Comment 35 for bug 652852

If there is more space free in a partition that could be resized than is available in unallocated space, then the unallocated-space option is dropped. I'm guessing that the theory here may be that you can just use the "Install alongside" option and leave the other OS' size unchanged, thereby reducing the number of automatic partitioning options we need to present. However, the "Install alongside" option doesn't actually let you use unallocated space - it always resizes. I think we should present unallocated space, as people may well prefer not to reduce the amount of space available to their other OS.

Another problem I notice is that if the only other partitions present are data partitions - that is, os-prober outputs nothing - then you get neither the unallocated-space option nor the resize option. This seems like a bug, as resizing is perfectly possible here. Perhaps the 'if os_count == 0:' branch in calculate_autopartitioning_options needs to consider resize options.

I'll ask Evan to comment on this, and reopen or spin off a new bug report as necessary.