chore(acir)!: remove UnknownWitness (#123)

acir/src/native_types/arithmetic.rs

@@ -6,8 +6,6 @@ use std::cmp::Ordering;
 use std::io::{Read, Write};
 use std::ops::{Add, Mul, Neg, Sub};
 
-use super::witness::UnknownWitness;
-
 // In the addition polynomial
 // We can have arbitrary fan-in/out, so we need more than wL,wR and wO
 // When looking at the arithmetic gate for the quotient polynomial in standard plonk
@@ -448,14 +446,6 @@ impl Sub<&Witness> for &Expression {
         self - &Expression::from(rhs)
     }
 }
-impl Sub<&UnknownWitness> for &Expression {
-    type Output = Expression;
-    fn sub(self, rhs: &UnknownWitness) -> Expression {
-        let mut cloned = self.clone();
-        cloned.linear_combinations.insert(0, (-FieldElement::one(), rhs.as_witness()));
-        cloned
-    }
-}
 
 impl Expression {
     // Checks if this polynomial can fit into one arithmetic identity

acir/src/native_types/witness.rs

@@ -28,10 +28,6 @@ impl Witness {
         true
     }
 
-    pub fn to_unknown(self) -> UnknownWitness {
-        UnknownWitness(self.0)
-    }
-
     pub fn to_bytes(
         witnesses: &std::collections::BTreeMap<Witness, acir_field::FieldElement>,
     ) -> Vec<u8> {
@@ -51,18 +47,3 @@ impl Witness {
         rmp_serde::from_slice(buf_d.as_slice()).unwrap()
     }
 }
-
-// This is a witness that is unknown relative to the rest of the witnesses in the arithmetic gate
-// We use this, so that they are pushed to the beginning of the array
-//
-// When they are pushed to the beginning of the array, they are less likely to be used in an intermediate gate
-// by the optimizer, which would mean two unknowns in an equation.
-// See Issue #20
-// TODO: can we find a better solution to this?
-pub struct UnknownWitness(pub u32);
-
-impl UnknownWitness {
-    pub fn as_witness(&self) -> Witness {
-        Witness(self.0)
-    }
-}