[feaLib] Handle dash in glyph names

I know this has been discussed before, but it’s still a pain, that glyphs2ufo chained to ufo2ft can fail. In my example:

fontTools.feaLib.error.FeatureLibError: features.fea:12:5179: Bad range: "LL" and "middleWelsh" should have the same length

I like to suggest two changes to feaLib, both of which will ideally be pushed to AFDKO / Fea spec as well:

• A dash, when following a backslash, can be part of a glyph name to mean a single ‘dash’ and as such work around the current limitation that dashes cannot be part of glyph names. In fact, I’d go as far as suggesting that a backslash would escape any punctuation to be part of the glyph name,
• When the above-mentioned error occurs, ie. when a dash range fails to parse, then try parsing the dashed sequence as a glyph name (only if there were no spaces involved). In fact, in most cases, either a range or a glyph name is valid, not both. It’s ok to fail if there is ambiguity.

Implementing one or both of these makes the glyphs2ufo+ufo2ft experience much better. Right now, fontmake replaces dashes with underscores before calling the above tools. That’s too much to ask each client to do.

@schriftgestalt @jamesgk

[brawer]

Personally, I think fonttools/feaLib should implement the published specification, not deviate from it. The proposed fallback logic sounds quite interesting, but I think it would need to become part of the spec before fonttools implements it. (Otherwise, we’ll have a chaos pretty quickly).

[readroberts]

No. I thought I had updated the MakeOTF user guide, but the new characters are currently documented nowhere. The current set is “- + * : ~ ^ !”. Note that the only spec for final glyph names in a font is still the Postscript and Type 1 specs, which do not permit these characters. I don’ t think there should be an official spec for development glyph names, which can be anything that a set of development tools support. I do agree that a set of shared conventions would be useful. I will add documentation for the FDK names to the MakeOTF user guide.