Implements automatic support $XDG_CONFIG_HOME, closes #3

conda/meta.yaml

@@ -27,11 +27,13 @@ requirements:
     - click {{ click }}
     - tomli {{ tomli }}
     - tomli-w {{ tomli_w }}
+    - xdg {{ xdg }}
   run:
     - python >=3.9
     - {{ pin_compatible('click') }}
     - {{ pin_compatible('tomli') }}
     - {{ pin_compatible('tomli-w') }}
+    - {{ pin_compatible('xdg') }}
 
 test:
   source_files:

doc/links.rst

@@ -11,3 +11,4 @@
 .. _click: http://click.pocoo.org/
 .. _click-plugins: https://github.com/click-contrib/click-plugins
 .. _logging-tree module: https://pypi.org/project/logging_tree/
+.. _xdg-defaults: https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html

doc/rc.rst

@@ -28,28 +28,16 @@ load such a file and provide access to values set therein:
 .. code-block:: python
 
    >>> from exposed import rc
-   >>> defaults = rc.UserDefaults("~/.myapprc.toml")
+   >>> defaults = rc.UserDefaults("myapprc.toml")
 
-The ``defaults`` object in this example is a subtype of :py:class:`dict`, with
-a few extra methods implemented. Values can optionally be organized in
-sections.
+.. note::
 
-You may also pass the name of an environment variable to be used to override
-the standard configuration file.  If that environment variable is set by the
-user, and is non-empty, then the object will load the file path pointed by the
-value stored on that variable instead of the default.  For example:
-
-.. code-block:: python
-
-   >>> import os
-   >>> os.environ["MYAPPRC"] = "~/.myapprc2.toml"
-   >>> from exposed import rc
-   >>> defaults = rc.UserDefaults("~/.myapprc.toml", "MYAPPRC")
-
-Because the environment variable is set to a non-empty value, then the
-``defaults`` object will consider ``~/.myapprc2.toml`` as the source
-configuration file instead of ``~/.myapprc.toml``.  All the following
-operations will be based on that setting.
+   If the input filename given upon the construction of
+   :py:class:`exposed.rc.UserDefaults` is not absolute, it is considered
+   relative to the value of the environment variable ``$XDG_CONFIG_HOME``. In
+   UNIX-style operating systems, the above example would typically resolve to
+   ``${HOME}/.config/myapprc.toml``. Check the `XDG defaults <xdg-defaults_>`_
+   for specifics.
 
 
 Reading and writing values

pyproject.toml

@@ -28,6 +28,7 @@ dependencies = [
     "click>=8",
     "tomli",
     "tomli-w",
+    "xdg",
 ]
 
 [project.urls]

src/exposed/rc.py

@@ -10,21 +10,22 @@ import collections.abc
 import io
 import json
 import logging
-import os
 import pathlib
 import typing
 
 import tomli
 import tomli_w
+import xdg
 
 
 class UserDefaults(collections.abc.MutableMapping):
     """Contains user defaults read from the user TOML configuration file.
 
     Upon intialisation, an instance of this class will read the user
-    configuration file defined by the first argument.  If ``envname`` is
-    provided, and it is set, it overrides the location of ``filename`` and the
-    configuration from that location is loaded instead.
+    configuration file defined by the first argument. If the input file is
+    specified as a relative path, then it is considered relative to the
+    environment variable ``${XDG_CONFIG_HOME}``, or its default setting (which is
+    operating system dependent, c.f. `XDG defaults`_).
 
     This object may be used (with limited functionality) like a dictionary.  In
     this mode, objects of this class read and write values to the ``DEFAULT``
@@ -34,15 +35,13 @@ class UserDefaults(collections.abc.MutableMapping):
 
     Arguments:
 
-        path: The path to the file typically containing the user defaults.
-            The use of ``~`` (tilde) is supported to refer to one's home
-            directory.
-
-
-        envname: If this value is provided, and it is set by the user, and is
-            non-empty, then loads the file path pointed by the value stored on
-            that environment variable instead of the default.  The use of ``~``
-            (tilde) is supported to refer to one's home directory.
+        path: The path, absolute or relative, to the file containing the user
+            defaults to read.  If `path` is a relative path, then it is
+            considered relative to the directory defined by the environment
+            variable ``${XDG_CONFIG_HOME}`` (read `XDG defaults`_ for details on
+            the default location of this directory in the various operating
+            systems).  The tilde (`~`) character may be used to represent the
+            user home, and is automatically expanded.
 
         logger: A logger to use for messaging operations.  If not set, use this
             module's logger.
@@ -51,29 +50,24 @@ class UserDefaults(collections.abc.MutableMapping):
     Attributes:
 
         path: The current path to the user defaults base file.
+
+
+    .. _XDG defaults: https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html
     """
 
     def __init__(
         self,
         path: str | pathlib.Path,
-        envname: str | None = None,
         logger: logging.Logger | None = None,
     ) -> None:
 
         self.logger = logger or logging.getLogger(__name__)
 
-        if (
-            envname is not None
-            and envname in os.environ
-            and os.environ[envname]
-        ):
-            self.path = pathlib.Path(os.environ[envname])
-            self.logger.debug(
-                f"User configuration file set by environment variable ${envname}"
-            )
-        else:
-            self.path = pathlib.Path(path)
-        self.path = self.path.expanduser()
+        self.path = pathlib.Path(path).expanduser()
+
+        if not self.path.is_absolute():
+            self.path = xdg.xdg_config_home() / self.path
+
         self.logger.info(f"User configuration file set to `{str(self.path)}'")
         self.data: dict[str, typing.Any] = {}
         self.read()

tests/test_rc.py

@@ -36,13 +36,19 @@ def test_rc_basic_loading(datadir):
         assert rc["float.error"] == 3.14
 
 
-def test_rc_env_loading(datadir):
-    # tests if we can simply read an RC file
-    envname = "_TEST_RC_ENV_LOADING"
-    os.environ[envname] = str(datadir / "userdefaults_ex1.cfg")
-    rc = UserDefaults("does-not-exist", envname)
+def test_rc_loading_from_xdg_config_home(datadir):
+    # tests if we can simply read an RC file from the XDG_CONFIG_HOME
+    _environ = dict(os.environ)  # or os.environ.copy()
+    try:
+        os.environ["XDG_CONFIG_HOME"] = str(datadir)
+        rc = UserDefaults("userdefaults_ex1.cfg")
         _check_userdefaults_ex1_contents(rc)
-    assert not os.path.exists("does-not-exist")
+
+        with pytest.raises(KeyError):
+            assert rc["float.error"] == 3.14
+    finally:
+        os.environ.clear()
+        os.environ.update(_environ)
 
 
 def test_rc_init_empty(tmp_path):