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/>.
*/
/**
 * @author Christian <c@ethdev.com>
 * @date 2015
 * Type analyzer and checker.
 */

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

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

#include <liblangutil/ErrorReporter.h>

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

#include <boost/algorithm/cxx11/all_of.hpp>
#include <boost/algorithm/string/join.hpp>
#include <boost/algorithm/string/predicate.hpp>

#include <memory>
#include <vector>

using namespace std;
using namespace dev;
using namespace langutil;
using namespace dev::solidity;

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(ASTNode const& _contract)
{
	_contract.accept(*this);
	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_scope = &_contract;

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

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


	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(
			_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(
			_functionCall.location(),
			"This function takes two arguments, but " +
			toString(arguments.size()) +
			" were provided."
		);

	if (arguments.size() >= 1)
	{
		BoolResult result = type(*arguments.front())->isImplicitlyConvertibleTo(*TypeProvider::bytesMemory());

		if (!result)
			m_errorReporter.typeErrorConcatenateDescriptions(
				arguments.front()->location(),
				"Invalid type for argument in function call. "
				"Invalid implicit conversion from " +
				type(*arguments.front())->toString() +
				" to bytes memory requested.",
				result.message()
			);
	}

	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(
			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(
					typeArgument->location(),
					"Decoding type " + actualType->toString(false) + " not supported."
				);
			components.push_back(actualType);
		}
		else
		{
			m_errorReporter.typeError(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(
			_functionCall.location(),
			"This function takes one argument, but " +
			toString(arguments.size()) +
			" were provided."
		);
		return {};
	}
	TypePointer firstArgType = type(*arguments.front());
	if (
		firstArgType->category() != Type::Category::TypeType ||
		dynamic_cast<TypeType const&>(*firstArgType).actualType()->category() != TypeType::Category::Contract
	)
	{
		m_errorReporter.typeError(
			arguments.front()->location(),
			"Invalid type for argument in function call. "
			"Contract type 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.");

	if (m_scope->isInterface())
		m_errorReporter.typeError(_inheritance.location(), "Interfaces cannot inherit.");

	if (base->isLibrary())
		m_errorReporter.typeError(_inheritance.location(), "Libraries cannot be inherited from.");

	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(
				_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(
					(*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(UsingForDirective const& _usingFor)
{
	ContractDefinition const* library = dynamic_cast<ContractDefinition const*>(
		_usingFor.libraryName().annotation().referencedDeclaration
	);
	if (!library || !library->isLibrary())
		m_errorReporter.fatalTypeError(_usingFor.libraryName().location(), "Library name expected.");
}

bool TypeChecker::visit(StructDefinition const& _struct)
{
	for (ASTPointer<VariableDeclaration> const& member: _struct.members())
		solAssert(type(*member)->canBeStored(), "Type cannot be used in struct.");

	// Check recursion, fatal error if detected.
	auto visitor = [&](StructDefinition const& _struct, CycleDetector<StructDefinition>& _cycleDetector, size_t _depth)
	{
		if (_depth >= 256)
			m_errorReporter.fatalDeclarationError(_struct.location(), "Struct definition exhausting cyclic dependency validator.");

		for (ASTPointer<VariableDeclaration> const& member: _struct.members())
		{
			Type const* memberType = type(*member);
			while (auto arrayType = dynamic_cast<ArrayType const*>(memberType))
			{
				if (arrayType->isDynamicallySized())
					break;
				memberType = arrayType->baseType();
			}
			if (auto structType = dynamic_cast<StructType const*>(memberType))
				if (_cycleDetector.run(structType->structDefinition()))
					return;
		}
	};
	if (CycleDetector<StructDefinition>(visitor).run(_struct) != nullptr)
		m_errorReporter.fatalTypeError(_struct.location(), "Recursive struct definition.");

	bool insideStruct = true;
	swap(insideStruct, m_insideStruct);
	ASTNode::listAccept(_struct.members(), *this);
	m_insideStruct = insideStruct;

	return false;
}

bool TypeChecker::visit(FunctionDefinition const& _function)
{
	bool isLibraryFunction = _function.inContractKind() == ContractDefinition::ContractKind::Library;
	if (_function.isPayable())
	{
		if (isLibraryFunction)
			m_errorReporter.typeError(_function.location(), "Library functions cannot be payable.");
		if (!_function.isConstructor() && !_function.isFallback() && !_function.isPartOfExternalInterface())
			m_errorReporter.typeError(_function.location(), "Internal functions cannot be payable.");
	}
	auto checkArgumentAndReturnParameter = [&](VariableDeclaration const& var) {
		if (type(var)->category() == Type::Category::Mapping)
		{
			if (var.referenceLocation() != VariableDeclaration::Location::Storage)
			{
				if (!isLibraryFunction && _function.isPublic())
					m_errorReporter.typeError(var.location(), "Mapping types can only have a data location of \"storage\" and thus only be parameters or return variables for internal or library functions.");
				else
					m_errorReporter.typeError(var.location(), "Mapping types can only have a data location of \"storage\"." );
			}
			else
			{
				solAssert(isLibraryFunction || !_function.isPublic(), "Mapping types for parameters or return variables can only be used in internal or library functions.");
			}
		}
		else
		{
			if (!type(var)->canLiveOutsideStorage() && _function.isPublic())
				m_errorReporter.typeError(var.location(), "Type is required to live outside storage.");
			if (_function.isPublic())
			{
				auto iType = type(var)->interfaceType(isLibraryFunction);

				if (!iType)
				{
					solAssert(!iType.message().empty(), "Expected detailed error message!");
					m_errorReporter.fatalTypeError(var.location(), iType.message());
				}
			}
		}
		if (
			_function.isPublic() &&
			!_function.sourceUnit().annotation().experimentalFeatures.count(ExperimentalFeature::ABIEncoderV2) &&
			!typeSupportedByOldABIEncoder(*type(var), isLibraryFunction)
		)
			m_errorReporter.typeError(
				var.location(),
				"This type is only supported in the new experimental ABI encoder. "
				"Use \"pragma experimental ABIEncoderV2;\" to enable the feature."
			);
	};
	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())
	{
		auto baseContracts = dynamic_cast<ContractDefinition const&>(*_function.scope()).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(modifier->location(), "Base constructor already provided.");
		}
		else
			modifiers.insert(decl);
	}
	if (m_scope->isInterface())
	{
		if (_function.isImplemented())
			m_errorReporter.typeError(_function.location(), "Functions in interfaces cannot have an implementation.");

		if (_function.visibility() != FunctionDefinition::Visibility::External)
			m_errorReporter.typeError(_function.location(), "Functions in interfaces must be declared external.");

		if (_function.isConstructor())
			m_errorReporter.typeError(_function.location(), "Constructor cannot be defined in interfaces.");
	}
	else if (m_scope->contractKind() == ContractDefinition::ContractKind::Library)
		if (_function.isConstructor())
			m_errorReporter.typeError(_function.location(), "Constructor cannot be defined in libraries.");
	if (_function.isImplemented())
		_function.body().accept(*this);
	else if (_function.isConstructor())
		m_errorReporter.typeError(_function.location(), "Constructor must be implemented if declared.");
	else if (isLibraryFunction && _function.visibility() <= FunctionDefinition::Visibility::Internal)
		m_errorReporter.typeError(_function.location(), "Internal library function must be implemented if declared.");
	return false;
}

bool TypeChecker::visit(VariableDeclaration const& _variable)
{
	// Forbid any variable declarations inside interfaces unless they are part of
	// * a function's input/output parameters,
	// * or inside of a struct definition.
	if (
		m_scope->isInterface()
		&& !_variable.isCallableParameter()
		&& !m_insideStruct
	)
		m_errorReporter.typeError(_variable.location(), "Variables cannot be declared in interfaces.");

	if (_variable.typeName())
		_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())
		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(_variable.location(), "Constants of non-value type not yet implemented.");
		}

		if (!_variable.value())
			m_errorReporter.typeError(_variable.location(), "Uninitialized \"constant\" variable.");
		else if (!_variable.value()->annotation().isPure)
			m_errorReporter.typeError(
				_variable.value()->location(),
				"Initial value for constant variable has to be compile-time constant."
			);
	}
	if (!_variable.isStateVariable())
	{
		if (varType->dataStoredIn(DataLocation::Memory) || varType->dataStoredIn(DataLocation::CallData))
			if (!varType->canLiveOutsideStorage())
				m_errorReporter.typeError(_variable.location(), "Type " + varType->toString() + " is only valid in storage.");
	}
	else if (_variable.visibility() >= VariableDeclaration::Visibility::Public)
	{
		FunctionType getter(_variable);
		if (!_variable.sourceUnit().annotation().experimentalFeatures.count(ExperimentalFeature::ABIEncoderV2))
		{
			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(_variable.location(),
					"The following types are only supported for getters in the new experimental ABI encoder: " +
					joinHumanReadable(unsupportedTypes) +
					". Either remove \"public\" or use \"pragma experimental ABIEncoderV2;\" to enable the feature."
				);
		}
		if (!getter.interfaceFunctionType())
			m_errorReporter.typeError(_variable.location(), "Internal or recursive type is not allowed for public state variables.");
	}

	switch (varType->category())
	{
	case Type::Category::Array:
		if (auto arrayType = dynamic_cast<ArrayType const*>(varType))
			if (
				((arrayType->location() == DataLocation::Memory) ||
				(arrayType->location() == DataLocation::CallData)) &&
				!arrayType->validForCalldata()
			)
				m_errorReporter.typeError(_variable.location(), "Array is too large to be encoded.");
		break;
	default:
		break;
	}

	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);

	{
		m_insideModifierInvocation = true;
		ScopeGuard resetFlag{[&] () { m_insideModifierInvocation = false; }};
		_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(_modifier.location(), "Referenced declaration is neither modifier nor base class.");
		return;
	}
	if (parameters->size() != arguments.size())
	{
		m_errorReporter.typeError(
			_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(
				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() > Declaration::Visibility::Internal, "");
	unsigned numIndexed = 0;
	for (ASTPointer<VariableDeclaration> const& var: _eventDef.parameters())
	{
		if (var->isIndexed())
			numIndexed++;
		if (!type(*var)->canLiveOutsideStorage())
			m_errorReporter.typeError(var->location(), "Type is required to live outside storage.");
		if (!type(*var)->interfaceType(false))
			m_errorReporter.typeError(var->location(), "Internal or recursive type is not allowed as event parameter type.");
		if (
			!_eventDef.sourceUnit().annotation().experimentalFeatures.count(ExperimentalFeature::ABIEncoderV2) &&
			!typeSupportedByOldABIEncoder(*type(*var), false /* isLibrary */)
		)
			m_errorReporter.typeError(
				var->location(),
				"This type is only supported in the new experimental ABI encoder. "
				"Use \"pragma experimental ABIEncoderV2;\" to enable the feature."
			);
	}
	if (_eventDef.isAnonymous() && numIndexed > 4)
		m_errorReporter.typeError(_eventDef.location(), "More than 4 indexed arguments for anonymous event.");
	else if (!_eventDef.isAnonymous() && numIndexed > 3)
		m_errorReporter.typeError(_eventDef.location(), "More than 3 indexed arguments for event.");
	return false;
}

void TypeChecker::endVisit(FunctionTypeName const& _funType)
{
	FunctionType const& fun = dynamic_cast<FunctionType const&>(*_funType.annotation().type);
	if (fun.kind() == FunctionType::Kind::External)
		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 size_t(-1);
		Declaration const* declaration = ref->second.declaration;
		solAssert(!!declaration, "");
		bool requiresStorage = ref->second.isSlot || ref->second.isOffset;
		if (auto var = dynamic_cast<VariableDeclaration const*>(declaration))
		{
			solAssert(var->type(), "Expected variable type!");
			if (var->isConstant())
			{
				if (!var->value())
				{
					m_errorReporter.typeError(_identifier.location, "Constant has no value.");
					return size_t(-1);
				}
				else if (!type(*var)->isValueType() || (
					dynamic_cast<Literal const*>(var->value().get()) == nullptr &&
					type(*var->value())->category() != Type::Category::RationalNumber
				))
				{
					m_errorReporter.typeError(_identifier.location, "Only direct number constants are supported by inline assembly.");
					return size_t(-1);
				}
				else if (_context == yul::IdentifierContext::LValue)
				{
					m_errorReporter.typeError(_identifier.location, "Constant variables cannot be assigned to.");
					return size_t(-1);
				}
				else if (requiresStorage)
				{
					m_errorReporter.typeError(_identifier.location, "The suffixes _offset and _slot can only be used on non-constant storage variables.");
					return size_t(-1);
				}
			}

			if (requiresStorage)
			{
				if (!var->isStateVariable() && !var->type()->dataStoredIn(DataLocation::Storage))
				{
					m_errorReporter.typeError(_identifier.location, "The suffixes _offset and _slot can only be used on storage variables.");
					return size_t(-1);
				}
				else if (_context != yul::IdentifierContext::RValue)
				{
					m_errorReporter.typeError(_identifier.location, "Storage variables cannot be assigned to.");
					return size_t(-1);
				}
			}
			else if (!var->isConstant() && var->isStateVariable())
			{
				m_errorReporter.typeError(_identifier.location, "Only local variables are supported. To access storage variables, use the _slot and _offset suffixes.");
				return size_t(-1);
			}
			else if (var->type()->dataStoredIn(DataLocation::Storage))
			{
				m_errorReporter.typeError(_identifier.location, "You have to use the _slot or _offset suffix to access storage reference variables.");
				return size_t(-1);
			}
			else if (var->type()->sizeOnStack() != 1)
			{
				if (var->type()->dataStoredIn(DataLocation::CallData))
					m_errorReporter.typeError(_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(_identifier.location, "Only types that use one stack slot are supported.");
				return size_t(-1);
			}
		}
		else if (requiresStorage)
		{
			m_errorReporter.typeError(_identifier.location, "The suffixes _offset and _slot can only be used on storage variables.");
			return size_t(-1);
		}
		else if (_context == yul::IdentifierContext::LValue)
		{
			m_errorReporter.typeError(_identifier.location, "Only local variables can be assigned to in inline assembly.");
			return size_t(-1);
		}

		if (_context == yul::IdentifierContext::RValue)
		{
			solAssert(!!declaration->type(), "Type of declaration required but not yet determined.");
			if (dynamic_cast<FunctionDefinition const*>(declaration))
			{
			}
			else if (dynamic_cast<VariableDeclaration const*>(declaration))
			{
			}
			else if (auto contract = dynamic_cast<ContractDefinition const*>(declaration))
			{
				if (!contract->isLibrary())
				{
					m_errorReporter.typeError(_identifier.location, "Expected a library.");
					return size_t(-1);
				}
			}
			else
				return size_t(-1);
		}
		ref->second.valueSize = 1;
		return size_t(1);
	};
	solAssert(!_inlineAssembly.annotation().analysisInfo, "");
	_inlineAssembly.annotation().analysisInfo = make_shared<yul::AsmAnalysisInfo>();
	yul::AsmAnalyzer analyzer(
		*_inlineAssembly.annotation().analysisInfo,
		m_errorReporter,
		Error::Type::SyntaxError,
		_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;
}

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(_return.location(), "Return arguments required.");
		return;
	}
	if (!params)
	{
		m_errorReporter.typeError(_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(_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(
					_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(_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(
				_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(_emit.eventCall().expression().location(), "Expression has to be an event invocation.");
	m_insideEmitStatement = false;
}

namespace
{
/**
 * @returns a suggested left-hand-side of a multi-variable declaration contairing
 * the variable declarations given in @a _decls.
 */
string createTupleDecl(vector<ASTPointer<VariableDeclaration>> const& _decls)
{
	vector<string> components;
	for (ASTPointer<VariableDeclaration> const& decl: _decls)
		if (decl)
		{
			solAssert(decl->annotation().type, "");
			components.emplace_back(decl->annotation().type->toString(false) + " " + decl->name());
		}
		else
			components.emplace_back();

	if (_decls.size() == 1)
		return components.front();
	else
		return "(" + boost::algorithm::join(components, ", ") + ")";
}

bool typeCanBeExpressed(vector<ASTPointer<VariableDeclaration>> const& decls)
{
	for (ASTPointer<VariableDeclaration> const& decl: decls)
	{
		// skip empty tuples (they can be expressed of course)
		if (!decl)
			continue;

		if (!decl->annotation().type)
			return false;

		if (auto functionType = dynamic_cast<FunctionType const*>(decl->annotation().type))
			if (
				functionType->kind() != FunctionType::Kind::Internal &&
				functionType->kind() != FunctionType::Kind::External
			)
				return false;
	}

	return true;
}
}

bool TypeChecker::visit(VariableDeclarationStatement const& _statement)
{
	if (!_statement.initialValue())
	{
		// No initial value is only permitted for single variables with specified type.
		if (_statement.declarations().size() != 1 || !_statement.declarations().front())
		{
			if (boost::algorithm::all_of_equal(_statement.declarations(), nullptr))
			{
				// The syntax checker has already generated an error for this case (empty LHS tuple).
				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;
			}
			else
				// Bailing out *fatal* here, as those (untyped) vars may be used later, and diagnostics wouldn't be helpful then.
				m_errorReporter.fatalTypeError(_statement.location(), "Use of the \"var\" keyword is disallowed.");
		}

		VariableDeclaration const& varDecl = *_statement.declarations().front();
		if (!varDecl.annotation().type)
			m_errorReporter.fatalTypeError(_statement.location(), "Use of the \"var\" keyword is disallowed.");

		if (auto ref = dynamic_cast<ReferenceType const*>(type(varDecl)))
		{
			if (ref->dataStoredIn(DataLocation::Storage))
			{
				string errorText{"Uninitialized storage pointer."};
				solAssert(varDecl.referenceLocation() != VariableDeclaration::Location::Unspecified, "Expected a specified location at this point");
				solAssert(m_scope, "");
				m_errorReporter.declarationError(varDecl.location(), errorText);
			}
		}
		else if (dynamic_cast<MappingType const*>(type(varDecl)))
			m_errorReporter.typeError(
				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(
			_statement.location(),
			"Different number of components on the left hand side (" +
			toString(variables.size()) +
			") than on the right hand side (" +
			toString(valueTypes.size()) +
			")."
		);

	bool autoTypeDeductionNeeded = false;

	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, "");
		if (!var.annotation().type)
		{
			autoTypeDeductionNeeded = true;

			// Infer type from value.
			solAssert(!var.typeName(), "");
			var.annotation().type = valueComponentType->mobileType();
			if (!var.annotation().type)
			{
				if (valueComponentType->category() == Type::Category::RationalNumber)
					m_errorReporter.fatalTypeError(
						_statement.initialValue()->location(),
						"Invalid rational " +
						valueComponentType->toString() +
						" (absolute value too large or division by zero)."
					);
				else
					solAssert(false, "");
			}
			else if (*var.annotation().type == *TypeProvider::emptyTuple())
				solAssert(false, "Cannot declare variable with void (empty tuple) type.");
			else if (valueComponentType->category() == Type::Category::RationalNumber)
			{
				string typeName = var.annotation().type->toString(true);
				string extension;
				if (auto type = dynamic_cast<IntegerType const*>(var.annotation().type))
				{
					unsigned numBits = type->numBits();
					bool isSigned = type->isSigned();
					solAssert(numBits > 0, "");
					string minValue;
					string maxValue;
					if (isSigned)
					{
						numBits--;
						minValue = "-" + bigint(bigint(1) << numBits).str();
					}
					else
						minValue = "0";
					maxValue = bigint((bigint(1) << numBits) - 1).str();
					extension = ", which can hold values between " + minValue + " and " + maxValue;
				}
				else
					solAssert(dynamic_cast<FixedPointType const*>(var.annotation().type), "Unknown type.");
			}

			var.accept(*this);
		}
		else
		{
			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(
							_statement.location(),
							errorMsg + ", but it can be explicitly converted."
						);
					else
						m_errorReporter.typeError(
							_statement.location(),
							errorMsg +
							". Try converting to type " +
							valueComponentType->mobileType()->toString() +
							" or use an explicit conversion."
						);
				}
				else
					m_errorReporter.typeErrorConcatenateDescriptions(
						_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());
	}

	if (autoTypeDeductionNeeded)
	{
		if (!typeCanBeExpressed(variables))
			m_errorReporter.syntaxError(
				_statement.location(),
				"Use of the \"var\" keyword is disallowed. "
				"Type cannot be expressed in syntax."
			);
		else
			m_errorReporter.syntaxError(
				_statement.location(),
				"Use of the \"var\" keyword is disallowed. "
				"Use explicit declaration `" + createTupleDecl(variables) + " = ...´ instead."
			);
	}

	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(_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(_statement.location(), "Return value of low-level calls not used.");
			else if (kind == FunctionType::Kind::Send)
				m_errorReporter.warning(_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(_conditional.trueExpression().location(), "Invalid mobile type in true expression.");
	else
		commonType = trueType;

	if (!falseType)
		m_errorReporter.typeError(_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(
					_conditional.location(),
					"True expression's type " +
					trueType->toString() +
					" doesn't 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().type = commonType;
	_conditional.annotation().isPure =
		_conditional.condition().annotation().isPure &&
		_conditional.trueExpression().annotation().isPure &&
		_conditional.falseExpression().annotation().isPure;

	if (_conditional.annotation().lValueRequested)
		m_errorReporter.typeError(
				_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))
	{
		auto const* tupleType = dynamic_cast<TupleType const*>(&_type);
		auto const& types = tupleType ? tupleType->components() : vector<TypePointer> { &_type };

		solAssert(
			tupleExpression->components().size() == types.size() || m_errorReporter.hasErrors(),
			"Array sizes don't match or 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.category() == Type::Category::Mapping)
	{
		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(_expression.location(), "Mappings cannot be assigned to.");
	}
}

bool TypeChecker::visit(Assignment const& _assignment)
{
	requireLValue(_assignment.leftHandSide());
	TypePointer t = type(_assignment.leftHandSide());
	_assignment.annotation().type = t;

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

	if (TupleType const* tupleType = dynamic_cast<TupleType const*>(t))
	{
		if (_assignment.assignmentOperator() != Token::Assign)
			m_errorReporter.typeError(
				_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(
				_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)
{
	vector<ASTPointer<Expression>> const& components = _tuple.components();
	TypePointers types;

	if (_tuple.annotation().lValueRequested)
	{
		if (_tuple.isInlineArray())
			m_errorReporter.fatalTypeError(_tuple.location(), "Inline array type cannot be declared as LValue.");
		for (auto const& component: components)
			if (component)
			{
				requireLValue(*component);
				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;
	}
	else
	{
		bool isPure = true;
		TypePointer inlineArrayType = nullptr;

		for (size_t i = 0; i < components.size(); ++i)
		{
			if (!components[i])
				m_errorReporter.fatalTypeError(_tuple.location(), "Tuple component cannot be empty.");
			else if (components[i])
			{
				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(components[i]->location(), "Array component cannot be empty.");
						m_errorReporter.typeError(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(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(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;
			}
			else
				types.push_back(TypePointer());
		}
		_tuple.annotation().isPure = isPure;
		if (_tuple.isInlineArray())
		{
			if (!inlineArrayType)
				m_errorReporter.fatalTypeError(_tuple.location(), "Unable to deduce common type for array elements.");
			else if (!inlineArrayType->canLiveOutsideStorage())
				m_errorReporter.fatalTypeError(_tuple.location(), "Type " + inlineArrayType->toString() + " 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));
		}

	}
	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());
	else
		_operation.subExpression().accept(*this);
	TypePointer const& subExprType = type(_operation.subExpression());
	TypePointer t = type(_operation.subExpression())->unaryOperatorResult(op);
	if (!t)
	{
		m_errorReporter.typeError(
			_operation.location(),
			"Unary operator " +
			string(TokenTraits::toString(op)) +
			" cannot be applied to type " +
			subExprType->toString()
		);
		t = subExprType;
	}
	_operation.annotation().type = t;
	_operation.annotation().isPure = !modifying && _operation.subExpression().annotation().isPure;
	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(
			_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;

	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(
					_operation.location(),
					"Result of " + operation + " has type " + commonType->toString() + " and thus "
					"might overflow. Silence this warning by converting the literal to the "
					"expected type."
				);
	}
}

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(
			_functionCall.location(),
			"Exactly one argument expected for explicit type conversion."
		);
	else if (!isPositionalCall)
		m_errorReporter.typeError(
			_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());
		if (argType->isExplicitlyConvertibleTo(*resultType))
		{
			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(
					_functionCall.location(), ssl,
					"Explicit type conversion not allowed from non-payable \"address\" to \"" +
					resultType->toString() +
					"\", which has a payable fallback function."
				);
			}
			else
				m_errorReporter.typeError(
					_functionCall.location(),
					"Explicit type conversion not allowed from \"" +
					argType->toString() +
					"\" to \"" +
					resultType->toString() +
					"\"."
				);
		}
		if (resultType->category() == Type::Category::Address)
		{
			bool const 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, "");

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

	// Check for event outside of emit statement
	if (!m_insideEmitStatement && _functionType->kind() == FunctionType::Kind::Event)
		m_errorReporter.typeError(
			_functionCall.location(),
			"Event invocations have to be prefixed by \"emit\"."
		);

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

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 = m_scope->sourceUnit().annotation().experimentalFeatures.count(
		ExperimentalFeature::ABIEncoderV2
	);

	// Check for named arguments
	if (!_functionCall.names().empty())
	{
		m_errorReporter.typeError(
			_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(
					arguments[i]->location(),
					"Fractional numbers cannot yet be encoded."
				);
				continue;
			}
			else if (!argType->mobileType())
			{
				m_errorReporter.typeError(
					arguments[i]->location(),
					"Invalid rational number (too large or division by zero)."
				);
				continue;
			}
			else if (isPacked)
			{
				m_errorReporter.typeError(
					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(
				arguments[i]->location(),
				"Type not supported in packed mode."
			);
			continue;
		}

		if (!argType->fullEncodingType(false, abiEncoderV2, !_functionType->padArguments()))
			m_errorReporter.typeError(
				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();

	solAssert(
		!isVariadic || _functionCall.annotation().kind == 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 =
			_functionCall.annotation().kind == FunctionCallKind::StructConstructorCall;

		string msg;

		if (isVariadic)
			msg +=
				"Need at least " +
				toString(parameterTypes.size()) +
				" arguments for " +
				string(isStructConstructorCall ? "struct constructor" : "function call") +
				", but provided only " +
				toString(arguments.size()) +
				".";
		else
			msg +=
				"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()) +
				".";

		// Extend error message in case we try to construct a struct with mapping member.
		if (isStructConstructorCall)
		{
			/// For error message: Struct members that were removed during conversion to memory.
			TypePointer const expressionType = type(_functionCall.expression());
			TypeType const& t = dynamic_cast<TypeType const&>(*expressionType);
			auto const& structType = dynamic_cast<StructType const&>(*t.actualType());
			set<string> membersRemovedForStructConstructor = structType.membersMissingInMemory();

			if (!membersRemovedForStructConstructor.empty())
			{
				msg += " Members that have to be skipped in memory:";
				for (auto const& member: membersRemovedForStructConstructor)
					msg += " " + member;
			}
		}
		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())
				msg +=
					" This function requires a single bytes argument."
					" Use \"\" as argument to provide empty calldata.";
			else
				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
		)
			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.";
		m_errorReporter.typeError(_functionCall.location(), msg);
		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(
							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 < paramArgMap.size(); i++)
			{
				size_t j;
				for (j = 0; j < argumentNames.size(); j++)
					if (parameterNames[i] == *argumentNames[j])
						break;

				if (j < argumentNames.size())
					paramArgMap[i] = arguments[j].get();
				else
				{
					paramArgMap[i] = nullptr;
					not_all_mapped = true;
					m_errorReporter.typeError(
						_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]))
		{
			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
			)
				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
			)
				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.";
			m_errorReporter.typeError(paramArgMap[i]->location(), msg);
		}
	}
}

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;

	// Determine and assign function call kind, 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();

		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)
		{
			functionType = dynamic_cast<StructType const&>(*actualType).constructorType();
			funcCallAnno.kind = FunctionCallKind::StructConstructorCall;
			funcCallAnno.isPure = argumentsArePure;
		}
		else
		{
			funcCallAnno.kind = FunctionCallKind::TypeConversion;
			funcCallAnno.isPure = argumentsArePure;
		}

		break;
	}

	default:
		m_errorReporter.typeError(_functionCall.location(), "Type is not callable");
		funcCallAnno.kind = FunctionCallKind::Unset;
		funcCallAnno.isPure = argumentsArePure;
		break;
	}

	// 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:
		{
			bool const abiEncoderV2 =
				m_scope->sourceUnit().annotation().experimentalFeatures.count(
					ExperimentalFeature::ABIEncoderV2
				);
			returnTypes = typeCheckABIDecodeAndRetrieveReturnType(_functionCall, abiEncoderV2);
			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;
	}

	case FunctionCallKind::Unset: // fall-through
	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;
}

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

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

		if (!contract)
			m_errorReporter.fatalTypeError(_newExpression.location(), "Identifier is not a contract.");
		if (contract->isInterface())
			m_errorReporter.fatalTypeError(_newExpression.location(), "Cannot instantiate an interface.");
		if (!contract->annotation().unimplementedFunctions.empty())
		{
			SecondarySourceLocation ssl;
			for (auto function: contract->annotation().unimplementedFunctions)
				ssl.append("Missing implementation:", function->location());
			string msg = "Trying to create an instance of an abstract contract.";
			ssl.limitSize(msg);
			m_errorReporter.typeError(
				_newExpression.location(),
				ssl,
				msg
			);
		}
		if (!contract->constructorIsPublic())
			m_errorReporter.typeError(_newExpression.location(), "Contract with internal constructor cannot be created directly.");

		solAssert(!!m_scope, "");
		m_scope->annotation().contractDependencies.insert(contract);
		solAssert(
			!contract->annotation().linearizedBaseContracts.empty(),
			"Linearized base contracts not yet available."
		);
		if (contractDependenciesAreCyclic(*m_scope))
			m_errorReporter.typeError(
				_newExpression.location(),
				"Circular reference for contract creation (cannot create instance of derived or same contract)."
			);

		_newExpression.annotation().type = FunctionType::newExpressionType(*contract);
	}
	else if (type->category() == Type::Category::Array)
	{
		if (!type->canLiveOutsideStorage())
			m_errorReporter.fatalTypeError(
				_newExpression.typeName().location(),
				"Type cannot live outside storage."
			);
		if (!type->isDynamicallySized())
			m_errorReporter.typeError(
				_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
		m_errorReporter.fatalTypeError(_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();

	// Retrieve the types of the arguments if this is used to call a function.
	auto const& arguments = _memberAccess.annotation().arguments;
	MemberList::MemberMap possibleMembers = exprType->members(m_scope).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;
	}

	auto& annotation = _memberAccess.annotation();

	if (possibleMembers.empty())
	{
		if (initialMemberCount == 0)
		{
			// 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(m_scope).membersByName(memberName).empty())
				m_errorReporter.fatalTypeError(
					_memberAccess.location(),
					"Member \"" + memberName + "\" is not available in " +
					exprType->toString() +
					" outside of storage."
				);
		}
		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))
		{
			auto const& t = funType->returnParameterTypes();

			if (memberName == "value")
			{
				if (funType->kind() == FunctionType::Kind::Creation)
					errorMsg = "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
				)
					errorMsg = "Member \"value\" is not allowed in delegated calls due to \"msg.value\" persisting.";
				else
					errorMsg = "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)
			)
				errorMsg += " Did you intend to call the function?";
		}
		else if (exprType->category() == Type::Category::Contract)
		{
			for (auto const& addressMember: TypeProvider::payableAddress()->nativeMembers(nullptr))
				if (addressMember.name == memberName)
				{
					Identifier const* var = dynamic_cast<Identifier const*>(&_memberAccess.expression());
					string varName = var ? var->name() : "...";
					errorMsg += " Use \"address(" + varName + ")." + memberName + "\" to access this address member.";
					break;
				}
		}
		else if (auto 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"
				);

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

		m_errorReporter.fatalTypeError(
			_memberAccess.location(),
			errorMsg
		);
	}
	else if (possibleMembers.size() > 1)
		m_errorReporter.fatalTypeError(
			_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;

	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 (auto const* structType = dynamic_cast<StructType const*>(exprType))
		annotation.isLValue = !structType->dataStoredIn(DataLocation::CallData);
	else if (exprType->category() == Type::Category::Array)
	{
		auto const& arrayType(dynamic_cast<ArrayType const&>(*exprType));
		annotation.isLValue = (
			memberName == "length" &&
			arrayType.location() == DataLocation::Storage &&
			arrayType.isDynamicallySized()
		);
	}
	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();
	}

	// 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 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;
			m_scope->annotation().contractDependencies.insert(
				&dynamic_cast<ContractType const&>(*magicType->typeArgument()).contractDefinition()
			);
			if (contractDependenciesAreCyclic(*m_scope))
				m_errorReporter.typeError(
					_memberAccess.location(),
					"Circular reference for contract code access."
				);
		}
		else if (magicType->kind() == MagicType::Kind::MetaType && memberName == "name")
			annotation.isPure = true;
	}

	return false;
}

bool TypeChecker::visit(IndexAccess const& _access)
{
	_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::Array:
	{
		ArrayType const& actualType = dynamic_cast<ArrayType const&>(*baseType);
		if (!index)
			m_errorReporter.typeError(_access.location(), "Index expression cannot be omitted.");
		else if (actualType.isString())
		{
			m_errorReporter.typeError(_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(_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(_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 (dynamic_cast<ContractType const*>(typeType.actualType()))
			m_errorReporter.typeError(_access.location(), "Index access for contracts or libraries is 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(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(_access.location(), "Index expression cannot be omitted.");
		else
		{
			if (!expectType(*index, *TypeProvider::uint256()))
				m_errorReporter.fatalTypeError(_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(_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(
			_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(Identifier const& _identifier)
{
	IdentifierAnnotation& annotation = _identifier.annotation();
	if (!annotation.referencedDeclaration)
	{
		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(_identifier.location(), "No matching declaration found after variable lookup.");
			else if (candidates.size() == 1)
				annotation.referencedDeclaration = candidates.front();
			else
				m_errorReporter.fatalTypeError(_identifier.location(), "No unique declaration found after variable lookup.");
		}
		else if (annotation.overloadedDeclarations.empty())
			m_errorReporter.fatalTypeError(_identifier.location(), "No candidates for overload resolution found.");
		else if (annotation.overloadedDeclarations.size() == 1)
			annotation.referencedDeclaration = *annotation.overloadedDeclarations.begin();
		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.empty())
				m_errorReporter.fatalTypeError(_identifier.location(), "No matching declaration found after argument-dependent lookup.");
			else if (candidates.size() == 1)
				annotation.referencedDeclaration = candidates.front();
			else
				m_errorReporter.fatalTypeError(_identifier.location(), "No unique declaration found after argument-dependent lookup.");
		}
	}
	solAssert(
		!!annotation.referencedDeclaration,
		"Referenced declaration is null after overload resolution."
	);
	annotation.isLValue = annotation.referencedDeclaration->isLValue();
	annotation.type = annotation.referencedDeclaration->type();
	if (!annotation.type)
		m_errorReporter.fatalTypeError(_identifier.location(), "Declaration referenced before type could be determined.");
	if (auto variableDeclaration = dynamic_cast<VariableDeclaration const*>(annotation.referencedDeclaration))
		annotation.isPure = annotation.isConstant = variableDeclaration->isConstant();
	else if (dynamic_cast<MagicVariableDeclaration const*>(annotation.referencedDeclaration))
	{
		if (dynamic_cast<FunctionType const*>(annotation.type))
			annotation.isPure = true;
	}
	else if (dynamic_cast<TypeType const*>(annotation.type))
		annotation.isPure = true;


	// 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(
				_identifier.location(),
				"\"sha3\" has been deprecated in favour of \"keccak256\"."
			);
		else if (_identifier.name() == "suicide" && fType->kind() == FunctionType::Kind::Selfdestruct)
			m_errorReporter.typeError(
				_identifier.location(),
				"\"suicide\" has been deprecated in favour of \"selfdestruct\"."
			);
	}

	if (!m_insideModifierInvocation)
		if (ModifierType const* type = dynamic_cast<decltype(type)>(_identifier.annotation().type))
		{
			m_errorReporter.typeError(
				_identifier.location(),
				"Modifier can only be referenced in function headers."
			);
		}

	return false;
}

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

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(
				_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(
			_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(
			_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(_literal.location(), "Invalid literal value.");

	_literal.annotation().isPure = true;
}

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);
	if (!type(_expression)->isImplicitlyConvertibleTo(_expectedType))
	{
		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(
					_expression.location(),
					errorMsg + ", but it can be explicitly converted."
				);
			else
				m_errorReporter.typeError(
					_expression.location(),
					errorMsg +
					". Try converting to type " +
					type(_expression)->mobileType()->toString() +
					" or use an explicit conversion."
				);
		}
		else
			m_errorReporter.typeError(_expression.location(), errorMsg + ".");
		return false;
	}
	return true;
}

void TypeChecker::requireLValue(Expression const& _expression)
{
	_expression.annotation().lValueRequested = true;
	_expression.accept(*this);

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

	return m_errorReporter.typeError(_expression.location(), [&]() {
		if (_expression.annotation().isConstant)
			return "Cannot assign to a constant variable.";

		if (auto indexAccess = dynamic_cast<IndexAccess const*>(&_expression))
		{
			if (type(indexAccess->baseExpression())->category() == Type::Category::FixedBytes)
				return "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 "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 "Calldata structs are read-only.";
			}
			else if (auto arrayType = dynamic_cast<ArrayType const*>(type(memberAccess->expression())))
				if (memberAccess->memberName() == "length")
					switch (arrayType->location())
					{
						case DataLocation::Memory:
							return "Memory arrays cannot be resized.";
						case DataLocation::CallData:
							return "Calldata arrays cannot be resized.";
						case DataLocation::Storage:
							break;
					}
		}

		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 "External function arguments of reference type are read-only.";

		return "Expression has to be an lvalue.";
	}());
}