new bug in ghc --make

[Simon Peyton-Jones]

Thanks for such a well-formed bug report.  This is territory that Simon
M has been working on, so I propose to leave it till he gets back.  (His
baby arrived fine on Sunday.)

Simon

| -----Original Message-----
| From: cvs-all-bounces at haskell.org [mailto:cvs-all-bounces at haskell.org]
On Behalf Of Malcolm
| Wallace
| Sent: 08 October 2003 11:38
| To: cvs-ghc at haskell.org
| Subject: new bug in ghc --make
| 
| Peter Simons and I have just stumbled on a bug in the CVS version
| of ghc --make that seems to have been introduced since the release
| of 6.0, so I assume it is also buggy in the yet-to-be-released 6.2.
| 
| The nub of the bug is that ghc --make now names the object file for
any
| module Main as Main.o, disregarding the actual filename of the source.
| (Previously, the .o was named to correspond to the .hs source file.)
| 
| When compiling more than one program which inhabit the same filesystem
| directory, this leads the re-compilation dependency analysis astray.
| ghc --make believes that the second Main module has already been
| compiled, and so links a /different/ program's Main.o with the modules
| imported by this program.  The resultant linking errors are highly
| confusing until you understand what is going on.
| 
| Here is an example.
| 
| file A.hs:
|     module Main where
|     import C
|     import D
|     main = do c; d
| 
| file B.hs:
|     module Main where
|     import C
|     main = do c
| 
| file C.hs:
|     module C where
|     c = putStrLn "hello"
| 
| file D.hs:
|     module D where
|     d = putStrLn "world"
| 
| Now try
|     ghc --make A; ghc --make B
| 
| In ghc-5.04.x and ghc-6.0, it works as expected.  In ghc-6.3, it
crashes like so:
| 
|     Chasing modules from: A
|     Compiling D                ( ./D.hs, ./D.o )
|     Compiling C                ( ./C.hs, ./C.o )
|     Compiling Main             ( ./A.hs, ./Main.o )
|     Linking ...
|     Chasing modules from: B
|     Skipping  C                ( ./C.hs, ./C.o )
|     Skipping  Main             ( ./B.hs, ./Main.o )		<--
error is here
|     Linking ...
|     ./Main.o: In function `__stginit_Main_':
|     ./Main.o(.text+0x25): undefined reference to `__stginit_D_'
|     ./Main.o: In function `Main_main_srt':
|     ./Main.o(.text+0x44): undefined reference to `D_d_closure'
|     ./Main.o: In function `sGy_ret':
|     ./Main.o(.text+0x5f): undefined reference to `D_d_closure'
|     collect2: ld returned 1 exit status
| 
| Regards,
|     Malcolm
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