crdt: Require `LWWReg` value to be `Semilattice`

* Also derive instances of `Semilattice` for built-in types.

Signed-off-by: Alexis Sellier <alexis@radicle.xyz>

radicle-crdt/Cargo.toml

@@ -4,12 +4,13 @@ version = "0.1.0"
 edition = "2021"
 
 [features]
-test = ["fastrand"]
+test = ["fastrand", "quickcheck"]
 
 [dependencies]
 fastrand = { version = "1.8.0", optional = true }
 num-traits = { version = "0.2.15", default-features = false, features = ["std"] }
 olpc-cjson = { version = "0.1.1" }
+quickcheck = { version = "1", optional = true }
 serde = { version = "1" }
 serde_json = { version = "1" }
 

radicle-crdt/src/lib.rs

@@ -1,4 +1,5 @@
 #![allow(clippy::collapsible_if)]
+#![allow(clippy::bool_assert_comparison)]
 #![allow(clippy::collapsible_else_if)]
 #![allow(clippy::type_complexity)]
 pub mod change;
@@ -15,6 +16,12 @@ pub mod test;
 ////////////////////////////////////////////////////////////////////////////////
 
 pub use change::*;
+pub use clock::LClock;
+pub use lwwmap::LWWMap;
+pub use lwwreg::LWWReg;
+pub use lwwset::LWWSet;
+pub use ord::{Max, Min};
+pub use redactable::Redactable;
 
 ////////////////////////////////////////////////////////////////////////////////
 
@@ -70,9 +77,78 @@ impl<K: Hash + PartialEq + Eq, V: Semilattice> Semilattice for HashMap<K, V> {
     }
 }
 
+impl<T: Semilattice> Semilattice for Option<T> {
+    fn merge(&mut self, other: Self) {
+        match (self, other) {
+            (this @ None, other @ Some(_)) => {
+                *this = other;
+            }
+            (Some(ref mut a), Some(b)) => {
+                a.merge(b);
+            }
+            (Some(_), None) => {}
+            (None, None) => {}
+        }
+    }
+}
+
+impl Semilattice for () {
+    fn merge(&mut self, _other: Self) {}
+}
+
+impl Semilattice for bool {
+    fn merge(&mut self, other: Self) {
+        match (&self, other) {
+            (false, true) => *self = true,
+            (true, false) => *self = true,
+            (false, false) | (true, true) => {}
+        }
+    }
+}
+
 pub fn fold<S>(i: impl IntoIterator<Item = S>) -> S
 where
     S: Semilattice + Default,
 {
     i.into_iter().fold(S::default(), S::join)
 }
+
+#[cfg(test)]
+mod tests {
+    use crate::{test, Max, Min, Semilattice};
+    use quickcheck_macros::quickcheck;
+
+    #[quickcheck]
+    fn prop_option_laws(a: Max<u8>, b: Max<u8>, c: Max<u8>) {
+        test::assert_laws(&a, &b, &c);
+    }
+
+    #[quickcheck]
+    fn prop_bool_laws(a: bool, b: bool, c: bool) {
+        test::assert_laws(&a, &b, &c);
+    }
+
+    #[test]
+    fn test_bool() {
+        assert_eq!(false.join(false), false);
+        assert_eq!(true.join(true), true);
+        assert_eq!(true.join(false), true);
+        assert_eq!(false.join(true), true);
+    }
+
+    #[test]
+    fn test_option() {
+        assert_eq!(None::<()>.join(None), None);
+        assert_eq!(None::<()>.join(Some(())), Some(()));
+        assert_eq!(Some(()).join(None), Some(()));
+        assert_eq!(Some(()).join(Some(())), Some(()));
+        assert_eq!(
+            Some(Max::from(0)).join(Some(Max::from(1))),
+            Some(Max::from(1))
+        );
+        assert_eq!(
+            Some(Min::from(0)).join(Some(Min::from(1))),
+            Some(Min::from(0))
+        );
+    }
+}

radicle-crdt/src/lwwmap.rs

@@ -10,7 +10,7 @@ pub struct LWWMap<K, V, C> {
     inner: BTreeMap<K, LWWReg<Option<V>, C>>,
 }
 
-impl<K: Ord, V: PartialOrd + Eq, C: PartialOrd + Ord + Copy> LWWMap<K, V, C> {
+impl<K: Ord, V: Semilattice + PartialOrd + Eq, C: PartialOrd + Ord + Copy> LWWMap<K, V, C> {
     pub fn singleton(key: K, value: V, clock: C) -> Self {
         Self {
             inner: BTreeMap::from_iter([(key, LWWReg::new(Some(value), clock))]),
@@ -66,7 +66,9 @@ impl<K, V, C> Default for LWWMap<K, V, C> {
     }
 }
 
-impl<K: Ord, V: PartialOrd + Eq, C: Copy + Ord> FromIterator<(K, V, C)> for LWWMap<K, V, C> {
+impl<K: Ord, V: Semilattice + PartialOrd + Eq, C: Copy + Ord> FromIterator<(K, V, C)>
+    for LWWMap<K, V, C>
+{
     fn from_iter<I: IntoIterator<Item = (K, V, C)>>(iter: I) -> Self {
         let mut map = LWWMap::default();
         for (k, v, c) in iter.into_iter() {
@@ -76,7 +78,9 @@ impl<K: Ord, V: PartialOrd + Eq, C: Copy + Ord> FromIterator<(K, V, C)> for LWWM
     }
 }
 
-impl<K: Ord, V: PartialOrd + Eq, C: Ord + Copy> Extend<(K, V, C)> for LWWMap<K, V, C> {
+impl<K: Ord, V: Semilattice + PartialOrd + Eq, C: Ord + Copy> Extend<(K, V, C)>
+    for LWWMap<K, V, C>
+{
     fn extend<I: IntoIterator<Item = (K, V, C)>>(&mut self, iter: I) {
         for (k, v, c) in iter.into_iter() {
             self.insert(k, v, c);
@@ -87,7 +91,7 @@ impl<K: Ord, V: PartialOrd + Eq, C: Ord + Copy> Extend<(K, V, C)> for LWWMap<K,
 impl<K, V, C> Semilattice for LWWMap<K, V, C>
 where
     K: Ord,
-    V: PartialOrd + Eq,
+    V: Semilattice + PartialOrd + Eq,
     C: Ord + Copy + Default,
 {
     fn merge(&mut self, other: Self) {
@@ -106,15 +110,17 @@ where
 
 #[cfg(test)]
 mod tests {
-    use super::*;
     use quickcheck_macros::quickcheck;
 
+    use super::*;
+    use crate::ord::Max;
+
     #[quickcheck]
     fn prop_semilattice(
-        a: Vec<(u8, u8, u16)>,
-        b: Vec<(u8, u8, u16)>,
-        c: Vec<(u8, u8, u16)>,
-        mix: Vec<(u8, u8, u16)>,
+        a: Vec<(u8, Max<u8>, u16)>,
+        b: Vec<(u8, Max<u8>, u16)>,
+        c: Vec<(u8, Max<u8>, u16)>,
+        mix: Vec<(u8, Max<u8>, u16)>,
     ) {
         let mut a = LWWMap::from_iter(a);
         let mut b = LWWMap::from_iter(b);
@@ -130,18 +136,18 @@ mod tests {
     fn test_insert() {
         let mut map = LWWMap::default();
 
-        map.insert('a', 1, 0);
-        map.insert('b', 2, 0);
-        map.insert('c', 3, 0);
+        map.insert('a', Max::from(1), 0);
+        map.insert('b', Max::from(2), 0);
+        map.insert('c', Max::from(3), 0);
 
-        assert_eq!(map.get('a'), Some(&1));
-        assert_eq!(map.get('b'), Some(&2));
+        assert_eq!(map.get('a'), Some(&Max::from(1)));
+        assert_eq!(map.get('b'), Some(&Max::from(2)));
         assert_eq!(map.get('?'), None);
 
-        let values = map.iter().collect::<Vec<(&char, &u8)>>();
-        assert!(values.contains(&(&'a', &1)));
-        assert!(values.contains(&(&'b', &2)));
-        assert!(values.contains(&(&'c', &3)));
+        let values = map.iter().collect::<Vec<(&char, &Max<u8>)>>();
+        assert!(values.contains(&(&'a', &Max::from(1))));
+        assert!(values.contains(&(&'b', &Max::from(2))));
+        assert!(values.contains(&(&'c', &Max::from(3))));
         assert_eq!(values.len(), 3);
     }
 
@@ -149,7 +155,7 @@ mod tests {
     fn test_insert_remove() {
         let mut map = LWWMap::default();
 
-        map.insert('a', "alice", 1);
+        map.insert('a', Max::from("alice"), 1);
         assert!(map.contains_key('a'));
 
         map.remove('a', 0);
@@ -168,16 +174,16 @@ mod tests {
     fn test_remove_insert() {
         let mut map = LWWMap::default();
 
-        map.insert('a', "alice", 1);
-        assert_eq!(map.get('a'), Some(&"alice"));
+        map.insert('a', Max::from("alice"), 1);
+        assert_eq!(map.get('a'), Some(&Max::from("alice")));
 
         map.remove('a', 2);
         assert!(!map.contains_key('a'));
 
-        map.insert('a', "alice", 1);
+        map.insert('a', Max::from("alice"), 1);
         assert!(!map.contains_key('a'));
 
-        map.insert('a', "amy", 2);
-        assert_eq!(map.get('a'), Some(&"amy"));
+        map.insert('a', Max::from("amy"), 2);
+        assert_eq!(map.get('a'), Some(&Max::from("amy")));
     }
 }

radicle-crdt/src/lwwreg.rs

@@ -3,55 +3,65 @@ use crate::Semilattice;
 
 /// Last-Write-Wins Register.
 ///
-/// In case of conflict, biased towards larger values.
+/// In case of conflict, uses the [`Semilattice`] instance of `T` to merge.
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct LWWReg<T, C> {
-    /// Nb. the order of the tuple types ensures we bias towards the clock before the value.
-    inner: Max<(C, T)>,
+    clock: Max<C>,
+    value: T,
 }
 
-impl<T: PartialOrd, C: PartialOrd> LWWReg<T, C> {
+impl<T: PartialOrd + Semilattice, C: PartialOrd> LWWReg<T, C> {
     pub fn new(value: T, clock: C) -> Self {
         Self {
-            inner: Max::from((clock, value)),
+            clock: Max::from(clock),
+            value,
         }
     }
 
-    pub fn set(&mut self, value: T, clock: C) {
-        self.inner.merge(Max::from((clock, value)));
+    pub fn set(&mut self, value: impl Into<T>, clock: C) {
+        let clock = Max::from(clock);
+        let value = value.into();
+
+        if clock == self.clock {
+            self.value.merge(value);
+        } else if clock > self.clock {
+            self.clock.merge(clock);
+            self.value = value;
+        }
     }
 
     pub fn get(&self) -> &T {
-        &self.inner.get().1
+        &self.value
     }
 
-    pub fn clock(&self) -> &C {
-        &self.inner.get().0
+    pub fn clock(&self) -> &Max<C> {
+        &self.clock
     }
 
     pub fn into_inner(self) -> (T, C) {
-        let (t, c) = self.inner.into_inner();
-        (c, t)
+        (self.value, self.clock.into_inner())
     }
 }
 
 impl<T, C> Semilattice for LWWReg<T, C>
 where
-    T: PartialOrd + Default,
+    T: PartialOrd + Default + Semilattice,
     C: PartialOrd + Default,
 {
     fn merge(&mut self, other: Self) {
-        self.inner.merge(other.inner);
+        self.set(other.value, other.clock.into_inner());
     }
 }
 
 #[cfg(test)]
 mod tests {
-    use super::*;
     use quickcheck_macros::quickcheck;
 
+    use super::*;
+    use crate::Min;
+
     #[quickcheck]
-    fn prop_semilattice(a: (u8, u16), b: (u8, u16), c: (u8, u16)) {
+    fn prop_semilattice(a: (Max<u8>, u16), b: (Max<u8>, u16), c: (Max<u8>, u16)) {
         let a = LWWReg::new(a.0, a.1);
         let b = LWWReg::new(b.0, b.1);
         let c = LWWReg::new(c.0, c.1);
@@ -59,31 +69,44 @@ mod tests {
         crate::test::assert_laws(&a, &b, &c);
     }
 
+    #[test]
+    fn test_merge() {
+        let a = LWWReg::new(Max::from(0), 0);
+        let b = LWWReg::new(Max::from(1), 0);
+
+        assert_eq!(a.join(b).get(), &Max::from(1));
+
+        let a = LWWReg::new(Min::from(0), 0);
+        let b = LWWReg::new(Min::from(1), 0);
+
+        assert_eq!(a.join(b).get(), &Min::from(0));
+    }
+
     #[test]
     fn test_set_get() {
-        let mut reg = LWWReg::new(42, 1);
-        assert_eq!(*reg.get(), 42);
+        let mut reg = LWWReg::new(Max::from(42), 1);
+        assert_eq!(*reg.get(), Max::from(42));
 
         reg.set(84, 0);
-        assert_eq!(*reg.get(), 42);
+        assert_eq!(*reg.get(), Max::from(42));
 
         reg.set(84, 2);
-        assert_eq!(*reg.get(), 84);
+        assert_eq!(*reg.get(), Max::from(84));
 
         // Smaller value, same clock: smaller value loses.
         reg.set(42, 2);
-        assert_eq!(*reg.get(), 84);
+        assert_eq!(*reg.get(), Max::from(84));
 
         // Bigger value, same clock: bigger value wins.
         reg.set(168, 2);
-        assert_eq!(*reg.get(), 168);
+        assert_eq!(*reg.get(), Max::from(168));
 
         // Smaller value, newer clock: smaller value wins.
         reg.set(42, 3);
-        assert_eq!(*reg.get(), 42);
+        assert_eq!(*reg.get(), Max::from(42));
 
         // Same value, newer clock: newer clock is set.
         reg.set(42, 4);
-        assert_eq!(*reg.clock(), 4);
+        assert_eq!(*reg.clock(), Max::from(4));
     }
 }

radicle-crdt/src/ord.rs

@@ -99,3 +99,28 @@ where
         other.0.partial_cmp(&self.0)
     }
 }
+
+impl<T: PartialOrd> Semilattice for Min<T> {
+    fn merge(&mut self, other: Self) {
+        if other.0 < self.0 {
+            self.0 = other.0;
+        }
+    }
+}
+
+#[cfg(any(test, feature = "test"))]
+mod arbitrary {
+    use super::*;
+
+    impl<T: quickcheck::Arbitrary> quickcheck::Arbitrary for Max<T> {
+        fn arbitrary(g: &mut quickcheck::Gen) -> Self {
+            Self::from(T::arbitrary(g))
+        }
+    }
+
+    impl<T: quickcheck::Arbitrary> quickcheck::Arbitrary for Min<T> {
+        fn arbitrary(g: &mut quickcheck::Gen) -> Self {
+            Self::from(T::arbitrary(g))
+        }
+    }
+}

radicle-crdt/src/redactable.rs

@@ -2,15 +2,19 @@ use crate::Semilattice;
 
 /// An object that can be either present or removed.
 ///
+/// The "redacted" state is the top-most element and takes precedence
+/// over other states.
+///
+/// There is no `Default` instance, as it wouldn't obbey semilattice laws.
+///
 /// Nb. The merge rules are such that if two redactables with different
 /// values present are merged; the result is redacted. This is the preserve
 /// the semilattice laws.
-#[derive(Default, Debug, Clone, Copy, PartialEq, Eq)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum Redactable<T> {
     /// When the object is present.
     Present(T),
     /// When the object has been removed.
-    #[default]
     Redacted,
 }
 

radicle/src/cob/thread.rs

@@ -95,6 +95,7 @@ impl store::FromHistory for Thread {
         }))
     }
 }
+
 impl Semilattice for Thread {
     fn merge(&mut self, other: Self) {
         self.comments.merge(other.comments);