(Imported from Trac #793, reported by @tibbe on 2011-01-18)
I managed to make Cabal fail to build a project by having
Author: Johan Tibell
Build-depends: base, vector
[1 of 2] Compiling PopCount ( PopCount.hs, dist/build/PopCount.o )
ld: duplicate symbol _popcount in dist/build/popcount.o and dist/build/PopCount.o for inferred architecture i386
Cabal ought to warn in this case.