functions (e.g. islink(), fileexists()) should work with $(this.promiser)

bundle agent init
{
  files:
      "/tmp/file-symlink-this-promiser"
        link_from => u_ln_s("/tmp/file"),
        move_obstructions => "true";

      "/tmp/file-symlink-file-exists"
        link_from => u_ln_s("/tmp/file"),
        move_obstructions => "true";


      "/tmp/file-symlink-explicit"
        link_from => u_ln_s("/tmp/file"),
        move_obstructions => "true";
}
bundle agent test
{
  files:
      "/tmp/file-symlink-this-promiser"
        delete => u_tidy,
        if => islink($(this.promiser));

       "/tmp/file-symlink-file-exists"
        delete => u_tidy,
        if => fileexists($(this.promiser));

      "/tmp/file-symlink-explicit"
        delete => u_tidy,
        if => islink("/tmp/file-symlink-explicit");
}
bundle agent check
{
  reports:
      "$(this.promise_filename) $(with)"
        with => ifelse( or( fileexists("/tmp/file-symlink-this-promiser"),
                            fileexists("/tmp/file-symlink-file-exists")),
                            "FAIL", "Pass" );

      "/tmp/file-symlink-this-promiser should have been deleted but wasn't"
        if => fileexists("/tmp/file-symlink-this-promiser");

      "/tmp/file-symlink-file-exists should have been deleted but wasn't"
        if => fileexists("/tmp/file-symlink-file-exists");

      "Note: /tmp/file-symlink-explicit was deleted as expected"
        unless => fileexists("/tmp/file-symlink-explicit");
}
bundle agent __main__
{
  methods:
      "init";
      "test";
      "check";
}
body link_from u_ln_s(x)
# @brief Symlink to `x`, even if it does not exist
# @param x Path to symlink
#@ **Example:**
#@ ```cf3
#@ bundle agent example u_ln_s {
#@   files:
#@     "$(symlink_path)"
#@       link_from => u_ln_s("$(python)"),
#@       move_obstructions => "true",
#@       if => isvariable("python");
#@ }
#@ ```
{
        link_type => "symlink";
        source => "$(x)";
        when_no_source => "force";
}
body delete u_tidy
{
        dirlinks => "delete";
        rmdirs   => "true";
}