Fix block proof generation with zero supply increase

Author: sebastiencs

ledger/src/proofs/block.rs

@@ -1375,7 +1375,6 @@ pub mod consensus {
 
         let (new_total_currency, _overflow) = {
             let total_currency: Amount = previous_state.total_currency;
-            w.exists(supply_increase.force_value());
             total_currency
                 .to_checked()
                 .add_signed_flagged(supply_increase, w)
@@ -1639,7 +1638,7 @@ fn block_main<'a>(
     };
 
     let supply_increase = w.exists_no_check(match txn_stmt_ledger_hashes_didn_t_change {
-        Boolean::True => CheckedSigned::zero(),
+        Boolean::True => CheckedSigned::const_zero(),
         Boolean::False => txn_snark.supply_increase.to_checked(),
     });
 

ledger/src/proofs/numbers/currency.rs

@@ -86,6 +86,14 @@ where
         Self::of_unsigned(T::zero())
     }
 
+    pub fn const_zero() -> Self {
+        Self {
+            magnitude: T::zero(),
+            sgn: Sgn::Pos,
+            value: Cell::new(None),
+        }
+    }
+
     pub fn negate(self) -> Self {
         Self {
             magnitude: self.magnitude,
@@ -215,15 +223,14 @@ where
     }
 
     pub fn equal(&self, other: &Self, w: &mut Witness<F>) -> Boolean {
-        // We decompose this way because of OCaml evaluation order
-        let t2 = other.value(w);
         let t1 = self.value(w);
+        let t2 = other.value(w);
         field::equal(t1, t2, w)
     }
 
     pub fn const_equal(&self, other: &Self, w: &mut Witness<F>) -> Boolean {
-        let t2 = other.value(w);
         let t1 = self.value(w);
+        let t2 = other.value(w);
         field::equal(t1, t2, w)
     }
 }