Couldn't merge the fonts (GPOS.table.FeatureList.FeatureCount)

While building a relatively small and simple variable font without features, I’m getting an error “Couldn’t merge the fonts, because some values were different, but should have been the same.” The UFOs are generated from a .glyphs file by glyphsLib. If I export the font inside Glyphs it works just fine (and the resulting ttf is good.)

However, if I remove all glyphs except /.undef /a and /A the build succeeds. So I’m guessing this is an issue related to anchor data in *.ufo/glyphs/*.glif files (which I guess is used to construct mark tables.)

I’m included a copy of the source files to be used for debugging and repro: src.zip

Example:

$ fontmake -o variable -m Intra.designspace --output-path Intra.var.ttf
# ... (regular output truncated)
INFO:fontTools.varLib:Merging OpenType Layout tables
fontmake: Error: In 'build/ufo/Intra.designspace': Generating fonts from Designspace failed:

Couldn't merge the fonts, because some values were different, but should have
been the same. This happened while performing the following operation:
GPOS.table.FeatureList.FeatureCount

The problem is likely to be in RSMS Intra Thin Regular:

Incompatible features between masters.
Expected: mark, mkmk.
Got: mark, mkmk.

Versions:

• fontmake --version # = 3.3.0
• python --version # = Python 3.9.12

[emmamarichal]

Hi @anthrotype ! Thanks, it works now 😃 I used New Tab with Kerning missing in masters script from mekkablue, and added some pairs.

[anthrotype]

yes, it looks like kern_dflt is missing from the Black master

Do you know what parameter in Glyphs can change this?

It’s ufo2ft’s kernFeatureWriter that is producing the kern feature from the kerning data in the master UFO’s kerning.plist, so it’s not something you can control from Glyphs.app.

What does the kern_dflt lookup contain in the Regular master? Could you maybe remove those kerning pairs from Regular as well, so it’s aligned with the Black? Or conversely add some to the Black so it’s aligned with Regular? By removing or adding kerning pairs, I don’t mean you go and edit the kern feature directly, but actually modify the kerning data in the font editor.