Runtime feature activation framework

runtime/src/feature_set.rs

@@ -0,0 +1,60 @@
+use solana_sdk::{
+    hash::{Hash, Hasher},
+    pubkey::Pubkey,
+};
+use std::collections::HashSet;
+
+/// The `FeatureSet` struct tracks the set of available and currently active runtime features
+#[derive(AbiExample)]
+pub struct FeatureSet {
+    /// Unique identifier of this feature set
+    pub id: Hash,
+
+    /// Features that are currently active
+    pub active: HashSet<Pubkey>,
+
+    /// Features that are currently inactive
+    pub inactive: HashSet<Pubkey>,
+}
+
+impl FeatureSet {
+    pub fn active(&self, feature_id: &Pubkey) -> bool {
+        self.active.contains(feature_id)
+    }
+}
+
+impl Default for FeatureSet {
+    // By default all features are disabled
+    fn default() -> Self {
+        let features: [Pubkey; 0] = [];
+
+        Self {
+            id: {
+                let mut hasher = Hasher::default();
+                for feature in features.iter() {
+                    hasher.hash(feature.as_ref());
+                }
+                hasher.result()
+            },
+            active: HashSet::new(),
+            inactive: features.iter().cloned().collect(),
+        }
+    }
+}
+
+impl FeatureSet {
+    // New `FeatureSet` with all features enabled
+    pub fn new_enabled() -> Self {
+        let default = Self::default();
+
+        Self {
+            id: default.id,
+            active: default
+                .active
+                .intersection(&default.inactive)
+                .cloned()
+                .collect::<HashSet<_>>(),
+            inactive: HashSet::new(),
+        }
+    }
+}