Cargo no longer excludes temp files from backups on macOS

[calebmarcus]

In 1.36.0, cargo no longer excludes directories in target from Time Machine backups on macOS machines (see #3884).

To reproduce: Delete the target directory for some project, and run a build. Run xattr -r target and note that there is no attribute com.apple.metadata:com_apple_backup_excludeItem applied to any subdirectories (if nothing has any extended attributes, it will not print anything.) Try the same with a prior version such as 1.35.0, and it will apply that attribute to subdirectories of target.

This regression seems to have been introduced in 8258ca4 -- from what I can tell (and it's entirely possible that I'm completely misreading the situation!), the issue is that the directory that is to be excluded from backups upon creation is actually not created in Layout::prepare as might be expected -- it winds up being created earlier, in Layout::at, when it calls open_rw on the flock::Filesystem. Reverting that change would fix the problem, but I hope there might be a more elegant way to fix it that still maintains the spirit of that change (not updating that bit of metadata every time!)

[alexcrichton]

Oops sorry about that, and thanks for the report! Mind testing out #7192 to see if it works for you?

[calebmarcus]

Hey - that does the trick. This is a neat feature, by the way -- At some point I realized how big these directories were, went to go figure out whether they were in my backups, and realized they were already magically excluded! So, thanks to @kornelski for thinking of this. Some third-party backup software respects that attribute too.

[alexcrichton]

Ok great, thanks for checking!