The problem with case sensitivity is UX. Sure, one can explain to someone that “A” and “a” are different to a computer, but will they understand?
“Report (final).docx” vs “Report (Final).docx”
Case insensitive comparison is less well defined than you might think. You need to know what language, because the rules are different in different languages. You need to know what version of unicode, because the rules can change. You need to know what to do if the data on disk doesn't conform to the rules. You need to know what to do when copying data from one filesystem to another when the names can't be stored on the destination.
I feel it's often better to train the user on how to use a simple system effectively, than to build a complex system. You have to put the complexity somewhere, and humans are easier to change than software and hardware.
You already need to know that, because filesystems are a jungle. This covers everything from special characters, to non-Unicode encodings, to different Unicode-like encodings, to special names, to file name length limits, and path length limits.
Consider that on Linux a filename is just an arbitrary sequence of bytes with some limitations, and on Windows it's an arbitrary sequence of 16-bit integers. You can put unpaired surrogate characters in a Windows path, and you can put 0xff in a Linux path.
> I feel it's often better to train the user on how to use a simple system effectively, than to build a complex system. You have to put the complexity somewhere, and humans are easier to change than software and hardware.
Filenames are something that affects everyone who uses computers for more than just browsing the web. By and large, these people have been using case-insensitive filesystems for the past 40 years, except the people using Unix-derivatives other than macOS--a small slice of people with a high percentage of experts.
So if you have an idea of how to train a billion people to deal with case sensitivity problems that they didn't have to do with before, I'm all ears.
And yes... the case folding and locale problems exist. I think we're already on the way to the right solution there... hide the filesystem completely from most people who use computers. The filesystem is a terrible way to organize data, so we are building more complicated filesystems and more complicated stacks on top of filesystems to make it easier for humans to work with, and rightly so.
I don't think these are as equivalent as you imply. While it's technically possible for Windows paths to contain unpaired surrogates, in practice it never happens outside of malicious software (and even that's rare),
Whereas on Linux, getting a "random" bag of bytes is relatively common because the convention of UTF-8 is new (and is a userspace convention). Of course it's usually not truly random but you have to play guess the encoding if you want to interpret it.
It's a bit harder for the people who had case insensitivity before, I'd imagine. But the basic way to train people for this is a) to work consistently and b) drop helpful examples in places. For a) When someone makes a new directory lowercse dotless i when they already have a folder named I, they might be surprised to have two directories with the same letter, but they'll figure it out. The same way that they figured out news.ycombinator.com/REPLY doesn't work, because the bytes aren't the same.
For b) make some tools expect a file called Makefile and not work if makefile is present. Done!
Computers are for end-users. OS and app developers are in the minority, and we should remember that when we write apps or filesystems.
But that being said, are many nontechnical users typing filenames anyways?
That doesn't mean they won't still have trouble working with filenames that differ only by case, and it can still be pretty hard to explain why two characters that are visually similar are distinct to the computer.
But the idea that letters that look different are different is not a hard one to understand. It's the default, and one that people have to actively unlearn.
For me case insensitive filenames are horrible UX, for my parents case sensitive filenames are horrible UX.
However I wouldn't advice my parents to use case insensitive filenames: there are too much complications that you might get from it in interaction with literally anything. The UX net effect would be negative for them.
Why is this the exception?