💥 refactor!: Simplify uncle computation.

We allow to return a leaf since the only place we use it is insert_case3
where this allows to skip an unnecessary null check.

BREAKING CHANGE: This breaks dependents relying on previous behaviour.

Author: make-github-pseudonymous-again

src/family/uncle.js

@@ -1,27 +1,22 @@
 import assert from 'assert';
 import Node from '../adt/Node.js';
+import Leaf from '../adt/Leaf.js';
 import grandparent from './grandparent.js';
 
 /**
  * Computes the uncle of the input node when the grandparent is guaranteed to
  * exist.
  *
  * @param {Node} node - The input node.
- * @returns {Node}
+ * @returns {Node|Leaf}
  */
 const uncle = (node) => {
 	assert(node instanceof Node);
 	const g = grandparent(node);
 	assert(g !== null);
-	if (node.parent === g.left) {
-		if (g.right.isLeaf()) return null;
-		assert(g.right instanceof Node);
-		return g.right;
-	}
-
-	if (g.left.isLeaf()) return null;
-	assert(g.left instanceof Node);
-	return g.left;
+	const u = node.parent === g.left ? g.right : g.left;
+	assert(u instanceof Node || u instanceof Leaf);
+	return u;
 };
 
 export default uncle;

src/insertion/insert_case3.js

@@ -36,7 +36,7 @@ const insert_case3 = (n) => {
 	 *     -   -                 -   -
 	 */
 
-	if (u !== null && u._color === RED) {
+	if (u._color === RED) {
 		n.parent._color = BLACK;
 		u._color = BLACK;
 		const g = grandparent(n);