[GHC] #1452: "undefined reference" while linking executable (for cyclic import project) in ghc-6.6.1

[GHC]

#1452: "undefined reference" while linking executable (for cyclic import project)
in ghc-6.6.1
------------------------------+---------------------------------------------
    Reporter:  guest          |        Owner:  guest           
        Type:  bug            |       Status:  assigned        
    Priority:  normal         |    Milestone:                  
   Component:  Compiler       |      Version:  6.6.1           
    Severity:  normal         |   Resolution:                  
    Keywords:  cyclic import  |   Difficulty:  Moderate (1 day)
          Os:  Linux          |     Testcase:                  
Architecture:  x86            |  
------------------------------+---------------------------------------------
Comment (by simonpj):

 Serge writes (in separate email)

 Recently I submitted a bug report  #1452  for ghc-6.6.1
 of undefined references at the stage of linking executable,
 and also of ignoring un-existing module import.

 Now I discovered the following strange effect
 (see the report source modules) which, probably, explains much.

 1. (minor note) The file  Match.hs-boot  is not needed. All the effects
 preserve after its removal.

 2. The name  `Match`  must be in the list  `other-modules:'
 in the file `dm.cabal`, which describes the package.

 But it is not in  dm.cabal !
 Because I have forgotten to put it there.
 Further,                                  make build
 still finds and compiles  Match.hs.
 The only point where  Match  is needed is  Reduce.hs:  it imports
 `Match'. But why GHC finds  Match.hs ?
 Probably, because it is in the current source directory.
 Then,
 {{{
 make install
 }}}
 succeeds.
 And further, the command
 {{{
 ghc $dmCpOpt --make Main
 }}}
 succeeds or not -- depending on whether `Match' is in  dm.cabal  or not!

 First, I think that there is my oversight here.
 But the  GHC + Cabal  system  behaves strange in this example.
 Must not it give a plain report of what is wrong with modules or
 package setting ?  Say,
 {{{
 "Error:  `Match' is not in the package but is imported by  Reduce.hs."
 }}}
 Probably, this is the matter of Cabal.

 Further, if GHC still finds Match.hs and builds the package, why this
 "undefined reference" appears while linking executable ?

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1452>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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