Broken doc build pipeline: pdf generation: invalid literal for int() with base 16: 'ig'

[farshidtz]

The documentation build pipeline is blocked since 5ee6cbf due to a failure in the Sphinx pdf generator.

The error is unrelated to the local changes.
The error is triggered because of changes to docs/explanation/rr_scheduler.svg.

This effectively prevents the build of versioned documentation by RTD.

Build error:

# Traceback:
Traceback (most recent call last):
  File "/home/farshid/projects/real-time/real-time-ubuntu-docs/docs/.sphinx/venv/lib/python3.12/site-packages/sphinx/cmd/build.py", line 337, in build_main
    app.build(args.force_all, args.filenames)
  File "/home/farshid/projects/real-time/real-time-ubuntu-docs/docs/.sphinx/venv/lib/python3.12/site-packages/sphinx/application.py", line 378, in build
    self.builder.build_update()
  File "/home/farshid/projects/real-time/real-time-ubuntu-docs/docs/.sphinx/venv/lib/python3.12/site-packages/sphinx/builders/__init__.py", line 294, in build_update
    self.build(['__all__'], to_build)
  File "/home/farshid/projects/real-time/real-time-ubuntu-docs/docs/.sphinx/venv/lib/python3.12/site-packages/sphinx/builders/__init__.py", line 367, in build
    self.write(docnames, list(updated_docnames), method)
  File "/home/farshid/projects/real-time/real-time-ubuntu-docs/docs/.sphinx/venv/lib/python3.12/site-packages/sphinx/builders/latex/__init__.py", line 304, in write
    doctree = self.assemble_doctree(
              ^^^^^^^^^^^^^^^^^^^^^^
  File "/home/farshid/projects/real-time/real-time-ubuntu-docs/docs/.sphinx/venv/lib/python3.12/site-packages/sphinx/builders/latex/__init__.py", line 370, in assemble_doctree
    self.env.resolve_references(largetree, indexfile, self)
  File "/home/farshid/projects/real-time/real-time-ubuntu-docs/docs/.sphinx/venv/lib/python3.12/site-packages/sphinx/environment/__init__.py", line 699, in resolve_references
    self.apply_post_transforms(doctree, fromdocname)
  File "/home/farshid/projects/real-time/real-time-ubuntu-docs/docs/.sphinx/venv/lib/python3.12/site-packages/sphinx/environment/__init__.py", line 711, in apply_post_transforms
    transformer.apply_transforms()
  File "/home/farshid/projects/real-time/real-time-ubuntu-docs/docs/.sphinx/venv/lib/python3.12/site-packages/sphinx/transforms/__init__.py", line 93, in apply_transforms
    super().apply_transforms()  # type: ignore[misc]
    ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/farshid/projects/real-time/real-time-ubuntu-docs/docs/.sphinx/venv/lib/python3.12/site-packages/docutils/transforms/__init__.py", line 182, in apply_transforms
    transform.apply(**kwargs)
  File "/home/farshid/projects/real-time/real-time-ubuntu-docs/docs/.sphinx/venv/lib/python3.12/site-packages/sphinx/transforms/post_transforms/images.py", line 34, in apply
    self.handle(node)
  File "/home/farshid/projects/real-time/real-time-ubuntu-docs/docs/.sphinx/venv/lib/python3.12/site-packages/sphinx/transforms/post_transforms/images.py", line 254, in handle
    if self.convert(abs_srcpath, destpath):
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/farshid/projects/real-time/real-time-ubuntu-docs/docs/.sphinx/venv/lib/python3.12/site-packages/sphinxcontrib/cairosvgconverter.py", line 54, in convert
    cairosvg.svg2pdf(file_obj=open(_from, 'rb'), write_to=_to)
  File "/home/farshid/projects/real-time/real-time-ubuntu-docs/docs/.sphinx/venv/lib/python3.12/site-packages/cairosvg/__init__.py", line 67, in svg2pdf
    return surface.PDFSurface.convert(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/farshid/projects/real-time/real-time-ubuntu-docs/docs/.sphinx/venv/lib/python3.12/site-packages/cairosvg/surface.py", line 133, in convert
    instance = cls(
               ^^^^
  File "/home/farshid/projects/real-time/real-time-ubuntu-docs/docs/.sphinx/venv/lib/python3.12/site-packages/cairosvg/surface.py", line 225, in __init__
    self.draw(tree)
  File "/home/farshid/projects/real-time/real-time-ubuntu-docs/docs/.sphinx/venv/lib/python3.12/site-packages/cairosvg/surface.py", line 472, in draw
    self.draw(child)
  File "/home/farshid/projects/real-time/real-time-ubuntu-docs/docs/.sphinx/venv/lib/python3.12/site-packages/cairosvg/surface.py", line 442, in draw
    *self.map_color(paint_color, fill_opacity))
     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/farshid/projects/real-time/real-time-ubuntu-docs/docs/.sphinx/venv/lib/python3.12/site-packages/cairosvg/surface.py", line 278, in map_color
    rgba = color(string, opacity)
           ^^^^^^^^^^^^^^^^^^^^^^
  File "/home/farshid/projects/real-time/real-time-ubuntu-docs/docs/.sphinx/venv/lib/python3.12/site-packages/cairosvg/colors.py", line 227, in color
    plain_color = tuple(
                  ^^^^^^
  File "/home/farshid/projects/real-time/real-time-ubuntu-docs/docs/.sphinx/venv/lib/python3.12/site-packages/cairosvg/colors.py", line 228, in <genexpr>
    int(value, 16) / 255 for value in (
    ^^^^^^^^^^^^^^
ValueError: invalid literal for int() with base 16: 'ig'

It can be reproduced locally:

sudo make pdf-prep-force
make pdf-prep
make pdf

[farshidtz]

What made this very hard to pinpoint is that the PDF build only happens and fails on read-the-doc, not on Github workflows triggered on PRs and main.

[farshidtz]

It looks like any DrawIO diagram exported to SVG via the current draw.io app (snapped v26.0.9) or https://app.diagrams.net/ trigger that error.

The light-dark css functions are at least one of the culprits, e.g. fill="light-dark(#000000, #ffffff)", style="color: light-dark(#000000, #ffffff);. Disabling the Appearance: Automatic when exporting to SVG doesn't remove those.