Use Artifact#getRunfilesPath to expand rootpath and rootpaths vars if --nolegacy_external_runfiles is specified.

PiperOrigin-RevId: 342051423
diff --git a/src/test/java/com/google/devtools/build/lib/analysis/LocationFunctionTest.java b/src/test/java/com/google/devtools/build/lib/analysis/LocationFunctionTest.java
index 8bb793a..7284784 100644
--- a/src/test/java/com/google/devtools/build/lib/analysis/LocationFunctionTest.java
+++ b/src/test/java/com/google/devtools/build/lib/analysis/LocationFunctionTest.java
@@ -164,6 +164,7 @@
   private final Label root;
   private final boolean multiple;
   private boolean execPaths;
+  private boolean legacyExternalRunfiles;
   private final Map<Label, Collection<Artifact>> labelMap = new HashMap<>();
 
   LocationFunctionBuilder(String rootLabel, boolean multiple) {
@@ -172,7 +173,8 @@
   }
 
   public LocationFunction build() {
-    return new LocationFunction(root, Suppliers.ofInstance(labelMap), execPaths, multiple);
+    return new LocationFunction(
+        root, Suppliers.ofInstance(labelMap), execPaths, legacyExternalRunfiles, multiple);
   }
 
   public LocationFunctionBuilder setExecPaths(boolean execPaths) {
@@ -180,6 +182,11 @@
     return this;
   }
 
+  public LocationFunctionBuilder setLegacyExternalRunfiles(boolean legacyExternalRunfiles) {
+    this.legacyExternalRunfiles = legacyExternalRunfiles;
+    return this;
+  }
+
   public LocationFunctionBuilder add(String label, String... paths) {
     labelMap.put(
         Label.parseAbsoluteUnchecked(label),