Couldn't merge the fonts, because one of the values in a list was empty when it shouldn't have been. ... GPOS.table.LookupList.Lookup[0][0][1].EntryAnchor

[dy]

With linefont we updated gftools from v0.9.15 to 0.9.33 and it began throwing error:

...
  File "/Users/div/projects/linefont/venv/lib/python3.11/site-packages/gftools/builder/__init__.py", line 336, in build_variable
    output_files = self.run_fontmake(source, args)
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/div/projects/linefont/venv/lib/python3.11/site-packages/gftools/builder/__init__.py", line 395, in run_fontmake
    FontProject().run_from_designspace(source, **args)
  File "/Users/div/projects/linefont/venv/lib/python3.11/site-packages/fontmake/font_project.py", line 1161, in run_from_designspace
    raise FontmakeError(
fontmake.errors.FontmakeError: In 'Linefont.designspace': Generating fonts from Designspace failed: 

Couldn't merge the fonts, because one of the values in a list was empty when
it shouldn't have been. This happened while performing the following
operation: GPOS.table.LookupList.Lookup[0][0][1].EntryAnchor

The problem is likely to be in Linefont SuperCondensed Thin:
.EntryAnchor==[None, None, None, None, None, None, None, None]

If anyone can have a look and diagnose the issue 🙏🏼

Related dy/linefont#9.

@RosaWagner recommended posting it here, because it's a blocker for the linefont.
Can't downgrade gftools because of another issue.

[dy]

Just wanted to ping if there's any possible considerations or I can somehow help @simoncozens @khaledhosny @verbosus

[simoncozens]

This is a bug in the merger. I've filed fonttools/fonttools#3247.

[simoncozens]

...and I've fixed the bug in the merger, so this will start magically working after the next fonttools release.