Document Witness offset of 1

[joss-aztec]

Problem

Recently added abi_gen::param_witnesses_from_abi_param uses an initial witness offset of 1 without explanation

Happy Case

We document it's significance, or generalise the offset into something that is backend agnostic.

Argument for keeping the offset:

• It's commonly the case that an ACIR makes use of a zero constant anyway - this means we could use the same zero index as used by the backend. Here's an example of 0 & 1 being special-cased by r1cs
• It removes the need for the backend to transform of the indices later

Argument for removing the offset:

• It leaks an abstraction which is backend specific

Alternatives Considered

No response

Additional Context

No response

Would you like to submit a PR for this Issue?

No

Support Needs

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