Unnecesary variable definitions not being removed

[fedemp]

I got this output from CoffeeScript due to the way it "compiles" anonymous functions.

(function(jQuery) {
  var $;
  $ = jQuery;
  $('body').addClass('foo');
})(jQuery);

$ is here just an alias for the received argument.

When minified (using this new version and the old one) I got:

(function(o){var a;a=o,a("body").addClass("foo")})(jQuery)

Should not uglify ignore the new defined variable and just use the same name from the argument? As in..

 (function(o){o("body").addClass("foo")})(jQuery)

[kzc]

If this:

  var $;
  $ = jQuery;

were to be transformed by reduce_vars or cascade into:

  var $ = jQuery;

then collapse_vars would produce:

!function(jQuery) {
    jQuery("body").addClass("foo");
}(jQuery);

[alexlamsl]

My current plan of attack:

• reduce_vars to detect $ is singularly assigned with jQuery (already implemented in enhance reduce_vars #1814)
• from the result above, convert $ = jQuery; (which is AST_Assign in AST_SimpleStatement) into var $ = jQuery; (which is AST_VarDef in AST_Var) (TODO in enhance reduce_vars #1814 or new PR)
• clean up duplicated definitions, i.e. eliminate var $; (already implemented in compress duplicated variable definitions #1817)
• collapse_vars should take care of the rest Unnecesary variable definitions not being removed #27 (comment)