flake8 consideres only one configuration file since v5

[hennjanssen]

how did you install flake8?

pip install flake8

unmodified output of flake8 --bug-report

{
  "platform": {
    "python_implementation": "CPython",
    "python_version": "3.10.4",
    "system": "Windows"
  },
  "plugins": [
    {
      "plugin": "mccabe",
      "version": "0.7.0"
    },
    {
      "plugin": "pycodestyle",
      "version": "2.9.1"
    },
    {
      "plugin": "pyflakes",
      "version": "2.5.0"
    }
  ],
  "version": "5.0.4"
}

describe the problem

what I expected to happen

In a "historically grown" project we have a setup.cfg as well as a .flake8, which both have some configurations for flake8.
With version 4 of flake8 both file were taken into account.

But with the upgrade to version 5, flake8 seems to ignore the .flake8-file. I went trough the changelog and the list of (un-)resolved issues, but could not find any explanation. #199 inspired me to take a look into its implementation:
flake8/src/flake8/options/config.py:

33    for candidate in ("setup.cfg", "tox.ini", ".flake8"):
34        ...
41        # only consider it a config if it contains flake8 sections
42        if "flake8" in cfg or "flake8:local-plugins" in cfg:
43             return cfg_path

Apparently, only the first configuration file in the list "setup.cfg", "tox.ini", ".flake8" is taken.

I don't know if this behaviour is desired or not and may be confirmed?

I think for my project I will take this issue as an occasion to merge the different configuration files.

sample code

MWE:

.
├── .flake8
├── setup.cfg
└── t.py

.flake8:

[flake8]
max-line-length = 88

setup.cfg:

[flake8]
extend-ignore = E203

t.py

print("Very, very, very, very, very, very, very, very, very, very, very long text")

commands ran

$ flake8 t.py
t.py:1:80: E501 line too long (83 > 79 characters)

[asottile]

dupe #1630 -- also it's part of "Don't consider a config file which does not contain flake8 settings" -- you were in undefined territory before