Edge case when the update of alias fails

[jtrmal]

My edge case was weird, but still valid -- the original job created a directory, say alias/directory/jobname/ with a symlink inside, pointing to work directory, i.e alias/directory/jobname/something -> work/....,
Then, the second version of that job wanted to actually create/update the alias alias/directory/jobname -> work/....
The test os.path.symlink() was therefore against alias/directory/jobname and that correctly returned False. However, I think that was processed as "does not exist" and directory was not unlinked/deleted.
Maybe checking for existence would be more appropriate? Not sure.

sisyphus/sisyphus/manager.py

Line 722 in b380df2

if os.path.islink(alias) and os.path.realpath(alias) != os.path.realpath(target):

[jtrmal]

Deleting all aliases and re-creating them of course resolved the issue. Just documenting it here in case someone will find time to fix it.

[michelwi]

If it is a folder containing other (possibly intentionally registered) links, then it might be wrong to just delete the folder. I think best we can do is fail with a meaningful error message in this case.