Add ToConstraintFieldGadget bounds to CurveVar and FieldVar (#144)

* Add `ToConstraintFieldGadget` bounds to `CurveVar` and `FieldVar`

* Update changelog

---------

Co-authored-by: Pratyush Mishra <[email protected]>

Author: winderica

CHANGELOG.md

@@ -23,6 +23,8 @@
     - Add `UInt::rotate_{left,right}_in_place`.
     - Add `{Boolean,UInt}::not_in_place`.
     - Add `UInt::{from_bytes_le, from_bytes_be, to_bytes_be}`.
+- [\#144](https://github.com/arkworks-rs/r1cs-std/pull/144)
+    - Add `ToConstraintFieldGadget` bounds to `CurveVar` and `FieldVar`
 
 ### Improvements
 

src/fields/mod.rs

@@ -5,7 +5,7 @@ use core::{
     ops::{Add, AddAssign, Mul, MulAssign, Sub, SubAssign},
 };
 
-use crate::convert::{ToBitsGadget, ToBytesGadget};
+use crate::convert::{ToBitsGadget, ToBytesGadget, ToConstraintFieldGadget};
 use crate::prelude::*;
 
 /// This module contains a generic implementation of cubic extension field
@@ -76,6 +76,7 @@ pub trait FieldVar<F: Field, ConstraintF: PrimeField>:
     + AllocVar<F, ConstraintF>
     + ToBytesGadget<ConstraintF>
     + CondSelectGadget<ConstraintF>
+    + ToConstraintFieldGadget<ConstraintF>
     + for<'a> FieldOpsBounds<'a, F, Self>
     + for<'a> AddAssign<&'a Self>
     + for<'a> SubAssign<&'a Self>

src/groups/mod.rs

@@ -1,5 +1,5 @@
 use crate::{
-    convert::{ToBitsGadget, ToBytesGadget},
+    convert::{ToBitsGadget, ToBytesGadget, ToConstraintFieldGadget},
     fields::emulated_fp::EmulatedFpVar,
     prelude::*,
 };
@@ -41,6 +41,7 @@ pub trait CurveVar<C: CurveGroup, ConstraintF: PrimeField>:
     + CondSelectGadget<ConstraintF>
     + AllocVar<C, ConstraintF>
     + AllocVar<C::Affine, ConstraintF>
+    + ToConstraintFieldGadget<ConstraintF>
     + for<'a> GroupOpsBounds<'a, C, Self>
     + for<'a> AddAssign<&'a Self>
     + for<'a> SubAssign<&'a Self>