Nonsensical paths are generated into setup-config

[nh2]

Originally found in NixOS/nixpkgs#28301

Issue description

I just had a look at a dist/setup-config file generated by cabal configure or equivalent Setup.hs call, and it contains things like this:

^@^@^@^@^@^@^@;/nix/store/66znhpqvqyvhgw4wxpl1f2rlfpqrbcsd-lz4-131/bin/tar^@^@^@^@^@^@^@A/nix/store/vmisgqfbqywgsw9php70bbx90czr398i-openssh-7.4p1/bin/tar^@^@^@^@^@^@^@?/nix/store/cjpyvkqqd55s8jgj7c2qv9wwmisw5ayg-rsync-3.1.2/bin/tar^@^@^@^@^@^@^@=/nix/store/2m6v6lnmnf9521ixd5v0x4qrmjkn30ws-gcc-5.4.0/bin/tar

The same thing happens for tar, alex, happy etc, so I suspect that this is about build-tools called during haskell builds.

The N*M combination of executables and paths they are in isn't anything new when it comes to stat()ing or execve()ing binaries, but it seems totally nonsensical to me that such paths would be written to a file (this also seems to blow up the file size of setup-config quite a bit, e.g. mine is 1.6 MB large).

The Haskell builder in nixpkgs passes in the paths that end up being recorded, but we think it's a cabal bug because it seems that these paths shouldn't be recorded in there.

CC @peti

[23Skidoo]

/cc @ttuegel

[ttuegel]

The Haskell builder in nixpkgs passes in the paths that end up being recorded, but we think it's a cabal bug because it seems that these paths shouldn't be recorded in there.

To clarify: The Nixpkgs Haskell builder passes in the correct paths only, right? Your statement makes it sound like it passes incorrect paths. In any case, only the paths of configured programs should be saved, so this is definitely not right.

I can't tell from your example which LocalBuildInfo field is capturing these values. I realize this may be too much to ask, but could you try to load the setup-config into GHCi? It should suffice to do something like,

$ ghci
> import Distribution.Simple.Configure
> getConfigStateFile "./path/to/the/bad/setup-config"