Fixed #26167 -- Added support for functional indexes.

Thanks Simon Charette, Mads Jensen, and Mariusz Felisiak for reviews.

Co-authored-by: Markus Holtermann <info@markusholtermann.eu>

docs/ref/contrib/postgres/indexes.txt

@@ -10,7 +10,7 @@ available from the ``django.contrib.postgres.indexes`` module.
 ``BloomIndex``
 ==============
 
-.. class:: BloomIndex(length=None, columns=(), **options)
+.. class:: BloomIndex(*expressions, length=None, columns=(), **options)
 
     .. versionadded:: 3.1
 
@@ -30,10 +30,15 @@ available from the ``django.contrib.postgres.indexes`` module.
 
     .. _bloom: https://www.postgresql.org/docs/current/bloom.html
 
+    .. versionchanged:: 3.2
+
+        Positional argument ``*expressions`` was added in order to support
+        functional indexes.
+
 ``BrinIndex``
 =============
 
-.. class:: BrinIndex(autosummarize=None, pages_per_range=None, **options)
+.. class:: BrinIndex(*expressions, autosummarize=None, pages_per_range=None, **options)
 
     Creates a `BRIN index
     <https://www.postgresql.org/docs/current/brin-intro.html>`_.
@@ -43,24 +48,34 @@ available from the ``django.contrib.postgres.indexes`` module.
 
     The ``pages_per_range`` argument takes a positive integer.
 
+    .. versionchanged:: 3.2
+
+        Positional argument ``*expressions`` was added in order to support
+        functional indexes.
+
     .. _automatic summarization: https://www.postgresql.org/docs/current/brin-intro.html#BRIN-OPERATION
 
 ``BTreeIndex``
 ==============
 
-.. class:: BTreeIndex(fillfactor=None, **options)
+.. class:: BTreeIndex(*expressions, fillfactor=None, **options)
 
     Creates a B-Tree 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.
 
+    .. versionchanged:: 3.2
+
+        Positional argument ``*expressions`` was added in order to support
+        functional indexes.
+
     .. _fillfactor: https://www.postgresql.org/docs/current/sql-createindex.html#SQL-CREATEINDEX-STORAGE-PARAMETERS
 
 ``GinIndex``
 ============
 
-.. class:: GinIndex(fastupdate=None, gin_pending_list_limit=None, **options)
+.. class:: GinIndex(*expressions, fastupdate=None, gin_pending_list_limit=None, **options)
 
     Creates a `gin index <https://www.postgresql.org/docs/current/gin.html>`_.
 
@@ -79,13 +94,18 @@ available from the ``django.contrib.postgres.indexes`` module.
     to tune the maximum size of the GIN pending list which is used when
     ``fastupdate`` is enabled.
 
+    .. versionchanged:: 3.2
+
+        Positional argument ``*expressions`` was added in order to support
+        functional indexes.
+
     .. _GIN Fast Update Technique: https://www.postgresql.org/docs/current/gin-implementation.html#GIN-FAST-UPDATE
     .. _gin_pending_list_limit: https://www.postgresql.org/docs/current/runtime-config-client.html#GUC-GIN-PENDING-LIST-LIMIT
 
 ``GistIndex``
 =============
 
-.. class:: GistIndex(buffering=None, fillfactor=None, **options)
+.. class:: GistIndex(*expressions, buffering=None, fillfactor=None, **options)
 
     Creates a `GiST index
     <https://www.postgresql.org/docs/current/gist.html>`_. These indexes are
@@ -109,13 +129,18 @@ available from the ``django.contrib.postgres.indexes`` module.
     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.
 
+    .. versionchanged:: 3.2
+
+        Positional argument ``*expressions`` was added in order to support
+        functional indexes.
+
     .. _buffering build: https://www.postgresql.org/docs/current/gist-implementation.html#GIST-BUFFERING-BUILD
     .. _fillfactor: https://www.postgresql.org/docs/current/sql-createindex.html#SQL-CREATEINDEX-STORAGE-PARAMETERS
 
 ``HashIndex``
 =============
 
-.. class:: HashIndex(fillfactor=None, **options)
+.. class:: HashIndex(*expressions, fillfactor=None, **options)
 
     Creates a hash index.
 
@@ -127,12 +152,17 @@ available from the ``django.contrib.postgres.indexes`` module.
         Hash indexes have been available in PostgreSQL for a long time, but
         they suffer from a number of data integrity issues in older versions.
 
+    .. versionchanged:: 3.2
+
+        Positional argument ``*expressions`` was added in order to support
+        functional indexes.
+
     .. _fillfactor: https://www.postgresql.org/docs/current/sql-createindex.html#SQL-CREATEINDEX-STORAGE-PARAMETERS
 
 ``SpGistIndex``
 ===============
 
-.. class:: SpGistIndex(fillfactor=None, **options)
+.. class:: SpGistIndex(*expressions, fillfactor=None, **options)
 
     Creates an `SP-GiST index
     <https://www.postgresql.org/docs/current/spgist.html>`_.
@@ -140,4 +170,30 @@ available from the ``django.contrib.postgres.indexes`` module.
     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.
 
+    .. versionchanged:: 3.2
+
+        Positional argument ``*expressions`` was added in order to support
+        functional indexes.
+
     .. _fillfactor: https://www.postgresql.org/docs/current/sql-createindex.html#SQL-CREATEINDEX-STORAGE-PARAMETERS
+
+``OpClass()`` expressions
+=========================
+
+.. versionadded:: 3.2
+
+.. class:: OpClass(expression, name)
+
+    An ``OpClass()`` expression represents the ``expression`` with a custom
+    `operator class`_ that can be used to define functional indexes. To use it,
+    you need to add ``'django.contrib.postgres'`` in your
+    :setting:`INSTALLED_APPS`. Set the ``name`` parameter to the name of the
+    `operator class`_.
+
+    For example::
+
+        Index(OpClass(Lower('username'), name='varchar_pattern_ops'))
+
+    creates an index on ``Lower('username')`` using ``varchar_pattern_ops``.
+
+    .. _operator class: https://www.postgresql.org/docs/current/indexes-opclass.html