Add path sibling traversal methods

* getPrevSibling
* getNextSibling
* forEachNextSibling
* forEachPrevSibling

packages/babel-traverse/src/path/family.js

@@ -67,6 +67,30 @@ export function getSibling(key) {
   });
 }
 
+export function getPrevSibling() {
+  return this.getSibling(this.key - 1);
+}
+
+export function getNextSibling() {
+  return this.getSibling(this.key + 1);
+}
+
+export function forEachNextSibling(callback = Function.prototype) {
+  let _key = this.key, nextSibling = this.getSibling(++_key);
+  while (nextSibling.node) {
+    callback(nextSibling);
+    nextSibling = this.getSibling(++_key);
+  }
+}
+
+export function forEachPrevSibling(callback = Function.prototype) {
+  let _key = this.key, nextSibling = this.getSibling(--_key);
+  while (nextSibling.node) {
+    callback(nextSibling);
+    nextSibling = this.getSibling(--_key);
+  }
+}
+
 export function get(key: string, context?: boolean | TraversalContext): NodePath {
   if (context === true) context = this.context;
   const parts = key.split(".");

packages/babel-traverse/test/family.js

@@ -52,6 +52,30 @@ describe("path/family", function () {
         assert.strictEqual(outerNodes[id], outerPaths[id].node, "nodes match");
       });
     });
+
+  });
+  describe("getSibling", function () {
+    const ast = parse("var a = 1, {b} = c, [d] = e; function f() {}");
+    let sibling = {};
+    traverse(ast, {
+      VariableDeclaration(path) {
+        sibling = path.getSibling(path.key);
+      }
+    });
+    it("should return traverse sibling nodes", function () {
+      assert.strictEqual(!!sibling.getNextSibling().node, true, "has property node");
+      assert.strictEqual(!!sibling.getNextSibling().getPrevSibling().node, true, "has property node");
+      let nextSiblings = 0, prevSiblings = 0;
+      sibling.forEachNextSibling(() => {
+        nextSiblings++;
+      });
+      assert.strictEqual(!!nextSiblings, true, "Has next sibling");
+
+      sibling.getNextSibling().forEachPrevSibling(() => {
+        prevSiblings++;
+      });
+      assert.strictEqual(!!prevSiblings, true, "Has prev sibling");
+    });
   });
 });