.isPure = isPure;
		}

	if (auto magicType = dynamic_cast<MagicType const*>(exprType))
	{
		if (magicType->kind() == MagicType::Kind::ABI)
			annotation.isPure = true;
		else if (magicType->kind() == MagicType::Kind::MetaType && (
			memberName == "creationCode" || memberName == "runtimeCode"
		))
		{
			annotation.isPure = true;
			ContractType const& accessedContractType = dynamic_cast<ContractType const&>(*magicType->typeArgument());
			if (
				memberName == "runtimeCode" &&
				!accessedContractType.immutableVariables().empty()
			)
				m_errorReporter.typeError(
					9274_error,
					_memberAccess.location(),
					"\"runtimeCode\" is not available for contracts containing immutable variables."
				);

			if (m_currentContract)
			{
				// TODO in the same way as with ``new``,
				// this is not properly detecting creation-cycles if they go through
				// internal library functions or free functions. It will be caught at
				// code generation time, but it would of course be better to catch it here.

				m_currentContract->annotation().contractDependencies.insert(&accessedContractType.contractDefinition());
				if (contractDependenciesAreCyclic(*m_currentContract))
					m_errorReporter.typeError(
						4224_error,
						_memberAccess.location(),
						"Circular reference for contract code access."
					);
			}
		}
		else if (magicType->kind() == MagicType::Kind::MetaType && memberName == "name")
			annotation.isPure = true;
		else if (magicType->kind() == MagicType::Kind::MetaType && memberName == "interfaceId")
			annotation.isPure = true;
		else if (
			magicType->kind() == MagicType::Kind::MetaType &&
			(memberName == "min" ||	memberName == "max")
		)
			annotation.isPure = true;
	}

	if (!annotation.isPure.set())
		annotation.isPure = false;

	return false;
}

bool TypeChecker::visit(IndexAccess const& _access)
{
	_access.annotation().isConstant = false;
	_access.baseExpression().accept(*this);
	TypePointer baseType = type(_access.baseExpression());
	TypePointer resultType = nullptr;
	bool isLValue = false;
	bool isPure = *_access.baseExpression().annotation().isPure;
	Expression const* index = _access.indexExpression();
	switch (baseType->category())
	{
	case Type::Category::ArraySlice:
	{
		auto const& arrayType = dynamic_cast<ArraySliceType const&>(*baseType).arrayType();
		if (arrayType.location() != DataLocation::CallData || !arrayType.isDynamicallySized())
			m_errorReporter.typeError(4802_error, _access.location(), "Index access is only implemented for slices of dynamic calldata arrays.");
		baseType = &arrayType;
		[[fallthrough]];
	}
	case Type::Category::Array:
	{
		ArrayType const& actualType = dynamic_cast<ArrayType const&>(*baseType);
		if (!index)
			m_errorReporter.typeError(9689_error, _access.location(), "Index expression cannot be omitted.");
		else if (actualType.isString())
		{
			m_errorReporter.typeError(9961_error, _access.location(), "Index access for string is not possible.");
			index->accept(*this);
		}
		else
		{
			expectType(*index, *TypeProvider::uint256());
			if (!m_errorReporter.hasErrors())
				if (auto numberType = dynamic_cast<RationalNumberType const*>(type(*index)))
				{
					solAssert(!numberType->isFractional(), "");
					if (!actualType.isDynamicallySized() && actualType.length() <= numberType->literalValue(nullptr))
						m_errorReporter.typeError(3383_error, _access.location(), "Out of bounds array access.");
				}
		}
		resultType = actualType.baseType();
		isLValue = actualType.location() != DataLocation::CallData;
		break;
	}
	case Type::Category::Mapping:
	{
		MappingType const& actualType = dynamic_cast<MappingType const&>(*baseType);
		if (!index)
			m_errorReporter.typeError(1267_error, _access.location(), "Index expression cannot be omitted.");
		else
			expectType(*index, *actualType.keyType());
		resultType = actualType.valueType();
		isLValue = true;
		break;
	}
	case Type::Category::TypeType:
	{
		TypeType const& typeType = dynamic_cast<TypeType const&>(*baseType);
		if (auto const* contractType = dynamic_cast<ContractType const*>(typeType.actualType()))
			if (contractType->contractDefinition().isLibrary())
				m_errorReporter.typeError(2876_error, _access.location(), "Index access for library types and arrays of libraries are not possible.");
		if (!index)
			resultType = TypeProvider::typeType(TypeProvider::array(DataLocation::Memory, typeType.actualType()));
		else
		{
			u256 length = 1;
			if (expectType(*index, *TypeProvider::uint256()))
			{
				if (auto indexValue = dynamic_cast<RationalNumberType const*>(type(*index)))
					length = indexValue->literalValue(nullptr);
				else
					m_errorReporter.fatalTypeError(3940_error, index->location(), "Integer constant expected.");
			}
			else
				solAssert(m_errorReporter.hasErrors(), "Expected errors as expectType returned false");

			resultType = TypeProvider::typeType(TypeProvider::array(
				DataLocation::Memory,
				typeType.actualType(),
				length
			));
		}
		break;
	}
	case Type::Category::FixedBytes:
	{
		FixedBytesType const& bytesType = dynamic_cast<FixedBytesType const&>(*baseType);
		if (!index)
			m_errorReporter.typeError(8830_error, _access.location(), "Index expression cannot be omitted.");
		else
		{
			if (!expectType(*index, *TypeProvider::uint256()))
				m_errorReporter.fatalTypeError(6318_error, _access.location(), "Index expression cannot be represented as an unsigned integer.");
			if (auto integerType = dynamic_cast<RationalNumberType const*>(type(*index)))
				if (bytesType.numBytes() <= integerType->literalValue(nullptr))
					m_errorReporter.typeError(1859_error, _access.location(), "Out of bounds array access.");
		}
		resultType = TypeProvider::fixedBytes(1);
		isLValue = false; // @todo this heavily depends on how it is embedded
		break;
	}
	default:
		m_errorReporter.fatalTypeError(
			2614_error,
			_access.baseExpression().location(),
			"Indexed expression has to be a type, mapping or array (is " + baseType->toString() + ")"
		);
	}
	_access.annotation().type = resultType;
	_access.annotation().isLValue = isLValue;
	if (index && !*index->annotation().isPure)
		isPure = false;
	_access.annotation().isPure = isPure;

	return false;
}

bool TypeChecker::visit(IndexRangeAccess const& _access)
{
	_access.annotation().isConstant = false;
	_access.baseExpression().accept(*this);

	bool isLValue = false; // TODO: set this correctly when implementing slices for memory and storage arrays
	bool isPure = *_access.baseExpression().annotation().isPure;

	if (Expression const* start = _access.startExpression())
	{
		expectType(*start, *TypeProvider::uint256());
		if (!*start->annotation().isPure)
			isPure = false;
	}
	if (Expression const* end = _access.endExpression())
	{
		expectType(*end, *TypeProvider::uint256());
		if (!*end->annotation().isPure)
			isPure = false;
	}

	_access.annotation().isLValue = isLValue;
	_access.annotation().isPure = isPure;

	TypePointer exprType = type(_access.baseExpression());
	if (exprType->category() == Type::Category::TypeType)
	{
		m_errorReporter.typeError(1760_error, _access.location(), "Types cannot be sliced.");
		_access.annotation().type = exprType;
		return false;
	}

	ArrayType const* arrayType = nullptr;
	if (auto const* arraySlice = dynamic_cast<ArraySliceType const*>(exprType))
		arrayType = &arraySlice->arrayType();
	else if (!(arrayType = dynamic_cast<ArrayType const*>(exprType)))
		m_errorReporter.fatalTypeError(4781_error, _access.location(), "Index range access is only possible for arrays and array slices.");

	if (arrayType->location() != DataLocation::CallData || !arrayType->isDynamicallySized())
		m_errorReporter.typeError(1227_error, _access.location(), "Index range access is only supported for dynamic calldata arrays.");
	else if (arrayType->baseType()->isDynamicallyEncoded())
		m_errorReporter.typeError(2148_error, _access.location(), "Index range access is not supported for arrays with dynamically encoded base types.");
	_access.annotation().type = TypeProvider::arraySlice(*arrayType);

	return false;
}

vector<Declaration const*> TypeChecker::cleanOverloadedDeclarations(
	Identifier const& _identifier,
	vector<Declaration const*> const& _candidates
)
{
	solAssert(_candidates.size() > 1, "");
	vector<Declaration const*> uniqueDeclarations;

	for (Declaration const* declaration: _candidates)
	{
		solAssert(declaration, "");
		// the declaration is functionDefinition, eventDefinition or a VariableDeclaration while declarations > 1
		solAssert(
			dynamic_cast<FunctionDefinition const*>(declaration) ||
			dynamic_cast<EventDefinition const*>(declaration) ||
			dynamic_cast<VariableDeclaration const*>(declaration) ||
			dynamic_cast<MagicVariableDeclaration const*>(declaration),
			"Found overloading involving something not a function, event or a (magic) variable."
		);

		FunctionTypePointer functionType {declaration->functionType(false)};
		if (!functionType)
			functionType = declaration->functionType(true);
		solAssert(functionType, "Failed to determine the function type of the overloaded.");

		for (TypePointer parameter: functionType->parameterTypes() + functionType->returnParameterTypes())
			if (!parameter)
				m_errorReporter.fatalDeclarationError(3893_error, _identifier.location(), "Function type can not be used in this context.");

		if (uniqueDeclarations.end() == find_if(
			uniqueDeclarations.begin(),
			uniqueDeclarations.end(),
			[&](Declaration const* d)
			{
				FunctionType const* newFunctionType = d->functionType(false);
				if (!newFunctionType)
					newFunctionType = d->functionType(true);
				return newFunctionType && functionType->hasEqualParameterTypes(*newFunctionType);
			}
		))
			uniqueDeclarations.push_back(declaration);
	}
	return uniqueDeclarations;
}

bool TypeChecker::visit(Identifier const& _identifier)
{
	IdentifierAnnotation& annotation = _identifier.annotation();

	if (!annotation.referencedDeclaration)
	{
		annotation.overloadedDeclarations = cleanOverloadedDeclarations(_identifier, annotation.candidateDeclarations);
		if (annotation.overloadedDeclarations.empty())
			m_errorReporter.fatalTypeError(7593_error, _identifier.location(), "No candidates for overload resolution found.");
		else if (annotation.overloadedDeclarations.size() == 1)
			annotation.referencedDeclaration = *annotation.overloadedDeclarations.begin();
		else if (!annotation.arguments)
		{
			// The identifier should be a public state variable shadowing other functions
			vector<Declaration const*> candidates;

			for (Declaration const* declaration: annotation.overloadedDeclarations)
			{
				if (VariableDeclaration const* variableDeclaration = dynamic_cast<decltype(variableDeclaration)>(declaration))
					candidates.push_back(declaration);
			}
			if (candidates.empty())
				m_errorReporter.fatalTypeError(2144_error, _identifier.location(), "No matching declaration found after variable lookup.");
			else if (candidates.size() == 1)
				annotation.referencedDeclaration = candidates.front();
			else
				m_errorReporter.fatalTypeError(7589_error, _identifier.location(), "No unique declaration found after variable lookup.");
		}
		else
		{
			vector<Declaration const*> candidates;

			for (Declaration const* declaration: annotation.overloadedDeclarations)
			{
				FunctionTypePointer functionType = declaration->functionType(true);
				solAssert(!!functionType, "Requested type not present.");
				if (functionType->canTakeArguments(*annotation.arguments))
					candidates.push_back(declaration);
			}
			if (candidates.size() == 1)
				annotation.referencedDeclaration = candidates.front();
			else
			{
				SecondarySourceLocation ssl;

				for (Declaration const* declaration: annotation.overloadedDeclarations)
					if (!declaration->location().isValid())
					{
						// Try to re-construct function definition
						string description;
						for (auto const& param: declaration->functionType(true)->parameterTypes())
							description += (description.empty() ? "" : ", ") + param->toString(false);
						description = "function " + _identifier.name() + "(" + description + ")";

						ssl.append("Candidate: " + description, declaration->location());
					}
					else
						ssl.append("Candidate:", declaration->location());
				if (candidates.empty())
					m_errorReporter.fatalTypeError(9322_error, _identifier.location(), ssl, "No matching declaration found after argument-dependent lookup.");
				else
					m_errorReporter.fatalTypeError(4487_error, _identifier.location(), ssl, "No unique declaration found after argument-dependent lookup.");
			}
		}
	}
	solAssert(
		!!annotation.referencedDeclaration,
		"Referenced declaration is null after overload resolution."
	);
	bool isConstant = false;
	annotation.isLValue = annotation.referencedDeclaration->isLValue();
	annotation.type = annotation.referencedDeclaration->type();
	solAssert(annotation.type, "Declaration referenced before type could be determined.");
	if (auto variableDeclaration = dynamic_cast<VariableDeclaration const*>(annotation.referencedDeclaration))
		annotation.isPure = isConstant = variableDeclaration->isConstant();
	else if (dynamic_cast<MagicVariableDeclaration const*>(annotation.referencedDeclaration))
		annotation.isPure = dynamic_cast<FunctionType const*>(annotation.type);
	else if (dynamic_cast<TypeType const*>(annotation.type))
		annotation.isPure = true;
	else if (dynamic_cast<ModuleType const*>(annotation.type))
		annotation.isPure = true;
	else
		annotation.isPure = false;

	annotation.isConstant = isConstant;

	annotation.requiredLookup =
		dynamic_cast<CallableDeclaration const*>(annotation.referencedDeclaration) ?
		VirtualLookup::Virtual : VirtualLookup::Static;

	// Check for deprecated function names.
	// The check is done here for the case without an actual function call.
	if (FunctionType const* fType = dynamic_cast<FunctionType const*>(_identifier.annotation().type))
	{
		if (_identifier.name() == "sha3" && fType->kind() == FunctionType::Kind::KECCAK256)
			m_errorReporter.typeError(
				3557_error,
				_identifier.location(),
				"\"sha3\" has been deprecated in favour of \"keccak256\"."
			);
		else if (_identifier.name() == "suicide" && fType->kind() == FunctionType::Kind::Selfdestruct)
			m_errorReporter.typeError(
				8050_error,
				_identifier.location(),
				"\"suicide\" has been deprecated in favour of \"selfdestruct\"."
			);
	}

	if (
		MagicVariableDeclaration const* magicVar =
		dynamic_cast<MagicVariableDeclaration const*>(annotation.referencedDeclaration)
	)
		if (magicVar->type()->category() == Type::Category::Integer)
		{
			solAssert(_identifier.name() == "now", "");
			m_errorReporter.typeError(
				7359_error,
				_identifier.location(),
				"\"now\" has been deprecated. Use \"block.timestamp\" instead."
			);
		}

	return false;
}

void TypeChecker::endVisit(ElementaryTypeNameExpression const& _expr)
{
	_expr.annotation().type = TypeProvider::typeType(TypeProvider::fromElementaryTypeName(_expr.type().typeName(), _expr.type().stateMutability()));
	_expr.annotation().isPure = true;
	_expr.annotation().isLValue = false;
	_expr.annotation().isConstant = false;
}

void TypeChecker::endVisit(Literal const& _literal)
{
	if (_literal.looksLikeAddress())
	{
		// Assign type here if it even looks like an address. This prevents double errors for invalid addresses
		_literal.annotation().type = TypeProvider::payableAddress();

		string msg;
		if (_literal.valueWithoutUnderscores().length() != 42) // "0x" + 40 hex digits
			// looksLikeAddress enforces that it is a hex literal starting with "0x"
			msg =
				"This looks like an address but is not exactly 40 hex digits. It is " +
				to_string(_literal.valueWithoutUnderscores().length() - 2) +
				" hex digits.";
		else if (!_literal.passesAddressChecksum())
		{
			msg = "This looks like an address but has an invalid checksum.";
			if (!_literal.getChecksummedAddress().empty())
				msg += " Correct checksummed address: \"" + _literal.getChecksummedAddress() + "\".";
		}

		if (!msg.empty())
			m_errorReporter.syntaxError(
				9429_error,
				_literal.location(),
				msg +
				" If this is not used as an address, please prepend '00'. " +
				"For more information please see https://solidity.readthedocs.io/en/develop/types.html#address-literals"
			);
	}

	if (_literal.isHexNumber() && _literal.subDenomination() != Literal::SubDenomination::None)
		m_errorReporter.fatalTypeError(
			5145_error,
			_literal.location(),
			"Hexadecimal numbers cannot be used with unit denominations. "
			"You can use an expression of the form \"0x1234 * 1 day\" instead."
		);

	if (_literal.subDenomination() == Literal::SubDenomination::Year)
		m_errorReporter.typeError(
			4820_error,
			_literal.location(),
			"Using \"years\" as a unit denomination is deprecated."
		);

	if (!_literal.annotation().type)
		_literal.annotation().type = TypeProvider::forLiteral(_literal);

	if (!_literal.annotation().type)
		m_errorReporter.fatalTypeError(2826_error, _literal.location(), "Invalid literal value.");

	_literal.annotation().isPure = true;
	_literal.annotation().isLValue = false;
	_literal.annotation().isConstant = false;
}

void TypeChecker::endVisit(UsingForDirective const& _usingFor)
{
	if (m_currentContract->isInterface())
		m_errorReporter.typeError(
			9088_error,
			_usingFor.location(),
			"The \"using for\" directive is not allowed inside interfaces."
		);
}

bool TypeChecker::contractDependenciesAreCyclic(
	ContractDefinition const& _contract,
	std::set<ContractDefinition const*> const& _seenContracts
) const
{
	// Naive depth-first search that remembers nodes already seen.
	if (_seenContracts.count(&_contract))
		return true;
	set<ContractDefinition const*> seen(_seenContracts);
	seen.insert(&_contract);
	for (auto const* c: _contract.annotation().contractDependencies)
		if (contractDependenciesAreCyclic(*c, seen))
			return true;
	return false;
}

Declaration const& TypeChecker::dereference(Identifier const& _identifier) const
{
	solAssert(!!_identifier.annotation().referencedDeclaration, "Declaration not stored.");
	return *_identifier.annotation().referencedDeclaration;
}

Declaration const& TypeChecker::dereference(UserDefinedTypeName const& _typeName) const
{
	solAssert(!!_typeName.annotation().referencedDeclaration, "Declaration not stored.");
	return *_typeName.annotation().referencedDeclaration;
}

bool TypeChecker::expectType(Expression const& _expression, Type const& _expectedType)
{
	_expression.accept(*this);
	BoolResult result = type(_expression)->isImplicitlyConvertibleTo(_expectedType);
	if (!result)
	{
		auto errorMsg = "Type " +
			type(_expression)->toString() +
			" is not implicitly convertible to expected type " +
			_expectedType.toString();
		if (
			type(_expression)->category() == Type::Category::RationalNumber &&
			dynamic_cast<RationalNumberType const*>(type(_expression))->isFractional() &&
			type(_expression)->mobileType()
		)
		{
			if (_expectedType.operator==(*type(_expression)->mobileType()))
				m_errorReporter.typeError(
					4426_error,
					_expression.location(),
					errorMsg + ", but it can be explicitly converted."
				);
			else
				m_errorReporter.typeErrorConcatenateDescriptions(
					2326_error,
					_expression.location(),
					errorMsg +
					". Try converting to type " +
					type(_expression)->mobileType()->toString() +
					" or use an explicit conversion.",
					result.message()
				);
		}
		else
			m_errorReporter.typeErrorConcatenateDescriptions(
				7407_error,
				_expression.location(),
				errorMsg + ".",
				result.message()
			);
		return false;
	}
	return true;
}

void TypeChecker::requireLValue(Expression const& _expression, bool _ordinaryAssignment)
{
	_expression.annotation().willBeWrittenTo = true;
	_expression.annotation().lValueOfOrdinaryAssignment = _ordinaryAssignment;
	_expression.accept(*this);

	if (*_expression.annotation().isLValue)
		return;

	auto [errorId, description] = [&]() -> tuple<ErrorId, string> {
		if (*_expression.annotation().isConstant)
			return { 6520_error, "Cannot assign to a constant variable." };

		if (auto indexAccess = dynamic_cast<IndexAccess const*>(&_expression))
		{
			if (type(indexAccess->baseExpression())->category() == Type::Category::FixedBytes)
				return { 4360_error, "Single bytes in fixed bytes arrays cannot be modified." };
			else if (auto arrayType = dynamic_cast<ArrayType const*>(type(indexAccess->baseExpression())))
				if (arrayType->dataStoredIn(DataLocation::CallData))
					return { 6182_error, "Calldata arrays are read-only." };
		}

		if (auto memberAccess = dynamic_cast<MemberAccess const*>(&_expression))
		{
			if (auto structType = dynamic_cast<StructType const*>(type(memberAccess->expression())))
			{
				if (structType->dataStoredIn(DataLocation::CallData))
					return { 4156_error, "Calldata structs are read-only." };
			}
			else if (dynamic_cast<ArrayType const*>(type(memberAccess->expression())))
				if (memberAccess->memberName() == "length")
					return { 7567_error, "Member \"length\" is read-only and cannot be used to resize arrays." };
		}

		if (auto identifier = dynamic_cast<Identifier const*>(&_expression))
			if (auto varDecl = dynamic_cast<VariableDeclaration const*>(identifier->annotation().referencedDeclaration))
				if (varDecl->isExternalCallableParameter() && dynamic_cast<ReferenceType const*>(identifier->annotation().type))
					return { 7128_error, "External function arguments of reference type are read-only." };

		return { 4247_error, "Expression has to be an lvalue." };
	}();

	m_errorReporter.typeError(errorId, _expression.location(), description);
}

bool TypeChecker::useABICoderV2() const
{
	solAssert(m_currentSourceUnit, "");
	if (m_currentContract)
		solAssert(m_currentSourceUnit == &m_currentContract->sourceUnit(), "");
	return *m_currentSourceUnit->annotation().useABICoderV2;

}