Opened 12 years ago

Closed 12 years ago

Last modified 47 years ago

#438 closed bug (Duplicate)

Recompilation check should include flags

Reported by: simonpj Owned by: nobody
Priority: low Milestone:
Component: None Version: None
Keywords: Cc:
Operating System: Architecture:
Type of failure: None/Unknown Test Case:
Blocked By: Blocking:
Related Tickets: Differential Rev(s):
Wiki Page:


GHC skips recompilation of a module if the module code 
hasn't changed, even if the flags in use *have* changed.  
A benign version is that switching on -O won't recompile 
modules that were compiled without -O.  But here's a 
nastier version: changing the -main-is flag can lead to an 
obscure link error.  Details below supplied by Niels 


Actually, i reproduced it now and the reason is a bit 
different. I have an
application Test and Test2. They both have a main 
function. Test imports Test2
for some other function. So this is how those files look 

~/pancake > cat Test.hs
module Test where
import Test2 hiding (main)

main = doit

~/pancake > cat Test2.hs
module Test2 where

doit = print "Test2.doit"
main = print "Test2.main"

I then first compile the first app:
~/pancake > ghc --make -main-is Test.main Test.hs
Chasing modules from: Test.hs
Compiling Test2            ( ./Test2.hs, ./Test2.o )
Compiling Test             ( Test.hs, Test.o )
Linking ...

then i compile the second app:
~/pancake > ghc --make -main-is Test2.main Test2.hs
Chasing modules from: Test2.hs
Skipping  Test2            ( Test2.hs, Test2.o )
Linking ...
/usr/lib/ghc-6.4/libHSrts.a(Main.o)(.text+0xe): In function 
: undefined reference to `__stginit_ZCMain'
/usr/lib/ghc-6.4/libHSrts.a(Main.o)(.text+0x28): In 
function `main':
: undefined reference to `ZCMain_main_closure'
collect2: ld returned 1 exit status

So I guess generating Test2.o the first time and using -
main-is renamed the main
in Test2.o . Since it is not recompiled when I want to 
compile the second app,
it fails because it cant find the main...I thought providing 
a -main-is flag
again when compiling the second app would somehow 
force recompilation of Test2.o
or at least fixing the 'renaming' that the first compilation 
of Test2.o had 

greetings, Niels.

Change History (1)

comment:1 Changed 12 years ago by simonmar

Status: assignedclosed
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