[es7] implement |do| expressions proposal

test/mjsunit/harmony/do-expressions.js

+// Copyright 2015 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --harmony-do-expressions --harmony-sloppy-let --allow-natives-syntax
+// Flags: --harmony-default-parameters
+
+function returnValue(v) { return v; }
+function MyError() {}
+var global = this;
+
+function TestBasic() {
+  // Looping and lexical declarations
+  assertEquals(512, returnValue(do {
+    let n = 2;
+    for (let i = 0; i < 4; i++) n <<= 2;
+  }));
+
+  // Strings do the right thing
+  assertEquals("spooky halloween", returnValue(do {
+    "happy halloween".replace('happy', 'spooky');
+  }));
+
+  // Do expressions with no completion produce an undefined value
+  assertEquals(undefined, returnValue(do {}));
+  assertEquals(undefined, returnValue(do { var x = 99; }));
+  assertEquals(undefined, returnValue(do { function f() {}; }));
+  assertEquals(undefined, returnValue(do { let z = 33; }));
+
+  // Propagation of exception
+  assertThrows(function() {
+    (do {
+      throw new MyError();
+      "potatoes";
+    });
+  }, MyError);
+
+  assertThrows(function() {
+    return do {
+      throw new MyError();
+      "potatoes";
+    };
+  }, MyError);
+
+  // Return value within do-block overrides `return |do-expression|`
+  assertEquals("inner-return", (function() {
+    return "outer-return" + do {
+      return "inner-return";
+      "";
+    };
+  })());
+
+  // Breaking out |do-expression|
+  assertEquals(3, (function() {
+    for (var i = 0; i < 10; ++i) (do { if (i === 3) break; });

[rossberg, 2015/10/16 12:09:40]

I'm mildly surprised that this one actually works right now. I bet it goes
haywire when you wrap some expression around the do (though you probably need
more than just return afterwards to observe the mess).

What I guess already works, though, is a break to a target local to the same do,
even if that do has an expression around it.

[caitp (gmail), 2015/10/16 13:12:18]

From local testing, it seems to be working fine --- or at least isn't causing
any crashes. It's possible that the operand stack isn't being unwound correctly,
though. The behaviour is that the expression isn't applied when the
break/continue occurs. I'm not sure how big of a test it would take to cause a
crash if the operand stack isn't being unwound correctly, or if it depends on
the operation being performed, either.

Either way, will push a bigger test

+    return i;
+  })());
+
+  // Continue in |do-expression|
+  assertEquals([1, 3, 5, 7, 9], (function() {
+    var values = [];
+    for (var i = 0; i < 10; ++i) {
+      (do {
+        if ((i & 1) === 0) continue;

[rossberg, 2015/10/16 12:09:40]

Same here.

+        values.push(i);
+      });
+    }
+    return values;
+  })());
+
+  assertThrows("(do { break; });", SyntaxError);
+  assertThrows("(do { continue; });", SyntaxError);
+
+  // Real-world use case for desugaring
+  var array = [1, 2, 3, 4, 5], iterable = [6, 7, 8,9];
+  assertEquals([1, 2, 3, 4, 5, 6, 7, 8, 9], do {
+    for (var element of iterable) array.push(element);
+    array;
+  });
+
+  // Nested do-expressions
+  assertEquals(125, do { (do { (do { 5 * 5 * 5 }) }) });
+
+  // Directives are not honoured
+  (do {
+    "use strict";
+    foo = 80;
+    assertEquals(foo, 80);
+  });
+
+  // Non-empty operand stack testing
+  var O = {
+    method1() {
+      let x = 256;
+      return x + do {
+        for (var i = 0; i < 4; ++i) x += i;
+      } + 17;
+    },
+    method2() {
+      let x = 256;
+      this.reset();
+      return x + do {
+        for (var i = 0; i < this.length(); ++i) x += this.index() * 2;
+      };
+    },
+    _index: 0,
+    index() {
+      return ++this._index;
+    },
+    _length: 4,
+    length() { return this._length; },
+    reset() { this._index = 0; }
+  };
+  assertEquals(535, O["method" + do { 1 } + ""]());
+  assertEquals(532, O["method" + do { ({ valueOf() { return "2"; } }); }]());
+  assertEquals(532, O[
+      do { let s = ""; for (let c of "method") s += c; } + "2"]());
+}
+TestBasic();
+
+
+function TestDeoptimization1() {
+  function f(v) {
+    return 88 + do {
+      v.a * v.b + v.c;
+    };
+  }
+
+  var o1 = {};
+  o1.a = 10;
+  o1.b = 5;
+  o1.c = 50;
+
+  var o2 = {};
+  o2.c = 100;
+  o2.a = 10;
+  o2.b = 10;
+
+  assertEquals(188, f(o1));
+  assertEquals(188, f(o1));
+  %OptimizeFunctionOnNextCall(f);
+  assertEquals(188, f(o1));
+  assertOptimized(f);
+  assertEquals(288, f(o2));
+  assertUnoptimized(f);
+  assertEquals(288, f(o2));
+}
+TestDeoptimization1();
+
+
+function TestInParameterInitializers() {
+  var first_name = "George";
+  var last_name = "Jetson";
+  function fn1(name = do { first_name + " " + last_name }) {
+    return name;
+  }
+  assertEquals("George Jetson", fn1());
+
+  var _items = [1, 2, 3, NaN, 4, 5];
+  function fn2(items = do {
+    let items = [];
+    for (var el of _items) {
+      if (el !== el) break;
+      items.push(el), items;
+    }
+  }) {
+    return items;
+  }
+  assertEquals([1, 2, 3], fn2());
+
+  function thrower() { throw new MyError(); }
+  function fn3(exception = do {  try { thrower(); } catch (e) { e } }) {
+    return exception;
+  }
+  assertDoesNotThrow(fn3);
+  assertInstanceof(fn3(), MyError);
+
+  function fn4(exception = do { throw new MyError() }) {}
+  function catcher(fn) {
+    try {
+      fn();
+      assertUnreachable("fn() initializer should throw");
+    } catch (e) {
+      assertInstanceof(e, MyError);
+    }
+  }
+  catcher(fn4);
+}
+TestInParameterInitializers();
+
+
+function TestWithEval() {
+  (function sloppy1() {
+    assertEquals(do { eval("var x = 5"), x }, 5);
+    assertEquals(x, 5);
+  })();
+
+  assertThrows(function strict1() {
+    "use strict";
+    (do { eval("var x = 5"), x }, 5);
+  }, ReferenceError);
+
+  assertThrows(function strict2() {
+    (do { eval("'use strict'; var x = 5"), x }, 5);
+  }, ReferenceError);
+}
+TestWithEval();
+
+
+function TestHoisting() {

[rossberg, 2015/10/16 12:09:40]

Can you add a test with do-var inside a parameter initialiser?

[caitp (gmail), 2015/10/16 12:21:00]

I don't expect it to work the way I'd think it would right now ---

EG:

```
function f(a = x, b = do { var x = "foo" }) {
  return a;
}
// a is initialized before hoisted `x` is initialized
assertEquals(undefined, f());

// x is hoisted and can be referenced from outside the function
assertEquals("foo", x);
```

But right now it doesn't end up working this way (x isn't hoisted to the right
declaration scope)

Can I mark this as a TODO? I think it would be fixed by building on top of
Adam's initializer scoping CL

[rossberg, 2015/10/16 12:37:02]

Sure, TODO is fine, just was curious in how far it works already.

FWIW, the ES6 semantics already is to introduce a separate var scope around each
parameter (remember sloppy eval!). Consequently, I don't think your example is
supposed to work the way you describe it. The expected behaviour consistent with
ES6 would be:
```
let x = 1

function f(a = do { var x = 2 }, b = x) { return b }
assertEquals(1, f())

function g(a = x, b = do { var x = 2 }) { return a }
assertEquals(1, g())

function h({a = do { var x = 2 }, b = x}) { return b }
assertEquals(2, h())

function i({a = x, b = do { var x = 2 }}) { return b }
assertEquals(undefined, i())

function j(a = do { var y = 0 }) {}
assertThrows(() => y, ReferenceError)
```
Essentially, the dynamic behaviour should be mostly like for an eval in place of
the do, except that vars are created immediately, as observed by i().

[caitp (gmail), 2015/10/16 13:12:18]

Yeah, you're right. Then this doesn't need a TODO because IIRC this already
works, fixing up the tests

[caitp (gmail), 2015/10/16 13:23:03]

Is this actually right? Each parameter with an initializer gets its own
VariableEnvironment, so the declaration in the initializer for `a` shouldn't be
visible to the declaration for `b`, is that wrong? I would expect this to return
the value for `let x`, regardless of language mode

[rossberg, 2015/10/16 13:28:28]

Note the curly braces: this is a single parameter destructuring, which is how it
differs from the preceding examples.

+  (do { var a = 1; });
+  assertEquals(a, 1);
+  assertEquals(global.a, undefined);
+
+  (do {
+    for (let it of [1, 2, 3, 4, 5]) {
+      var b = it;
+    }
+  });
+  assertEquals(b, 5);
+  assertEquals(global.b, undefined);
+
+  // TODO(caitp): Always block-scope function declarations in |do| expressions
+  //(do {
+  //  assertEquals(true, inner_func());
+  //  function inner_func() { return true; }
+  //});
+  //assertThrows(function() { return innerFunc(); }, ReferenceError);
+}
+TestHoisting();
+
+
+function TestOSR() {
+  var numbers = do {
+    let nums = [];
+    for (let i = 0; i < 1000; ++i) {
+      let value = (Math.random() * 100) | 0;
+      nums.push(value === 0 ? 1 : value), nums;
+    }
+  };
+  assertEquals(numbers.length, 1000);
+}
+
+for (var i = 0; i < 64; ++i) TestOSR();