Greek 'ccmp' rules don’t match NFC input

[dscorbett]

Fonts

NotoSans-Regular.otf
NotoSansMono-Regular.otf
NotoSerif-Regular.otf

Where the fonts came from, and when

Site: https://github.com/googlefonts/noto-fonts/blob/d65fc3fa348cb08f8274c9af8dfac00bbaef0844/unhinted/otf/NotoSans/NotoSans-Regular.otf
Site: https://github.com/googlefonts/noto-fonts/blob/d65fc3fa348cb08f8274c9af8dfac00bbaef0844/unhinted/otf/NotoSansMono/NotoSansMono-Regular.otf
Site: https://github.com/googlefonts/noto-fonts/blob/d65fc3fa348cb08f8274c9af8dfac00bbaef0844/unhinted/otf/NotoSerif/NotoSerif-Regular.otf
Date: 2021-03-26

Font versions

Noto Sans: Version 2.005
Noto Sans Mono: Version 2.006
Noto Serif: Version 2.004

Issue

These three fonts include glyphs for alpha, iota, and upsilon, followed by three diacritics. However, these glyphs are seldom actually emitted: NFC combines the letter and the first diacritic together, but the 'ccmp' rule expects them to not be composed. To get the intended rendering, you have to insert a CGJ (or similar) to block the composition. The fonts should be able to handle NFC input.

Character data

ᾰ̓̀α
U+03B1 GREEK SMALL LETTER ALPHA
U+0306 COMBINING BREVE
U+0313 COMBINING COMMA ABOVE
U+0300 COMBINING GRAVE ACCENT
U+03B1 GREEK SMALL LETTER ALPHA
U+034F COMBINING GRAPHEME JOINER
U+0306 COMBINING BREVE
U+0313 COMBINING COMMA ABOVE
U+0300 COMBINING GRAVE ACCENT

Screenshots