Ensure backward compatibility but allow overwriting

If no metadata plugin has been specified, the default `metadata` plugins
loads one of `metadata_pyexiv` or `metadata_piexif` (depending on the
installed backend). If a specific backend is configured, they it is
ensured that `metadata` does not interfere.

This is achieved by deferring the loading of the `metadata` plugin to
the end of all plugins. At that point `metadata` can check if another
metadata plugin has been loaded, and if so, do nothing.

vimiv/plugins/__init__.py

@@ -98,6 +98,10 @@ def load() -> None:
     user_plugins = _get_plugins(_user_plugin_directory)
     _logger.debug("Available user plugins: %s", quotedjoin(user_plugins))
     for plugin, info in _plugins.items():
+        if plugin == "metadata":
+            # Skip metadata plugin and load it manually after all other plugins. This way the plugin can check whether another metadata plugin has been loaded
+            _logger.debug("Deffer loading of metadata plugin")
+            continue
         if plugin in app_plugins:
             _load_plugin(plugin, info, _app_plugin_directory)
         elif plugin in user_plugins:
@@ -113,6 +117,7 @@ def load() -> None:
                 quotedjoin(user_plugins),
                 _user_plugin_directory,
             )
+    _load_plugin("metadata", _plugins["metadata"], _app_plugin_directory)
     _logger.debug("Plugin loading completed")
     api.signals.plugins_loaded.emit()
 

vimiv/plugins/metadata.py

@@ -10,12 +10,20 @@
 
 from vimiv.plugins import metadata_piexif, metadata_pyexiv2
 from vimiv.utils import log
+from vimiv.imutils import metadata
 
 _logger = log.module_logger(__name__)
 
 
 def init(*_args: Any, **_kwargs: Any) -> None:
-    """Initialize metadata plugin depending on available backend."""
+    """Initialize metadata plugin depending on available backend.
+
+    If any other backend has already been registered, do not register any new one.
+    """
+    if metadata.has_metadata_support():
+        _logger.info("Not loading a default metadata backend, as one has been loaded manually")
+        return
+
     if metadata_pyexiv2.pyexiv2 is not None:
         metadata_pyexiv2.init()
     elif metadata_piexif.piexif is not None: