TypeError when using macro in root BUILD file

[thejcannon]

Describe the bug
Given BUILD.pants:

docker_environment(
  name="focal-docker",
  image=wo_get_pinned_name("ubuntu:focal")
)

and macro:

def wo_get_pinned_name(x):
    return x

Pants version
2.16.0rc2

OS
Linux

Additional info

Exception caught: (pants.engine.internals.scheduler.ExecutionError)
  File "/home/josh/.cache/nce/ae553d873185fa750061b1a3d4226442fb99fb55d4403b0227ec972406554da3/bindings/venvs/2.16.0rc2/bin/pants", line 8, in <module>
    sys.exit(main())
  File "/home/josh/.cache/nce/ae553d873185fa750061b1a3d4226442fb99fb55d4403b0227ec972406554da3/bindings/venvs/2.16.0rc2/lib/python3.9/site-packages/pants/bin/pants_loader.py", line 123, in main
    PantsLoader.main()
  File "/home/josh/.cache/nce/ae553d873185fa750061b1a3d4226442fb99fb55d4403b0227ec972406554da3/bindings/venvs/2.16.0rc2/lib/python3.9/site-packages/pants/bin/pants_loader.py", line 110, in main
    cls.run_default_entrypoint()
  File "/home/josh/.cache/nce/ae553d873185fa750061b1a3d4226442fb99fb55d4403b0227ec972406554da3/bindings/venvs/2.16.0rc2/lib/python3.9/site-packages/pants/bin/pants_loader.py", line 92, in run_default_entrypoint
    exit_code = runner.run(start_time)
  File "/home/josh/.cache/nce/ae553d873185fa750061b1a3d4226442fb99fb55d4403b0227ec972406554da3/bindings/venvs/2.16.0rc2/lib/python3.9/site-packages/pants/bin/pants_runner.py", line 99, in run
    runner = LocalPantsRunner.create(
  File "/home/josh/.cache/nce/ae553d873185fa750061b1a3d4226442fb99fb55d4403b0227ec972406554da3/bindings/venvs/2.16.0rc2/lib/python3.9/site-packages/pants/bin/local_pants_runner.py", line 90, in create
    build_config = options_initializer.build_config(options_bootstrapper, env)
  File "/home/josh/.cache/nce/ae553d873185fa750061b1a3d4226442fb99fb55d4403b0227ec972406554da3/bindings/venvs/2.16.0rc2/lib/python3.9/site-packages/pants/init/options_initializer.py", line 111, in build_config
    return _initialize_build_configuration(self._plugin_resolver, options_bootstrapper, env)
  File "/home/josh/.cache/nce/ae553d873185fa750061b1a3d4226442fb99fb55d4403b0227ec972406554da3/bindings/venvs/2.16.0rc2/lib/python3.9/site-packages/pants/init/options_initializer.py", line 48, in _initialize_build_configuration
    working_set = plugin_resolver.resolve(options_bootstrapper, env)
  File "/home/josh/.cache/nce/ae553d873185fa750061b1a3d4226442fb99fb55d4403b0227ec972406554da3/bindings/venvs/2.16.0rc2/lib/python3.9/site-packages/pants/init/plugin_resolver.py", line 137, in resolve
    for resolved_plugin_location in self._resolve_plugins(
  File "/home/josh/.cache/nce/ae553d873185fa750061b1a3d4226442fb99fb55d4403b0227ec972406554da3/bindings/venvs/2.16.0rc2/lib/python3.9/site-packages/pants/init/plugin_resolver.py", line 161, in _resolve_plugins
    params = Params(request, determine_bootstrap_environment(session))
  File "/home/josh/.cache/nce/ae553d873185fa750061b1a3d4226442fb99fb55d4403b0227ec972406554da3/bindings/venvs/2.16.0rc2/lib/python3.9/site-packages/pants/core/util_rules/environments.py", line 443, in determine_bootstrap_environment
    session.product_request(ChosenLocalEnvironmentName, [Params()])[0],
  File "/home/josh/.cache/nce/ae553d873185fa750061b1a3d4226442fb99fb55d4403b0227ec972406554da3/bindings/venvs/2.16.0rc2/lib/python3.9/site-packages/pants/engine/internals/scheduler.py", line 569, in product_request
    return self.execute(request)
  File "/home/josh/.cache/nce/ae553d873185fa750061b1a3d4226442fb99fb55d4403b0227ec972406554da3/bindings/venvs/2.16.0rc2/lib/python3.9/site-packages/pants/engine/internals/scheduler.py", line 513, in execute
    self._raise_on_error([t for _, t in throws])
  File "/home/josh/.cache/nce/ae553d873185fa750061b1a3d4226442fb99fb55d4403b0227ec972406554da3/bindings/venvs/2.16.0rc2/lib/python3.9/site-packages/pants/engine/internals/scheduler.py", line 497, in _raise_on_error
    raise ExecutionError(

Exception message: 1 Exception encountered:

MappingError: Failed to parse ./BUILD.pants:
TypeError: _unrecognized_symbol_func() takes 0 positional arguments but 1 was given