Join assignment

[thejh]

See #223 - basically, this is about joining assignment statements into expressions when appropriate:

a=1;f(2,5,1)
f(2,5,a=1)

[michaelficarra]

Can you explain this change to me? Why do you have to walk the rvalue before the lvalue?

[thejh]

@michaelficarra consider this example:

a.b = 3;
c.d = 3;

If I'd walk lvalue first, c.d would prevent me from joining those two because my code would (incorrectly) assume that c.d gets evaluated before the second 3 and therefore could trigger a setter that alters state or so. My code depends on the walkers going through the code in the order the code would be evaluated in.

[michaelficarra]

Oh, alright. Thanks.

[mishoo]

This one is buggy:

// problem 1: this.foo is dropped
this.foo = 0;
this.bar = 0;
this.baz = 0;
// problem 2: b -= b += 5?
if (a < 0) b += 5;
else b -= 5;

===> uglified:

this.baz = this.bar = 0, a < 0 && (b -= b += 5);

[thejh]

Fixed one easy bug, only simple assignments (=) are treated this way now, but the problems with this.foo being dropped and if (a) b=2; else c=2 getting compiled to a&&(c=b=2) still remain. :(