Derive clone for ConstraintRef (#3241)

Derives `Clone` (and some other traits) for `ConstraintRef`. Since it is
a reference, it should implement Clone.

Note that `Clone` for `AlgebraicConstraint` is only auto-derived if `V`
is `Clone`, which is the case if `V` is a reference.

autoprecompiles/src/constraint_optimizer.rs

@@ -222,7 +222,7 @@ fn remove_free_variables<T: FieldElement, V: Clone + Ord + Eq + Hash + Display>(
         .filter(|(variable, constraint)| match constraint {
             // Remove the algebraic constraint if we can solve for the variable.
             ConstraintRef::AlgebraicConstraint(constr) => {
-                can_always_be_satisfied_via_free_variable(constr.clone(), variable)
+                can_always_be_satisfied_via_free_variable(*constr, variable)
             }
             ConstraintRef::BusInteraction(bus_interaction) => {
                 let bus_id = bus_interaction.bus_id.try_to_number().unwrap();

constraint-solver/src/algebraic_constraint/mod.rs

@@ -10,7 +10,7 @@ use num_traits::{One, Zero};
 pub mod solve;
 
 /// An algebraic constraint
-#[derive(Clone, Debug, Hash, Eq, PartialEq)]
+#[derive(Copy, Clone, Debug, Hash, Eq, PartialEq)]
 pub struct AlgebraicConstraint<V> {
     /// The expression representing the constraint, which must evaluate to 0 for the constraint to be satisfied.
     pub expression: V,

constraint-solver/src/constraint_system.rs

@@ -267,6 +267,7 @@ impl<T: FieldElement> BusInteractionHandler<T> for DefaultBusInteractionHandler<
     }
 }
 
+#[derive(Clone, Copy, Debug, Hash, Eq, PartialEq)]
 pub enum ConstraintRef<'a, T, V> {
     AlgebraicConstraint(AlgebraicConstraint<&'a GroupedExpression<T, V>>),
     BusInteraction(&'a BusInteraction<GroupedExpression<T, V>>),

constraint-solver/src/solver/base.rs

@@ -364,7 +364,7 @@ where
         while let Some(item) = self.constraint_system.pop_front() {
             let effects = match item {
                 ConstraintRef::AlgebraicConstraint(c) => {
-                    if let Some((v1, expr)) = try_to_simple_equivalence(c.clone()) {
+                    if let Some((v1, expr)) = try_to_simple_equivalence(c) {
                         self.apply_assignment(&v1, &expr);
                         continue;
                     }