[BUG] Extending a state with an empty body triggers StopIteration in state compiler

[a-wildman]

Description
An empty state declaration (e.g. empty_declaration: {}) is legal, and is a no-op. Extending the state (via extends) with a similarly empty body triggers a StopIteration in the state compiler.

Setup
(Please provide relevant configs and/or SLS files (be sure to remove sensitive info. There is no general set-up of Salt.)

Please be as specific as possible and give set-up details.

• on-prem machine
• VM (Virtualbox, KVM, etc. please specify)
• VM running on a cloud service, please be explicit and add details
• container (Kubernetes, Docker, containerd, etc. please specify)
• or a combination, please be explicit
• jails if it is FreeBSD
• classic packaging
• onedir packaging
• used bootstrap to install

Steps to Reproduce the behavior

extend_fail.sls:

empty_declaration: {}

extend:
  empty_declaration: {}

State application:

$ salt-call state.apply extend_fail saltenv=base
[ERROR   ] An un-handled exception was caught by Salt's global exception handler:
StopIteration: 
Traceback (most recent call last):
  File "/opt/salt/salt-call", line 23, in <module>
    sys.exit(salt_call())
  File "/opt/salt/lib/python3.10/site-packages/salt/scripts.py", line 443, in salt_call
    client.run()
  File "/opt/salt/lib/python3.10/site-packages/salt/cli/call.py", line 50, in run
    caller.run()
  File "/opt/salt/lib/python3.10/site-packages/salt/cli/caller.py", line 95, in run
    ret = self.call()
  File "/opt/salt/lib/python3.10/site-packages/salt/cli/caller.py", line 202, in call
    ret["return"] = self.minion.executors[fname](
  File "/opt/salt/lib/python3.10/site-packages/salt/loader/lazy.py", line 159, in __call__
    ret = self.loader.run(run_func, *args, **kwargs)
  File "/opt/salt/lib/python3.10/site-packages/salt/loader/lazy.py", line 1245, in run
    return self._last_context.run(self._run_as, _func_or_method, *args, **kwargs)
  File "/opt/salt/lib/python3.10/site-packages/salt/loader/lazy.py", line 1260, in _run_as
    return _func_or_method(*args, **kwargs)
  File "/opt/salt/lib/python3.10/site-packages/salt/executors/direct_call.py", line 10, in execute
    return func(*args, **kwargs)
  File "/opt/salt/lib/python3.10/site-packages/salt/loader/lazy.py", line 159, in __call__
    ret = self.loader.run(run_func, *args, **kwargs)
  File "/opt/salt/lib/python3.10/site-packages/salt/loader/lazy.py", line 1245, in run
    return self._last_context.run(self._run_as, _func_or_method, *args, **kwargs)
  File "/opt/salt/lib/python3.10/site-packages/salt/loader/lazy.py", line 1260, in _run_as
    return _func_or_method(*args, **kwargs)
  File "/opt/salt/lib/python3.10/site-packages/salt/modules/state.py", line 833, in apply_
    return sls(mods, **kwargs)
  File "/opt/salt/lib/python3.10/site-packages/salt/modules/state.py", line 1479, in sls
    ret = st_.state.call_high(high_, orchestration_jid)
  File "/opt/salt/lib/python3.10/site-packages/salt/state.py", line 3493, in call_high
    high, ext_errors = self.reconcile_extend(high)
  File "/opt/salt/lib/python3.10/site-packages/salt/state.py", line 1731, in reconcile_extend
    state_type = next(x for x in body if not x.startswith("__"))
StopIteration
Traceback (most recent call last):
  File "/opt/salt/salt-call", line 23, in <module>
    sys.exit(salt_call())
  File "/opt/salt/lib/python3.10/site-packages/salt/scripts.py", line 443, in salt_call
    client.run()
  File "/opt/salt/lib/python3.10/site-packages/salt/cli/call.py", line 50, in run
    caller.run()
  File "/opt/salt/lib/python3.10/site-packages/salt/cli/caller.py", line 95, in run
    ret = self.call()
  File "/opt/salt/lib/python3.10/site-packages/salt/cli/caller.py", line 202, in call
    ret["return"] = self.minion.executors[fname](
  File "/opt/salt/lib/python3.10/site-packages/salt/loader/lazy.py", line 159, in __call__
    ret = self.loader.run(run_func, *args, **kwargs)
  File "/opt/salt/lib/python3.10/site-packages/salt/loader/lazy.py", line 1245, in run
    return self._last_context.run(self._run_as, _func_or_method, *args, **kwargs)
  File "/opt/salt/lib/python3.10/site-packages/salt/loader/lazy.py", line 1260, in _run_as
    return _func_or_method(*args, **kwargs)
  File "/opt/salt/lib/python3.10/site-packages/salt/executors/direct_call.py", line 10, in execute
    return func(*args, **kwargs)
  File "/opt/salt/lib/python3.10/site-packages/salt/loader/lazy.py", line 159, in __call__
    ret = self.loader.run(run_func, *args, **kwargs)
  File "/opt/salt/lib/python3.10/site-packages/salt/loader/lazy.py", line 1245, in run
    return self._last_context.run(self._run_as, _func_or_method, *args, **kwargs)
  File "/opt/salt/lib/python3.10/site-packages/salt/loader/lazy.py", line 1260, in _run_as
    return _func_or_method(*args, **kwargs)
  File "/opt/salt/lib/python3.10/site-packages/salt/modules/state.py", line 833, in apply_
    return sls(mods, **kwargs)
  File "/opt/salt/lib/python3.10/site-packages/salt/modules/state.py", line 1479, in sls
    ret = st_.state.call_high(high_, orchestration_jid)
  File "/opt/salt/lib/python3.10/site-packages/salt/state.py", line 3493, in call_high
    high, ext_errors = self.reconcile_extend(high)
  File "/opt/salt/lib/python3.10/site-packages/salt/state.py", line 1731, in reconcile_extend
    state_type = next(x for x in body if not x.startswith("__"))
StopIteration

Expected behavior
The above example compiles cleanly, and (expectedly) does nothing, i.e.

local:

Summary for local
-----------
Succeeded: 0
Failed:   0
-----------
Total states run:    0
Total run time:  0.000 ms

Versions Report

salt --versions-report

(Provided by running salt --versions-report. Please also mention any differences in master/minion versions.)

Salt Version:
          Salt: 3006.3
 
Python Version:
        Python: 3.10.13 (main, Sep  6 2023, 02:16:00) [Clang 14.0.0 (clang-1400.0.29.202)]
 
Dependency Versions:
          cffi: 1.14.6
      cherrypy: 18.6.1
      dateutil: 2.8.0
     docker-py: Not Installed
         gitdb: 4.0.5
     gitpython: 3.1.32
        Jinja2: 3.1.2
       libgit2: Not Installed
  looseversion: 1.0.2
      M2Crypto: Not Installed
          Mako: Not Installed
       msgpack: 1.0.2
  msgpack-pure: Not Installed
  mysql-python: Not Installed
     packaging: 22.0
     pycparser: 2.21
      pycrypto: Not Installed
  pycryptodome: 3.9.8
        pygit2: Not Installed
  python-gnupg: 0.4.8
        PyYAML: 6.0.1
         PyZMQ: 23.2.0
        relenv: 0.13.10
         smmap: 3.0.2
       timelib: 0.2.4
       Tornado: 4.5.3
           ZMQ: 4.3.4
 
System Versions:
          dist: darwin 22.6.0 
        locale: utf-8
       machine: x86_64
       release: 22.6.0
        system: Darwin
       version: 13.5.1 x86_64

Additional context
This issue does not present in Salt 3002.x

git blame suggests that the regression was introduced in the following commit: 8ec0c32

[OrangeDog]

Is there documentation that an empty state is legal?

If you want a no-op state you are supposed to use test.nop.

[a-wildman]

I'm not aware of any documentation which says this is legal (or illegal, for that matter!) -- this may very well be an undocumented corner case. If it's illegal, that's fine (I understand the use case for test.nop), but in that scenario, the state compiler should definitely inform the user of that instead of raising an unhandled exception.

FWIW, I encountered this issue not in my own Salt definitions, but in a zabbix-formula state (in the context of an os_family which falls into the else-its-nothing case here)

[a-wildman]

For clarity, the empty state declaration itself does not trigger the issue -- the empty extends does.

Compiles cleanly:

empty_declaration: {}

Raises StopIteration:

empty_declaration: {}

extend:
  empty_declaration: {}

[Ch3LL]

When I'm able to dive into the code for this issue I'll know what is expected behavior but I do agree we shouldn't be stack tracing here, so we should atleast clean that up. I'll assign to myself to look at a later date.