[ ghc-Bugs-1039993 ] ghc --make + hi-boot + class declarations = trouble

Bugs item #1039993, was opened at 2004-10-04 10:41
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Category: Compiler
Group: 6.2.1
Status: Open
Resolution: None
Priority: 5
Submitted By: Jon Cast (jcast)
Assigned to: Nobody/Anonymous (nobody)
Summary: ghc --make + hi-boot + class declarations = trouble

Initial Comment:
Consider the following test case:

-- Main.hs --
module Main where

import Module1
import Module2

main = return ()

-- Module1.hs --
module Module1 where

import Module2

class Three alpha where
  three :: Kappa alpha -> Kappa alpha -> Kappa alpha

-- Module1.hi-boot --
module Module2 where

import {-# SOURCE #-} Module1

data Kappa alpha = Kappa alpha alpha

f :: Three alpha => Kappa alpha -> alpha
f k = case three k k of
        Kappa x y -> x

-- Module1.hi-boot --
module Module1 where

class Three alpha where
  three :: Module2.Kappa alpha -> Module2.Kappa alpha
        -> Module2.Kappa alpha

-- Compilation Results --
cd /home/jcast/Source/tmp/      # -*-compilation-*-
Entering directory `/home/jcast/Source/tmp/'
ghc --make Main
Chasing modules from: Main
Compiling Module2          ( ./Module2.hs, ./Module2.o )

./Module2.hs:1:
    Failed to find interface decl for `Module1.$dmthree'
    from module `Module1'

Compilation exited abnormally with code 1 at Mon Oct  4
09:38:50

No, for the real program it's not strictly necessary to
employ mutual recursion between the modules in
question---but it is by far the most natural design.

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