MyST-Parser
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executablebooks
Add warning for invalid footnotes reference (and unused definitions)
What version of myst-parser are you using?
3.0.1
What version dependencies are you using?
Sphinx 7.2.6 docutils 0.20.1
What operating system are you using?
Mac
Describe the Bug
If a Markdown footnote does not have a corresponding reference in either direction, no warnings are emitted. Compare the equivalent RST and Markdown:
Lorem ipsum [#f1]_ dolor sit amet ... [#f2]_
.. rubric:: Footnotes
.. [#f1] Text of the first footnote.
.. [#f3] Text of the second footnote.
Lorem ipsum [^f1] dolor sit amet ... [^f2]
```{rubric} Footnotes
```
[^f1]: Text of the first footnote.
[^f3]: Text of the second footnote.
The first one gives two warnings in the build
test.rst:1: ERROR: Too many autonumbered footnote references: only 0 corresponding footnotes available.
test.rst:1: ERROR: Unknown target name: "f2".
The second one gives no warnings. The resulting document just has a literal [^f2] in the text.
Expected Behavior
An invalid footnote should produce a warning, ideally in both directions, since it is an invalid cross-reference.
To Reproduce
No response
The resulting document just has a literal [^f2] in the text.
Note, a problem with this is it is basically an intended part of commonmark; that square brackets [] are parsed as text, if there are no definitions: https://github.com/commonmark/commonmark-spec/issues/702
footnote references are generally treated in the same way, although perhaps you could make the case that [^ is a more explicit syntax, so that we could remove this "lazy evaluation"; it would be a breaking change for myst, but shouldn't affect too many.
Looking at djot, they do indeed always treat [^...] as a footnote, even if no definition is given: https://djot.net/playground/?text=%5B%5Ea%5D&sourcepos=false
(you'll note in https://github.com/jgm/djot, general shortcut link syntax [...] is removed)
Thinking about this now actually, perhaps a route to removing the annoying "lazy" behaviour of shortcut link references like [...] for myst, would be to introduce a more "specific" syntax like [=...], e.g.
footnote references are never parsed as text [^footnote]
link shortcuts starting with `[=` are never parsed as text (and the `=` is removed from the link) [=reference]
[^footnote]: This is a footnote
[reference]: https://example.com
goes to:
<p>footnote references are never parsed as text <a id="fnref1" href="#fn1"><sup>1</sup></a></p>
<p>link shortcuts starting with <code>[=</code> are never parsed as text (and the <code>=</code> is removed from the link) <a href="https://example.com">reference</a></p>
<section role="doc-endnotes">
<hr>
<ol>
<li id="fn1">
<p>This is a footnote<a href="#fnref1">↩︎</a></p>
</li>
</ol>
</section>