add --dry-run option to reapply_extensions command

lms/djangoapps/instructor/management/commands/reapply_extensions.py

 #!/usr/bin/python
 from django.http import Http404
-from django.core.management.base import BaseCommand, CommandError
+from django.core.management.base import BaseCommand, CommandError, make_option
 
 from courseware.courses import get_course_by_id
 from instructor.views.tools import reapply_all_extensions
@@ -9,12 +9,20 @@ from instructor.views.tools import reapply_all_extensions
 class Command(BaseCommand):
     args = "<course_id>"
     help = "Reapply all extensions (fixes extensions for newly added problems)"
+    option_list = BaseCommand.option_list + (
+        make_option('--dry-run',
+                    dest='dry_run',
+                    action='store_true',
+                    default=False,
+                    help='Show what would be done without actually doing '
+                    'anything'),
+    )
 
     def handle(self, *args, **options):
         if len(args) != 1:
             raise CommandError("insufficient arguments")
         try:
             course = get_course_by_id(args[0])
-            reapply_all_extensions(course)
+            reapply_all_extensions(course, dry_run=options['dry_run'])
         except (ValueError, Http404) as e:
             raise CommandError(e)

lms/djangoapps/instructor/views/tools.py

@@ -254,7 +254,12 @@ def dump_student_extensions(course, student):
         "data": data}
 
 
-def reapply_all_extensions(course):
+def reapply_all_extensions(course, dry_run=False):
+    """
+    Recursively reapply all extensions to each extended unit in course. This
+    fixes an issue where new xmodule children (ie new <problem> children) don't
+    inherit the same 'extended_due' as their parent.
+    """
     units = get_units_with_due_date(course)
     units = dict([(u.location.url(), u) for u in units])
     msks = units.keys()
@@ -272,6 +277,10 @@ def reapply_all_extensions(course):
             if not edue:
                 continue
             unit = units.get(module.module_state_key)
+            if dry_run:
+                print('would reapply extension %s to %s for user %s' %
+                      (edue, unit.location.url(), student.username))
+            else:
                 print('reapplying extension %s to %s for user %s' %
                       (edue, unit.location.url(), student.username))
                 set_due_date_extension(course, unit, student, edue)