-fhpc assumes original sources relative to the current directory

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.

Trac metadata

Trac field	Value
Version	6.10.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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