[GHC] #13885: Template Haskell doesn't freshen GADT type variables properly

[GHC]

#13885: Template Haskell doesn't freshen GADT type variables properly
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  closed
        Priority:  normal            |            Milestone:  8.4.1
       Component:  Template Haskell  |              Version:  8.0.1
      Resolution:  fixed             |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |            Test Case:  th/T13885
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D3867
       Wiki Page:                    |
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Comment (by Ryan Scott <ryan.gl.scott@…>):

 In [changeset:"6330b0b0938bc7b27463b3bbfa0df661e4a966b1/ghc" 6330b0b/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="6330b0b0938bc7b27463b3bbfa0df661e4a966b1"
 Document the intricacies of ForallC variable quantification better

 Summary:
 I recently (re-)discovered that `ForallC` quantifies different type
 variables
 depending on whether `GadtC` is present or not. This is an important
 enough gotcha where I feel like this fact should also be advertised in the
 `template-haskell` documentation itself, so this patch does just that.

 Test Plan: Read it

 Reviewers: goldfire, austin, bgamari

 Subscribers: rwbarton, thomie

 GHC Trac Issues: #13885

 Differential Revision: https://phabricator.haskell.org/D3880
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13885#comment:10>
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