Jordan Rose 4a8f81db2b Special-case diagnostic for when you just need @unknown default (#21695) ...

This is a new feature of Swift 5 mode, so it deserves at least a
little bit of explanation right in the diagnostic. If you have an
otherwise-fully-covered switch but can't assume the enum is frozen,
you'll now get this message:

    switch covers known cases, but 'MusicGenre' may have additional
    unknown values

Furthermore, if the enum comes from a system header, it looks like
this:

    switch covers known cases, but 'NSMusicGenre' may have additional
    unknown values, possibly added in future versions

...to further suggest the idea that even though your switch is covered
/now/, it might not handle everything in the /future/. This extra bit
is limited to system headers to avoid showing up on C enums defined in
your own project, for which it sounds silly. (The main message is
still valid though, since you can cram whatever you want into a C
enum, and people use this pattern to implement "private cases".)

rdar://problem/39367045

2019-01-08 08:45:23 -08:00

1.1 KiB

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