[instantiator] Fix assertion error in instantiator with sparse/virtual masters#983
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Designspaces with sparse or virtual masters can have multiple sources at different locations but only the default source carries fontinfo. collect_info_masters() skips non-default layer-only sources, so info_mutator ends up with a single master and is_static_font() returns True. Generating an instance at any non-default location then trips `assert all(v == 0.0 for v in location_normalized.values())` in _generate_instance_info. This commit only adds the regression test; the fix follows in the next commit. #981
…ation The single-master path in _generate_instance_info copies ALL fontinfo.plist attributes (including instance-specific ones like postscriptFontName, styleName, openTypeNameUniqueID) from the default source. That's only safe when the instance is actually at the default location. Designspaces with sparse or virtual masters can have a single info master but generate instances at non-default locations, which used to trip the assertion guarding this branch. Tighten the gate to require both is_static_font() AND location_normalized == default. Sparse-master cases at non-default locations now fall through to the multi-master path, which correctly skips instance-specific attributes; VariationModel with one master at the origin returns the master's values at any location, so the extractInfo call is a no-op there. Fixes #981
simoncozens
approved these changes
May 19, 2026
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Fix
AssertionErrorin_generate_instance_infowhen generating instances at non-default locations in designspaces with sparse or virtual masters (wherecollect_info_masterscan yield a single default info master despite multiple non-default sources)Gate the single-master fontinfo inheritance path on both
is_static_font()andis_at_default, so that non-default instances fall through to the multi-master path, which correctly skips instance-specific attributesFixes #981