[MacPorts] #63048: Big Sur - MacPorts can't install python to "/Applications/MacPorts"

[MacPorts]

#63048: Big Sur - MacPorts can't install python to "/Applications/MacPorts"
-----------------------+--------------------
  Reporter:  cpragman  |      Owner:  (none)
      Type:  defect    |     Status:  new
  Priority:  Normal    |  Milestone:
 Component:  ports     |    Version:
Resolution:            |   Keywords:
      Port:            |
-----------------------+--------------------

Comment (by cpragman):

 My experience w/ Big Sur so far is that unless I'm installing signed apps,
 it won't let me make any other modifications to the contents of the
 /Applications folder unless I reboot into Recovery and turn off
 Gatekeeper.  I'd rather leave Gatekeeper on, so that is why I've set a
 custom folder for MacPorts applications in the config file
 /opt/local/Applications/MacPorts

 I deleted everything per the instructions here -
 https://guide.macports.org/chunked/installing.macports.uninstalling.html
 Then verified /opt/local/etc/macports.conf has application_dir set to
 /opt/local/Applications/MacPorts
 Then reinstalled macports from the MacPorts-2.7.1-11-BigSur.pkg
 Ran $ sudo port selfupdate
 Then tried to install youtube-dl.  $ sudo port install youtube-dl

 It progresses, up until it gets to Python39, at which point it fails...
 --->  Installing python39 @3.9.5_0
 Error: Failed to install python39: no destroot found at:
 /opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_lang_python39/python39/work/destroot
 Error: See
 /opt/local/var/macports/logs/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_lang_python39/python39/main.log
 for details.
 Error: Follow https://guide.macports.org/#project.tickets if you believe
 there is a bug.
 Error: Processing of port youtube-dl failed

 Looking at the log file for Python39 [
 /opt/local/var/macports/logs/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_lang_python39/python39/main.log
 ]

 I see that it is still trying to install Python into
 /Applications/MacPorts, instead of /opt/local/Applications/MacPorts.  The
 OS is denying write access to /Applications/MacPorts.

 Python39 Log excerpt:
 :debug:activate activating directory: /
 :debug:activate activating directory: /Applications
 :debug:activate activating directory: /Applications/MacPorts
 :debug:activate Activation failed, rolling back.
 :error:activate Failed to activate python39: can't create directory
 "/Applications/MacPorts": not owner
 :debug:activate Error code: POSIX EPERM {not owner}
 :debug:activate Backtrace: can't create directory
 "/Applications/MacPorts": not owner

-- 
Ticket URL: <https://trac.macports.org/ticket/63048#comment:3>
MacPorts <https://www.macports.org/>
Ports system for macOS