lix/src/libexpr/eval-settings.cc

#include "globals.hh"
#include "profiles.hh"
#include "eval.hh"
#include "eval-settings.hh"

namespace nix {

/* Very hacky way to parse $NIX_PATH, which is colon-separated, but
   can contain URLs (e.g. "nixpkgs=https://bla...:foo=https://"). */
static Strings parseNixPath(const std::string & s)
{
    Strings res;

    auto p = s.begin();

    while (p != s.end()) {
        auto start = p;
        auto start2 = p;

        while (p != s.end() && *p != ':') {
            if (*p == '=') start2 = p + 1;
            ++p;
        }

        if (p == s.end()) {
            if (p != start) res.push_back(std::string(start, p));
            break;
        }

        if (*p == ':') {
            auto prefix = std::string(start2, s.end());
            if (EvalSettings::isPseudoUrl(prefix) || prefix.starts_with("flake:")) {
                ++p;
                while (p != s.end() && *p != ':') ++p;
            }
            res.push_back(std::string(start, p));
            if (p == s.end()) break;
        }

        ++p;
    }

    return res;
}

EvalSettings::EvalSettings()
{
    auto var = getEnv("NIX_PATH");
    if (var) nixPath = parseNixPath(*var);
}

Strings EvalSettings::getDefaultNixPath()
{
    Strings res;
    auto add = [&](const Path & p, const std::string & s = std::string()) {
        if (pathAccessible(p)) {
            if (s.empty()) {
                res.push_back(p);
            } else {
                res.push_back(s + "=" + p);
            }
        }
    };

    if (!evalSettings.restrictEval && !evalSettings.pureEval) {
        add(getNixDefExpr() + "/channels");
        add(rootChannelsDir() + "/nixpkgs", "nixpkgs");
        add(rootChannelsDir());
    }

    return res;
}

bool EvalSettings::isPseudoUrl(std::string_view s)
{
    if (s.compare(0, 8, "channel:") == 0) return true;
    size_t pos = s.find("://");
    if (pos == std::string::npos) return false;
    std::string scheme(s, 0, pos);
    return scheme == "http" || scheme == "https" || scheme == "file" || scheme == "channel" || scheme == "git" || scheme == "s3" || scheme == "ssh";
}

std::string EvalSettings::resolvePseudoUrl(std::string_view url)
{
    if (url.starts_with("channel:"))
        return "https://nixos.org/channels/" + std::string(url.substr(8)) + "/nixexprs.tar.xz";
    else
        return std::string(url);
}

const std::string & EvalSettings::getCurrentSystem()
{
    const auto & evalSystem = currentSystem.get();
    return evalSystem != "" ? evalSystem : settings.thisSystem.get();
}

EvalSettings evalSettings;

static GlobalConfig::Register rEvalSettings(&evalSettings);

Path getNixDefExpr()
{
    return settings.useXDGBaseDirectories
        ? getStateDir() + "/nix/defexpr"
        : getHome() + "/.nix-defexpr";
}

}