- as source file not allowed when using the --stdin-filename option (unlike in Black)

[my-tien]

Describe the bug
I have the Black Formatter extension and configured darker in the black formatter path.
When formatting on save in VSCode, the output log will contain below error.

NOTE: everything works fine when not using the Black Formatter extension, but using the formatter feature of the Python extension (ms-python.python) instead.

  File "C:\Program Files\Python39\lib\runpy.py", line 197, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "C:\Program Files\Python39\lib\runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "C:\Users\xxx\envs\yyy\Scripts\darker.exe\__main__.py", line 7, in <module>
  File "C:\Users\xxx\Envs\yyy\lib\site-packages\darker\__main__.py", line 631, in main_with_error_handling
    return main()
  File "C:\Users\xxx\Envs\yyy\lib\site-packages\darker\__main__.py", line 484, in main
    args, config, config_nondefault = parse_command_line(argv)
  File "C:\Users\xxx\Envs\yyy\lib\site-packages\darker\command_line.py", line 150, in parse_command_line
    validate_stdin_src(args.stdin_filename, args.src)
  File "C:\Users\xxx\Envs\yyy\lib\site-packages\darker\config.py", line 114, in validate_stdin_src
    raise ConfigurationError(
darker.config.ConfigurationError: No Python source files are allowed when using the `stdin-filename` option

To Reproduce
Steps to reproduce the behavior:

1. pip install darker
2. In VSCode install extension Black Formatter (ms-python.black-formatter)
3. Configure Black as default formatter for python files.
4. In settings.json:

  "black-formatter.path": [
    "path\\to\\darker.exe"
  ],
  "python.formatting.provider": "black",
  "python.formatting.blackArgs": [
    "--line-length",
    "100"
  ],
  "[python]": {
    "editor.formatOnSave": true
  }

5. Add whitespace after a line in a python file and save.

Expected behavior
Reformatted file

Environment (please complete the following information):

• OS: Windows 10
• Python 3.9.13
• Git version 2.39.1.windows.1
• Darker version 1.7.1
• Black version 22.3.0

[akaihola]

Hi @my-tien, thanks for the report!

Can you find the full Darker command line in an output/debug window?

The correct format is

darker --line-length 100 --stdin-filename path/to/file.py

So the path of the file must immediately follow the --stdin-filename option, or alternatively be expressed using an equals sign like --stdin-filename=path/to/file.py.

If you can't find the used command line inside VSCode, you can modify Darker's source code to catch the exception at darker/command_line.py:150, print repr(argv) to stderr and re-raise. You should then be able to see whether the Darker command line used by the Black Formatter extension is correct.

[my-tien]

Hi, this is the generated Darker command:

path\to\darker.exe --line-length 100 --stdin-filename path\to\python\file.py -

So maybe the hyphen at the end is the problem?

[akaihola]

Yes, probably the hyphen is the problem. So Darker is then not fully compatible as a drop-in replacement for Black. This should certainly be fixed. Could you still verify that Black indeed works with a similar command line:

path\to\black.exe --line-length 100 --stdin-filename path\to\python\file.py -

Thanks! I'll then think about how to best create the fix for the problem.

[my-tien]

I did not have time to test this on my initial machine again, but on my Linux machine at home I successfully reproduced the problem on the command line. Since the hyphen at the end expects something on stdin, you need to adapt the command like below:

$ cat test.py | black --line-length 100 --stdin-filename test.py -

print("hello")
reformatted test.py

All done! ✨ 🍰 ✨
1 file reformatted.

$ cat test.py | darker --line-length 100 --stdin-filename test.py -

Traceback (most recent call last):
  File "/home/tieni/.local/bin/darker", line 8, in <module>
    sys.exit(main_with_error_handling())
             ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/tieni/.local/lib/python3.11/site-packages/darker/__main__.py", line 631, in main_with_error_handling
    return main()
           ^^^^^^
  File "/home/tieni/.local/lib/python3.11/site-packages/darker/__main__.py", line 484, in main
    args, config, config_nondefault = parse_command_line(argv)
                                      ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/tieni/.local/lib/python3.11/site-packages/darker/command_line.py", line 150, in parse_command_line
    validate_stdin_src(args.stdin_filename, args.src)
  File "/home/tieni/.local/lib/python3.11/site-packages/darker/config.py", line 114, in validate_stdin_src
    raise ConfigurationError(
darker.config.ConfigurationError: No Python source files are allowed when using the `stdin-filename` option