Only ExtraLight weight works with variable font on Linux

[P3RC3NTAG3]

Hello!
I noticed that on Linux, the variable font only seems to work with the extra-light weight. Could you please fix this?

Thanks!

[Shide]

Same issue here!

[KTibow]

I asked Claude Fable to look into this and it found a root cause, so passing along its findings.

The v2.0 variable font ships inconsistent weight metadata: OS/2.usWeightClass is 400, but the fvar wght axis default is 200 (ExtraLight). On Linux, fontconfig labels each named instance with usWeightClass × (instance wght ÷ default wght) — it assumes usWeightClass describes the default instance (fcfreetype.c, the weight_mult logic). With this font the multiplier is wght/200, so every instance is advertised at double its real weight: ExtraLight is labeled Regular, Regular is labeled ExtraBold, everything ≥500 clamps to the top of the scale. Any app that selects faces through fontconfig metadata (Firefox, Pango/GTK, …) then picks ExtraLight when asked for regular text. Chromium is unaffected because it sets wght from CSS itself, which is why the bug is easy to miss.

FC_DEBUG=256 fc-query 'MonaSansVF[wdth,wght,opsz,ital].ttf' shows it directly — this is the true Regular instance (wght=400) being labeled ExtraBold:

os2 weight class 400 multiplier 2 maps to weight 205

Supporting evidence that the mismatch arrived with the v2 rebuild:

• Hubot Sans v1.0.1 has usWeightClass = 200, matching its fvar default of 200 → indexes correctly, not affected.
• The Google Fonts build (ofl/monasans) also uses usWeightClass = 200 = default → verified to index and render correctly on the same system.

Either of these fixes the release fonts (both locally verified):

1. Set usWeightClass to 200 to match the fvar default (what the Google Fonts build does), or
2. Move the fvar default to 400 with rebased deltas, e.g. fonttools varLib.instancer "MonaSansVF[wdth,wght,opsz,ital].ttf" "wght=200:400:900" — arguably nicer since the default instance then matches what font-weight: normal means everywhere. (Note a plain edit of the fvar defaultValue is not sufficient — without rebasing the gvar deltas, wght=400 renders the old 200 outlines.)