[tor-bugs] #33629 [Core Tor/Tor]: Use stale bot to close old pull requests

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#33629: Use stale bot to close old pull requests
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     Reporter:  teor          |      Owner:  teor
         Type:  task          |     Status:  assigned
     Priority:  Medium        |  Milestone:  Tor: 0.4.4.x-final
    Component:  Core Tor/Tor  |    Version:
     Severity:  Normal        |   Keywords:  tor-github
Actual Points:                |  Parent ID:
       Points:  0.5           |   Reviewer:
      Sponsor:                |
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 Should we automatically close stale pull request on GitHub?

 Some GitHub users won't contribute to a project with lots of open pull
 requests, because they think it's been abandoned. (Or they think we're bad
 at merging PRs.)

 But lots of our PRs get left open because we've squashed and merged the
 PR, and GitHub doesn't recognise the squashed commits, so GitHub doesn't
 auto-close the PR.

 Closing a PR:
 * hides it from the default list of PRs
 * hides its CI results in the PR itself (but they still appear in the PR
 list)

 Anyone can reopen a closed PR. Re-opening a PR re-runs CI (which is
 usually what we want for old PRs).

 I suggest we use probot stale:
 https://probot.github.io/apps/stale/

 With the following options:
 * daysUntilStale: 60
   * some backport PRs are older than 60 days, but their CI should have
 been checked when they were reviewed
   * we don't merge very many stale PRs to master
   * any period from 30 days (most reviews completed) to 6 months (release
 cycle) would probably work for us
 * daysUntilClose: 7
 * exemptLabels: pinned
 * staleLabel: stale-closed
 * markComment: (like the suggested one, but mention the "pinned" label)
 * closeComment: false

 On the following network team repositories:
 * tor
   * ~400 older than 2 months
   * ~270 older than 6 months
 * torspec
   * 8 older than 2 months
   * 6 older than 6 months
 * chutney
   * 1 older than 6 months, needs to be pinned?
 * fallback-scripts

 And the top-level GitHub config repository:
 * .github

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/33629>
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