When you permanently destroy a specific project from the command line, the following
additional good things now happen:

• the direct orhpan milestones are removed too (instead of leaving them orphan, broken, invisible forever)
• all children projects emerge like cute bubbles by one level (instead of having them orphan, broken, invisible forever)
• the parent project is eventually restored as "without sub-projects" (instead of having a broken root-project with bugged memberships)

This change has nothing to do with archived projects.

This change will only affect future usages of the destroy workflow, that is:

./bin/remove destroy PHID-OF-YOUR-PROJECT-TO-BE-DESTROYED

Example initial situation:

Project A
 [projectDepth: 0]
 [hasSubprojects: 1]
 [members: *automatic*, foo, bar]
 > Project B
  [projectDepth: 1]
  [hasSubprojects: 1]
  [members: *automatic*, foo, bar]
  > Project C
   [hasSubprojects: 0]
   [projectDepth: 2]
   [members: foo, bar]
   > Milestone C.1
    [projectDepth: 3]

Situation after destroying only project A:

Project B
 [projectDepth: 0]
 [hasSubprojects: 1]
 [members: *automatic*, foo, bar]
 > Project C
  [projectDepth: 1]
  [hasSubprojects: 0]
  [members: foo, bar]
  > Milestone C.1
   [projectDepth: 2]

Situation after destroying only project B:

Project A
 [projectDepth: 0]
 [hasSubprojects: 1]
 [members: *automatic*, foo, bar]
 > Project C
  [projectDepth: 1]
  [hasSubprojects: 0]
  [members: foo, bar]
  > Milestone C.1
   [projectDepth: 2]

Situation after destroying only project C:

Project A
 [projectDepth: 0]
 [hasSubprojects: 1]
 [members: *automatic*, foo, bar]
 > Project B
  [projectDepth: 1]
  [hasSubprojects: 0]
  [members: foo, bar]

Situation after destroying only milestone C.1:

Project A
 [projectDepth: 0]
 [hasSubprojects: 1]
 [members: *automatic*, foo, bar]
 > Project B
  [projectDepth: 1]
  [hasSubprojects: 1]
  [members: *automatic*, foo, bar]
  > Project C
   [hasSubprojects: 0]
   [projectDepth: 2]
   [members: foo, bar]

Closes T15697
Closes T15913
Closes T15918
Closes T16043

Run multiple times the destroy workflow under every imaginable case,
to violently destroy a projects tree, leaf by leaf. We suggest to run it
with the trace option. Example:

./bin/remove destroy --trace PHID-PROJ-s0met1ng

To run the above workflow multiple times, you may appreciate a dump:

./bin/storage dump | gzip > dump.sql.gz

So you can easily restore it whenever you want:

zcat dump.sql.gz | ./bin/storage shell

• Delete simple milestone
  • create a new simple project "A" with milestone "M" and delete "M"
  • deletion still works on milestone "M"
• Delete simple project
  • create a new simple project "A" with a workboard and destroy "A":
  • deletion still works on project "A"
  • workboard is still not accessible
  • if there were tasks, they are still there but without tag "A"
• Delete project with milestone (T15913)
  • create a new project "A" with a milestone "B" and delete "A"
  • deletion still works on project "A"
  • milestone "B" is finally nuked from the database and you do not see it anymore in the phabricator_project table
• Delete a project with sub-projects (T15918)
  • create a new project "A" with a sub-project called "B" and delete "A"
  • deletion still works on project "A"
  • project "B" becomes a root-project and it has depth "0" again and it's usable, instead of having it borked with "You Shall Not Pass"
• Delete a sub-project (T15697)
  • create a new project "A" with a sub-project called "B" and delete "B"
  • deletion still works on project "B"
  • project "A" is usable again like "B" never existed, so you can change memberships and all the things, instead of having it borked

If you don't have enough time to test this, just enjoy the new unit tests covering the destroy process (T16043):

arc unit src/applications/project/storage/PhabricatorProject.php

In particular, in the unit test results, check the new green light about this method:

PhabricatorProjectCoreTestCase::testProjectDestroy