macOS 11 has been announced; can_use_xz() should be updated

[DeeDeeG]

Hi,

Apple has announced a macOS 11 release for some time in the future.

For inferring xz support, we currently look for the minor macOS version number (>= 9), but I reckon we should now also accept major version >= 11.

[shadowspawn]

Um, yes, we didn't check the major version! Has not changed in soooooo long.

[DeeDeeG]

By the way, nvs does something clever for version comparisons. For comparing major.minor.patch versions, it converts each component to having three digits (padded with leading zeroes) and concatenates just the digits (no more dots). For example, 1.22.333 becomes 001022333. With versions represented this way, you can just use normal integer comparison on them.

(This amount of padding would be enough up until any of the version components requires more than three digits to write. I find it unlikely that macOS will ever release a version with one of the components being 1000 or larger, so it should be good enough.)

• This "clever" way would work by checking for macOS >= 10.9.0 (>= "010009000")
• or else we can do two separate checks (macOS major version >= 11, or minor version >= 9).

[shadowspawn]

I would prefer two separate checks for this. The unified version approach is handy if doing sorting or multiple checks, but for a single check, no need to be clever.

[DeeDeeG]

I also just remembered that in macOS releases with xz support there is a shared/dynamic library /usr/lib/liblzma.dylib (which is actually a symlink to /usr/lib/liblzma.5.dylib).

Checking for the existence of this file should work for macOS, irrespective of OS version.

So the options are down to:

• macOS major version check, followed by a macOS minor version check.
• Check for the existence of /usr/lib/liblzma.dylib on macOS.

[DeeDeeG]

A PR is up with the simple fix/staying close to the existing solution. #624

[DeeDeeG]

I can do a version of this at nvh too.

(It will take until there is a beta of macOS 11 to really confirm this is the right approach, but I'd be surprised if it isn't. And I think it's worth being ahead of the curve, so it "just works" for more users right on day one if macOS 11 usage. And to preempt any issue spam.)

[shadowspawn]

I agree, in that ideally I would try it on macOS 11 first, but I am happy shipping sooner as the change is consistent with the existing implementation and likely to Just Work.

PR for nvh welcome, or I'll get to it myself eventually. :-)

[DeeDeeG]

FWIW there is a developer beta for macOS 11 "Big Sur", but I don't own a Mac, I only borrow them from time to time... And I'm not going to pay $100 to join the Apple Developer Program.

https://www.digitaltrends.com/computing/how-to-download-macos-big-sur/

[shadowspawn]

Shipped in n v6.6.0

Thanks @DeeDeeG