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Keep default ignorables that GSUB substituted - #406

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lehni wants to merge 1 commit into
foliojs:masterfrom
lineto:fix/substituted-default-ignorables
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lehni wants to merge 1 commit into
foliojs:masterfrom
lineto:fix/substituted-default-ignorables

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@lehni

@lehni lehni commented Oct 18, 2026

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Observed with real fonts: Fira Sans (already in the test data) and our Akkurat family ship a case form of the soft hyphen (uni00AD.case). HarfBuzz shows it in "A­B" with case on; fontkit swaps it for an invisible space.

  • The substituted glyph keeps the soft hyphen's code point (since [Followup] Compose canonical decompositions (NFC) in the default shaper #403), so it was still hidden as a default ignorable
  • Hide only default ignorables that still show their nominal glyph, as HarfBuzz does (hb-shape --features=case FiraSans-Regular.ttf "A­B" gives A uni00AD.case B)
  • Add tests for hiding a soft hyphen and keeping its case form, with Fira Sans

- A soft hyphen replaced by its case form was still swapped for an invisible space, as the substituted glyph keeps the soft hyphen's code point
- Hide only default ignorables that still show their nominal glyph, as HarfBuzz does
- Add tests for hiding a soft hyphen and keeping its case form, with Fira Sans
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