Add tox.ini to the default discovered config files (right after setup.cfg)

doc/whatsnew/fragments/9727.bugfix

@@ -0,0 +1,5 @@
+Fix a bug where a ``tox.ini`` file with pylint configuration was ignored and it exists in the current directory.
+
+``.cfg`` and ``.ini`` files containing a ``Pylint`` configuration may now use a section named ``[pylint]``. This enhancement impacts the scenario where these file types are used as defaults when they are present and have not been explicitly referred to, using the ``--rcfile`` option.
+
+Closes #9727

pylint/config/find_default_config_files.py

@@ -22,7 +22,7 @@
     Path(".pylintrc.toml"),
 )
 PYPROJECT_NAME = Path("pyproject.toml")
-CONFIG_NAMES = (*RC_NAMES, PYPROJECT_NAME, Path("setup.cfg"))
+CONFIG_NAMES = (*RC_NAMES, PYPROJECT_NAME, Path("setup.cfg"), Path("tox.ini"))
 
 
 def _find_pyproject() -> Path:
@@ -55,13 +55,16 @@ def _toml_has_config(path: Path | str) -> bool:
     return "pylint" in content.get("tool", [])
 
 
-def _cfg_has_config(path: Path | str) -> bool:
+def _cfg_or_ini_has_config(path: Path | str) -> bool:
     parser = configparser.ConfigParser()
     try:
         parser.read(path, encoding="utf-8")
     except configparser.Error:
         return False
-    return any(section.startswith("pylint.") for section in parser.sections())
+    return any(
+        section == "pylint" or section.startswith("pylint.")
+        for section in parser.sections()
+    )
 
 
 def _yield_default_files() -> Iterator[Path]:
@@ -71,7 +74,10 @@ def _yield_default_files() -> Iterator[Path]:
             if config_name.is_file():
                 if config_name.suffix == ".toml" and not _toml_has_config(config_name):
                     continue
-                if config_name.suffix == ".cfg" and not _cfg_has_config(config_name):
+                if config_name.suffix in {
+                    ".cfg",
+                    ".ini",
+                } and not _cfg_or_ini_has_config(config_name):
                     continue
 
                 yield config_name.resolve()

tests/config/test_find_default_config_files.py

@@ -18,7 +18,10 @@
 from pytest import CaptureFixture
 
 from pylint import config, testutils
-from pylint.config.find_default_config_files import _cfg_has_config, _toml_has_config
+from pylint.config.find_default_config_files import (
+    _cfg_or_ini_has_config,
+    _toml_has_config,
+)
 from pylint.lint.run import Run
 
 
@@ -307,12 +310,13 @@ def test_toml_has_config(content: str, expected: bool, tmp_path: Path) -> None:
         ],
     ],
 )
-def test_cfg_has_config(content: str, expected: bool, tmp_path: Path) -> None:
-    """Test that a cfg file has a pylint config."""
-    fake_cfg = tmp_path / "fake.cfg"
-    with open(fake_cfg, "w", encoding="utf8") as f:
-        f.write(content)
-    assert _cfg_has_config(fake_cfg) == expected
+def test_has_config(content: str, expected: bool, tmp_path: Path) -> None:
+    """Test that a .cfg file or .ini file has a pylint config."""
+    for file_name in ("fake.cfg", "tox.ini"):
+        fake_conf = tmp_path / file_name
+        with open(fake_conf, "w", encoding="utf8") as f:
+            f.write(content)
+        assert _cfg_or_ini_has_config(fake_conf) == expected
 
 
 def test_non_existent_home() -> None: