[GHC] #14343: bad pretty-printing of types with promoted data types

[GHC]

#14343: bad pretty-printing of types with promoted data types
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        Reporter:  lspitzner         |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by lspitzner):

 I am fine with '[' being lexed as it is, so i don't mind a wont-fix for
 that aspect. But why does the error message for syntactically valid input
 contain source fragments that are not syntactically valid?

 Just as a test for how input is transformed (on 8.2.1 as well):

 {{{
 Prelude> _ :: Proxy '[  'True ]                           -- 2 spaces in
 input

 <interactive>:8:1: error:
     • Found hole: _ :: Proxy '['True]                     -- 0 spaces
     • In the expression: _ :: Proxy '[ 'True]             -- 1 spaces
       In an equation for ‘it’: it = _ :: Proxy '[ 'True]  -- 1 spaces
     • Relevant bindings include
         it :: Proxy '['True] (bound at <interactive>:8:1) -- 0 spaces
 }}}

 The zeros are problematic, and i think the ones only avoid the problem
 because they don't really re-layout, they just merge whitespace (at least
 that's what i suspect; haven't looked at the source).

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14343#comment:2>
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