[tor-bugs] #18718 [metrics-lib]: remove last impl. dependency from api

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#18718: remove last impl. dependency from api
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 Reporter:  iwakeh       |          Owner:  karsten
     Type:  defect       |         Status:  new
 Priority:  Medium       |      Milestone:
Component:  metrics-lib  |        Version:
 Severity:  Normal       |     Resolution:
 Keywords:               |  Actual Points:
Parent ID:               |         Points:
 Reviewer:               |        Sponsor:
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Comment (by karsten):

 Hmm, I wonder how to do the first step, but it's certainly possible that
 I'm overlooking something.  If I make that change in my local metrics-lib
 repository, my local metrics-db repository breaks, because
 `descriptorParser.parseDescriptors()` suddenly throws an exception that
 metrics-db doesn't know about.  This currently only works, because the
 exception that metrics-db doesn't know about is a subclass of the
 exception it expects.

 But I agree that we should make the base package independent of its impl
 subpackage.  Looks like the patch where we moved that exception is from
 September 2014.  I could see us putting out a version 2.0.0 this April.
 What do you think?  That shouldn't distract you too much from your
 CollecTor improvements, so I could do most of the work on metrics-lib.

 Regarding other things for version 2.0.0, I could see how a parent ticket
 would work, though a keyword is probably a bit more flexible.  (There's an
 annoying problem with closing parent tickets when not all their child
 tickets are closed.)  How about `descriptor-2.0.0` as keyword, which would
 also be the Git tag for that version?

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/18718#comment:3>
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