During a merge this comes up, but I've seen it in other hg actions. The merge won't complete.  This has been a problem for a long time and finally taking a moment to report it.  

• • • failed to import extension mercurial-credential-manager from /Applications/Sourcetree.app/Contents/Resources/mercurial_local/hgext/mercurial_credential_manager.py: inconsistent use of tabs and spaces in indentation (mercurial_credential_manager.py, line 222)

There are indeed tabs on that line instead of spaces on the rest of the file.

The really annoying thing is this comes up and I'm not using the embedded mercurial. But I just figured out how to exclude that in hgrc.  Still, this tabs/spaces issue probably needs fixed.  Not sure why its not come up for anyone else yet.