Is it possible to get Sphinx to generate the index based on existing labels and :ref: in the text? Say if you have a label:
.. _my_label:
My Section
and later refer to it through multiple :ref:`my_label` , is there a way to get the equivalent of an automatic generation of:
.. index:: My Section
where the label is, and the same before the paragraph where the :ref: lives?
The official doc does not list labels or :ref: as index-generating markup and I could not find any extension doing it. But maybe there is one?
There's an official list of Sphinx extensions, and there are a few lists of unoffical extensions on Github but none of them implement the functionality specified in the question.
The closest approach to the problem specified in the question would be using autosectionlabel to automatically create a target label having the section name, and place an :index: or .. index:: adjacent to the reST section to place it in the index. However, this would only save having to declare the label, declaring the index entry would still be necessary.
The functionality (directive) you ask for provides little tangible gain beyond writing one less line or block of reST code (the .. index:: directive or :index: role), be it for sections or targets.
Sphinx being open source would allow implementing a custom directive for this, however using a non-standard directive having as only aim shortening standard syntax by a single construct would stand to create more difficulty than gain for readers of your source code.