1 files changed, 55 insertions, 0 deletions
diff --git a/src/libutil/experimental-features.cc b/src/libutil/experimental-features.cc
new file mode 100644
index 000000000..d1235d8a4
--- /dev/null
+++ b/src/libutil/experimental-features.cc
@@ -0,0 +1,55 @@
+#include "experimental-features.hh"
+#include "nlohmann/json.hpp"
+
+namespace nix {
+
+std::map<ExperimentalFeature, std::string> stringifiedXpFeatures = {
+    { Xp::CaDerivations, "ca-derivations" },
+    { Xp::Flakes, "flakes" },
+    { Xp::NixCommand, "nix-command" },
+    { Xp::RecursiveNix, "recursive-nix" },
+    { Xp::NoUrlLiterals, "no-url-literals" },
+};
+
+const std::optional<ExperimentalFeature> parseExperimentalFeature(const std::string_view & name)
+{
+    using ReverseXpMap = std::map<std::string_view, ExperimentalFeature>;
+    static ReverseXpMap * reverseXpMap;
+    if (!reverseXpMap) {
+        reverseXpMap = new ReverseXpMap{};
+        for (auto & [feature, name] : stringifiedXpFeatures)
+            (*reverseXpMap)[name] = feature;
+    }
+
+    auto featureIter = reverseXpMap->find(name);
+    if (featureIter == reverseXpMap->end())
+        return std::nullopt;
+    return {featureIter->second};
+}
+
+std::string_view showExperimentalFeature(const ExperimentalFeature feature)
+{
+    return stringifiedXpFeatures.at(feature);
+}
+
+std::set<ExperimentalFeature> parseFeatures(const std::set<std::string> & rawFeatures)
+{
+    std::set<ExperimentalFeature> res;
+    for (auto & rawFeature : rawFeatures) {
+        if (auto feature = parseExperimentalFeature(rawFeature))
+            res.insert(*feature);
+    }
+    return res;
+}
+
+MissingExperimentalFeature::MissingExperimentalFeature(ExperimentalFeature feature)
+    : Error("experimental Nix feature '%1%' is disabled; use '--extra-experimental-features %1%' to override", showExperimentalFeature(feature))
+    , missingFeature(feature)
+    {}
+
+std::ostream & operator <<(std::ostream & str, const ExperimentalFeature & feature)
+{
+    return str << showExperimentalFeature(feature);
+}
+
+}