Support SFD?

[rsheeter]

Per remarks on google/fonts#10490 we will need sfd2ir if sfd is a format we need to support on an ongoing basis. The other option is to convert source formats, but if we take that path the converted source needs to become the one used for modification. I do not want a long lasting sfd | babelfont | fontc pipeline, that means we don't compile the form used for modification, e.g. we don't compile the source.

[simoncozens]

I don't understand the part about "we don't compile the source". Babelfont ingests source and emits IR which gets handed to fontbe. We absolutely do compile the source. Babelfont is already "various-source-formats2ir".

[rsheeter]

It seems like a fairly odd setup to have a subset of frontends in babelfont while others live in fontc. Naively, might we simply move sfd2ir into fontc if sfd is a format we must support?

On that note ... must we support sfd? Is migrating permanently away from sfd - a one-time conversion to glyphs or ufo+ds files that are the actual sources - the ones used to make changes - an option?

[simoncozens]

It seems like a fairly odd setup to have a subset of frontends in babelfont

Well, technically it's a superset. Babelfont only has one IR emitter which converts the babelfont object model to IR. It just has ingesters for eight different font source formats into its own object model, which is a superset of all of them.

For the past few years the story has been "fontc only supports Glyphs and UFO, users of other formats are out of luck, onboarders can fork the source and convert". And that still seems to be your underlying desire:

On that note ... must we support sfd? Is migrating permanently away from sfd - a one-time conversion to glyphs or ufo+ds files that are the actual sources - the ones used to make changes - an option?

Which is a legitimate design choice; I don't agree with it, but it's a fair enough way to scope the fontc project. But if that is the choice, then it's not at all odd for other projects to pick up the slack. I think it's absolutely fine to say "the Google Fonts compiler compiles only Glyphs and Designspace." But then it is odd to say "and no other compilers ever need to exist."