Incorrect compiler error when comparing the index of a "for" loop with a non-casted value.

[pventuzelo]

Aim

We (@FuzzingLabs) find that the compiler incorrectly raises an error when comparing the index of a "for" loop with a non-casted value.

Expected Behavior

The compiler should not treat the compared value as a field type but as a u64

Bug

This error seems to be caused by the compiler treating the compared value as a field type, while the index of a 'for' loop is always treated as a u64, as stated here in the documentation: https://noir-lang.org/docs/noir/syntax/control_flow

As indicated in the code comments, this error doesn't appear with a u64 variable, and it specifically occurs when using the '>'; '<'; ‘≥’; ‘≤’ operators."

The panic crash occurs with the latest compiler version of the main branch. The error message is as follows:

error: Comparisons are invalid on Field types. Try casting the operands to a sized integer type first

To Reproduce

1. Create a Noir project with the following command: nargo new test_issue
2. Paste the code below into the file main.nr
3. Compile the project using the following command: nargo compile

fn main() {
    // Raises an error because the compiler interprets '1' as a Field and not as a u64.
    for i in 0..10 {
        assert(i > 1);
    }

    // Same issue persists even if the value is stored in a variable.
    for i in 0..10 {
        let val = 1;
        assert(i < val);
    }

    // Error only occurs with '<' '>' '<=' '>=' operators.
    for i in 0..10 {
        assert(i == 1);
    }

    // Error only occurs with the index of a "for" loop, not with every u64.
    let i: u64 = 5;
    assert(i > 1);

    // Casting the value as u64 resolves the problem.
    for i in 0..10 {
        assert(i < 1 as u64);
    }
}

Installation Method

None

Nargo Version

No response

Additional Context

No response

Would you like to submit a PR for this Issue?

No

Support Needs

No response

[jfecher]

Possibly a duplicate of #3639

The PR which fixes the duplicate #4118 should test this case as well.