Links starting with # are marked as "external"

[mgeier]

Describe the bug

This might be a docutils problem ...

When creating a same-page-link that starts with #, the link is formatted as "external", even though it points to the same page, which I would consider "internal", right?

How to Reproduce

index.rst:

Title
=====

`link to subsection <#a-subsection>`_


A Subsection
------------

`link to top <#>`_

conf.py:

# empty

Run:

python -m sphinx . _build

After that, _build/index.html contains this:

<p><a class="reference external" href="#a-subsection">link to subsection</a></p>
...
<p><a class="reference external" href="#">link to top</a></p>

Environment Information

Platform:              linux; (Linux-6.1.0-6-amd64-x86_64-with-glibc2.36)
Python version:        3.11.2 (main, Mar 13 2023, 12:18:29) [GCC 12.2.0])
Python implementation: CPython
Sphinx version:        6.2.0+/0fb6716f3
Docutils version:      0.19.1b.dev
Jinja2 version:        3.1.2
Pygments version:      2.14.0

Sphinx extensions

No response

Additional context

spatialaudio/nbsphinx#530

[picnixz]

I edited my comment because I was wrong before.

---

This should be because of:

sphinx/sphinx/writers/html5.py

Lines 208 to 213 in 5a6b2b1

	def visit_reference(self, node: Element) -> None:
	atts = {'class': 'reference'}
	if node.get('internal') or 'refuri' not in node:
	atts['class'] += ' internal'
	else:
	atts['class'] += ' external'

An "internal" reference would point to an explicit (hard-coded) label (see https://docutils.sourceforge.io/docs/ref/rst/restructuredtext.html#hyperlink-targets). Since there is no explicit label being created, it does not work. Now, by looking at the Sphinx implementation, I think we should mark internal=True when a reference has an explicit target starting with #.

[gmilde]

An "internal" reference would point to an explicit (hard-coded) label (see https://docutils.sourceforge.io/docs/ref/rst/restructuredtext.html#hyperlink-targets).

An "internal reference" uses a refname instead of a refuri. The "reference name" may be established by an explicit target or an implicit target (like a section title).

Since there is no explicit label being created, it does not work.

Actually,

`link to subsection <a subsection_>`__


A Subsection
------------

works fine and creates an internal reference.

Now, by looking at the Sphinx implementation, I think we should mark internal=True when a reference has an explicit target starting with #.

This may be an enhancement for the Docutils HTML5 writer. It is a backwards incompatible change, though.