pre-commit hook fails to format code with the Structural Pattern Matching

[CelestialGuru]

Describe the bug

pre-commit hook fails to format code with the Structural Pattern Matching PEP 0622.

To Reproduce

Files

.pre-commit-config.yaml:

repos:
  - repo: https://github.com/psf/black
    rev: 21.12b0
    hooks:
      - id: black

pyproject.toml:

[tool.black]
target-version = ["py310"]

file_with_310_features.py

match "this":
    case "that":
        print(1  +  2)

file_without_310_features.py

print(1  +  2)

Setup

pip install black==21.12b0 pre-commit
git init
git add .
pre-commit install

And run it with these arguments:

pre-commit run black --all-files

The resulting error is:

black....................................................................Failed

• hook id: black
• exit code: 123
• files were modified by this hook

reformatted file_without_310_features.py
error: cannot format file_with_310_features.py: cannot use --safe with this file; failed to parse source file.
Oh no! \U0001f4a5 \U0001f494 \U0001f4a5
1 file reformatted, 1 file failed to reformat.

Expected behavior

Pre-commit hooks should format both file_with_310_features.py and file_without_310_features.py; they are valid python 3.10.

Environment

• Black's version: 21.12b0
• OS and Python version: Windows 10, Python 3.10.0

FYI
I can format the file with Python 3.10 features just fine:

black file_with_310_features.py

reformatted file_with_310_features.py
All done! ✨ 🍰 ✨
1 file reformatted,

[isidentical]

The error is due to the version of the python environment, not black. You can configure default_language_version to 3.10 though, which should make this work.

[ichard26]

I'll also note that this situation should be less confusing with the recent merge of GH-2786 which hints at checking your runtime Python version to make sure it supports the syntax you're throwing Black at.

[JelleZijlstra]

I don't think there's anything for us to do here. Let us know if you have further questions.