Add TagError.object_id.

For #266.

src/reader/_storage.py

@@ -5,6 +5,7 @@
 from datetime import timedelta
 from functools import partial
 from typing import Any
+from typing import cast
 from typing import Dict
 from typing import Iterable
 from typing import Mapping
@@ -1205,7 +1206,7 @@ def delete_tag(self, object_id: Tuple[str, ...], key: str) -> None:
 
         with self.db:
             cursor = self.db.execute(query, params)
-        rowcount_exactly_one(cursor, lambda: TagNotFoundError(key=key))
+        rowcount_exactly_one(cursor, lambda: TagNotFoundError(key, cast(str, None)))
 
 
 def make_get_feeds_query(

src/reader/core.py

@@ -2016,7 +2016,7 @@ def get_tag(
         """
         return zero_or_one(
             (v for _, v in self.get_tags(resource, key=key)),
-            lambda: TagNotFoundError(key),
+            lambda: TagNotFoundError(key, _feed_argument(resource)),
             default,
         )
 
@@ -2078,8 +2078,9 @@ def delete_tag(
         feed_url = _feed_argument(resource)
         try:
             self._storage.delete_tag((feed_url,), key)
-        except TagNotFoundError:
+        except TagNotFoundError as e:
             if not missing_ok:
+                e.object_id = feed_url
                 raise
 
     def make_reader_reserved_name(self, key: str) -> str:

src/reader/exceptions.py

@@ -1,5 +1,6 @@
 from typing import Any
 from typing import Tuple
+from typing import Union
 
 from ._vendor.functools import cached_property
 
@@ -267,17 +268,22 @@ class TagError(ReaderError):
 
     """
 
-    # TODO: object_id: tuple[str, ...] | None
-
-    def __init__(self, key: str, message: str = '') -> None:
+    def __init__(
+        self, key: str, object_id: Union[str, Tuple[str, str]], message: str = ''
+    ) -> None:
         super().__init__(message)
 
         #: The tag key.
         self.key = key
 
+        # TODO: tuple[str, ...], once FeedError.object_id becomes tuple[str]
+
+        #: The resource id.
+        self.object_id = object_id
+
     @property
     def _str(self) -> str:
-        return repr(self.key)
+        return f"{self.object_id!r}: {self.key!r}"
 
 
 class TagNotFoundError(TagError):

tests/test_exceptions.py

@@ -85,5 +85,5 @@ def test_metadata_error_str(exc_type):
 
 @pytest.mark.parametrize('exc_type', all_classes(TagError))
 def test_tag_error_str(exc_type):
-    exc = exc_type('key')
-    assert repr('key') in str(exc)
+    exc = exc_type('key', 'object')
+    assert "'object': 'key'" in str(exc)