New auxiliary functions to be called by other packages

[eroux]

It would be very useful to have auxiliary functions that could be called by other packages. This would be like a "font API", and would prevent updates in luaotfload to break everything in other packages. The useful functions would be:

the functions you can find in fontspec.lua (https://github.com/eroux/fontspec/blob/master/fontspec.dtx#L6668), with quite explicit names:

• check_script(font_id, script)
• check_language(font_id, language, script)
• check_feature(font_id, feature, language, script)
• set_capheight(fontdata)
• get_mathfontdimen(fontdata, dimen)

the function in unicode-math.lua (https://github.com/eroux/unicode-math/blob/master/unicode-math.dtx#L1453)

• set_sscale_dimens(fontdata)
• patch_cambria_domh(fontdata)

the function in polyglossia : (https://github.com/eroux/polyglossia/blob/master/lua/polyglossia.lua#L40)

• check_char (font_id, char) returning a boolean if char is present in the font with id font_id

maybe other functions from ConTeXt (from the .lfg files in the fonts/ directory)?

[phi-gamma]

Interestingly, commenting on this issue I just closed, Khaled says that the set_sscale_dimens related stuff was moved from luaotfload, which contained it initially, to unicode-math, its only user. So for the moment I’d assume that whoever needs it will load unicode-math anyways.

The patch_cambria_domh is too specific to a single font and math, also we already keep the code around in tests/font_patch.tex. Maybe it had been migrated from luaotfload as well? Idk the package history well enough.

[eroux]

This might have been consistant at a certain time and might be again in the future, but in the situation we are in right now, I think it's definitely better to get them back (maybe not cambria? not sure) in luaotfload. The reason is that Will is not responding and we have no control on unicode-math nor fontspec, so we cannot update luaotfload... If fontspec and unicode-math were depending only on an API of luaotfload and not on the internal structure of otfl-merged.lua, we could make new releases of luaotfload, independant from an update of fontspec or unicode-math... When we'll reach 1.0 version, then code could go outside, but I'm not 100% sure it's relevant either... What do you think?

[eroux]

We should also include

name_to_slot(font_id, name)

from microtype.lua; it will be less maintainance from Robert, I think he'll be happy with that!

[phi-gamma]

see here #30

[phi-gamma]

Can we close this?

[eroux]

Affirmative!