Fix comments regarding rpackages when a file has no ancestor BUILD file

PiperOrigin-RevId: 405464912

src/main/java/com/google/devtools/build/lib/query2/RBuildFilesVisitor.java

diff --git a/src/main/java/com/google/devtools/build/lib/query2/RBuildFilesVisitor.java b/src/main/java/com/google/devtools/build/lib/query2/RBuildFilesVisitor.java
index eb292f9..6e5efa3 100644
--- a/src/main/java/com/google/devtools/build/lib/query2/RBuildFilesVisitor.java
+++ b/src/main/java/com/google/devtools/build/lib/query2/RBuildFilesVisitor.java
@@ -173,6 +173,9 @@
    * of SkyKeys whose transitive reverse dependencies must contain the exact same set of packages.
    *
    * <p>Note that there may not be nodes in the graph corresponding to the returned SkyKeys.
+   *
+   * <p>Note also that we assume there'll be a PackageLookupValue node for some ancestor directory
+   * of every file to which a symlink could possibly point otherwise the file will not be included.
    */
   private static Collection<SkyKey> getSkyKeysForFileFragments(
       WalkableGraph graph, Iterable<PathFragment> pathFragments) throws InterruptedException {