[BUG] __sls__ variable empty when called with slsutil.renderer

Description

When an sls file is rendered with the py renderer using salt.slsutil.renderer, the __sls__ variable is empty. According to the py renderer documentation at https://docs.saltproject.io/en/latest/ref/renderers/all/salt.renderers.py.html#module-salt.renderers.py the __sls__ variable should be set to the path of the file:

__sls__ - The SLS path of the file. For example, if the root of the base environment is /srv/salt, and the SLS file is /srv/salt/foo/bar/baz.sls, then __sls__ in that file will be foo.bar.baz.

Feature Request: really what I would like a simple way to render an sls file in the same directory using a relative path similar to how the path in an jinja import statement can start with the ./ prefix to import a file in the same directory. Example: __salt__.slsutil.renderer("./relative_file.sls)

Setup

• ec2 instance running rhel 7.9

• classic packaging (yum install salt-minion)

• create /srv/salt/myformula/init.sls:

  {% set myformula_vars = salt.slsutil.renderer("salt://" ~ tpldir ~ "vars.sls")
  

• create /srv/salt/myformula/defaults.sls:

  my_var_1: value1
  my_var_2: value2
  

• create /srv/salt/myformula/vars.sls:

  #!py
  import logging
  from pathlib import Path
  LOGGER = logging.getLogger(__name__)
  def run():
      logging.info("sls: %s;", __sls__)
      _slsdir = Path('/'.join(__sls__.split('.')).parent
      _defaults = __salt__.slsutil.renderer(f"salt://{_slsdir}/defaults.sls)
  

Steps to Reproduce the behavior

salt-call -l info --local state.apply myformula

Log output is

[INFO ] sls: ;

Expected behavior

__sls__ should be set to the SLS path of the file myformula.vars and the log message should show:

[INFO ] sls: myformula.vars;

Versions Report

Salt Version:
        Salt: 3004.1

Dependency Versions:
    Jinja2: 2.11.1
    Python: 3.6.8 (default, Aug 13 2020, 07:46:32)
    PyYAML: 3.13

System Versions:
      dist: rhel 7.9 Maipo
    locale: UTF-8
   release: 3.10.0-1160.15.2.el7.x86_64
   system: Linux

Start with the salt.slsutil.renderer entry point and the Python renderer behavior used by myformula/init.sls and myformula/vars.sls. Reproduce with salt-call --local state.apply myformula, then verify that rendering sets sls to myformula.vars and supports the requested relative-path behavior.