[tor-bugs] #20667 [Core Tor/Tor]: Clarify FetchUselessDescriptors and UseMicrodescriptors in 0.3.0

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#20667: Clarify FetchUselessDescriptors and UseMicrodescriptors in 0.3.0
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     Reporter:  teor          |      Owner:
         Type:  defect        |     Status:  new
     Priority:  Medium        |  Milestone:  Tor: 0.3.0.x-final
    Component:  Core Tor/Tor  |    Version:  Tor: 0.3.0.0-alpha-dev
     Severity:  Normal        |   Keywords:  doc
Actual Points:                |  Parent ID:
       Points:  0.1           |   Reviewer:
      Sponsor:                |
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 `FetchUselessDescriptors 1` used to imply `UseMicrodescriptors 0`, but due
 to #6769, it doesn't in 0.3.0 and later.

 Therefore, clients that want to download a full consensus have to
 explictly set `UseMicrodescriptors 0`.

 We should document this in the man page and probably the changelog
 summary, as it is a breaking change for many configs that used to obtain a
 full consensus.

 (Alternately, we could fix this bug by FetchUselessDescriptors download a
 full consensus, even on clients, and document that behaviour.)

 Discovered when running a test bandwidth authority - see #20621.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/20667>
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