Fix cabal-project-nix-path test

Author: hamishmack

test/cabal-project-nix-path/default.nix

@@ -1,17 +1,24 @@
 { lib, cabalProject', tool, recurseIntoAttrs, testSrc, compiler-nix-name, evalPackages }:
 let
+  # Kind of round about way of getting the source for the hello package from hackage
+  # so we can use it in this test.
+  hello-src = evalPackages.runCommand "hello-src" { nativeBuildInputs = [ evalPackages.gnutar ]; } ''
+    mkdir -p $out
+    tar -xzf ${(tool compiler-nix-name "hello" { inherit evalPackages; }).src} -C $out
+    mv $out/hello-*/* $out
+  '';
   project = cabalProject' {
     name = "cabal-project-nix-path";
     inherit compiler-nix-name evalPackages;
     src = testSrc "cabal-project-nix-path";
     cabalProject = ''
-      packages: ${(tool compiler-nix-name "hello" { inherit evalPackages; }).project.args.src}
+      packages: ${hello-src}
     '';
   };
   # The same but with source in a subdir of the store path
   projectSubDir = project.appendModule {
     cabalProject = lib.mkForce ''
-      packages: ${evalPackages.runCommand "hello-src" {} "mkdir -p $out && cp -r ${(tool compiler-nix-name "hello" { inherit evalPackages; }).project.args.src} $out/subdir"}/subdir
+      packages: ${evalPackages.runCommand "hello-src-in-subdir" {} "mkdir -p $out && cp -r ${hello-src} $out/subdir"}/subdir
     '';
   };