Improve error message when an option is valid, but is being applied to a subsystem/goal, rather than globally

[rtpg]

My pants.toml

[GLOBAL]
v2=true
v1=false
v2_ui=true
pants_version="1.27.0rc0"

# no v1 packages
backend_packages = []

# v2 backends
backend_packages2 = []

# v2 plugins
plugins2 = []

I wanted to try out the backends goal, but hit a failure. Then I wanted to see the actual stacktrace and ended up with the following stacktrace about... not being able to see the stacktrace

~/proj/pants-test                                                                                                           
$ ./pants backends                                                                                                                       

ERROR: max() arg is an empty sequence

(Use --print-exception-stacktrace to see more error details.)

~/proj/pants-test                                                                                                           
$ ./pants backends --print-exception-stacktrace                                                                                          
timestamp: 2020-04-24T13:17:30.874773
Exception caught: (pants.option.errors.ParseError)
  File "/home/rtpg/.cache/pants/setup/bootstrap-Linux-x86_64/1.27.0rc0_py37/bin/pants", line 8, in <module>
    sys.exit(main())
  File "/home/rtpg/.cache/pants/setup/bootstrap-Linux-x86_64/1.27.0rc0_py37/lib/python3.7/site-packages/pants/bin/pants_loader.py", line 94, in main
    PantsLoader.run()
  File "/home/rtpg/.cache/pants/setup/bootstrap-Linux-x86_64/1.27.0rc0_py37/lib/python3.7/site-packages/pants/bin/pants_loader.py", line 90, in run
    cls.load_and_execute(entrypoint)
  File "/home/rtpg/.cache/pants/setup/bootstrap-Linux-x86_64/1.27.0rc0_py37/lib/python3.7/site-packages/pants/bin/pants_loader.py", line 83, in load_and_execute
    entrypoint_main()
  File "/home/rtpg/.cache/pants/setup/bootstrap-Linux-x86_64/1.27.0rc0_py37/lib/python3.7/site-packages/pants/bin/pants_exe.py", line 33, in main
    runner.run(start_time)
  File "/home/rtpg/.cache/pants/setup/bootstrap-Linux-x86_64/1.27.0rc0_py37/lib/python3.7/site-packages/pants/bin/pants_runner.py", line 100, in run
    runner = LocalPantsRunner.create(env=self.env, options_bootstrapper=options_bootstrapper)
  File "/home/rtpg/.cache/pants/setup/bootstrap-Linux-x86_64/1.27.0rc0_py37/lib/python3.7/site-packages/pants/bin/local_pants_runner.py", line 188, in create
    options.for_scope(scope)
  File "/home/rtpg/.cache/pants/setup/bootstrap-Linux-x86_64/1.27.0rc0_py37/lib/python3.7/site-packages/pants/util/memo.py", line 123, in memoize
    result = func(*args, **kwargs)
  File "/home/rtpg/.cache/pants/setup/bootstrap-Linux-x86_64/1.27.0rc0_py37/lib/python3.7/site-packages/pants/option/options.py", line 535, in for_scope
    self._parser_hierarchy.get_parser_by_scope(scope).parse_args(parse_args_request)
  File "/home/rtpg/.cache/pants/setup/bootstrap-Linux-x86_64/1.27.0rc0_py37/lib/python3.7/site-packages/pants/option/parser.py", line 320, in parse_args
    levenshtein_max_distance=levenshtein_max_distance,
  File "/home/rtpg/.cache/pants/setup/bootstrap-Linux-x86_64/1.27.0rc0_py37/lib/python3.7/site-packages/pants/option/parser.py", line 394, in _raise_error_for_invalid_flag_names
    suggestions_message=suggestions_message,

Exception message: Unrecognized command line flags on scope 'backends': --print-exception-stacktrace. Suggestions:
--print-exception-stacktrace: [--print-exception-stacktrace]

[Eric-Arellano]

Try out ./pants --print-exception-stacktrace backends.

./pants backends --print-exception-stacktrace doesn't work as you'd expect because it's really a shorthand for ./pants --backends-print-exception-stacktrace backends.

Another example: ./pants run --args='arg1 -o' is shorthand for ./pants --run-args='arg1 -o' run.

--

With the original issue, yes, unfortunately, we realized a few days ago that ./pants backends doesn't work properly when you installed Pants from a wheel, like you would normally do and how we recommend :/ We'll be temporarily disabling it soon until we fix this. Sorry about that!

[rtpg]

OK passing in the param in the front works, good to know. That issue is a bit subtle but I get why this would happen

[Eric-Arellano]

FYI we took a first pass at improving the error message in #9795. Your message would now read:

Exception message: Unrecognized command line flag `--print-exception-stacktrace` on scope 'backends'. Suggestions:
--print-exception-stacktrace

(Run `./pants help-advanced backends` for all available options.)

This does still have the same major issue of showing options that don't make sense - I hope to address that in a followup this week or next.

[Eric-Arellano]

Fixed by #10872. Thanks for reporting this @rtpg!

We released 2.0.0rc0 yesterday, and it makes lots of big improvements. Check out https://www.pantsbuild.org/docs/how-to-upgrade-pants-2-0 for an upgrade guide, and https://www.pantsbuild.org/docs/community for how to join our Slack. We'd love to help you out with upgrading and trying it out.