Fixed #22436: More careful checking on method ref'ce serialization

1 files changed, 22 insertions, 6 deletions

diff --git a/django/db/migrations/writer.py b/django/db/migrations/writer.py
index f73c4b78a0..d709c91707 100644
--- a/django/db/migrations/writer.py
+++ b/django/db/migrations/writer.py
@@ -12,7 +12,7 @@ import types
 from django.apps import apps
 from django.db import models
 from django.db.migrations.loader import MigrationLoader
-from django.utils import datetime_safe, six
+from django.utils import datetime_safe, six, importlib
 from django.utils.encoding import force_text
 from django.utils.functional import Promise
 
@@ -284,13 +284,29 @@ class MigrationWriter(object):
                 klass = value.__self__
                 module = klass.__module__
                 return "%s.%s.%s" % (module, klass.__name__, value.__name__), set(["import %s" % module])
-            elif value.__name__ == '<lambda>':
+            # Further error checking
+            if value.__name__ == '<lambda>':
                 raise ValueError("Cannot serialize function: lambda")
-            elif value.__module__ is None:
+            if value.__module__ is None:
                 raise ValueError("Cannot serialize function %r: No module" % value)
-            else:
-                module = value.__module__
-                return "%s.%s" % (module, value.__name__), set(["import %s" % module])
+            # Python 3 is a lot easier, and only uses this branch if it's not local.
+            if getattr(value, "__qualname__", None) and getattr(value, "__module__", None):
+                if "<" not in value.__qualname__:  # Qualname can include <locals>
+                    return "%s.%s" % (value.__module__, value.__qualname__), set(["import %s" % value.__module__])
+            # Python 2/fallback version
+            module_name = value.__module__
+            # Make sure it's actually there and not an unbound method
+            module = importlib.import_module(module_name)
+            if not hasattr(module, value.__name__):
+                raise ValueError(
+                    "Could not find function %s in %s.\nPlease note that "
+                    "due to Python 2 limitations, you cannot serialize "
+                    "unbound method functions (e.g. a method declared\n"
+                    "and used in the same class body). Please move the "
+                    "function into the main module body to use migrations.\n"
+                    "For more information, see https://docs.djangoproject.com/en/1.7/topics/migrations/#serializing-values"
+                )
+            return "%s.%s" % (module_name, value.__name__), set(["import %s" % module_name])
         # Classes
         elif isinstance(value, type):
             special_cases = [