add get_next_by_FOO, get_previous_by_FOO for date,datetime fields

test-data/typecheck/fields/test_related.yml

@@ -183,6 +183,7 @@
 -   case: models_imported_inside_init_file_one_to_one_field
     main: |
         from myapp2.models import Profile
+        reveal_type(Profile().user)  # N: Revealed type is 'myapp.models.user.User*'
         reveal_type(Profile().user.profile)  # N: Revealed type is 'myapp2.models.Profile'
     installed_apps:
         - myapp

test-data/typecheck/models/test_extra_methods.yml

@@ -18,3 +18,39 @@
                 class MyUser(models.Model):
                     name = models.CharField(max_length=100)
                     gender = models.CharField(max_length=100, choices=GENDER_CHOICES)
+
+-   case: date_datetime_fields_have_get_next_by_get_previous_by
+    main: |
+        from myapp.models import MyUser
+        reveal_type(MyUser().get_next_by_date())  # N: Revealed type is 'myapp.models.MyUser'
+        reveal_type(MyUser().get_next_by_datetime())  # N: Revealed type is 'myapp.models.MyUser'
+        reveal_type(MyUser().get_previous_by_date())  # N: Revealed type is 'myapp.models.MyUser'
+        reveal_type(MyUser().get_previous_by_datetime())  # N: Revealed type is 'myapp.models.MyUser'
+
+        # accept arbitrary kwargs
+        MyUser().get_next_by_date(arg1=1, arg2=2)
+    installed_apps:
+        - myapp
+    files:
+        -   path: myapp/__init__.py
+        -   path: myapp/models.py
+            content: |
+                from django.db import models
+                class MyUser(models.Model):
+                    date = models.DateField()
+                    datetime = models.DateTimeField()
+
+-   case: get_next_by_get_previous_by_absent_if_null_true
+    main: |
+        from myapp.models import MyUser
+        MyUser().get_next_by_date()  # E: "MyUser" has no attribute "get_next_by_date"
+        MyUser().get_previous_by_date()  # E: "MyUser" has no attribute "get_previous_by_date"
+    installed_apps:
+        - myapp
+    files:
+        -   path: myapp/__init__.py
+        -   path: myapp/models.py
+            content: |
+                from django.db import models
+                class MyUser(models.Model):
+                    date = models.DateField(null=True)