Destructuring: Fix handling of impure computed keys with object rest (b…

…abel#9416)

src/index.js

@@ -44,6 +44,19 @@ export default declare((api, options) => {
     return false;
   }
 
+  /**
+   * Test if an ObjectPattern's elements contain any RestElements.
+   */
+
+  function hasObjectRest(pattern) {
+    for (const elem of (pattern.properties: Array)) {
+      if (t.isRestElement(elem)) {
+        return true;
+      }
+    }
+    return false;
+  }
+
   const STOP_TRAVERSAL = {};
 
   // NOTE: This visitor is meant to be used via t.traverse
@@ -263,6 +276,31 @@ export default declare((api, options) => {
         objRef = temp;
       }
 
+      // Replace impure computed key expressions if we have a rest parameter
+      if (hasObjectRest(pattern)) {
+        let copiedPattern;
+        for (let i = 0; i < pattern.properties.length; i++) {
+          const prop = pattern.properties[i];
+          if (t.isRestElement(prop)) {
+            break;
+          }
+          const key = prop.key;
+          if (prop.computed && !this.scope.isPure(key)) {
+            const name = this.scope.generateUidIdentifierBasedOnNode(key);
+            this.nodes.push(this.buildVariableDeclaration(name, key));
+            if (!copiedPattern) {
+              copiedPattern = pattern = {
+                ...pattern,
+                properties: pattern.properties.slice(),
+              };
+            }
+            copiedPattern.properties[i] = {
+              ...copiedPattern.properties[i],
+              key: name,
+            };
+          }
+        }
+      }
       //
 
       for (let i = 0; i < pattern.properties.length; i++) {

test/fixtures/destructuring/object-rest-impure-computed-keys/exec.js

@@ -0,0 +1,34 @@
+var key, x, y, z;
+// impure
+key = 1;
+var { [key++]: y, ...x } = { 1: 1, a: 1 };
+expect(x).toEqual({ a: 1 });
+expect(key).toBe(2);
+expect(1).toBe(y);
+
+// takes care of the order
+
+key = 1;
+var { [++key]: y, [++key]: z, ...rest} = {2: 2, 3: 3};
+expect(y).toBe(2);
+expect(z).toBe(3);
+
+// pure, computed property should remain as-is
+key = 2;
+({ [key]: y, z, ...x } = {2: "two", z: "zee"});
+expect(y).toBe("two");
+expect(x).toEqual({});
+expect(z).toBe("zee");
+
+// rhs evaluated before lhs
+var order = [];
+function left() {
+  order.push("left");
+  return 0;
+}
+function right() {
+  order.push("right");
+  return {};
+}
+var { [left()]: y, ...x} = right();
+expect(order).toEqual(["right", "left"]);

test/fixtures/destructuring/object-rest-impure-computed-keys/input.js

@@ -0,0 +1 @@
+var { [fn()]: x, ...y } = z;

test/fixtures/destructuring/object-rest-impure-computed-keys/output.js

@@ -0,0 +1,4 @@
+var _z = z,
+    _fn = fn(),
+    x = _z[_fn],
+    y = babelHelpers.objectWithoutProperties(_z, [_fn].map(babelHelpers.toPropertyKey));