Change the key type we keep around in our fileset mappings.

There is no need to throw away the fact that the mapping is artifact -> fileset symlinks so early.

This CL is otherwise a no-op.

RELNOTES: None
PiperOrigin-RevId: 211808154

src/test/java/com/google/devtools/build/lib/exec/SpawnInputExpanderTest.java

diff --git a/src/test/java/com/google/devtools/build/lib/exec/SpawnInputExpanderTest.java b/src/test/java/com/google/devtools/build/lib/exec/SpawnInputExpanderTest.java
index 581dfc6..b7fd511 100644
--- a/src/test/java/com/google/devtools/build/lib/exec/SpawnInputExpanderTest.java
+++ b/src/test/java/com/google/devtools/build/lib/exec/SpawnInputExpanderTest.java
@@ -68,6 +68,7 @@
 
   private FileSystem fs;
   private Path execRoot;
+  private ArtifactRoot rootDir;
   private SpawnInputExpander expander;
   private Map<PathFragment, ActionInput> inputMappings;
 
@@ -75,6 +76,7 @@
   public final void createSpawnInputExpander() {
     fs = new InMemoryFileSystem();
     execRoot = fs.getPath("/root");
+    rootDir = ArtifactRoot.asDerivedRoot(execRoot, fs.getPath("/root/out"));
     expander = new SpawnInputExpander(execRoot, /*strict=*/ true);
     inputMappings = Maps.newHashMap();
   }
@@ -391,13 +393,21 @@
         PathFragment.create(from), PathFragment.create(to));
   }
 
-  private ImmutableMap<PathFragment, ImmutableList<FilesetOutputSymlink>> simpleFilesetManifest() {
+  private ImmutableMap<Artifact, ImmutableList<FilesetOutputSymlink>> simpleFilesetManifest() {
     return ImmutableMap.of(
-        PathFragment.create("out"),
+        createFileset("out"),
         ImmutableList.of(
             filesetSymlink("workspace/bar", "foo"), filesetSymlink("workspace/foo", "/foo/bar")));
   }
 
+  private SpecialArtifact createFileset(String execPath) {
+    return new SpecialArtifact(
+        rootDir,
+        PathFragment.create(execPath),
+        ArtifactOwner.NullArtifactOwner.INSTANCE,
+        SpecialArtifactType.FILESET);
+  }
+
   @Test
   public void testManifestWithErrorOnRelativeSymlink() throws Exception {
     expander = new SpawnInputExpander(execRoot, /*strict=*/ true, ERROR);