[GHC] #13799: -ddump-splices prints out declarations in the wrong order

[GHC]

#13799: -ddump-splices prints out declarations in the wrong order
-------------------------------------+-------------------------------------
        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Template Haskell  |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Debugging         |  Unknown/Multiple
  information is incorrect           |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by RyanGlScott):

 More generally, GHC seems to be pretty cavalier in modifying the
 quasiquoted declarations before pretty-printing them. Here's another
 example:

 {{{#!hs
 {-# LANGUAGE TemplateHaskell #-}
 {-# LANGUAGE TypeOperators #-}
 {-# OPTIONS_GHC -ddump-splices #-}
 module Bug where

 $([d| infixr 5 :*:
       data a :*: b = a :*: b
     |])
 }}}
 {{{
 $ /opt/ghc/8.2.1/bin/runghc Bug.hs
 Bug.hs:(6,3)-(8,6): Splicing declarations
     [d| infixr 5 :*:_a1pB, :*:_a1pA

         data a_a1pC :*:_a1pA b_a1pD = a_a1pC :*:_a1pB b_a1pD |]
   ======>
     infixr 5 :*:_a4aj
     infixr 5 :*:_a4ai
     data (:*:_a4ai) a_a4ak b_a4al = a_a4ak :*:_a4aj b_a4al

 Bug.hs:6:3: error:
     Multiple fixity declarations for ‘:*:_a4aj’
     also at  Bug.hs:(6,3)-(8,6)
   |
 6 | $([d| infixr 5 :*:
   |   ^^^^^^^^^^^^^^^^...
 }}}

 Because `(:*:)` is used in both the type and value namespace, GHC seems to
 be creating //two// `newName`s for `:*:` behind the hood, and changing the
 data/fixity declarations accordingly. (Notice that the fixity declaration
 has two identifiers now!) It then proceeds to fail to compile due to
 #13054, but that's a separate issue. The issue at hand is that `-ddump-
 splices` is printing out internal details in the quasiquoted `[d| ... |]`
 declarations, when it really needn't.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13799#comment:1>
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