U+00DF ('ß') has had an uppercase form (U+1E9E) available since
Unicode 5.1, but Unicode lacks the case mappings for it due to
stability policy. when I added support for the new character in commit
1a63a9fc30, I omitted the mapping in the
lowercase-to-uppercase direction. this choice was not based on any
actual information, only assumptions.
this commit adds bidirectional case mappings between U+00DF and
U+1E9E, and removes the special-case hack that allowed U+00DF to be
identified as lowecase despite lacking a mapping. aside from strong
evidence that this is the "right" behavior for real-world usage of
these characters, several factors informed this decision:
- the other "potentially correct" mapping, to "SS", is not
representable in the C case-mapping system anyway.
- leaving one letter in lowercase form when transforming a string to
uppercase is obviously wrong.
- having a character which is nominally lowercase but which is fixed
under case mapping violates reasonable invariants.
Rich Felker
4674809bdf