kmx git

keysyms: Fix Unicode handling

- `xkb_utf32_to_keysym`: Allow [Unicode noncharacters]. There is no
  requirement to drop them and this would be the only function of our
  API doing so.

  From the Unicode Standard 16.0, section 23.7 “Noncharacters”:

  > Applications are free to use any of these noncharacter code points
  > internally. They have no standard interpretation when exchanged
  > outside the context of internal use. However, they are not illegal
  > in interchange, nor does their presence cause Unicode text to be
  > ill-formed.

  > If a noncharacter is received in open interchange, an application is
  > not required to interpret it in any way. It is good practice,
  > however, to recognize it as a noncharacter and to take appropriate
  > action, such as replacing it with `U+FFFD` REPLACEMENT CHARACTER,
  > to indicate the problem in the text.

  The key part is:

  > an application is not required to interpret it in any way

  Since we handle the reverse conversion with `xkb_keysym_to_utf32` just
  fine, I do not see a good motivation to keep this asymmetry. This is
  the only function with a special case for these code points.
- `xkb_keysym_from_name`:
  - Unicode format `UNNNN`: allow control characters C0 and C1 and use
    `xkb_utf32_to_keysym` for the conversion when `NNNN < 0x100`, for
    backward compatibility.
  - Numeric hexadecimal format `0xNNNN`: *unchanged*. Contrary to the
    Unicode format, it does not normalize any keysym values in order to
    enable roundtrip with `xkb_keysym_get_name`.

Also added tests to ensure various properties and consistency.

Note about *surrogates*: they are valid valid *code points* but invalid
Unicode *scalar values*, i.e. they cannot be encoded in any Unicode
encoding form (UTF-8, UTF-16, UTF-32). So their corresponding Unicode
keysyms are valid, but:
- cannot be used as input of `xkb_keysym_to_utf32` nor `xkb_keysym_to_utf8`
- cannot result as output of `xkb_utf32_to_keysym`.
Otherwise they are valid e.g. in the Unicode keysym notation.

[Unicode noncharacters]: https://en.wikipedia.org/wiki/Universal_Character_Set_characters#Noncharacters
kc3-lang/libxkbcommon/changes/api/715.feature.md

Commit

Source

changes/api/715.feature.md
