Indexing by non-empty mask

[orenbenkiki]

Synthetic example:

function mask(flag::Bool)::Vector{Bool}
    return Bool[flag, false]
end

function oops(flag::Bool)::Nothing
    values = Int[1, 2]
    used = mask(flag)
    if length(used) == length(values) && any(used)
        values[used]
    end
    return nothing
end

oops(true)
oops(false)

Will fail with an error pointing to the innards of Base.LogicalIndex. I'm not 100% sure whether the problem is that the system thinks used may be the wrong length, or that it may be all-false, or something else, but either way, it is a false positive.

I actually like it that JET emits an error here, forcing one to think about this (though the actual error is extremely opaque).

The problem is, there's currently no way to tell JET "kindly shut up about this, I know what I'm doing" (#515, #346, #148, ...).

Is there a workaround?