Potential optimization: compile-time spreads about haxe-react

[elsassph]

I did a first spike: it is definitely possible and easy enough: basically if the object assigned is of an anonymous type (like a local anonymous object or state/props typedefs), then the props and this object's fields (as defined in the anonymous type) can be assigned field by field.

Example:

var p = { title: 'bar', items: props.items };
return jsx('<Comp className="foo" {...p}/>');
// normally generated as:
return React.createElement(Comp, Object.assign({}, p, {className:"foo"}));
// could be optimized into:
return React.createElement(Comp, {className:"foo", title:p.title, items:p.items});
// and even further optimized by Haxe dce into
return React.createElement(Comp, {className:"foo", title:"bar", items:this.props.items});

However I'm suspecting it may have unwanted side effects (especially if I try to push it to merge state/props objects where lots of fields can be optional). Feedback? cc @francescoagati @zabojad @kevinresol @jeremyfa

[elsassph]

You can try the spike in branch feature/merge_spreads. It's limited to simple anonymous objects and it looks like it could be quite neat.