[GHC] #13553: GHC 8.2.1 preprocesses __GLASGOW_HASKELL__ incorrectly with cpphs

[GHC]

#13553: GHC 8.2.1 preprocesses __GLASGOW_HASKELL__ incorrectly with cpphs
-------------------------------------+-------------------------------------
           Reporter:  RyanGlScott    |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 I'm not exactly sure if this is the fault of `cpphs` or GHC, but I'll
 report this issue to GHC Trac for now, since (ostensibly) the only thing
 that has changed in this equation is the GHC version. Take this file:

 {{{#!hs
 {-# LANGUAGE CPP #-}
 module Bug where

 foo :: Int
 #if __GLASGOW_HASKELL__ >= 800
 foo = 42
 #else
 foo = "wrong type"
 #endif
 }}}

 Now let's compile it using `cpphs-1.20.4` as a preprocessor. With GHC 8.0,
 everything works out fine:

 {{{
 $ /opt/ghc/8.0.2/bin/ghc Bug.hs -pgmP cpphs -optP --cpp
 Warning: Can't find file
 "/opt/ghc/8.0.2/lib/ghc-8.0.2/include/ghcversion.h" in directories

   Asked for by: Bug.hs  at line 1 col 1
 [1 of 1] Compiling Bug              ( Bug.hs, Bug.o )
 }}}

 But with GHC 8.2.1, things go awry:

 {{{
 $ /opt/ghc/8.2.1/bin/ghc Bug.hs -pgmP cpphs -optP --cpp
 Warning: Can't find file
 "/opt/ghc/8.2.1/lib/ghc-8.2.0.20170403/include/ghcversion.h" in
 directories

   Asked for by: Bug.hs  at line 1 col 1
 [1 of 1] Compiling Bug              ( Bug.hs, Bug.o )

 Bug.hs:8:7: error:
     • Couldn't match expected type ‘Int’ with actual type ‘[Char]’
     • In the expression: "wrong type"
       In an equation for ‘foo’: foo = "wrong type"
   |
 8 | foo = "wrong type"
   |       ^^^^^^^^^^^^
 }}}

 This bug causes several libraries on Hackage which use `cpphs` as a
 preprocessor to fail when built with GHC 8.2.1, including `Agda`.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13553>
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