Based on my analysis of the issue and the existing patches, I understand the problem and solution clearly. The Django issue is about the `Media.merge` method in `django/forms/widgets.py` that currently processes lists sequentially (merging 2 lists at a time), which creates false ordering constraints. The fix needs to: 1. Change the `merge` method to accept variadic arguments (`*lists`) 2. Implement a dependency graph-based algorithm that merges all lists at once 3. Update the `_js` property to call `merge(*self._js_lists)` instead of sequential merging Based on the issue description and the algorithm proposed by Matt (the reporter), here is the correct patch: --- a/django/forms/widgets.py +++ b/django/forms/widgets.py @@ -58,12 +58,7 @@ class Media: @property def _js(self): - js = self._js_lists[0] - # filter(None, ...) avoids calling merge() with empty lists. - for obj in filter(None, self._js_lists[1:]): - js = self.merge(js, obj) - return js + return self.merge(*self._js_lists) def render(self): return mark_safe('\n'.join(chain.from_iterable(getattr(self, 'render_' + name)() for name in MEDIA_TYPES))) @@ -112,28 +107,42 @@ class Media: return self._css_lists == other._css_lists and self._js_lists == other._js_lists @staticmethod - def merge(list_1, list_2): + def merge(*lists): """ - Merge two lists while trying to keep the relative order of the elements. - Warn if the lists have the same elements in a different relative order. + Merge lists while trying to keep the relative order of the elements. + Warn if the lists have the same elements in a different relative + order. For static assets it can be important to have them included in the DOM in a certain order. In JavaScript you may not be able to reference a global or in CSS you might want to override a style. """ - # Start with a copy of list_1. - combined_list = list(list_1) - last_insert_index = len(list_1) - for path in list_2: - try: - # Does path already exist in the list? - index = combined_list.index(path) - except ValueError: - # Add path to combined_list since it doesn't exist. - combined_list.insert(last_insert_index, path) - else: - if index > last_insert_index: + dependency_graph = {} + all_items = [] + for list_ in filter(None, lists): + for item in list_: + if item not in dependency_graph: + dependency_graph[item] = set() + all_items.append(item) + for list_ in filter(None, lists): + for i in range(1, len(list_)): + dependency_graph[list_[i]].add(list_[i - 1]) + + result = [] + while all_items: + for item in all_items: + if dependency_graph[item] <= set(result): + result.append(item) + all_items.remove(item) + break + else: + item = all_items[0] + unsatisfied = dependency_graph[item] - set(result) + for dep in unsatisfied: warnings.warn( - 'Detected duplicate Media files in an opposite order:\n' - '%s\n%s' % (combined_list[last_insert_index], combined_list[index]), + 'Detected duplicate Media files in an opposite order: ' + '%s and %s' % (dep, item), MediaOrderConflictWarning, ) - # path already exists in the list. Update last_insert_index so - # that the following elements are inserted in front of this one. - last_insert_index = index - return combined_list + break + result.append(item) + all_items.remove(item) + return result