checkPackageFiles does not work for subdirs in Cabal 2.2

[snoyberg]

I believe this is a regression between Cabal 2.0 and 2.2. I discovered this when using a stack built against Cabal 2.2. When running the command stack sdist ./some-subdir, I got an error message about the cabal file not existing in the local directory. You can see the original report at commercialhaskell/stack#3919.

Repro I'm including Stack script headers to make it easier to test against both Cabal 2.0 (shipped with GHC 8.2.2) and Cabal 2.2 (shipped with GHC 8.4.1), but testing directly with GHC will produce the same result. Working code for GHC 8.2.2:

#!/usr/bin/env stack
-- stack --resolver ghc-8.2.2 script
import Distribution.PackageDescription.Check
import Distribution.PackageDescription.Parse
import System.Environment (getArgs)
import System.FilePath (takeDirectory)
import Distribution.PackageDescription.Configuration (flattenPackageDescription)

main :: IO ()
main = getArgs >>= mapM_ go

go :: FilePath -> IO ()
go fp = do
  putStrLn $ "Checking: " ++ fp
  gpd <- readGenericPackageDescription minBound fp
  let dir = takeDirectory fp
      pd = flattenPackageDescription gpd
  checkPackageFiles pd dir >>= print
  putStrLn "\n\n"

Runs with:

$ ./check-ghc-822.hs http-client/http-client/http-client.cabal 
Checking: http-client/http-client/http-client.cabal
[]

Tweaked slightly to use GHC 8.4.1 instead:

#!/usr/bin/env stack
-- stack --resolver ghc-8.4.1 script
import Distribution.PackageDescription.Check
import Distribution.PackageDescription.Parsec
import System.Environment (getArgs)
import System.FilePath (takeDirectory)
import Distribution.PackageDescription.Configuration (flattenPackageDescription)

main :: IO ()
main = getArgs >>= mapM_ go

go :: FilePath -> IO ()
go fp = do
  putStrLn $ "Checking: " ++ fp
  gpd <- readGenericPackageDescription minBound fp
  let dir = takeDirectory fp
      pd = flattenPackageDescription gpd
  checkPackageFiles pd dir >>= print
  putStrLn "\n\n"

Results in:

$ ./check-ghc-841.hs http-client/http-client/http-client.cabal 
Checking: http-client/http-client/http-client.cabal
check-ghc-841.hs: ./http-client.cabal: openBinaryFile: does not exist (No such file or directory)

However, running the script from inside the directory works fine:

$ cd http-client/http-client
$ ../../check-ghc-841.hs http-client.cabal 
Checking: http-client.cabal
[]

Personally, I'd rate this as a blocker for the cabal-install 2.2 release, but perhaps the codepaths work differently there than I'm expecting.

[hvr]

Can this also be reproduced w/o Stack? If so I'd appreciate repro instructions in that spirit.

[snoyberg]

Yes, it's reproducible with just runghc on the file.

[snoyberg]

Turned out to be a simple fix of adding a relative call. PR opened at #5208.

It looks like the regression was introduced in 96bcbf1.

[hvr]

wow... that one went undetected for a very long time...

[23Skidoo]

This was fixed by #5208, both in master and 2.2. Fix is included in Cabal-2.2.0.1 onwards.