[GHC] #12998: libraries/base/System/Posix/Types.hs: tries to define Floating instance for opaque type

[GHC]

#12998: libraries/base/System/Posix/Types.hs: tries to define Floating instance for
opaque type
-------------------------------------+-------------------------------------
        Reporter:  slyfox            |                Owner:
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #12795            |  Differential Rev(s):  Phab:D2876
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by Ryan Scott <ryan.gl.scott@…>):

 In [changeset:"513eb6a0638a1c64b9d76bcab39ed80cdd9dbb27/ghc"
 513eb6a0/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="513eb6a0638a1c64b9d76bcab39ed80cdd9dbb27"
 Fix #12998 by removing CTimer

 Summary:
 CTimer is a wrapper around `timer_t`, which is a typedef for `void*`
 on most platforms. The issue is that GHC's `FPTOOLS_CHECK_HTYPE` is not
 robust
 enough to discern pointer types from non-pointer types, so it mistakenly
 labels
 `timer_t` as a `Double` or `Int32` (depending on how many bits a pointer
 takes
 up on your platform). This wreaks havoc when trying to give it certain
 type
 class instances, as noted in
 https://phabricator.haskell.org/rGHCffc2327070dbb664bdb407a804121eacb2a7c734.

 For now, the simplest thing to do would be removing `CTimer`, since:

 1. The original author (@DanielG) didn't have a particular use in mind for
    `timer_t` when he fixed #12795.
 2. `CTimer` hasn't appeared in a release of `base` yet.

 Fixes #12998.

 Reviewers: austin, hvr, bgamari, DanielG, trofi

 Reviewed By: bgamari, trofi

 Subscribers: thomie, DanielG, erikd

 Differential Revision: https://phabricator.haskell.org/D2876

 GHC Trac Issues: #12795, #12998
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12998#comment:6>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler