test/mjsunit/es6/generators-runtime.js

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// Test aspects of the generator runtime.

// See:
// http://people.mozilla.org/~jorendorff/es6-draft.html#sec-generatorfunction-objects

function f() { }
function* g() { yield 1; }
var GeneratorFunctionPrototype = Object.getPrototypeOf(g);
var GeneratorFunction = GeneratorFunctionPrototype.constructor;
var GeneratorObjectPrototype = GeneratorFunctionPrototype.prototype;

// A generator function should have the same set of properties as any
// other function.
function TestGeneratorFunctionInstance() {
  var f_own_property_names = Object.getOwnPropertyNames(f);
  var g_own_property_names = Object.getOwnPropertyNames(g);

  f_own_property_names.sort();
  g_own_property_names.sort();

  assertArrayEquals(f_own_property_names, g_own_property_names);
  var i;
  for (i = 0; i < f_own_property_names.length; i++) {
    var prop = f_own_property_names[i];
    var f_desc = Object.getOwnPropertyDescriptor(f, prop);
    var g_desc = Object.getOwnPropertyDescriptor(g, prop);
    assertEquals(f_desc.configurable, g_desc.configurable, prop);
    if (prop === 'arguments' || prop === 'caller') {
      // Unlike sloppy functions, which have read-only data arguments and caller
      // properties, sloppy generators have a poison pill implemented via
      // accessors
      assertFalse('writable' in g_desc, prop);
      assertTrue(g_desc.get instanceof Function, prop);
      assertEquals(g_desc.get, g_desc.set, prop);
    } else {
      assertEquals(f_desc.writable, g_desc.writable, prop);
    }
    assertEquals(f_desc.enumerable, g_desc.enumerable, prop);
  }
}
TestGeneratorFunctionInstance();


// Generators have an additional object interposed in the chain between
// themselves and Function.prototype.
function TestGeneratorFunctionPrototype() {
  // Sanity check.
  assertSame(Object.getPrototypeOf(f), Function.prototype);
  assertFalse(GeneratorFunctionPrototype === Function.prototype);
  assertSame(Function.prototype,
             Object.getPrototypeOf(GeneratorFunctionPrototype));
  assertSame(GeneratorFunctionPrototype,
             Object.getPrototypeOf(function* () {}));
}
TestGeneratorFunctionPrototype();


// Functions that we associate with generator objects are actually defined by
// a common prototype.
function TestGeneratorObjectPrototype() {
  assertSame(Object.prototype,
             Object.getPrototypeOf(GeneratorObjectPrototype));
  assertSame(GeneratorObjectPrototype,
             Object.getPrototypeOf((function*(){yield 1}).prototype));

  var expected_property_names = ["next", "throw", "constructor"];
  var found_property_names =
      Object.getOwnPropertyNames(GeneratorObjectPrototype);

  expected_property_names.sort();
  found_property_names.sort();

  assertArrayEquals(expected_property_names, found_property_names);

  iterator_desc = Object.getOwnPropertyDescriptor(GeneratorObjectPrototype,
      Symbol.iterator);
  assertTrue(iterator_desc !== undefined);
  assertFalse(iterator_desc.writable);
  assertFalse(iterator_desc.enumerable);
  assertFalse(iterator_desc.configurable);

  // The generator object's "iterator" function is just the identity.
  assertSame(iterator_desc.value.call(42), 42);
}
TestGeneratorObjectPrototype();


// This tests the object that would be called "GeneratorFunction", if it were
// like "Function".
function TestGeneratorFunction() {
  assertSame(GeneratorFunctionPrototype, GeneratorFunction.prototype);
  assertTrue(g instanceof GeneratorFunction);

  assertSame(Function, Object.getPrototypeOf(GeneratorFunction));
  assertTrue(g instanceof Function);

  assertEquals("function* g() { yield 1; }", g.toString());

  // Not all functions are generators.
  assertTrue(f instanceof Function);  // Sanity check.
  assertTrue(!(f instanceof GeneratorFunction));

  assertTrue((new GeneratorFunction()) instanceof GeneratorFunction);
  assertTrue(GeneratorFunction() instanceof GeneratorFunction);
}
TestGeneratorFunction();


function TestPerGeneratorPrototype() {
  assertTrue((function*(){}).prototype !== (function*(){}).prototype);
  assertTrue((function*(){}).prototype !== g.prototype);
  assertTrue(g.prototype instanceof GeneratorFunctionPrototype);
  assertSame(GeneratorObjectPrototype, Object.getPrototypeOf(g.prototype));
  assertTrue(!(g.prototype instanceof Function));
  assertSame(typeof (g.prototype), "object");

  assertArrayEquals([], Object.getOwnPropertyNames(g.prototype));
}
TestPerGeneratorPrototype();