subroutineexpand_file_includesrecursiveprivate

recursive subroutine expand_file_includes(lines, options, depth)
    type(string_t), allocatable, intent(inout) :: lines(:)  !! the lines
    type(markdown_options_t), intent(in) :: options         !! what rendering depends on
    integer, intent(in) :: depth                            !! how many includes deep this is
    type(string_t), allocatable :: out(:), included(:)
    character(len=:), allocatable :: contents, msg, path, before, after
    integer :: k, a, b, stat, j

    if (depth > 16) return
    if (.not. allocated(options%base_path)) return
    if (.not. any([(index(lines(k)%s, '{!') > 0, k=1, size(lines))])) return
    allocate (out(0))
    do k = 1, size(lines)
        a = index(lines(k)%s, '{!')
        b = 0
        if (a > 0) b = index(lines(k)%s(a + 2:), '!}')
        if (a == 0 .or. b == 0) then
            call push(out, lines(k)%s)
            cycle
        end if
        ! not `join_path`, which returns a deferred-length string
        path = strip(lines(k)%s(a + 2:a + b))
        if (.not. starts_with(path, '/')) path = options%base_path//'/'//path
        call read_whole_file(path, contents, stat, msg)
        if (stat /= 0) then
            call warn('could not include '//path)
            call push(out, lines(k)%s)
            cycle
        end if
        included = split_lines(contents)
        call normalize_lines(included)
        call expand_file_includes(included, options, depth + 1)
        before = lines(k)%s(:a - 1)
        after = lines(k)%s(a + b + 3:)
        if (size(included) == 0) then
            call push(out, before//after)
            cycle
        end if
        included(1)%s = before//included(1)%s
        included(size(included))%s = included(size(included))%s//after
        do j = 1, size(included)
            call push(out, included(j)%s)
        end do
    end do
    call move_alloc(out, lines)
end subroutine expand_file_includes