id	summary	reporter	owner	description	type	status	priority	milestone	component	version	severity	resolution	keywords	cc	difficulty	ghcversion	platform
264	unionBuildInfo should not always use nub	igloo		"The below report was originally filed as
http://hackage.haskell.org/trac/ghc/ticket/2190

In libraries/Cabal/Distribution/PackageDescription.hs, the unionBuildInfo function combines, for example, ldOptions from two BuildInfos, using nub to eliminate duplicate arguments.  This is wrong for ldOptions and some other elements.  For example, if ldOptions contains:

{{{-Xlinker -R -Xlinker /dir1 -Xlinker -R -Xlinker /dir2}}}

Then the nubbed result is:

{{{-Xlinker -R /dir1 /dir2}}}

which doesn't work at all.  There may be some redundancy that could be eliminated, but for arguments passed to external programs, it can only be done safely by understanding the semantics of the arguments.  Similarly for extraLibs, {{{-lfoo -lbar -lfoo}}} may be necessary if {{{libfoo}}} and {{{libbar}}} reference each other's symbols.

Using nub is wrong for at least cppOptions, ccOptions, ldOptions, and extraLibs.  But I think it is necessary for some other BuildInfo components, like hsSourceDirs, so it can't be removed completely; that results in an error while building GHC:

{{{
Preprocessing library unix-2.3.0.0...
Generating Makefile unix-2.3.0.0...
Setup: makefile: can't cope with multiple hs-source-dirs yet, sorry
}}}

So {{{combine}}} could take an extra arguments, which would be nub in some cases or id in others.
"	defect	closed	normal	Cabal-1.4	Cabal library	1.2.3.0	normal	fixed		prj-site-hackage.haskell.org@…	easy (<4 hours)	6.8.2