Re: [GHC] #12993: GHC 8.0.2-rc2 template Haskell interface file issue

2 Aug 2017

      #12993: GHC 8.0.2-rc2 template Haskell interface file issue
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        Reporter:  glguy             |                Owner:  (none)
            Type:  bug               |               Status:  closed
        Priority:  highest           |            Milestone:  8.0.2
       Component:  Template Haskell  |              Version:  8.0.2-rc2
      Resolution:  fixed             |             Keywords:
Operating System:  MacOS X           |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by niteria):

 I just run into this in our `ghc-8.0.2-facebook` branch (we cut from
 ghc-8.0 before the revert happened).
 It reproduces in an interesting way with `haddock` +
 `DuplicateRecordFields`:
 {{{
 $ cat A.hs Main.hs; haddock A.hs Main.hs
 {-# LANGUAGE DuplicateRecordFields #-}
 {-# LANGUAGE DuplicateRecordFields #-}
 module A where

 data A = A {
   func :: Int -> Int
 }

 a :: A
 a = A { func = (*2) }
 module Main where

 import A

 main :: IO ()
 main = print (func a 10)
 Haddock coverage:
    0% (  0 /  3) in 'A'
   Missing documentation for:
     Module header
     A (A.hs:4)
     a (A.hs:8)

 Main.hs:6:15: error:
     • Can't find interface-file declaration for variable A.$sel:func:A
         Probable cause: bug in .hi-boot file, or inconsistent .hi file
         Use -ddump-if-trace to get an idea of which file caused the error
     • In the first argument of ‘print’, namely ‘(func a 10)’
       In the expression: print (func a 10)
       In an equation for ‘main’: main = print (func a 10)
   |
 6 | main = print (func a 10)
   |
 }}}

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12993#comment:12
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