fix: the config file's directory no longer decides the rootdir alone

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.breaking.rst

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+The directory of a configuration file passed via :option:`-c` no longer determines the ``rootdir`` on its own: the ``rootdir`` is now the common ancestor of that directory and the collected test paths, falling back to the invocation directory when no paths are given. Keeping the configuration in a subdirectory -- the common ``-c config/pytest.ini`` layout -- previously moved the ``rootdir`` into that subdirectory, which broke ``conftest.py`` discovery and node IDs.

changelog/14705.bugfix.rst

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+TOML configuration files passed via :option:`-c` now also read their configuration from the ``[pytest]`` table, the one pytest's own configuration files use. The ``[tool.pytest]`` and ``[tool.pytest.ini_options]`` tables such files were previously restricted to keep working; using both styles in one file is an error.

changelog/14716.breaking.rst

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+: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.breaking.rst

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+The directory of a configuration file passed via :option:`-c` no longer determines the ``rootdir`` on its own: the ``rootdir`` is now the common ancestor of that directory and the collected test paths, falling back to the invocation directory when no paths are given. Keeping the configuration in a subdirectory -- the common ``-c config/pytest.ini`` layout -- previously moved the ``rootdir`` into that subdirectory, which broke ``conftest.py`` discovery and node IDs.

doc/en/reference/customize.rst

@@ -187,7 +187,15 @@ Finding the ``rootdir``
 
 Here is the algorithm which finds the rootdir from ``args``:
 
-- If :option:`-c` is passed in the command-line, use that as configuration file, and its directory as ``rootdir``.
+- If :option:`-c` is passed in the command-line, use that as configuration file, and the common ancestor
+  of its directory and the ``args`` that are recognised as existing paths as ``rootdir``. When no such
+  paths are given, the directory pytest was invoked from takes their place; when the configuration file
+  and the paths share no ancestor other than the root of the file system, the configuration file's
+  directory is used.
+
+  .. versionchanged:: 10.0
+      The configuration file's directory used to become the ``rootdir`` on its own, which moved the
+      ``rootdir`` into e.g. ``config/`` for the common ``-c config/pytest.ini`` layout.
 
 - Determine the common ancestor directory for the specified ``args`` that are
   recognised as paths that exist in the file system. If no such paths are