[GHC] #8827: Inferring Safe mode with GeneralizedNewtypeDeriving is wrong

[GHC]

#8827: Inferring Safe mode with GeneralizedNewtypeDeriving is wrong
-------------------------------------+------------------------------------
        Reporter:  goldfire          |            Owner:
            Type:  bug               |           Status:  new
        Priority:  normal            |        Milestone:  7.8.1
       Component:  Compiler          |          Version:  7.8.1-rc2
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:  8226, 8745
-------------------------------------+------------------------------------

Comment (by goldfire):

 I'll admit to liking the general flavor of comment:27, but the details
 elude me somewhat. What, precisely, would go after the word `deriving`?
 What's the interaction between derived instances and role annotations?
 Could a derived instance be more restrictive than the assigned roles? (It
 certainly couldn't be ''less'' restrictive!) How would a user specify
 that?

 On a separate note, and with no intention to start a flame war, this
 process would have been easier if we had had a more accurate timeline on
 the 7.8 release. When some of this debate started in October, we debated
 under the "late hour" premise, as well. The RCs hadn't gone out,
 obviously, but any less-than-almost-fully-baked idea was discarded as "too
 much work too late". If we had known that we had a few months to work out
 a proposal and implement it, it's possible that we'd be in a better place
 today. Of course, schedules slip, but communicating a best guess (even as
 that guess changes) would have been helpful.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8827#comment:29>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler