Add outPath short-circuiting tests

tests/default.nix

@@ -1,4 +1,4 @@
-{ pkgs ? import <nixpkgs> {} }:
+{ pkgs ? import <nixpkgs> {}, lib ? pkgs.lib }:
 
 let
   testdata = import ./testdata.nix { inherit pkgs; };
@@ -22,13 +22,31 @@ in
   subdir-9 = runner.makeTest { name = "subdir-9"; rootDir = testdata.sourceUnfiltered + "/test-tree"; subpath = "9-expected"; };
   subdir-10 = runner.makeTest { name = "subdir-10"; rootDir = testdata.sourceUnfiltered + "/test-tree"; subpath = "10-subdir-ignoring-itself"; };
 
+  # Make sure the files aren't added to the store before filtering.
+  shortcircuit = runner.makeTest {
+    name = "nested";
+    rootDir = testdata.sourceUnfilteredRecursive + "/test-tree";
+    preCheck = ''
+      # Instead of a file, create a fifo so that the filter would error out if it tries to add it to the store.
+      rm 1-simpl/1
+      mkfifo 1-simpl/1
+    '';
+  };
+
   unit-tests =
     let gitignoreNix = import ../default.nix { inherit (pkgs) lib; };
-        inherit (gitignoreNix) gitignoreFilterWith;
+        inherit (gitignoreNix) gitignoreFilterWith gitignoreSourceWith;
         example = gitignoreFilterWith { basePath = ./.; extraRules = ''
           *.foo
           !*.bar
         ''; };
+        shortcircuit = gitignoreSourceWith {
+          path = {
+            inherit (lib.cleanSource ./.) _isLibCleanSourceWith filter name;
+            outPath = throw "do not use outPath";
+            origSrc = ./.;
+          };
+        };
     in
 
     # Test that extraRules works:
@@ -36,6 +54,9 @@ in
     assert example ./x.bar "regular" == true;
     assert example ./x.qux "regular" == true;
 
+    # Make sure outPath is not used. (It's not about the store path)
+    assert lib.hasPrefix builtins.storeDir "${shortcircuit}";
+
     # End of test. (a drv to show a buildable attr when successful)
     pkgs.emptyFile or null;
 }

tests/runner.nix

@@ -24,11 +24,11 @@ let
                                discover rootDir by itself.
 
    */
-  makeTest = {name ? "source", rootDir, subpath ? ""}:
+  makeTest = {name ? "source", rootDir, subpath ? "", preCheck ? ""}:
     pkgs.runCommand "test-${name}" {
       inherit name;
       viaGit = listingViaGit { inherit name rootDir subpath; };
-      viaNix = listingViaNixGitignore { inherit name rootDir subpath; };
+      viaNix = listingViaNixGitignore { inherit name rootDir subpath preCheck; };
     } ''
       if diff $viaNix $viaGit; then
         touch $out
@@ -64,7 +64,7 @@ let
       installPhase = ":";
     };
 
-  listingViaNixGitignore = {name ? "source", rootDir, subpath}:
+  listingViaNixGitignore = {name ? "source", rootDir, subpath, preCheck}:
     pkgs.stdenv.mkDerivation {
       name = "${name}-listing-via-nix";
       src = rootDir;
@@ -79,6 +79,7 @@ let
         export NIX_LOG_DIR=$TMPDIR
         export NIX_STATE_DIR=$TMPDIR
         test -n "$subpath" && cd $subpath
+        ${preCheck}
         nix-instantiate --eval --expr --json \
             --readonly-mode --option sandbox false \
             '(import ${gitignoreSource ../.}/tests/runner.nix {}).toStringNixGitignore ./.' \