Having settings located in pyproject.toml doesn't work correctly

Hi, I have config located in a pyproject.toml file as described here: https://mypy.readthedocs.io/en/stable/config_file.html?highlight=pyproject.toml#using-a-pyproject-toml-file

This does not get automatically detected by this hook, but I can force it to look there by making the hook look as follows:

    - repo: https://github.com/pre-commit/mirrors-mypy
      # Type checks
      rev: "" # Use the sha / tag you want to point at
      hooks:
          - id: mypy
            args: [--config-file=pyproject.toml]

And while this does work with very basic toml files it breaks once one of your tools uses multiline strings… So with the following config pre-commit will fail:

[tool.black]
line-length = 119
target-version = ['py38']
include = '\.pyi?$'
exclude = '''
/(
    \.eggs
  | \.git
  | \.hg
  | \.mypy_cache
  | \.tox
  | \.venv
  | _build
  | buck-out
  | build
  | dist
  # The following are specific to Black, you probably don't want those.
  | blib2to3
  | tests/data
  | profiling
)/
'''

[tool.isort]
known_first_party = ["paperbag", "gels_and_blots"]
profile = "black"
filter_files = true

[mypy]
python_version = 3.8
warn_return_any = true
warn_unused_configs = true
disallow_untyped_defs = true
ignore_missing_imports = true

Error message:

mypy.....................................................................Failed
- hook id: mypy
- exit code: 1

pyproject.toml: Source contains parsing errors: 'pyproject.toml'
	[line  6]: '/(\n'
	[line 21]: ')/\n'
	[line 22]: "'''\n"

[RonnyPfannschmidt]

@asottile im observing this with the most recent mirrors-mypy, i’l tr to debug this week

[asottile]

yep, figured as much!