Support Flake8 version 5, drop support for earlier versions.

As of version 5.0.0, due to some refactoring, Flake8 locates and parses
the config files differently. The old hook therefore no longer works
and was replaced with a new one tailored to Flake8 5.0+.

Consequently, we no longer support Flake8 4.x and earlier. But the
dependency declarations should take care of it, so that an older version,
which supported Flake8 4.x, is pip-installed in that case.

One test case, `config_mixed`, had to be modified. It seems that Flake8
will no longer merge configurations from multiple config files, such as
when `pyproject.toml` and `.flake8` and `tox.ini` are all found in the
project folder. We now test that the configuration is read from
`pyproject.toml` in such a scenario, provided it defines a `tool.flake8`
section.

Author: john-hen

flake8p/hook.py

@@ -1,23 +1,26 @@
 """Hooks TOML parser into Flake8."""
 
+import flake8.main.cli
+import flake8.options.config
 import tomli
 from pathlib import Path
-from flake8.main.cli import main as flake8_main
-from flake8.options import config as flake8_config
 
 
-class PyprojectRawConfigParser(flake8_config.configparser.RawConfigParser):
-    """Mixes the TOML parser into Flake8's INI parser."""
+# Remember original Flake8 objects.
+flake8_RawConfigParser  = flake8.options.config.configparser.RawConfigParser
+flake8_find_config_file = flake8.options.config._find_config_file
+
+
+# Implement derived objects that are aware of `pyproject.toml`.
+
+class RawConfigParser(flake8_RawConfigParser):
+    """Mixes the TOML parser into Flake8's config-file parser."""
 
     def _read(self, stream, path):
         file = Path(path)
         if file.name == 'pyproject.toml':
             with file.open('rb') as f:
                 settings = tomli.load(f)
-            if 'tool' not in settings:
-                return
-            if 'flake8' not in settings['tool']:
-                return
             if not self.has_section('flake8'):
                 self.add_section('flake8')
             for (key, value) in settings['tool']['flake8'].items():
@@ -28,15 +31,20 @@ def _read(self, stream, path):
             super()._read(stream, path)
 
 
-class PyprojectConfigFileFinder(flake8_config.ConfigFileFinder):
-    """Adds `pyproject.toml` to the list of accepted configuration files."""
-
-    def __init__(self, *args, **kwargs):
-        super().__init__(*args, **kwargs)
-        self.project_filenames = self.project_filenames + ('pyproject.toml',)
+def find_config_file(path):
+    """Convinces Flake8 to prefer `pyproject.toml` over other config files."""
+    file = Path(path)/'pyproject.toml'
+    if file.exists():
+        with file.open('rb') as f:
+            settings = tomli.load(f)
+        if 'tool' in settings and 'flake8' in settings['tool']:
+            return str(file)
+    return flake8_find_config_file(path)
 
 
-flake8_config.configparser.RawConfigParser = PyprojectRawConfigParser
-flake8_config.ConfigFileFinder             = PyprojectConfigFileFinder
+# Monkey-patch Flake8 with our modified objects.
+flake8.options.config.configparser.RawConfigParser = RawConfigParser
+flake8.options.config._find_config_file = find_config_file
 
-main = flake8_main
+# Just call Flake8 when we are called.
+main = flake8.main.cli.main

pyproject.toml

@@ -18,9 +18,9 @@ readme = 'PyPI.md'
 dynamic = ['version', 'description']
 requires-python = '>=3.6'
 dependencies = [
-    'Flake8<5',
+    'Flake8 >= 5, < 6',
     'TOMLi',
-    'TOMLi<2; python_version < "3.7"',
+    'TOMLi < 2; python_version < "3.7"',
 ]
 
 [project.scripts]

tests/fixtures/config_mixed/.flake8

@@ -1,3 +1,2 @@
 [flake8]
 per-file-ignores =
-    module.py:F401

tests/fixtures/config_mixed/pyproject.toml

@@ -3,3 +3,6 @@ ignore = [
     'E231',        # Missing whitespace after ',', ';', or ':'.
     'E241',        # Multiple spaces after ','.
 ]
+per-file-ignores = ['module.py:F401']
+max-line-length = 70
+count = true

tests/fixtures/config_mixed/setup.cfg

@@ -1,2 +1,2 @@
 [flake8]
-max-line-length = 70
+max-line-length = 80

tests/fixtures/config_mixed/tox.ini

@@ -1,2 +1,2 @@
 [flake8]
-count = true
+count = false