8000 [otlLib] `buildCoverage` does not remove duplicate glyphs · Issue #2433 · fonttools/fonttools · GitHub
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[otlLib] buildCoverage does not remove duplicate glyphs #2433

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dscorbett opened this issue Oct 24, 2021 · 4 comments · Fixed by #2440
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[otlLib] buildCoverage does not remove duplicate glyphs #2433

dscorbett opened this issue Oct 24, 2021 · 4 comments · Fixed by #2440

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@dscorbett
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If a class in a feature file includes duplicate glyphs, buildCoverage is called on a list that includes duplicate glyphs. buildCoverage sorts the input glyphs but does not remove duplicates.

>>> import fontTools.otlLib.builder
>>> fontTools.otlLib.builder.buildCoverage(['A', 'B', 'A'], {'A': 1, 'B': 2}).glyphs
['A', 'A', 'B']

The spec says “A Coverage table defines a unique index value, the Coverage Index, for each covered glyph”, but a glyph listed multiple times won’t have a unique index.

This can cause a problem when using the OpenType Sanitizer: if a CoverageFormat1 table lists more glyphs than are declared in 'maxp', OTS reports an error.
@jenskutilek
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It’s at least consistent with what Adobe’s makeotf does, which also doesn’t remove guplicates.

@dscorbett dscorbett mentioned this issue Nov 6, 2021
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@anthrotype
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I'm actually not sure about this. A853 Can @khaledhosny or @simoncozens take a look?

@simoncozens
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Related problem I've been wanting to fix for a while: feaLib allows empty classes, which it then hands to the builder, and the builder dies. Both issues should be caught earlier.

@khaledhosny
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I defer to @dscorbett expertise here, but it looks like the right thing to do in general.

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[otlLib] Remove duplicates when building coverage
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@khaledhosny @simoncozens @dscorbett @jenskutilek @anthrotype
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