Fix setting deopt properly after evaluating multiple expressions (#6882)

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

@@ -211,11 +211,11 @@ function _evaluate(path, state) {
   if (path.isArrayExpression()) {
     const arr = [];
     const elems: Array<NodePath> = path.get("elements");
-    for (let elem of elems) {
+    for (const elem of elems) {
-      elem = elem.evaluate();
+      const elemValue = elem.evaluate();
 
-      if (elem.confident) {
+      if (elemValue.confident) {
-        arr.push(elem.value);
+        arr.push(elemValue.value);
       } else {
         return deopt(elem, state);
       }
@@ -268,7 +268,7 @@ function _evaluate(path, state) {
     switch (node.operator) {
       case "||":
         // TODO consider having a "truthy type" that doesn't bail on
-        // left uncertainity but can still evaluate to truthy.
+        // left uncertainty but can still evaluate to truthy.
         if (left && leftConfident) {
           state.confident = true;
           return left;

packages/babel-traverse/test/evaluation.js

@@ -216,4 +216,48 @@ describe("evaluation", function() {
       "\\d",
     );
   });
+
+  it("sets deopt properly when not confident after evaluating multiple expressions", () => {
+    const ast = parse(`
+      const parts = [foo, bar];
+      console.log(parts.join('-'));
+    `);
+
+    let result;
+
+    traverse(ast, {
+      MemberExpression: {
+        enter(path) {
+          result = path.get("object").evaluate();
+        },
+      },
+    });
+
+    assert.strictEqual(result.confident, false);
+    assert.strictEqual(result.deopt.type, "Identifier");
+    assert.strictEqual(result.deopt.node.name, "foo");
+  });
+
+  it("sets deopt properly when confident after evaluating multiple expressions", () => {
+    const ast = parse(`
+      const foo = 'foo';
+      const bar = 'bar';
+      const parts = [foo, bar];
+      console.log(parts.join('-'))
+    `);
+
+    let result;
+
+    traverse(ast, {
+      MemberExpression: {
+        enter(path) {
+          result = path.get("object").evaluate();
+        },
+      },
+    });
+
+    assert.strictEqual(result.confident, true);
+    assert.strictEqual(result.deopt, null);
+    assert.deepStrictEqual(result.value, ["foo", "bar"]);
+  });
 });