I thought the generally recommended way to deal with file names is to treat as a block of bytes (to the extent that e.g. rust has an entirely separate string type for OS provided strings), or just to allow direct encoding/decoding but not normalisation or alteration.
Or you could have one file `göteborg.txt`, and when you try to ask for it as `göteborg.txt`, the system tells you "no file by that name".
Unicode normalization is the solution to this. And the unicode normalization algorithms are pretty good. The bug in this case is that the system did not apply unicode normalization consistently. It required a non-default config option to be turned on to do so? I don't really understand what's going on here, but it sounds like a bug in the system to me that this would be a non-default config option.
Dealing with the entire universe of human language is inherently complicated. But unicode gives us some actually pretty marvelous tools for doing it consistently and reasonably. But you still have to use them, and use them right, and with all software bugs are possible.
But I don't think you get fewer crazy edge cases by not normalizing at all. (In some cases you can even get security concerns, think about usernames and the risk of `jöhn` and `jöhn` being two different users...). I know that this is the choice some traditional/legacy OSs/file systems make, in order to keep pre-unicode-hegemony backwards compat. It has problems as well. I think the right choice for any greenfield possibilities is consistent unicode normalization, so `göteborg.txt` and `göteborg.txt` can't be two different files with two different filenames.
[btw I tried to actually use the two common different forms of ö in this text; I don't believe HN normalizes them so they should remain.]
Unless it was meant to be for performance?
Linux filenames are a sequence of non-zero bytes (they might be ASCII, or at least UTF-8, they might be an old 8-bit charset, but they also might just be arbitrary non-zero bytes) and Windows file names are a sequence of non-zero 16-bit unsigned integers, which you could think of as UTF-16 code units but they don't promise to encode UTF-16.
Probably the files have human readable names, but, maybe not. If you're accepting command line file names it's not crazy to insist on human readable (thus, Unicode) names, but if you process arbitrary input files you didn't create, particularly files you just found by looking around on disks unsupervised - you need to accept that utter gibberish is inevitable sooner or later and you must cope with that successfully.
Rust's OSStr variants match this reality.
A) The programmer is a almighty god who knows everything, we just expose him to the raw thing
B) The programmer is a immature toddler who cannot be trusted, so we handle things for them
And then brought it back. It normalizes now.
As for APFS, it ~~doesn’t~~didn’t normalize but I believe it still requires UTF-8. And the OS will normalize filenames at a higher level. EDIT: they added native normalization. At least for iOS, I didn’t dig enough to check it macOS is doing native normalizing or is just normalization-insensitive.
(On the use of version 3.1, note that in practice version 3.2 is used, correcting one typo: see <https://www.unicode.org/versions/corrigendum3.html>.)
I find a few references to it being slightly different, but not one of them actually says what’s different; Wikipedia is the only one with a citation (<https://en.wikipedia.org/wiki/HFS_Plus>: “and normalized to a form very nearly the same as Unicode Normalization Form D (NFD)[12]”), and that citation says it’s UAX #15 NFD, no deviations. One library that handles HFS+ differently switches to UCD 3.2.0 for HFS+ <https://github.com/ksze/filename-sanitizer/blob/e990e963dc5b...>, but my impression from UAX #15 is that this should be superfluous, not actually changing anything. (Why is UCD 3.2.0 still around there? Probably because IDNA 2003 needs it: <https://bugs.python.org/issue42157#msg379674>.)
Update: https://developer.apple.com/library/archive/technotes/tn/tn1... has actual technical information, but the table in question doesn’t show Unicode version changes like they claim it does, so I dunno. Looks like maybe from macOS 10.3 it’s exactly UAX #15, but 8.1–10.2 was a precursor? I’m fuzzy on where the normalisation actually happens, anyway.
# FIXME: improve HFS+ handling, because it does not use the standard NFD. It's
# close, but it's not exactly the same thing.
'hfs+': (255, 'characters', 'utf-16', 'NFD'),
> The characters with codes in the range u+2000 through u+2FFF are punctuation, symbols, dingbats, arrows, box drawing, etc. The u+24xx block, for example, has single characters for things like "(a)". The characters in this range are not fully decomposed; they are left unchanged in HFS Plus strings. This allows strings in Mac OS encodings to be converted to Unicode and back without loss of information. This is not unnatural since a user would not necessarily expect a dingbat "(a)" to be equivalent to the three character sequence "(", "a", ")" in a file name.
> The characters in the range u+F900 through u+FAFF are CJK compatibility ideographs, and are not decomposed in HFS Plus strings.
The bit about the u+24xx block is misleading, the decomposition of the characters I looked at there (such as ⒜) are compatibility canonicalizations. However the CJK compatibility ideographs is a working example. U+F902 (車) decomposes to U+8ECA (車) regardless of normalization form but the technote says these must not be decomposed.
$ echo test > $'\xc3\xb6'
$ cat $'\x6f\xcc\x88'
cat: ö: No such file or directory
$ zfs create -o normalization=formD pool/dataset
$ echo test > $'\xc3\xb6'
$ cat $'\x6f\xcc\x88'
testOne example is when you submit a file in Safari it doesn't normalize the file name while js file.name does.
> Wrappers around it like whatever Nextcloud is doing should be treating the filenames as a dumb pile of bytes.
What do you do when the input isn't a dumb pile of bytes, but actual text? (Like from a text box the user typed into?)
The point I'm trying to get at being, you need to worry about the representation at multiple layers, not just at the bottom FS layer.
do capital letters have a good enough usage case to justify their continued existence?
Second one: no, emails are not filenames, and more generally distinguishability is more important for identifiers. In cases where identifiers like emails need to be mapped to filenames, like caches, they should be normalized.
Case (in)sensitivity for filenames is a non-issue in my experience. Never had problems with either convention. As for emails, I do think insensitivity was the right choice.
The local-part of a mailbox MUST BE treated as case sensitive.
Section 2.4 RFC 2821, https://www.ietf.org/rfc/rfc2821.txt
I have just been arguing the same thing in far too much detail in this thread: https://news.ycombinator.com/item?id=29722019
I don't think I've seen any good argument against normalization, though.
Sorry to say I tend to use case sensitivity as a filter for me offering support to other developers. I'm not willing to find time for people who can't get their head around "turn on/off caps lock". You don't do it in professional writeups or applications (and I hope not in a CV) so don't pollute my filesystems or codebases with that madness.
If the mapping is non trivial then unless you're careful you end up breaking basic consistency between input and stored data hence the weird issues with mangling the unicode chars. If the mapping is trivial theres almost nothing to discuss. If the mapping is many to many you're going to have a bad time unless your consistent with your use of the maps. Then the fun is broken mappings where you get data loss due to incorrect many to one and one to many mappings.
There are times when caps matter, I e. code and filesystems are human readable so should not be arbitrary, but searching these for instance makes sense to be insensitive when needed (perhaps even default)
I don't know about anyone else, but I read WORD as someone yelling, Word as designating/specifying a "word" with some importance, and woRD as the mocking Spongebob meme. I absolutely don't read "case insensitive" and I don't think filesystems should either.
Imagine if you could only search for ‘dog’ if you had to specify whether the author yelled it or not before you could find it.
Dog in bold, italics, red, green, uppercase, lowercase, initialcaps, smallcaps, are all the same word. What "the same" means has fuzzy boundaries and sometimes needs very precise specification, but I personally want the default to be the fuzzy convenient and the hyper-literal to be available as a fallback.
[I notice that I used 'color' and 'colour' here. My native language is UK English and programming languages and much of the internet use US English. I'm not sure if I would want `vim colour.txt` to open `color.txt`. Probably not. PowerShell 7 has a suggestions feature for "you typed a command which wasn't found, here are the most similar command names:" - mentioned in https://github.com/PowerShell/PowerShell/issues/10546 ]
But that is a feature of the word Dog, try the German words maßen (limited amounts) and massen (large amounts), historically they share the same upper case rendering MASSEN. Now someone versed in German could change to the alternative MASZEN or use the rather modern upper case version of ß. However the default naive (and most of the time correct) conversion between cases looses a significant amount of information.
What about people who CAN read English that way, but think having to match case when searching or referencing text hinders more than it helps?
Only if different case-variants do not have meaning. When two words that differ only in case have different meaning, we distinguish them (e.g. "moon" and "Moon").
Meaning doesn't go when the case changes in anything like the way meaning goes when the letters change. "neil armstrong was the first human to walk on the roof" is a very different sentence, you can't get anything like that difference with just case changes. If I spoke it, you wouldn't be able to tell if I spoke the correct case or not. Would you want school children searching for "one small step for man, one giant leap for mankind" and Google says "no results" because they used a lowercase m in mankind? Would you want a TV quiz show asking "What is Europa?" and a contenstant answers "a moon of jupiter" and the host asks "do you mean moon with a capital m or lowercase m?" before they decide whether the answer is correct?
In Japanese, くるま, クルマ, and 車 are all the same word (the first two are the phonetic spelling "kuruma", the later is the Chinese character). However in order to know that 車 is read くるま you need to be a native Japanese speaker (or have a dictionary) -- should filesystems have dictionaries to match what a human would think? Search engines that support Japanese have to handle this to some degree, but I humbly suggest implement Google Search's language handling code into a filesystem would be an ill-advised decision.
If you wanted to implement the most minimal version of this you would map between katakana and hiragana, but that means you'll need to do this for other languages. For instance, Serbian. Serbian uses two scripts (both of which have upper and lower case forms) and any native Serbian speaker would see "tuđa ljuta paprika" and "туђа љута паприка" as the same text (note that lj became љ). Should that also be automatically translated in the filesystem?
In German, capitalisation is not reversible. ß becomes SS when capitalised but will be lowercased as ss. (There is now a capital version -- ẞ -- but from what I gather it's not widely used.)
Even in English you have British and American spellings of a given word -- native speakers would recognise them as the same thing but it would not be reasonable to expect a filesystem to map them to the same thing. Initialisms can have different identical representations (N.S.A vs NSA). And you also have cases where capitalisation actually does distinguish words (May vs may, PRISM vs prism, CAT vs cat, etc). What about fullwidth and halfwidth latin characters (Ｈｅｌｌｏ vs Hello)? Arguably those are even more identical than upper and lower case.
For all of the above reasons, case insensitivity is something which most systems will only ever implement for English and a few other European languages, meaning that it's more of a wart than a fully-working feature. If the argument really is "well, a human would recognise these two names as the same thing, so the filesystem should too" then why are none of the other examples given above handled? If it's too difficult to do correctly (which is my view) then why support any of this in the first place? However, everything should be normalised (NFC or NFD depending on your usecase).
The same applies for a.txt and A.txt on case insensitive file systems (as someone pointed out the most common desktop file systems are).