ExportSolidity when using uints result in additional public input element

[bernard-wagner]

Trying to figure out why when I export the verifier key to Solidity, the witness requires an additional unknown element.

Started with a far more complicated circuit, but this is the simplest version that I could get to manifest the issue.

package circuits

import (
	"os"
	"testing"

	"github.com/consensys/gnark-crypto/ecc"
	"github.com/consensys/gnark/backend/groth16"
	"github.com/consensys/gnark/frontend"
	"github.com/consensys/gnark/frontend/cs/r1cs"
	"github.com/consensys/gnark/std/math/uints"
	"github.com/consensys/gnark/test"
)

type Circuit struct {
	Hash [32]uints.U8 `gnark:",public"`
}

func (circuit *Circuit) Define(api frontend.API) error {

	uapi, err := uints.New[uints.U32](api)
	if err != nil {
		return err
	}

	uapi.ByteAssertEq(circuit.Hash[0], uints.NewU8(0x0a))

	return nil
}

func TestHashCircuit(t *testing.T) {
	assert := test.NewAssert(t)

	circuit := &Circuit{}

	r1cs, err := frontend.Compile(ecc.BN254.ScalarField(), r1cs.NewBuilder, circuit)
	assert.NoError(err)

	_, vk, err := groth16.Setup(r1cs)
	assert.NoError(err)

	vk.ExportSolidity(os.Stdout)
}

function verifyProof(
        uint256[8] calldata proof,
        uint256[33] calldata input
    ) public view {

The input should only be uint256[32] calldata input. When generating a witness, it only outputs 32 bytes as expected and I am able to successfully prove and verify using gnark. Issue is only in the generated Solidity code.

I have no idea what element to add to the input to get it to work.

Using gnark 0.9.1.