fix: watch map incorrectly reported size

src/internal/mapping.rs

@@ -27,6 +27,16 @@ impl<TId: ArenaId, TValue> Mapping<TId, TValue> {
         Self::with_capacity(1)
     }
 
+    /// Returns the total number of values that can be stored in the mapping without reallocating.
+    pub fn capacity(&self) -> usize {
+        self.chunks.len() * VALUES_PER_CHUNK
+    }
+
+    /// Returns the total number of bytes allocated by this instance.
+    pub fn size_in_bytes(&self) -> usize {
+        self.capacity() * std::mem::size_of::<Option<TValue>>()
+    }
+
     /// Constructs a new arena with a capacity for `n` values pre-allocated.
     pub fn with_capacity(n: usize) -> Self {
         let n = cmp::max(1, n);

src/solver/watch_map.rs

@@ -1,7 +1,6 @@
-use crate::solver::clause::Literal;
 use crate::{
     internal::{id::ClauseId, mapping::Mapping},
-    solver::clause::ClauseState,
+    solver::clause::{ClauseState, Literal},
 };
 
 /// A map from solvables to the clauses that are watching them
@@ -25,7 +24,7 @@ impl WatchMap {
 
     #[cfg(feature = "diagnostics")]
     pub fn size_in_bytes(&self) -> usize {
-        self.len() * std::mem::size_of::<(Literal, ClauseId)>()
+        self.map.size_in_bytes()
     }
 
     pub(crate) fn start_watching(&mut self, clause: &mut ClauseState, clause_id: ClauseId) {