[designspaceLib] "Recursive" linkedUserValue valid?

I noticed that Adobe seems to link upright and italic VFs “recursively”, i.e. on the Italic axis, the upright has linkedUserValue=“1”, and the italic has linkedUserValue=“0”. As seen in Source Code Variable:

Such configuration can not be built with designspaceLib, it throws a RecursionError.

Should it be possible to build such fonts? Or is that kind of linking disallowed? The ital axis spec doesn’t say anything about linkedUserValue.

Reproducer: linkeduservalue.zip

Traceback (most recent call last):
  File "/Users/kuti/Code/variable-fonts/Test/test.py", line 12, in <module>
    names = getStatNames(ds, loc)
  File "/Users/kuti/Quellen/fonttools-github/Lib/fontTools/designspaceLib/statNames.py", line 126, in getStatNames
    regularStatNames = getStatNames(doc, regularUserLocation)
  File "/Users/kuti/Quellen/fonttools-github/Lib/fontTools/designspaceLib/statNames.py", line 126, in getStatNames
    regularStatNames = getStatNames(doc, regularUserLocation)
  File "/Users/kuti/Quellen/fonttools-github/Lib/fontTools/designspaceLib/statNames.py", line 126, in getStatNames
    regularStatNames = getStatNames(doc, regularUserLocation)
  [Previous line repeated 987 more times]
  File "/Users/kuti/Quellen/fonttools-github/Lib/fontTools/designspaceLib/statNames.py", line 66, in getStatNames
    defaultSource: Optional[SourceDescriptor] = doc.findDefault()
  File "/Users/kuti/Quellen/fonttools-github/Lib/fontTools/designspaceLib/__init__.py", line 2768, in findDefault
    print(sourceDescriptor)
  File "/Users/kuti/Quellen/fonttools-github/Lib/fontTools/designspaceLib/__init__.py", line 116, in __repr__
    attrs = indent('\n'.join(attrs), '    ')
  File "/Library/Frameworks/Python.framework/Versions/3.10/lib/python3.10/textwrap.py", line 488, in indent
    return ''.join(prefixed_lines())
  File "/Library/Frameworks/Python.framework/Versions/3.10/lib/python3.10/textwrap.py", line 487, in prefixed_lines
    yield (prefix + line if predicate(line) else line)
  File "/Library/Frameworks/Python.framework/Versions/3.10/lib/python3.10/textwrap.py", line 483, in predicate
    return line.strip()
RecursionError: maximum recursion depth exceeded while calling a Python object

[jenskutilek]

Thanks! I think the problem is here:

https://github.com/fonttools/fonttools/blob/bc03f0932208c71ecb1bca40a348fdf0170f5abe/Lib/fontTools/designspaceLib/statNames.py#L200-L225

The comparison urpright_label.linkedUserValue == userLocation[axis.name] is true for both locations on the italic axis.

[belluzj]

Ah right, sorry I forgot about that issue. I’ll push a PR