lix/src/libexpr/eval-cache.cc

#include "eval-cache.hh"
#include "sqlite.hh"
#include "eval.hh"
#include "eval-inline.hh"

namespace nix::eval_cache {

// FIXME: inefficient representation of attrs
static const char * schema = R"sql(
create table if not exists Attributes (
    parent      integer not null,
    name        text,
    type        integer not null,
    value       text,
    primary key (parent, name)
);
)sql";

struct AttrDb
{
    struct State
    {
        SQLite db;
        SQLiteStmt insertAttribute;
        SQLiteStmt queryAttribute;
        SQLiteStmt queryAttributes;
        std::unique_ptr<SQLiteTxn> txn;
    };

    std::unique_ptr<Sync<State>> _state;

    AttrDb(const Hash & fingerprint)
        : _state(std::make_unique<Sync<State>>())
    {
        auto state(_state->lock());

        Path cacheDir = getCacheDir() + "/nix/eval-cache-v1";
        createDirs(cacheDir);

        Path dbPath = cacheDir + "/" + fingerprint.to_string(Base16, false) + ".sqlite";

        state->db = SQLite(dbPath);
        state->db.isCache();
        state->db.exec(schema);

        state->insertAttribute.create(state->db,
            "insert or replace into Attributes(parent, name, type, value) values (?, ?, ?, ?)");

        state->queryAttribute.create(state->db,
            "select rowid, type, value from Attributes where parent = ? and name = ?");

        state->queryAttributes.create(state->db,
            "select name from Attributes where parent = ?");

        state->txn = std::make_unique<SQLiteTxn>(state->db);
    }

    ~AttrDb()
    {
        try {
            auto state(_state->lock());
            state->txn->commit();
            state->txn.reset();
        } catch (...) {
            ignoreException();
        }
    }

    AttrId setAttrs(
        AttrKey key,
        const std::vector<Symbol> & attrs)
    {
        auto state(_state->lock());

        state->insertAttribute.use()
            (key.first)
            (key.second)
            (AttrType::FullAttrs)
            (0, false).exec();

        AttrId rowId = state->db.getLastInsertedRowId();
        assert(rowId);

        for (auto & attr : attrs)
            state->insertAttribute.use()
                (rowId)
                (attr)
                (AttrType::Placeholder)
                (0, false).exec();

        return rowId;
    }

    AttrId setString(
        AttrKey key,
        std::string_view s)
    {
        auto state(_state->lock());

        state->insertAttribute.use()
            (key.first)
            (key.second)
            (AttrType::String)
            (s).exec();

        return state->db.getLastInsertedRowId();
    }

    AttrId setPlaceholder(AttrKey key)
    {
        auto state(_state->lock());

        state->insertAttribute.use()
            (key.first)
            (key.second)
            (AttrType::Placeholder)
            (0, false).exec();

        return state->db.getLastInsertedRowId();
    }

    AttrId setMissing(AttrKey key)
    {
        auto state(_state->lock());

        state->insertAttribute.use()
            (key.first)
            (key.second)
            (AttrType::Missing)
            (0, false).exec();

        return state->db.getLastInsertedRowId();
    }

    AttrId setMisc(AttrKey key)
    {
        auto state(_state->lock());

        state->insertAttribute.use()
            (key.first)
            (key.second)
            (AttrType::Misc)
            (0, false).exec();

        return state->db.getLastInsertedRowId();
    }

    AttrId setFailed(AttrKey key)
    {
        auto state(_state->lock());

        state->insertAttribute.use()
            (key.first)
            (key.second)
            (AttrType::Failed)
            (0, false).exec();

        return state->db.getLastInsertedRowId();
    }

    std::optional<std::pair<AttrId, AttrValue>> getAttr(
        AttrKey key,
        SymbolTable & symbols)
    {
        auto state(_state->lock());

        auto queryAttribute(state->queryAttribute.use()(key.first)(key.second));
        if (!queryAttribute.next()) return {};

        auto rowId = (AttrType) queryAttribute.getInt(0);
        auto type = (AttrType) queryAttribute.getInt(1);

        if (type == AttrType::Placeholder)
            return {{rowId, placeholder_t()}};
        else if (type == AttrType::FullAttrs) {
            // FIXME: expensive, should separate this out.
            std::vector<Symbol> attrs;
            auto queryAttributes(state->queryAttributes.use()(rowId));
            while (queryAttributes.next())
                attrs.push_back(symbols.create(queryAttributes.getStr(0)));
            return {{rowId, attrs}};
        } else if (type == AttrType::String) {
            return {{rowId, queryAttribute.getStr(2)}};
        } else if (type == AttrType::Missing) {
            return {{rowId, missing_t()}};
        } else if (type == AttrType::Misc) {
            return {{rowId, misc_t()}};
        } else if (type == AttrType::Failed) {
            return {{rowId, failed_t()}};
        } else
            throw Error("unexpected type in evaluation cache");
    }
};

EvalCache::EvalCache(
    bool useCache,
    const Hash & fingerprint,
    EvalState & state,
    RootLoader rootLoader)
    : db(useCache ? std::make_shared<AttrDb>(fingerprint) : nullptr)
    , state(state)
    , rootLoader(rootLoader)
{
}

Value * EvalCache::getRootValue()
{
    if (!value) {
        debug("getting root value");
        value = allocRootValue(rootLoader());
    }
    return *value;
}

std::shared_ptr<AttrCursor> EvalCache::getRoot()
{
    return std::make_shared<AttrCursor>(ref(shared_from_this()), std::nullopt);
}

AttrCursor::AttrCursor(
    ref<EvalCache> root,
    Parent parent,
    Value * value,
    std::optional<std::pair<AttrId, AttrValue>> && cachedValue)
    : root(root), parent(parent), cachedValue(std::move(cachedValue))
{
    if (value)
        _value = allocRootValue(value);
}

AttrKey AttrCursor::getKey()
{
    if (!parent)
        return {0, root->state.sEpsilon};
    if (!parent->first->cachedValue) {
        parent->first->cachedValue = root->db->getAttr(
            parent->first->getKey(), root->state.symbols);
        assert(parent->first->cachedValue);
    }
    return {parent->first->cachedValue->first, parent->second};
}

Value & AttrCursor::getValue()
{
    if (!_value) {
        if (parent) {
            auto & vParent = parent->first->getValue();
            root->state.forceAttrs(vParent);
            auto attr = vParent.attrs->get(parent->second);
            if (!attr)
                throw Error("attribute '%s' is unexpectedly missing", getAttrPathStr());
            _value = allocRootValue(attr->value);
        } else
            _value = allocRootValue(root->getRootValue());
    }
    return **_value;
}

std::vector<Symbol> AttrCursor::getAttrPath() const
{
    if (parent) {
        auto attrPath = parent->first->getAttrPath();
        attrPath.push_back(parent->second);
        return attrPath;
    } else
        return {};
}

std::vector<Symbol> AttrCursor::getAttrPath(Symbol name) const
{
    auto attrPath = getAttrPath();
    attrPath.push_back(name);
    return attrPath;
}

std::string AttrCursor::getAttrPathStr() const
{
    return concatStringsSep(".", getAttrPath());
}

std::string AttrCursor::getAttrPathStr(Symbol name) const
{
    return concatStringsSep(".", getAttrPath(name));
}

Value & AttrCursor::forceValue()
{
    debug("evaluating uncached attribute %s", getAttrPathStr());

    auto & v = getValue();

    try {
        root->state.forceValue(v);
    } catch (EvalError &) {
        debug("setting '%s' to failed", getAttrPathStr());
        if (root->db)
            cachedValue = {root->db->setFailed(getKey()), failed_t()};
        throw;
    }

    if (root->db && (!cachedValue || std::get_if<placeholder_t>(&cachedValue->second))) {
        if (v.type == tString)
            cachedValue = {root->db->setString(getKey(), v.string.s), v.string.s};
        else if (v.type == tAttrs)
            ; // FIXME: do something?
        else
            cachedValue = {root->db->setMisc(getKey()), misc_t()};
    }

    return v;
}

std::shared_ptr<AttrCursor> AttrCursor::maybeGetAttr(Symbol name)
{
    if (root->db) {
        if (!cachedValue)
            cachedValue = root->db->getAttr(getKey(), root->state.symbols);

        if (cachedValue) {
            if (auto attrs = std::get_if<std::vector<Symbol>>(&cachedValue->second)) {
                for (auto & attr : *attrs)
                    if (attr == name)
                        return std::make_shared<AttrCursor>(root, std::make_pair(shared_from_this(), name));
                return nullptr;
            } else if (std::get_if<placeholder_t>(&cachedValue->second)) {
                auto attr = root->db->getAttr({cachedValue->first, name}, root->state.symbols);
                if (attr) {
                    if (std::get_if<missing_t>(&attr->second))
                        return nullptr;
                    else if (std::get_if<failed_t>(&attr->second))
                        throw EvalError("cached failure of attribute '%s'", getAttrPathStr(name));
                    else
                        return std::make_shared<AttrCursor>(root,
                            std::make_pair(shared_from_this(), name), nullptr, std::move(attr));
                }
                // Incomplete attrset, so need to fall thru and
                // evaluate to see whether 'name' exists
            } else
                return nullptr;
                //throw TypeError("'%s' is not an attribute set", getAttrPathStr());
        }
    }

    auto & v = forceValue();

    if (v.type != tAttrs)
        return nullptr;
        //throw TypeError("'%s' is not an attribute set", getAttrPathStr());

    auto attr = v.attrs->get(name);

    if (!attr) {
        if (root->db) {
            if (!cachedValue)
                cachedValue = {root->db->setPlaceholder(getKey()), placeholder_t()};
            root->db->setMissing({cachedValue->first, name});
        }
        return nullptr;
    }

    std::optional<std::pair<AttrId, AttrValue>> cachedValue2;
    if (root->db) {
        if (!cachedValue)
            cachedValue = {root->db->setPlaceholder(getKey()), placeholder_t()};
        cachedValue2 = {root->db->setPlaceholder({cachedValue->first, name}), placeholder_t()};
    }

    return std::make_shared<AttrCursor>(
        root, std::make_pair(shared_from_this(), name), attr->value, std::move(cachedValue2));
}

std::shared_ptr<AttrCursor> AttrCursor::maybeGetAttr(std::string_view name)
{
    return maybeGetAttr(root->state.symbols.create(name));
}

std::shared_ptr<AttrCursor> AttrCursor::getAttr(Symbol name)
{
    auto p = maybeGetAttr(name);
    if (!p)
        throw Error("attribute '%s' does not exist", getAttrPathStr(name));
    return p;
}

std::shared_ptr<AttrCursor> AttrCursor::getAttr(std::string_view name)
{
    return getAttr(root->state.symbols.create(name));
}

std::shared_ptr<AttrCursor> AttrCursor::findAlongAttrPath(const std::vector<Symbol> & attrPath)
{
    auto res = shared_from_this();
    for (auto & attr : attrPath) {
        res = res->maybeGetAttr(attr);
        if (!res) return {};
    }
    return res;
}

std::string AttrCursor::getString()
{
    if (root->db) {
        if (!cachedValue)
            cachedValue = root->db->getAttr(getKey(), root->state.symbols);
        if (cachedValue && !std::get_if<placeholder_t>(&cachedValue->second)) {
            if (auto s = std::get_if<std::string>(&cachedValue->second)) {
                debug("using cached string attribute '%s'", getAttrPathStr());
                return *s;
            } else
                throw TypeError("'%s' is not a string", getAttrPathStr());
        }
    }

    auto & v = forceValue();

    if (v.type != tString)
        throw TypeError("'%s' is not a string", getAttrPathStr());

    return v.string.s;
}

std::vector<Symbol> AttrCursor::getAttrs()
{
    if (root->db) {
        if (!cachedValue)
            cachedValue = root->db->getAttr(getKey(), root->state.symbols);
        if (cachedValue && !std::get_if<placeholder_t>(&cachedValue->second)) {
            if (auto attrs = std::get_if<std::vector<Symbol>>(&cachedValue->second)) {
                debug("using cached attrset attribute '%s'", getAttrPathStr());
                return *attrs;
            } else
                throw TypeError("'%s' is not an attribute set", getAttrPathStr());
        }
    }

    auto & v = forceValue();

    if (v.type != tAttrs)
        throw TypeError("'%s' is not an attribute set", getAttrPathStr());

    std::vector<Symbol> attrs;
    for (auto & attr : *getValue().attrs)
        attrs.push_back(attr.name);
    std::sort(attrs.begin(), attrs.end(), [](const Symbol & a, const Symbol & b) {
        return (const string &) a < (const string &) b;
    });

    if (root->db)
        cachedValue = {root->db->setAttrs(getKey(), attrs), attrs};

    return attrs;
}

bool AttrCursor::isDerivation()
{
    auto aType = maybeGetAttr("type");
    return aType && aType->getString() == "derivation";
}

}