From d92c745427c8c78f47820f11c2e23c8cfed642a7 Mon Sep 17 00:00:00 2001
From: Boopathi Rajaa <boopathi@users.noreply.github.com>
Date: Wed, 8 Feb 2017 16:37:14 +0100
Subject: [PATCH] Deopt evaluation of undefined with a local binding. Fix #5204
 (#5206)

---
 packages/babel-traverse/src/path/evaluation.js |  6 +++---
 packages/babel-traverse/test/evaluation.js     | 18 ++++++++++++++++++
 2 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/packages/babel-traverse/src/path/evaluation.js b/packages/babel-traverse/src/path/evaluation.js
index 57699b561fd8..971a66a4095d 100644
--- a/packages/babel-traverse/src/path/evaluation.js
+++ b/packages/babel-traverse/src/path/evaluation.js
@@ -176,11 +176,11 @@ export function evaluate(): { confident: boolean; value: any } {
         return binding.value;
       } else {
         if (node.name === "undefined") {
-          return undefined;
+          return binding ? deopt(binding.path) : undefined;
         } else if (node.name === "Infinity") {
-          return Infinity;
+          return binding ? deopt(binding.path) : Infinity;
         } else if (node.name === "NaN") {
-          return NaN;
+          return binding ? deopt(binding.path) : NaN;
         }
 
         const resolved = path.resolve();
diff --git a/packages/babel-traverse/test/evaluation.js b/packages/babel-traverse/test/evaluation.js
index 5a3d93f76550..148173fa7d01 100644
--- a/packages/babel-traverse/test/evaluation.js
+++ b/packages/babel-traverse/test/evaluation.js
@@ -101,4 +101,22 @@ describe("evaluation", function () {
       false
     );
   });
+
+  it("should evaluate undefined, NaN and Infinity", () => {
+    assert.strictEqual(getPath("undefined").get("body.0.expression").evaluate().confident, true);
+    assert.strictEqual(getPath("NaN").get("body.0.expression").evaluate().confident, true);
+    assert.strictEqual(getPath("Infinity").get("body.0.expression").evaluate().confident, true);
+  });
+
+  it("should deopt redefined primitives - undefined, NaN and Infinity", () => {
+    const eval_undef = getPath("let undefined; undefined;").get("body.1.expression").evaluate();
+    const eval_nan = getPath("let NaN; NaN;").get("body.1.expression").evaluate();
+    const eval_inf = getPath("let Infinity; Infinity;").get("body.1.expression").evaluate();
+    assert.strictEqual(eval_undef.confident, false);
+    assert.strictEqual(eval_nan.confident, false);
+    assert.strictEqual(eval_inf.confident, false);
+
+    assert.strictEqual(eval_undef.deopt.type, "VariableDeclarator");
+    assert.strictEqual(eval_undef.deopt.parentPath.node.kind, "let");
+  });
 });