Private fields of KzgDecider get in the way of implementing new loaders

[gnull]

Hi!

I ran into an issue trying to implement my own loader for Plonk with Kzg10. I was trying to impl<M, MOS> AccumulationDecider<M::G1Affine, MyOwnLoader> for KzgAs<M, MOS> analogously to

snark-verifier/snark-verifier/src/pcs/kzg/decider.rs

Line 58 in fedd7a8

impl<M, MOS> AccumulationDecider<M::G1Affine, NativeLoader> for KzgAs<M, MOS>

The problem is that the fields of KzgDecidingKey are private and AccumulationDecider implementations defined outside of snark-verifier can't use them:

snark-verifier/snark-verifier/src/pcs/kzg/decider.rs

Lines 6 to 13 in fedd7a8

	pub struct KzgDecidingKey<M: MultiMillerLoop> {
	svk: KzgSuccinctVerifyingKey<M::G1Affine>,
	/// Generator on G2.
	g2: M::G2Affine,
	/// Generator to the trusted-setup secret on G2.
	s_g2: M::G2Affine,
	_marker: PhantomData<M>,
	}

I'm guessing that this wasn't the intention, and I thought it can make the API more convenient to use if we exposed g2 and s_g2 to external AccumulationDecider implementations, so they could do something like this:

snark-verifier/snark-verifier/src/pcs/kzg/decider.rs

Line 70 in fedd7a8

let terms = [(&lhs, &dk.g2.into()), (&rhs, &(-dk.s_g2).into())];

Would you be willing to accept a PR for this? If so, which way of exposing the fields would you find most appropriate (making field pub, writing a getter method, an Into instance, etc.)?

Ivan

[han0110]

Hi, the use case sounds totally reasonable, feel free to open a PR to expose that!