Support functions with optional arguments

[TomAFrench]

Problem

As described in #1939, we want to be able to provide an optional assert message to be displayed in the situation where a constraint is unsatisfied.

assert is in the process of being changed into a built-in function, we then need to be able to have two version of assert_eq both with and without the assert message.

Happy Case

Ideally we'd be able to have an optional argument to assert_eq as so

#[builtin(assert_eq)]
fn assert_eq<T>(lhs: T, rhs: T, msg?: str) {}

Alternatives Considered

We could also allow shadowing of a function name as long as the signature was different.

fn assert_eq<T>(lhs: T, rhs: T) {
    assert_eq(lhs, rhs, "")
}

#[builtin(assert_eq)]
fn assert_eq<T>(lhs: T, rhs: T, msg?: str) {}

Additional Context

No response

Would you like to submit a PR for this Issue?

No

Support Needs

No response

[jfecher]

We could also simply not convert assert_eq into a builtin function and keep it as a keyword. Supporting an optional extra message argument is the reason assert is still a keyword for example.

[kevaundray]

Changed to P-LOW due to this being a nice to have if we have it as a keyword. The thing that Rust has that we don't which makes it possible in Rust without optional arguments is macro_rules

[kevaundray]

Closing this as not actionable, we can re-open if we do decide to have optional arguments