woff2 with hmtx transform but no glyf transform is rejected

[anthrotype]

The following zip archive contains two WOFF2 fonts. In the first ("TestTTF-Regular+hmtx+glyf.woff2") both the glyf (and loca) and hmtx table are transformed; in the second font ("TestTTF-Regular+hmtx-glyf.woff2") only the hmtx table is transformed, whereas glyf and loca are stored in their original form without pre-processing transformation.

When running the opentype sanitizer on the two fonts, the first (with all tables trasformed) passes, whereas the second font (where only hmtx is transformed but not glyf+loca) fails to decompress.

test-woff2-hmtx-transform.zip

As far as I know, the WOFF2 spec doesn't say that whenever hmtx is transformed, glyf should also be transformed. Only glyf and loca have to be transformed or not transformed together.

These are test fonts that I produced while adding support for hmtx transfom in fontTools woff2 encoder/decoder.

This is probably an upstream issue in google/woff2 (I will report the issue over there as well), since the OTS uses the latter to decode WOFF2.

[khaledhosny]

Once this is fixed in google/woff2 I’ll update our submodule.