Simplify injection context & improve solver comments

src/main/java/org/grouplens/grapht/solver/DependencySolver.java

@@ -66,8 +66,7 @@ public class DependencySolver {
      * @return The context from the initial injection.
      */
     public static InjectionContext initialContext() {
-        return InjectionContext.singleton(ROOT_SATISFACTION.getSatisfaction(),
-                                          new AttributesImpl());
+        return InjectionContext.singleton(ROOT_SATISFACTION.getSatisfaction());
     }
 
     /**
@@ -244,9 +243,10 @@ private void replaceNode(DAGNode<CachedSatisfaction,DesireChain> old, DAGNode<Ca
      *
      * @param tree The unmerged tree to merge in.
      * @param mergeTarget The graph to merge with.
-     * @param mergeRoot Whether to merge this with the root of the global graph.  If {@code true},
+     * @param mergeRoot Whether to merge this with the root of the merge target.  If {@code true},
      *                  the outgoing edges of {@code tree} are added to the outgoing edges of
-     *                  the root of the global graph and the resulting graph returned.
+     *                  {@code mergeTarget} and the resulting graph is returned; otherwise, just the
+     *                  transformation of {@code tree} is returned.
      * @return The new merged graph.
      */
     private DAGNode<CachedSatisfaction,DesireChain> merge(DAGNode<CachedSatisfaction,DesireChain> tree,

src/main/java/org/grouplens/grapht/solver/InjectionContext.java

@@ -21,6 +21,7 @@
 import org.apache.commons.lang3.tuple.Pair;
 import org.grouplens.grapht.spi.Attributes;
 import org.grouplens.grapht.spi.Satisfaction;
+import org.grouplens.grapht.spi.reflect.AttributesImpl;
 import org.grouplens.grapht.util.AbstractChain;
 
 /**
@@ -36,11 +37,26 @@
  */
 public class InjectionContext extends AbstractChain<Pair<Satisfaction,Attributes>> {
     private static final long serialVersionUID = 1L;
-
+
+    /**
+     * Construct a singleton injection context.
+     * @param satisfaction The satisfaction.
+     * @param attrs The attributes.
+     * @return The injection context.
+     */
     public static InjectionContext singleton(Satisfaction satisfaction, Attributes attrs) {
         return new InjectionContext(null, satisfaction, attrs);
     }
 
+    /**
+     * Construct a singleton injection context with no attributes.
+     * @param satisfaction The satisfaction.
+     * @return The injection context.
+     */
+    public static InjectionContext singleton(Satisfaction satisfaction) {
+        return singleton(satisfaction, new AttributesImpl());
+    }
+
     private InjectionContext(InjectionContext prior, Satisfaction satisfaction, Attributes attrs) {
         super(prior, Pair.of(satisfaction, attrs));
     }