Merge pull request #3192 from babel/eval-bug

Evaluation may succeed even when not confident

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

@@ -99,11 +99,14 @@ export function evaluate(): { confident: boolean; value: any } {
         if (expr) str += String(evaluate(expr));
       }
 
-      if (confident) return str;
+      if (!confident) return;
+      return str;
     }
 
     if (path.isConditionalExpression()) {
-      if (evaluate(path.get("test"))) {
+      let testResult = evaluate(path.get("test"));
+      if (!confident) return;
+      if (testResult) {
         return evaluate(path.get("consequent"));
       } else {
         return evaluate(path.get("alternate"));
@@ -162,6 +165,7 @@ export function evaluate(): { confident: boolean; value: any } {
       }
 
       let arg = evaluate(argument);
+      if (!confident) return;
       switch (node.operator) {
         case "!": return !arg;
         case "+": return +arg;
@@ -218,7 +222,9 @@ export function evaluate(): { confident: boolean; value: any } {
 
     if (path.isBinaryExpression()) {
       let left = evaluate(path.get("left"));
+      if (!confident) return;
       let right = evaluate(path.get("right"));
+      if (!confident) return;
 
       switch (node.operator) {
         case "-": return left - right;

packages/babel-traverse/test/evaluation.js

@@ -0,0 +1,26 @@
+var traverse = require("../lib").default;
+var assert = require("assert");
+var parse = require("babylon").parse;
+
+function getPath(code) {
+  var ast = parse(code);
+  var path;
+  traverse(ast, {
+    Program: function (_path) {
+      path = _path;
+      _path.stop();
+    }
+  });
+  return path;
+}
+
+suite("evaluation", function () {
+  suite("evaluateTruthy", function () {
+    test("it should work with null", function () {
+      assert.strictEqual(
+        getPath("false || a.length === 0;").get("body")[0].evaluateTruthy(),
+        undefined
+      );
+    });
+  });
+});