path: root/libsolidity/analysis/TypeChecker.cpp

/*
    This file is part of cpp-ethereum.

    cpp-ethereum 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.

    cpp-ethereum 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 cpp-ethereum.  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 <memory>
#include <boost/range/adaptor/reversed.hpp>
#include <libsolidity/ast/AST.h>

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


bool TypeChecker::checkTypeRequirements(const ContractDefinition& _contract)
{
    try
    {
        visit(_contract);
    }
    catch (FatalError const&)
    {
        // We got a fatal error which required to stop further type checking, but we can
        // continue normally from here.
        if (m_errors.empty())
            throw; // Something is weird here, rather throw again.
    }
    return Error::containsOnlyWarnings(m_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;

    // We force our own visiting order here.
    //@TODO structs will be visited again below, but it is probably fine.
    ASTNode::listAccept(_contract.definedStructs(), *this);
    ASTNode::listAccept(_contract.baseContracts(), *this);

    checkContractDuplicateFunctions(_contract);
    checkContractIllegalOverrides(_contract);
    checkContractAbstractFunctions(_contract);
    checkContractAbstractConstructors(_contract);

    FunctionDefinition const* function = _contract.constructor();
    if (function && !function->returnParameters().empty())
        typeError(function->returnParameterList()->location(), "Non-empty \"returns\" directive for constructor.");

    FunctionDefinition const* fallbackFunction = nullptr;
    for (FunctionDefinition const* function: _contract.definedFunctions())
    {
        if (function->name().empty())
        {
            if (fallbackFunction)
            {
                auto err = make_shared<Error>(Error::Type::DeclarationError);
                *err << errinfo_comment("Only one fallback function is allowed.");
                m_errors.push_back(err);
            }
            else
            {
                fallbackFunction = function;
                if (!fallbackFunction->parameters().empty())
                    typeError(fallbackFunction->parameterList().location(), "Fallback function cannot take parameters.");
            }
        }
        if (!function->isImplemented())
            _contract.annotation().isFullyImplemented = false;
    }

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

    checkContractExternalTypeClashes(_contract);
    // check for hash collisions in function signatures
    set<FixedHash<4>> hashes;
    for (auto const& it: _contract.interfaceFunctionList())
    {
        FixedHash<4> const& hash = it.first;
        if (hashes.count(hash))
            typeError(
                _contract.location(),
                string("Function signature hash collision for ") + it.second->externalSignature()
            );
        hashes.insert(hash);
    }

    if (_contract.isLibrary())
        checkLibraryRequirements(_contract);

    return false;
}

void TypeChecker::checkContractDuplicateFunctions(ContractDefinition const& _contract)
{
    /// Checks that two functions with the same name defined in this contract have different
    /// argument types and that there is at most one constructor.
    map<string, vector<FunctionDefinition const*>> functions;
    for (FunctionDefinition const* function: _contract.definedFunctions())
        functions[function->name()].push_back(function);

    // Constructor
    if (functions[_contract.name()].size() > 1)
    {
        SecondarySourceLocation ssl;
        auto it = ++functions[_contract.name()].begin();
        for (; it != functions[_contract.name()].end(); ++it)
            ssl.append("Another declaration is here:", (*it)->location());

        auto err = make_shared<Error>(Error(Error::Type::DeclarationError));
        *err <<
            errinfo_sourceLocation(functions[_contract.name()].front()->location()) <<
            errinfo_comment("More than one constructor defined.") <<
            errinfo_secondarySourceLocation(ssl);
        m_errors.push_back(err);
    }
    for (auto const& it: functions)
    {
        vector<FunctionDefinition const*> const& overloads = it.second;
        for (size_t i = 0; i < overloads.size(); ++i)
            for (size_t j = i + 1; j < overloads.size(); ++j)
                if (FunctionType(*overloads[i]).hasEqualArgumentTypes(FunctionType(*overloads[j])))
                {
                    auto err = make_shared<Error>(Error(Error::Type::DeclarationError));
                    *err <<
                        errinfo_sourceLocation(overloads[j]->location()) <<
                        errinfo_comment("Function with same name and arguments defined twice.") <<
                        errinfo_secondarySourceLocation(SecondarySourceLocation().append(
                            "Other declaration is here:", overloads[i]->location()));
                    m_errors.push_back(err);
                }
    }
}

void TypeChecker::checkContractAbstractFunctions(ContractDefinition const& _contract)
{
    // Mapping from name to function definition (exactly one per argument type equality class) and
    // flag to indicate whether it is fully implemented.
    using FunTypeAndFlag = std::pair<FunctionTypePointer, bool>;
    map<string, vector<FunTypeAndFlag>> functions;

    // Search from base to derived
    for (ContractDefinition const* contract: boost::adaptors::reverse(_contract.annotation().linearizedBaseContracts))
        for (FunctionDefinition const* function: contract->definedFunctions())
        {
            auto& overloads = functions[function->name()];
            FunctionTypePointer funType = make_shared<FunctionType>(*function);
            auto it = find_if(overloads.begin(), overloads.end(), [&](FunTypeAndFlag const& _funAndFlag)
            {
                return funType->hasEqualArgumentTypes(*_funAndFlag.first);
            });
            if (it == overloads.end())
                overloads.push_back(make_pair(funType, function->isImplemented()));
            else if (it->second)
            {
                if (!function->isImplemented())
                    typeError(function->location(), "Redeclaring an already implemented function as abstract");
            }
            else if (function->isImplemented())
                it->second = true;
        }

    // Set to not fully implemented if at least one flag is false.
    for (auto const& it: functions)
        for (auto const& funAndFlag: it.second)
            if (!funAndFlag.second)
            {
                _contract.annotation().isFullyImplemented = false;
                return;
            }
}

void TypeChecker::checkContractAbstractConstructors(ContractDefinition const& _contract)
{
    set<ContractDefinition const*> argumentsNeeded;
    // check that we get arguments for all base constructors that need it.
    // If not mark the contract as abstract (not fully implemented)

    vector<ContractDefinition const*> const& bases = _contract.annotation().linearizedBaseContracts;
    for (ContractDefinition const* contract: bases)
        if (FunctionDefinition const* constructor = contract->constructor())
            if (contract != &_contract && !constructor->parameters().empty())
                argumentsNeeded.insert(contract);

    for (ContractDefinition const* contract: bases)
    {
        if (FunctionDefinition const* constructor = contract->constructor())
            for (auto const& modifier: constructor->modifiers())
            {
                auto baseContract = dynamic_cast<ContractDefinition const*>(
                    &dereference(*modifier->name())
                );
                if (baseContract)
                    argumentsNeeded.erase(baseContract);
            }


        for (ASTPointer<InheritanceSpecifier> const& base: contract->baseContracts())
        {
            auto baseContract = dynamic_cast<ContractDefinition const*>(&dereference(base->name()));
            solAssert(baseContract, "");
            if (!base->arguments().empty())
                argumentsNeeded.erase(baseContract);
        }
    }
    if (!argumentsNeeded.empty())
        _contract.annotation().isFullyImplemented = false;
}

void TypeChecker::checkContractIllegalOverrides(ContractDefinition const& _contract)
{
    // TODO unify this at a later point. for this we need to put the constness and the access specifier
    // into the types
    map<string, vector<FunctionDefinition const*>> functions;
    map<string, ModifierDefinition const*> modifiers;

    // We search from derived to base, so the stored item causes the error.
    for (ContractDefinition const* contract: _contract.annotation().linearizedBaseContracts)
    {
        for (FunctionDefinition const* function: contract->definedFunctions())
        {
            if (function->isConstructor())
                continue; // constructors can neither be overridden nor override anything
            string const& name = function->name();
            if (modifiers.count(name))
                typeError(modifiers[name]->location(), "Override changes function to modifier.");
            FunctionType functionType(*function);
            // function should not change the return type
            for (FunctionDefinition const* overriding: functions[name])
            {
                FunctionType overridingType(*overriding);
                if (!overridingType.hasEqualArgumentTypes(functionType))
                    continue;
                if (
                    overriding->visibility() != function->visibility() ||
                    overriding->isDeclaredConst() != function->isDeclaredConst() ||
                    overridingType != functionType
                )
                    typeError(overriding->location(), "Override changes extended function signature.");
            }
            functions[name].push_back(function);
        }
        for (ModifierDefinition const* modifier: contract->functionModifiers())
        {
            string const& name = modifier->name();
            ModifierDefinition const*& override = modifiers[name];
            if (!override)
                override = modifier;
            else if (ModifierType(*override) != ModifierType(*modifier))
                typeError(override->location(), "Override changes modifier signature.");
            if (!functions[name].empty())
                typeError(override->location(), "Override changes modifier to function.");
        }
    }
}

void TypeChecker::checkContractExternalTypeClashes(ContractDefinition const& _contract)
{
    map<string, vector<pair<Declaration const*, FunctionTypePointer>>> externalDeclarations;
    for (ContractDefinition const* contract: _contract.annotation().linearizedBaseContracts)
    {
        for (FunctionDefinition const* f: contract->definedFunctions())
            if (f->isPartOfExternalInterface())
            {
                auto functionType = make_shared<FunctionType>(*f);
                // under non error circumstances this should be true
                if (functionType->interfaceFunctionType())
                    externalDeclarations[functionType->externalSignature()].push_back(
                        make_pair(f, functionType)
                    );
            }
        for (VariableDeclaration const* v: contract->stateVariables())
            if (v->isPartOfExternalInterface())
            {
                auto functionType = make_shared<FunctionType>(*v);
                // under non error circumstances this should be true
                if (functionType->interfaceFunctionType())
                    externalDeclarations[functionType->externalSignature()].push_back(
                        make_pair(v, functionType)
                    );
            }
    }
    for (auto const& it: externalDeclarations)
        for (size_t i = 0; i < it.second.size(); ++i)
            for (size_t j = i + 1; j < it.second.size(); ++j)
                if (!it.second[i].second->hasEqualArgumentTypes(*it.second[j].second))
                    typeError(
                        it.second[j].first->location(),
                        "Function overload clash during conversion to external types for arguments."
                    );
}

void TypeChecker::checkLibraryRequirements(ContractDefinition const& _contract)
{
    solAssert(_contract.isLibrary(), "");
    if (!_contract.baseContracts().empty())
        typeError(_contract.location(), "Library is not allowed to inherit.");

    for (auto const& var: _contract.stateVariables())
        if (!var->isConstant())
            typeError(var->location(), "Library cannot have non-constant state variables");
}

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

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

    auto const& arguments = _inheritance.arguments();
    TypePointers parameterTypes = ContractType(*base).constructorType()->parameterTypes();
    if (!arguments.empty() && parameterTypes.size() != arguments.size())
    {
        typeError(
            _inheritance.location(),
            "Wrong argument count for constructor call: " +
            toString(arguments.size()) +
            " arguments given but expected " +
            toString(parameterTypes.size()) +
            "."
        );
        return;
    }

    for (size_t i = 0; i < arguments.size(); ++i)
        if (!type(*arguments[i])->isImplicitlyConvertibleTo(*parameterTypes[i]))
            typeError(
                arguments[i]->location(),
                "Invalid type for argument in constructor call. "
                "Invalid implicit conversion from " +
                type(*arguments[i])->toString() +
                " to " +
                parameterTypes[i]->toString() +
                " requested."
                        );
}

void TypeChecker::endVisit(UsingForDirective const& _usingFor)
{
    ContractDefinition const* library = dynamic_cast<ContractDefinition const*>(
        _usingFor.libraryName().annotation().referencedDeclaration
    );
    if (!library || !library->isLibrary())
        typeError(_usingFor.libraryName().location(), "Library name expected.");
}

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

    // Check recursion, fatal error if detected.
    using StructPointer = StructDefinition const*;
    using StructPointersSet = set<StructPointer>;
    function<void(StructPointer,StructPointersSet const&)> check = [&](StructPointer _struct, StructPointersSet const& _parents)
    {
        if (_parents.count(_struct))
            fatalTypeError(_struct->location(), "Recursive struct definition.");
        StructPointersSet parents = _parents;
        parents.insert(_struct);
        for (ASTPointer<VariableDeclaration> const& member: _struct->members())
            if (type(*member)->category() == Type::Category::Struct)
            {
                auto const& typeName = dynamic_cast<UserDefinedTypeName const&>(*member->typeName());
                check(&dynamic_cast<StructDefinition const&>(*typeName.annotation().referencedDeclaration), parents);
            }
    };
    check(&_struct, StructPointersSet{});

    ASTNode::listAccept(_struct.members(), *this);

    return false;
}

bool TypeChecker::visit(FunctionDefinition const& _function)
{
    bool isLibraryFunction = dynamic_cast<ContractDefinition const&>(*_function.scope()).isLibrary();
    for (ASTPointer<VariableDeclaration> const& var: _function.parameters() + _function.returnParameters())
    {
        if (!type(*var)->canLiveOutsideStorage())
            typeError(var->location(), "Type is required to live outside storage.");
        if (_function.visibility() >= FunctionDefinition::Visibility::Public && !(type(*var)->interfaceType(isLibraryFunction)))
            fatalTypeError(var->location(), "Internal type is not allowed for public or external functions.");
    }
    for (ASTPointer<ModifierInvocation> const& modifier: _function.modifiers())
        visitManually(
            *modifier,
            _function.isConstructor() ?
            dynamic_cast<ContractDefinition const&>(*_function.scope()).annotation().linearizedBaseContracts :
            vector<ContractDefinition const*>()
        );
    if (_function.isImplemented())
        _function.body().accept(*this);
    return false;
}

bool TypeChecker::visit(VariableDeclaration const& _variable)
{
    // Variables can be declared without type (with "var"), in which case the first assignment
    // sets the type.
    // Note that assignments before the first declaration are legal because of the special scoping
    // rules inherited from JavaScript.

    // 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, "Failed to infer variable type.");
    if (_variable.isConstant())
    {
        if (!dynamic_cast<ContractDefinition const*>(_variable.scope()))
            typeError(_variable.location(), "Illegal use of \"constant\" specifier.");
        if (!_variable.value())
            typeError(_variable.location(), "Uninitialized \"constant\" variable.");
        if (!varType->isValueType())
        {
            bool constImplemented = false;
            if (auto arrayType = dynamic_cast<ArrayType const*>(varType.get()))
                constImplemented = arrayType->isByteArray();
            if (!constImplemented)
                typeError(
                    _variable.location(),
                    "Illegal use of \"constant\" specifier. \"constant\" "
                    "is not yet implemented for this type."
                );
        }
    }
    if (_variable.value())
        expectType(*_variable.value(), *varType);
    if (!_variable.isStateVariable())
    {
        if (varType->dataStoredIn(DataLocation::Memory) || varType->dataStoredIn(DataLocation::CallData))
            if (!varType->canLiveOutsideStorage())
                typeError(_variable.location(), "Type " + varType->toString() + " is only valid in storage.");
    }
    else if (
        _variable.visibility() >= VariableDeclaration::Visibility::Public &&
        !FunctionType(_variable).interfaceFunctionType()
    )
        typeError(_variable.location(), "Internal type is not allowed for public state variables.");
    return false;
}

void TypeChecker::visitManually(
    ModifierInvocation const& _modifier,
    vector<ContractDefinition const*> const& _bases
)
{
    std::vector<ASTPointer<Expression>> const& arguments = _modifier.arguments();
    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)
    {
        typeError(_modifier.location(), "Referenced declaration is neither modifier nor base class.");
        return;
    }
    if (parameters->size() != arguments.size())
    {
        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 < _modifier.arguments().size(); ++i)
        if (!type(*arguments[i])->isImplicitlyConvertibleTo(*type(*(*parameters)[i])))
            typeError(
                arguments[i]->location(),
                "Invalid type for argument in modifier invocation. "
                "Invalid implicit conversion from " +
                type(*arguments[i])->toString() +
                " to " +
                type(*(*parameters)[i])->toString() +
                " requested."
            );
}

bool TypeChecker::visit(EventDefinition const& _eventDef)
{
    unsigned numIndexed = 0;
    for (ASTPointer<VariableDeclaration> const& var: _eventDef.parameters())
    {
        if (var->isIndexed())
            numIndexed++;
        if (_eventDef.isAnonymous() && numIndexed > 4)
            typeError(_eventDef.location(), "More than 4 indexed arguments for anonymous event.");
        else if (!_eventDef.isAnonymous() && numIndexed > 3)
            typeError(_eventDef.location(), "More than 3 indexed arguments for event.");
        if (!type(*var)->canLiveOutsideStorage())
            typeError(var->location(), "Type is required to live outside storage.");
        if (!type(*var)->interfaceType(false))
            typeError(var->location(), "Internal type is not allowed as event parameter type.");
    }
    return false;
}


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

bool TypeChecker::visit(WhileStatement const& _whileStatement)
{
    expectType(_whileStatement.condition(), BoolType());
    _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(), BoolType());
    if (_forStatement.loopExpression())
        _forStatement.loopExpression()->accept(*this);
    _forStatement.body().accept(*this);
    return false;
}

void TypeChecker::endVisit(Return const& _return)
{
    if (!_return.expression())
        return;
    ParameterList const* params = _return.annotation().functionReturnParameters;
    if (!params)
    {
        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()).get()))
    {
        if (tupleType->components().size() != params->parameters().size())
            typeError(_return.location(), "Different number of arguments in return statement than in returns declaration.");
        else if (!tupleType->isImplicitlyConvertibleTo(TupleType(returnTypes)))
            typeError(
                _return.expression()->location(),
                "Return argument type " +
                type(*_return.expression())->toString() +
                " is not implicitly convertible to expected type " +
                TupleType(returnTypes).toString(false) +
                "."
            );
    }
    else if (params->parameters().size() != 1)
        typeError(_return.location(), "Different number of arguments in return statement than in returns declaration.");
    else
    {
        TypePointer const& expected = type(*params->parameters().front());
        if (!type(*_return.expression())->isImplicitlyConvertibleTo(*expected))
            typeError(
                _return.expression()->location(),
                "Return argument type " +
                type(*_return.expression())->toString() +
                " is not implicitly convertible to expected type (type of first return variable) " +
                expected->toString() +
                "."
            );
    }
}

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())
            fatalTypeError(_statement.location(), "Assignment necessary for type detection.");
        VariableDeclaration const& varDecl = *_statement.declarations().front();
        if (!varDecl.annotation().type)
            fatalTypeError(_statement.location(), "Assignment necessary for type detection.");
        if (auto ref = dynamic_cast<ReferenceType const*>(type(varDecl).get()))
        {
            if (ref->dataStoredIn(DataLocation::Storage))
            {
                auto err = make_shared<Error>(Error::Type::Warning);
                *err <<
                    errinfo_sourceLocation(varDecl.location()) <<
                    errinfo_comment("Uninitialized storage pointer. Did you mean '<type> memory " + varDecl.name() + "'?");
                m_errors.push_back(err);
            }
        }
        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()).get()))
        valueTypes = tupleType->components();
    else
        valueTypes = TypePointers{type(*_statement.initialValue())};

    // Determine which component is assigned to which variable.
    // If numbers do not match, fill up if variables begin or end empty (not both).
    vector<VariableDeclaration const*>& assignments = _statement.annotation().assignments;
    assignments.resize(valueTypes.size(), nullptr);
    vector<ASTPointer<VariableDeclaration>> const& variables = _statement.declarations();
    if (variables.empty())
    {
        if (!valueTypes.empty())
            fatalTypeError(
                _statement.location(),
                "Too many components (" +
                toString(valueTypes.size()) +
                ") in value for variable assignment (0) needed"
            );
    }
    else if (valueTypes.size() != variables.size() && !variables.front() && !variables.back())
        fatalTypeError(
            _statement.location(),
            "Wildcard both at beginning and end of variable declaration list is only allowed "
            "if the number of components is equal."
        );
    size_t minNumValues = variables.size();
    if (!variables.empty() && (!variables.back() || !variables.front()))
        --minNumValues;
    if (valueTypes.size() < minNumValues)
        fatalTypeError(
            _statement.location(),
            "Not enough components (" +
            toString(valueTypes.size()) +
            ") in value to assign all variables (" +
            toString(minNumValues) + ")."
        );
    if (valueTypes.size() > variables.size() && variables.front() && variables.back())
        fatalTypeError(
            _statement.location(),
            "Too many components (" +
            toString(valueTypes.size()) +
            ") in value for variable assignment (" +
            toString(minNumValues) +
            " needed)."
        );
    bool fillRight = !variables.empty() && (!variables.back() || variables.front());
    for (size_t i = 0; i < min(variables.size(), valueTypes.size()); ++i)
        if (fillRight)
            assignments[i] = variables[i].get();
        else
            assignments[assignments.size() - i - 1] = variables[variables.size() - i - 1].get();

    for (size_t i = 0; i < assignments.size(); ++i)
    {
        if (!assignments[i])
            continue;
        VariableDeclaration const& var = *assignments[i];
        solAssert(!var.value(), "Value has to be tied to statement.");
        TypePointer const& valueComponentType = valueTypes[i];
        solAssert(!!valueComponentType, "");
        if (!var.annotation().type)
        {
            // Infer type from value.
            solAssert(!var.typeName(), "");
            if (
                valueComponentType->category() == Type::Category::IntegerConstant &&
                !dynamic_pointer_cast<IntegerConstantType const>(valueComponentType)->integerType()
            )
                fatalTypeError(_statement.initialValue()->location(), "Invalid integer constant " + valueComponentType->toString() + ".");
            var.annotation().type = valueComponentType->mobileType();
            var.accept(*this);
        }
        else
        {
            var.accept(*this);
            if (!valueComponentType->isImplicitlyConvertibleTo(*var.annotation().type))
                typeError(
                    _statement.location(),
                    "Type " +
                    valueComponentType->toString() +
                    " is not implicitly convertible to expected type " +
                    var.annotation().type->toString() +
                    "."
                );
        }
    }
    return false;
}

void TypeChecker::endVisit(ExpressionStatement const& _statement)
{
    if (type(_statement.expression())->category() == Type::Category::IntegerConstant)
        if (!dynamic_pointer_cast<IntegerConstantType const>(type(_statement.expression()))->integerType())
            typeError(_statement.expression().location(), "Invalid integer constant.");
}

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

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

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

    TypePointer commonType = Type::commonType(trueType, falseType);
    if (!commonType)
    {
        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;

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

    return false;
}

bool TypeChecker::visit(Assignment const& _assignment)
{
    requireLValue(_assignment.leftHandSide());
    TypePointer t = type(_assignment.leftHandSide());
    _assignment.annotation().type = t;
    if (TupleType const* tupleType = dynamic_cast<TupleType const*>(t.get()))
    {
        // Sequenced assignments of tuples is not valid, make the result a "void" type.
        _assignment.annotation().type = make_shared<TupleType>();
        expectType(_assignment.rightHandSide(), *tupleType);
    }
    else if (t->category() == Type::Category::Mapping)
    {
        typeError(_assignment.location(), "Mappings cannot be assigned to.");
        _assignment.rightHandSide().accept(*this);
    }
    else if (_assignment.assignmentOperator() == Token::Assign)
        expectType(_assignment.rightHandSide(), *t);
    else
    {
        // compound assignment
        _assignment.rightHandSide().accept(*this);
        TypePointer resultType = t->binaryOperatorResult(
            Token::AssignmentToBinaryOp(_assignment.assignmentOperator()),
            type(_assignment.rightHandSide())
        );
        if (!resultType || *resultType != *t)
            typeError(
                _assignment.location(),
                "Operator " +
                string(Token::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())
            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 = make_shared<TupleType>(types);
        // If some of the components are not LValues, the error is reported above.
        _tuple.annotation().isLValue = true;
    }
    else
    {
        TypePointer inlineArrayType;
        for (size_t i = 0; i < components.size(); ++i)
        {
            // Outside of an lvalue-context, the only situation where a component can be empty is (x,).
            if (!components[i] && !(i == 1 && components.size() == 2))
                fatalTypeError(_tuple.location(), "Tuple component cannot be empty.");
            else if (components[i])
            {
                components[i]->accept(*this);
                types.push_back(type(*components[i]));
                if (_tuple.isInlineArray())
                    solAssert(!!types[i], "Inline array cannot have empty components");
                if (i == 0 && _tuple.isInlineArray())
                    inlineArrayType = types[i]->mobileType();
                else if (_tuple.isInlineArray() && inlineArrayType)
                    inlineArrayType = Type::commonType(inlineArrayType, types[i]->mobileType());
            }
            else
                types.push_back(TypePointer());
        }
        if (_tuple.isInlineArray())
        {
            if (!inlineArrayType) 
                fatalTypeError(_tuple.location(), "Unable to deduce common type for array elements.");
            _tuple.annotation().type = make_shared<ArrayType>(DataLocation::Memory, inlineArrayType, types.size());
        }
        else
        {
            if (components.size() == 1)
                _tuple.annotation().type = type(*components[0]);
            else
            {
                if (components.size() == 2 && !components[1])
                    types.pop_back();
                _tuple.annotation().type = make_shared<TupleType>(types);
            }
        }

    }
    return false;
}

bool TypeChecker::visit(UnaryOperation const& _operation)
{
    // Inc, Dec, Add, Sub, Not, BitNot, Delete
    Token::Value op = _operation.getOperator();
    if (op == Token::Value::Inc || op == Token::Value::Dec || op == Token::Value::Delete)
        requireLValue(_operation.subExpression());
    else
        _operation.subExpression().accept(*this);
    TypePointer const& subExprType = type(_operation.subExpression());
    TypePointer t = type(_operation.subExpression())->unaryOperatorResult(op);
    if (!t)
    {
        typeError(
            _operation.location(),
            "Unary operator " +
            string(Token::toString(op)) +
            " cannot be applied to type " +
            subExprType->toString()
        );
        t = subExprType;
    }
    _operation.annotation().type = t;
    return false;
}

void TypeChecker::endVisit(BinaryOperation const& _operation)
{
    TypePointer const& leftType = type(_operation.leftExpression());
    TypePointer const& rightType = type(_operation.rightExpression());
    TypePointer commonType = leftType->binaryOperatorResult(_operation.getOperator(), rightType);
    if (!commonType)
    {
        typeError(
            _operation.location(),
            "Operator " +
            string(Token::toString(_operation.getOperator())) +
            " not compatible with types " +
            leftType->toString() +
            " and " +
            rightType->toString()
        );
        commonType = leftType;
    }
    _operation.annotation().commonType = commonType;
    _operation.annotation().type =
        Token::isCompareOp(_operation.getOperator()) ?
        make_shared<BoolType>() :
        commonType;
}

bool TypeChecker::visit(FunctionCall const& _functionCall)
{
    bool isPositionalCall = _functionCall.names().empty();
    vector<ASTPointer<Expression const>> arguments = _functionCall.arguments();
    vector<ASTPointer<ASTString>> const& argumentNames = _functionCall.names();

    // We need to check arguments' type first as they will be needed for overload resolution.
    shared_ptr<TypePointers> argumentTypes;
    if (isPositionalCall)
        argumentTypes = make_shared<TypePointers>();
    for (ASTPointer<Expression const> const& argument: arguments)
    {
        argument->accept(*this);
        // only store them for positional calls
        if (isPositionalCall)
            argumentTypes->push_back(type(*argument));
    }
    if (isPositionalCall)
        _functionCall.expression().annotation().argumentTypes = move(argumentTypes);

    _functionCall.expression().accept(*this);
    TypePointer expressionType = type(_functionCall.expression());

    if (auto const* typeType = dynamic_cast<TypeType const*>(expressionType.get()))
    {
        _functionCall.annotation().isStructConstructorCall = (typeType->actualType()->category() == Type::Category::Struct);
        _functionCall.annotation().isTypeConversion = !_functionCall.annotation().isStructConstructorCall;
    }
    else
        _functionCall.annotation().isStructConstructorCall = _functionCall.annotation().isTypeConversion = false;

    if (_functionCall.annotation().isTypeConversion)
    {
        TypeType const& t = dynamic_cast<TypeType const&>(*expressionType);
        TypePointer resultType = t.actualType();
        if (arguments.size() != 1)
            typeError(_functionCall.location(), "Exactly one argument expected for explicit type conversion.");
        else if (!isPositionalCall)
            typeError(_functionCall.location(), "Type conversion cannot allow named arguments.");
        else
        {
            TypePointer const& argType = type(*arguments.front());
            if (auto argRefType = dynamic_cast<ReferenceType const*>(argType.get()))
                // do not change the data location when converting
                // (data location cannot yet be specified for type conversions)
                resultType = ReferenceType::copyForLocationIfReference(argRefType->location(), resultType);
            if (!argType->isExplicitlyConvertibleTo(*resultType))
                typeError(_functionCall.location(), "Explicit type conversion not allowed.");
        }
        _functionCall.annotation().type = resultType;

        return false;
    }

    // Actual function call or struct constructor call.

    FunctionTypePointer functionType;

    /// For error message: Struct members that were removed during conversion to memory.
    set<string> membersRemovedForStructConstructor;
    if (_functionCall.annotation().isStructConstructorCall)
    {
        TypeType const& t = dynamic_cast<TypeType const&>(*expressionType);
        auto const& structType = dynamic_cast<StructType const&>(*t.actualType());
        functionType = structType.constructorType();
        membersRemovedForStructConstructor = structType.membersMissingInMemory();
    }
    else
        functionType = dynamic_pointer_cast<FunctionType const>(expressionType);

    if (!functionType)
    {
        typeError(_functionCall.location(), "Type is not callable");
        _functionCall.annotation().type = make_shared<TupleType>();
        return false;
    }
    else if (functionType->returnParameterTypes().size() == 1)
        _functionCall.annotation().type = functionType->returnParameterTypes().front();
    else
        _functionCall.annotation().type = make_shared<TupleType>(functionType->returnParameterTypes());

    TypePointers parameterTypes = functionType->parameterTypes();
    if (!functionType->takesArbitraryParameters() && parameterTypes.size() != arguments.size())
    {
        string msg =
            "Wrong argument count for function call: " +
            toString(arguments.size()) +
            " arguments given but expected " +
            toString(parameterTypes.size()) +
            ".";
        // Extend error message in case we try to construct a struct with mapping member.
        if (_functionCall.annotation().isStructConstructorCall && !membersRemovedForStructConstructor.empty())
        {
            msg += " Members that have to be skipped in memory:";
            for (auto const& member: membersRemovedForStructConstructor)
                msg += " " + member;
        }
        typeError(_functionCall.location(), msg);
    }
    else if (isPositionalCall)
    {
        // call by positional arguments
        for (size_t i = 0; i < arguments.size(); ++i)
        {
            auto const& argType = type(*arguments[i]);
            if (functionType->takesArbitraryParameters())
            {
                if (auto t = dynamic_cast<IntegerConstantType const*>(argType.get()))
                    if (!t->integerType())
                        typeError(arguments[i]->location(), "Integer constant too large.");
            }
            else if (!type(*arguments[i])->isImplicitlyConvertibleTo(*parameterTypes[i]))
                typeError(
                    arguments[i]->location(),
                    "Invalid type for argument in function call. "
                    "Invalid implicit conversion from " +
                    type(*arguments[i])->toString() +
                    " to " +
                    parameterTypes[i]->toString() +
                    " requested."
                );
        }
    }
    else
    {
        // call by named arguments
        auto const& parameterNames = functionType->parameterNames();
        if (functionType->takesArbitraryParameters())
            typeError(
                _functionCall.location(),
                "Named arguments cannnot be used for functions that take arbitrary parameters."
            );
        else if (parameterNames.size() > argumentNames.size())
            typeError(_functionCall.location(), "Some argument names are missing.");
        else if (parameterNames.size() < argumentNames.size())
            typeError(_functionCall.location(), "Too many arguments.");
        else
        {
            // check duplicate 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;
                        typeError(arguments[i]->location(), "Duplicate named argument.");
                    }

            // check actual types
            if (!duplication)
                for (size_t i = 0; i < argumentNames.size(); i++)
                {
                    bool found = false;
                    for (size_t j = 0; j < parameterNames.size(); j++)
                        if (parameterNames[j] == *argumentNames[i])
                        {
                            found = true;
                            // check type convertible
                            if (!type(*arguments[i])->isImplicitlyConvertibleTo(*parameterTypes[j]))
                                typeError(
                                    arguments[i]->location(),
                                    "Invalid type for argument in function call. "
                                    "Invalid implicit conversion from " +
                                    type(*arguments[i])->toString() +
                                    " to " +
                                    parameterTypes[i]->toString() +
                                    " requested."
                                );
                            break;
                        }

                    if (!found)
                        typeError(
                            _functionCall.location(),
                            "Named argument does not match function declaration."
                        );
                }
        }
    }

    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)
            fatalTypeError(_newExpression.location(), "Identifier is not a contract.");
        if (!contract->annotation().isFullyImplemented)
            typeError(_newExpression.location(), "Trying to create an instance of an abstract contract.");

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

        auto contractType = make_shared<ContractType>(*contract);
        TypePointers parameterTypes = contractType->constructorType()->parameterTypes();
        _newExpression.annotation().type = make_shared<FunctionType>(
            parameterTypes,
            TypePointers{contractType},
            strings(),
            strings(),
            FunctionType::Location::Creation
        );
    }
    else if (type->category() == Type::Category::Array)
    {
        if (!type->canLiveOutsideStorage())
            fatalTypeError(
                _newExpression.typeName().location(),
                "Type cannot live outside storage."
            );
        if (!type->isDynamicallySized())
            typeError(
                _newExpression.typeName().location(),
                "Length has to be placed in parentheses after the array type for new expression."
            );
        type = ReferenceType::copyForLocationIfReference(DataLocation::Memory, type);
        _newExpression.annotation().type = make_shared<FunctionType>(
            TypePointers{make_shared<IntegerType>(256)},
            TypePointers{type},
            strings(),
            strings(),
            FunctionType::Location::ObjectCreation
        );
    }
    else
        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& argumentTypes = _memberAccess.annotation().argumentTypes;
    MemberList::MemberMap possibleMembers = exprType->members(m_scope).membersByName(memberName);
    if (possibleMembers.size() > 1 && argumentTypes)
    {
        // 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(*argumentTypes, exprType)
            )
                it = possibleMembers.erase(it);
            else
                ++it;
    }
    if (possibleMembers.size() == 0)
    {
        auto storageType = ReferenceType::copyForLocationIfReference(
            DataLocation::Storage,
            exprType
        );
        if (!storageType->members(m_scope).membersByName(memberName).empty())
            fatalTypeError(
                _memberAccess.location(),
                "Member \"" + memberName + "\" is not available in " +
                exprType->toString() +
                " outside of storage."
            );
        fatalTypeError(
            _memberAccess.location(),
            "Member \"" + memberName + "\" not found or not visible "
            "after argument-dependent lookup in " + exprType->toString()
        );
    }
    else if (possibleMembers.size() > 1)
        fatalTypeError(
            _memberAccess.location(),
            "Member \"" + memberName + "\" not unique "
            "after argument-dependent lookup in " + exprType->toString()
        );

    auto& annotation = _memberAccess.annotation();
    annotation.referencedDeclaration = possibleMembers.front().declaration;
    annotation.type = possibleMembers.front().type;

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

    if (exprType->category() == Type::Category::Struct)
        annotation.isLValue = true;
    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;

    return false;
}

bool TypeChecker::visit(IndexAccess const& _access)
{
    _access.baseExpression().accept(*this);
    TypePointer baseType = type(_access.baseExpression());
    TypePointer resultType;
    bool isLValue = false;
    Expression const* index = _access.indexExpression();
    switch (baseType->category())
    {
    case Type::Category::Array:
    {
        ArrayType const& actualType = dynamic_cast<ArrayType const&>(*baseType);
        if (!index)
            typeError(_access.location(), "Index expression cannot be omitted.");
        else if (actualType.isString())
        {
            typeError(_access.location(), "Index access for string is not possible.");
            index->accept(*this);
        }
        else
        {
            expectType(*index, IntegerType(256));
            if (auto integerType = dynamic_cast<IntegerConstantType const*>(type(*index).get()))
                if (!actualType.isDynamicallySized() && actualType.length() <= integerType->literalValue(nullptr))
                    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)
            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 (!index)
            resultType = make_shared<TypeType>(make_shared<ArrayType>(DataLocation::Memory, typeType.actualType()));
        else
        {
            index->accept(*this);
            if (auto length = dynamic_cast<IntegerConstantType const*>(type(*index).get()))
                resultType = make_shared<TypeType>(make_shared<ArrayType>(
                    DataLocation::Memory,
                    typeType.actualType(),
                    length->literalValue(nullptr)
                ));
            else
                typeError(index->location(), "Integer constant expected.");
        }
        break;
    }
    case Type::Category::FixedBytes:
    {
        FixedBytesType const& bytesType = dynamic_cast<FixedBytesType const&>(*baseType);
        if (!index)
            typeError(_access.location(), "Index expression cannot be omitted.");
        else
        {
            expectType(*index, IntegerType(256));
            if (auto integerType = dynamic_cast<IntegerConstantType const*>(type(*index).get()))
                if (bytesType.numBytes() <= integerType->literalValue(nullptr))
                    typeError(_access.location(), "Out of bounds array access.");
        }
        resultType = make_shared<FixedBytesType>(1);
        isLValue = false; // @todo this heavily depends on how it is embedded
        break;
    }
    default:
        fatalTypeError(
            _access.baseExpression().location(),
            "Indexed expression has to be a type, mapping or array (is " + baseType->toString() + ")"
        );
    }
    _access.annotation().type = move(resultType);
    _access.annotation().isLValue = isLValue;

    return false;
}

bool TypeChecker::visit(Identifier const& _identifier)
{
    IdentifierAnnotation& annotation = _identifier.annotation();
    if (!annotation.referencedDeclaration)
    {
        if (!annotation.argumentTypes)
            fatalTypeError(_identifier.location(), "Unable to determine overloaded type.");
        if (annotation.overloadedDeclarations.empty())
            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)
            {
                TypePointer function = declaration->type();
                solAssert(!!function, "Requested type not present.");
                auto const* functionType = dynamic_cast<FunctionType const*>(function.get());
                if (functionType && functionType->canTakeArguments(*annotation.argumentTypes))
                    candidates.push_back(declaration);
            }
            if (candidates.empty())
                fatalTypeError(_identifier.location(), "No matching declaration found after argument-dependent lookup.");
            else if (candidates.size() == 1)
                annotation.referencedDeclaration = candidates.front();
            else
                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)
        fatalTypeError(_identifier.location(), "Declaration referenced before type could be determined.");
    return false;
}

void TypeChecker::endVisit(ElementaryTypeNameExpression const& _expr)
{
    _expr.annotation().type = make_shared<TypeType>(Type::fromElementaryTypeName(_expr.typeName()));
}

void TypeChecker::endVisit(Literal const& _literal)
{
    _literal.annotation().type = Type::forLiteral(_literal);
    if (!_literal.annotation().type)
        fatalTypeError(_literal.location(), "Invalid literal value.");
}

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;
}

void TypeChecker::expectType(Expression const& _expression, Type const& _expectedType)
{
    _expression.accept(*this);

    if (!type(_expression)->isImplicitlyConvertibleTo(_expectedType))
        typeError(
            _expression.location(),
            "Type " +
            type(_expression)->toString() +
            " is not implicitly convertible to expected type " +
            _expectedType.toString() +
            "."
        );
}

void TypeChecker::requireLValue(Expression const& _expression)
{
    _expression.annotation().lValueRequested = true;
    _expression.accept(*this);
    if (!_expression.annotation().isLValue)
        typeError(_expression.location(), "Expression has to be an lvalue.");
}

void TypeChecker::typeError(SourceLocation const& _location, string const& _description)
{
    auto err = make_shared<Error>(Error::Type::TypeError);
    *err <<
        errinfo_sourceLocation(_location) <<
        errinfo_comment(_description);

    m_errors.push_back(err);
}

void TypeChecker::fatalTypeError(SourceLocation const& _location, string const& _description)
{
    typeError(_location, _description);
    BOOST_THROW_EXCEPTION(FatalError());
}