[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
-------------------------------------+-------------------------------------

Comment (by Alan Zimmerman <alan.zimm@…>):

 In [changeset:"c553e980e4a5d149af13bb705ec02819a15937ee/ghc"]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="c553e980e4a5d149af13bb705ec02819a15937ee"
 ApiAnnotations : AST version of nested forall loses forall annotation

 Summary:
 When parsing

     {-# LANGUAGE ScopedTypeVariables #-}

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

 the parser creates nested HsForAllTy's for the two forall statements.

 These get flattened into a single one in `HsTypes.mk_forall_ty`

 This patch removes the flattening, so that API Annotations are not lost in
 the
 process.

 Test Plan: ./validate

 Reviewers: goldfire, austin, simonpj

 Reviewed By: simonpj

 Subscribers: bgamari, mpickering, thomie, goldfire

 Differential Revision: https://phabricator.haskell.org/D836

 GHC Trac Issues: #10278, #10315, #10354, #10363
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10278#comment:6>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler