IIRC Os X can now resize its own FS, so we can probably let my beautiful (just kidding) HFS code RIP. I won't talk for the other FS code, I have no special knowledge of them.
I have had no involvement in Parted for years (i'm doing radically different things), but as the one who wrote the HFS shrinking code I think and can explain my opinion on the subject. In summary it's a good idea to remove FS code if it has unknown status because the environment changed, and nobody is there to check every details.
Data security is to be taken very seriously in that kind of tool, and getting confident enough that a good level was achieved was actually what took most of the time when i wrote the hfs shrinker (I even unplugged the computer tens of times while resizing, then checked that the whole content of all files on the whole fs did not changed, then checked that OS X still booted and worked properly, + checked some internal metadata field of the FS, and so over). A correct review + tests in the modern context would take a lot of time, and I don't know if somebody have it but I haven't had in the last few years, still don't have, plus I don't even have the needed hardware anymore, so nobody should count on me.
Also one would have to check that the HFS+/HFSX has not evolved and implement support for interesting additional features Apple could have introduced in recent years.
That makes me a little nostalgic, but I 100% agree that without a careful review it is better to remove it (people who know what they are doing can still use an older version of the software, it's free software after all) than leave that kind of code that is now having an unknown status since the context of the environment has changed.
Of course that opinion is only relevant for the HFS code. I know nearly nothing about the other parts.
I am at this very moment working with 4k support in filesystem code, and it is a royal pain. You're quite right about the testing. My development on this is turning out to be largely test-driven.
I have had no involvement in Parted for years (i'm doing radically different things), but as the one who wrote the HFS shrinking code I think and can explain my opinion on the subject. In summary it's a good idea to remove FS code if it has unknown status because the environment changed, and nobody is there to check every details.
Data security is to be taken very seriously in that kind of tool, and getting confident enough that a good level was achieved was actually what took most of the time when i wrote the hfs shrinker (I even unplugged the computer tens of times while resizing, then checked that the whole content of all files on the whole fs did not changed, then checked that OS X still booted and worked properly, + checked some internal metadata field of the FS, and so over). A correct review + tests in the modern context would take a lot of time, and I don't know if somebody have it but I haven't had in the last few years, still don't have, plus I don't even have the needed hardware anymore, so nobody should count on me.
Also one would have to check that the HFS+/HFSX has not evolved and implement support for interesting additional features Apple could have introduced in recent years.
That makes me a little nostalgic, but I 100% agree that without a careful review it is better to remove it (people who know what they are doing can still use an older version of the software, it's free software after all) than leave that kind of code that is now having an unknown status since the context of the environment has changed.
Of course that opinion is only relevant for the HFS code. I know nearly nothing about the other parts.