[GHC] #13887: Template Haskell pretty-printer doesn't parenthesize infix datatype names in data declarations

[GHC]

#13887: Template Haskell pretty-printer doesn't parenthesize infix datatype names
in data declarations
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Template Haskell  |              Version:  8.0.1
      Resolution:                    |             Keywords:  newcomer
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by ak3n):

 I am not sure, but I think that it's enough to change `pprName' Alone` to
 `pprName' Applied` [https://git.haskell.org/ghc.git/blob/HEAD:/libraries
 /template-haskell/Language/Haskell/TH/PprLib.hs#l123 here].

 There are 8 failed tests in `testsuite/tests/th` because of this change:

 - `GHC.Types.:` becomes `(GHC.Types.:)`
 - `Data.Type.Equality.~` becomes `(Data.Type.Equality.~)`
 - and something else

 There is another way to fix it.

 Change `ppr t` to `pprName' Applied t`
 [https://git.haskell.org/ghc.git/blob/HEAD:/libraries/template-
 haskell/Language/Haskell/TH/Ppr.hs#l401 here], which outputs:

 {{{
 data (:~:_0) a_1 b_2 where Refl1_3 :: :~:_0 a_4 a_4
 data (:~~:_0) a_1 b_2 = a_1 ~ b_2 => Refl2_3
 }}}

 This [https://git.haskell.org/ghc.git/blob/HEAD:/libraries/template-
 haskell/Language/Haskell/TH/Ppr.hs#l402 line] is responsible for the kind
 of `Refl1_3`, but I haven't figured out how to fix it yet.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13887#comment:1>
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