Add support for ts_headline

[Hannes Ljungberg]

It would be nice to get support for the Postgres full text search function ts_headline. See ​https://www.postgresql.org/docs/current/textsearch-controls.html#TEXTSEARCH-HEADLINE

SearchHeadline would also accept an optional options argument which is a where configuration options like StartSel and StopSel can be specified.

My proposed implementation work look like this:

>>> from django.contrib.postgres.search import SearchHeadline, SearchQuery
>>> query = SearchQuery('brave sir robin')
>>> first_line = Line.objects.annotate(
...     headline=SearchHeadline('dialogue', query, options={
...         'StartSel': '<b>',
...         'StopSel': '</b>'
...     })
... ).first()
>>> print(first_line.headline)
'<b>Robin</b>. He was not at all afraid to be killed in nasty ways. <b>Brave</b>, <b>brave</b>, <b>brave</b>, <b>brave</b> <b>Sir</b> <b>Robin</b>'

I have this implementation ready if this would be accepted: ​https://github.com/django/django/compare/master...hannseman:ts_headline?expand=1

[Hannes Ljungberg]

PR: ​https://github.com/django/django/pull/12297

[Mariusz Felisiak <felisiak.mariusz@…>]

In 65ab4f9f:

Fixed #31147 -- Added SearchHeadline to django.contrib.postgres.