This is the beginning of the process to enable full floor planning
capabilities in `halo2`. For now, all that a floor planner can do is
synthesize a circuit, which makes it no more powerful than a layouter,
but easier to use (as moving to a multi-pass layouter no longer requires
changes to `Circuit::synthesize`).
Enabling selectors to be used in gates at non-zero rotations leads to
confusing gates, and inhibits our ability to create visualizations of
circuits. In most cases, a gate can be rearranged so that the selectors
have no rotation; in cases where cross-gate selector optimisations are
required, these can still be implemented using fixed columns.
The closure passed to `ConstraintSystem::create_gate` can now return:
- Tuples of `(&'static str, Expression<F>)`
- Anything implementing `IntoIterator` (e.g. `Some(Expression<F>)`)
Jack Grigg
Sean Bowe
therealyingtong