[feaLib] Upgrade single substitutions mixed with ligature ones #3805
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If a lookup has only single and ligature substitutions, we now upgrade single substitutions to ligature ones. Previously this would cause an error in named lookup, and would result in splitting lookups in anonymous ones. This is similar to what we have done with multiple substitutions in #1133, but back then I incorrectly convinced myself that ligature substitutions can’t have a single source glyph, which is obviously not true.
Doing this is Block.build() is less of a hack than modifying the parsed ast tree during parsing.
We even have code in HB to treat them as single substitutions not ligatures, for further processing purposes. |
anthrotype
approved these changes
Apr 23, 2025
cmyr
added a commit
to googlefonts/fontc
that referenced
this pull request
May 21, 2025
This was added to fonttools a few months back (fonttools/fonttools#3805); this patch gets us back to parity.
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If a lookup has only single and ligature substitutions, we now upgrade single substitutions to ligature ones. Previously this would cause an error in named lookup, and would result in splitting lookups in anonymous ones.
This is similar to what we have done with multiple substitutions in #1133, but back then I incorrectly convinced myself that ligature substitutions can’t have a single source glyph, which is obviously not true.