Nested toc produces multiply-defined labels in LaTeX output

[NarvinSingh]

Describe the bug

If you have a toctree that includes another toctree, then run make latexpdf, you will get a warning that there are multiply-defined labels.

How to Reproduce

Starting from a conf.py generated by running sphinx-quickstart, create subindex.rst which will have a toctree and be included in the toctree of index.rst. In the subindex.rst toctree, reference another document, page1.rst.

index.rst

Abbreviated file contents.

.. toctree::
   :maxdepth: 2
   :caption: Contents:

   subindex.rst

subindex.rst

Full file contents.

.. toctree::

   page1.rst

page1.rst

Full file contents.

Hello

tex Output

\label{\detokenize{page1:page-one}}\label{\detokenize{page1::doc}}\label{\detokenize{page1::doc}}

Proposed Fix

In writers/latex.py change this:

    def hypertarget_to(self, node: Element, anchor: bool = False) -> str:
        labels = ''.join(self.hypertarget(node_id, anchor=False) for node_id in node['ids'])

to this:

    def hypertarget_to(self, node: Element, anchor: bool = False) -> str:
        labels = ''.join(self.hypertarget(node_id, anchor=False) for node_id in {*node['ids']})

Environment Information

Python 3.12.2
Sphinx 7.2.6

Sphinx extensions

No response

Additional context

No response

[picnixz]

Just wondering but does this also happen with HTML? or is it only with the latex build?

Also, your fix makes builds nonreproducible due to the arbitrary order of a set. In addition, I'm not sure that it would work if you end up with nested labels that could then collapse to a top-label.

I cannot check this this week though so it'll need to wait a bit.

[NarvinSingh]

If the order is important, then how about something like

labels = ''.join(self.hypertarget(node_id, anchor=False) for node_id in {k: None for k in node['ids']})

I don't know if it also happens in HTML. I'll check when I get a minute.

I don't know enough to comment about collapsing.

[NarvinSingh]

I don't see it happening in HTML.

[picnixz]

Thank you. This needs investigation on our side then to make the fix as smooth as possible.