Load the last plugin class found in the namespace (#6100)

- Modified `_get_plugin` function to use `reversed()` when iterating
through `namespace.__dict__.values()`
- This ensures that we load _the last_ plugin class found in the
namespace.

Fixes #6093

beets/plugins.py

@@ -228,9 +228,9 @@ class BeetsPlugin(metaclass=abc.ABCMeta):
         # In order to verify the config we need to make sure the plugin is fully
         # configured (plugins usually add the default configuration *after*
         # calling super().__init__()).
-        self.register_listener("pluginload", self.verify_config)
+        self.register_listener("pluginload", self._verify_config)
 
-    def verify_config(self, *_, **__) -> None:
+    def _verify_config(self, *_, **__) -> None:
         """Verify plugin configuration.
 
         If deprecated 'source_weight' option is explicitly set by the user, they
@@ -422,6 +422,12 @@ def _get_plugin(name: str) -> BeetsPlugin | None:
     Attempts to import the plugin module, locate the appropriate plugin class
     within it, and return an instance. Handles import failures gracefully and
     logs warnings for missing plugins or loading errors.
+
+    Note we load the *last* plugin class found in the plugin namespace. This
+    allows plugins to define helper classes that inherit from BeetsPlugin
+    without those being loaded as the main plugin class.
+
+    Returns None if the plugin could not be loaded for any reason.
     """
     try:
         try:
@@ -429,7 +435,7 @@ def _get_plugin(name: str) -> BeetsPlugin | None:
         except Exception as exc:
             raise PluginImportError(name) from exc
 
-        for obj in namespace.__dict__.values():
+        for obj in reversed(namespace.__dict__.values()):
             if (
                 inspect.isclass(obj)
                 and not isinstance(

docs/changelog.rst

@@ -15,6 +15,9 @@ New features:
 
 Bug fixes:
 
+- |BeetsPlugin|: load the last plugin class defined in the plugin namespace.
+  :bug:`6093`
+
 For packagers:
 
 - Fixed dynamic versioning install not disabled for source distribution builds.
@@ -23,7 +26,7 @@ For packagers:
 Other changes:
 
 - Removed outdated mailing list contact information from the documentation
-  (:bug:`5462`).
+  :bug:`5462`.
 - :doc:`guides/main`: Modernized the *Getting Started* guide with tabbed
   sections and dropdown menus. Installation instructions have been streamlined,
   and a new subpage now provides additional setup details.
@@ -66,7 +69,7 @@ Bug fixes:
 - :doc:`plugins/discogs` Fixed inconsistency in stripping disambiguation from
   artists but not labels. :bug:`5366`
 - :doc:`plugins/chroma` :doc:`plugins/bpsync` Fix plugin loading issue caused by
-  an import of another :class:`beets.plugins.BeetsPlugin` class. :bug:`6033`
+  an import of another |BeetsPlugin| class. :bug:`6033`
 - :doc:`/plugins/fromfilename`: Fix :bug:`5218`, improve the code (refactor
   regexps, allow for more cases, add some logging), add tests.
 - Metadata source plugins: Fixed data source penalty calculation that was
@@ -188,8 +191,8 @@ For plugin developers:
   art sources might need to be adapted.
 - We split the responsibilities of plugins into two base classes
 
-  1. :class:`beets.plugins.BeetsPlugin` is the base class for all plugins, any
-     plugin needs to inherit from this class.
+  1. |BeetsPlugin| is the base class for all plugins, any plugin needs to
+     inherit from this class.
   2. :class:`beets.metadata_plugin.MetadataSourcePlugin` allows plugins to act
      like metadata sources. E.g. used by the MusicBrainz plugin. All plugins in
      the beets repo are opted into this class where applicable. If you are
@@ -5072,7 +5075,7 @@ BPD). To "upgrade" an old database, you can use the included ``albumify`` plugin
   list of plugin names) and ``pluginpath`` (a colon-separated list of
   directories to search beyond ``sys.path``). Plugins are just Python modules
   under the ``beetsplug`` namespace package containing subclasses of
-  ``beets.plugins.BeetsPlugin``. See `the beetsplug directory`_ for examples or
+  |BeetsPlugin|. See `the beetsplug directory`_ for examples or
   :doc:`/plugins/index` for instructions.
 - As a consequence of adding album art, the database was significantly
   refactored to keep track of some information at an album (rather than item)

docs/conf.py

@@ -82,6 +82,7 @@ man_pages = [
 rst_epilog = """
 .. |Album| replace:: :class:`~beets.library.models.Album`
 .. |AlbumInfo| replace:: :class:`beets.autotag.hooks.AlbumInfo`
+.. |BeetsPlugin| replace:: :class:`beets.plugins.BeetsPlugin`
 .. |ImportSession| replace:: :class:`~beets.importer.session.ImportSession`
 .. |ImportTask| replace:: :class:`~beets.importer.tasks.ImportTask`
 .. |Item| replace:: :class:`~beets.library.models.Item`

docs/dev/plugins/autotagger.rst

@@ -95,9 +95,9 @@ starting points include:
 Migration guidance
 ------------------
 
-Older metadata plugins that extend :py:class:`beets.plugins.BeetsPlugin` should
-be migrated to :py:class:`MetadataSourcePlugin`. Legacy support will be removed
-in **beets v3.0.0**.
+Older metadata plugins that extend |BeetsPlugin| should be migrated to
+:py:class:`MetadataSourcePlugin`. Legacy support will be removed in **beets
+v3.0.0**.
 
 .. seealso::
 

docs/dev/plugins/index.rst

@@ -40,8 +40,8 @@ or your plugin subpackage
     anymore.
 
 The meat of your plugin goes in ``myawesomeplugin.py``. Every plugin has to
-extend the :class:`beets.plugins.BeetsPlugin` abstract base class [2]_ . For
-instance, a minimal plugin without any functionality would look like this:
+extend the |BeetsPlugin| abstract base class [2]_ . For instance, a minimal
+plugin without any functionality would look like this:
 
 .. code-block:: python
 
@@ -52,6 +52,12 @@ instance, a minimal plugin without any functionality would look like this:
     class MyAwesomePlugin(BeetsPlugin):
         pass
 
+.. attention::
+
+    If your plugin is composed of intermediate |BeetsPlugin| subclasses, make
+    sure that your plugin is defined *last* in the namespace. We only load the
+    last subclass of |BeetsPlugin| we find in your plugin namespace.
+
 To use your new plugin, you need to package [3]_ your plugin and install it into
 your ``beets`` (virtual) environment. To enable your plugin, add it it to the
 beets configuration

docs/reference/config.rst

@@ -77,10 +77,10 @@ pluginpath
 ~~~~~~~~~~
 
 Directories to search for plugins. Each Python file or directory in a plugin
-path represents a plugin and should define a subclass of :class:`BeetsPlugin`. A
-plugin can then be loaded by adding the filename to the ``plugins``
-configuration. The plugin path can either be a single string or a list of
-strings---so, if you have multiple paths, format them as a YAML list like so:
+path represents a plugin and should define a subclass of |BeetsPlugin|. A plugin
+can then be loaded by adding the plugin name to the ``plugins`` configuration.
+The plugin path can either be a single string or a list of strings---so, if you
+have multiple paths, format them as a YAML list like so:
 
 ::
 

extra/release.py

@@ -19,6 +19,8 @@ from packaging.version import Version, parse
 from sphinx.ext import intersphinx
 from typing_extensions import TypeAlias
 
+from docs.conf import rst_epilog
+
 BASE = Path(__file__).parent.parent.absolute()
 PYPROJECT = BASE / "pyproject.toml"
 CHANGELOG = BASE / "docs" / "changelog.rst"
@@ -104,11 +106,21 @@ def create_rst_replacements() -> list[Replacement]:
     plugins = "|".join(
         r.split("/")[-1] for r in refs if r.startswith("plugins/")
     )
+    explicit_replacements = dict(
+        line.removeprefix(".. ").split(" replace:: ")
+        for line in filter(None, rst_epilog.splitlines())
+    )
     return [
-        # Replace Sphinx :ref: and :doc: directives by documentation URLs
+        # Replace explicitly defined substitutions from rst_epilog
+        #    |BeetsPlugin| -> :class:`beets.plugins.BeetsPlugin`
+        (
+            r"\|\w[^ ]*\|",
+            lambda m: explicit_replacements.get(m[0], m[0]),
+        ),
+        # Replace Sphinx directives by documentation URLs, e.g.,
         #   :ref:`/plugins/autobpm` -> [AutoBPM Plugin](DOCS/plugins/autobpm.html)
         (
-            r":(?:ref|doc):`+(?:([^`<]+)<)?/?([\w./_-]+)>?`+",
+            r":(?:ref|doc|class):`+(?:([^`<]+)<)?/?([\w./_-]+)>?`+",
             lambda m: make_ref_link(m[2], m[1]),
         ),
         # Convert command references to documentation URLs