Gracefully handle 404s when importing from MusicBrainz. (#6292)

A 404 error can be raised when fetching from MusicBrainz in the case of
re-importing an album that has since been deleted from MusicBrainz.

beetsplug/musicbrainz.py

@@ -792,7 +792,13 @@ class MusicBrainzPlugin(MusicBrainzAPIMixin, MetadataSourcePlugin):
             self._log.debug("Invalid MBID ({}).", album_id)
             return None
 
-        res = self.mb_api.get_release(albumid, includes=RELEASE_INCLUDES)
+        # A 404 error here is fine. e.g. re-importing a release that has
+        # been deleted on MusicBrainz.
+        try:
+            res = self.mb_api.get_release(albumid, includes=RELEASE_INCLUDES)
+        except HTTPNotFoundError:
+            self._log.debug("Release {} not found on MusicBrainz.", albumid)
+            return None
 
         # resolve linked release relations
         actual_res = None

test/plugins/test_musicbrainz.py

@@ -15,10 +15,12 @@
 """Tests for MusicBrainz API wrapper."""
 
 import unittest
+import uuid
 from typing import ClassVar
 from unittest import mock
 
 import pytest
+import requests
 
 from beets import config
 from beets.library import Item
@@ -1106,3 +1108,32 @@ class TestMusicBrainzPlugin(PluginMixin):
         assert len(candidates) == 1
         assert candidates[0].tracks[0].track_id == self.RECORDING["id"]
         assert candidates[0].album == "hi"
+
+    def test_import_handles_404_gracefully(self, mb, requests_mock):
+        id_ = uuid.uuid4()
+        response = requests.Response()
+        response.status_code = 404
+        requests_mock.get(
+            f"/ws/2/release/{id_}",
+            exc=requests.exceptions.HTTPError(response=response),
+        )
+        res = mb.album_for_id(str(id_))
+        assert res is None
+
+    def test_import_propagates_non_404_errors(self, mb):
+        class DummyResponse:
+            status_code = 500
+
+        error = requests.exceptions.HTTPError(response=DummyResponse())
+
+        def raise_error(*args, **kwargs):
+            raise error
+
+        # Simulate mb.mb_api.get_release raising a non-404 HTTP error
+        mb.mb_api.get_release = raise_error
+
+        with pytest.raises(requests.exceptions.HTTPError) as excinfo:
+            mb.album_for_id(str(uuid.uuid4()))
+
+        # Ensure the exact error is propagated, not swallowed
+        assert excinfo.value is error