Fix determinism bug from new combined ruleset code

src/ast/mod.rs

@@ -48,7 +48,12 @@ impl Display for Id {
 #[derive(Clone, Debug)]
 /// The egglog internal representation of already compiled rules
 pub(crate) enum Ruleset {
-    Rules(Symbol, HashMap<Symbol, CompiledRule>),
+    /// Represents a ruleset with a set of rules.
+    /// Use an [`IndexMap`] to ensure egglog is deterministic.
+    /// Rules added to the [`IndexMap`] first apply their
+    /// actions first.
+    Rules(Symbol, IndexMap<Symbol, CompiledRule>),
+    /// A combined ruleset may contain other rulesets.
     Combined(Symbol, Vec<Symbol>),
 }
 

src/lib.rs

@@ -1100,8 +1100,10 @@ impl EGraph {
             match rules {
                 Ruleset::Rules(_, rules) => {
                     match rules.entry(name) {
-                        Entry::Occupied(_) => panic!("Rule '{name}' was already present"),
-                        Entry::Vacant(e) => e.insert(compiled_rule),
+                        indexmap::map::Entry::Occupied(_) => {
+                            panic!("Rule '{name}' was already present")
+                        }
+                        indexmap::map::Entry::Vacant(e) => e.insert(compiled_rule),
                     };
                     Ok(name)
                 }