Add datadir env var before running the exe

cabal-install/Distribution/Client/CmdRun.hs

@@ -49,9 +49,12 @@ import Distribution.Types.Executable
 import Distribution.Types.UnqualComponentName
          ( UnqualComponentName, unUnqualComponentName )
 import Distribution.Types.PackageDescription
-         ( PackageDescription(executables) )
+         ( PackageDescription(executables, dataDir) )
 import Distribution.Simple.Program.Run
-         ( runProgramInvocation, simpleProgramInvocation )
+         ( runProgramInvocation, ProgramInvocation(..),
+           emptyProgramInvocation )
+import Distribution.Simple.Build.PathsModule
+         ( pkgPathEnvVar )
 import Distribution.Types.PackageId
          ( PackageIdentifier(..) )
 
@@ -61,6 +64,8 @@ import Data.Function
          ( on )
 import System.FilePath
          ( (</>) )
+import System.Directory
+         ( getCurrentDirectory )
 
 
 runCommand :: CommandUI (ConfigFlags, ConfigExFlags, InstallFlags, HaddockFlags)
@@ -227,10 +232,17 @@ runAction (configFlags, configExFlags, installFlags, haddockFlags)
                                   pkg
                                   exe
                </> exe
-    let args = drop 1 targetStrings
+    curDir <- getCurrentDirectory
+    let dataDirEnvVar = (pkgPathEnvVar (elabPkgDescription pkg) "datadir",
+                         Just $ curDir </> dataDir (elabPkgDescription pkg))
+        args = drop 1 targetStrings
     runProgramInvocation
       verbosity
-      (simpleProgramInvocation exePath args)
+      emptyProgramInvocation {
+        progInvokePath  = exePath,
+        progInvokeArgs  = args,
+        progInvokeEnv   = [dataDirEnvVar]
+      }
   where
     verbosity = fromFlagOrDefault normal (configVerbosity configFlags)
     cliConfig = commandLineFlagsToProjectConfig

cabal-testsuite/PackageTests/NewBuild/CmdRun/Datafiles/Datafiles.cabal

@@ -0,0 +1,11 @@
+name: Datafiles
+version: 1.0
+build-type: Simple
+cabal-version: >= 1.10
+data-dir: data
+data-files: hello.txt
+
+executable foo
+    main-is: Main.hs
+    build-depends: base
+    default-language: Haskell2010

cabal-testsuite/PackageTests/NewBuild/CmdRun/Datafiles/Main.hs

@@ -0,0 +1,4 @@
+import Paths_Datafiles
+
+main = putStrLn =<< readFile =<< getDataFileName "hello.txt"
+

cabal-testsuite/PackageTests/NewBuild/CmdRun/Datafiles/cabal.out

@@ -0,0 +1,8 @@
+# cabal new-run
+Resolving dependencies...
+Build profile: with-compiler: ghc-<GHCVER>, optimisation: NormalOptimisation
+In order, the following will be built:
+ - Datafiles-1.0 (exe:foo) (first run)
+Configuring executable 'foo' for Datafiles-1.0..
+Preprocessing executable 'foo' for Datafiles-1.0..
+Building executable 'foo' for Datafiles-1.0..

cabal-testsuite/PackageTests/NewBuild/CmdRun/Datafiles/cabal.project

@@ -0,0 +1 @@
+packages: .

cabal-testsuite/PackageTests/NewBuild/CmdRun/Datafiles/cabal.test.hs

@@ -0,0 +1,4 @@
+import Test.Cabal.Prelude
+main = cabalTest $
+    cabal' "new-run" ["foo"] >>= assertOutputContains "Hello World"
+

cabal-testsuite/PackageTests/NewBuild/CmdRun/Datafiles/data/hello.txt

@@ -0,0 +1 @@
+Hello World