[tor-bugs] #19028 [Core Tor/Tor]: Merge the header checks in configure.ac

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#19028: Merge the header checks in configure.ac
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     Reporter:  cypherpunks   |      Owner:
         Type:  defect        |     Status:  new
     Priority:  Medium        |  Milestone:
    Component:  Core Tor/Tor  |    Version:  Tor: 0.2.8.1-alpha
     Severity:  Normal        |   Keywords:
Actual Points:                |  Parent ID:
       Points:                |   Reviewer:
      Sponsor:                |
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 The build configuration contains
 [https://gitweb.torproject.org/tor.git/tree/configure.ac#n945 two sets of
 header checks] where one checks headers that are deemed essential and one
 checks headers that are not. The only difference being that missing
 essential headers display a non-fatal warning when they aren't found.

 For the following reasons i think it is better to merge the sets and
 discard the warning.

 - Commit
 [https://gitweb.torproject.org/tor.git/commit/?id=e8cc839e41adc4975a61fee62abe7f6664fd0c0e
 e8cc839e41adc4975a61fee62abe7f6664fd0c0e] adds `sys/capability.h` to the
 essential header set but Tor runs fine without capabilities being
 available. IMO it is in the wrong set.
 - Having two sets requires developers to make a choice whether headers are
 essential or not. Instead developers should write code that handles cases
 where the headers are unavailable (like the capabilities code).
 - The current warning is truncated because its message is incorrectly
 quoted. This means the part about sending the `orconfig.h` file isn't
 shown and has been ineffective.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/19028>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
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