Print children in ArtifactNestedSetKey#toString.

The old #toString method was only a placeholder that didn't offer much
information.

RELNOTES: None
PiperOrigin-RevId: 282559367

src/main/java/com/google/devtools/build/lib/collect/nestedset/NestedSet.java

diff --git a/src/main/java/com/google/devtools/build/lib/collect/nestedset/NestedSet.java b/src/main/java/com/google/devtools/build/lib/collect/nestedset/NestedSet.java
index c8d05a2..e21e477 100644
--- a/src/main/java/com/google/devtools/build/lib/collect/nestedset/NestedSet.java
+++ b/src/main/java/com/google/devtools/build/lib/collect/nestedset/NestedSet.java
@@ -381,7 +381,7 @@
   }
 
   // TODO:  this leaves LINK_ORDER backwards
-  private static String childrenToString(Object children) {
+  public static String childrenToString(Object children) {
     if (children instanceof Object[]) {
       return Arrays.stream((Object[]) children)
           .map(NestedSet::childrenToString)

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

diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/ArtifactNestedSetKey.java b/src/main/java/com/google/devtools/build/lib/skyframe/ArtifactNestedSetKey.java
index 64aa236..1437850 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/ArtifactNestedSetKey.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/ArtifactNestedSetKey.java
@@ -13,9 +13,11 @@
 // limitations under the License.
 package com.google.devtools.build.lib.skyframe;
 
+import com.google.common.base.MoreObjects;
 import com.google.common.base.Preconditions;
 import com.google.common.collect.ImmutableSet;
 import com.google.devtools.build.lib.actions.Artifact;
+import com.google.devtools.build.lib.collect.nestedset.NestedSet;
 import com.google.devtools.build.skyframe.SkyFunctionName;
 import com.google.devtools.build.skyframe.SkyKey;
 import java.util.Arrays;
@@ -74,7 +76,9 @@
 
   @Override
   public String toString() {
-    return rawChildren.toString();
+    return MoreObjects.toStringHelper(this)
+        .add("rawChildren", NestedSet.childrenToString(rawChildren))
+        .toString();
   }
 
   /**