[GHC] #10891: `reify` doesn't find associated type families

[GHC]

#10891: `reify` doesn't find associated type families
-------------------------------------+-------------------------------------
        Reporter:  antalsz           |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.0.1
       Component:  Template Haskell  |              Version:  7.10.2
      Resolution:                    |             Keywords:  type
                                     |  families; newcomer
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D1254
-------------------------------------+-------------------------------------

Comment (by Ben Gamari <ben@…>):

 In [changeset:"b4d43b4e9f4f4fba068ab1e132113c4cd305dfe3/ghc"
 b4d43b4e/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="b4d43b4e9f4f4fba068ab1e132113c4cd305dfe3"
 reify associated types when reifying typeclasses(#10891)

 As reported in Trac #10891, Template Haskell's `reify` was not
 generating Decls for associated types. This patch fixes that.

 Note that even though `reifyTyCon` function used in this patch returns
 some type instances, I'm ignoring that.

 Here's an example of how associated types are encoded with this patch:

 (Simplified representation)

     class C a where
       type F a :: *

     -->

     OpenTypeFamilyD "F" ["a"]

 With default type instances:

     class C a where
       type F a :: *
       type F a = a

     -->

     OpenTypeFamilyD "F" ["a"]
     TySynInstD "F" (TySynEqn [VarT "a"] "a")

 Test Plan:
 This patch was already reviewed and even merged. The patch is later
 reverted because apparently it broke the build some time between the
 validation of this patch and merge. Creating this new ticket to fix the
 validation.

 Reviewers: goldfire, austin, bgamari

 Reviewed By: bgamari

 Subscribers: thomie

 Differential Revision: https://phabricator.haskell.org/D1277

 GHC Trac Issues: #10891
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10891#comment:13>
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