Consider scripts with no directionality to be LTR

[simoncozens]

• Test for Kern writer fails when script tag not in unicodedata.ot_tag_to_script #575
• Force scripts with no inherent directionality to LTR for kerning purposes; fixes Kern writer fails when script tag not in unicodedata.ot_tag_to_script #575

[anthrotype]

LGTM, thank you!

[anthrotype]

or you could also do direction = unicodedata.script_horizontal_direction(scriptCode, default="LTR")

[anthrotype]

actually that may hide other bugs, it's better like you did (we still get a KeyError if a not-None scriptCode is not found by script_horizontal_direction)

[khaledhosny]

What does HarfBuzz do for these scripts? Math can be set RTL, not sure about the others.

[anthrotype]

I don't know if related, but it looks like the fontTools.unicodedata' list of RTL scripts could be not up to date with latest Unicode 14, see the link in the comment at
https://github.com/fonttools/fonttools/blob/e778f2c3f485101ad11cb595c427f579955c0714/Lib/fontTools/unicodedata/__init__.py#L137-L203
I believe I copied those from harfbuzz source code, but i forgot exactly where. Might be a good idea to update them just in case.

[anthrotype]

(ok, it's not related to this issue, but it's good that I checked: we were actually missing Old Uyghur from the RTL script list, it was added with Unicode 14.0 => fonttools/fonttools#2499)