id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	os	architecture	failure	difficulty	testcase	blockedby	blocking	related
3321	-fhpc assumes original sources relative to the current directory	duncan		"For the most part, ghc can be invoked in a manner that is independent of the current directory by suitable use of `-i` options.

With `-fhpc` it appears that the hpc bits always look in the current directory to find original source files.

Consider the following file layout:
{{{
Codec/Compression/Zlib/Stream.hsc
dist/build/Codec/Compression/Zlib/Stream.hs
examples/gunzip.hs
}}}

Now if we `cd` to `examples` and run:
{{{
ghc --make gunzip.hs -lz -i../ -i../dist/build
}}}
then it works fine. It finds `Codec/Compression/Zlib/Stream.hs` in `../dist/build` and it never bothers to look for the original source of course.

Now in `-fhpc` mode it has to also find the original sources so that it can match things back to them. However just adding -fhpc to the above command fails:
{{{
ghc --make gunzip.hs -lz -i../ -i../dist/build -fhpc
[1 of 4] Compiling Codec.Compression.Zlib.Stream ( ../dist/build/Codec/Compression/Zlib/Stream.hs, ../dist/build/Codec/Compression/Zlib/Stream.o )
Codec/Compression/Zlib/Stream.hsc: getModificationTime: does not exist (No such file or directory)
}}}

So it's clearly not looking in the directory given by `-i..` for the original sources. Also, the failure mode is a bit unfriendly.

Cabal sometimes takes advantage of the fact that ghc can be invoked in a manner that is independent of the current directory, and we would like to add hpc support into Cabal."	bug	new	lowest	7.6.2	Compiler	6.10.1				Unknown/Multiple	Unknown/Multiple		Unknown