[skrifa] NamedInstance.postscript_name_id "not present" case

[simoncozens]

In an instance record, the postscript name ID is optional. postscript_name_id is therefore typed as Option<NameId>. All good.

However, in the binary, the "not present" case is represented as binary 0xFFFF. When the postscript name ID is not present, both skrifa NamedInstance.postscript_name_id and read-fonts InstanceRecord.post_script_name_id do not return None but instead return Some(65535) - so in fact this Option always returns Some.

I feel that certainly in skrifa as a "mid-level" library, and possibly also in read-fonts, the "not-present" case should be interpreted from the binary value and returned as a None.

[dfrg]

Are you using an older version of read-fonts? This was changed a couple months ago:

fontations/read-fonts/src/tables/instance_record.rs

Line 56 in d52fd0c

(id.to_u16() != 0xFFFF).then_some(id)