macbookpro:gecko anatal$ rm -rf ../obj-x86_64-apple-darwin20.
obj-x86_64-apple-darwin20.4.0/ obj-x86_64-apple-darwin20.6.0/
macbookpro:gecko anatal$ rm -rf ../obj-x86_64-apple-darwin20.*
macbookpro:gecko anatal$ ./mach lint --fix -l flake8 js/src/intgemm/detect_avx2.py
The "mach" virtualenv is not up-to-date, please run "./mach create-mach-environment"
macbookpro:gecko anatal$ ./mach create-mach-environment
created virtual environment CPython3.9.8.final.0-64 in 118ms
  creator CPython3Posix(dest=/Users/anatal/.mozbuild/_virtualenvs/mach, clear=False, no_vcs_ignore=False, global=False)
  activators BashActivator,CShellActivator,FishActivator,PowerShellActivator,PythonActivator
Collecting glean-sdk==40.0.0
  Using cached glean_sdk-40.0.0-cp36-abi3-macosx_10_7_x86_64.whl (873 kB)
Collecting glean-parser==3.6.0
  Using cached glean_parser-3.6.0-py3-none-any.whl (80 kB)
Collecting cffi>=1.13.0
  Using cached cffi-1.15.0-cp39-cp39-macosx_10_9_x86_64.whl (178 kB)
Requirement already satisfied: diskcache>=4 in ./third_party/python/diskcache (from glean-parser==3.6.0->glean-sdk==40.0.0) (4.1.0)
Requirement already satisfied: Jinja2>=2.10.1 in ./third_party/python/Jinja2 (from glean-parser==3.6.0->glean-sdk==40.0.0) (2.11.3)
Requirement already satisfied: yamllint>=1.18.0 in ./third_party/python/yamllint (from glean-parser==3.6.0->glean-sdk==40.0.0) (1.23.0)
Requirement already satisfied: Click>=7 in ./third_party/python/Click (from glean-parser==3.6.0->glean-sdk==40.0.0) (7.0)
Requirement already satisfied: PyYAML>=5.3.1 in ./third_party/python/PyYAML/lib3 (from glean-parser==3.6.0->glean-sdk==40.0.0) (5.4.1)
Requirement already satisfied: jsonschema<4,>=3.0.2 in ./third_party/python/jsonschema (from glean-parser==3.6.0->glean-sdk==40.0.0) (3.2.0)
Requirement already satisfied: appdirs>=1.4 in ./third_party/python/appdirs (from glean-parser==3.6.0->glean-sdk==40.0.0) (1.4.4)
Collecting pycparser
  Using cached pycparser-2.21-py2.py3-none-any.whl (118 kB)
Requirement already satisfied: MarkupSafe>=0.23 in ./third_party/python/MarkupSafe/src (from Jinja2>=2.10.1->glean-parser==3.6.0->glean-sdk==40.0.0) (1.1.1)
Requirement already satisfied: six>=1.11.0 in ./third_party/python/six (from jsonschema<4,>=3.0.2->glean-parser==3.6.0->glean-sdk==40.0.0) (1.13.0)
Requirement already satisfied: pyrsistent>=0.14.0 in ./third_party/python/pyrsistent (from jsonschema<4,>=3.0.2->glean-parser==3.6.0->glean-sdk==40.0.0) (0.16.0)
Requirement already satisfied: attrs>=17.4.0 in ./third_party/python/attrs (from jsonschema<4,>=3.0.2->glean-parser==3.6.0->glean-sdk==40.0.0) (19.1.0)
Requirement already satisfied: setuptools in ./third_party/python/setuptools (from jsonschema<4,>=3.0.2->glean-parser==3.6.0->glean-sdk==40.0.0) (51.2.0)
Requirement already satisfied: pathspec>=0.5.3 in ./third_party/python/pathspec (from yamllint>=1.18.0->glean-parser==3.6.0->glean-sdk==40.0.0) (0.8.0)
Installing collected packages: pycparser, glean-parser, cffi, glean-sdk
Successfully installed cffi-1.15.0 glean-parser-3.6.0 glean-sdk-40.0.0 pycparser-2.21
Collecting psutil<=5.8.0,>=5.4.2
  Using cached psutil-5.8.0-cp39-cp39-macosx_10_9_x86_64.whl (236 kB)
Installing collected packages: psutil
Successfully installed psutil-5.8.0
Collecting zstandard<=0.16.0,>=0.11.1
  Using cached zstandard-0.16.0-cp39-cp39-macosx_10_9_x86_64.whl (621 kB)
Installing collected packages: zstandard
Successfully installed zstandard-0.16.0
Mach environment created.
macbookpro:gecko anatal$ ./mach lint --fix -l flake8 js/src/intgemm/detect_avx2.py
created virtual environment CPython3.9.8.final.0-64 in 89ms
  creator CPython3Posix(dest=/Users/anatal/projects/mozilla/obj-x86_64-apple-darwin20.6.0/_virtualenvs/common, clear=False, no_vcs_ignore=False, global=False)
  activators BashActivator,CShellActivator,FishActivator,PowerShellActivator,PythonActivator
✖ 0 problems (0 errors, 0 warnings, 0 fixed)
macbookpro:gecko anatal$ ./mach lint --fix -l black js/src/intgemm/detect_avx2.py
Traceback (most recent call last):
  File "/Users/anatal/projects/mozilla/gecko/python/mozlint/mozlint/roller.py", line 66, in _run_worker
    res = func(paths, config, **lintargs)
  File "/Users/anatal/projects/mozilla/gecko/python/mozlint/mozlint/types.py", line 57, in __call__
    return self._lint(paths, config, **lintargs)
  File "/Users/anatal/projects/mozilla/gecko/python/mozlint/mozlint/types.py", line 148, in _lint
    return func(files, config, **lintargs)
  File "/Users/anatal/projects/mozilla/gecko/tools/lint/python/black.py", line 168, in lint
    return run_black(
  File "/Users/anatal/projects/mozilla/gecko/tools/lint/python/black.py", line 147, in run_black
    log.debug("Black version {}".format(get_black_version(binary)))
  File "/Users/anatal/projects/mozilla/gecko/tools/lint/python/black.py", line 55, in get_black_version
    return re.match(r"black.*, version (.*)$", output)[1]
TypeError: 'NoneType' object is not subscriptable
A failure occurred in the black linter.
✖ 1 problem (0 errors, 0 warnings, 1 failure, 0 fixed)

Hmm, weird.
Which revision are you on? Can you reproduce this on current central?

bookmarks/central on hg::https://hg.mozilla.org/mozilla-unified

The "mach" virtualenv is not up-to-date, please run "./mach create-mach-environment"

This behaviour was gone as of fc578092665f, which landed in late November.
Perhaps you need to update your local checkout?

Yes, I can't reproduce this anymore. Thanks!

Generally we use works for me as a resolution when something is fixed but we don't know what it was, or we use duplicate when we do know what fixed it.

This is related to 1717051, but not quite a dupe.