Missing ruff executable breaks other linters

[chris-reeves]

If the executable configuration param is specified but points to an executable that does not exist then run_ruff() throws an exception and prevents other python-lsp-server linters from running. With a valid executable specified multiple lint errors are flagged from multiple linters (including ruff). With an invalid executable specified no lint errors are flagged (not even from other linters).

For example:

2023-12-22 13:21:14,431 GMT - DEBUG - pylsp_ruff.plugin - Calling ruff with args: ['--quiet', '--exit-zero', '--output-format=json', '--extension=ipynb:python', '--no-fix', '--force-exclude', '--stdin-filename=<redacted>', '--preview', '--extend-select=E,W,F', '--', '-'] on '<redacted>''
2023-12-22 13:21:14,439 GMT - ERROR - pylsp_ruff.plugin - Can't execute ruff with given executable 'ruff'.
2023-12-22 13:21:14,440 GMT - WARNING - pylsp.config.config - Failed to load hook pylsp_lint: cannot access local variable 'p' where it is not associated with a value
Traceback (most recent call last):
  File "/<redacted>/.config/coc/extensions/@yaegassy/coc-pylsp-data/pylsp/venv/lib/python3.11/site-packages/pylsp/config/config.py", line 40, in _hookexec
    return self._inner_hookexec(hook_name, methods, kwargs, firstresult)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/<redacted>/.config/coc/extensions/@yaegassy/coc-pylsp-data/pylsp/venv/lib/python3.11/site-packages/pluggy/_manager.py", line 457, in traced_hookexec
    return outcome.get_result()
           ^^^^^^^^^^^^^^^^^^^^
  File "/<redacted>/.config/coc/extensions/@yaegassy/coc-pylsp-data/pylsp/venv/lib/python3.11/site-packages/pluggy/_result.py", line 114, in get_result
    raise exc.with_traceback(exc.__traceback__)
  File "/<redacted>/.config/coc/extensions/@yaegassy/coc-pylsp-data/pylsp/venv/lib/python3.11/site-packages/pluggy/_result.py", line 76, in from_call
    result = func()
             ^^^^^^
  File "/<redacted>/.config/coc/extensions/@yaegassy/coc-pylsp-data/pylsp/venv/lib/python3.11/site-packages/pluggy/_manager.py", line 454, in <lambda>
    lambda: oldcall(hook_name, hook_impls, caller_kwargs, firstresult)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/<redacted>/.config/coc/extensions/@yaegassy/coc-pylsp-data/pylsp/venv/lib/python3.11/site-packages/pluggy/_callers.py", line 113, in _multicall
    raise exception.with_traceback(exception.__traceback__)
  File "/<redacted>/.config/coc/extensions/@yaegassy/coc-pylsp-data/pylsp/venv/lib/python3.11/site-packages/pluggy/_callers.py", line 77, in _multicall
    res = hook_impl.function(*args)
          ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/<redacted>/.config/coc/extensions/@yaegassy/coc-pylsp-data/pylsp/venv/lib/python3.11/site-packages/pylsp_ruff/plugin.py", line 172, in pylsp_lint
    checks = run_ruff_check(document=document, settings=settings)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/<redacted>/.config/coc/extensions/@yaegassy/coc-pylsp-data/pylsp/venv/lib/python3.11/site-packages/pylsp_ruff/plugin.py", line 442, in run_ruff_check
    result = run_ruff(
             ^^^^^^^^^
  File "/<redacted>/.config/coc/extensions/@yaegassy/coc-pylsp-data/pylsp/venv/lib/python3.11/site-packages/pylsp_ruff/plugin.py", line 525, in run_ruff
    (stdout, stderr) = p.communicate(document_source.encode())
                       ^
UnboundLocalError: cannot access local variable 'p' where it is not associated with a value

Versions:

• python: 3.11.6
• python-lsp-server: 1.9.0
• python-lsp-ruff: 2.0.0

Prior to commit ea5f874a, python-lsp-ruff would silently (apart from a debug message) fall back to running ruff via the python module if the specified executable was not found. Now an error message is logged following the Popen() failure, but the code still attempts to use the pipe (which is not defined following the exception). That throws an exception which is not caught and as a result any subsequent linters aren't run (so not only do we not se

I see two options for resolving this (other than making sure the executable config param is set correctly :-p):

• return an empty string after logging the error on line 520;
• fall back to running ruff via the python module (similar to previous behaviour, but with the option to not even attempt to run the executable if it's not specified).

I'd suggest the second option as that will provide a better user experience. That assumes commit ea5f874a was simply intended to shortcut the attempt to call the executable if it was not set, rather than intended to remove the fallback behaviour.

This issue was discovered while investigating yaegassy/coc-pylsp#24.