libutil: Optimize feature checks

Instead of doing a linear search on an std::set, we use a bitset enum.

Change-Id: Ide537f6cffdd16d06e59aaeb2e4ac0acb6493421

src/libutil/config-impl.hh

@@ -30,11 +30,11 @@ template<> struct BaseSetting<StringMap>::trait
 {
     static constexpr bool appendable = true;
 };
-template<> struct BaseSetting<std::set<ExperimentalFeature>>::trait
+template<> struct BaseSetting<ExperimentalFeatures>::trait
 {
     static constexpr bool appendable = true;
 };
-template<> struct BaseSetting<std::set<DeprecatedFeature>>::trait
+template<> struct BaseSetting<DeprecatedFeatures>::trait
 {
     static constexpr bool appendable = true;
 };
@@ -54,8 +54,8 @@ bool BaseSetting<T>::isAppendable()
 template<> void BaseSetting<Strings>::appendOrSet(Strings newValue, bool append);
 template<> void BaseSetting<StringSet>::appendOrSet(StringSet newValue, bool append);
 template<> void BaseSetting<StringMap>::appendOrSet(StringMap newValue, bool append);
-template<> void BaseSetting<std::set<ExperimentalFeature>>::appendOrSet(std::set<ExperimentalFeature> newValue, bool append);
-template<> void BaseSetting<std::set<DeprecatedFeature>>::appendOrSet(std::set<DeprecatedFeature> newValue, bool append);
+template<> void BaseSetting<ExperimentalFeatures>::appendOrSet(ExperimentalFeatures newValue, bool append);
+template<> void BaseSetting<DeprecatedFeatures>::appendOrSet(DeprecatedFeatures newValue, bool append);
 
 template<typename T>
 void BaseSetting<T>::appendOrSet(T newValue, bool append)
@@ -120,8 +120,8 @@ DECLARE_CONFIG_SERIALISER(bool)
 DECLARE_CONFIG_SERIALISER(Strings)
 DECLARE_CONFIG_SERIALISER(StringSet)
 DECLARE_CONFIG_SERIALISER(StringMap)
-DECLARE_CONFIG_SERIALISER(std::set<ExperimentalFeature>)
-DECLARE_CONFIG_SERIALISER(std::set<DeprecatedFeature>)
+DECLARE_CONFIG_SERIALISER(ExperimentalFeatures)
+DECLARE_CONFIG_SERIALISER(DeprecatedFeatures)
 
 template<typename T>
 T BaseSetting<T>::parse(const std::string & str) const

src/libutil/config.cc

@@ -330,55 +330,61 @@ template<> std::string BaseSetting<StringSet>::to_string() const
     return concatStringsSep(" ", value);
 }
 
-template<> std::set<ExperimentalFeature> BaseSetting<std::set<ExperimentalFeature>>::parse(const std::string & str) const
+template<> ExperimentalFeatures BaseSetting<ExperimentalFeatures>::parse(const std::string & str) const
 {
-    std::set<ExperimentalFeature> res;
+    ExperimentalFeatures res{};
     for (auto & s : tokenizeString<StringSet>(str)) {
         if (auto thisXpFeature = parseExperimentalFeature(s); thisXpFeature)
-            res.insert(thisXpFeature.value());
+            res = res | thisXpFeature.value();
         else
             warn("unknown experimental feature '%s'", s);
     }
     return res;
 }
 
-template<> void BaseSetting<std::set<ExperimentalFeature>>::appendOrSet(std::set<ExperimentalFeature> newValue, bool append)
+template<> void BaseSetting<ExperimentalFeatures>::appendOrSet(ExperimentalFeatures newValue, bool append)
 {
-    if (!append) value.clear();
-    value.insert(std::make_move_iterator(newValue.begin()), std::make_move_iterator(newValue.end()));
+    if (append)
+        value = value | newValue;
+    else
+        value = newValue;
 }
 
-template<> std::string BaseSetting<std::set<ExperimentalFeature>>::to_string() const
+template<> std::string BaseSetting<ExperimentalFeatures>::to_string() const
 {
     StringSet stringifiedXpFeatures;
-    for (const auto & feature : value)
-        stringifiedXpFeatures.insert(std::string(showExperimentalFeature(feature)));
+    for (size_t tag = 0; tag < sizeof(ExperimentalFeatures) * CHAR_BIT; tag++)
+        if ((value & ExperimentalFeature(tag)) != ExperimentalFeatures{})
+            stringifiedXpFeatures.insert(std::string(showExperimentalFeature(ExperimentalFeature(tag))));
     return concatStringsSep(" ", stringifiedXpFeatures);
 }
 
-template<> std::set<DeprecatedFeature> BaseSetting<std::set<DeprecatedFeature>>::parse(const std::string & str) const
+template<> DeprecatedFeatures BaseSetting<DeprecatedFeatures>::parse(const std::string & str) const
 {
-    std::set<DeprecatedFeature> res;
+    DeprecatedFeatures res{};
     for (auto & s : tokenizeString<StringSet>(str)) {
         if (auto thisDpFeature = parseDeprecatedFeature(s); thisDpFeature)
-            res.insert(thisDpFeature.value());
+            res = res | thisDpFeature.value();
         else
             warn("unknown deprecated feature '%s'", s);
     }
     return res;
 }
 
-template<> void BaseSetting<std::set<DeprecatedFeature>>::appendOrSet(std::set<DeprecatedFeature> newValue, bool append)
+template<> void BaseSetting<DeprecatedFeatures>::appendOrSet(DeprecatedFeatures newValue, bool append)
 {
-    if (!append) value.clear();
-    value.insert(std::make_move_iterator(newValue.begin()), std::make_move_iterator(newValue.end()));
+    if (append)
+        value = value | newValue;
+    else
+        value = newValue;
 }
 
-template<> std::string BaseSetting<std::set<DeprecatedFeature>>::to_string() const
+template<> std::string BaseSetting<DeprecatedFeatures>::to_string() const
 {
     StringSet stringifiedDpFeatures;
-    for (const auto & feature : value)
-        stringifiedDpFeatures.insert(std::string(showDeprecatedFeature(feature)));
+    for (size_t tag = 0; tag < sizeof(DeprecatedFeatures) * CHAR_BIT; tag++)
+        if ((value & DeprecatedFeature(tag)) != DeprecatedFeatures{})
+            stringifiedDpFeatures.insert(std::string(showDeprecatedFeature(DeprecatedFeature(tag))));
     return concatStringsSep(" ", stringifiedDpFeatures);
 }
 
@@ -417,8 +423,8 @@ template class BaseSetting<std::string>;
 template class BaseSetting<Strings>;
 template class BaseSetting<StringSet>;
 template class BaseSetting<StringMap>;
-template class BaseSetting<std::set<ExperimentalFeature>>;
-template class BaseSetting<std::set<DeprecatedFeature>>;
+template class BaseSetting<ExperimentalFeatures>;
+template class BaseSetting<DeprecatedFeatures>;
 
 static Path parsePath(const AbstractSetting & s, const std::string & str)
 {
@@ -562,7 +568,7 @@ static GlobalConfig::Register rSettings(&experimentalFeatureSettings);
 bool FeatureSettings::isEnabled(const ExperimentalFeature & feature) const
 {
     auto & f = experimentalFeatures.get();
-    return std::find(f.begin(), f.end(), feature) != f.end();
+    return (f & feature) != ExperimentalFeatures{};
 }
 
 void FeatureSettings::require(const ExperimentalFeature & feature) const
@@ -584,7 +590,7 @@ void FeatureSettings::require(const std::optional<ExperimentalFeature> & feature
 bool FeatureSettings::isEnabled(const DeprecatedFeature & feature) const
 {
     auto & f = deprecatedFeatures.get();
-    return std::find(f.begin(), f.end(), feature) != f.end();
+    return (f & feature) != DeprecatedFeatures{};
 }
 
 void FeatureSettings::require(const DeprecatedFeature & feature) const

src/libutil/config.hh

@@ -444,7 +444,7 @@ extern GlobalConfig globalConfig;
 
 struct FeatureSettings : Config {
 
-    Setting<std::set<ExperimentalFeature>> experimentalFeatures{
+    Setting<ExperimentalFeatures> experimentalFeatures{
         this, {}, "experimental-features",
         R"(
           Experimental features that are enabled.
@@ -484,8 +484,7 @@ struct FeatureSettings : Config {
      * disabled, and so the function does nothing in that case.
      */
     void require(const std::optional<ExperimentalFeature> &) const;
-
-    Setting<std::set<DeprecatedFeature>> deprecatedFeatures{
+    Setting<DeprecatedFeatures> deprecatedFeatures{
         this, {}, "deprecated-features",
         R"(
           Deprecated features that are allowed.

src/libutil/deprecated-features.cc

@@ -77,12 +77,12 @@ nlohmann::json documentDeprecatedFeatures()
     return (nlohmann::json) res;
 }
 
-std::set<DeprecatedFeature> parseDeprecatedFeatures(const std::set<std::string> & rawFeatures)
+DeprecatedFeatures parseDeprecatedFeatures(const std::set<std::string> & rawFeatures)
 {
-    std::set<DeprecatedFeature> res;
+    DeprecatedFeatures res{};
     for (auto & rawFeature : rawFeatures)
         if (auto feature = parseDeprecatedFeature(rawFeature))
-            res.insert(*feature);
+            res = res | *feature;
     return res;
 }
 

src/libutil/deprecated-features.hh

@@ -18,9 +18,23 @@ namespace nix {
  */
 enum struct DeprecatedFeature
 {
-    UrlLiterals
+    UrlLiterals,
 };
 
+enum struct DeprecatedFeatures {};
+
+inline DeprecatedFeatures operator| (DeprecatedFeatures a, DeprecatedFeatures b) {
+    return static_cast<DeprecatedFeatures>(static_cast<size_t>(a) | static_cast<size_t>(b));
+}
+
+inline DeprecatedFeatures operator| (DeprecatedFeatures a, DeprecatedFeature b) {
+    return a | static_cast<DeprecatedFeatures>(1 << static_cast<size_t>(b));
+}
+
+inline DeprecatedFeatures operator& (DeprecatedFeatures a, DeprecatedFeature b) {
+    return static_cast<DeprecatedFeatures>(static_cast<size_t>(a) & (1 << static_cast<size_t>(b)));
+}
+
 /**
  * Just because writing `DeprecatedFeature::UrlLiterals` is way too long
  */
@@ -50,7 +64,7 @@ std::ostream & operator<<(
  * Parse a set of strings to the corresponding set of deprecated
  * features, ignoring (but warning for) any unknown feature.
  */
-std::set<DeprecatedFeature> parseDeprecatedFeatures(const std::set<std::string> &);
+DeprecatedFeatures parseDeprecatedFeatures(const std::set<std::string> &);
 
 /**
  * A deprecated feature used for some

src/libutil/experimental-features.cc

@@ -293,12 +293,12 @@ nlohmann::json documentExperimentalFeatures()
     return (nlohmann::json) res;
 }
 
-std::set<ExperimentalFeature> parseFeatures(const std::set<std::string> & rawFeatures)
+ExperimentalFeatures parseFeatures(const std::set<std::string> & rawFeatures)
 {
-    std::set<ExperimentalFeature> res;
+    ExperimentalFeatures res {};
     for (auto & rawFeature : rawFeatures)
         if (auto feature = parseExperimentalFeature(rawFeature))
-            res.insert(*feature);
+            res = res | *feature;
     return res;
 }
 

src/libutil/experimental-features.hh

@@ -33,6 +33,20 @@ enum struct ExperimentalFeature
     ReplAutomation,
 };
 
+enum struct ExperimentalFeatures {};
+
+inline ExperimentalFeatures operator| (ExperimentalFeatures a, ExperimentalFeatures b) {
+    return static_cast<ExperimentalFeatures>(static_cast<size_t>(a) | static_cast<size_t>(b));
+}
+
+inline ExperimentalFeatures operator| (ExperimentalFeatures a, ExperimentalFeature b) {
+    return a | static_cast<ExperimentalFeatures>(1 << static_cast<size_t>(b));
+}
+
+inline ExperimentalFeatures operator& (ExperimentalFeatures a, ExperimentalFeature b) {
+    return static_cast<ExperimentalFeatures>(static_cast<size_t>(a) & (1 << static_cast<size_t>(b)));
+}
+
 /**
  * Just because writing `ExperimentalFeature::CaDerivations` is way too long
  */
@@ -62,7 +76,7 @@ std::ostream & operator<<(
  * Parse a set of strings to the corresponding set of experimental
  * features, ignoring (but warning for) any unknown feature.
  */
-std::set<ExperimentalFeature> parseFeatures(const std::set<std::string> &);
+ExperimentalFeatures parseFeatures(const std::set<std::string> &);
 
 /**
  * An experimental feature was required for some (experimental)

src/nix/main.cc

@@ -378,11 +378,10 @@ void mainWrapped(int argc, char * * argv)
     }
 
     if (argc == 2 && std::string(argv[1]) == "__dump-language") {
-        experimentalFeatureSettings.experimentalFeatures = {
-            Xp::Flakes,
-            Xp::FetchClosure,
-            Xp::DynamicDerivations,
-        };
+        experimentalFeatureSettings.experimentalFeatures = ExperimentalFeatures{}
+            | Xp::Flakes
+            | Xp::FetchClosure
+            | Xp::DynamicDerivations;
         evalSettings.pureEval = false;
         EvalState state({}, openStore("dummy://"));
         auto res = nlohmann::json::object();