Add a reference to the pertinent RunfilesTree to RunfilesArtifactValue.

RELNOTES: None.
PiperOrigin-RevId: 599787221
Change-Id: Id0808314613f8b387fef59f83f76fe0e892fa20f

src/main/java/com/google/devtools/build/lib/skyframe/RunfilesArtifactValue.java

diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/RunfilesArtifactValue.java b/src/main/java/com/google/devtools/build/lib/skyframe/RunfilesArtifactValue.java
index ec76bfc..cc8e3f2 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/RunfilesArtifactValue.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/RunfilesArtifactValue.java
@@ -20,6 +20,7 @@
 import com.google.common.collect.ImmutableList;
 import com.google.devtools.build.lib.actions.Artifact;
 import com.google.devtools.build.lib.actions.FileArtifactValue;
+import com.google.devtools.build.lib.actions.RunfilesSupplier.RunfilesTree;
 import com.google.devtools.build.lib.util.HashCodes;
 import com.google.devtools.build.skyframe.SkyValue;
 
@@ -32,6 +33,7 @@
   }
 
   private final FileArtifactValue metadata;
+  private final RunfilesTree runfilesTree;
 
   // Parallel lists.
   private final ImmutableList<Artifact> files;
@@ -43,11 +45,13 @@
 
   RunfilesArtifactValue(
       FileArtifactValue metadata,
+      RunfilesTree runfilesTree,
       ImmutableList<Artifact> files,
       ImmutableList<FileArtifactValue> fileValues,
       ImmutableList<Artifact> trees,
       ImmutableList<TreeArtifactValue> treeValues) {
     this.metadata = checkNotNull(metadata);
+    this.runfilesTree = checkNotNull(runfilesTree);
     this.files = checkNotNull(files);
     this.fileValues = checkNotNull(fileValues);
     this.trees = checkNotNull(trees);
@@ -63,6 +67,11 @@
     return metadata;
   }
 
+  /** Returns the runfiles tree this value represents. */
+  RunfilesTree getRunfilesTree() {
+    return runfilesTree;
+  }
+
   /** Visits the file artifacts that this runfiles artifact expands to, together with their data. */
   void forEachFile(RunfilesConsumer<FileArtifactValue> consumer) throws InterruptedException {
     for (int i = 0; i < files.size(); i++) {
@@ -79,6 +88,22 @@
 
   @Override
   public boolean equals(Object o) {
+    // This method, seemingly erroneously, does not check whether the runfilesTree of the two
+    // objects is equivalent. This is because it's costly (it involves flattening nested sets and
+    // even if one caches a fingerprint, it's still a fair amount of CPU) and because it's
+    // currently not necessary: RunfilesArtifactValue is only ever created as the SkyValue of
+    // runfiles middlemen and those are special-cased in ActionCacheChecker (see
+    // ActionCacheChecker.checkMiddlemanAction()): the checksum of a middleman artifact is the
+    // function of the checksum of all the artifacts on the inputs of the middleman action, which
+    // includes both the artifacts the runfiles tree links to and the runfiles input manifest,
+    // which in turn encodes the structure of the runfiles tree. The checksum of the middleman
+    // artifact is here as the "metadata" field, which *is* compared here, so the
+    // RunfilesArtifactValues of two runfiles middlemen will be equals iff they represent the same
+    // runfiles tree.
+    //
+    // Eventually, if we ever do away with runfiles input manifests, it will be necessary to change
+    // this (it's weird that one needs to do a round-trip to the file system to determine the
+    // checksum of a runfiles tree), but that's not happening anytime soon.
     if (this == o) {
       return true;
     }