Fixed two more bugs with SVG inheritance-diagram links

[ayshih]

Subject: Fixed two more bugs with SVG inheritance-diagram links

Feature or Bugfix

• Bugfix

Purpose

This PR is a follow-on to fixes to inheritance-diagram links (#10614), because I discovered two bugs when trying to re-enable SVG inheritance diagrams on matplotlib (see matplotlib/matplotlib#26567). One of these bugs is actually in the graphviz writer, so affects use cases beyond just inheritance diagrams.

Detail

• The bug in the graphviz writer (see Fix relative references in SVGs generated by sphinx.ext.graphviz #11078) is that it uses self.builder.outdir (e.g., build/html) as the base directory for relative URLs rather than the directory of the current document (e.g., build/html/api for build/html/api/doc1.rst). This happens to still work fine for many cases because the base directory can "cancel out" when determining the correct relative path from the image directory (e.g., build/html/_images). However, when the relative URL doesn't need to go all the way down to self.builder.outdir (e.g., build/html/api/doc1.rst pointing to build/html/api/doc2.rst means that the relative URL is simply doc2.rst), parts of the provided base directory get pulled into the generated relative path, and so passing in the wrong base directory results in an incorrect relative path (e.g., ../html/doc2.rst instead of ../api/doc2.rst).
• When the inheritance diagram is in the same document as the class description, Fixes missing and broken links in inheritance diagrams #10614 accidentally kept the relative path from self.builder.outdir instead of using just the filename.

Relates

• Use SVG inheritance diagrams now that linking has been fixed matplotlib/matplotlib#26567

[AA-Turner]

Looking at 7.2.5.

A

[AA-Turner]

@ayshih would you be able to look over the changes I've made here?

A

[ayshih]

Hmm, one of your changes has caused this PR to no longer fix the matplotlib docs, so I'll track down why (and also expand the test accordingly).

[AA-Turner]

6c10c76 probably fixes matplotlib, please would you be able to test?

A

[ayshih]

Thanks for fixing this PR! I have verified that the matplotlib docs build correctly with the most recent changes. I have also expanded the unit test to cover what was being missed (linking between files in the same subdirectory), and verified that the unit test correctly fails when run on the earlier version (commit af8a1f4).