path: root/libsolidity/analysis/ViewPureChecker.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/>.
*/

#include <libsolidity/analysis/ViewPureChecker.h>

#include <libevmasm/SemanticInformation.h>

#include <libsolidity/inlineasm/AsmData.h>
#include <libsolidity/ast/ExperimentalFeatures.h>

#include <functional>

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

namespace
{

class AssemblyViewPureChecker: public boost::static_visitor<void>
{
public:
    explicit AssemblyViewPureChecker(std::function<void(StateMutability, SourceLocation const&)> _reportMutability):
        m_reportMutability(_reportMutability) {}

    void operator()(assembly::Label const&) { }
    void operator()(assembly::Instruction const& _instruction)
    {
        checkInstruction(_instruction.location, _instruction.instruction);
    }
    void operator()(assembly::Literal const&) {}
    void operator()(assembly::Identifier const&) {}
    void operator()(assembly::FunctionalInstruction const& _instr)
    {
        checkInstruction(_instr.location, _instr.instruction);
        for (auto const& arg: _instr.arguments)
            boost::apply_visitor(*this, arg);
    }
    void operator()(assembly::ExpressionStatement const& _expr)
    {
        boost::apply_visitor(*this, _expr.expression);
    }
    void operator()(assembly::StackAssignment const&) {}
    void operator()(assembly::Assignment const& _assignment)
    {
        boost::apply_visitor(*this, *_assignment.value);
    }
    void operator()(assembly::VariableDeclaration const& _varDecl)
    {
        if (_varDecl.value)
            boost::apply_visitor(*this, *_varDecl.value);
    }
    void operator()(assembly::FunctionDefinition const& _funDef)
    {
        (*this)(_funDef.body);
    }
    void operator()(assembly::FunctionCall const& _funCall)
    {
        for (auto const& arg: _funCall.arguments)
            boost::apply_visitor(*this, arg);
    }
    void operator()(assembly::If const& _if)
    {
        boost::apply_visitor(*this, *_if.condition);
        (*this)(_if.body);
    }
    void operator()(assembly::Switch const& _switch)
    {
        boost::apply_visitor(*this, *_switch.expression);
        for (auto const& _case: _switch.cases)
        {
            if (_case.value)
                (*this)(*_case.value);
            (*this)(_case.body);
        }
    }
    void operator()(assembly::ForLoop const& _for)
    {
        (*this)(_for.pre);
        boost::apply_visitor(*this, *_for.condition);
        (*this)(_for.body);
        (*this)(_for.post);
    }
    void operator()(assembly::Block const& _block)
    {
        for (auto const& s: _block.statements)
            boost::apply_visitor(*this, s);
    }

private:
    std::function<void(StateMutability, SourceLocation const&)> m_reportMutability;
    void checkInstruction(SourceLocation _location, solidity::Instruction _instruction)
    {
        if (eth::SemanticInformation::invalidInViewFunctions(_instruction))
            m_reportMutability(StateMutability::NonPayable, _location);
        else if (eth::SemanticInformation::invalidInPureFunctions(_instruction))
            m_reportMutability(StateMutability::View, _location);
    }
};

}

bool ViewPureChecker::check()
{
    vector<ContractDefinition const*> contracts;

    for (auto const& node: m_ast)
    {
        SourceUnit const* source = dynamic_cast<SourceUnit const*>(node.get());
        solAssert(source, "");
        contracts += source->filteredNodes<ContractDefinition>(source->nodes());
    }

    // Check modifiers first to infer their state mutability.
    for (auto const& contract: contracts)
        for (ModifierDefinition const* mod: contract->functionModifiers())
            mod->accept(*this);

    for (auto const& contract: contracts)
        contract->accept(*this);

    return !m_errors;
}



bool ViewPureChecker::visit(FunctionDefinition const& _funDef)
{
    solAssert(!m_currentFunction, "");
    m_currentFunction = &_funDef;
    m_bestMutabilityAndLocation = {StateMutability::Pure, _funDef.location()};
    return true;
}

void ViewPureChecker::endVisit(FunctionDefinition const& _funDef)
{
    solAssert(m_currentFunction == &_funDef, "");
    if (
        m_bestMutabilityAndLocation.mutability < _funDef.stateMutability() &&
        _funDef.stateMutability() != StateMutability::Payable &&
        _funDef.isImplemented() &&
        !_funDef.isConstructor() &&
        !_funDef.isFallback() &&
        !_funDef.annotation().superFunction
    )
        m_errorReporter.warning(
            _funDef.location(),
            "Function state mutability can be restricted to " + stateMutabilityToString(m_bestMutabilityAndLocation.mutability)
        );
    m_currentFunction = nullptr;
}

bool ViewPureChecker::visit(ModifierDefinition const& _modifier)
{
    solAssert(m_currentFunction == nullptr, "");
    m_bestMutabilityAndLocation = {StateMutability::Pure, _modifier.location()};
    return true;
}

void ViewPureChecker::endVisit(ModifierDefinition const& _modifierDef)
{
    solAssert(m_currentFunction == nullptr, "");
    m_inferredMutability[&_modifierDef] = std::move(m_bestMutabilityAndLocation);
}

void ViewPureChecker::endVisit(Identifier const& _identifier)
{
    Declaration const* declaration = _identifier.annotation().referencedDeclaration;
    solAssert(declaration, "");

    StateMutability mutability = StateMutability::Pure;

    bool writes = _identifier.annotation().lValueRequested;
    if (VariableDeclaration const* varDecl = dynamic_cast<VariableDeclaration const*>(declaration))
    {
        if (varDecl->isStateVariable() && !varDecl->isConstant())
            mutability = writes ? StateMutability::NonPayable : StateMutability::View;
    }
    else if (MagicVariableDeclaration const* magicVar = dynamic_cast<MagicVariableDeclaration const*>(declaration))
    {
        switch (magicVar->type()->category())
        {
        case Type::Category::Contract:
            solAssert(_identifier.name() == "this" || _identifier.name() == "super", "");
            if (!dynamic_cast<ContractType const&>(*magicVar->type()).isSuper())
                // reads the address
                mutability = StateMutability::View;
            break;
        case Type::Category::Integer:
            solAssert(_identifier.name() == "now", "");
            mutability = StateMutability::View;
            break;
        default:
            break;
        }
    }

    reportMutability(mutability, _identifier.location());
}

void ViewPureChecker::endVisit(InlineAssembly const& _inlineAssembly)
{
    AssemblyViewPureChecker{
        [=](StateMutability _mutability, SourceLocation const& _location) { reportMutability(_mutability, _location); }
    }(_inlineAssembly.operations());
}

void ViewPureChecker::reportMutability(
    StateMutability _mutability,
    SourceLocation const& _location,
    boost::optional<SourceLocation> const& _nestedLocation
)
{
    if (_mutability > m_bestMutabilityAndLocation.mutability)
        m_bestMutabilityAndLocation = MutabilityAndLocation{_mutability, _location};
    if (!m_currentFunction || _mutability <= m_currentFunction->stateMutability())
        return;

    // Check for payable here, because any occurrence of `msg.value`
    // will set mutability to payable.
    if (_mutability == StateMutability::View || (
        _mutability == StateMutability::Payable &&
        m_currentFunction->stateMutability() == StateMutability::Pure
    ))
    {
        m_errorReporter.typeError(
            _location,
            "Function declared as pure, but this expression (potentially) reads from the "
            "environment or state and thus requires \"view\"."
        );
        m_errors = true;
    }
    else if (_mutability == StateMutability::NonPayable)
    {
        m_errorReporter.typeError(
            _location,
            "Function declared as " +
            stateMutabilityToString(m_currentFunction->stateMutability()) +
            ", but this expression (potentially) modifies the state and thus "
            "requires non-payable (the default) or payable."
        );
        m_errors = true;
    }
    else if (_mutability == StateMutability::Payable)
    {
        // We do not warn for library functions because they cannot be payable anyway.
        // Also internal functions should be allowed to use `msg.value`.
        if (m_currentFunction->isPublic() && m_currentFunction->inContractKind() != ContractDefinition::ContractKind::Library)
        {
            if (_nestedLocation)
                m_errorReporter.typeError(
                    _location,
                    SecondarySourceLocation().append("\"msg.value\" appears here inside the modifier.", *_nestedLocation),
                    "This modifier uses \"msg.value\" and thus the function has to be payable or internal."
                );
            else
                m_errorReporter.typeError(
                    _location,
                    "\"msg.value\" can only be used in payable public functions. Make the function "
                    "\"payable\" or use an internal function to avoid this error."
                );
            m_errors = true;
        }
    }
    else
        solAssert(false, "");

    solAssert(
        m_currentFunction->stateMutability() == StateMutability::View ||
        m_currentFunction->stateMutability() == StateMutability::Pure ||
        m_currentFunction->stateMutability() == StateMutability::NonPayable,
        ""
    );
}

void ViewPureChecker::endVisit(FunctionCall const& _functionCall)
{
    if (_functionCall.annotation().kind != FunctionCallKind::FunctionCall)
        return;

    StateMutability mutability = dynamic_cast<FunctionType const&>(*_functionCall.expression().annotation().type).stateMutability();
    // We only require "nonpayable" to call a payble function.
    if (mutability == StateMutability::Payable)
        mutability = StateMutability::NonPayable;
    reportMutability(mutability, _functionCall.location());
}

bool ViewPureChecker::visit(MemberAccess const& _memberAccess)
{
    // Catch the special case of `this.f.selector` which is a pure expression.
    ASTString const& member = _memberAccess.memberName();
    if (
        _memberAccess.expression().annotation().type->category() == Type::Category::Function &&
        member == "selector"
    )
        if (auto const* expr = dynamic_cast<MemberAccess const*>(&_memberAccess.expression()))
            if (auto const* exprInt = dynamic_cast<Identifier const*>(&expr->expression()))
                if (exprInt->name() == "this")
                    // Do not continue visiting.
                    return false;
    return true;
}

void ViewPureChecker::endVisit(MemberAccess const& _memberAccess)
{
    StateMutability mutability = StateMutability::Pure;
    bool writes = _memberAccess.annotation().lValueRequested;

    ASTString const& member = _memberAccess.memberName();
    switch (_memberAccess.expression().annotation().type->category())
    {
    case Type::Category::Address:
        if (member == "balance")
            mutability = StateMutability::View;
        break;
    case Type::Category::Magic:
    {
        using MagicMember = pair<MagicType::Kind, string>;
        set<MagicMember> static const pureMembers{
            {MagicType::Kind::ABI, "decode"},
            {MagicType::Kind::ABI, "encode"},
            {MagicType::Kind::ABI, "encodePacked"},
            {MagicType::Kind::ABI, "encodeWithSelector"},
            {MagicType::Kind::ABI, "encodeWithSignature"},
            {MagicType::Kind::Block, "blockhash"},
            {MagicType::Kind::Message, "data"},
            {MagicType::Kind::Message, "sig"}
        };
        set<MagicMember> static const payableMembers{
            {MagicType::Kind::Message, "value"}
        };

        auto const& type = dynamic_cast<MagicType const&>(*_memberAccess.expression().annotation().type);
        MagicMember magicMember(type.kind(), member);

        if (!pureMembers.count(magicMember))
            mutability = StateMutability::View;
        if (payableMembers.count(magicMember))
            mutability = StateMutability::Payable;
        break;
    }
    case Type::Category::Struct:
    {
        if (_memberAccess.expression().annotation().type->dataStoredIn(DataLocation::Storage))
            mutability = writes ? StateMutability::NonPayable : StateMutability::View;
        break;
    }
    case Type::Category::Array:
    {
        auto const& type = dynamic_cast<ArrayType const&>(*_memberAccess.expression().annotation().type);
        if (member == "length" && type.isDynamicallySized() && type.dataStoredIn(DataLocation::Storage))
            mutability = writes ? StateMutability::NonPayable : StateMutability::View;
        break;
    }
    default:
        break;
    }
    reportMutability(mutability, _memberAccess.location());
}

void ViewPureChecker::endVisit(IndexAccess const& _indexAccess)
{
    if (!_indexAccess.indexExpression())
        solAssert(_indexAccess.annotation().type->category() == Type::Category::TypeType, "");
    else
    {
        bool writes = _indexAccess.annotation().lValueRequested;
        if (_indexAccess.baseExpression().annotation().type->dataStoredIn(DataLocation::Storage))
            reportMutability(writes ? StateMutability::NonPayable : StateMutability::View, _indexAccess.location());
    }
}

void ViewPureChecker::endVisit(ModifierInvocation const& _modifier)
{
    solAssert(_modifier.name(), "");
    if (ModifierDefinition const* mod = dynamic_cast<decltype(mod)>(_modifier.name()->annotation().referencedDeclaration))
    {
        solAssert(m_inferredMutability.count(mod), "");
        auto const& mutAndLocation = m_inferredMutability.at(mod);
        reportMutability(mutAndLocation.mutability, _modifier.location(), mutAndLocation.location);
    }
    else
        solAssert(dynamic_cast<ContractDefinition const*>(_modifier.name()->annotation().referencedDeclaration), "");
}