Change features default behavior in Env (RIPD-1460):

Enable all supported amendments in Env by default. Rename `features()`
to `with_features()` and add `all_features_except()` to support feature
subsets in Env. Refactor internal feature handling based on a bitset.

src/ripple/protocol/Feature.h

@@ -21,18 +21,124 @@
 #define RIPPLE_PROTOCOL_FEATURE_H_INCLUDED
 
 #include <ripple/basics/base_uint.h>
+#include <boost/container/flat_map.hpp>
+#include <boost/optional.hpp>
+#include <array>
+#include <bitset>
 #include <string>
 
+/**
+ * @page Feature How to add new features
+ *
+ * Steps required to add new features to the code:
+ *
+ * 1) add the new feature name to the featureNames array below
+ * 2) add a uint256 declaration for the feature to the bottom of this file
+ * 3) add a uint256 definition for the feature to the corresponding source
+ *    file (Feature.cpp)
+ * 4) if the feature is going to be supported in the near future, add its
+ *    sha512half value and name (matching exactly the featureName here) to the
+ *    supportedAmendments in Amendments.cpp.
+ *
+ */
+
 namespace ripple {
 
-/** Convert feature description to feature id. */
-/** @{ */
-uint256
-feature (std::string const& name);
+namespace detail {
+
+class FeatureCollections
+{
+    static constexpr char const* const featureNames[] =
+        {"MultiSign",
+         "Tickets",
+         "TrustSetAuth",
+         "FeeEscalation",
+         "OwnerPaysFee",
+         "CompareFlowV1V2",
+         "SHAMapV2",
+         "PayChan",
+         "Flow",
+         "CompareTakerFlowCross",
+         "FlowCross",
+         "CryptoConditions",
+         "TickSize",
+         "fix1368",
+         "Escrow",
+         "CryptoConditionsSuite",
+         "fix1373",
+         "EnforceInvariants"};
+
+    std::vector<uint256> features;
+    boost::container::flat_map<uint256, std::size_t> featureToIndex;
+    boost::container::flat_map<std::string, uint256> nameToFeature;
+
+public:
+    FeatureCollections();
+
+    static constexpr std::size_t numFeatures()
+    {
+        return sizeof (featureNames) / sizeof (featureNames[0]);
+    }
+
+    boost::optional<uint256>
+    getRegisteredFeature(std::string const& name) const;
+
+    std::size_t
+    featureToBitsetIndex(uint256 const& f) const;
+
+    uint256 const&
+    bitsetIndexToFeature(size_t i) const;
+};
+
+} // detail
+
+boost::optional<uint256>
+getRegisteredFeature (std::string const& name);
+
+using FeatureBitset = std::bitset<detail::FeatureCollections::numFeatures()>;
+
+size_t
+featureToBitsetIndex(uint256 const& f);
 
 uint256
-feature (const char* name);
-/** @} */
+bitsetIndexToFeature(size_t i);
+
+template <class F>
+void
+foreachFeature(FeatureBitset bs, F&& f)
+{
+    for (size_t i = 0; i < bs.size(); ++i)
+        if (bs[i])
+            f(bitsetIndexToFeature(i));
+}
+
+template <class Col>
+FeatureBitset
+makeFeatureBitset(Col&& fs)
+{
+    FeatureBitset result;
+    for (auto const& f : fs)
+        result.set(featureToBitsetIndex(f));
+    return result;
+}
+
+template <class Col>
+FeatureBitset
+addFeatures(FeatureBitset bs, Col&& fs)
+{
+    for (auto const& f : fs)
+        bs.set(featureToBitsetIndex(f));
+    return bs;
+}
+
+template <class Col>
+FeatureBitset
+removeFeatures(FeatureBitset bs, Col&& fs)
+{
+    for (auto const& f : fs)
+        bs.reset(featureToBitsetIndex(f));
+    return bs;
+}
 
 extern uint256 const featureMultiSign;
 extern uint256 const featureTickets;