Added TreeQuery.root().

Author: ntwigg

src/com/diffplug/common/base/TreeQuery.java

@@ -28,6 +28,17 @@
 
 /** Queries against {@link TreeDef} trees, e.g. lowest common ancestor, list of parents, etc. */
 public class TreeQuery {
+	/** Returns the root of the given tree. */
+	public static <T> T root(TreeDef.Parented<T> treeDef, T node) {
+		T lastParent;
+		T parent = node;
+		do {
+			lastParent = parent;
+			parent = treeDef.parentOf(lastParent);
+		} while (parent != null);
+		return lastParent;
+	}
+
 	/** Creates a mutable list whose first element is {@code node}, and last element is its root parent. */
 	public static <T> List<T> toRoot(TreeDef.Parented<T> treeDef, T node) {
 		List<T> list = new ArrayList<>();

test/com/diffplug/common/base/TreeQueryTest.java

@@ -19,6 +19,13 @@
 import org.junit.Test;
 
 public class TreeQueryTest {
+	@Test
+	public void testToRoot() {
+		Assert.assertEquals(root, TreeQuery.root(TreeNode.treeDef(), root));
+		Assert.assertEquals(root, TreeQuery.root(TreeNode.treeDef(), root.findByContent("src")));
+		Assert.assertEquals(root, TreeQuery.root(TreeNode.treeDef(), root.findByContent("Array.java")));
+	}
+
 	@Test
 	public void testLowestCommonAncestor() {
 		// test the trivial case