Data files not working in new-build projects

[fgaz]

Here's the problem: https://github.com/haskell/cabal/blob/484bb6c/cabal-install/Distribution/Client/CmdRun.hs#L211

We use the current directory as the base path for data files in new-run, but "current directory == package root" was true only before new-build.

Replacing curDir with the actual package root should fix this.

[hvr]

I just ran into this problem, and didn't realise you were fully aware of this already :-)

As this made new-run unusable for some of my use-case, I had to yak-shave and fix this in my local cabal, and here's what I did including a few TODO-notes on what is missing:

diff --git a/cabal-install/Distribution/Client/CmdRun.hs b/cabal-install/Distribution/Client/CmdRun.hs
index 4d49167..807c5cb 100644
--- a/cabal-install/Distribution/Client/CmdRun.hs
+++ b/cabal-install/Distribution/Client/CmdRun.hs
@@ -19,6 +19,7 @@ import Distribution.Client.Compat.Prelude
 
 import Distribution.Client.ProjectOrchestration
 import Distribution.Client.CmdErrorMessages
+import Distribution.Client.Types (PackageLocation(..))
 
 import Distribution.Client.Setup
          ( GlobalFlags, ConfigFlags(..), ConfigExFlags, InstallFlags
@@ -57,8 +58,6 @@ import qualified Data.Map as Map
 import qualified Data.Set as Set
 import System.FilePath
          ( (</>) )
-import System.Directory
-         ( getCurrentDirectory )
 
 
 runCommand :: CommandUI (ConfigFlags, ConfigExFlags, InstallFlags, HaddockFlags)
@@ -203,21 +202,29 @@ runAction (applyFlagDefaults -> (configFlags, configExFlags, installFlags, haddo
         ++ exeName
         ++ ":\n"
         ++ unlines (fmap (\p -> " - in package " ++ display (elabUnitId p)) elabPkgs)
+
     let exePath = binDirectoryFor (distDirLayout baseCtx)
                                   (elaboratedShared buildCtx)
                                   pkg
                                   exeName
                </> exeName
-    curDir <- getCurrentDirectory
-    let dataDirEnvVar = (pkgPathEnvVar (elabPkgDescription pkg) "datadir",
-                         Just $ curDir </> dataDir (elabPkgDescription pkg))
+
+    mexeDataDir <- case elabPkgSourceLocation pkg of
+                     LocalUnpackedPackage d -> pure $ Just (d </> dataDir (elabPkgDescription pkg))
+                     -- TODO/FIXME: figure out how to handle remaing constructors of PackageLocation
+
+    -- TODO/FIXME: dataDirEnvVars could be more than one variable, if local/inplace packages w/ package-data are involved!
+    let dataDirEnvVars = case mexeDataDir of
+                          Just _ -> [(pkgPathEnvVar (elabPkgDescription pkg) "datadir",
+                                      mexeDataDir)]
+                          Nothing -> []
         args = drop 1 targetStrings
     runProgramInvocation
       verbosity
       emptyProgramInvocation {
         progInvokePath  = exePath,
         progInvokeArgs  = args,
-        progInvokeEnv   = [dataDirEnvVar]
+        progInvokeEnv   = dataDirEnvVars
       }
   where
     verbosity = fromFlagOrDefault normal (configVerbosity configFlags)