Re: [I18ndir] I-D on filesystem I18N

[Nico Williams <[e-mail]>]

Apparently, with APFS Apple switched from normalize-on-create to
form-insensitivity:

https://developer.apple.com/library/archive/documentation/FileManagement/Conceptual/APFS_Guide/FAQ/FAQ.html#//apple_ref/doc/uid/TP40016999-CH6-DontLinkElementID_3

| APFS accepts only valid UTF-8 encoded filenames for creation, and
| preserves both case and normalization of the filename on disk in all
| variants. APFS, like HFS+, is case-sensitive on iOS and is available in
| case-sensitive and case-insensitive variants on macOS, with
| case-insensitive being the default.
| 
| In macOS High Sierra, APFS is normalization-insensitive in both the
| case-insensitive and case-sensitive variants, using a hash-based native
| normalization scheme. In iOS 11, APFS is normalization-insensitive as
| well, using either a native normalization scheme (erase restores only)
| or runtime normalization scheme (upgrades from previous versions).
| Runtime normalization will also be available in iOS 10.3.3 and macOS
| Sierra 10.12.6. Being normalization-insensitive ensures that
| normalization variants of a filename cannot be created in the same
| directory, and that a filename can be found with any of its
| normalization variants. This means that you don’t need to do any
| additional work to ensure correct normalization behavior in these
| versions of macOS and iOS.

With this I think it's fair to say then that form-insensitivity is now
the best common practice in filesystems!

(It'd be nice to have a survey of Unicode support in the various Linux
and *BSD filesystems, like BTRFS, HAMMER, HAMMER2, etc.
https://en.wikipedia.org/wiki/Comparison_of_file_systems does not
mention this stuff.)

Earlier versions of APFS though did not do any normalization or form-
insensitivity:

| In iOS 10.3 and in the case-sensitive variant of the developer preview
| of APFS in macOS Sierra, APFS is normalization-sensitive ...

which yielded this complaint:

https://eclecticlight.co/2017/04/06/apfs-is-currently-unusable-with-most-non-english-languages/

Ooops.  So Apple says:

| To avoid introducing bugs in your code with mismatched Unicode
| normalization (for iOS 10.3.0, 10.3.1 and 10.3.2) in filenames, do the
| following:
|
|  o Use high-level Foundation APIs such as NSFileManager and NSURL when
|    interacting with the filesystem.
|
|  o Use the fileSystemRepresentation property of NSURL objects when
|    creating and opening files with lower-level filesystem APIs such
|    as POSIX open(2), or when storing filenames externally from the
|    filesystem.

So... like Git and rsync as mentioned here earlier.  But Apple did fix
APFS.

Nico
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