@babel/traverse: Fix NodePath.getData (#9415)

* @babel/traverse: Fix NodePath.getData

Currently, if the obtained value is `false`, it will be replaced by the given default value, which is invalid. This makes sure that we only set the default value when the value is `undefined`, instead of falsy.

* Add test and fix object protoype

* Allow false as default value

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

@@ -28,7 +28,7 @@ export default class NodePath {
     this.parent = parent;
     this.hub = hub;
     this.contexts = [];
-    this.data = {};
+    this.data = Object.create(null);
     this.shouldSkip = false;
     this.shouldStop = false;
     this.removed = false;
@@ -116,7 +116,7 @@ export default class NodePath {
 
   getData(key: string, def?: any): any {
     let val = this.data[key];
-    if (!val && def) val = this.data[key] = def;
+    if (val === undefined && def !== undefined) val = this.data[key] = def;
     return val;
   }
 

packages/babel-traverse/test/path/index.js

@@ -0,0 +1,43 @@
+import { NodePath } from "../../lib";
+
+describe("NodePath", () => {
+  describe("setData/getData", () => {
+    it("can set default value", () => {
+      const path = new NodePath({}, {});
+
+      expect(path.getData("foo", "test")).toBe("test");
+    });
+    it("can set false", () => {
+      const path = new NodePath({}, {});
+      path.setData("foo", false);
+
+      expect(path.getData("foo", true)).toBe(false);
+    });
+
+    it("can set true", () => {
+      const path = new NodePath({}, {});
+      path.setData("foo", true);
+
+      expect(path.getData("foo", false)).toBe(true);
+    });
+
+    it("can set null", () => {
+      const path = new NodePath({}, {});
+      path.setData("foo", null);
+
+      expect(path.getData("foo", true)).toBe(null);
+    });
+
+    it("can use false as default", () => {
+      const path = new NodePath({}, {});
+
+      expect(path.getData("foo", false)).toBe(false);
+    });
+
+    it("does not use object base properties", () => {
+      const path = new NodePath({}, {});
+
+      expect(path.getData("__proto__", "test")).toBe("test");
+    });
+  });
+});