Bash Autocompletion - How to pass this array to compgen without significant whitespace being collapsed?

Why bother with compgen? Just add them to COMPREPLY manually. The following will complete the matching filenames from /some/path, handling filenames safely.

some_completion_function() {
    local files=("/some/path/$2"*)
    [[ -e ${files[0]} ]] && COMPREPLY=( "${files[@]##*/}" )
}

It's not possible to have compgen handle filenames safely.