fix: Open contract functions are unconstrained

[sirasistant]

Description

Problem*

Open functions are unconstrained since they are run inside a public (open) VM, not as a private circuit. Make the function unconstrained if it has a contracttype "open"

Summary*

Documentation

• This PR requires documentation updates when merged.

  • I will submit a noir-lang/docs PR.
  • I will request for and support Dev Rel's help in documenting this PR.

Additional Context

PR Checklist*

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings.

[vezenovm]

@sirasistant Should we enforce that open functions need to also have an unconstrained keyword? So that the barrier b/w unconstrained and constrained is clear?

[sirasistant]

At least in aztec that would be confusing for the user because open functions will be "constrained" by a VM that will run them. Maybe when we abstract noir contracts we can think more about it though, but for aztec this will always be the case

[kevaundray]

Can you add a comment to this issue: #1168 ?

Hmm whats the difference between unconstrained and open then in the context of Noir?

[sirasistant]

Only the resulting ABI type would be different