[post frontend-backend split] Move types/functions from common to frontend/backend

[ed255]

After the frontend-backend split a new package halo2_common was added that contains functions and types used by both frontend and backend. These functions/types are now pub but are meant for internal usage only of the halo2 repository.

As future work we should try to move more stuff to either frontend/backend, creating mirror lightweight types as necessary; or splitting functionality between frontend and backend. After types/functions are moved to frontend/backend, they should recover the pub(crate) status.

Here's a non-exhaustive list of affected types:

• halo2_common::poly::Polynomial -> Backend https://github.com/privacy-scaling-explorations/halo2/issues/257
• halo2_common::arithmetic::* -> Frontend Backend https://github.com/privacy-scaling-explorations/halo2/pull/281
• halo2_common::plonk::Challenge* -> Backend https://github.com/privacy-scaling-explorations/halo2/pull/287
• halo2_common::plonk::transcript -> Backend https://github.com/privacy-scaling-explorations/halo2/pull/287
• halo2_common::plonk::error::Error -> Backend / Frontend https://github.com/privacy-scaling-explorations/halo2/pull/290
• halo2_common::plonk::circuit::Expression -> Backend / Frontend https://github.com/privacy-scaling-explorations/halo2/pull/290
• halo2_common::plonk::circuit::{sealed, *Phase} -> Frontend https://github.com/privacy-scaling-explorations/halo2/pull/290
• halo2_common::plonk::circuit::Selector -> Frontend https://github.com/privacy-scaling-explorations/halo2/pull/290
• halo2_common::plonk::circuit::Circuit -> Frontend https://github.com/privacy-scaling-explorations/halo2/pull/290
• halo2_common::plonk::permutation::Assembly -> Frontend https://github.com/privacy-scaling-explorations/halo2/pull/290
• halo2_common::plonk::lookup::Argument -> Backend https://github.com/privacy-scaling-explorations/halo2/pull/290
• halo2_common::circuit::Value -> Frontend https://github.com/privacy-scaling-explorations/halo2/pull/290
• halo2_common::circuit::Chip -> Frontend https://github.com/privacy-scaling-explorations/halo2/pull/290
• halo2_common::circuit::Region* -> Frontend https://github.com/privacy-scaling-explorations/halo2/pull/290
• halo2_common::circuit::layouter::* -> Frontend https://github.com/privacy-scaling-explorations/halo2/pull/290
• halo2_common::circuit::floor_planner::* -> Frontend https://github.com/privacy-scaling-explorations/halo2/pull/290
• halo2_common::circuit::Table -> Frontend https://github.com/privacy-scaling-explorations/halo2/pull/290
• halo2_common::poly::Queires -> Backend #298
• halo2_common::multicore::TryFoldAndReduce -> Middleware #298
• halo2_common::helpers::{SerdeFormat, CurveRead, SerdeCurveAffine, SerdePrimeField, pack, unpack} -> Backend #298

Blocked by https://github.com/privacy-scaling-explorations/halo2/pull/254

[ed255]

I'm currently working on halo2_common::plonk::circuit::Expression (and will also probably work on the halo2_common::plonk::circuit::ConstraintSystem. My current approach is to define a single Expression type that can be generic and instantiated into 2 cases: one for the frontend, and one for the backend.

[duguorong009]

I work on task - move halo2_common::arithmetic to halo2_backend. https://github.com/privacy-scaling-explorations/halo2/pull/281

[duguorong009]

I work on task - move plonk::Challenge* & plonk::transcript from common to backend. #287

[ed255]

@duguorong009 will work on the remaining points of this issue.

[duguorong009]

@ed255 I've just merged the #298 . After this, there is no halo2_common crate(the post-split tech debt) in the repo. Hence, I think we can close this issue as completed.

What do you think?

[ed255]

@ed255 I've just merged the #298 . After this, there is no halo2_common crate(the post-split tech debt) in the repo. Hence, I think we can close this issue as completed.

What do you think?

I agree! This issue has now been completed, I'll just close it; thanks for the reminder!