TOC in navigation side bar is generated incorrectly for depth > 3

[khanxmetu]

Describe the bug

The global table of contents in the navigation side bar isn’t generated correctly when the depth of the current document is more than 3.

How to Reproduce

$ cat index.rst 
index
------

.. toctree::

    a

$ cat a.rst 
a
--

.. toctree::

    b

$ cat b.rst 
b
--

.. toctree::

    c

$ cat c.rst 
c
--

.. toctree::

    d
$ cat d.rst 
d
--

$ sphinx-build -m html . _build

Output
Table of contents in navigation sidebar on page d.html only shows link to page a

Expected Output
All the ancestors till the current page: a, b, c, d were expected to be shown.

Environment Information

Platform:              linux; (Linux-6.6.31+rpt-rpi-v8-aarch64-with-glibc2.36)
Python version:        3.11.2 (main, Aug 26 2024, 07:20:54) [GCC 12.2.0])
Python implementation: CPython
Sphinx version:        8.1.0+/1b08b66d1
Docutils version:      0.20.1
Jinja2 version:        3.1.4
Pygments version:      2.18.0

Sphinx extensions

No response

Additional context

No response

[khanxmetu]

Not really sure if this was an intended behavior in global toctree generation to avoid generating siblings at every level of depth in order to reduce build times.

[mgeier]

This likely depends on the HTML theme you are using. With the default alabaster theme I'm seeing links to a, b, c and d.

What theme are you using?

[khanxmetu]

This likely depends on the HTML theme you are using. With the default alabaster theme I'm seeing links to a, b, c and d.

What theme are you using?

I'm using alabaster too. Sorry for the wrong assumption, the issue
isn't related to tree depth.

I had a hard time reproducing as well and I figured that the problem occurred due to adding a toctree entry of some document and building the second time while keeping previous build's files.

Here is the reproducer:

$ cat index.rst
index
-----

.. toctree::
    a

$ cat b.rst 
b
--

.. toctree::


$ cat c.rst 
c
--


$ sphinx-build -b html . _build/

$ # add doc c into b's toctree
$ vi b.rst
$ cat b.rst 
b
--

.. toctree::
    c

$ # build again
$ sphinx-build -b html . _build/

$ cat _build/c.html | grep 'href="a.html"'
<li class="toctree-l1"><a class="reference internal" href="a.html">a</a></li>
$ cat _build/c.html | grep 'href="b.html"'
$ cat _build/c.html | grep 'href="#"'

c.html should contain links to a,b and self, however it only contains a link to a.html