Fixed #26974 -- Added HashIndex to django.contrib.postgres.

Thanks Akshesh Doshi for the initial implementation.

docs/ref/contrib/postgres/indexes.txt

@@ -72,3 +72,22 @@ available from the ``django.contrib.postgres.indexes`` module.
 
     .. _buffering build: https://www.postgresql.org/docs/current/static/gist-implementation.html#GIST-BUFFERING-BUILD
     .. _fillfactor: https://www.postgresql.org/docs/current/static/sql-createindex.html#SQL-CREATEINDEX-STORAGE-PARAMETERS
+
+``HashIndex``
+=============
+
+.. class:: HashIndex(fillfactor=None, **options)
+
+    .. versionadded:: 2.2
+
+    Creates a hash index.
+
+    Provide an integer value from 10 to 100 to the fillfactor_ parameter to
+    tune how packed the index pages will be. PostgreSQL's default is 90.
+
+    .. admonition:: Use this index only on PostgreSQL 10 and later
+
+        Hash indexes have been available in PostgreSQL for a long time, but
+        they suffer from a number of data integrity issues in older versions.
+
+    .. _fillfactor: https://www.postgresql.org/docs/current/static/sql-createindex.html#SQL-CREATEINDEX-STORAGE-PARAMETERS

docs/releases/2.2.txt

@@ -82,6 +82,9 @@ Minor features
   :class:`~django.contrib.postgres.aggregates.StringAgg` determines the
   ordering of the aggregated elements.
 
+* The new :class:`~django.contrib.postgres.indexes.HashIndex` class
+  allows creating ``hash`` indexes in the database.
+
 :mod:`django.contrib.redirects`
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~