Removed hack for now, fixed explanations

src/egraph.rs

@@ -1020,7 +1020,7 @@ impl<L: Language, N: Analysis<L>> EGraph<L, N> {
         } else {
             let id = self.make_new_eclass(enode, original.clone());
             if let Some(explain) = self.explain.as_mut() {
-                explain.add(original, id);
+                explain.initialize_up_to(original, id);
             }
 
             // now that we updated explanations, run the analysis for the new eclass
@@ -1035,20 +1035,15 @@ impl<L: Language, N: Analysis<L>> EGraph<L, N> {
         let id = self.unionfind.make_set();
         log::trace!("  ...adding to {}", id);
 
-        // This is a hack to avoid needing a default for L, or to clone `original`
-        debug_assert_eq!(Id::from(self.nodes.len()), id);
-        self.nodes.push(enode.clone());
+        self.nodes.push(original.clone());
 
         let class = EClass {
             id,
-            nodes: vec![enode],
+            nodes: vec![enode.clone()],
             data: N::make(self, &original),
             parents: Default::default(),
         };
 
-        let mut enode = original;
-        std::mem::swap(&mut enode, &mut self.nodes[id.0 as usize]);
-
         // add this enode to the parent lists of its children
         enode.for_each(|child| {
             self[child].parents.push(id);

src/explain.rs

@@ -923,6 +923,27 @@ impl<L: Language> Explain<L> {
         set
     }
 
+    pub(crate) fn initialize_up_to(&mut self, node: L, set: Id) -> usize {
+        let mut ix = self.explainfind.len();
+        let mut added = 0;
+        while ix < usize::from(set) {
+            let set_ix = ix.into();
+            self.uncanon_memo.insert(node.clone(), set_ix);
+            self.explainfind.push(ExplainNode {
+                neighbors: vec![],
+                parent_connection: Connection {
+                    justification: Justification::Congruence,
+                    is_rewrite_forward: false,
+                    next: set_ix,
+                    current: set_ix,
+                },
+            });
+            ix += 1;
+            added += 1;
+        }
+        added
+    }
+
     // reverse edges recursively to make this node the leader
     fn make_leader(&mut self, node: Id) {
         let next = self.explainfind[usize::from(node)].parent_connection.next;