Fix CS::one() bug in solver. (#24)

* Test and fix solver CS::one() bug.

* Remove unused linear-combination evaluations.

* rustfmt

* Clippy.

Co-authored-by: porcuquine <porcuquine@users.noreply.github.com>

tests/num.rs

@@ -0,0 +1,77 @@
+use bellperson::{gadgets::num::AllocatedNum, ConstraintSystem, SynthesisError};
+use ff::PrimeField;
+use nova_snark::bellperson::{
+  r1cs::{NovaShape, NovaWitness},
+  shape_cs::ShapeCS,
+  solver::SatisfyingAssignment,
+};
+
+fn synthesize_use_cs_one<Fr: PrimeField, CS: ConstraintSystem<Fr>>(
+  cs: &mut CS,
+) -> Result<(), SynthesisError> {
+  let a = AllocatedNum::alloc(cs.namespace(|| "a"), || Ok(Fr::one()))?;
+  let b = AllocatedNum::alloc(cs.namespace(|| "b"), || Ok(Fr::one()))?;
+  cs.enforce(
+    || "check a = b",
+    |lc| lc + a.get_variable() - b.get_variable(),
+    |lc| lc + CS::one(),
+    |lc| lc,
+  );
+  let _ = a.inputize(cs.namespace(|| "a is input"));
+  let _ = b.inputize(cs.namespace(|| "b is input"));
+  Ok(())
+}
+
+fn synthesize_use_cs_one_after_inputize<Fr: PrimeField, CS: ConstraintSystem<Fr>>(
+  cs: &mut CS,
+) -> Result<(), SynthesisError> {
+  let a = AllocatedNum::alloc(cs.namespace(|| "a"), || Ok(Fr::one()))?;
+  let b = AllocatedNum::alloc(cs.namespace(|| "b"), || Ok(Fr::one()))?;
+  let _ = a.inputize(cs.namespace(|| "a is input"));
+  cs.enforce(
+    || "check a = b",
+    |lc| lc + a.get_variable() - b.get_variable(),
+    |lc| lc + CS::one(),
+    |lc| lc,
+  );
+  let _ = b.inputize(cs.namespace(|| "b is input"));
+  Ok(())
+}
+
+#[test]
+fn test_use_cs_one() {
+  type G = pasta_curves::pallas::Point;
+
+  //First create the shape
+  let mut cs: ShapeCS<G> = ShapeCS::new();
+  let _ = synthesize_use_cs_one(&mut cs);
+  let shape = cs.r1cs_shape();
+  let gens = cs.r1cs_gens();
+
+  //Now get the assignment
+  let mut cs: SatisfyingAssignment<G> = SatisfyingAssignment::new();
+  let _ = synthesize_use_cs_one(&mut cs);
+  let (inst, witness) = cs.r1cs_instance_and_witness(&shape, &gens).unwrap();
+
+  //Make sure that this is satisfiable
+  assert!(shape.is_sat(&gens, &inst, &witness).is_ok());
+}
+
+#[test]
+fn test_use_cs_one_after_inputize() {
+  type G = pasta_curves::pallas::Point;
+
+  //First create the shape
+  let mut cs: ShapeCS<G> = ShapeCS::new();
+  let _ = synthesize_use_cs_one_after_inputize(&mut cs);
+  let shape = cs.r1cs_shape();
+  let gens = cs.r1cs_gens();
+
+  //Now get the assignment
+  let mut cs: SatisfyingAssignment<G> = SatisfyingAssignment::new();
+  let _ = synthesize_use_cs_one_after_inputize(&mut cs);
+  let (inst, witness) = cs.r1cs_instance_and_witness(&shape, &gens).unwrap();
+
+  //Make sure that this is satisfiable
+  assert!(shape.is_sat(&gens, &inst, &witness).is_ok());
+}