refactor: dispatch config file loading by filename, then suffix

changelog/11502.bugfix.rst

@@ -0,0 +1 @@
+The ``rootdir`` is no longer derived from a configuration file that is not a regular file, such as ``--config-file=/dev/null``.

changelog/13246.bugfix.rst

@@ -0,0 +1 @@
+The directory of a configuration file passed via :option:`-c` no longer determines the ``rootdir`` on its own; it is now the common ancestor of that directory and the collected test paths. Keeping the configuration in a subdirectory previously broke ``conftest.py`` discovery and node IDs.

changelog/14705.bugfix.rst

@@ -0,0 +1 @@
+TOML configuration files passed via :option:`-c` now read their configuration from the ``[pytest]`` table instead of ``[tool.pytest.ini_options]``, which remains reserved for ``pyproject.toml``.

changelog/14716.breaking.rst

@@ -0,0 +1 @@
+:option:`-c` now raises a usage error for a path that does not exist, is a directory, or is in a format pytest has no loader for. Such paths were previously either ignored or reported as an unhandled ``FileNotFoundError``.

changelog/9703.bugfix.rst

@@ -0,0 +1 @@
+The directory of a configuration file passed via :option:`-c` no longer determines the ``rootdir`` on its own; it is now the common ancestor of that directory and the collected test paths. Keeping the configuration in a subdirectory previously broke ``conftest.py`` discovery and node IDs.

testing/test_config.py

@@ -763,11 +763,13 @@ def pytest_addoption(parser):
         config = pytester.parseconfig("--config-file", "custom_tool_pytest_section.cfg")
         assert config.getini("custom") == "1"
 
+        # Custom TOML files read their configuration from [pytest] directly;
+        # [tool.pytest] is reserved for pyproject.toml (#14705).
         pytester.makefile(
             ".toml",
             custom="""
-                [tool.pytest.ini_options]
-                custom = 1
+                [pytest]
+                custom = "1"
                 value = [
                 ]  # this is here on purpose, as it makes this an invalid '.ini' file
             """,
@@ -777,6 +779,53 @@ def pytest_addoption(parser):
         config = pytester.parseconfig("--config-file", "custom.toml")
         assert config.getini("custom") == "1"
 
+    @pytest.mark.parametrize(
+        "name", ["missing.ini", "missing.in", "missing.toml", "missing"]
+    )
+    def test_explicitly_specified_config_file_missing(
+        self, pytester: Pytester, name: str
+    ) -> None:
+        """A nonexistent -c path is a UsageError, whatever its extension (#14716).
+
+        Previously this either silently proceeded with an empty configuration
+        (unrecognized extension) or crashed with a raw FileNotFoundError
+        traceback (recognized extension).
+        """
+        with pytest.raises(UsageError, match=r"Config file .* not found"):
+            pytester.parseconfig("-c", name)
+
+    def test_explicitly_specified_config_file_unsupported_format(
+        self, pytester: Pytester
+    ) -> None:
+        """An existing -c path with an unsupported extension is a UsageError (#14716)."""
+        pytester.makefile(".in", config="[pytest]\naddopts = -v\n")
+        with pytest.raises(UsageError, match="unsupported format"):
+            pytester.parseconfig("-c", "config.in")
+
+    def test_explicitly_specified_config_file_is_a_directory(
+        self, pytester: Pytester
+    ) -> None:
+        """A directory passed to -c is a UsageError rather than a confusing no-op."""
+        pytester.mkdir("somedir")
+        with pytest.raises(UsageError, match="is a directory"):
+            pytester.parseconfig("-c", "somedir")
+
+    @pytest.mark.skipif(
+        sys.platform.startswith("win32"), reason="requires a POSIX null device"
+    )
+    def test_explicitly_specified_config_file_not_a_regular_file(
+        self, pytester: Pytester
+    ) -> None:
+        """``--config-file=/dev/null`` loads no config and does not set rootdir to /dev.
+
+        Deriving the rootdir from a character device made the cache plugin try to
+        write to ``/dev/.pytest_cache`` (#11502).
+        """
+        pytester.makepyfile(test_it="def test(): pass")
+        config = pytester.parseconfig("--config-file", os.devnull, str(pytester.path))
+        assert config.rootpath == pytester.path
+        assert config.inipath == Path(os.devnull)
+
     def test_absolute_win32_path(self, pytester: Pytester) -> None:
         temp_ini_file = pytester.makeini("[pytest]")
         from os.path import normpath
@@ -2281,6 +2330,182 @@ def test_explicit_config_file_sets_rootdir(
         assert rootpath == tmp_path
         assert found_inipath == inipath
 
+    def test_config_file_in_subdir_keeps_project_rootdir(
+        self, tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+    ) -> None:
+        """``-c config/pytest.ini`` must not move the rootdir into ``config/``.
+
+        Doing so broke conftest discovery and node ids (#13246, #9703). The
+        config file's directory takes part in the rootdir decision but does not
+        make it alone.
+        """
+        config_dir = tmp_path / "config"
+        config_dir.mkdir()
+        inipath = config_dir / "pytest.ini"
+        inipath.touch()
+        tests_dir = tmp_path / "tests"
+        tests_dir.mkdir()
+        monkeypatch.chdir(tmp_path)
+
+        # With test paths: common ancestor of the config dir and the paths.
+        rootpath, found_inipath, *_ = determine_setup(
+            inifile=str(inipath),
+            override_ini=None,
+            args=[str(tests_dir)],
+            rootdir_cmd_arg=None,
+            invocation_dir=tmp_path,
+        )
+        assert rootpath == tmp_path
+        assert found_inipath == inipath
+
+        # Without test paths the invocation dir stands in for them.
+        rootpath, _, *_ = determine_setup(
+            inifile=str(inipath),
+            override_ini=None,
+            args=[],
+            rootdir_cmd_arg=None,
+            invocation_dir=tmp_path,
+        )
+        assert rootpath == tmp_path
+
+    def test_config_file_sibling_of_invocation_dir(
+        self, tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+    ) -> None:
+        """Invoking from a subdir with a sibling config dir roots at their ancestor."""
+        config_dir = tmp_path / "config"
+        config_dir.mkdir()
+        inipath = config_dir / "pytest.ini"
+        inipath.touch()
+        sub = tmp_path / "sub"
+        sub.mkdir()
+        sub_tests = sub / "tests"
+        sub_tests.mkdir()
+        monkeypatch.chdir(sub)
+
+        rootpath, *_ = determine_setup(
+            inifile=str(inipath),
+            override_ini=None,
+            args=[str(sub_tests)],
+            rootdir_cmd_arg=None,
+            invocation_dir=sub,
+        )
+        assert rootpath == tmp_path
+
+    def test_config_file_with_unrelated_invocation_dir(self, tmp_path: Path) -> None:
+        """The rootdir follows the project, not an unrelated working directory."""
+        project = tmp_path / "proj"
+        config_dir = project / "config"
+        config_dir.mkdir(parents=True)
+        inipath = config_dir / "pytest.ini"
+        inipath.touch()
+        tests_dir = project / "tests"
+        tests_dir.mkdir()
+        elsewhere = tmp_path / "elsewhere"
+        elsewhere.mkdir()
+
+        rootpath, *_ = determine_setup(
+            inifile=str(inipath),
+            override_ini=None,
+            args=[str(tests_dir)],
+            rootdir_cmd_arg=None,
+            invocation_dir=elsewhere,
+        )
+        assert rootpath == project
+
+    def test_config_file_and_args_in_unrelated_trees(self, tmp_path: Path) -> None:
+        """With no meaningful common ancestor, keep the config file's directory.
+
+        An argument at the filesystem root leaves nothing but the root itself in
+        common with the config file, and the whole disk is never a useful rootdir.
+        """
+        config_dir = tmp_path / "config"
+        config_dir.mkdir()
+        inipath = config_dir / "pytest.ini"
+        inipath.touch()
+
+        rootpath, *_ = determine_setup(
+            inifile=str(inipath),
+            override_ini=None,
+            args=[tmp_path.anchor],
+            rootdir_cmd_arg=None,
+            invocation_dir=tmp_path,
+        )
+        assert rootpath == config_dir
+
+    @pytest.mark.skipif(
+        sys.platform.startswith("win32"), reason="requires a POSIX null device"
+    )
+    def test_non_regular_config_file_with_unrelated_args(self, tmp_path: Path) -> None:
+        """A non-regular config file plus rootless args falls back to the invocation dir."""
+        rootpath, *_ = determine_setup(
+            inifile=os.devnull,
+            override_ini=None,
+            args=[tmp_path.anchor],
+            rootdir_cmd_arg=None,
+            invocation_dir=tmp_path,
+        )
+        assert rootpath == tmp_path
+
+    @pytest.mark.skipif(
+        sys.platform.startswith("win32"), reason="requires a POSIX null device"
+    )
+    def test_non_regular_config_file_honours_explicit_rootdir(
+        self, tmp_path: Path
+    ) -> None:
+        """``--rootdir`` still wins when the config file is not a regular file."""
+        explicit = tmp_path / "explicit"
+        explicit.mkdir()
+
+        rootpath, *_ = determine_setup(
+            inifile=os.devnull,
+            override_ini=None,
+            args=[str(tmp_path)],
+            rootdir_cmd_arg=str(explicit),
+            invocation_dir=tmp_path,
+        )
+        assert rootpath == explicit
+
+    def test_config_file_in_subdir_nodeids(self, pytester: Pytester) -> None:
+        """Node ids stay relative to the project root, and per-directory
+        conftests keep their own fixtures (#9703)."""
+        tests_dir = pytester.mkdir("tests")
+        tests_dir.joinpath("test_file1.py").write_text(
+            textwrap.dedent(
+                """\
+                import pytest
+
+                @pytest.fixture(autouse=True)
+                def some_fixture():
+                    print("Fixture called")
+
+                def test_in_file1():
+                    pass
+                """
+            ),
+            encoding="utf-8",
+        )
+        tests_dir.joinpath("test_file2.py").write_text(
+            "def test_in_file2():\n    pass\n", encoding="utf-8"
+        )
+        config_dir = pytester.mkdir("config")
+        config_dir.joinpath("pytest.ini").write_text("[pytest]\n", encoding="utf-8")
+
+        result = pytester.runpytest(
+            "-c",
+            "config/pytest.ini",
+            "-v",
+            "tests/test_file1.py",
+            "tests/test_file2.py",
+        )
+        assert result.ret == 0
+        result.stdout.fnmatch_lines(
+            [
+                f"rootdir: {pytester.path}",
+                "*tests/test_file1.py::test_in_file1*",
+                "*tests/test_file2.py::test_in_file2*",
+            ]
+        )
+
     def test_with_arg_outside_cwd_without_inifile(
         self, tmp_path: Path, monkeypatch: MonkeyPatch
     ) -> None:

testing/test_doctest.py

@@ -1613,14 +1613,16 @@ def func():
             encoding="utf-8",
         )
 
-        # The conftest is both the config file and at the rootdir, and the
+        testing.joinpath("pytest.ini").write_text("[pytest]\n", encoding="utf-8")
+
+        # The config file sits next to the conftest at the rootdir, and the
         # collection argument (``xclim``) is a *parent* of the rootdir
         # (``xclim/testing``) -- the exact setup from #14683.
         result = pytester.runpytest(
             "--rootdir",
             str(testing),
             "--config-file",
-            str(testing / "conftest.py"),
+            str(testing / "pytest.ini"),
             "--doctest-modules",
             "xclim",
         )

testing/test_findpaths.py

@@ -73,7 +73,7 @@ def test_invalid_toml_file(self, tmp_path: Path) -> None:
             load_config_dict_from_file(fn)
 
     def test_custom_toml_file(self, tmp_path: Path) -> None:
-        """.toml files without [tool.pytest] are not considered for configuration."""
+        """Custom .toml files without a [pytest] table hold no configuration."""
         fn = tmp_path / "myconfig.toml"
         fn.write_text(
             dedent(
@@ -84,12 +84,46 @@ def test_custom_toml_file(self, tmp_path: Path) -> None:
             ),
             encoding="utf-8",
         )
-        assert load_config_dict_from_file(fn) is None
+        assert load_config_dict_from_file(fn) == {}
 
-    def test_valid_toml_file(self, tmp_path: Path) -> None:
-        """.toml files with [tool.pytest.ini_options] are read correctly, including changing
-        data types to str/list for compatibility with other configuration options."""
+    def test_custom_toml_file_reads_pytest_table(self, tmp_path: Path) -> None:
+        """Custom .toml files read native configuration from [pytest] (#14705)."""
+        fn = tmp_path / "myconfig.toml"
+        fn.write_text(
+            dedent(
+                """
+            [pytest]
+            xfail_strict = true
+            testpaths = ["tests", "integration"]
+            """
+            ),
+            encoding="utf-8",
+        )
+        assert load_config_dict_from_file(fn) == {
+            "xfail_strict": ConfigValue(True, origin="file", mode="toml"),
+            "testpaths": ConfigValue(
+                ["tests", "integration"], origin="file", mode="toml"
+            ),
+        }
+
+    def test_custom_toml_file_ignores_tool_pytest(self, tmp_path: Path) -> None:
+        """[tool.pytest] is reserved for pyproject.toml, not custom files (#14705)."""
         fn = tmp_path / "myconfig.toml"
+        fn.write_text(
+            dedent(
+                """
+            [tool.pytest]
+            xfail_strict = true
+            """
+            ),
+            encoding="utf-8",
+        )
+        assert load_config_dict_from_file(fn) == {}
+
+    def test_valid_toml_file(self, tmp_path: Path) -> None:
+        """pyproject.toml files with [tool.pytest.ini_options] are read correctly, including
+        changing data types to str/list for compatibility with other configuration options."""
+        fn = tmp_path / "pyproject.toml"
         fn.write_text(
             dedent(
                 """