Bug 906891: Short-circuit isSealed and isFrozen for typed arrays. r=sfink

js/src/jit-test/tests/basic/typed-array-sealed-frozen.js

@@ -0,0 +1,53 @@
+// Any copyright is dedicated to the Public Domain.
+// http://creativecommons.org/licenses/publicdomain/
+
+// Typed arrays are always sealed.
+
+load(libdir + "asserts.js")
+
+const constructors = [
+  Int8Array,
+  Uint8Array,
+  Uint8ClampedArray,
+  Int16Array,
+  Uint16Array,
+  Int32Array,
+  Uint32Array,
+  Float32Array,
+  Float64Array
+];
+
+for (constructor of constructors) {
+  print("testing non-empty " + constructor.name);
+  let a = new constructor(10);
+  assertEq(Object.isExtensible(a), false);
+  assertEq(Object.isSealed(a), true);
+  assertEq(Object.isFrozen(a), false);
+
+  // Should not throw.
+  Object.seal(a);
+
+  // Should complain that it can't change attributes of indexed typed array properties.
+  assertThrowsInstanceOf(() => Object.freeze(a), InternalError);
+}
+
+print();
+
+for (constructor of constructors) {
+  print("testing zero-length " + constructor.name);
+  let a = new constructor(0);
+  assertEq(Object.isExtensible(a), false);
+  assertEq(Object.isSealed(a), true);
+  assertEq(Object.isFrozen(a), true);
+
+  // Should not throw.
+  Object.seal(a);
+  Object.freeze(a);
+}
+
+// isSealed and isFrozen should not try to build an array of all the
+// property names of a typed array, since they're often especially large.
+// This should not throw an allocation error.
+let a = new Uint8Array(1 << 24);
+Object.isSealed(a);
+Object.isFrozen(a);

js/src/jsobj.cpp

@@ -1186,6 +1186,18 @@ JSObject::isSealedOrFrozen(JSContext *cx, HandleObject obj, ImmutabilityType it,
         return true;
     }
 
+    if (obj->is<TypedArrayObject>()) {
+        if (it == SEAL) {
+            // Typed arrays are always sealed.
+            *resultp = true;
+        } else {
+            // Typed arrays cannot be frozen, but an empty typed array is
+            // trivially frozen.
+            *resultp = (obj->as<TypedArrayObject>().length() == 0);
+        }
+        return true;
+    }
+
     AutoIdVector props(cx);
     if (!GetPropertyNames(cx, obj, JSITER_HIDDEN | JSITER_OWNONLY, &props))
         return false;