Simplify destructuring for single assignment and identifier cases.

Simplify destructuring for single assignment and identifier cases.

Also, tries not to use parens if not necessary.

BUG=http://code.google.com/p/traceur-compiler/issues/detail?id=141
TEST=test/feature/Destructuring/Simplify.js

[usrbincc, 2012-10-22 18:57:03]

I have some cases that will probably never be found in a destructuring, and I
didn't know how to handle cascade expressions so I just left that case out.

#--cut--
git apply --reject issue*.diff

# don't build yet

cat > simp-dest.js <<END
var a = { x:1,y:2 };
var {x,y} = a;
var b = { b:{x:1,y:2,z:3} };
var {z} = b.b;
var {w} = {w:42};
var {x,y} = b.b; // purposely not simplified. This could be a getter.
var [[x]] = [[1],2,[3]];
END

# before...
./traceurc --private-names=false simp-dest.js
cat out/simp-dest.compiled.js

build/build

# after...
./traceurc --private-names=false simp-dest.js
cat out/simp-dest.compiled.js
#--cut--

[arv, 2012-10-22 20:34:05]

https://codereview.appspot.com/6709068/diff/1/src/codegeneration/Destructurin...
File src/codegeneration/DestructuringTransformer.js (right):

https://codereview.appspot.com/6709068/diff/1/src/codegeneration/Destructurin...
src/codegeneration/DestructuringTransformer.js:242: var tempIdent_assign =
createAssignmentExpression(tempIdent, rvalue);
no underscores... tempIdentAsign

https://codereview.appspot.com/6709068/diff/1/src/codegeneration/Destructurin...
src/codegeneration/DestructuringTransformer.js:501: // - tree.initializer is an
IDENTIFIER_EXPRESSION.
Conceptually this could break if the identifier refers to a getter of the global
object. I'd rather be safe here and not do this optimization.

https://codereview.appspot.com/6709068/diff/1/src/codegeneration/Destructurin...
src/codegeneration/DestructuringTransformer.js:503: // (paren not necessary)
// Paren not necessary

Skip the parens in the comments

[usrbincc, 2012-10-22 20:59:00]

I didn't think about the global object's getters. No wonder it's so hard to
statically optimize Javascript. This ends up not being as much of a win
as I'd hoped for, in that case.

https://codereview.appspot.com/6709068/diff/1/src/codegeneration/Destructurin...
File src/codegeneration/DestructuringTransformer.js (right):

https://codereview.appspot.com/6709068/diff/1/src/codegeneration/Destructurin...
src/codegeneration/DestructuringTransformer.js:242: var tempIdent_assign =
createAssignmentExpression(tempIdent, rvalue);
On 2012/10/22 20:34:05, arv-chromium wrote:
> no underscores... tempIdentAsign
The thing I was having trouble with is trying to distinguish between:
"tempIdent assign" and "temp identAssign". In that case, I'll probably
revert this hunk and just reformat the line to <= 80 columns. (My new
pre-commit hook flagged this line, or I wouldn't have bothered editing
this part in the first place)

[arv, 2012-10-23 14:41:25]

LGTM

I'll clean up the style violations and commit this for you

https://codereview.appspot.com/6709068/diff/4/src/codegeneration/Destructurin...
File src/codegeneration/DestructuringTransformer.js (right):

https://codereview.appspot.com/6709068/diff/4/src/codegeneration/Destructurin...
src/codegeneration/DestructuringTransformer.js:245:
createAssignmentExpression(tempIdent, rvalue));
Fix indentation, indent 4 spaces in this case.

https://codereview.appspot.com/6709068/diff/4/src/codegeneration/Destructurin...
src/codegeneration/DestructuringTransformer.js:524: initializer = initializer ||
createParenExpression(tree.initializer);
Another option is to have another transformation pass that cleans up paren
expressions that do not have a location (generated by us).

https://codereview.appspot.com/6709068/diff/4/test/feature/Destructuring/Simp...
File test/feature/Destructuring/Simplify.js (right):

https://codereview.appspot.com/6709068/diff/4/test/feature/Destructuring/Simp...
test/feature/Destructuring/Simplify.js:11: function check_a() {
No underscores: checkA

https://codereview.appspot.com/6709068/diff/4/test/feature/Destructuring/Simp...
test/feature/Destructuring/Simplify.js:46: x = { x:{ a:1, b:2, c:3 } };
No space after {
No space before }
Space after :

https://codereview.appspot.com/6709068/diff/4/test/feature/Destructuring/Simp...
test/feature/Destructuring/Simplify.js:53: x = { x: [1,2,3] };
space after comma

[arv, 2012-10-23 14:57:14]

Committed as

http://code.google.com/p/traceur-compiler/source/detail?r=c292c0008aa9c6ddf3f...