Add path sibling traversal methods

* getPrevSibling
* getNextSibling
* getAllNextSiblings
* getAllPrevSiblings

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

@@ -67,6 +67,37 @@ export function getSibling(key) {
   });
 }
 
+export function getPrevSibling() {
+  return this.getSibling(this.key - 1);
+}
+
+export function getNextSibling() {
+  return this.getSibling(this.key + 1);
+}
+
+export function getAllNextSiblings() {
+  let _key = this.key;
+  let sibling = this.getSibling(++_key);
+  const siblings = [];
+  while (sibling.node) {
+    siblings.push(sibling);
+    sibling = this.getSibling(++_key);
+  }
+  return siblings;
+}
+
+export function getAllPrevSiblings() {
+  let _key = this.key;
+  let sibling = this.getSibling(--_key);
+  const siblings = [];
+  while (sibling.node) {
+    siblings.push(sibling);
+    sibling = this.getSibling(--_key);
+  }
+  return siblings;
+}
+
+
 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 +52,28 @@ 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.ok(sibling.getNextSibling().node, "has property node");
+      assert.ok(sibling.getNextSibling().getPrevSibling().node, "has property node");
+      assert.equal(!!sibling.getPrevSibling().node, false, "out of scope");
+      assert.equal(!!sibling.getNextSibling().getNextSibling().node, false, "out of scope");
+    });
+
+    it("should return all preceding and succeeding sibling nodes", function () {
+      assert.ok(sibling.getAllNextSiblings().length, "Has next sibling");
+      assert.ok(sibling.getNextSibling().getAllPrevSiblings().length, "Has prev sibling");
+    });
   });
 });