AttributeError: 'ShowChangeDiff' object has no attribute 'change'

[sentry-io]

This seems to be a regression from #15279.

Sentry Issue: WEBLATE-30V1

AttributeError: 'ShowChangeDiff' object has no attribute 'change'
(22 additional frame(s) were not displayed)
...
  File "weblate/accounts/notifications.py", line 309, in render_template
    return render_to_string(template_name, context).strip()
  File "weblate/trans/templatetags/translations.py", line 1780, in format_last_changes_content
    "history_data": get_change_history_context(change),
  File "weblate/trans/change_display.py", line 343, in get_change_history_context
    return ShowChangeDiff(change).get_context()
  File "weblate/trans/change_display.py", line 361, in get_context
    "change_details_fields": self.get_change_details_fields(),
  File "weblate/trans/change_display.py", line 520, in get_change_details_fields
    change = self.change

[gersona]

This is a bit hard to reproduce.
It complains about not finding self.change despite it being set in the __init__ method.

weblate/weblate/trans/change_display.py

Lines 351 to 355 in 701ebd5

	class BaseChangeHistoryContext:
	"""Base class for change history context rendering."""
	def __init__(self, change: Change) -> None:
	self.change = change

@nijel are you aware of any situation where __init__ method might be somehow skipped ? Maybe a race condition issue or another runtime condition ?

[nijel]

I don't see anything obvious either. It's strange that __init__ would not be invoked. I've made some fixes to type annotations while looking at the code in #15402.