[GHC] #10361: DeriveAnyClass does not fill in associated type defaults

[GHC]

#10361: DeriveAnyClass does not fill in associated type defaults
-------------------------------------+-------------------------------------
        Reporter:  kosmikus          |                Owner:  dreixel
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  7.10.1
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D1283
-------------------------------------+-------------------------------------

Comment (by Ben Gamari <ben@…>):

 In [changeset:"2f74be9c8af1e167b21df1a27b96b6626cd446a9/ghc"
 2f74be9c/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="2f74be9c8af1e167b21df1a27b96b6626cd446a9"
 Fill in associated type defaults with DeriveAnyClass

 Summary:
 Unlike `-XDefaultSignatures`, `-XDeriveAnyClass` would not fill in
 associated type family defaults when deriving a class which contained
 them.

 In order to fix this properly, `tcATDefault` needed to be used from
 `TcGenDeriv`. To avoid a module import cycle, `tcATDefault` was moved
 from `TcInstDcls` to `TcClsDcl`.

 Fixes #10361.

 Test Plan: ./validate

 Reviewers: kosmikus, dreixel, bgamari, austin, simonpj

 Subscribers: thomie

 Differential Revision: https://phabricator.haskell.org/D1283

 GHC Trac Issues: #10361
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10361#comment:7>
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