path: root/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 <memory>
#include <boost/algorithm/string/predicate.hpp>
#include <boost/range/adaptor/reversed.hpp>
#include <libsolidity/ast/AST.h>
#include <libsolidity/inlineasm/AsmAnalysis.h>
#include <libsolidity/inlineasm/AsmAnalysisInfo.h>
#include <libsolidity/inlineasm/AsmData.h>
#include <libsolidity/interface/ErrorReporter.h>

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


bool TypeChecker::checkTypeRequirements(ASTNode const& _contract)
{
    try
    {
        _contract.accept(*this);
    }
    catch (FatalError const&)
    {
        // We got a fatal error which required to stop further type checking, but we can
        // continue normally from here.
        if (m_errorReporter.errors().empty())
            throw; // Something is weird here, rather throw again.
    }
    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;

    // We force our own visiting order here. The structs have to be excluded below.
    set<ASTNode const*> visited;
    for (auto const& s: _contract.definedStructs())
        visited.insert(s);
    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)
    {
        if (!function->returnParameters().empty())
            m_errorReporter.typeError(function->returnParameterList()->location(), "Non-empty \"returns\" directive for constructor.");
        if (function->stateMutability() != StateMutability::NonPayable && function->stateMutability() != StateMutability::Payable)
            m_errorReporter.typeError(
                function->location(),
                "Constructor must be payable or non-payable, but is \"" +
                stateMutabilityToString(function->stateMutability()) +
                "\"."
            );
        if (function->visibility() != FunctionDefinition::Visibility::Public && function->visibility() != FunctionDefinition::Visibility::Internal)
            m_errorReporter.typeError(function->location(), "Constructor must be public or internal.");
    }

    FunctionDefinition const* fallbackFunction = nullptr;
    for (FunctionDefinition const* function: _contract.definedFunctions())
    {
        if (function->isFallback())
        {
            if (fallbackFunction)
            {
                m_errorReporter.declarationError(function->location(), "Only one fallback function is allowed.");
            }
            else
            {
                fallbackFunction = function;
                if (_contract.isLibrary())
                    m_errorReporter.typeError(fallbackFunction->location(), "Libraries cannot have fallback functions.");
                if (function->stateMutability() != StateMutability::NonPayable && function->stateMutability() != StateMutability::Payable)
                    m_errorReporter.typeError(
                        function->location(),
                        "Fallback function must be payable or non-payable, but is \"" +
                        stateMutabilityToString(function->stateMutability()) +
                        "\"."
                );
                if (!fallbackFunction->parameters().empty())
                    m_errorReporter.typeError(fallbackFunction->parameterList().location(), "Fallback function cannot take parameters.");
                if (!fallbackFunction->returnParameters().empty())
                    m_errorReporter.typeError(fallbackFunction->returnParameterList()->location(), "Fallback function cannot return values.");
            }
        }
    }

    for (auto const& n: _contract.subNodes())
        if (!visited.count(n.get()))
            n->accept(*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))
            m_errorReporter.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());

        m_errorReporter.declarationError(
            functions[_contract.name()].front()->location(),
            ssl,
            "More than one constructor defined."
        );
    }
    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])))
                {
                    m_errorReporter.declarationError(
                        overloads[j]->location(),
                        SecondarySourceLocation().append(
                            "Other declaration is here:",
                            overloads[i]->location()
                        ),
                        "Function with same name and arguments defined twice."
                    );
                }
    }
}

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())
        {
            // Take constructors out of overload hierarchy
            if (function->isConstructor())
                continue;
            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())
                    m_errorReporter.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)
            {
                FunctionDefinition const* function = dynamic_cast<FunctionDefinition const*>(&funAndFlag.first->declaration());
                solAssert(function, "");
                _contract.annotation().unimplementedFunctions.push_back(function);
                break;
            }
}

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())
        for (ContractDefinition const* contract: argumentsNeeded)
            _contract.annotation().unimplementedFunctions.push_back(contract->constructor());
}

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))
                m_errorReporter.typeError(modifiers[name]->location(), "Override changes function to modifier.");

            for (FunctionDefinition const* overriding: functions[name])
                checkFunctionOverride(*overriding, *function);

            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))
                m_errorReporter.typeError(override->location(), "Override changes modifier signature.");
            if (!functions[name].empty())
                m_errorReporter.typeError(override->location(), "Override changes modifier to function.");
        }
    }
}

void TypeChecker::checkFunctionOverride(FunctionDefinition const& function, FunctionDefinition const& super)
{
    FunctionType functionType(function);
    FunctionType superType(super);

    if (!functionType.hasEqualArgumentTypes(superType))
        return;

    if (function.visibility() != super.visibility())
        overrideError(function, super, "Overriding function visibility differs.");

    else if (function.stateMutability() != super.stateMutability())
        overrideError(
            function,
            super,
            "Overriding function changes state mutability from \"" +
            stateMutabilityToString(super.stateMutability()) +
            "\" to \"" +
            stateMutabilityToString(function.stateMutability()) +
            "\"."
        );

    else if (functionType != superType)
        overrideError(function, super, "Overriding function return types differ.");
}

void TypeChecker::overrideError(FunctionDefinition const& function, FunctionDefinition const& super, string message)
{
    m_errorReporter.typeError(
        function.location(),
        SecondarySourceLocation().append("Overriden function is here:", super.location()),
        message
    );
}

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))
                    m_errorReporter.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())
        m_errorReporter.typeError(_contract.location(), "Library is not allowed to inherit.");

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

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()));

    bool fillRight = !lhs.components().empty() && (!lhs.components().back() || lhs.components().front());
    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].get());
        if (!ref || !ref->dataStoredIn(DataLocation::Storage) || ref->isPointer())
            continue;
        size_t rhsPos = fillRight ? i : rhs.components().size() - (lhs.components().size() - i);
        solAssert(rhsPos < rhs.components().size(), "");
        toStorageCopies++;
        if (rhs.components()[rhsPos]->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."
        );
}

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

    if (m_scope->contractKind() == ContractDefinition::ContractKind::Interface)
        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->contractKind() != ContractDefinition::ContractKind::Interface)
        // Interfaces do not have constructors, so there are zero parameters.
        parameterTypes = ContractType(*base).newExpressionType()->parameterTypes();

    if (!arguments.empty() && 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()) +
            "."
        );
        return;
    }

    for (size_t i = 0; i < arguments.size(); ++i)
        if (!type(*arguments[i])->isImplicitlyConvertibleTo(*parameterTypes[i]))
            m_errorReporter.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())
        m_errorReporter.fatalTypeError(_usingFor.libraryName().location(), "Library name expected.");
}

bool TypeChecker::visit(StructDefinition const& _struct)
{
    if (m_scope->contractKind() == ContractDefinition::ContractKind::Interface)
        m_errorReporter.typeError(_struct.location(), "Structs cannot be defined in interfaces.");

    for (ASTPointer<VariableDeclaration> const& member: _struct.members())
        if (!type(*member)->canBeStored())
            m_errorReporter.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))
            m_errorReporter.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()) &&
        dynamic_cast<ContractDefinition const*>(_function.scope())->isLibrary();
    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.");
    }
    for (ASTPointer<VariableDeclaration> const& var: _function.parameters() + _function.returnParameters())
    {
        if (!type(*var)->canLiveOutsideStorage())
            m_errorReporter.typeError(var->location(), "Type is required to live outside storage.");
        if (_function.visibility() >= FunctionDefinition::Visibility::Public && !(type(*var)->interfaceType(isLibraryFunction)))
            m_errorReporter.fatalTypeError(var->location(), "Internal type is not allowed for public or external functions.");

        var->accept(*this);
    }
    set<Declaration const*> modifiers;
    for (ASTPointer<ModifierInvocation> const& modifier: _function.modifiers())
    {
        visitManually(
            *modifier,
            _function.isConstructor() ?
            dynamic_cast<ContractDefinition const&>(*_function.scope()).annotation().linearizedBaseContracts :
            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->contractKind() == ContractDefinition::ContractKind::Interface)
    {
        if (_function.isImplemented())
            m_errorReporter.typeError(_function.location(), "Functions in interfaces cannot have an implementation.");
        if (_function.visibility() < FunctionDefinition::Visibility::Public)
            m_errorReporter.typeError(_function.location(), "Functions in interfaces cannot be internal or private.");
        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.
    if (
        m_scope->contractKind() == ContractDefinition::ContractKind::Interface
        && !_variable.isCallableParameter()
    )
        m_errorReporter.typeError(_variable.location(), "Variables cannot be declared in interfaces.");

    // 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.value())
        expectType(*_variable.value(), *varType);
    if (_variable.isConstant())
    {
        if (!_variable.isStateVariable())
            m_errorReporter.typeError(_variable.location(), "Illegal use of \"constant\" specifier.");
        if (!_variable.type()->isValueType())
        {
            bool allowed = false;
            if (auto arrayType = dynamic_cast<ArrayType const*>(_variable.type().get()))
                allowed = arrayType->isString();
            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.warning(
                _variable.value()->location(),
                "Initial value for constant variable has to be compile-time constant. "
                "This will fail to compile with the next breaking version change."
            );
    }
    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(_variable).interfaceFunctionType()
    )
        m_errorReporter.typeError(_variable.location(), "Internal type is not allowed for public state variables.");

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

    return false;
}

bool TypeChecker::visit(EnumDefinition const& _enum)
{
    if (m_scope->contractKind() == ContractDefinition::ContractKind::Interface)
        m_errorReporter.typeError(_enum.location(), "Enumerable cannot be declared in interfaces.");
    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)
    {
        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 < _modifier.arguments().size(); ++i)
        if (!type(*arguments[i])->isImplicitlyConvertibleTo(*type(*(*parameters)[i])))
            m_errorReporter.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 (!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 type is not allowed as event parameter type.");
    }
    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)
        if (!fun.canBeUsedExternally(false))
            m_errorReporter.typeError(_funType.location(), "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.
    julia::ExternalIdentifierAccess::Resolver identifierAccess = [&](
        assembly::Identifier const& _identifier,
        julia::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, "");
        if (auto var = dynamic_cast<VariableDeclaration const*>(declaration))
        {
            if (ref->second.isSlot || ref->second.isOffset)
            {
                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 != julia::IdentifierContext::RValue)
                {
                    m_errorReporter.typeError(_identifier.location, "Storage variables cannot be assigned to.");
                    return size_t(-1);
                }
            }
            else if (var->isConstant())
            {
                m_errorReporter.typeError(_identifier.location, "Constant variables not supported by inline assembly.");
                return size_t(-1);
            }
            else if (!var->isLocalVariable())
            {
                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 prefix 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 (_context == julia::IdentifierContext::LValue)
        {
            m_errorReporter.typeError(_identifier.location, "Only local variables can be assigned to in inline assembly.");
            return size_t(-1);
        }

        if (_context == julia::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<assembly::AsmAnalysisInfo>();
    assembly::AsmAnalyzer analyzer(
        *_inlineAssembly.annotation().analysisInfo,
        m_errorReporter,
        false,
        identifierAccess
    );
    if (!analyzer.analyze(_inlineAssembly.operations()))
        return false;
    return true;
}

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)
    {
        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()).get()))
    {
        if (tupleType->components().size() != params->parameters().size())
            m_errorReporter.typeError(_return.location(), "Different number of arguments in return statement than in returns declaration.");
        else if (!tupleType->isImplicitlyConvertibleTo(TupleType(returnTypes)))
            m_errorReporter.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)
        m_errorReporter.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))
            m_errorReporter.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())
            m_errorReporter.fatalTypeError(_statement.location(), "Assignment necessary for type detection.");
        VariableDeclaration const& varDecl = *_statement.declarations().front();
        if (!varDecl.annotation().type)
            m_errorReporter.fatalTypeError(_statement.location(), "Assignment necessary for type detection.");
        if (auto ref = dynamic_cast<ReferenceType const*>(type(varDecl).get()))
        {
            if (ref->dataStoredIn(DataLocation::Storage))
            {
                string errorText{"Uninitialized storage pointer."};
                if (varDecl.referenceLocation() == VariableDeclaration::Location::Default)
                    errorText += " Did you mean '<type> memory " + varDecl.name() + "'?";
                m_errorReporter.warning(varDecl.location(), errorText);
            }
        }
        else if (dynamic_cast<MappingType const*>(type(varDecl).get()))
            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()).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())
            m_errorReporter.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())
        m_errorReporter.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)
        m_errorReporter.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())
        m_errorReporter.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(), "");
            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 divison by zero)."
                    );
                else
                    solAssert(false, "");
            }
            else if (*var.annotation().type == TupleType())
                m_errorReporter.typeError(
                    var.location(),
                    "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.get()))
                {
                    int numBits = type->numBits();
                    bool isSigned = type->isSigned();
                    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.get()), "Unknown type.");

                m_errorReporter.warning(
                    _statement.location(),
                    "The type of this variable was inferred as " +
                    typeName +
                    extension +
                    ". This is probably not desired. Use an explicit type to silence this warning."
                );
            }

            var.accept(*this);
        }
        else
        {
            var.accept(*this);
            if (!valueComponentType->isImplicitlyConvertibleTo(*var.annotation().type))
            {
                if (
                    valueComponentType->category() == Type::Category::RationalNumber &&
                    dynamic_cast<RationalNumberType const&>(*valueComponentType).isFractional() &&
                    valueComponentType->mobileType()
                )
                    m_errorReporter.typeError(
                        _statement.location(),
                        "Type " +
                        valueComponentType->toString() +
                        " is not implicitly convertible to expected type " +
                        var.annotation().type->toString() +
                        ". Try converting to type " +
                        valueComponentType->mobileType()->toString() +
                        " or use an explicit conversion." 
                    );
                else
                    m_errorReporter.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::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()).get()))
        {
            auto kind = callType->kind();
            if (
                kind == FunctionType::Kind::BareCall ||
                kind == FunctionType::Kind::BareCallCode ||
                kind == FunctionType::Kind::BareDelegateCall
            )
                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(), BoolType());

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

    TypePointer trueType = type(_conditional.trueExpression())->mobileType();
    TypePointer falseType = type(_conditional.falseExpression())->mobileType();
    if (!trueType)
        m_errorReporter.fatalTypeError(_conditional.trueExpression().location(), "Invalid mobile type.");
    if (!falseType)
        m_errorReporter.fatalTypeError(_conditional.falseExpression().location(), "Invalid mobile type.");

    TypePointer 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;
}

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()))
    {
        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 = make_shared<TupleType>();
        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()).get()))
            checkDoubleStorageAssignment(_assignment);
    }
    else if (t->category() == Type::Category::Mapping)
    {
        m_errorReporter.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)
            m_errorReporter.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())
            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 = make_shared<TupleType>(types);
        // If some of the components are not LValues, the error is reported above.
        _tuple.annotation().isLValue = true;
    }
    else
    {
        bool isPure = true;
        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))
                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 (_tuple.isInlineArray())
                    solAssert(!!types[i], "Inline array cannot have empty components");
                if (_tuple.isInlineArray())
                {
                    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.");
            _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();
    bool const modifying = (op == Token::Value::Inc || op == Token::Value::Dec || op == Token::Value::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(Token::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());
    TypePointer commonType = leftType->binaryOperatorResult(_operation.getOperator(), rightType);
    if (!commonType)
    {
        m_errorReporter.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;
    _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."
                );
    }
}

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();

    bool isPure = true;

    // 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);
        if (!argument->annotation().isPure)
            isPure = false;
        // 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()))
    {
        if (typeType->actualType()->category() == Type::Category::Struct)
            _functionCall.annotation().kind = FunctionCallKind::StructConstructorCall;
        else
            _functionCall.annotation().kind = FunctionCallKind::TypeConversion;

    }
    else
        _functionCall.annotation().kind = FunctionCallKind::FunctionCall;
    solAssert(_functionCall.annotation().kind != FunctionCallKind::Unset, "");

    if (_functionCall.annotation().kind == FunctionCallKind::TypeConversion)
    {
        TypeType const& t = dynamic_cast<TypeType const&>(*expressionType);
        TypePointer resultType = t.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
        {
            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))
                m_errorReporter.typeError(
                    _functionCall.location(),
                    "Explicit type conversion not allowed from \"" +
                    argType->toString() +
                    "\" to \"" +
                    resultType->toString() +
                    "\"."
                );
        }
        _functionCall.annotation().type = resultType;
        _functionCall.annotation().isPure = isPure;

        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().kind == FunctionCallKind::StructConstructorCall)
    {
        TypeType const& t = dynamic_cast<TypeType const&>(*expressionType);
        auto const& structType = dynamic_cast<StructType const&>(*t.actualType());
        functionType = structType.constructorType();
        membersRemovedForStructConstructor = structType.membersMissingInMemory();
        _functionCall.annotation().isPure = isPure;
    }
    else if ((functionType = dynamic_pointer_cast<FunctionType const>(expressionType)))
        _functionCall.annotation().isPure =
            isPure &&
            _functionCall.expression().annotation().isPure &&
            functionType->isPure();

    if (!functionType)
    {
        m_errorReporter.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->padArguments())
    {
        for (size_t i = 0; i < arguments.size(); ++i)
        {
            auto const& argType = type(*arguments[i]);
            if (auto literal = dynamic_cast<RationalNumberType const*>(argType.get()))
            {
                /* If no mobile type is available an error will be raised elsewhere. */
                if (literal->mobileType())
                    m_errorReporter.warning(
                        _functionCall.location(),
                        "The type of \"" +
                        argType->toString() +
                        "\" was inferred as " +
                        literal->mobileType()->toString() +
                        ". This is probably not desired. Use an explicit type to silence this warning."
                    );
            }
        }
    }

    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().kind == FunctionCallKind::StructConstructorCall && !membersRemovedForStructConstructor.empty())
        {
            msg += " Members that have to be skipped in memory:";
            for (auto const& member: membersRemovedForStructConstructor)
                msg += " " + member;
        }
        m_errorReporter.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<RationalNumberType const*>(argType.get()))
                    if (!t->mobileType())
                        m_errorReporter.typeError(arguments[i]->location(), "Invalid rational number (too large or division by zero).");
            }
            else if (!type(*arguments[i])->isImplicitlyConvertibleTo(*parameterTypes[i]))
                m_errorReporter.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())
            m_errorReporter.typeError(
                _functionCall.location(),
                "Named arguments cannnot be used for functions that take arbitrary parameters."
            );
        else if (parameterNames.size() > argumentNames.size())
            m_errorReporter.typeError(_functionCall.location(), "Some argument names are missing.");
        else if (parameterNames.size() < argumentNames.size())
            m_errorReporter.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;
                        m_errorReporter.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]))
                                m_errorReporter.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)
                        m_errorReporter.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)
            m_errorReporter.fatalTypeError(_newExpression.location(), "Identifier is not a contract.");
        if (contract->contractKind() == ContractDefinition::ContractKind::Interface)
                m_errorReporter.fatalTypeError(_newExpression.location(), "Cannot instantiate an interface.");
        if (!contract->annotation().unimplementedFunctions.empty())
            m_errorReporter.typeError(
                _newExpression.location(),
                SecondarySourceLocation().append(
                    "Missing implementation:",
                    contract->annotation().unimplementedFunctions.front()->location()
                ),
                "Trying to create an instance of an abstract contract."
            );
        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 = ReferenceType::copyForLocationIfReference(DataLocation::Memory, type);
        _newExpression.annotation().type = make_shared<FunctionType>(
            TypePointers{make_shared<IntegerType>(256)},
            TypePointers{type},
            strings(),
            strings(),
            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& 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())
            m_errorReporter.fatalTypeError(
                _memberAccess.location(),
                "Member \"" + memberName + "\" is not available in " +
                exprType->toString() +
                " outside of storage."
            );
        m_errorReporter.fatalTypeError(
            _memberAccess.location(),
            "Member \"" + memberName + "\" not found or not visible "
            "after argument-dependent lookup in " + exprType->toString() +
            (memberName == "value" ? " - did you forget the \"payable\" modifier?" : "")
        );
    }
    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?" : "")
        );

    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()))
            m_errorReporter.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;
    else if (TypeType const* typeType = dynamic_cast<decltype(typeType)>(exprType.get()))
    {
        if (ContractType const* contractType = dynamic_cast<decltype(contractType)>(typeType->actualType().get()))
            annotation.isLValue = annotation.referencedDeclaration->isLValue();
    }

    if (exprType->category() == Type::Category::Contract)
    {
        if (auto callType = dynamic_cast<FunctionType const*>(type(_memberAccess).get()))
        {
            auto kind = callType->kind();
            auto contractType = dynamic_cast<ContractType const*>(exprType.get());
            solAssert(!!contractType, "Should be contract type.");

            if (
                (kind == FunctionType::Kind::Send || kind == FunctionType::Kind::Transfer) &&
                !contractType->isPayable()
            )
                m_errorReporter.typeError(
                    _memberAccess.location(),
                    "Value transfer to a contract without a payable fallback function."
                );
        }
    }

    // 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.get()))
        if (tt->actualType()->category() == Type::Category::Enum)
            annotation.isPure = true;

    return false;
}

bool TypeChecker::visit(IndexAccess const& _access)
{
    _access.baseExpression().accept(*this);
    TypePointer baseType = type(_access.baseExpression());
    TypePointer resultType;
    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, IntegerType(256));
            if (auto numberType = dynamic_cast<RationalNumberType const*>(type(*index).get()))
            {
                if (!numberType->isFractional()) // error is reported above
                    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 (!index)
            resultType = make_shared<TypeType>(make_shared<ArrayType>(DataLocation::Memory, typeType.actualType()));
        else
        {
            expectType(*index, IntegerType(256));
            if (auto length = dynamic_cast<RationalNumberType const*>(type(*index).get()))
                resultType = make_shared<TypeType>(make_shared<ArrayType>(
                    DataLocation::Memory,
                    typeType.actualType(),
                    length->literalValue(nullptr)
                ));
            else
                m_errorReporter.fatalTypeError(index->location(), "Integer constant expected.");
        }
        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
        {
            expectType(*index, IntegerType(256));
            if (auto integerType = dynamic_cast<RationalNumberType const*>(type(*index).get()))
                if (bytesType.numBytes() <= integerType->literalValue(nullptr))
                    m_errorReporter.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:
        m_errorReporter.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;
    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.argumentTypes)
        {
            // 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)
            {
                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())
                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.get()))
            annotation.isPure = true;
    return false;
}

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

void TypeChecker::endVisit(Literal const& _literal)
{
    if (_literal.looksLikeAddress())
    {
        if (_literal.passesAddressChecksum())
            _literal.annotation().type = make_shared<IntegerType>(0, IntegerType::Modifier::Address);
        else
            m_errorReporter.warning(
                _literal.location(),
                "This looks like an address but has an invalid checksum. "
                "If this is not used as an address, please prepend '00'."
            );
    }
    if (!_literal.annotation().type)
        _literal.annotation().type = Type::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;
}

void TypeChecker::expectType(Expression const& _expression, Type const& _expectedType)
{
    _expression.accept(*this);
    if (!type(_expression)->isImplicitlyConvertibleTo(_expectedType))
    {
        if (
            type(_expression)->category() == Type::Category::RationalNumber &&
            dynamic_pointer_cast<RationalNumberType const>(type(_expression))->isFractional() &&
            type(_expression)->mobileType()
        )
            m_errorReporter.typeError(
                _expression.location(),
                "Type " +
                type(_expression)->toString() +
                " is not implicitly convertible to expected type " +
                _expectedType.toString() +
                ". Try converting to type " +
                type(_expression)->mobileType()->toString() +
                " or use an explicit conversion."
            );
        else
            m_errorReporter.typeError(
                _expression.location(),
                "Type " +
                type(_expression)->toString() +
                " is not implicitly convertible to expected type " +
                _expectedType.toString() +
                "."
            );
    }

    if (
        type(_expression)->category() == Type::Category::RationalNumber &&
        _expectedType.category() == Type::Category::FixedBytes
    )
    {
        auto literal = dynamic_cast<Literal const*>(&_expression);

        if (literal && !literal->isHexNumber())
            m_errorReporter.warning(
                _expression.location(),
                "Decimal literal assigned to bytesXX variable will be left-aligned. "
                "Use an explicit conversion to silence this warning."
            );
    }

}

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

    if (_expression.annotation().isConstant)
        m_errorReporter.typeError(_expression.location(), "Cannot assign to a constant variable.");
    else if (!_expression.annotation().isLValue)
        m_errorReporter.typeError(_expression.location(), "Expression has to be an lvalue.");
}