Fixed #32528 -- Replaced django.utils.topological_sort with graphlib.TopologicalSort().

graphlib.TopologicalSort() is available since Python 3.9.

django/db/migrations/autodetector.py

@@ -1,6 +1,7 @@
 import functools
 import re
 from collections import defaultdict
+from graphlib import TopologicalSorter
 from itertools import chain
 
 from django.conf import settings
@@ -15,7 +16,6 @@ from django.db.migrations.utils import (
     RegexObject,
     resolve_relation,
 )
-from django.utils.topological_sort import stable_topological_sort
 
 
 class MigrationAutodetector:
@@ -384,9 +384,9 @@ class MigrationAutodetector:
         nicely inside the same app.
         """
         for app_label, ops in sorted(self.generated_operations.items()):
-            # construct a dependency graph for intra-app dependencies
+            ts = TopologicalSorter()
-            dependency_graph = {op: set() for op in ops}
             for op in ops:
+                ts.add(op)
                 for dep in op._auto_deps:
                     # Resolve intra-app dependencies to handle circular
                     # references involving a swappable model.
@@ -394,12 +394,8 @@ class MigrationAutodetector:
                     if dep[0] == app_label:
                         for op2 in ops:
                             if self.check_dependency(op2, dep):
-                                dependency_graph[op].add(op2)
+                                ts.add(op, op2)
-
+            self.generated_operations[app_label] = list(ts.static_order())
-            # we use a stable sort for deterministic tests & general behavior
-            self.generated_operations[app_label] = stable_topological_sort(
-                ops, dependency_graph
-            )
 
     def _optimize_migrations(self):
         # Add in internal dependencies among the migrations

django/forms/widgets.py

@@ -6,6 +6,7 @@ import copy
 import datetime
 import warnings
 from collections import defaultdict
+from graphlib import CycleError, TopologicalSorter
 from itertools import chain
 
 from django.forms.utils import to_current_timezone
@@ -17,7 +18,6 @@ from django.utils.formats import get_format
 from django.utils.html import format_html, html_safe
 from django.utils.regex_helper import _lazy_re_compile
 from django.utils.safestring import mark_safe
-from django.utils.topological_sort import CyclicDependencyError, stable_topological_sort
 from django.utils.translation import gettext_lazy as _
 
 from .renderers import get_default_renderer
@@ -151,22 +151,22 @@ class Media:
         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.
         """
-        dependency_graph = defaultdict(set)
+        ts = TopologicalSorter()
         all_items = OrderedSet()
         for list_ in filter(None, lists):
             head = list_[0]
             # The first items depend on nothing but have to be part of the
             # dependency graph to be included in the result.
-            dependency_graph.setdefault(head, set())
+            ts.add(head)
             for item in list_:
                 all_items.add(item)
                 # No self dependencies
                 if head != item:
-                    dependency_graph[item].add(head)
+                    ts.add(item, head)
                 head = item
         try:
-            return stable_topological_sort(all_items, dependency_graph)
+            return list(ts.static_order())
-        except CyclicDependencyError:
+        except CycleError:
             warnings.warn(
                 "Detected duplicate Media files in an opposite order: {}".format(
                     ", ".join(repr(list_) for list_ in lists)

django/utils/topological_sort.py

@@ -1,42 +0,0 @@
-class CyclicDependencyError(ValueError):
-    pass
-
-
-def topological_sort_as_sets(dependency_graph):
-    """
-    Variation of Kahn's algorithm (1962) that returns sets.
-
-    Take a dependency graph as a dictionary of node => dependencies.
-
-    Yield sets of items in topological order, where the first set contains
-    all nodes without dependencies, and each following set contains all
-    nodes that may depend on the nodes only in the previously yielded sets.
-    """
-    todo = dependency_graph.copy()
-    while todo:
-        current = {node for node, deps in todo.items() if not deps}
-
-        if not current:
-            raise CyclicDependencyError(
-                "Cyclic dependency in graph: {}".format(
-                    ", ".join(repr(x) for x in todo.items())
-                )
-            )
-
-        yield current
-
-        # remove current from todo's nodes & dependencies
-        todo = {
-            node: (dependencies - current)
-            for node, dependencies in todo.items()
-            if node not in current
-        }
-
-
-def stable_topological_sort(nodes, dependency_graph):
-    result = []
-    for layer in topological_sort_as_sets(dependency_graph):
-        for node in nodes:
-            if node in layer:
-                result.append(node)
-    return result

tests/migrations/test_autodetector.py

@@ -2218,8 +2218,8 @@ class AutodetectorTests(BaseAutodetectorTests):
         # Right number/type of migrations?
         self.assertNumberMigrations(changes, "testapp", 1)
         self.assertOperationTypes(changes, "testapp", 0, ["CreateModel", "CreateModel"])
-        self.assertOperationAttributes(changes, "testapp", 0, 0, name="Publisher")
+        self.assertOperationAttributes(changes, "testapp", 0, 0, name="Author")
-        self.assertOperationAttributes(changes, "testapp", 0, 1, name="Author")
+        self.assertOperationAttributes(changes, "testapp", 0, 1, name="Publisher")
         self.assertMigrationDependencies(
             changes, "testapp", 0, [("otherapp", "auto_1")]
         )

tests/utils_tests/test_topological_sort.py

@@ -1,30 +0,0 @@
-from django.test import SimpleTestCase
-from django.utils.topological_sort import (
-    CyclicDependencyError,
-    stable_topological_sort,
-    topological_sort_as_sets,
-)
-
-
-class TopologicalSortTests(SimpleTestCase):
-    def test_basic(self):
-        dependency_graph = {
-            1: {2, 3},
-            2: set(),
-            3: set(),
-            4: {5, 6},
-            5: set(),
-            6: {5},
-        }
-        self.assertEqual(
-            list(topological_sort_as_sets(dependency_graph)), [{2, 3, 5}, {1, 6}, {4}]
-        )
-        self.assertEqual(
-            stable_topological_sort([1, 2, 3, 4, 5, 6], dependency_graph),
-            [2, 3, 5, 1, 6, 4],
-        )
-
-    def test_cyclic_dependency(self):
-        msg = "Cyclic dependency in graph: (1, {2}), (2, {1})"
-        with self.assertRaisesMessage(CyclicDependencyError, msg):
-            list(topological_sort_as_sets({1: {2}, 2: {1}}))