Fixed #21142: Dependency failures on unmigrated apps.

django/db/migrations/autodetector.py

@@ -299,6 +299,7 @@ class MigrationAutodetector(object):
                 for migration in migrations:
                     name_map[(app_label, migration.name)] = (app_label, "__first__")
                 del changes[app_label]
+                continue
             # Work out the next number in the sequence
             if app_leaf is None:
                 next_number = 1

django/db/migrations/graph.py

@@ -63,14 +63,14 @@ class MigrationGraph(object):
             raise ValueError("Node %r not a valid node" % (node, ))
         return self.dfs(node, lambda x: self.dependents.get(x, set()))
 
-    def root_nodes(self):
+    def root_nodes(self, app=None):
         """
         Returns all root nodes - that is, nodes with no dependencies inside
         their app. These are the starting point for an app.
         """
         roots = set()
         for node in self.nodes:
-            if not any(key[0] == node[0] for key in self.dependencies.get(node, set())):
+            if not any(key[0] == node[0] for key in self.dependencies.get(node, set())) and (not app or app == node[0]):
                 roots.add(node)
         return roots
 
@@ -145,6 +145,9 @@ class MigrationGraph(object):
             project_state = self.nodes[node].mutate_state(project_state)
         return project_state
 
+    def __contains__(self, node):
+        return node in self.nodes
+
 
 class CircularDependencyError(Exception):
     """

django/db/migrations/loader.py

@@ -5,6 +5,9 @@ import sys
 from django.apps import apps
 from django.db.migrations.recorder import MigrationRecorder
 from django.db.migrations.graph import MigrationGraph
+from django.db.migrations.migration import Migration
+from django.db.migrations.state import ModelState
+from django.db.migrations import operations
 from django.utils import six
 from django.conf import settings
 
@@ -191,6 +194,38 @@ class MigrationLoader(object):
             self.graph.add_node(key, migration)
         for key, migration in normal.items():
             for parent in migration.dependencies:
+                # Special-case __first__, which means "the first migration" for
+                # migrated apps, and is ignored for unmigrated apps. It allows
+                # makemigrations to declare dependencies on apps before they
+                # even have migrations.
+                if parent[1] == "__first__" and parent not in self.graph:
+                    if parent[0] in self.unmigrated_apps:
+                        # This app isn't migrated, but something depends on it.
+                        # We'll add a fake initial migration for it into the
+                        # graph.
+                        app_config = apps.get_app_config(parent[0])
+                        ops = []
+                        for model in app_config.get_models():
+                            model_state = ModelState.from_model(model)
+                            ops.append(
+                                operations.CreateModel(
+                                    name=model_state.name,
+                                    fields=model_state.fields,
+                                    options=model_state.options,
+                                    bases=model_state.bases,
+                                )
+                            )
+                        new_migration = type(
+                            "FakeInitialMigration",
+                            (Migration, ),
+                            {"operations": ops},
+                        )(parent[1], parent[0])
+                        self.graph.add_node(parent, new_migration)
+                        self.applied_migrations.add(parent)
+                    elif parent[0] in self.migrated_apps:
+                        parent = (parent[0], list(self.graph.root_nodes(parent[0]))[0])
+                    else:
+                        raise ValueError("Dependency on unknown app %s" % parent[0])
                 self.graph.add_dependency(key, parent)
 
     def detect_conflicts(self):

tests/migrations/test_loader.py

@@ -49,7 +49,10 @@ class LoaderTests(TestCase):
         migration_loader = MigrationLoader(connection)
         self.assertEqual(
             migration_loader.graph.forwards_plan(("migrations", "0002_second")),
-            [("migrations", "0001_initial"), ("migrations", "0002_second")],
+            [
+                ("migrations", "0001_initial"),
+                ("migrations", "0002_second"),
+            ],
         )
         # Now render it out!
         project_state = migration_loader.graph.project_state(("migrations", "0002_second"))
@@ -67,6 +70,30 @@ class LoaderTests(TestCase):
             ["id", "author"]
         )
 
+    @override_settings(MIGRATION_MODULES={"migrations": "migrations.test_migrations_unmigdep"})
+    def test_load_unmigrated_dependency(self):
+        """
+        Makes sure the loader can load migrations with a dependency on an unmigrated app.
+        """
+        # Load and test the plan
+        migration_loader = MigrationLoader(connection)
+        self.assertEqual(
+            migration_loader.graph.forwards_plan(("migrations", "0001_initial")),
+            [
+                ("auth", "__first__"),
+                ("migrations", "0001_initial"),
+            ],
+        )
+        # Now render it out!
+        project_state = migration_loader.graph.project_state(("migrations", "0001_initial"))
+        self.assertEqual(len(project_state.models), 4)
+
+        book_state = project_state.models["migrations", "book"]
+        self.assertEqual(
+            [x for x, y in book_state.fields],
+            ["id", "user"]
+        )
+
     @override_settings(MIGRATION_MODULES={"migrations": "migrations.test_migrations"})
     def test_name_match(self):
         "Tests prefix name matching"

tests/migrations/test_migrations/0002_second.py

@@ -3,7 +3,9 @@ from django.db import migrations, models
 
 class Migration(migrations.Migration):
 
-    dependencies = [("migrations", "0001_initial")]
+    dependencies = [
+        ("migrations", "0001_initial"),
+    ]
 
     operations = [
 

tests/migrations/test_migrations_unmigdep/0001_initial.py

@@ -0,0 +1,20 @@
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("auth", "__first__"),
+    ]
+
+    operations = [
+
+        migrations.CreateModel(
+            "Book",
+            [
+                ("id", models.AutoField(primary_key=True)),
+                ("user", models.ForeignKey("auth.User", null=True)),
+            ],
+        )
+
+    ]