[1.11.x] Fixed #27915 -- Allowed Meta.indexes to be defined in abstract models.

Thanks Markus Holtermann for review.

Backport of 3d19d1428a05b514afb771b52870d1f7c25670d1 from master

3 files changed, 18 insertions, 6 deletions

diff --git a/django/db/migrations/state.py b/django/db/migrations/state.py
index e44f737106..b6540f5f10 100644
--- a/django/db/migrations/state.py
+++ b/django/db/migrations/state.py
@@ -460,6 +460,11 @@ class ModelState(object):
                 elif name == "index_together":
                     it = model._meta.original_attrs["index_together"]
                     options[name] = set(normalize_together(it))
+                elif name == "indexes":
+                    indexes = [idx.clone() for idx in model._meta.indexes]
+                    for index in indexes:
+                        index.set_name_with_model(model)
+                    options['indexes'] = indexes
                 else:
                     options[name] = model._meta.original_attrs[name]
         # Force-convert all options to text_type (#23226)
diff --git a/django/db/models/base.py b/django/db/models/base.py
index 53b761f45a..217bde1e2a 100644
--- a/django/db/models/base.py
+++ b/django/db/models/base.py
@@ -303,12 +303,14 @@ class ModelBase(type):
                 else:
                     new_class.add_to_class(field.name, copy.deepcopy(field))
 
-        # Set the name of _meta.indexes. This can't be done in
-        # Options.contribute_to_class() because fields haven't been added to
-        # the model at that point.
-        for index in new_class._meta.indexes:
-            if not index.name:
-                index.set_name_with_model(new_class)
+        if base_meta and base_meta.abstract and not abstract:
+            new_class._meta.indexes = [copy.deepcopy(idx) for idx in new_class._meta.indexes]
+            # Set the name of _meta.indexes. This can't be done in
+            # Options.contribute_to_class() because fields haven't been added
+            # to the model at that point.
+            for index in new_class._meta.indexes:
+                if not index.name:
+                    index.set_name_with_model(new_class)
 
         if abstract:
             # Abstract base models can't be instantiated and don't appear in
diff --git a/django/db/models/indexes.py b/django/db/models/indexes.py
index 1ef5a4ab50..0ee2bf3610 100644
--- a/django/db/models/indexes.py
+++ b/django/db/models/indexes.py
@@ -77,6 +77,11 @@ class Index(object):
         path = path.replace('django.db.models.indexes', 'django.db.models')
         return (path, (), {'fields': self.fields, 'name': self.name})
 
+    def clone(self):
+        """Create a copy of this Index."""
+        path, args, kwargs = self.deconstruct()
+        return self.__class__(*args, **kwargs)
+
     @staticmethod
     def _hash_generator(*args):
         """