[GHC] #10278: ApiAnnotations : Nested forall loses forall annotation

[GHC]

#10278: ApiAnnotations : Nested forall loses forall annotation
-------------------------------------+-------------------------------------
        Reporter:  alanz             |                   Owner:  alanz
            Type:  bug               |                  Status:  patch
        Priority:  normal            |               Milestone:  7.10.2
       Component:  Compiler          |                 Version:  7.10.1
  (Parser)                           |                Keywords:
      Resolution:                    |  ApiAnnotations
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  None/Unknown      |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:                    |                Blocking:
                                     |  Differential Revisions:
                                     |  Phab:D833,Phab:D836
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Comment (by Austin Seipp <austin@…>):

 In [changeset:"81030ede73c4e3783219b2a8d7463524e847cfce/ghc"]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="81030ede73c4e3783219b2a8d7463524e847cfce"
 ApiAnnotations : Nested forall loses forall annotation

 When parsing

     {-# LANGUAGE ScopedTypeVariables #-}

     extremumNewton :: forall tag. forall tag1.
                        tag -> tag1 -> Int
     extremumNewton = undefined

 The parser attaches an AnnForall to the second forall, which appears as
 a nested HsForAllTy.

 Somewhere this nesting is flattened, and the tyvarbndrs are collapsed
 into a single HsForAllTy. In this process the second AnnForAll loses its
 anchor in the AST.

 Reviewed By: austin

 Differential Revision: https://phabricator.haskell.org/D833

 GHC Trac Issues: #10278
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10278#comment:5>
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