[GHC] #14808: GHC HEAD regression: GADT constructors no longer quantify tyvars in topological order

[GHC]

#14808: GHC HEAD regression: GADT constructors no longer quantify tyvars in
topological order
-------------------------------------+-------------------------------------
        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  patch
        Priority:  highest           |            Milestone:  8.6.1
       Component:  Compiler (Type    |              Version:  8.5
  checker)                           |
      Resolution:                    |             Keywords:  GADTs
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #14529, #14796    |  Differential Rev(s):  Phab:D4413
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by Ben Gamari <ben@…>):

 In [changeset:"043466b9aac403553e2aaf8054c064016f963f80/ghc"
 043466b9/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="043466b9aac403553e2aaf8054c064016f963f80"
 Rename the types in a GADT constructor in toposorted order

 Previously, we were extracting the free variables from a
 GADT constructor in an incorrect order, which caused the type
 variables for the constructor's type signature to end up in
 non-toposorted order. Thankfully, rearranging the order of types
 during renaming makes swift work of this bug.

 This fixes a regression introduced in commit
 fa29df02a1b0b926afb2525a258172dcbf0ea460.
 For whatever reason, that commit also commented out a
 significant portion of the `T13123` test. This code appears
 to work, so I've opted to uncomment it.

 Test Plan: make test TEST=T14808

 Reviewers: simonpj, bgamari

 Reviewed By: bgamari

 Subscribers: rwbarton, thomie, carter

 GHC Trac Issues: #14808

 Differential Revision: https://phabricator.haskell.org/D4413
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14808#comment:2>
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