build.hxml

-main Main
-js run.js
-dce full

Foo.hx

package ;

#if (eval || macro)
import haxe.macro.Expr;
#end

abstract Foo<T>(T) {
    @:from public static macro function fromThing<T>(e:ExprOf<Thing>):ExprOf<Foo<T>> {
        return macro null;
    }
}

Main.hx

package ;

import Thing;

class Main {
    public static function main() {
        var foo:Foo<String> = BOO;
        trace( foo );
    }
}

Thing.hx

package ;

enum Thing {
    BOO;
}