Passing an array of booleans as input to the circuit is not implemented.

[Mickanos]

Problem

Although the documentation does not forbid to pass arrays of booleans as input to the main function of the circuit, the noirc_abi does not handle this situation.
The problem is easy to reproduce:
Create a noir project with main.nr:

fn main(sel: [bool;2], y : pub Field) {
        if sel[0] {
                if sel[1] {
                        constrain y==0;
                } else {
                        constrain y==1;
                }
        } else {
                if sel[1] {
                        constrain y==2;
                } else {
                        constrain y==3;
                }
        }
}

now try the following Prover.toml files:

sel = ["true","false"] 
y = 1

sel = [true,false]
y=1

and

sel = "[true,false]"
y=1

Running nargo prove results in three different error messages depending on each case. In the first case, we get Expected witness values to be integers, provided value causes `invalid digit found in string` error. With the second approach, we get input.toml file is badly formed, could not parse, data did not match any variant of untagged enum TomlTypes for key `sel` at line 1 column 1. Finally, the third approach yields cannot parse a string toml type into Array { length: 2, typ: Boolean }.

Solution

Getting each approach to work requires different fixes.
The first format requires implementing a function parse_str_to_bool and using it in the TomlTypes::ArrayString(arr_str) case of the match in function try_from_toml.

The second format is simpler to implement. Add a variant ArrayBool(Vec<bool>) in the definition of the TomlTypes enum.

I am not sure that the third format is desired, since it is not implemented for arrays of integers either. This would require parsing a string of the form "[,...,]" into an array of the appropriate type. Note however that using nargo check when an array is part of the input of the main function creates a line of the form key = "[]" in Prover.toml, thus encouraging usage of an unsupported syntax.

Alternatives considered

Specify in the Noir book that arrays of booleans are not supported as input to the main function.

[TomAFrench]

Hey @Mickanos, thanks for opening this issue! I think that the second approach would be best and would fit most with the current style.

Would you like to open a PR to address this issue? Ideally the fix would also include a test case for a circuit which takes an array of bools as an argument (You can see examples of this sort of test in https://github.com/noir-lang/noir/tree/master/crates/nargo/tests/test_data)

[Mickanos]

Sure, I'll look into it.
This is my first time opening a pull request, so please bear with me while I figure it out.