fix(modify): parse typed values when selecting objects at the confirmation prompt

beets/ui/commands/modify.py

@@ -29,12 +29,17 @@ def modify_items(lib, mods, dels, query, write, move, album, confirm, inherit):
     templates = {
         key: functemplate.template(value) for key, value in mods.items()
     }
-    for obj in objs:
-        obj_mods = {
+
+    def parse_mods(obj):
+        # Parse the raw assignment strings into properly typed values for the
+        # given object (e.g. dates into timestamps).
+        return {
             key: model_cls._parse(key, obj.evaluate_template(templates[key]))
             for key in mods.keys()
         }
-        if print_and_modify(obj, obj_mods, dels) and obj not in changed:
+
+    for obj in objs:
+        if print_and_modify(obj, parse_mods(obj), dels) and obj not in changed:
             changed.append(obj)
 
     # Still something to do?
@@ -56,7 +61,7 @@ def modify_items(lib, mods, dels, query, write, move, album, confirm, inherit):
         changed = ui.input_select_objects(
             f"Really modify{extra}",
             changed,
-            lambda o: print_and_modify(o, mods, dels),
+            lambda o: print_and_modify(o, parse_mods(o), dels),
         )
 
     # Apply changes to database and files

docs/changelog.rst

@@ -34,6 +34,9 @@ Bug fixes
   example a multi-disc album whose cover lives in the album root rather than a
   per-disc directory); the missing art is skipped instead. :bug:`4692`
 - :doc:`plugins/tidal`: Normalize Tidal album types to lowercase.
+- ``modify``: Fix a crash when choosing ``select`` at the confirmation prompt
+  while modifying a non-string field such as ``added``; the per-object value is
+  now parsed before being applied. :bug:`4880`
 
 ..
     For plugin developers

test/ui/commands/test_modify.py

@@ -108,6 +108,14 @@ def test_selective_modify(self):
         assert len(list(original_items)) == 3
         assert len(list(new_items)) == 7
 
+    def test_selective_modify_typed_field(self):
+        # Regression test for a crash when selecting individual objects to
+        # modify a non-string (here date) field: the confirmation callback
+        # used to re-apply the raw string instead of the parsed value.
+        self.modify_inp(["s", "y"], "added=2002-06-03 00:00:00")
+        item = self.lib.items().get()
+        assert item.added == pytest.approx(1023062400, abs=24 * 60 * 60)
+
     def test_modify_formatted(self):
         for i in range(3):
             self.add_item_fixture(