Implement impl Trait for function parameters

[jfecher]

Problem

Using traits can be somewhat cumbersome when it requires extra ceremony just for a single parameter:

fn log<T>(x: T) where T: ToString {
    let string = x.to_string();
    println(f"log: {s}");
}

Happy Case

Adopt rust's impl Trait syntax for parameters as well (Noir already mostly supports this for return types):

fn log(x: impl ToString) {
    let string = x.to_string();
    println(f"log: {s}");
}

Alternatives Considered

No response

Additional Context

No response

Would you like to submit a PR for this Issue?

No

Support Needs

No response

[jfecher]

Adding "good first issue" here. Whenever we see impl Trait in a parameter position we can desugar it to an extra generic and constraint on the function. E.g:

fn log(x: impl ToString) {
    let string = x.to_string();
    println(f"log: {s}");
}

Would get desugared directly to:

fn log<T>(x: T) where T: ToString {
    let string = x.to_string();
    println(f"log: {s}");
}

This'd likely be done during name resolution when we can cleanly create fresh type variables that are guaranteed not to be in scope elsewhere.

[michaeljklein]

Newer version of this issue that's part of an Epic: #4540